Faculty Profiles - AOKI Takaaki

Papers - AOKI Takaaki

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An RDM Interview Sheet to Inspire Graduate Students’ Awareness of Data Management

ASAKAWA Makiko, AOKI Takaaki

The Journal of Information Science and Technology Association Vol. 75 ( 2 ) page： 79 - 85 2025.2

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Information Science and Technology Association, Japan

In recent years, the importance of Research Data Management (RDM) has been increasing, driven by the perspectives of research openness and strengthening research integrity. Graduate students, as early-career researchers, must acquire foundational RDM knowledge and integrate it into their research practices. However, effective methods to raise awareness and provide practical strategies for RDM implementation remain underdeveloped. This paper presents the design and application of the “RDM Interview Sheet”, a tool created to guide graduate students in reflecting on and explaining their research data management practices.

DOI： 10.18919/jkg.75.2_79

Enhancing accessibility of research data through metadata conversion and registration in institutional repositories: Practices in the field of Solar-Terrestrial Physics

Masahito NOSÉ, Atsuki SHINBORI, Yoshizumi MIYOSHI, Tomoaki HORI, Tsukasa OOHIRA, Maiko OKAMOTO, Chizuko NAOE, Rui GAKIYA, Sachie TANAKA, Takeshi SAGARA, Takaaki AOKI, Shigeki MATSUBARA, Ichiro TAKAHASHI, Hidekazu HAYASHI, Kazunari YAMADA, Yasuyuki MINAMIYAMA, Yoshimasa TANAKA, Yasuo SAITO, Shuji ABE, Satoru UENO, Shun IMAJO, Takuya ASHIKITA, Yuko HORI, Toshiyuki SHIMIZU, Nanako OKAMURA, Kaoru HIRANO

The Journal of Information Science and Technology Association Vol. 74 ( 11 ) page： 487 - 493 2024.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Information Science and Technology Association, Japan

<p>The “Inter-university Upper atmosphere Global Observation NETwork (IUGONET)” project has developed a metadata database for ground-based observation data in Solar-Terrestrial Physics. In order to make this metadata database accessible to a wide range of research communities and the general public, we converted metadata in different metadata schema and registered them in academic institutional repositories. As a result, through regular harvesting between databases, the metadata has also been registered in the Institutional Repositories Database (IRDB), the Data Catalog Cross-Search System, and Google’s Dataset Search, significantly enhancing the visibility and accessibility of research data. Furthermore, effective metadata management was implemented in response to research metadata maintenance requests from policy-making bodies.</p>

DOI： 10.18919/jkg.74.11_487

Organizational Initiatives to Support Research Data Management in Japanese Academic Institutions Invited

Takaaki Aoki

The Journal of Information Science and Technology Association Vol. 74 ( 4 ) page： 124 - 128 2024.4

Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Information Science and Technology Association, Japan

The open science movement, initiated in the early 2010s along with the context of data-driven science and concerns over research reproducibility and accountability, demands practical actions for managing and sharing research data effectively. This requires the response of all stakeholders involved in academic activities, not only researchers but also disciplinary communities and funding agencies and so on. In particular, academic institutions face diverse and complex issues as they mediate between researchers and other stakeholders. This paper discusses the approach to organizational support for research data management required for academic institutions and the initiative efforts being made.

DOI： 10.18919/jkg.74.4_124

User Evaluation of Sakai LMS Feature Enhancements by Comfortable Sakai

Kazuki Takeda, Yasuyuki Nakamura, Takaaki Aoki, Shoji Kajita

SIG Technical Reports Vol. 2024-CLE-42 ( 2 ) page： 1 - 6 2024.3

Language：Japanese Publishing type：Research paper (conference, symposium, etc.) Publisher：Information Processing Society of Japan

In this presentation, we introduce a browser extension named “Comfortable Sakai,” which was developed by students to enhance the functionality of the Sakai LMS. Initially developed as “Comfortable PandA” specifically for Kyoto University, it lacked compatibility with other Sakai LMS platforms, leading to a limited usage. To address this, while keeping its core features, we added support for internationalization (i18n) and localization (l10n) and removed dependencies unique to Kyoto University. This development aimed to make the extension usable with various Sakai LMS systems around the world. This report will cover the development of this extension and its evaluation by Sakai LMS users.

Designing a self-assessment framework for research data management services maturity level in academic institutions

Yasuyuki Minamiyama, Ui Ikeuchi, Kosuke Tanabe, Kenji Yuki, Kazuhiro Hayashi, Takaaki Aoki

SIG Technical Reports Vol. 2023-IOT-60 ( 23 ) page： 1 - 10 2023.3

Language：Japanese Publishing type：Research paper (conference, symposium, etc.) Publisher：Information Processing Society of Japan

Developing research data management services that support research data lifecycle has become an international trend in response to today's movement promoting open science. On the one hand, the selection and use of the developed research data management services are left to the discretion of each researcher. On the other hand, universities and academic institutions must establish research data management services at the institutional level to support researchers and strengthen their institutional governance. However, due to the wide range of functions required of research data management services, it is difficult for institutions to evaluate the achievement of their service maturity level. It is essential to establish a self-assessment framework to measure the degree of achievement for developing the services comprehensively and consistently. In this study, we design a self-assessment framework for evaluating the maturity level of research data management services in academic institutions. We analyzed the existing RDM service maturity models and extracted common elements to understand the services provided by each institution. We also developed key performance areas by each element and evaluated the framework through a large-scale questionnaire survey targeting institutions of different scales and characteristics. The self-assessment framework used in this study structures institutional research data management services and enables quantitative comparisons from the perspective of service providers. Also, the framework helps identify issues or points of investment in implementing new research data management services by institutional scales or characteristics.

Consideration and production of Research Data Management(RDM) teaching materials for Information and Communications Technology (ICT) staff

Masakazu Motoki, Masako Furukawa, Takaaki Aoki

IPSJ SIG Technical Report Vol. 2022-IOT-56 ( 15 ) page： 1 - 8 2022.3

Language：Japanese Publishing type：Research paper (conference, symposium, etc.)

One can say that 2021 is a year of change in Open Science and Research Data Management (RDM) in Japan, for example, the announcement of the 6th Science, Technology, and Innovation Basic Plan and the launch of the Research Data Cloud (NII-RDC) by National Institute of Informatics. This paper reports on the collaborative efforts of volunteers from AXIES (Academic eXchange for Information Environment and Strategies) and JPCOAR (Japan Consortium for Open Access Repository) pertaining to RDM teaching materials to information infrastructure staff to support as many academic institutions as possible with the aim of supporting organizational RDM.

Enterprise Architecture Approach for Institutionalized Research Data Management Service

AOKI, Takaaki

Vol. 2021-IOT-55 ( 7 ) page： 1 - 5 2021.8

Authorship：Lead author Language：Japanese Publishing type：Research paper (conference, symposium, etc.)

Research data management (RDM) is the practice of defining what research data is to be handled and how it is to be handled from the beginning to the end of a study. This includes all operations on research data, such as obtaining, storing, sharing, publishing, and destroying, which are often chosen at the discretion of each researcher. On the other hand, with the spread of open science and the strengthening of governance in academic institutions today, there is a need to unify and standardize RDM methods at the institutional level. The introduction of the institutional-wide RDM support services may include various conflicts, such as the intentions of the organization and researchers, cost effectiveness, etc. It is necessary to clarify these gaps and find a point of agreement between the institution and the researchers. In this article, we will discuss the concept of the business model assumed when an organization introduces RDM support service, and how to compose an enterprise architecture to realize it.

オープンサイエンスと研究データ管理の動向 Invited

青木学聡

情報処理 Vol. 62 ( 5 ) page： d1 - d11 2021.4

MeV-SIMS measurement of lithium-containing electrolyte

Toshio Seki, Tomoya Nonomura, Takaaki Aoki, Jiro Matsuo

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms Vol. 479 page： 229 - 232 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier B.V.

Secondary ion mass spectrometry (SIMS) is a method with high surface sensitivity that allows both elemental and molecular analysis. The MeV-SIMS technique uses heavy ion beams with energy in the MeV range, and samples can be measured under ambient conditions because of the high transmission capability of these ions at low vacuum pressures. Ambient MeV-SIMS is a suitable method for investigating the reactions at the electrode–electrolyte interface. In contrast, however, in this method, chemical noise originating from ionized residual gases can be found with high intensity. Under the conditions, signals from the surface have to be distinguished from the chemical noise. In this paper, MeV-SIMS measurements of a Li-containing electrolyte were performed and a method was established for separating out chemical noise and signals from the sample surface. The detection of a number of Li-containing electrolytic compounds from the sample surface by an ambient MeV-SIMS system was successful.

DOI： 10.1016/j.nimb.2020.07.007

A Campus-wide Survey of Consciousness on Research Datasets

Toshihiko Iyemori, Takaaki Aoki, Shoji Kajita, Tamaki Motoki, Tomoko Kawaguchi, Eriko Amano

2020 9th International Congress on Advanced Applied Informatics (IIAI-AAI) page： 312 - 315 2020.9

Design and Implementation of Questionnaire to Researchers on Research Data Management

Takaaki Aoki, Miho Funamori, Shigeki Matsubara, Kenji Yuki, Takao Miyamoto, Kouji Nishimura

IPSJ SIG Technical Report Vol. 2020-IOT-48 ( 14 ) page： 1 - 7 2020.2

Authorship：Lead author Language：Japanese Publishing type：Research paper (conference, symposium, etc.)

Under the social demands for the promotion of open science and the research fairness, academic institutions are urged to facilitate the organizational research data management (RDM) framework, such as policy development, provision of IT infrastructure, education for research data literacy, etc. The survey about the comprehension of the RDM and demand to the organization considered by the members is one of the initial actions for the institutes to design the organizational RDM environment. Several research institutes jointly developed the standard questionnaire template and guideline to survey the awareness and demand of RDM among their researchers. The development of a questionnaire template was useful to reduce the initial effort survey and to compare the results between institutes. The paper will report the structure of the standard questionnaire template and discuss the framework for promoting the organizational RDM environment at institutions.

Current situation and Issues of "Database on Education and Research, Kyoto University"

Hiroki Kajiwara, Hirofumi Sawada, Hirokazu Akasaka, Noritoshi Atsumi, Takaaki Aoki

AXIES Annual Conference 2019 page： . 2019.12

Issues and attempts to introduce research data management at academic institutions

Miho Funamori, Takaaki Aoki, Katsuhiko Toyama, Kazutuna Yamaji

IPSJ SIG Technical Report Vol. 2019-IOT-47 ( 17 ) page： 1 - 8 2019.9

Language：Japanese Publishing type：Research paper (conference, symposium, etc.)

There is a worldwide trend to manage and share research data resulting from research activities. Research data, resulting from research activities, are in general managed by researchers; however, seen from efficiency and accountability point of view, academic institutions are increasingly held responsible for providing infrastructure and support research activities of researchers within institution as well as being accountable as an institution in case of scientific misconducts. Nonetheless, as research data management is a relatively new trend, it has not made that far at Japanese academic institutions. This work attempted to clarify the issues the academic institutions face when introducing research data management into the institution by discussing the issues with a workgroup of several universities. The need of having various stakeholders within institution on the same page, the need of research data management to be properly positioned in the university strategy, the need to recognize the research data as assets of the institution, the need of institution to provide e-infrastructure and support system for research data management, and the need for research data management training were raised. To address these issues and raise awareness of university administration, AXIES, which is the association of ICT centers of Japanese universities, drafted the “Recommendations for Research Data Management at Academic Institutions.” This work is to be followed by 1) questionnaire survey template to be used by universities to understand the needs of researchers on research data management and 2) collection of case studies of research data management implementation.

Promoting Common Understanding on Research Data Management using Rubric Reviewed International journal

AOKI Takaaki, KAJITA Shoji, MOTOKI Tamaki, IYEMORI Toshihiko, KAWAGUCHI Tomoko

Proc. 2019 8th International Congress on Advanced Applied Informatics (IIAI-AAI) page： 387 - 390 2019.7

研究データマネジメントルーブリックによる自己評価と共通認識の醸成

青木学聡, 梶田将司, 元木環, 家森俊彦, 川口朋子

DEIM Forum 2019 page： C2-1 2019.3

Optimized Alkali-Metal Cationization in Secondary Ion Mass Spectrometry of Polyethylene Glycol Oligomers with up to m/ z 10000: Dependence on Cation Species and Concentration

Gnaser, H., Oki, R., Aoki, T., Seki, T., Matsuo, J.

Analytical Chemistry Vol. 92 ( 1 ) page： 1511 - 1517 2019

研究データ管理に関するeラーニング教材への反応と、研究支援者向けの新教材の開発について

芝翔太郎, 林正治, 常川真央, 山地一禎, 尾城孝一, 南山泰之, 青木学聡, 天野絵里子, 西薗由依

大学ICT推進協議会2018年度年次大会 (AXIES2018) 論文集 Vol. TB1-4 page： 1 - 4 2018.11

SIMS技術の飛躍的発展を支える新技術：新奇なイオンビーム開発から先端質量分析法まで

Takaaki Aoki

表面と真空 Vol. 61 ( 7 ) page： 426 - 434 2018.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Vacuum and Surface Science

<p>Recent progress of SIMS technique is reported in conjunction with novel primary ion beams and advanced mass spectrometers. Numerous applications of SIMS have been proposed and demonstrated in last decade, covering from organic semiconductors to cells and tissues. One of the biggest problems was "Static-Limit" for analysis of organic molecules, which is very fragile for ion bombardment. After innovation of massive cluster ion beams, the issue of "Static-Limit" has been overcame. This opens a new possibility for SIMS to analyze organic materials. Ultra-high mass resolution mass spectrometer, MS/MS technique, cationization enhancement and future prospects of SIMS are discussed.</p>

DOI： 10.1380/vss.61.426

Analysis of Organic Materials with SIMS Using New Probe Ions

Vol. 2018 ( 22 ) page： 29-33 2018.3

Cationization and fragmentation of molecular ions sputtered from polyethylene glycol under gas cluster bombardment: An analysis by MS and MS/MS Reviewed International journal

Thopan, Prutchayawoot, Gnaser, Hubert, Oki, Rika, Aoki, Takaaki, Seki, Toshio, Matsuo, Jiro

International Journal of Mass Spectrometry Vol. 430 page： 149 - 157 2018

Development and Deployment of Research Data Preservation Policy at a Japanese Research University in 2016 International journal

Takaaki Aoki, Shoji Kajita, Hirokazu Akasaka, Hagane Takeda

2017 6th IIAI International Congress on Advanced Applied Informatics (IIAI-AAI) page： 120 - 123 2017.7

Planning on Campus-wide Research Infrastructure enhancement through Academic Data Management support Environment along Research Lifecycle

KAJITA Shoji, AOKI Takaaki

IPSJ SIG TECHNICAL REPORT Vol. 2017-IOT-38 ( 4 ) page： 1 - 6 2017.6

Angled etching of Si by ClF3–Ar gas cluster injection Reviewed International journal

Toshio Seki, Hiroki Yamamoto, Takahiro Kozawa, Tadashi Shojo, Kunihiko Koike, Takaaki Aoki, Jiro Matsuo

Japanese Journal of Applied Physics Vol. 56 ( 6S2 ) page： 06HB02 2017.5

Fabrication of a Si lever structure made by double-angled etching with reactive gas cluster injection Reviewed International journal

T. Seki, H. Yamamoto, T. Kozawa, K. Koike, T. Aoki, J. Matsuo

APPLIED PHYSICS LETTERS Vol. 110 ( 18 ) 2017.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The reactive gas cluster injection process is an etching method that uses a neutral cluster beam without plasma. Low-damage Si etching can be realized with this method because of the very low irradiation energy; the product is free of charge-up problems and vacuum UV light damage. The ClF3-Ar neutral cluster injection system for angled etching was constructed with a nozzle that was placed at 45 degrees from the sample normal. The angled anisotropic Si etching is demonstrated with a high aspect ratio. The lever structure, which is often used in microelectromechanical systems (MEMSs), was fabricated by double-angled etching with reactive gas cluster injection. A simple fabrication process for the lever structure was achieved by double-angled etching with reactive gas cluster injection. These results show that various three-dimensional (3D) structures can be fabricated by repeated anisotropic etching with varying angles and directions. It is expected that the angled anisotropic etching process will enable the creation of unprecedented structures for use in MEMSs or photonic crystals.

DOI： 10.1063/1.4982970

Course Development of Electric and Electronic Circuit Exercise utilizing BYOD-PC and Course Management System

青木学聡, 久門尚史, 木村真之, 蛯原義雄, 下田宏

研究報告教育学習支援情報システム(CLE) Vol. 2017 ( 3 ) page： 1 - 5 2017.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：情報処理学会

Kyoto University Undergraduate School of Electrical and Electronic Engineering deployed a course of circuit exercise on the premise of BYOD-PC from FY 2016. This course is a compulsory subject for the school, so that the course curriculum was designed in consideration with "selection of relevant software and hardware" and "ICT facility support". This course was operated utilizing course management system to organize "distribution of textbook and related materials" and "submission of weekly and midterm reports" electronically. By use of BYOD-PC and course management system, we were able to introduce novel learning style for exercise subjects as well, such as flipped learning for acquisition of individual unit skills, and collaboration of project activities by group works.

Building and Development of Research Data Management Training Tool Reviewed

Mao Tsunekawa, Eriko Amano, Hayahiko Ozono, Yui Nishizono, Shota Maeda, Yuko Matsumoto, Yasuyuki Minamiyama, Taro Misumi, Takaki Aoki, Koichi Ojiro, Kazutsuna Yamaji

Joho Chishiki Gakkaishi Vol. 27 ( 4 ) page： 362 - 365 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Information and Knowledge

<p>　Research Data Management (RDM) is one of the important research process for promoting researchintegrity and open science. But, in Japan, there are few human resources have skill of RDM yet. So we, “Research Data Task Force” (RD-TF) be organized by JPCOAR, developed “RDM Training Tool” that is a training tool for learning skill of RDM and have published RDM Training Tool on 2017-06-06. Furthermore, we are cooperating with National Institute of Informatics (NII) for beginning online lecture courses named “Research data management in the open science era”. In this proposal, we introduced activities about supporting learning about Research Data Management, and discussion.</p>

DOI： 10.2964/jsik_2017_042

Development and Deployment of Research Data Preservation Policy at a Japanese Research University in 2016

Aoki Takaaki, Kajita Shoji, Akasaka Hirokazu, Takeda Hagane

2017 6th IIAI International Congress on Advanced Applied Informatics (IIAI-AAI) page： 120 - 123 2017

Language：English Publishing type：Research paper (scientific journal)

This paper reviews the policy development and deployment for research data preservation at Kyoto University, Japan, during fiscal year (FY) 2016. The universitys regulations and guidelines for research integrity and data preservation were formulated in FY2014 and 2015, in response to statements from the Ministry of Education, Culture, Sports, Science and Technology, and supplemental comments by Science Council of Japan (in FY2014). In FY2016, several departments at KU developed a prototype system for research data preservation using open source web frameworks with preference to agility of deployment rather than robustness. The prototype system also worked as the proof of concept for a full-service research data preservation system, which is due to be deployed by KUs central IT department in FY2017 for university-wide use.

Design of Long-term Data Preservation System using Enterprise Content Management and Optical Disc Archive Storage

AOKI Takaaki, KAJITA Shoji, AKASAKA Hirokazu, TAKEDA Hagane

AXIES Annucal Conference 2016 2016.12

Improvement of CMS Operation at User Side -- A Case of Assignment Tool on Sakai

Aoki, Takaaki, Kita, Hajime

2016.12

Language：Japanese Publishing type：Research paper (scientific journal)

AXIES: 大学ICT推進協議会 2016年度年次大会Webベースの情報システムは操作面での改善をユーザサイドでは行いにくいという欠点がある．コース管理システム(CMS)も教員が本格的に利用する上では授業を受講する多くの学生と個々にインタラクションする場合の操作量が相当に多いという課題があるがこれを実運用するサーバ側で改善することは管理上の問題なども発生する．本報告では Sakai の課題ツールで回答を一括ダウンロードできることを利用し，回答を効果的に閲覧するプログラムを作成することでユーザ側での運用を改善する試みについて報告する．

Molecular dynamics simulations study of nano particle migration by cluster impact Reviewed

Takaaki Aoki, Toshio Seki, Jiro Matsuo

Surface and Coatings Technology Vol. 306 page： 63 - 68 2016.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier {BV}

© 2016 Elsevier B.V.Molecular dynamics (MD) simulations are performed in order to investigate the radiation effects of a huge and slow gas cluster for the surface cleaning process. When a large argon cluster with the size ranging from 20,000 to 300,000 is accelerated with a total of 30. keV, each constituent atom carries very low energy ranging from 1.5. eV/atom to 0.1. eV/atom. In many cases, the cluster does not penetrate the solid target surface but is deflected in a lateral direction. This collisional process results in a high density particle flow spreading along the surface plane due to cohesion of the cluster, which suggests the capability to modify the irregular surface structure, without damage in the target. The MD simulations demonstrate that such a huge cluster sweeps a nano particle (NP, 3. nm in radius) attached on a planar silicon target's surface. From the investigation of various conditions of cluster impact, it is found that the migration distance is correlated with the kinetic energy applied on the NP by the impact of cluster atoms. Additionally, the MD results suggest the existence of optimized parameters for the maximum migration distance for the offset distance between the cluster and the NP, and the cluster size for constant total energy (equivalent to energy per atom or kinetic energy density). The optimized offset distance was estimated as the summation of radii of the incident cluster and the NP. The optimized energy per atom was suggested around 0.6. eV/atom, where the cluster efficiently spreads in lateral direction keeping higher kinetic energy density of particle flow.

DOI： 10.1016/j.surfcoat.2016.04.053

Other Link： http://orcid.org/0000-0002-5926-4903

Reactive etching by ClF

Seki Toshio, Yoshino Yu, Senoo Takehiko, Koike Kunihiko, Aoki Takaaki, Matsuo Jiro

Jpn. J. Appl. Phys. Vol. 55 ( 6 ) page： 06HB01 2016.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Physics

A reactive gas cluster injection system with a scanning function was developed in order to increase the processing area. High-precision anisotropic etching with an aspect ratio of 7 was achieved for ClF<inf>3</inf>cluster etching without scanning. However, with scanning, the aspect ratio for etching decreased to 1.5 because the side walls were etched by the gas retained in the trench. By reducing the source gas pressure, increasing the target distance, and mixing He in the source gas, anisotropic etching with an aspect ratio of about 6.3 was achieved with this apparatus.

DOI： 10.7567/JJAP.55.06HB01

Development of ambient SIMS using mega-electron-volt-energy ion probe Reviewed

Masakazu Kusakari, Makiko Fujii, Toshio Seki, Takaaki Aoki, Jiro Matsuo

Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics Vol. 34 ( 3 ) 2016.5

Language：English Publishing type：Research paper (scientific journal) Publisher：American Institute of Physics Inc.

A new secondary ion mass spectrometry device using an ion probe in the heavy mega-electron-volt (MeV) energy range was developed for detecting large intact molecules with high sensitivity under ambient conditions. The instrument is based on the characteristics induced by the MeV-energy heavy ions, namely, electronic excitation induced in the near-surface region and the high transmission capability under ambient conditions. The secondary ions were transported to the mass analyzer effectively by an electric field and atmospheric gas flow, whereas the chemical impurities from the gas were cleared by using an electric field. In addition, this new ambient analysis approach enables evaluation not only of solid samples, but also of liquid samples that were evaporated under advanced vacuum. In this study, liquid water and samples of a benzoic acid solution were measured under ambient conditions.

DOI： 10.1116/1.4941724

Development of ambient SIMS using mega-electron-volt-energy ion probe Reviewed

Masakazu Kusakari, Makiko Fujii, Toshio Seki, Takaaki Aoki, Jiro Matsuo

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Vol. 34 ( 3 ) page： 4 2016.5

Language：English Publishing type：Research paper (scientific journal) Publisher：A V S AMER INST PHYSICS

A new secondary ion mass spectrometry device using an ion probe in the heavy mega-electron-volt (MeV) energy range was developed for detecting large intact molecules with high sensitivity under ambient conditions. The instrument is based on the characteristics induced by the MeV-energy heavy ions, namely, electronic excitation induced in the near-surface region and the high transmission capability under ambient conditions. The secondary ions were transported to the mass analyzer effectively by an electric field and atmospheric gas flow, whereas the chemical impurities from the gas were cleared by using an electric field. In addition, this new ambient analysis approach enables evaluation not only of solid samples, but also of liquid samples that were evaporated under advanced vacuum. In this study, liquid water and samples of a benzoic acid solution were measured under ambient conditions. (C) 2016 American Vacuum Society.

DOI： 10.1116/1.4941724

Secondary ion emission from leucine and isoleucine under argon gas-cluster ion bombardment Reviewed

Hubert Gnaser, Masakazu Kusakari, Makiko Fujii, Toshio Seki, Takaaki Aoki, Jiro Matsuo

JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B Vol. 34 ( 3 ) 2016.5

Language：English Publishing type：Research paper (scientific journal) Publisher：A V S AMER INST PHYSICS

The emission of sputtered ions from isoleucine and leucine specimens under bombardment by 10 keV argon gas-cluster ions Ar-1000(+) was investigated by orthogonal time-of-flight secondary ion mass spectrometry, in an attempt to examine the possibility of discriminating these amino acids by means of specific differences in their mass spectra. Apart from of the protonated molecular ions (M+H)(+) a prolific flux of singly charged and doubly charged molecular cluster ions, (M-n+H)(+) (1 <= n <= 15) and (M-n+2H)(2+) (8 <= n <= 29) was observed. The distributions of the cluster yields Y-n as a function of their size n were found to be very similar for both amino acids. In addition, the fraction of emitted fragment and other ion species is typically low, and no distinct differences were detected for isoleucine and leucine. Therefore, the present data seem to indicate that a discrimination of isoleucine and leucine via mass spectrometric means is not possible. (C) 2016 American Vacuum Society.

DOI： 10.1116/1.4939497

Observation of Liquid Water with Ambient SIMS

Kusakari M., Fujii M., Seki T., Aoki T., Matsuo J.

Transactions of the Materials Research Society of Japan Vol. 41 ( 3 ) page： 309 - 311 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：The Materials Research Society of Japan

<p> Secondary ion mass spectrometry (SIMS) is powerful method for obtaining component information from solid samples, such as semiconductor devices and biological tissue. Moreover, SIMS has high surface sensitivity because of the use of a primary ion probe. The keV-energy ion probe is, however, unstable under low vacuum conditions and this makes evaluation of volatile liquid samples difficult. A new SIMS technique that uses an MeV-energy heavy ion probe, called ambient SIMS, enables measuring volatile liquid samples under ambient conditions by high transmission capability of the primary probe. In this study, water in liquid form, which has a relatively high vapor pressure (2,339 Pa at 20℃), was evaluated by ambient SIMS and gave some cluster ions with high intensity. This result suggests that ambient SIMS has significant potential for evaluating both solid and liquid samples with high sensitivity.</p>

DOI： 10.14723/tmrsj.41.309

Ambient analysis of liquid materials with Wet-SIMS Reviewed

Seki, T., Kusakari, M., Fujii, M., Aoki, T., Matsuo, J.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms Vol. 371 page： 189 - 193 2016

Language：English Publishing type：Research paper (scientific journal)

© 2015 Elsevier B.V. All rights reserved.Secondary ion mass spectrometry (SIMS) is a method with high surface sensitivity that allows both elemental and molecular analysis. However, volatile liquid (wet) samples are difficult to measure using conventional SIMS, because samples must be dried and introduced into a high vacuum chamber. The mean free path of ions with energy in the keV range is very short in low vacuum and these ions cannot penetrate the surface. In contrast, ions in the MeV-energy range have high transmission capability in low vacuum and wet samples can be measured using heavy ions without dry sample preparation. Ion beams in the MeV-energy range also excite electrons near the surface and enhance the ionization of high-mass molecules and thus fragment-suppressed SIMS spectra of ionized molecules can be obtained. We have developed an ambient analysis system with secondary ion mass spectrometry for wet samples (Wet-SIMS) that operates from low vacuum to 30 kPa using MeV-energy heavy ion beams. The system is equipped with fine apertures that avoid vacuum degradation at both the primary beam incidence and the secondary ion measurement sides, even when the target chamber is filled with He gas at 30 kPa. Water evaporation was suppressed in a He atmosphere of 16.5 kPa and a solution of benzoic acid could be measured using MeV-energy heavy ions.

DOI： 10.1016/j.nimb.2015.09.046

Development of Low-vacuum SIMS instruments with large cluster Ion beam Reviewed

Suzuki, K., Kusakari, M., Fujii, M., Seki, T., Aoki, T., Matsuo, J.

Surface and Interface Analysis Vol. 48 ( 11 ) page： 1121 - 1121 2016

Development of ambient SIMS using mega-electron-volt-energy ion probe Reviewed

Masakazu Kusakari, Makiko Fujii, Toshio Seki, Takaaki Aoki, Jiro Matsuo

Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena Vol. 34 ( 3 ) 2016

Secondary ion emission from leucine and isoleucine under argon gas-cluster ion bombardment Reviewed

Gnaser, H., Kusakari, M., Fujii, M., Seki, T., Aoki, T., Matsuo, J.

Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics Vol. 34 ( 3 ) page： 5 2016

Language：English Publishing type：Research paper (scientific journal)

© 2016 American Vacuum Society.The emission of sputtered ions from isoleucine and leucine specimens under bombardment by 10 keV argon gas-cluster ions Ar 1000 + was investigated by orthogonal time-of-flight secondary ion mass spectrometry, in an attempt to examine the possibility of discriminating these amino acids by means of specific differences in their mass spectra. Apart from of the protonated molecular ions (M+H)+ a prolific flux of singly charged and doubly charged molecular cluster ions, (Mn+H)+ (1 ≤ n ≤ 15) and (Mn+2H)2+ (8 ≤ n ≤ 29) was observed. The distributions of the cluster yields Yn as a function of their size n were found to be very similar for both amino acids. In addition, the fraction of emitted fragment and other ion species is typically low, and no distinct differences were detected for isoleucine and leucine. Therefore, the present data seem to indicate that a discrimination of isoleucine and leucine via mass spectrometric means is not possible.

DOI： 10.1116/1.4939497

Yields and images of secondary ions from organic materials by different primary Bi ions in time-of-flight secondary ion mass spectrometry Reviewed

Shishido, R., Fujii, M., Seki, T., Aoki, T., Matsuo, J., Suzuki, S.

Rapid Communications in Mass Spectrometry Vol. 30 ( 4 ) page： 476 - 482 2016

Language：English Publishing type：Research paper (scientific journal)

© 2016 John Wiley & Sons, Ltd.Rationale Bi cluster ions are used as a source of primary ions for time-of-flight secondary ion mass spectrometry (TOF-SIMS), and it has been recognized that secondary ion yields of macromolecules are higher with Bi cluster ions than with monomer ions or other cluster ions such as Cs+, Ga+ and Aun+. However, the analysis conditions of Bi cluster TOF-SIMS are not sufficiently established. This study provides information on the secondary ion yields, damage cross-section and spatial resolution obtained with different primary Bi ions. Methods We investigated the secondary ion yields, damage cross-section and spatial resolution using three different primary Bi ions in TOF-SIMS. The primary ions selected were Bi1+, Bi3+ and Bi32+ that were accelerated with 25 kV and the positively charged secondary ions were analyzed. The samples were 1, 2-distearoyl-sn-glycero-3-phosphocholine (C44H88NO8P, DSPC), which is a typical lipid, and N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine (C44H32N2, NPD) and 4,4',4"-tris[2-naphthyl(phenyl)amino]triphenylamine (C66H48N4, 2-TNATA), which are organic functional materials. Results Although the secondary ion yields of DSPC were highest when measured with Bi3+, the spatial resolution obtained from all DSPC analyses could not be evaluated because of the low intensity of the secondary molecular ions. On the other hand, for both NPD and 2-TNATA, the secondary ion yields were highest when imaged with Bi32+. Also, we obtained the highest spatial resolution using Bi32+. In the analysis of all molecules, the damage cross-section obtained with Bi32+ was also the highest. Conclusions When secondary ions were sensitively detected, images of the high spatial resolution were obtained by using Bi32+. On the other hand, when the secondary ion sensitivity was low, the spatial resolution depended on the yields of secondary ions, implying that the selection of the primary ion species is crucial for SIMS analysis of large molecules.

DOI： 10.1002/rcm.7455

Recent progress in cluster beam technique Reviewed

Matsuo, J., Fujii, M., Seki, T., Aoki, T.

Seimitsu Kogaku Kaishi/Journal of the Japan Society for Precision Engineering Vol. 82 ( 4 ) page： 309 - 314 2016

Recent Developments of Cluster Ion Beam —From Nano-fabrication to Analysis of Bio-materials—

MATSUO Jiro, FUJII Makiko, SEKI Toshio, AOKI Takaaki

Journal of the Vacuum Society of Japan Vol. 59 ( 5 ) page： 113 - 120 2016

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Vacuum Society of Japan

&emsp;Recent progress of cluster ion beam was overviewed. Various applications, such as nano-fabrication and biological material analysis, have been developed by using cluster effects, which are due to high-density and multiple collision between cluster ion and surface. Control of size and energy of cluster beam is essential. High speed etching with high anisotropy is realized with neutral cluster beam, which has very low energy/atom. Both molecular depth profiling of organic multilayer and high resolution molecular imaging were demonstrated by using cluster ions. These new XPS and SIMS techniques provide new opportunities for polymer, molecular electronics, biological materials and life science.<br>

DOI： 10.3131/jvsj2.59.113

Molecular cluster emission in sputtering of amino acids by argon gas-cluster ions

Masakazu Kusakari, Hubert Gnaser, Makiko Fujii, Toshio Seki, Takaaki Aoki, Jiro Matsuo

INTERNATIONAL JOURNAL OF MASS SPECTROMETRY Vol. 383 ( 1 ) page： 31 - 37 2015.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Ten pure amino acid specimens (alanine, arginine, asparagine, glutamine, glutamic acid, isoleucine, leucine, phenylalanine, threonine, and tyrosine) and three binary mixtures (phenylalanine/tyrosine, phenylalanine/arginine, and arginine/tyrosine) were bombarded by 10 key argon gas-cluster ions Ar-1000(+) and the sputter-induced emission of positive secondary ions was investigated by orthogonal time-of-flight secondary ion mass spectrometry (TOF-SIMS). A prolific flux of protonated molecular cluster ions (M-n+H)(+) was observed, with up to n=22 for alanine. In most cases, the cluster yields Y-n were found to follow an overall exponential decay with cluster size n, Y-n proportional to exp(-beta n), although a non-monotonous decrease was found for some clusters. The parameter beta varies between similar to 0.2 and similar to 0.65 for the different amino acids; it seems to scale inversely with the respective sputtering yields of the materials. Generally, the yields of dimers relative to monomers are surprisingly high, amounting to 20-170% whereas those of trimers and tetramers are in the range of 10-90%. In amino acid samples with an (unintentionally) enhanced Na content, Na-cationized cluster (M-n+Na)(+) were found in addition to (M-n+H)(+). For both molecular cluster species the yields exhibit a very similar dependence on the cluster size n. From the binary mixtures, the emission of both homo- and heteromolecular clusters was observed; their size distributions seem to indicate that the two components were not homogeneously distributed within the samples. (C) 2015 Published by Elsevier B.V.

DOI： 10.1016/j.ijms.2015.04.003

Progress and applications of cluster ion beam technology Reviewed

I. Yamada, J. Matsuo, N. Toyoda, T. Aoki, T. Seki

CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE Vol. 19 ( 1 ) page： 12 - 18 2015.2

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Cluster ion beam processing has been extensively developed during the 25 years since the concept originated. Low energy surface interaction effects, lateral sputtering phenomena and high-rate chemical reaction effects have been explored experimentally and have been explained by means of molecular dynamics (MD) modeling. Practical production equipment for a wide range of applications has also been successfully developed. The technology is now advancing rapidly in the fields of sub-nanoscale processing of metals, semiconductors and insulating materials. This paper reviews important events which have taken place during the development with emphasis placed on emerging new advances which have occurred during several recent years. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.cossms.2014.11.002

Analysis of liquid materials in low vacuum with Wet-SIMS Reviewed

Toshio Seki, Makiko Fujii, Masakazu Kusakari, Shunichiro Nakagawa, Takaaki Aoki, Jiro Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 46 ( 12-13 ) page： 1133 - 1136 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

In conventional SIMS with keV-energy ion beams, elastic collisions occur between projectiles and atoms in the constituent molecules. The collisions produce fragments, making the acquisition of molecular information difficult. Volatile liquid samples (wet samples) are also difficult to measure using conventional SIMS because samples must be dried first and then introduced into the high-vacuum chamber. In contrast, ion beams with MeV-energy excite electrons near the surface and enhance the ionization of high-mass molecules; hence, a fragment-suppressed SIMS spectrum of ionized molecules can be obtained. We developed a SIMS analysis system for wet samples (Wet-SIMS) that works under low-vacuum pressures up to 1000Pa using heavy MeV-energy ion beams. The evaporation of heptanoic acid was suppressed under the low-vacuum pressure of 1000Pa, and the wet samples, which included volatile materials with different vapor pressures, could be measured using heavy MeV-energy ions. Copyright (c) 2014 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.5528

Quantitative analysis of lipids with argon gas cluster ion beam secondary ion mass spectrometry

Makiko Fujii, Shunichirou Nakagawa, Toshio Seki, Takaaki Aoki, Jiro Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 46 ( 12-13 ) page： 1129 - 1132 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Ar gas cluster ion beam (Ar-GCIB) SIMS has been developed as one of the powerful tools used for analyzing organic materials because of the high secondary ion yield of large organic molecules due to soft' sputtering mechanism of this technique. However, for practical analysis of complex biological samples, high quantitative accuracy is strongly required besides high sensitivity. In this study, some pure and compound lipid samples were measured with our originally equipped Ar-GCIB SIMS apparatus with the aim of determining the quantitative accuracy of this technique. It was found that the detection limit of the Ar-GCIB SIMS apparatus was lower than 0.1%. In addition, there was almost no matrix effect between the organic substances of similar chemical structures. Copyright (c) 2014 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.5518

Lipid compounds analysis with MeV-SIMS apparatus for biological applications

Makiko Fujii, Masakazu Kusakari, Kazuhiro Matsuda, Naoki Man, Toshio Seki, Takaaki Aoki, Jiro Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 46 ( S1 ) page： 353 - 356 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Secondary ion mass spectrometry (SIMS) is one of the powerful methods that can be applied to high sensitivity mass analysis and high-spatial resolution mass imaging. For the analysis of minor components of the complex biological samples, however, superior sensitivity with low background is required. We have developed an MeV-SIMS apparatus with distinctively high secondary ion yield for large organic molecules. In this study, the detection limit of our original MeV-SIMS apparatus was investigated using compounds of two lipids. In the acquired mass spectra, the molecular ions of both lipids were clearly observed with high quantitativity. In addition, the results were compared with conventional time-of-flight-SIMS results. As a result, the detection limit of MeV-SIMS apparatus was found to be below 0.1% and was much lower than that of the conventional Bi cluster SIMS. Copyright (c) 2014 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.5524

Biomaterial imaging with MeV-energy heavy ion beams Reviewed

Toshio Seki, Yoshinobu Wakamatsu, Shunichiro Nakagawa, Takaaki Aoki, Akihiko Ishihara, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 332 page： 326 - 329 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The spatial distribution of several chemical compounds in biological tissues and cells can be obtained with mass spectrometry imaging (MSI). In conventional secondary ion mass spectrometry (SIMS) with key-energy ion beams, elastic collisions occur between projectiles and atoms of constituent molecules. The collisions produce fragments, making the acquisition of molecular information difficult. In contrast, ion beams with MeV-energy excite near-surface electrons and enhance the ionization of high-mass molecules; hence, SIMS spectra of fragment-suppressed ionized molecules can be obtained with MeV-SIMS. To compare between MeV and conventional SIMS, we used the two methods based on MeV and Bi-3-keV ions, respectively, to obtain molecular images of rat cerebellum. Conventional SIMS images of m/z 184 were clearly observed, but with the Bi-3 ion, the distribution of the molecule with m/z 772.5 could be observed with much difficulty. This effect was attributed to the low secondary ion yields and we could not get many signal counts with key-energy beam. On the other hand, intact molecular ion distributions of lipids were clearly observed with MeV-SIMS, although the mass of all lipid molecules was higher than 500 Da. The peaks of intact molecular ions in MeV-SIMS spectra allowed us to assign the mass. The high secondary ion sensitivity with MeV-energy heavy ions is very useful in biomaterial analysis. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2014.02.088

Novel SIMS system with focused massive cluster ion source for mass imaging spectrometry with high lateral resolution Reviewed

Jiro Matsuo, Souta Torii, Kazuki Yamauchi, Keisuke Wakamoto, Masakazu Kusakari, Shunichiro Nakagawa, Makiko Fujii, Takaaki Aoki, Toshio Seki

APPLIED PHYSICS EXPRESS Vol. 7 ( 5 ) page： 1 - 56602 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

Recent developments in cluster ion beams for secondary ion mass spectrometry (SIMS) have enabled the realization of molecular depth profiling and mass imaging of organic and biological materials. Massive Ar cluster beams present reduced surface damage and fragmented ion generation and are suitable as primary beams for SIMS. We recently obtained a finely focused massive 1.2-mu m-diameter cluster ion beam and combined it with an orthogonal acceleration time-of-flight mass spectrometer. A mesh pattern of a phospholipid thin film was clearly reproduced in the mass images of molecular ions with a measurement time of 100 s. (C) 2014 The Japan Society of Applied Physics

DOI： 10.7567/APEX.7.056602

Study on the detection limits of a new argon gas cluster ion beam secondary ion mass spectrometry apparatus using lipid compound samples Reviewed

Makiko Fujii, Shunichirou Nakagawa, Kazuhiro Matsuda, Naoki Man, Toshio Seki, Takaaki Aoki, Jiro Matsuo

RAPID COMMUNICATIONS IN MASS SPECTROMETRY Vol. 28 ( 8 ) page： 917 - 920 2014.4

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

RATIONALEAr gas cluster ion beam secondary ion mass spectrometry (Ar-GCIB SIMS) has been developed as one of the most powerful tools used for analyzing complex biological materials because of its distinctively high secondary ion yield of large organic molecules. However, for the practical analysis of minor components in complex biological materials, the sensitivity of the technique is still insufficient.
METHODSThe detection limits of our original Ar-GCIB SIMS apparatus were investigated by measuring lipid compound samples in positive ion mode. The samples were mixtures of 1,2-distearoyl-sn-glycero-3-phosphocholine (C44H88NO8P, DSPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (C40H80NO8P, DPPC). The primary ions were accelerated with 10keV and the mean cluster size was 1500. The secondary [M+H](+) ions emitted from the sample were analyzed using an orthogonal acceleration time-of-flight mass spectrometer (oa-TOF-MS). In addition, the isotope abundance ratio and the ratio of the [M+H](+) ion signal to the fragment ion signal acquired with Ar-GCIB SIMS were compared with those obtained with conventional Bi cluster SIMS.
RESULTSSecondary [M+H](+) ions and some characteristic fragment ions were clearly observed with high quantitative accuracy in the mass spectra acquired with Ar-GCIB SIMS. The results were clearly better than those obtained with conventional Bi cluster SIMS.
CONCLUSIONSThe detection limit of Ar-GCIB SIMS was found to be below 0.1% and was much lower than that of conventional Bi cluster SIMS because of the high [M+H](+) ion yield and the low background. The results suggested that the new Ar-GCIB SIMS apparatus has the capability to acquire valuable information on complex biological materials. Copyright (c) 2014 John Wiley & Sons, Ltd.

DOI： 10.1002/rcm.6867

Molecular dynamics simulations of cluster impacts on solid targets: implantation, surface modification, and sputtering Reviewed

Takaaki Aoki

JOURNAL OF COMPUTATIONAL ELECTRONICS Vol. 13 ( 1 ) page： 108 - 121 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The collisions of cluster projectiles on solid targets were studied using molecular dynamics (MD) simulations. The penetration range and damage induced by small boron and carbon cluster implantations are compared with those induced by monomers with the same energy per atom. The simulations indicated enhanced penetration depth and the formation of dense track damage at the surface region. In addition, large argon and fluorine clusters (up to 1 million atoms) have shown effects such as crater formation and low-damage surface etching of silicon. The MD simulations revealed that cluster penetration and crater formation depends not on the total incident energy, but on the incident energy per atom, and that the damage threshold for the argon cluster is several eV/atom. In the impact of a very large and slow fluorine cluster on silicon, an enhancement of chemical reactivity at the near surface region was observed because of the high density of fluorine molecules depositing kinetic energy.

DOI： 10.1007/s10825-013-0504-5

Other Link： http://orcid.org/0000-0002-5926-4903

Prolific cluster emission in sputtering of phenylalanine by argon-cluster ion bombardment Reviewed

Hubert Gnaser, Makiko Fujii, Shunichirou Nakagawa, Toshio Seki, Takaaki Aoki, Jiro Matsuo

INTERNATIONAL JOURNAL OF MASS SPECTROMETRY Vol. 360 ( 1 ) page： 54 - 57 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Large Ar-n(+) cluster ions (with n similar to 1500 Ar atoms per cluster) with a bombarding energy of 10 keV were used to investigate the sputter-induced emission of positive secondary ions from a phenylalanine specimen by orthogonal time-of-flight SIMS. An abundant flux of phenylalanine cluster ions (M-n+H)(+) with n <= 12 was observed. The yield of dimers relative to monomers is found to amount to 50 - 60% whereas that of turners and tetramers is roughly 10%. Tentatively, this prolific formation of these cluster species can then be ascribed to the concerted action of the large number of Ar atoms within their impact zone at the surface: these low-energy Ar species (with an average energy of only few eV) may effect the soft cleavage of the phenylalanine bonds in the solid and lead, eventually, to the intact emission of these phenylalanine moieties. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ijms.2013.12.024

クラスターSIMS法による脂質分子の高感度検出とイメージングへの応用

Takaaki Aoki

表面科学 Vol. 35 ( 7 ) page： 351 - 355 2014.1

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Surface Science Society of Japan

In recent years, the analysis of biological samples has been extensively performed in pharmacokinetic and metabolic studies. The use of Secondary Ion Mass Spectrometry (SIMS) with conventional monomer ion beams, such as Ar<sup>+</sup>, Cs<sup>+</sup> or Ga<sup>+</sup>, in biological applications is difficult because of the low secondary ion yield of large organic molecules and the complicated fragment ion signals. The use of cluster ions as primary projectiles in SIMS has spread dramatically in the past decade. Bismuth (Bi) cluster ions are now the most familiarized primary ions in cluster SIMS because of the high convergence property and the high molecular ion yield. Argon gas cluster ion beam (Ar-GCIB) is also one of the most attractive primary projectiles for biological application because of the soft sputtering without damage accumulation. However, our knowledge of detection limit and sensitivity is still insufficient for the practical analysis of complex biological samples with cluster SIMS. In addition, imaging mass spectrometry with high spatial resolution is crucially essential for tissue and cell analysis. In this study, lipid standard samples were measured in order to examine the detection limit and the spatial resolution of our Ar-GCIB SIMS, and the results were compared with those of the commercial Bi cluster SIMS. The results indicated that Ar-GCIB SIMS has a capability to obtain the valuable information in biological analysis, however, the improvement on spatial resolution and sensitivity is still required.

DOI： 10.1380/jsssj.35.351

Low Vacuum SIMS Measurements of Higher Alcohols with MeV-energy Heavy Ion Beam

Kusakari Masakazu, Fujii Makiko, Seki Toshio, Aoki Takaaki, Matsuo Jiro

Trans. Mat. Res. Soc. Japan Vol. 39 ( 3 ) page： 265 - 268 2014

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Materials Research Society of Japan

The technique of secondary ion mass spectrometry (SIMS) using an ion beam with MeV-energy has been developed to visualize the spatial distribution of biological tissues and cells with high spatial resolution. In this analytical technique, low vacuum is essential for keeping the samples wet. The effect of evaporation of volatile samples on the SIMS spectra was investigated under vacuum pressures of 50 and 500 Pa by using two higher alcohols, 1-decanol and 1-dodecanol. The results indicated that secondary ions of monomer and multimer species were generated by different phases in the sample. Moreover, the comparison of mass spectra obtained under the vacuum conditions of 50 and 500 Pa separately demonstrated that the secondary ion yields were affected by the gas flow adjusting the vacuum, whereas analysis at lower vacuum conditions allowed obtaining constant secondary ion intensity from volatile samples. The results clearly indicated the advantage of ambient analysis with the MeV-SIMS apparatus.

DOI： 10.14723/tmrsj.39.265

An electrostatic quadrupole doublet focusing system for MeV heavy ions in MeV-SIMS Reviewed

T. Seki, S. Shitomoto, S. Nakagawa, T. Aoki, J. Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 315 page： 356 - 359 2013.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The importance of imaging mass spectrometry (MS) for visualizing the spatial distribution of molecular species in biological tissues and cells is growing. In conventional SIMS with key-energy ion beams, elastic collisions occur between projectiles and atoms in constituent molecules. The collisions produce fragments, making acquisition of molecular information difficult. In contrast, MeV-energy ion beams excite electrons near the surface and enhance the ionization of high-mass molecules, hence, fragment suppressed SIMS spectrum of ionized molecules can be obtained. This work is a further step on our previous report on the successful development of a MeV secondary ion mass spectrometry (MeV-SIMS) for biological samples. We have developed an electrostatic quadrupole doublet (EQ doublet) focusing system, made of two separate lenses, Q1 and Q2, to focus the MeV heavy ion beam and reduce measurement time. A primary beam of 6 MeV Cu4+ was focused with this EQ doublet. We applied 1120 V to the 121 lens and 1430 V to the Q2 lens, and the current density increased by a factor of about 60. Using this arrangement, we obtained an MeV-SIMS image of 100 x 100 pixels of cholesterol-OH+ of cerebellum (m/z = 369.3) over a 4 mm x 4 mm field of view, with a pixel size of 40 mu m within 5 min, showing that our EQ doublet reduces the measurement time of current imaging by a factor of about 30. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2013.05.069

Molecular dynamics simulation study of damage formation and sputtering with huge fluorine cluster impact on silicon Reviewed

Takaaki Aoki, Toshio Seki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 303 page： 170 - 173 2013.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Damage formation and sputtering processes by large reactive cluster impact on solid target were studied by molecular dynamics (MD) simulation. A (F-2)(500.000) cluster was accelerated at 1 MeV (1 eV/atom, 3.2 km/s) and projected toward a Si(100) target which consisted of more than 130,000,000 atoms. The MD simulation result showed that wide and shallow crater is formed due to the impingement of the bottom part of the incident cluster. The target atoms in a large area surrounding the impact point were largely displaced and some of them remained as a point defect or as a stacking fault, which reached more than 10 nm deep into the target surface. By the single impact of the cluster, about 12,000 silicon atoms were desorbed into the vacuum. The desorbed products were in the form of not only mono-silicon fluoride but also in larger silicon-fluoride composite clusters. The distribution of initial position of desorbed silicon atoms showed that most of desorbed products were generated in the region close to the crater edge corresponding to the radius of incident cluster. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2012.10.040

Other Link： http://orcid.org/0000-0002-5926-4903

Development of gas cluster ion beam irradiation system with an orthogonal acceleration TOF instrument Reviewed

K. Ichiki, J. Tamura, T. Seki, T. Aoki, J. Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 45 ( 1 ) page： 522 - 524 2013.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Surface damage induced on biomolecules with gas cluster ion beam (GCIB) irradiation is significantly lower than with atomic or small cluster ion beams, and for this reason, surface analysis techniques such as secondary ion mass spectrometry (SIMS) have become one of the most important applications of GCIB, particularly for microscale chemical imaging of biomolecular species. Because of the low duty-cycle in time-of-flight (TOF)-SIMS, only less than 0.1 % of the incident ion beam is used for analysis, meaning that analysis with high spatial resolution can practically be extremely lengthy. The duty cycle can be significantly improved with the orthogonal acceleration (oa) TOF method because with this method secondary ion mass spectra can be measured at high mass resolution without requiring a pulsed primary ion beam. In this study, we developed a gas cluster ion irradiation system mounted on an oa-TOF instrument and investigated the sputtering yield and secondary ion yield of arginine. Copyright (C) 2012 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.5092

Ion-induced damage evaluation with Ar cluster ion beams Reviewed

Yasuyuki Yamamoto, Kazuya Ichiki, Toshio Seki, Takaaki Aoki, Jiro Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 45 ( 1 ) page： 167 - 170 2013.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

Ion-induced damage on organic materials has been evaluated with secondary ion mass spectrometry. However, conventional sputtering beams such as SF5+ and C-60(+) cannot etch organic materials without inducing damage, and evaluating the damage depth distribution in these materials is difficult. Large gas cluster ions can etch organic materials without damage, and in this study, the damaged layer thickness was evaluated by molecular depth profiling with Ar cluster ion beam. The characteristic molecular ions were not detected in the spectra after etching with Ar monomer beam, indicating that the chemical structures of phenyl-C61-butyric acid methyl ester (PCBM) and polystyrene (PS) were seriously damaged. The intensity of the fullerene molecular ion reached a peak at the depth of about 35 nm. For PS, the peak intensity of m/z 91 increased with sputtering depth and saturated at about 45 nm. These values agreed with the projection range of Ar+ in PCBM and PS, respectively. These results indicate that the ion-induced damage depth was the same as the projection range of its ion. Copyright (C) 2012 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.5014

Other Link： http://orcid.org/0000-0002-5926-4903

Peptide dissociation patterns in secondary ion mass spectrometry under large argon cluster ion bombardment Reviewed

Hubert Gnaser, Makiko Fujii, Shunichirou Nakagawa, Toshio Seki, Takaaki Aoki, Jiro Matsuo

Rapid Communications in Mass Spectrometry Vol. 27 ( 13 ) page： 1490 - 1496 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

RATIONALE The analysis of organic and biological substances by secondary ion mass spectrometry (SIMS) has greatly benefited from the use of cluster ions as primary bombarding species. Thereby, depth profiling and three-dimensional (3D) imaging of such systems became feasible. Large Arn+ cluster ions may constitute a further improvement in this direction. METHODS To explore this option, large Arn+ cluster ions (with n ~1500 Ar atoms per cluster) were used to investigate the emission of positive secondary ions from two peptide specimens (angiotensin I and bradykinin) by orthogonal time-of-flight SIMS using bombarding energies 6, 10 and 14 keV. RESULTS For both peptides, the protonated molecular ion is observed in the mass spectra. In addition, distinct fragmentation patterns were observed
these indicate that fragment ions under Ar cluster irradiation form primarily via cleavage of bonds along the peptide backbone whereas the rapture of side chains occurs much less frequently. These features appear to be similar to low-energy collision-induced dissociation pathways. CONCLUSIONS Tentatively, these findings can then be ascribed to the concerted action of the large number of Ar atoms in the impact zone of cluster at the surface: these low-energy Ar species (with an average energy of few eV) may effect the cleavage of the peptide bonds and lead, eventually, to the emission of the fragment ions. Copyright © 2013 John Wiley &amp
Sons, Ltd. Copyright © 2013 John Wiley &amp
Sons, Ltd.

DOI： 10.1002/rcm.6599

Other Link： http://orcid.org/0000-0002-5926-4903

Ultrafine particle removal using gas cluster ion beam technology

Kazuya Dobashi, Kensuke Inai, Misako Saito, Toshio Seki, Takaaki Aoki, Jiro Matsuo

IEEE Transactions on Semiconductor Manufacturing Vol. 26 ( 3 ) page： 328 - 334 2013

Language：English Publishing type：Research paper (scientific journal)

In this paper, the ultrafine particle removal using CO2 gas cluster ion beam (GCIB) technology is investigated. The CO2 GCIB is irradiated the sample at an angle of 0 with respect to the surface normal. The higher particle removal efficiency can be achieved at the higher kinetic energy of the gas cluster, and the inside space of line and space pattern particles can be removed. We also suggested that the CO2 GCIB process has the high particle removal uniformity without redeposition of the removed particles. It is possible to remove the ultrafine particle as small as 12 nm in diameter (which is required for 2014 by ITRS 2011). The pattern damage is not observed for 45 nm poly-Si pattern. Moreover, the molecular dynamics simulation is performed to investigate the mechanisms of the particle removal by GCIB irradiation. © 1988-2012 IEEE.

DOI： 10.1109/TSM.2013.2268871

Ultrafine particle removal using gas cluster ion beam technology Reviewed

Kazuya Dobashi, Kensuke Inai, Misako Saito, Toshio Seki, Takaaki Aoki, Jiro Matsuo

IEEE Transactions on Semiconductor Manufacturing Vol. 26 ( 3 ) page： 328 - 334 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

In this paper, the ultrafine particle removal using CO2 gas cluster ion beam (GCIB) technology is investigated. The CO2 GCIB is irradiated the sample at an angle of 0 with respect to the surface normal. The higher particle removal efficiency can be achieved at the higher kinetic energy of the gas cluster, and the inside space of line and space pattern particles can be removed. We also suggested that the CO2 GCIB process has the high particle removal uniformity without redeposition of the removed particles. It is possible to remove the ultrafine particle as small as 12 nm in diameter (which is required for 2014 by ITRS 2011). The pattern damage is not observed for 45 nm poly-Si pattern. Moreover, the molecular dynamics simulation is performed to investigate the mechanisms of the particle removal by GCIB irradiation. © 1988-2012 IEEE.

DOI： 10.1109/TSM.2013.2268871

Molecular dynamics study of crater formation by core-shell structured cluster impact Reviewed

Takaaki Aoki, Toshio Seki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 282 page： 29 - 32 2012.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Crater formation processes by the impacts of large clusters with binary atomic species were studied using molecular dynamics (MD) simulations. Argon and xenon atoms are artificially organized in core-shell cluster structures with various component ratios and irradiated on a Si(100) target surface. When the cluster has Xe-1000 core covered with 1000 Ar atoms, and impacts at a total of 20 key, the core Xe cluster penetrates into the deep area, and a crater with a conical shape is left on the target. On the other hand, in the case of a cluster with the opposite structure, Ar-1000 core covered with 1000 Xe atoms, the cluster stops at a shallow area of the target. The incident cluster atoms are mixed and tend to spread in a lateral direction, which results in a square shaped crater with a shallower hole and wider opening. The MD simulations suggest that large cluster impacts cause different irradiation effects by changing the structure, even if the component ratio is the same. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2011.08.061

Depth profiling analysis of damaged arginine films with Ar cluster ion beams Reviewed

J. Matsuo, K. Ichiki, Y. Yamamoto, T. Seki, T. Aoki

SURFACE AND INTERFACE ANALYSIS Vol. 44 ( 6 ) page： 729 - 731 2012.6

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Ar cluster ion beams provide unique opportunities for organic material analysis. SIMS with Ar cluster ion beams have been utilized for thin films of biomaterials and organic semiconductor multilayers. No degradation in SIMS spectra was found after sputtering with Ar cluster ion beams. In addition, a damage layer formed with ion irradiation of monomer Ga at a dose of 1?X?1014?ions/cm2 was removed with an Ar cluster beam without additional damage being created. The structure and depth of damage induced with monomer ions can be evaluated with Ar cluster SIMS. The measured thickness of the damaged layer is very close to the value calculated with TRIM. These results indicate that damage in organic materials introduced with energetic ions can be evaluated with this technique. Copyright (c) 2012 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.4856

Etching of metallic materials with Cl-2 gas cluster ion beam Reviewed

T. Seki, T. Aoki, J. Matsuo

SURFACE & COATINGS TECHNOLOGY Vol. 206 ( 5 ) page： 789 - 791 2011.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Cluster ion beam processes exhibit high rate sputtering with low damage, and in particular, extremely high sputtering rates are expected using reactive cluster ion beams. Si could be sputtered at extremely high rates using reactive cluster ion beams, such as SF6, Cl-2, CF4, CHF3, and CH2F2. However, processing of metallic materials with reactive cluster ion beams has not been studied yet. It was expected that high-speed etching of metallic materials can be realized with Cl-2 cluster ion irradiation, because such a beam would reactively sputter these materials. We generated a Cl-2 cluster ion beam and investigated the etching characteristics of various metallic materials, such as Ni and Al films, under this irradiation. The size of the Cl-2 cluster, as measured with a time-of-flight (TOF) system, was about 1400 molecules. The sputtering yield for each metal was more than 10 times higher than that obtained with Ar cluster ions, showing that Cl-2 cluster ion irradiation reactively sputtered the metallic materials. These results indicated that Cl-2 cluster ion irradiation was suitable for high-speed processing of metallic materials. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2011.04.054

Low-damage milling of an amino acid thin film with cluster ion beam Reviewed

Masaki Hada, Sachi Ibuki, Yusaku Hontani, Yasuyuki Yamamoto, Kazuya Ichiki, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

JOURNAL OF APPLIED PHYSICS Vol. 110 ( 9 ) 2011.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

In this work, we characterized the surface damage layer and sputtering yield of polycrystalline L-leucine films before and after irradiation with Ar cluster or monomer ion beams with x ray photoelectron spectroscopy and ellipsometry. Irradiation with Ar monomer ion beams induced heavy damage on the surface of L-leucine films, such as bond breaking and carbonization. In contrast, no significant surface damage was observed in the films irradiated with Ar cluster ion beams. The sputtering yield of L-leucine decreased dramatically with increasing fluence of monomer Ar ions and approached the value of the sputtering yield of graphite; but under irradiation with Ar cluster ion beams, the sputtering yield remained constant with fluence. The differences in sputtering yield behavior were explained in relation with the surface damage layer on organic materials. Thus, cluster ion beams could potentially be used to mill down biological materials without significant damage on the surface and could contribute to various applications in the analysis and processing of life matter. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658220]

DOI： 10.1063/1.3658220

Highly sensitive molecular detection with swift heavy ions Reviewed

Yoshinobu Wakamatsu, Hideaki Yamada, Satoshi Ninomiya, Brian N. Jones, Toshio Seki, Takaaki Aoki, Roger Webb, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 269 ( 20 ) page： 2251 - 2253 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Various imaging techniques using microbeam have been applied in biology. Secondary ion mass spectrometry (SIMS) is one of the prominent tools for biological imaging; SIMS can provide data on molecular distribution in biological samples smaller than 1 mu m. However, conventional SIMS has only low sensitivity for molecular ions; therefore there is a need for beams of more sensitive primary ions. Plasma desorption mass spectrometry (PDMS) is a method using high energy fission fragments from excitation of a Cf-252 source, and it allows ionization of large molecules (typically up to 20 kDa) due to the dense electronic excitation. Although PDMS is not in use today because of the development of soft ionization methods, ionization induced by high energy ion collision still remains the only method which combines high spatial resolution and sensitive detection of large molecules. In this work, the secondary ion yield of amino acid and phospholipid was measured for 6 MeV Cu4+. The yields were compared to bismuth cluster ions, which achieve relatively high yield. It was confirmed that the swift heavy ion has a couple of hundred times higher yield for large molecules than bismuth cluster ions. (C) 2011 Published by Elsevier B.V.

DOI： 10.1016/j.nimb.2011.02.069

The effects of cluster size on sputtering and surface smoothing of PMMA with gas cluster ion beams Reviewed International journal

Kazuya Ichiki, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

Transactions of the Materials Research Society of Japan Vol. 36 ( 3 ) page： 309 - 312 2011.9

Language：English Publishing type：Research paper (scientific journal) Publisher：The Materials Research Society of Japan

We investigated the sputtering rate and surface morphology of polymethylmethacrylate (PMMA) samples bombarded with Ar cluster ion beam with selected energy of 12.5 eV/atom. The incident cluster energy range was 10–60 keV/ion. The incident cluster ion was selected before irradiation by using the time-of-flight (TOF) method. Both the sputtering rates and the average surface roughness increased rapidly with increasing incident cluster size under bombardment with small cluster ion. Under bombardment with large cluster ion, the average surface roughness does not increase rapidly, although sputtering rates increased nonlinearly. It suggests that a cluster ion beam with large size would be effective for high speed etching without roughing the surface.

DOI： 10.14723/tmrsj.36.309

Molecular dynamics simulations of large fluorine cluster impact on silicon with supersonic velocity Reviewed

Takaaki Aoki, Toshio Seki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 269 ( 14 ) page： 1582 - 1585 2011.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The etching process by very large reactive gas cluster impact was investigated by molecular dynamics (MD) simulations. Fluorine-molecule clusters with the size up to 100,000 atoms (50,000 F(2) molecules) were irradiated on silicon (1 0 0) targets at supersonic velocity regime (0.1-1 eV/atom, 1.0-3.2 km/s). The MD simulations revealed that the existence of threshold energy-per-atom around 0.3 eV/atom (1.75 km/s) to cause surface deformation and enhancement of Si desorption. When the incident energy-per-atom is less than the threshold, the incident cluster breaks up itself on the target without surface deformation. The fluorine molecules in the cluster spread in the lateral direction along the target surface, and some part of them decompose and adsorbs on the target to form silicon fluoride composites. On the other hand, the clusters penetrate the surface of silicon target when the energy-per-atom is larger than 0.3 eV/atom. In these collisional processes, the target surface is deformed to create shallow crater shape. The incident fluorine molecules are preferentially concentrated at the bottom of the crater, which resulted in high desorption yield of silicon as in the form of SiF(2), SiF(3) and SiF(4). (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2010.12.013

Analysis of organic semiconductor multilayers with Ar cluster secondary ion mass spectrometry Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Hideaki Yamada, Yoshihiko Nakata, Toshio Seki, Takaaki Aoki, Jiro Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 43 ( 1-2 ) page： 95 - 98 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

The demand for direct analytical techniques for characterization and damage evaluation of organic devices has increased dramatically in recent years, along with an increase in the importance of these devices. In this study, we demonstrate direct analysis of model structures for organic light emitting diode (OLED) devices by using SIMS with large Ar cluster ion beams. We prepared single and multilayer films of organic semiconductor materials by vacuum evaporation and analyzed their surfaces with time-of-flight secondary ion mass spectrometry (ToF-SIMS). Under bombardment with large Ar cluster ions, the predominant species observed were molecular ions from the organic materials, while small fragment ions were strongly suppressed. Moreover, the multilayer films were depth profiled with Ar cluster ion beams, and the interfaces between the organic layers could be clearly distinguished. These results show the promising potential of large Ar cluster ion beams for direct analysis of real organic semiconductor devices. Copyright (C) 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.3587

MeV-energy probe SIMS imaging of major components in washed and fractured animal cells Reviewed

H. Yamada, Y. Nakata, S. Ninomiya, T. Seki, T. Aoki, J. Tamura, J. Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 43 ( 1-2 ) page： 363 - 366 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Molecular images of pretreated animal cells were measured by secondary ion mass spectrometry (SIMS) with MeV-energy ion beam. SIMS analysis was performed for cell surfaces washed with buffers not only at high vacuum, but also at several tens Pa by using an orthogonal acceleration time of flightmass spectrometer (oaTOFMS) system. Moreover, molecular images of major components from washed and freeze fractured cells were obtained using MeV-energy probe SIMS. Copyright (C) 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.3408

The effect of incident energy on molecular depth profiling of polymers with large Ar cluster ion beams Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Hideaki Yamada, Yoshihiko Nakata, Toshio Seki, Takaaki Aoki, Jiro Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 43 ( 1-2 ) page： 221 - 224 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

In this study, we evaluated the damage caused by large Ar cluster ion irradiation on polymeric materials, and demonstrated a technique for molecular depth profiling of polymer films. The surface chemical states of the polymers were analyzed with XPS. The chemical states of the polymethyl methacrylate (PMMA) sample etched with Ar monomer ion beams differed significantly from those of the unirradiated sample, but were preserved for the sample etched with Ar cluster ion beams. SIMS depth profiling of the PMMA and polystyrene (PS) films were also carried out by using large Ar cluster ion beams at incident energies between 5.5 and 13 keV, and the effects of incident energy on damage accumulation and depth resolution were investigated. The ratios of the signal intensity at zero fluence to the signal intensity at steady state decreased with increasing incident energy, whereas the depth resolution was little affected by incident energy. Copyright (C) 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.3656

Surface morphology of PMMA surfaces bombarded with size-selected gas cluster ion beams Reviewed

K. Ichiki, S. Ninomiya, Y. Nakata, H. Yamada, T. Seki, T. Aoki, J. Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 43 ( 1-2 ) page： 120 - 122 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

The surface morphology and sputtering rate of polymethylmethacrylate (PMMA) samples bombarded with size-selected Ar cluster ion beam (1000-16 000 atoms/cluster) was investigated. The incident cluster ion size was selected before irradiation by using the time-of-flight (TOF) method. The sputtering rates decreased with increasing incident cluster size at constant total energy. The average surface roughness values measured by AFM after 25 nm etching with 20 keV Ar-1000 + and Ar-16 000 + were 4.0 +/- 0.4 and 0.78 +/- 0.09 nm, respectively. Thus, small clusters would be effective for high-speed etching, and large clusters would be suitable for low-damage etching. Copyright (C) 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.3444

Using ellipsometry for the evaluation of surface damage and sputtering yield in organic films with irradiation of argon cluster ion beams Reviewed

Masaki Hada, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

SURFACE AND INTERFACE ANALYSIS Vol. 43 ( 1-2 ) page： 84 - 87 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

The film thickness and surface damage layer of vapor-deposited L-leucine amino acid films irradiated with Ar cluster ion beams were characterized by PSC(R)A ellipsometry. The damaged layer on the surface of the L-leucine film irradiated with Ar cluster ion beam was quite thin, less than 1 nm in thickness. In contrast, films irradiated with Ar monomer ion beam have changed into totally different films. The ellipsometry method also allowed accurate measurements of the sputtering yield from the L-leucine film irradiated with Ar cluster ion beams at nm-order resolution. These results suggested that with proper analysis, the optical method of ellipsometry enables estimation of the surface damage layer and measurement of sputtering yield of organic films irradiated with cluster ion beams. Copyright (C) 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.3452

Evaluation of damage depth on arginine films with molecular depth profiling by Ar cluster ion beam

Yamamoto Yasuyuki, Ichiki Kazuya, Seki Toshio, Aoki Takaaki, Matsuo Jiro

Trans. Mat. Res. Soc. Japan Vol. 36 ( 3 ) page： 313 - 316 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：The Materials Research Society of Japan

Ion-induced damage on organic materials has been evaluated with secondary ion mass spectrometry (SIMS). However, conventional sputter beams, such as SF<sub>5</sub><sup>+</sup>, C<sub>60</sub><sup>+</sup> cannot etch the organic materials without inducing damage, and it is difficult to evaluate the depth distribution of the damage in these materials. Large gas cluster ion can etch organic materials without damage, and in this study the damaged layer thickness was evaluated by molecular depth profiling with Ar cluster ion beam. Arginine films were irradiated with 10 keV Ga<sup>+</sup> at a dose of 1.0 × 10<sup>14</sup> ions/cm<sup>2</sup> with the aim of forming a damaged layer on the surface. The chemical structure of arginine was seriously damaged, as indicated by the non-detection of protonated arginine molecular ions after Ga<sup>+</sup> ions irradiation. The peak intensity of the protonated arginine ion increased with increasing sputtering depth and saturated at the depth of about 30 nm. This value agreed with the projection range of the Ga<sup>+</sup> ion indicating that the depth of the ion-induced damage was the same as projection range of the ion. Ion-induced damage layer thickness on arginine films were accurately evaluated by molecular depth profiling with Ar cluster ion beam.

DOI： 10.14723/tmrsj.36.313

Processing Techniques of Biomaterials: Using Gas Cluster Ion Beam for Imaging Mass Spectrometry Reviewed International journal

H Yamada, K Ichiki, Y Nakata, S Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

Transactions of the Materials Research Society of Japan Vol. 35 ( 4 ) page： 793 - 796 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：The Materials Research Society of Japan

We investigated secondary ion mass spectrometry (SIMS) for cellular imaging with high spatial resolution. Cellular level imaging would require nanoscale processing techniques for removal of contamination from cell surfaces and exposing the inner matter of cells. In this study, we applied gas cluster ion beams to the etching of biological samples. Molecular ions were detected with high-intensity from cholesterol samples etched with Ar cluster ions. Additionally, the intensity of secondary molecular ions with gas cluster ion irradiation was compared to that with Au<sub>3</sub><sup>+</sup> or C<sub>60</sub><sup>+</sup> beam irradiation and we demonstrated the advantage of using gas cluster ions as etching beams for biological samples with low damage. Finally, we performed etching of animal cells with Ar cluster ions and SIMS analysis of the etched cells. We demonstrated that the cell surfaces were etched with low damage by using gas cluster ion beam.

DOI： 10.14723/tmrsj.35.793

Sputtering Properties of Si by Size-Selected Ar Gas Cluster Ion Beam Reviewed International journal

K Ichiki, S Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

Transactions of the Materials Research Society of Japan Vol. 35 ( 4 ) page： 789 - 792 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：The Materials Research Society of Japan

Large gas cluster ion beam technology answers expectations in the field of material modification, because it provides unique capabilities, such as atomic-scale surface smoothing, shallow implantation and high sputtering yield. The relationship between incident cluster size and irradiation effects observed with large gas cluster ion beam is not yet clearly understood, and in this work we used size-selected Ar cluster ion beam to study the effects of incident energy-per-atom and cluster size on sputtering and secondary ion emission. Incident Ar cluster ions were size-selected by using the time-of-flight (TOF) method. It was found that the secondary ion yields decreased more rapidly with decreasing incident energy-per-atom and that the threshold energy-per-atom for sputtering of Si and Si<sup>+</sup> were different, because the ionization energy of Si was higher than the surface binding energy of Si. It indicates that cluster ion irradiation sputtered only neutral Si from the surface by under the specific conditions.

DOI： 10.14723/tmrsj.35.789

SIMS Depth Profiling of Organic Materials with Ar Cluster Ion Beam Reviewed International journal

Satoshi Ninomiya, Kazuya Ichiki, Hideaki Yamada, Yoshihiko Nakata, Toshio Seki, Takaaki Aoki, Jiro Matsuo

Transactions of the Materials Research Society of Japan Vol. 35 ( 4 ) page： 785 - 788 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：The Materials Research Society of Japan

Depth profiling has been rarely used with secondary ion mass spectrometry (SIMS) of organic materials, because the primary keV atomic ions produce weak signals for large molecules and often damage them during the etching process. In previous studies, we have found extremely low-damage secondary ion emission from organic materials bombarded with large Ar cluster ions, and proposed to use large gas cluster ions as primary ions for SIMS. In this study, secondary ions were measured with a linear type time-of-flight (TOF) technique, and the application of large Ar cluster ion beams to molecular depth profiling of organic films is demonstrated. The intensities of molecular ions were kept constant, though the primary ion beam fluence exceeded the static SIMS limit. These results indicate that large Ar cluster ion beams could be used as powerful tools for SIMS depth profiling.

DOI： 10.14723/tmrsj.35.785

ガスクラスタイオンビームによるナノ加工技術 Reviewed International journal

Takaaki Aoki

トライボロジスト Vol. 55 ( 11 ) page： 776 - 782 2010.11

SIMS with highly excited primary beams for molecular depth profiling and imaging of organic and biological materials Reviewed

Jiro Matsuo, Satoshi Ninomiya, Hideaki Yamada, Kazuya Ichiki, Yoshinobu Wakamatsu, Masaki Hada, Toshio Seki, Takaaki Aoki

SURFACE AND INTERFACE ANALYSIS Vol. 42 ( 10-11 ) page： 1612 - 1615 2010.10

Language：English Publishing type：Research paper (scientific journal) Publisher：JOHN WILEY & SONS LTD

Recent developments in SIMS with both Ar cluster ions and swift heavy ions are presented. With these primary beams, the analysis of organic semiconductors and animal cells shows that one of the key factors to realizing the SIMS analysis of organic materials is high-energy deposition near the surface. Molecular depth profiling and images of organic materials were demonstrated by using SIMS. Copyright (C) 2010 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.3585

MeV-energy probe SIMS imaging of major components in animal cells etched using large gas cluster ions Reviewed

Hideaki Yamada, Kazuya Ichiki, Yoshihiko Nakata, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 268 ( 11-12 ) page： 1736 - 1740 2010.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular imaging of animal cells was successfully obtained by using the technique of MeV-energy probe secondary ion mass spectrometry (MeV-SIMS) and sample etching with Ar cluster ion beam. In order to indicate benefits of using Ar cluster beam for etching biomaterials, cholesterol and phospholipids were etched with Ar cluster ions and SIMS measurements for the before and after etching samples were performed. Moreover, secondary ion images of the animal cells etched with Ar cluster ions were acquired by using MeV-energy ion beam as a probe. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2010.02.038

Molecular dynamics simulations for gas cluster ion beam processes Reviewed

Takaaki Aoki, Toshio Seki, Jiro Matsuo

VACUUM Vol. 84 ( 8 ) page： 994 - 998 2010.3

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Molecular dynamics (MD) simulations of large argon clusters impacting on silicon targets were performed. The characteristics of crater formation, a typical collisional effect with large cluster impact were examined from the viewpoint of incident energy, cluster size and incident angle. The MD simulation results suggested that the condition where an incident cluster penetrates into the solid target and causes a crater is mainly dominated by the incident energy-per-atom rather than total incident energy of the cluster. Additionally, the MD simulations of sequential multiple cluster impacts and grazing-angle cluster irradiation on irregular surface structures were studied to characterize the surface modification effects with large cluster ion beam process. (C)2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.vacuum.2009.11.018

Anisotropic Etching Using Reactive Cluster Beams Reviewed

Kunihiko Koike, Yu Yoshino, Takehiko Senoo, Toshio Seki, Satoshi Ninomiya, Takaaki Aoki, Jiro Matsuo

APPLIED PHYSICS EXPRESS Vol. 3 ( 12 ) 2010

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN SOC APPLIED PHYSICS

The characteristics of Si etching using nonionic cluster beams with highly reactive chlorine-trifluoride (ClF(3)) gas were examined. An etching rate of 40 mu m/min or higher was obtained even at room temperature when a ClF(3) molecular cluster was formed and irradiated on a single-crystal Si substrate in high vacuum. The etching selectivity of Si with respect to a photoresist and SiO(2) was at least 1 : 1000. We also succeeded in highly anisotropic etching with an aspect ratio of 10 or higher. Moreover, this etching method has a great advantage of low damage, compared with the conventional plasma process. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/APEX.3.126501

MD simulation of small boron cluster implantation

Takaaki Aoki, Toshio Seki, Jiro Matsuo

IWJT-2010: Extended Abstracts - 2010 International Workshop on Junction Technology page： 114 - 115 2010

Language：English Publishing type：Research paper (international conference proceedings)

Molecular dynamics (MD) simulations of small boron clusters impacting on silicon (100) surface were carried out. The impacts of B10, B18 and B36 accelerated with 2keV, 3.6keV and 7.6keV (200eV per boron atom) showed characteristic irradiation effect, heavy mixing or amourphosization, and crater formation at the impact point. The MD results also suggested, when the incident energy per atom is several hundreds eV/atom and is kept constant for various cluster sizes, the depth profiles of implanted boron atoms and damage increases as the cluster size. © 2010 IEEE.

DOI： 10.1109/IWJT.2010.5474974

High Speed Si Etching with ClF3 Cluster Injection

T. Seki, Y. Yoshino, T. Senoo, K. Koike, S. Ninomiya, T. Aoki, J. Matsuo

ION IMPLANTATION TECHNOLOGY 2010 Vol. 1321 page： 317 - + 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The reactive gas cluster injection process is an etching method that uses a neutral cluster beam without plasma. ClF3-Ar neutral cluster was generated and the Si etching characteristics with this beam were investigated. ClF3 is very high reactive gas. Adiabatic expansion of a high-pressure gas through a conical nozzle is utilized for the formation of cluster beams. The source gas was a mixture of ClF3 (6%) with Ar (94%). The etching rate increased with source gas pressure nonlinearly, and the etching rate achieved more than 30 mu m/min at 0.85 MPa. Although the irradiation energy was very low (<1 eV/atom or molecule), the chemical etching was enhanced with cluster impacts and the cluster bombarded area on the surface was etched selectively. These results indicated that high speed anisotropic etching with low damage can be realized with the ClF3 cluster injection process.

DOI： 10.1063/1.3548393

Evaluation of surface damage on organic materials irradiated with Ar cluster ion beam

Y. Yamamoto, K. Ichiki, S. Ninomiya, T. Seki, T. Aoki, J. Matsuo

ION IMPLANTATION TECHNOLOGY 2010 Vol. 1321 page： 298 - + 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The sputtering yields of organic materials under large cluster ion bombardment are much higher than those under conventional monomer ion bombardment. The sputtering rate of arginine remains constant with fluence for an Ar cluster ion beam, but decreases with fluence for Ar monomer. Additionally, because Ar cluster etching induces little damage, Ar cluster ion can be used to achieve molecular depth profiling of organic materials. In this study, we evaluated the damage to poly methyl methacrylate (PMMA) and arginine samples irradiated with Ar atomic and Ar cluster ion beams. Arginine samples were analyzed by secondary ion mass spectrometry (SIMS) and PMMA samples were analyzed by X-ray photoelectron spectroscopy (XPS). The chemical structure of organic materials remained unchanged after Ar cluster irradiation, but was seriously damaged. These results indicated that bombardment with Ar cluster ions induced less surface damage than bombardment with Ar atomic ion. The damage layer thickness with 5 keV Ar cluster ion bombardment was less than 1 nm.

DOI： 10.1063/1.3548386

Evaluation of Surface Damage of Organic Films due to Irradiation with Energetic Ion Beams

Masaki Hada, Yusaku Hontani, Sachi Ibuki, Kazuya Ichiki, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

ION IMPLANTATION TECHNOLOGY 2010 Vol. 1321 page： 314 - + 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The surface of L-leucine films irradiated with an Ar-5000 cluster ion beam (5 keV) was characterized by using the X-ray reflective (XRR) measurement method, atomic force microscopy (AFM) and ellipsometry. No significant damage was detected on the surface of the L-leucine films irradiated with the Ar cluster ion beam. Therefore, the large cluster-low-energy (about 1 eV/atom) beam would be suitable for low-damage etching of organic materials.

DOI： 10.1063/1.3548390

Evaluation of Damage Layer in an Organic Film with Irradiation of Energetic Ion Beams Reviewed

Masaki Hada, Sachi Ibuki, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 49 ( 3 ) 2010

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN SOC APPLIED PHYSICS

We characterized the thickness and surface damage layer of poly(methyl metacrylate) (PMMA) organic films irradiated with Ar cluster or monomer ion beam using ellipsometry. A heavily damaged layer was detected on the surface of the PMMA film irradiated with Ar monomer ion beam; more than 2-3 nm of the surface were completely metamorphosed into a carbon-like layer and damage had accumulated with irradiation. On the other hand, no significant damage was detected on PMMA films irradiated with Ar cluster ion beams. These results corresponded with measurements of the irradiated surface by X-ray photoelectron spectroscopy (XPS). The sputtering depth from PMMA film irradiated with Ar cluster/monomer ion beams can also be measured using the ellipsometry method at nanometer-order resolution. The optical method of ellipsometry may be a desirable tool for sputtering yield measurement and surface damage layer estimation for organic films. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.036503

Energy effects on the sputtering yield of Si bombarded with gas cluster ion beams

K. Ichiki, S. Ninomiya, T. Seki, T. Aoki, J. Matsuo

ION IMPLANTATION TECHNOLOGY 2010 Vol. 1321 page： 294 - + 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Gas cluster ion presents various irradiation effects such as high sputtering yields. It is important to study the optimum condition of incident cluster ion beam for applications in surface modification technology. In this study, the effects of incident energy and chamber pressure on the sputtering yield with gas cluster ion bombardment were investigated. The incident mean cluster size was 2000 atoms/ion and incident energy was 10-80 keV. The number of collisions with residual gas during transportation was in the range 1-20. The sputtering yield with gas cluster ion beam increased nonlinearly with increasing incident cluster energy. However, cluster ion beam easily lose their energy by collision with residual gas, and the sputtering yield decreased rapidly. For using gas cluster ion beam efficiently, the collision frequency along transportation should be kept less than a few times.

DOI： 10.1063/1.3548384

Biomolecular Emission by Swift Heavy Ion Bombardment

Yoshinobu Wakamatsu, Hideaki Yamada, Satoshi Ninomiya, Brian N. Jones, Toshio Seki, Takaaki Aoki, Roger Webb, Jiro Matsuo

ION IMPLANTATION TECHNOLOGY 2010 Vol. 1321 page： 233 - + 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Secondary Ion Mass spectrometry (SIMS) has been generally used in the field of material sciences. In recent years, it has also been applied for molecular imaging of biological samples. Nevertheless, molecular ions derived from the large molecules (more than 1 kDa) were detected with very low sensitivity. Plasma desorption mass spectrometry (PDMS) is known as mass spectrometry for large organic molecule. In PDMS, fission fragments bombard samples and the impact induces molecular ionization by electronic excitation. Large organic molecules are detected by using swift heavy ions in SIMS. In this work, 6 MeV Cu4+ we irradiated angiotensin II, a class of peptides. The intact molecular ions generated by swift heavy ion irradiation were analyzed by time-of-flight (TOF) measurement. The yields are compared with some other probe ions, bismuth or flurane. Swift heavy ion bombardment ionized large organic molecules more effectively than other probes. Therefore, high energy ion can be applied in high resolution molecular imaging.

DOI： 10.1063/1.3548357

Anisotropic Etching Using Reactive Cluster Beams

Kunihiko Koike, Yu Yoshino, Takehiko Senoo, Toshio Seki, Satoshi Ninomiya, Takaaki Aoki, Jiro Matsuo

APPLIED PHYSICS EXPRESS Vol. 3 ( 12 ) 2010

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN SOC APPLIED PHYSICS

The characteristics of Si etching using nonionic cluster beams with highly reactive chlorine-trifluoride (ClF(3)) gas were examined. An etching rate of 40 mu m/min or higher was obtained even at room temperature when a ClF(3) molecular cluster was formed and irradiated on a single-crystal Si substrate in high vacuum. The etching selectivity of Si with respect to a photoresist and SiO(2) was at least 1 : 1000. We also succeeded in highly anisotropic etching with an aspect ratio of 10 or higher. Moreover, this etching method has a great advantage of low damage, compared with the conventional plasma process. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/APEX.3.126501

Nano Processing with Gas Cluster Ion Beams International journal

Jiro Matsuo, Teruyuki Kitagawa, Toshio Seki, Takaaki Aoki

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 55 ( 11 ) page： 776 - 782 2010

Molecular depth profiling of multilayer structures of organic semiconductor materials by secondary ion mass spectrometry with large argon cluster ion beams Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Hideaki Yamada, Yoshihiko Nakata, Toshio Seki, Takaaki Aoki, Jiro Matsuo

RAPID COMMUNICATIONS IN MASS SPECTROMETRY Vol. 23 ( 20 ) page： 3264 - 3268 2009.10

Language：English Publishing type：Research paper (scientific journal) Publisher：JOHN WILEY & SONS LTD

in this study, we present molecular depth profiling of multilayer structures composed of organic semiconductor materials such as tris(8-hydroxyquinoline)aluminum (Alq(3)) and 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD). Molecular ions produced from Alq(3) and NPD were measured by linear-type time-of-flight (TOF) mass spectrometry under 5.5 keV Ar(700) ion bombardment. The organic multilayer films were analyzed and etched with large Ar cluster ion beams, and the interfaces between the organic layers were clearly distinguished. The effect of temperature on the diffusion of these materials was also investigated by the depth profiling analysis with Ar cluster ion beams. The thermal diffusion behavior was found to depend on the specific materials, and the diffusion of Alq(3) molecules was observed to start at a lower temperature than that of NPD molecules. These results prove the great potential of large gas cluster ion beams for molecular depth profiling of organic multilayer samples. Copyright (C) 2009 John Wiley & Sons, Ltd.

DOI： 10.1002/rcm.4250

Study of density effect of large gas cluster impact by molecular dynamics simulations Reviewed

Takaaki Aoki, Toshio Seki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 267 ( 18 ) page： 2999 - 3001 2009.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Large gas cluster impacts cause unique surface modification effects because a large number of target atoms are moved simultaneously due to high-density particle collisions between cluster and surface atoms. Molecular dynamics (MID) simulations of large gas cluster impacts on solid targets were carried out in order to investigate the effect of high-density irradiation with a cluster ion beam from the viewpoint of crater formation and sputtering. An Ar cluster with the size of 2000 was accelerated with 20 keV (10 eV for each constituent atom) and irradiated on a Si(100) solid target consisting of 2 000 000 atoms. The radius of the Ar cluster was scaled by ranging from 2.3 nm (corresponding to the solid state of Ar) to 9.2 nm (64 x lower density than solid state). When the Ar cluster was as dense as solid state, the incident cluster penetrated the target surface and generated crater-like damage. On the other hand, as the cluster radius increased and the irradiation particle density decreased, the depth of crater caused by cluster impact was reduced. MID results also revealed that crater depth was mainly dominated by the horizontal scaling rather than vertical scaling. A high sputtering yield of more than several tens of Si atoms per impact was observed with clusters of 4-20x lower volume density than solid state. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2009.06.019

The emission process of secondary ions from solids bombarded with large gas cluster ions Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Toshio Seki, Takaaki Aoki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 267 ( 16 ) page： 2601 - 2604 2009.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We investigated the effects of size and energy of large incident Ar cluster ions on the secondary ion emission of Si. The secondary ions were measured using a double deflection method and a time-of-flight (TOF) technique. The size of the incident Ar cluster ions was between a few hundreds and several tens of thousands of atoms, and the energy up to 60 keV. Under the incidence of keV energy atomic Ar ions, mainly atomic Si ions were detected, whereas Si cluster ions were rarely observed. On the other hand, under the incidence of large Ar cluster ions, the dominant secondary ions were Si(n)(+) (2 <= n <= 11). It has become clear that the yield ratio of secondary Si cluster ions was determined by the velocity of the incident cluster ions, and this strong dependence of the yield ratio on incident velocity should be related to the mechanisms of secondary ion emission under large Ar cluster ion bombardment. (C) 2009 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.nimb.2009.05.019

Imaging mass spectrometry with nuclear microprobes for biological applications Reviewed

Y. Nakata, H. Yamada, Y. Honda, S. Ninomiya, T. Seki, T. Aoki, J. Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 267 ( 12-13 ) page： 2144 - 2148 2009.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

A mass spectrometric technique using nuclear microprobes is presented in this paper for biological applications. In recent years, imaging mass spectrometry has become an increasingly important technique for visualizing the spatial distribution of molecular species in biological tissues and cells. However, due to low yields of large molecular ions, the conventional secondary ion mass spectrometry (SIMS), that uses keV primary ion beams, is typically applied for imaging of either elements or low mass compounds. In this study, we performed imaging mass spectrometry using MeV ion beams collimated to about 10 mu m, and successfully obtained molecular ion images from plant and animal cell sections. The molecular ion imaging of the pollen section showed high intensities of PO(3)(-) ions in the pollen cytoplasm, compared to the pollen wall, and indicated the heterogeneous distribution in the cytoplasm. The 3T3-L1 cell image revealed the high intensity of PO(3)(-) ions, in particular from the cell nucleus. The result showed that not only the individual cell, but also the cell nucleus could be identified with the present imaging technique. (C) 2009 Published by Elsevier B.V.

DOI： 10.1016/j.nimb.2009.03.094

Precise and fast secondary ion mass spectrometry depth profiling of polymer materials with large Ar cluster ion beams Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Hideaki Yamada, Yoshihiko Nakata, Toshio Seki, Takaaki Aoki, Jiro Matsuo

RAPID COMMUNICATIONS IN MASS SPECTROMETRY Vol. 23 ( 11 ) page： 1601 - 1606 2009.6

Language：English Publishing type：Research paper (scientific journal) Publisher：JOHN WILEY & SONS LTD

We demonstrate depth profiling of polymer materials by using large argon (Ar) cluster ion beams. In general, depth profiling with secondary ion mass spectrometry (SIMS) presents serious problems in organic materials, because the primary keV atomic ion beams often damage them and the molecular ion yields decrease with increasing incident ion fluence. Recently, we have found reduced damage of organic materials during sputtering with large gas cluster ions, and reported on the unique secondary ion emission of organic materials. Secondary ions from the polymer films were measured with a linear type time-of-flight (TOF) technique; the films were also etched with large Ar cluster ion beams. The mean cluster size of the primary ion beams was Ar(700) and incident energy was 5.5 keV. Although the primary ion fluence exceeded the static SIMS limit, the molecular ion intensities from the polymer films remained constant, indicating that irradiation with large Ar cluster ion beams rarely leads to damage accumulation on the surface of the films, and this characteristic is excellently suitable for SIMS depth profiling of organic materials. Copyright (C) 2009 John Wiley & Sons, Ltd.

DOI： 10.1002/rcm.4046

Study of damage accumulation and annealing process at low energy boron implantation using molecular dynamics simulations Reviewed

T. Aoki, J. Matsuo

Extended Abstracts of the 9th International Workshop on Junction Technology, IWJT 2009 page： 131 - 132 2009.6

High-speed processing with Cl-2 cluster ion beam Reviewed

T. Seki, T. Aoki, J. Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 267 ( 8-9 ) page： 1444 - 1446 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Cluster ion beam processes can produce high rate sputtering with low damage compared with monomer ion beam processes. Cl-2 cluster ion beams with different size distributions were generated with controlling the ionization conditions. Size distributions were measured using the time-of-flight (TOF) method. Si substrates and SiO2 films were irradiated with the Cl-2 cluster ions at acceleration energies of 10-30 keV and the etching ratio of Si/SiO2 Was investigated. The sputtering yield increased with acceleration energy and was a few thousand times higher than that of Ar monomer ions. The sputtering yield of Cl-2 cluster ions was about 4400 atoms/ion at 30 keV acceleration energy. The etching ratio of Si/SiO2 was above eight at acceleration energies in the range 10-30 keV. Thus, SiO2 can be used as a mask for irradiation with Cl-2 cluster ion beam, which is an advantage for semiconductor processing. In order to keep high sputtering yield and high etching ratio, the cluster size needs to be sufficiently large and size control is important. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2009.01.069

Study of crater formation and sputtering process with large gas cluster impact by molecular dynamics simulations Reviewed

Takaaki Aoki, Toshio Seki, Satoshi Ninomiya, Kazuya Ichiki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 267 ( 8-9 ) page： 1424 - 1427 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular dynamics (MD) simulations of large argon clusters impacting on silicon solid targets were performed in order to study the transient process of crater formation and sputtering. The MID simulations demonstrate that the initial momentum of incident cluster is transferred to target surface atoms through multiple collision mechanism, where the initial momentum, which is along to the surface normal before impact, is deflected to lateral direction. This momentum transfer process was analyzed by the calculation of the velocity at the crater edge (the interface between cluster and target). In the case of Ar(1000) cluster impact on Si(100) target at low energy per atom less than 40 eV/atom, the maximum value of lateral velocity of the crater edge increases in proportional to the velocity of incident cluster atoms. On the other hand, the crater edge velocity saturates over 40 eV/atom of incident energy per atom. In this case, the whole of constituent cluster atoms are implanted into the target and expand in both lateral and reflective directions at the subsurface region of the target. These MD simulations demonstrated that this collisional process result in the high yield sputtering of the target atoms. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2009.01.162

Low Damage Etching of Polymer Materials for Depth Profile Analysis Using Large Ar Cluster Ion Beam Reviewed International journal

Takaaki Aoki

Journal of surface analysis Vol. 15 ( 3 ) 2009.2

Matrix-free high-resolution imaging mass spectrometry with high-energy ion projectiles Reviewed

Yoshihiko Nakata, Yoshiro Honda, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Jiro Matsuo

JOURNAL OF MASS SPECTROMETRY Vol. 44 ( 1 ) page： 128 - 136 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：JOHN WILEY & SONS LTD

The importance of imaging mass spectrometry (MS) for visualizing the spatial distribution of molecular species in biological tissues and cells is growing. We have developed a new system for imaging MS using MeV ion beams, termed MeV-secondary ion mass spectrometry (MeV-SIMS) here, and demonstrated more than 1000-fold increase in molecular ion yield from a peptide sample (1154 Da), compared to keV ion irradiation. This significant enhancement of the molecular ion yield is attributed to electronic excitation induced in the near-surface region by the impact of high energy ions. In addition, the secondary ion efficiency for biologically important compounds (> 1 kDa) increased to more than 10(10) cm(-2), demonstrating that the current technique could, in principle, achieve micrometer lateral resolution. In addition to MeV-SIMS, peptide compounds were also analyzed with cluster-SIMS and the results indicated that in the former method the molecular ion yields increased substantially compared to the latter. To assess the capability of MeV-SIMS to acquire heavy-ion images, we have prepared a micropatterned peptide surface and successfully obtained mass spectrometric imaging of the deprotonated peptides (m/z 1153) without any matrix enhancement. The results obtained in this study indicate that the MeV-SIMS technique can be a powerful tool for high-resolution imaging in the mass range from 100 to over 1000 Da. Copyright (c) 2008 John Wiley & Sons, Ltd.

DOI： 10.1002/jms.1482

A Processing Technique for Cell Surfaces Using Gas Cluster Ions for Imaging Mass Spectrometry International journal

YAMADA Hideaki, ICHIKI Kazuya, NAKATA Yoshihiko, NINOMIYA Satoshi, SEKI Toshio, AOKI Takaaki, MATSUO Jiro

Journal of the Mass Spectrometry Society of Japan Vol. 57 ( 3 ) page： 117 - 121 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：The Mass Spectrometry Society of Japan

We developed a processing technique for biological samples, that is, animal cells, for imaging mass spectrometry using gas cluster ion beams. Secondary ion mass spectrometry has been investigated for cellular imaging with high spatial resolution. Nanoscale processing techniques are needed for cellular level imaging, for example, for removing contamination from cell surfaces and exposing the insides of cells. In this study, we compared the mass spectrum of the unetched cell sample to that of the cell irradiated with an Ar cluster ion beam. The contamination was removed from the sample surface and the signals of intracellular components were detected. The results indicate that the cells were etched with low damage using the gas cluster ion beam. Finally, we compared the ion image of an unetched cell to that of an etched cell and demonstrated that the technique of cluster ion irradiation could be applied to the processing of samples for cellular level imaging mass spectrometry.

DOI： 10.5702/massspec.57.117

Other Link： https://jlc.jst.go.jp/DN/JALC/00332526476?from=CiNii

Stress measurement of carbon cluster implanted layers with in-plane diffraction technique Reviewed

Jiro Matsuo, Kazuya Ichiki, Masaki Hada, Satoshi Ninomiya, Toshio Seki, Takaaki Aoki, Tsutomu Nagayama, Masayasu Tanjyo

Extended Abstracts of the 9th International Workshop on Junction Technology, IWJT 2009 page： 84 - 85 2009

Language：English Publishing type：Research paper (international conference proceedings)

Cluster ion implantation has a great potential for semiconductor manufacturing, such as ultra shallow junction formation and strain engineering of channel. Stress in Si implanted with carbon cluster ions (C7H 7) was much higher than that in Si implanted with carbon monomer ions. Multiple collisions of atoms occurred during cluster ion implantation, and a fully amorphized Si layer can be formed. The stress in the implanted layer strongly depends on the annealing condition. There are two different directions for the stress. One is parallel to the surface, which is usually measured with conventional X-ray diffraction. The other is perpendicular to the surface, which can be measured with in-plane X-ray diffraction technique. The stress perpendicular to the surface was about 50% of the stress parallel to the surface even after flash lamp annealing. ©2009 IEEE.

DOI： 10.1109/IWJT.2009.5166225

A fragment-free ionization technique for organic mass spectrometry with large Ar cluster ions Reviewed

Satoshi Ninomiya, Yoshihiko Nakata, Yoshiro Honda, Kazuya Ichiki, Toshio Seki, Takaaki Aoki, Jiro Matsuo

APPLIED SURFACE SCIENCE Vol. 255 ( 4 ) page： 1588 - 1590 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

In this report, we propose to use the incidence of cluster ions that are much larger than molecular ions as a fragment-free ionization technique for organic secondary ion mass spectrometry. Secondary ions were measured for amino acid and peptide targets bombarded with 3, 8 and 13 keV large Ar cluster ions. The relative yields of the fragment ions decreased drastically with increasing incident cluster size. Fragment-free ionization of the molecule was accomplished when large cluster ions with optimized size and energy were incident on a biomolecular sample. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.05.004

MD simulation study of the sputtering process by high-energy gas cluster impact Reviewed

Takaaki Aoki, Toshio Seki, Satoshi Ninomiya, Jiro Matsuo

APPLIED SURFACE SCIENCE Vol. 255 ( 4 ) page： 944 - 947 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We performed molecular dynamics (MD) simulations to study the characteristic sputtering process with large cluster ion impact. The statistical properties of incident Ar and sputtered Si atoms were examined using 100 different MD simulations with Ar(1000) cluster impacting on a Si(0 0 1) target at a total acceleration energy of 50 keV. The results show that the kinetic energy distribution of Ar atoms after impact obeys the high-temperature Boltzmann distribution due to thermalization through high-density multiple collisions on the target. On the other hand, the kinetic energy distribution of sputtered target atoms demonstrates a hybrid model of thermalization and collision-cascade desorption processes. (C) 2008 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.05.008

Low Damage Etching and SIMS Depth Profiling with Large Ar Cluster Ions Reviewed International journal

Takaaki Aoki

Transactions of the Materials Research Society of Japan Vol. 33 ( 4 ) 2008.12

High-Speed Nano-Processing with Cluster Ion Beams Reviewed International journal

Takaaki Aoki

Transactions of the Materials Research Society of Japan Vol. 33 ( 4 ) 2008.12

High sputtering yields of organic compounds by large gas cluster ions Reviewed

K. Ichiki, S. Ninomiya, Y. Nakata, Y. Honda, T. Seki, T. Aoki, J. Matsuo

APPLIED SURFACE SCIENCE Vol. 255 ( 4 ) page： 1148 - 1150 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We measured the sputtering yield, surface roughness and surface damage of thin leucine films bombarded with Ar cluster ions and examined the usefulness of large gas cluster ions for the depth pro. ling of organic compounds. Ar cluster ion beams with a mean size of 2000 atoms/cluster and energies from 5 to 30 keV were used. Sputtering yields increased linearly with incident ion energy and were extremely high compared to inorganic materials. Surface damage was investigated by measuring positive secondary ions emitted from the leucine film before and after cluster ion irradiation. After irradiation the leucine surface became smoother. The yield ratio of protonated leucine ions to other fragment ions kept constant before and after Ar cluster ion irradiation. These results indicate that large gas cluster ions are useful for depth pro. ling of organic compounds. (c) 2008 Published by Elsevier B.V.

DOI： 10.1016/j.apsusc.2008.05.032

Secondary ion emission from Si bombarded with large Ar cluster ions under UHV conditions Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Yoshihiko Nakata, Yoshiro Honda, Toshio Seki, Takaaki Aoki, Jiro Matsuo

APPLIED SURFACE SCIENCE Vol. 255 ( 4 ) page： 880 - 882 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Si was bombarded with size-selected 40 keV Ar cluster ions and positive secondary ions were measured using the time-of-flight technique under high and ultra-high vacuum (HV and UHV respectively) conditions. Si(+) ions were main species detected under the incidence of 40 keV Ar cluster ions, and the yields of Si cluster ions such as Si(4)(+) were also extremely high under both conditions. On the other hand, oxidized secondary ions such as SiO(+) were detected with high intensity only under the HV condition. The yield ratios of oxidized ions decreased in UHV to less than 1% of their values in HV. The effect of residual gas pressure on Si cluster ion yields is relatively low compared to oxidized ions, and the UHV condition is required to obtain accurate secondary ion yields. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.05.063

SIMS Analysis of Biological Mixtures with Fast Heavy Ion Irradiation Reviewed International journal

Takaaki Aoki

Transactions of the Materials Research Society of Japan Vol. 33 ( 4 ) 2008.12

What size of cluster is most appropriate for SIMS? Reviewed

Jiro Matsuo, Satoshi Ninomiya, Yoshihiko Nakata, Yoshiro Honda, Kazuya Ichiki, Toshio Seki, Takaaki Aoki

APPLIED SURFACE SCIENCE Vol. 255 ( 4 ) page： 1235 - 1238 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Secondary ion emission with large gas cluster ion is reviewed from the point of view of secondary ion mass spectroscopy (SIMS). We have proposed to use large cluster ions to realize fragment-free ionization for SIMS analysis for various organic materials, such as amino acids and peptides. When large cluster ions with optimized size and energy were incident on biomolecular samples, the relative yields of the fragment ions decreased drastically with the velocity of incident cluster ions. Molecular depth pro. ling capability is also demonstrated by using large gas cluster ions as the primary ion for SIMS. (C) 2008 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.05.057

Yield enhancement of molecular ions with MeV ion-induced electronic excitation Reviewed

Y. Nakata, Y. Honda, S. Ninomiya, T. Seki, T. Aoki, J. Matsuo

APPLIED SURFACE SCIENCE Vol. 255 ( 4 ) page： 1591 - 1594 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We performed secondary ion mass spectrometry for arginine thin films in the incident energy range from 10 keV to 2 MeV, in which electronic energy loss in the surface region increases with energy and exceeds the nuclear energy loss. The yield of protonated arginine increased with incident energy, and at 2 MeV it was approximately two orders of magnitude larger than at 10 keV, where the nuclear collision process is dominant. It was found that the molecular ion desorption is enhanced by the electronic excitation induced in the near-surface region. In addition, the yield ratios of the fragment ions to the protonated arginine decreased with incident energy, which indicates that the nuclear energy deposition significantly affects molecular fragmentation. These results demonstrate a soft desorption and ionization of biomolecules by the MeV ion-induced electronic excitation. (C) 2008 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.apsusc.2008.05.108

Carbon nanotubes from a divided catalyst: the carbon transmission method Reviewed

Takeshi Hikata, Kazuhiko Hayashi, Tomoyuki Mizukoshi, Yoshiaki Sakurai, Itsuo Ishigami, Takaaki Aoki, Toshio Seki, Jiro Matsuo

APPLIED PHYSICS EXPRESS Vol. 1 ( 3 ) page： 0340021 - 0340023 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We have fabricated carbon nanotubes (CNTs) using a catalyzed growth technique that we call the carbon transmission method (CTM). We could control independently functions for carbon source gas supply and CNT growth by using a foil barrier (Ag) penetrated by pure Fe fibers. CNTs grew on one end of the Fe fibers, formed from diffused carbon that originates in carbon source gas at the other end of the fibers. Long CNTs with length over 100 mu m were obtained on the end of the Fe fibers in the carbon transmitted side. (C) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.034002

Low damage smoothing of magnetic materials using off-nonnal gas cluster ion beam irradiation Reviewed

S. Kakuta, S. Sasaki, K. Furusawa, T. Seki, T. Aoki, J. Matsuo

SURFACE & COATINGS TECHNOLOGY Vol. 201 ( 19-20 ) page： 8632 - 8636 2007.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

A damage-free smoothing process for magnetic materials using a gas cluster ion beam (GCIB) has been studied. As the areal density of hard disk drives (HDDs) has increased, the flying height of the magnetic recording head above the disk has been decreasing. In order to further reduce the flying height and improve the sensitivity of sensors, a damage-free smoothing technology for magnetic materials is imperative. A GCIB process has been proposed as a novel smoothing technique for various materials. With this process it is expected that the damage will be low, since the gas clusters are aggregations of a few to thousands of atoms or molecules. In this paper, oblique GCIB irradiation has been studied in order to achieve low damage smoothing of PtMn and NiFe thin films. The surface morphology after GCIB irradiation was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). A smooth surface with an average roughness of less than 1 nm was obtained by using oblique GCIB irradiation. Irradiation damage, such as fluctuations in the ratio of the material components and oxidation of the surface, were investigated by secondary ion mass spectrometry (SIMS). The fluctuations were suppressed by using oblique GCIB irradiation with incident angles larger than 80 degrees. Consequently, irradiation from a GCIB at grazing incidence can be applied to achieve low-damage smoothing of magnetic materials. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2006.03.064

Molecular dynamics study of glancing angle gas cluster irradiation on irregular-structured surfaces Reviewed

Takaaki Aoki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 261 ( 1-2 ) page： 639 - 642 2007.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Surface modification processes resulting from glancing angle gas cluster ion irradiation were studied by molecular dynamics (MD) simulations. Large Ar-2000 gas clusters accelerated with 20 keV were irradiated onto Si(100) substrates to which were attached small Si block-shaped (size of 4096, 16384 or 65536 atoms) structures. The MD simulations revealed that when an Ar cluster is irradiated at 80 degrees of incident angle, the cluster slides on the substrate surface without damage and impacts on the wall of the block structures causing multiple collisions, and dynamic deformation of the blocks. Especially, in the case of the impact on the small surface block (Si-4096), a large part of the block was sputtered as a large chunk, and the target substrate was smoothed with only one cluster impact. The evaluation of the damage distribution showed that silicon interstitials, caused by the multiple collision mechanism, reside within 15 angstrom from the surface, which suggests that low-damage and high-performance surface modification processing would be realized by utilizing a glancing angle gas cluster ion beam irradiation technique. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2007.04.005

Molecular dynamics study of monomer and dimer emission processes with high energy gas cluster ion impact Reviewed

Takaaki Aoki, Toshio Seki, Satoshi Ninomiya, Jiro Matsuo

SURFACE & COATINGS TECHNOLOGY Vol. 201 ( 19-20 ) page： 8427 - 8430 2007.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The mechanism of the sputtering process by energetic large cluster ion impacts was studied using molecular dynamics (MD) simulations. MD simulations of Ar-1000 clusters accelerated with 50 keV total energy impacting on a Si(100) target were performed with 50 trials at different impact points in order to improve the statistical reliance. From these MD simulations, a sputtering yield of about 20 Si atoms/impact was obtained. Si clusters such as Si-2, Si-3, etc. were also found in the sputtered particles, and the sputtering yields for each cluster size obey the power-decay rule with a decay index of 2.3-3. The investigation of trajectories of sputtered Si-1 and Si-2 showed that initial coordinates of sputtered particles residing within a region corresponds to a crater-shaped hole caused by cluster impact. As for the sputtering of dimers, it is found that, not only the emission of a preformed dimer (i.e. a pair of target atoms initially bound before the cluster impact), but the emission of dynamically formed dimers through multiple collisions is also probable event for cluster impact. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2006.09.325

Molecular dynamics simulations of surface smoothing and sputtering process with glancing-angle gas cluster ion beams Reviewed

Takaaki Aoki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 257 ( 1-2 SPEC. ISS. ) page： 645 - 648 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Surface modification processes with glancing-angle large gas cluster irradiation were studied by molecular dynamics simulations. The MD simulation of an Ar-2000 gas cluster impacting on Si(1 0 0) substrate with small Si-4096 block structure attached on the surface was performed. The MD result has shown that, when the Ar cluster impacts on the target at 20 keV of total acceleration energy and at 80 degrees of incident angle, the incident cluster slides on the target surface without creating surface damage and most of the constituent atoms in the cluster collide with the sidewall of the surface block. Up to 10 keV of kinetic energy of the incident cluster was transferred to the target irregular structure, which results in the sputtering or stretching of the surface block and the target surface is smoothed. This characteristic surface modification effect was observed when the surface block is located farther than 200 angstrom from the point where the incident cluster contacts with the target surface. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2007.01.048

Size effect in cluster collision on solid surfaces Reviewed

Jiro Matsuo, Satoshi Ninomiya, Yoshihiko Nakata, Kazuya Ichiki, Takaaki Aoki, Toshio Seki

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 257 ( 1-2 SPEC. ISS. ) page： 627 - 631 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

New surface modification processes have been demonstrated using gas cluster ion irradiations. Multiple collision and high energy density collision of cluster ions are responsible for "non-linear phenomena", which play an important role in the surface modification process. Because of the unique interaction between cluster ions and surface atoms, atomistic mechanisms of cluster ion bombardment must be understood for the further developments of this technology. Cluster size is a unique parameter for cluster ions. One of the fundamental questions in this surface modification technique is the cluster size effect. It is important to use appropriate cluster size in each process. Size dependence of sputtering yields and secondary ion yields with large Ar cluster (N > 300) have been measured. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2007.01.164

Measurements of secondary ions emitted from organic compounds bombarded with large gas cluster ions Reviewed

Satoshi Ninomiya, Yoshihiko Nakata, Kazuya Ichiki, Toshio Seki, Takaaki Aoki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 256 ( 1 ) page： 493 - 496 2007.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We propose to use cluster ions that are much larger than the molecular ions as primary ions for organic secondary ion mass spectrometry. Incident Ar cluster ion beams with energies from 10 to 20 keV and a mean size of about 1000 atoms/cluster were used. Secondary ions were measured for a thin arginine film target (200 nm) bombarded with large Ar cluster ions using a time-of-flight technique. Molecular ions of arginine and characteristic fragment ions were detected with high sensitivity. When large Ar cluster ions such as Ar-1500 were incident on the arginine target, molecular ions of arginine were detected with little fragment ions. This indicates that large cluster ions can ionize arginine molecules without damaging them. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2006.12.047

Surface oxidation of Si assisted by irradiation with large gas cluster ion beam in an oxygen atmosphere Reviewed

K. Ichiki, S. Ninomiya, T. Seki, T. Aoki, J. Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 256 ( 1 ) page： 350 - 353 2007.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Surface oxidation of Si assisted by Ar cluster impact with a current density of a few mu A/cm(2) under O(2) atmosphere was investigated. Thin-film formation by cluster ion beam presents a number of advantages such as atomic-scale surface smoothing, high density and precise stoichiometry. We used an Ar cluster ion beam with 20 keV and a mean size of 1000 atoms per cluster and measured the emission yields of Si(+) and SiO(+) after Ar cluster ion irradiation in O(2) atmosphere using a quadrupole mass spectrometer to investigate the dependence of Si surface oxidation on oxygen partial pressure. It was found that the Si surface was oxidized by Ar cluster ion irradiation in O(2) atmosphere. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2006.12.026

The effect of incident cluster ion energy and size on secondary ion yields emitted from Si Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Yoshihiko Nakata, Toshio Seki, Takaaki Aoki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 256 ( 1 ) page： 528 - 531 2007.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Secondary ions produced from a Si target bombarded with Ar cluster ions much larger than the molecular ions have been investigated. Secondary ions have been measured for a Si target bombarded with large Ar cluster ions at an incident energy between 7.5 and 27.5 keV using a time-of-flight technique. The mean size of the Ar cluster ion was about 1000 atoms/cluster, and then the collision energy per atom is between a few tens of eV and a few hundreds of eV. Secondary silicon cluster ions were detected under large Ar cluster ion bombardment. In this study, we succeeded to accurately measure the dependence of secondary ion spectra obtained by large Ar cluster ions on the incident cluster-ion size using a time-of-flight technique combined a primary-ion beam deflector and a secondary-ion deflector. The dependence of the secondary ion spectra under large Ar cluster ion bombardment on the incident cluster size is discussed. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2006.12.074

Molecular dynamics study of surface modification with a glancing angle gas cluster ion beam Reviewed

Takaaki Aoki, Jiro Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 255 ( 1 ) page： 265 - 268 2007.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The collisional process of glancing angle gas cluster ion impact was studied using molecular dynamics (MD) simulations. Ar-2000 Clusters accelerated to 20 keV were irradiated onto a Si(100) target at various incident angles ranging from 0 degrees to 80 degrees. The investigation of the surface profile after collision revealed that there is a certain incident angle where the incident cluster penetrates the target surface to cause crater-like damage. For larger incident angles, such as 80 degrees from the surface normal, the cluster slides on the target surface without creating displacements. This mechanism of non-damage irradiation was examined with respect to the perpendicular component of incident energy. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2006.11.071

The effect of incident cluster ion size on secondary ion yields produced from Si Reviewed

Satoshi Ninomiya, Kazuya Ichiki, Yoshihiko Nakata, Toshio Seki, Takaaki Aoki, Jiro Matsuo

TRANSACTIONS OF THE MATERIALS RESEARCH SOCIETY OF JAPAN, VOL 32, NO 4 Vol. 32 ( 4 ) page： 895 - 898 2007

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY JAPAN-MRS-J

Secondary ions emitted from a Si target have been investigated under large Ar cluster ion bombardment. Incident ion beams with energies from 10 to 30 keV were used and the mean size of the Ar cluster ion beam was about 1000 atoms per cluster. Secondary Si(n)(+)(n=1-11) ions were measured from Si under Ar cluster ion bombardment, while only atomic ions were measured under Ar monomer ion bombardment. In this study, we Succeeded to accurately measure the incident size dependence of secondary ion spectra for Si under large Ar cluster ion bombardment using a time-of-flight technique combined a primary-ion beam deflector and a secondary-ion deflector. When the total incident ion energy was kept constant, the yields of secondary cluster ions such as Si(6)(+) relative to those of Si(+) increased with size. On the other hand, when the incident Ar cluster size was kept constant, the yields of secondary cluster ions relative to those of Si(+) decreased with energy. The effect of incident cluster size on secondary ion yields is discussed.

High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions Reviewed

Satoshi Ninomiya, Takaaki Aoki, Toshio Seki, Jiro Matsuo

APPLIED SURFACE SCIENCE Vol. 252 ( 19 ) page： 6550 - 6553 2006.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si-n(+) ions with n values up to n = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size. (c) 2006 Published by Elsevier B.V.

DOI： 10.1016/j.apsusc.2006.02.100

Molecular dynamics study of particle emission by reactive cluster ion impact Reviewed

Takaaki Aoki, Jiro Matsuo

APPLIED SURFACE SCIENCE Vol. 252 ( 19 ) page： 6466 - 6469 2006.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular dynamics (MD) simulations of sputtering process with fluorine cluster impact onto silicon targets were performed. By iterating collisional simulations on a same target, accumulation of incident atoms and evolution of surface morphology were examined as well as emission process of precursors. When (F(2))(300) clusters were sequentially irradiated on Si(100) target at 6 keV of total incident energy, column-like surface structure covered with F atoms was formed. As the number of incident clusters increased, sputtering yield of Si atoms also increased because the target surface was well fluoridised to provide SiF(x) precursors. Size distribution of emitted particles showed that SiF(2) was the major sputtered particle, but various types of silicon-fluoride compounds such like Si(2)F(x), Si(3)f(x) and very large molecules consists of 100 atoms were also observed. This size distribution and kinetic energy distribution of desorbed materials were studied, which showed that the sputtering mechanism with reactive cluster ions is similar to that under thermal equilibrium condition at high-temperature. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2006.02.195

Secondary ion measurements for oxygen cluster ion SIMS Reviewed

Satoshi Ninomiya, Takaaki Aoki, Toshio Seki, Jiro Matsuo

APPLIED SURFACE SCIENCE Vol. 252 ( 19 ) page： 7290 - 7292 2006.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We have proposed to use oxygen cluster ions, which are much larger than molecular ions, as primary ions for secondary ion mass spectrometry (SIMS). A high intensity gas cluster ion source with a current density of a few mu As/cm(2) has been developed. Secondary ions emitted from Si have been investigated under O(2) and Ar cluster ion bombardment. A large enhancement of the yield of secondary ions produced by large O(2) and Ar cluster ions was found. The SIMS system utilizing large O(2) cluster ions must give both excellent depth resolution and high secondary ion yield. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2006.02.138

Molecular Dynamics Simulations of Cluster-size Effect on Sputtering Process with Reactive Gas Cluster Ions Reviewed

Takaaki Aoki

MRS Proceedings Vol. 908 page： 18 - 24 2006.2

Molecular dynamics simulations of surface modification and damage formation by gas cluster ion impacts Reviewed

T Aoki, J Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 242 ( 1-2 ) page： 517 - 519 2006.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Damage formation process by gas cluster impact was studied using molecular dynamics simulations. At gas clusters with various sizes (several tens to several thousand) and energies (several to several tens keV, totally) were irradiated on Si substrates. The relationship between mean damage depth, incident energy and cluster size was examined and the model and conditions to cause damage by cluster impact were discussed. (c) 2005 Published by Elsevier B.V.

DOI： 10.1016/j.nimb.2005.09.011

Molecular dynamics study of the angular dependence of reactive cluster impacts Reviewed

T Aoki, J Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 241 ( 1-4 ) page： 594 - 598 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The collisional processes of fluorine clusters impacting at various incident angles on bare silicon surfaces were studied, and the change of the surface profile, sticking probabilities of F atoms, sputtering yield and the distribution of the sputtered particles were examined. When a (F-2)(300) cluster with 10 eV/atom impacts on a Si(100) surface at normal incident, the cluster penetrates the surface causing a spherical crater structure with the F atoms densely covered. As the incident angle increases, the penetration depth of cluster decreases and the simulation shows an asymmetric crater profile. Especially at an incident angle of 75 degrees, the surface profile did not change but F atoms were deposited over a wide area. The distribution of sputtered particles also depends on incident angle. At normal incidence, the Si atoms are sputtered as well as silicon-fluoride molecules such as SiF and SiF2, while only SiF, molecules are sputtered at 75 degrees of incident angle. From these results the surface etching process caused by reactive cluster impacts are discussed. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2005.07.108

A Comparison of Ions with Neutrals Emitted from Semiconductors Bombarded by MeV Si Ions Reviewed International journal

Yoshihiko Nakata, Satoshi Ninomiya, Takaaki Aoki, Hidetsugu Tsuchida, Jiro Matsuo, Akio Itoh

Transactions of the Materials Research Society of Japan Vol. 30 ( 3 ) page： 797 - 800 2005.6

Low Damage Smoothing of Magnetic Materials using Oblique Irradiation of Gas Cluster Ion Beam

Takaaki Aoki

MRS Proceedings 2005.2

Molecular dynamics study of suface structure and sputtering process by sequencial fluorine cluster impacts Reviewed

T Aoki, J Matsuo

Surface Engineering 2004 - Fundamentals and Applications Vol. 843 page： 189 - 194 2005

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY

In order to study the surface reaction process under cluster ion impact, molecular dynamics simulations of sequential cluster impacts of fluorine and neon clusters were performed. (F-2)(300) and Ne-600 clusters were accelerated with totally 6keV and irradiated on bare Si(100) target. By iterating impact simulation sequentially, change of surface morphology and composition of desorbed materials were studied. In the case of fluorine cluster impact, the rough surface structure was made compared with neon cluster impact because fluorine atoms adsorb on the target, which work to keep pillar structure on the surface, whereas Ne atoms evaporate immediately leaving spherical mound structure on the surface. From the study of desorption process, it was observed that large number of Si atoms are desorbed in the form of silicon fluorides. The major sputtered material was SiF2, but various types of silicon-fluorides, including the molecules consists of several tens to hundreds silicon and fluorine atoms, were observed. The distribution of clusters in desorbed materials obeyed the classical model of cluster emission from quasi-liquid phase excited with ion bombardment. From these results, the irradiation effects of reactive cluster ions were discussed.

DOI： 10.1557/proc-843-t5.7

A new secondary ion mass spectrometry (SIMS) system with high-intensity cluster ion source Reviewed International journal

J Matsuo, C Okubo, T Seki, T Aoki, N Toyoda, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 219 ( 1-4 ) page： 463 - 467 2004.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Secondary ion mass spectrometry (SIMS) with gas cluster ion beams (GCIB) was investigated with experiments and molecular dynamics (MD) simulations. A new cluster SIMS system with high-intensity cluster ion source has been developed. Ar cluster ion beam with the average size of 2000 was utilized as a primary ion beam. The beam diameter is less than 1 mm at the target position, and a current density of 10 muA/cm(2) is obtained. The etch rate of Si with this current density is more than 20 nm/min, which is far beyond the etch rate in recent low energy SIMS system. The secondary ion intensity linearly increases with the acceleration voltage. A threshold voltage of a few keV for secondary ion emission was found. These results are consistent with previous sputtering experiments. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2004.01.103

Molecular effect on projected range in ultralow-energy ion implantation

K Kimura, Y Oota, K Nakajima, M Suzuki, T Aoki, J Matsuo, A Agarwal, B Freer, A Stevenson, M Ameen

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 211 ( 2 ) page： 206 - 210 2003.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Silicon wafers of (100) orientation are implanted with 3 keV As+ or 6 keV As+ ions at room temperature with fluences 1 x 10(14)-4 x 10(14) atoms cm(-2). The depth pro,files of implanted As are measured by high-resolution Rutherford backscattering spectroscopy. The observed projected range for As+ implantation is larger than that for As+ by several percent, showing a molecular effect on the projected range. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0168-583X(03)01249-7

Atomistic study of cluster collision on solid surfaces Reviewed International journal

J Matsuo, T Seki, T Aoki, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 206 page： 838 - 841 2003.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

New surface modification processes have been demonstrated using gas cluster ion irradiations, because of the unique interaction between cluster ions and surface atoms, atomistic mechanisms of cluster ion bombardment must be understood for the further developments of this technology. Variable temperature scanning tunneling microscope in ultra high vacuum allows us to study ion bombardment effects on surfaces and nucleation growth at various temperatures.
In the STM image of cluster-irradiated surface, large craters with diameter of about 10 nm were observed on Si(1 1 1)7 x 7 surfaces. The structure and size of the traces agree well with theoretical calculation. When the sample irradiated with Ar cluster was annealed at 600 degreesC, the hole remained, but the outer rim of the crater disappeared and the surface structure was reconstructed at the site of the rim. The depth of damage region in the target became shallower with decrease of the impact energy. These results indicate that low damage and useful surface modification can be realized using the cluster ion beam. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(03)00874-7

Defect characteristics by boron cluster ion implantation International journal

T Aoki, J Matsuo, G Takaoka, N Toyoda, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 206 page： 855 - 860 2003.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Cluster ion implantation using decaborane (B10H14) has been proposed as a shallow implantation technique for LSI devices with gate lengths of several-tens nanometers. Experiments and computer simulations of low-energy boron monomers and decaborane clusters implantation were performed. Molecular dynamics simulations of B-10 cluster implantation have shown similar implant depth but different damage density and damage structure compared to monomer (B-1) ion implantation with the same energy-per-atom. For monomer implantation, point-defects such as vacancy-interstitial pairs are mainly formed. On the other hand, B-10 generates large numbers of defects within a highly-amorphised region at the impact location. This difference in damage structure produced during implantation is expected to cause different annihilation processes. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(03)00878-4

Cluster species and cluster size dependence of damage formation by cluster ion impact Reviewed International journal

T Aoki, J Matsuo, G Takaoka, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 206 page： 861 - 865 2003.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular dynamics simulations of Ne, Ar and Xe clusters with various sizes impacting on Si surfaces were performed in order to study damage formation processes. When cluster size ranged from several tens to several thousands and accelerated energy is 20 keV in total, each cluster impact caused surface damage in the shape of a crater. A larger number of displacements was found with the Xe cluster than Ne and Ar clusters of the same cluster size because the Xe cluster had a larger mass and momentum. However, when cluster size exceeded several thousands, different surface damage structures were formed depending on the cluster species. At a cluster size of 10,000, for example, a crater-like trace was still formed with a Ne cluster impact. However, both the depth of the crater and the number of displacements decreased as the atomic number of the cluster atom increased, which meant that the atomic and energy density irradiated on the surface is a dominant parameter in causing surface damage. These results indicate that the damage formation by cluster impact can be controlled by changing the cluster species as well as the incident energy and cluster size. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(03)00879-6

Modeling of surface smoothing process by cluster ion beam irradiation Reviewed International journal

A Nakai, T Aoki, T Seki, J Matsuo, GH Takaoka, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 206 page： 842 - 845 2003.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Smoothing effect is one of the advantages of cluster ion beam. It is important to estimate an ion dose to achieve required surface smoothness. The smoothing rate with cluster ion beam depends on surface profiles. In this work, modeling of surface smoothing process with cluster ion beams was examined. Ar cluster ions with an energy of 20 keV was irradiated on rough Si Surface. Fast Fourier transform was applied to atomic force microscope data of 100 x 100 mum(2), and power spectra were calculated. Smoothing rate depends on the wave number as well as the ion dose. Relationship between smoothing rate and wave number was derived. The surface smoothing process was modeled with the use of the wave number dependence of the smoothing rate. The calculated and the experimental surface profiles are in good agreements. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(03)00875-9

Molecular dynamics study of damage formation characteristics by large cluster ion impacts Reviewed International journal

T Aoki, J Matsuo, G Takaoka

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 202 page： 278 - 282 2003.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular dynamics simulations of various Ar clusters, with the size ranging 1-50,000 and the energy up to totally 50 keV, impacting on Si surfaces were performed. The cluster size and incident energy dependence on damage formation was examined. Two cluster-size depending parameters, the threshold energy to cause displacements and displacement yield, were proposed and modeled. These two parameters showed non-linearity depending on cluster size. The model function using above parameters reproduced the characteristics of damage formation by cluster ion impact. Two specific cluster sizes to cause maximum and no displacements on the surface were discussed, which is expected to provide useful information about optimized cluster ion beam conditions for various surface modification and thin-film formation processes. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(02)01869-4

クラスターイオン衝突における非線形照射効果とそのプロセス応用 Reviewed

Takaaki Aoki

高温学会誌 Vol. 29 ( 5 ) 2003

Molecular Dynamics Study Of Surface Morphological Evolution By Cluster Impacts

Takaaki Aoki

MRS Proceedings Vol. 792 page： 497 - 502 2003

Secondary ion mass spectrometry with gas cluster ion beams Reviewed

N Toyoda, J Matsuo, T Aoki, Yamada, I, DB Fenner

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 190 ( 1-4 ) page： 860 - 864 2002.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Secondary ion mass spectrometry (SIMS) with gas cluster ion beams was studied with experiments and molecular dynamics (MD) simulations to achieve a high-resolution depth profiling. For this purpose, it is important to prevent both ion mixing and the surface roughening due to energetic ions. As the Ar cluster ion beams shows high secondary ion yield and surface smoothing effects in the low-energy regime, it is suitable for the primary ion beam of SIMS. From MID simulations of Ar cluster ion impact on Si, ion mixing is heavier than than those for Ar monomer ions at the same energy per atom, because the energy density at the impact point is extremely high. However, the sputtering yields with Ar cluster ions are one or two orders of magnitude higher than that with Ar monomer ions at the same energy per atom. Comparing at the ion energy where the ion-mixing depths are the same by both Ar cluster and Ar monomer ions, cluster ions show almost 10 times higher sputtering yield than by Ar monomer ions. A preliminary experiment of SIMS with Ar cluster ion was performed and a mass resolution of several inn was achieved for a Ta film. (C) 2002 Published by Elsevier Science B.V.

DOI： 10.1016/S0168-583X(02)00463-9

Study of Surface Morphological Evolution by Cluster Ion Irradiation on Solid Targets

Aoki, T., Nakai, A., Matsuo, J., Takaoka, G.

Materials Research Society Symposium - Proceedings Vol. 749 page： 311 - 316 2002

Cluster size effect on reactive sputtering by fluorine cluster impact using molecular dynamics simulation Reviewed

T Aoki, J Matsuo, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 180 page： 164 - 170 2001.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The mechanism of high-yield sputtering induced by reactive cluster impact was investigated using molecular dynamics (MD) simulations. Various sizes of fluorine clusters were radiated on clean silicon surface. At an incident energy of 1 eV/atom. F atom and F-2 molecule are only adsorbed on the surface and sputtering of Si atom does not occur. However, fluorine cluster. which consists of more than several tens molecules causes sputtering. In this case, most of Si atoms are sputtered as fluorinated material such as SiFx. This effect is due to the fact that cluster impact induces high-density particle and energy deposition, which enhances both formation of precursors and desorption of etching products. The deposition of atoms and energy becomes denser as the incident cluster size increases, so that larger clusters have shown higher sputtering yield. (C) 2001 Elsevier Science B.V. All rights reserved.

Molecular dynamics simulation of fluorine ion etching of silicon Reviewed

S Chiba, T Aoki, J Matsuo

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 180 page： 317 - 321 2001.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Formation of precursors and desorption of etching products by fluorine ion irradiation were studied using molecular dynamics (MD) simulation. When F atoms impact sequentially on a Si substrate, a mixed layer of F and Si atoms is formed on the surface. When the incident energy is below 30 eV, the fluorine coverage reaches steady state after 1.0 x 10(16) atoms/cm(2) irradiation. The ratio of F to Si in the mixed layer is about 1:1. At an incident energy of 15 eV, the mixed layer at steady state consists of 4.5 ML of fluorine with a depth of 20 Angstrom and the main etching products are SiF3 and SiF4. At 30 eV incident energy, the mixed layer at steady state is 6.5 ML with a depth of 30 A and the main etching products are SiF2 and SiF3. When F atoms were irradiated onto a Si substrate heated at 1000 K, a significant reduction of F coverage was observed due to diffusion of F atoms. (C) 2001 Elsevier Science B.V. All rights reserved.

Molecular dynamics and Monte-Carlo simulation of sputtering and mixing by ion irradiation Reviewed

T Aoki, S Chiba, J Matsuo, Yamada, I, JP Biersack

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 180 page： 312 - 316 2001.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular dynamics (MD) and Monte-Carlo (MC) simulations of low-energy (< 500 eV) Ar ion irradiation on Si substrates were performed in order to investigate the mixing and sputtering effects. Both MD and MC simulation show similar results in sputtering yield. depth profile of projectile and mixing of substrate. For these incident energies, the depth of the mixed region is determined by the implant range of incident ions. For example, when the incident energy is 500 eV, the Ar ions reach a depth of 40 Angstrom so that the Si atoms that reside shallower than 40 Angstrom are fully mixed at an ion dose of about 5.0 x 10(16) atoms/cm(2). The resolution of secondary ion mass spectrometry (SIMS) was also studied. It was found that the resolution of SIMS depends on the depth of mixing, which depends in turn on the implant range of the probe ions. This is because the mixing of substrate atoms occurs more frequently than sputtering, so that the information about the depth profile in the mixing region is disturbed. (C) 2001 Elsevier Science B.V. All rights reserved.

Characterization of damage induced by cluster ion implantation

Aoki, T., Matsuo, J., Takaoka, G.

Materials Research Society Symposium - Proceedings Vol. 669 page： J451 - J456 2001.3

Secondary ion mass spectrometry with gas cluster ion beams

Toyoda, N., Matsuo, J., Aoki, T., Chiba, S., Yamada, I., Fenner, D.B., Torti, R.

Materials Research Society Symposium - Proceedings Vol. 647 2001.3

Molecular dynamics simulations of cluster ion implantation for shallow junction formation Reviewed

T Aoki, JMG Takaoka, Yamada, I

APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY Vol. 576 page： 967 - 970 2001

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Cluster ion implantation is a useful technique for low energy implantation. In order to investigate the implant and damage formation by cluster ions, molecular dynamics simulations of boron monomer (B-1) and cluster with the size ranging from 2 (B-2) to 10 (B-10) impacting on silicon substrate were performed. When atom/clusters with the same energy per atom of 230eV/atom, all impacts show a similar implant profile, except for a vertical chain-like cluster with the size larger than 4. The latter finding is attributed to the clearing way effect. B-10 impact induces displacements several times larger than B-1; this is because the high-density particle and energy deposition by B-10 causes more knocked-on substrate atoms in the shallow substrate region and these knocked-on atoms tend to remain as displacements, an effect which is not observed in impacts of B-1. This higher displacement yield by B-10 is believed to avoid the formation of point defects at low ion dose and to suppress transient enhanced diffusion.

Ar cluster ion bombardment effects on semiconductor surfaces

T. Seki, K. Tsumura, T. Aoki, J. Matsuo, G. H. Takaoka, I. Yamada

Materials Research Society Symposium - Proceedings Vol. 647 page： O9.4.6 2001

Language：English Publishing type：Research paper (international conference proceedings)

New surface modification processes have been demonstrated using gas cluster ion irradiations because of their unique interaction between cluster ions and surface atoms. For example, high quality ITO films could be obtained by O2 cluster ion assisted deposition at room temperature. It is necessary to understand the role of cluster ion bombardment during film formation for the further developments of this technology. Variable Temperature Scanning Tunneling Microscope (VT-STM) in Ultra High Vacuum (UHV) allows us to study ion bombardment effects on surfaces and nucleation growth at various temperatures. The irradiation effects between Ar cluster ion and Xe monomer ion were compared. When a Si(111) surface with Ge deposited to a few Å was annealed to 400°C, it was observed that many islands of Ge were formed. The surface with the Ge islands was irradiated by these ions. In the STM image of cluster-irradiated surface. large craters with diameter of about 100 Å were observed, while only small traces with diameter of about 20 Å were observed in monomer-irradiated surface. The number of Ge atoms displaced by one Ar cluster ion impact was much larger than that by one Xe ion impact. This result indicates that Ar cluster ion impacts can enhance the physical modification of Ge islands. When the sample irradiated with Ar cluster was annealed at 600°C, the hole remained, but the outer rim of the crater disappeared and the surface structure was reconstructed at the site of the rim. The depth of damage region in the target became shallower with decrease of the impact energy. These results indicate that low damage and useful surface modification can be realized using the cluster ion beam.

Molecular dynamics simulations of cluster ion impact on diamond surface

T. Aoki, J. Matsuo, G. Takaoka, I. Yamada

Materials Research Society Symposium - Proceedings Vol. 650 page： R3.40.1 2001

Language：English Publishing type：Research paper (international conference proceedings)

Molecular dynamics (MD) simulations of various cluster ions impacting on solid targets were performed in order to examine the implant and damage formation processes. Ne and Ar rare gas cluster with various cluster sizes, and fullerene (C60) were impacted on diamond (001) surface. It was shown that the impact process of cluster ion depends on the cluster size. When the cluster size is small and incident energy-per-atom is high, such as Ar15 with 800eV/atom, all incident Ar atoms penetrate the surface and reside in the substrate. As the cluster size increases and the incident energy-per-atom decreases, the implant depth decreases and the profile of the displacement becomes shallower. A large cluster, such as Ar60 with 200eV/atom, shows a shallower implant depth and a higher sputtering yield than Ar15. However, Ar240 with 50eV/atom shows a shallower implant depth, but less sputtering yield than Ar60. These results suggest that there is proper cluster size and incident energy where the maximum sputtering yield is achieved.

STM observation of surface vacancies created by ion impact Reviewed

T Seki, T Aoki, J Matsuo, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 164 page： 650 - 655 2000.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The formation, structure and extinction of surface defects created at high temperature were observed with a variable temperature scanning tunneling microscope (VT-STM). A Si(1 1 1) 7 x 7 surface was irradiated with Xe+ ions and single ion impact traces of about 20 Angstrom diameter were clearly observed with atomic resolution. The average size of the trace does not depend on the impact energy in the range from 1 to 5 keV. When the sample is annealed at 400 degrees C, the vacancies created in subsurface by the impact start to diffuse toward the surface and appear on the surface, but the interstitial atoms generated together with the vacancies remain in the bulk. At 600 degrees C, vacancy clusters are formed whose sizes correspond to the number of vacancies created near the surfaces. At 650 degrees C, the interstitial atoms diffuse and recombine with surface vacancies and the size of the vacancy cluster decreases with annealing time. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(99)01112-X

Nano-processing with gas cluster ion beams Reviewed

Yamada, I, J Matsuo, Z Insepov, T Aoki, T Seki, N Toyoda

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 164 page： 944 - 959 2000.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

This paper describes the fundamental principles and experimental status of gas cluster ion beam (GCIB) processing as a new technique with promise for practical industrial applications. A review is presented of the theoretical and experimental characteristics of new gas cluster ion bombardment processes and of related equipment development. The impacts of accelerated cluster ions upon substrate surfaces impart very high-energy densities in the impact regions of individual clusters and produce non-linear processes that are not present in the impacts of individual atomic ions. These unique bombardment characteristics are expected to facilitate new industrial applications that would not be possible by traditional ion beam processing. Among these are shallow ion implantation, high rate sputtering, surface cleaning and smoothing, and low-temperature thin film formation. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(99)01163-5

Molecular dynamics simulation of fluorine cluster ion impact Reviewed

T Aoki, J Matsuo, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 164 page： 546 - 552 2000.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular dynamics (MD) simulations of fluorine atoms, molecules and clusters impacting a silicon substrate were performed in order to investigate the impact process of a reactive cluster ion. This result shows that when the incident energy of the impacting fluorine atom or molecule is less than 10 eV/atom, the species are only adsorbed on the surface and sputtering of substrate atoms does not occur. On the other hand, a fluorine cluster consisting of 30 molecules produces sputtering even at a low incident energy of 1 eV/atom. At these conditions, the surface atoms are desorbed as fluorine-containing species, such as SiF or SiF2, indicating that chemical desorption is enhanced by irradiation with fluorine clusters. As the incident energy of the cluster increases to values as high as 100 eV/atom, almost all the fluorine atoms penetrate the surface and a crater-shaped damage is formed. The incident F atoms reside at the bottom region of the crater. In this case, silicon atoms leave the surface as monomers, dimers or clusters without F atoms, i.e., in this regime physical sputtering through atomic collisions has a higher probability than chemical reactions, like in the case of Ne or Ar cluster impact. (C) 2000 Elsevier Science B.V.zd All rights reserved.

Cluster size dependence of the impact process on a carbon substrate Reviewed

T Aoki, T Seki, J Matsuo, Z Insepov, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 153 ( 1-4 ) page： 264 - 269 1999.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Molecular dynamics simulations of various sizes of carbon molecule as clusters impacting a carbon substrate are performed in order to examine the size-dependence of the cluster ion on the impact process. Highly Oriented Pyrolitic Graphite (HOPG) was irradiated with C-1, C-4, C-8, C-19 and C-60 clusters carrying the same energy-per-atom of 2 keV/ atom. When the cluster size is less than eight, interspersed damage is formed by the cascade-collision mechanism, whereas C-19 and C-60 impacts show homogeneously damaged regions in the surface of the substrate. In the case of large cluster ion impacts, all the incident energy of a cluster is deposited with high density in narrow region on the surface. These results show good agreement with experimental STM observations of single traces induced by the impact of C-60 and small carbon molecules. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0168-583X(99)00201-3

Applications of cluster ion implantation in microelectronics devices Reviewed

Yamada, I, J Matsuo, N Toyoda, T Aoki

APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY, PTS 1 AND 2 Vol. 475 page： 379 - 382 1999

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Ultra-shallow ion implantation by gas cluster ion beams has been demonstrated experimentally and confirmed by molecular dynamics simulations. Implantation of B10H14 in Si (100) at 2keV does not cause transient enhanced diffusion (TED) of boron atoms during annealing at 900 degrees C for 10sec. In order to reveal the diffusion mechanism of B atoms, the diffusivity of B atoms in ultra low-energy B10H14 ion implantation was measured by Secondary Ion Mass Spectroscopy (SIMS). B10H14 ions were implanted at 2, 3, 5 and 10keV. Subsequent annealing was performed at 900 degrees C and 1000 degrees C for 10 sec, respectively. In the case of the 900 degrees C annealing, TED was suppressed as the implant energy decreased and at energy less than 3keV, the TED of B atoms no longer occurred during annealing. High performance 40nm p-MOSFETs with ultra shallow junctions have been fabricated using B10H14 cluster ion implantation. The unique characteristics of gas cluster ion beam processes for sputtering has also been applied to very high-rate etching. Yields more than two orders of magnitude higher than those by monomer ions having the same energy and atomic scale smoothing of surfaces to average roughness less than 0.2nm have been demonstrated. This paper will discuss the status of cluster ion beam processes based upon our recent experimental and molecular dynamics simulation results.

Molecular dynamics study of implant and damage formation in low-energy boron cluster ion implantation

Takaaki Aoki, Jiro Matsuo, Zinetulla Insepov, Isao Yamada

Proceedings of the International Conference on Ion Implantation Technology Vol. 2 page： 1254 - 1257 1999

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Cluster ion implantation using decaborane (B10H14) has been proposed as a useful technique for shallow junction formation. In order to examine the characteristics and advantages of cluster ion implantation, molecular dynamics simulations of small B cluster and monomer implantation were performed. B1, B4 and B10 are irradiated on Si (001) substrates with acceleration energy of 230 eV/atom so that B4 and B10 are accelerated with 0.92 keV and 2.3 keV, respectively. Those three show the same implant profile and implant efficiency, which agrees with the experimental result of B10H14 implantation. This result suggests that each B atom in a B cluster acts individually in similar way to a monomer ion. B clusters show the same properties in projection range and implant efficiency as the monomer whereas non-linearity is shown in damage formation. The number of displacements by one B atom once increases to the same maximum value for both a B cluster and a B monomer. However, the damage recovery process is different depending on the cluster size. Damage induced by B10 recovers more slowly and 4 times as many displacements remain compared to B1 8 ps after impact. These displacements by B10 clusters concentrate in the near surface region of the impact point, while the ones by B1 reside around the implanted B atom as the end-of-range damage. This characteristic damage formation by B10 cluster is expected to avoid transient-enhanced-diffusion of incident B atoms and achieve the formation of high-quality shallow p-type junction.

Non-linear processes in the gas cluster ion beam modification of solid surfaces Reviewed

Yamada, I, J Matsuo, N Toyoda, T Aoki, E Jones, Z Insepov

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING Vol. 253 ( 1-2 ) page： 249 - 257 1998.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The unique characteristics of gas cluster ion beam processing are reviewed. Cluster ion beams consisting of hundreds to thousands of atoms have been generated from various kinds of gas materials. Multiple collisions during the impact of accelerated cluster ions upon the substrate surfaces produce fundamentally non-linear bombarding processes. These bombarding characteristics can be applied to shallow ion implantation, high yield sputtering and smoothing, surface cleaning and low temperature thin him formation. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0921-5093(98)00733-3

Angular distributions of the particles sputtered with Ar cluster ions Reviewed

N Toyoda, H Kitani, N Hagiwara, T Aoki, J Matsuo, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 262 - 265 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

This paper discusses angular distributions of sputtered particles from the target in cluster ion beam irradiation. For a copper target, the angular distribution of Cu particles with Ar cluster ion beams bombarding at a normal incidence was found to follow under-cosine law, whereas for Ar monomer ions the distribution follows the cosine law, as predicted from the linear cascade collision theory. From our molecular dynamics simulations, the sputtering mechanism with Ar cluster ions is as follows. At the impact of a cluster on a target a crater is formed. Numerous atoms acquire high lateral momentum and are ejected in the lateral direction. Subsequently, these particles cause an under-cosine distribution, and thus the behavior is drastically different from that with monomer ion bombardment. Experimental results show that the angular particle distribution is not strongly dependent on the incident angle above 10 degrees, but is very sensitive to the incidence angle below that. Microscopic images of a trace observed with scanning tunneling microscopy (STM) reinforce these results. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0254-0584(98)00101-1

Reduction of boron transient enhanced diffusion in silicon by low-energy cluster ion implantation Reviewed

N Shimada, T Aoki, J Matsuo, Yamada, I, K Goto, T Sugui

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 80 - 83 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Future integrated circuits require shallow pn junctions with a depth below 50 nm and, therefore, low energy ion beams are necessary. Cluster ions can realize both goals of low-energy and high-current ion beams quite easily, because the kinetic energy of a cluster is shared among constituent atoms. Another advantage of cluster ion implantation is that the substrate damage induced by ion bombardment can be controlled by changing the cluster size. As a consequence, the transient enhanced diffusion (TED) of the dopant during annealing can be controlled in cluster ion implantation. We have used the polyatomic cluster, decaborane (B10H14) to form very shallow p(+) junctions. During 900 degrees C annealing, the diffusion of boron atoms implanted at 3 keV was strongly suppressed compared with that implanted at 10 keV implantation. The difference in defect distribution between 10 and 3 keV implantation caused the different annealing behavior. (C) 1998 Elsevier Science S.A. All rights reserved.

Molecular dynamics simulation of a carbon cluster ion impacting on a carbon surface Reviewed

T Aoki, T Seki, J Matsuo, Z Insepov, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 139 - 142 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

High-density irradiation effects were studied by molecular dynamics simulations of fullerene (C-60) impacting on a carbon surface. When a C-60 ion with the incident energy of nearly 200 eV per atom impacts on the solid surface, an effect termed 'clearing-way (CW) effect' occurs. This effect is due to the high energy density and coherency of incident atoms. The penetration depth of C-60 is deeper than that of the carbon monomer (C-1) with 200 eV because of the CW effect, but shallower than that of the carbon monomer with 12 keV (200 eV per atom x 60). This result is attributed to a second effect termed 'multiple-collision (MC) effect'. This effect is caused by a large number of collisions between the incident and surface atoms that occur at the impact, and these collisions transfer the larger component of the momenta of the cluster to the lateral direction, unlike the monomer ion impact. Therefore, the penetration depth is proportional to the cube root of the incident energy, and the stopping power is magnified compared with the carbon monomer. When the incident energy of the cluster increases, both the cross-section of the impact and the number of collisions decrease, the MC effect is reduced and the behavior of incident atoms becomes similar to that of the monomer ions. On the contrary, when the incident energy of a cluster is less than the threshold energy of implantation, a cluster dissociates on the solid surface without implantation and the MC effect does not occur. It is shown that the range of incident energy where C-60 shows a non-linear impact effect is from about 100 eV per atom to 2 keV per atom. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0254-0584(98)00096-0

Low-temperature formation of perovskite PbTiO3 films by O-2 cluster ion-assisted deposition Reviewed

M Akizuki, J Matsuo, W Qin, T Aoki, M Harada, S Ogasawara, K Yodoshi, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 255 - 257 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The formation of PbTiO3 films on Pt films using O-2 cluster ions, Pb and Ti(i-OC3H7)(4), was examined. Perovskite-PbTiO3 films could be formed at a substrate temperature of 400 degrees C, which was about 100 degrees C lower than that which is possible with CVD and sol-gel methods. An acceleration energy of 1 keV was sufficient to form the perovskite structure. These films were obtained owing to a high oxidant Aux to the surface and high-density energy deposition during growth. Another feature of the O-2 cluster ion assisted deposition was that no pyrochlore structure was observed at lower substrate temperatures. This might be due to surface reactions in the high vacuum (3 X 10(-5) Torr). (C) 1998 Elsevier Science S.A. All rights reserved.

Energy dependence of a single trace created by C-60 ion impact Reviewed

T Seki, T Aoki, M Tanomura, J Matsuo, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 143 - 146 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Cluster ion beams provide new surface modification processes, because of the unique interaction between cluster atoms and surface atoms. In order to reveal cluster-surface interaction, single traces formed by C-60 ion impact on solid surfaces were investigated using scanning tunneling microscopy. Large hill shape traces and crater shape traces were observed on a highly oriented pyrolitic graphite surface irradiated by C-60 ions. The crater formation by the C-60 impact is an effect of high-density energy deposition and multiple-collision between cluster atoms and surface atoms. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0254-0584(98)00097-2

Cluster ion bombardment on atomically flat Au(111) solid surfaces Reviewed

D Takeuchi, T Seki, T Aoki, J Matsuo, Yamada, I

MATERIALS CHEMISTRY AND PHYSICS Vol. 54 ( 1-3 ) page： 76 - 79 1998.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Energetic cluster ion bombardment shows unique and complicated interactions between constituents of the cluster and atoms of the target surface. Scanning tunneling microscopy (STM) observation is one of the most powerful methods to investigate the cluster ion-solid surface interaction. We have observed crater-shape traces on highly oriented pyrolitic graphite (HOPG) surface bombarded by energetic Ar cluster ions. However, STM images of HOPG surfaces are influenced by special electronic surface states. In this paper, Ar monomer and cluster ions are bombarded on Au( iii) surfaces on mica to observe ion traces by STM. In addition, the relationship between the parameters of cluster ion beams and the features of ion traces are discussed. The STM observation showed that Ar cluster ion bombardment had circular crater-like shapes, and their diameters were proportional to the cubic root of ion energy. These indicate that the kinetic energy of cluster ions is deposited on the surface isotropically. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0254-0584(98)00052-2

Size Dependence of Bombardment Characteristics Produced by Cluster Ion Beams

Takaaki Aoki

MRS Proceedings Vol. 504 page： 93 - 98 1998.2

Cluster Ion Implantation and Device Processes

Isao Yamada, Jiro Matsuo, Noriaki Toyoda, Takaaki Aoki

Shinku/Journal of the Vacuum Society of Japan Vol. 41 ( 11 ) page： 932 - 939 1998

Gas cluster ion beam processing Reviewed

Yamada, I, J Matsuo, N Toyoda, T Aoki, E Jones, Z Insepov

SIMILARITIES AND DIFFERENCES BETWEEN ATOMIC NUCLEI AND CLUSTERS ( 416 ) page： 310 - 329 1998

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Unique characteristics of gas cluster ion beam processing are reviewed. Cluster ion beams consisting of a few hundreds to thousands of atoms have been generated from various kinds of gas materials. Multi-collisions during the impact of accelerated cluster ions upon the substrate surfaces produce fundamentally low energy bombarding effects in a range of a few eV to hundreds of eV per atom at very high density. These bombarding characteristics can be applied to shallow ion implantation high yield sputtering and smoothing, surface cleaning and low temperature thin film formation.

Molecular dynamics simulation of damage formation by cluster ion impact Reviewed

T Aoki, J Matsuo, Z Insepov, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 121 ( 1-4 ) page： 49 - 52 1997.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The irradiation of a surface with a cluster ion beam is known to give superior surface modification effects compared with monomer ions. Surface smoothing processes and sputtering yield are both better off. The irradiation process by cluster ions has proved to be quite different from that by monomer ions. We have examined the process of cluster impacts on a solid surface by molecular dynamics simulation to investigate these differences. We simulated an Ar cluster, with size from 13 to 3000 atoms, impacting on a Si(100) substrate, with acceleration energies from 0.5 keV to 55 keV. The Ar cluster atoms penetrate into the Si substrate keeping the cluster state, and the penetration depth is deeper than that of a monomer ion of the same velocity. Si atoms around the Ar cluster are displaced, some of them recover, and the Ar atoms of the cluster are reflected back into the vacuum. Consequently, the displaced Si atoms concentrate in a shallow surface area, and crater-like damage remains. The radius and the depth of the crater are almost the same and are proportional to the cube root of the acceleration energy of the cluster ion. This means that the peculiar damage formation process, created by a cluster ion impact, is caused by an isotropic energy transportation through many interactions between cluster and surface atoms.

STM observation of HOPG surfaces irradiated with Ar cluster ions Reviewed

T Seki, T Kaneko, D Takeuchi, T Aoki, J Matsuo, Z Insepov, Yamada, I

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS Vol. 121 ( 1-4 ) page： 498 - 502 1997.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Cluster ion beams offer new surface modification processes because of their unique interaction between cluster atoms and solid surfaces, For example, surface smoothing and shallow implantation by cluster ion beam have been demonstrated. Ln order to reveal such cluster-surface interaction, a single trace formed by a cluster ion impact on a solid surface has been investigated using Scanning Tunneling Microscopy (STM).
STM images of Highly Oriented Pyrolitic Graphite (HOPG) surfaces, were obtained after irradiation with 150 keV Ar cluster or 1.5 keV monomer ions. The 150 keV cluster ions, with a size of about 100 atoms, were used in comparison with 1.5 keV monomer ion. The velocity of an atom in each case was the same. In spite of these equal velocities, large craters with diameter of about 180 Angstrom were observed in the STM image of cluster-irradiated HOPG surface, while only small hills were observed in monomer-irradiated surface.

DOI： 10.1016/S0168-583X(96)00557-5

Non-linear effects in high energy cluster ion implantation International journal

Takeuchi D, Aoki T, Matsuo J, Yamada I

APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY - PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL CONFERENCE, PTS 1 AND 2 ( 392 ) page： 491 - 494 1997

Range and damage distribution in cluster ion implantation International journal

Yamada I, Matsuo J, Jones EC, Takeuchi D, Aoki T, Goto K, Sugii T

MATERIALS MODIFICATION AND SYNTHESIS BY ION BEAM PROCESSING Vol. 438 page： 363 - 374 1997

Non-linear effects in high energy cluster ion implantation Reviewed

D Takeuchi, T Aoki, J Matsuo, Yamada, I

APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY - PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL CONFERENCE, PTS 1 AND 2 ( 392 ) page： 491 - 494 1997

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP PRESS

Cluster ion implantation realizes ultra-shallow (<50nm) junction formation. Cluster ions can provide a low-energy and high-current beam, because each constituent atom in the cluster, with sizes of a few thousands, has an energy of only a few eV. Non-linear effects of high energy cluster ion implantation caused by multiple-collisions and high-density energy deposition within a local surface region, have been investigated. Decaborane (B(10)G(14)), C-60 and large A cluster ions with sizes of from 100 to 3000 were implanted into Si and sapphire substrates at energies up to 300keV. The number of disordered substrate atoms per atom in a cluster ion was much larger than the damage done by a monomer ion with the same velocity. Single traces of cluster ions on solid surfaces were observed by STM and AFM to investigate the mechanism of the non-linear effects. Those of large At cluster ions looked like crater shapes where the crater diameter was proportional to one-third of the cluster ion energy.

Range and damage distribution in cluster ion implantation

Yamada, I., Matsuo, J., Jones, E.C., Takeuchi, D., Aoki, T., Goto, K., Sugii, T.

Materials Research Society Symposium - Proceedings Vol. 438 page： 363 - 374 1996.9

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