Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

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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

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

DOI： 10.1109/iiai-aai50415.2020.00070

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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.

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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.

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DOI： 10.1109/IIAI-AAI.2019.00085

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DOI： 10.1021/acs.analchem.9b04770

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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

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DOI： 10.1016/j.ijms.2018.05.012

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

DOI： 10.1109/iiai-aai.2017.129

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

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

DOI： 10.7567/jjap.56.06hb02

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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

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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.

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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

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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．

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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&#039;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

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

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

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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

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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

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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 &lt;= n &lt;= 15) and (M-n+2H)(2+) (8 &lt;= n &lt;= 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

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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

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© 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

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DOI： 10.1116/1.4941724

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DOI： 10.1002/sia.6121

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© 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

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Precision Engineering  

DOI： 10.2493/jjspe.82.309

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

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

&amp;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.&lt;br&gt;

DOI： 10.3131/jvsj2.59.113

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© 2016 John Wiley &amp; 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&#039;-di(1-naphthyl)-N,N&#039;-diphenylbenzidine (C44H32N2, NPD) and 4,4&#039;,4&quot;-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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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

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 &lt;= 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

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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⁺, Cs⁺ or Ga⁺, 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

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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

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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

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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

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

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

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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

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

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

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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 SF₅⁺, C₆₀⁺ 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⁺ at a dose of 1.0 × 10¹⁴ ions/cm² 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⁺ 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⁺ 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

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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 Au₃⁺ or C₆₀⁺ 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

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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

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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⁺ 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

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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

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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

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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

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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

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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

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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

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC TRIBOLOGISTS  

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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

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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 (&lt;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

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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

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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

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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

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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

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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&apos;-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

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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

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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 &lt;= n &lt;= 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

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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

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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

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DOI： 10.1109/IWJT.2009.5166237

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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

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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

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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

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

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 (&gt; 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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 &gt; 300) have been measured. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2007.01.164

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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

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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

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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

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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

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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.

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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

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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

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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

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DOI： 10.1557/PROC-0908-OO05-07

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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

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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

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

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DOI： 10.1557/PROC-843-T5.5

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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

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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

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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

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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

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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

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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

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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

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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

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

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DOI： 10.1557/proc-792-r4.7

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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

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DOI： 10.1557/PROC-749-W17.9

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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.

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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.

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Molecular dynamics (MD) and Monte-Carlo (MC) simulations of low-energy (&lt; 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.

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DOI： 10.1557/PROC-669-J4.5

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DOI： 10.1557/PROC-647-O5.5

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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.

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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.

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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.

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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

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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

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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.

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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

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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.

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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.

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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

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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

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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.

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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

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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.

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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

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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

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

DOI： 10.1557/PROC-504-93

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

DOI： 10.3131/jvsj.41.932

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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.

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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.

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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

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

Cluster ion implantation realizes ultra-shallow (&lt;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.

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

DOI： 10.1557/PROC-438-363

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Language：Japanese   Publisher：電気学会  

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J-GLOBAL

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Language：English   Publisher：Quantum Science and Engineering Center, Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University  

CiNii Books

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Language：English   Publisher：Quantum Science and Engineering Center, Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University  

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J-GLOBAL

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J-GLOBAL

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Publisher：The Surface Science Society of Japan  

脂肪酸や脂質分子は、細胞膜の主要構成分子だけでなく様々なシグナル伝達物質としての役目も負っている興味深い分子である。クラスターSIMS法では多数の脂質分子イオンを同時に高感度に検出でき、その分布を可視化する分子イメージングできるという利点がある。脂質分子の高感度検出とその分子イメージングへの応用について、実サンプルの評価結果交えて議論する。

DOI： 10.14886/sssj2008.35.0_347

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Publisher：The Surface Science Society of Japan  

一次イオンにクラスターを用いたStaticタイプのSIMSが市販化されるようになると、分析の対象が無機材料から生体材料、ポリマー材料などのソフトマテリアルへと広がった。更に、LMIGを用いた電界放射でのイオン化により、高輝度なイオンビーム照射が実現し、高空間分解能でのイメージング分析が可能になってきた。本発表では、一次イオンにBiクラスターを採用したTOF-SIMSを用いて、一次イオン種がイメージ分解能に与える影響について議論する。

DOI： 10.14886/sssj2008.35.0_245

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Publisher：The Surface Science Society of Japan  

近年、クラスターSIMS法を用いた有機材料分析が盛んに行われている。しかしながら、一般に複雑な組成や構造を持つ生体試料に対しては、その高精細な分析は未だ困難である。我々の研究グループでは、独自に作製した種々の有機モデル試料を用いて、クラスターSIMS法を用いた生体試料分析における質量分解能、空間分解能、検出限界や定量性に関する評価を行った。本発表では現在の課題と将来展望に関する議論を行う。

DOI： 10.14886/sssj2008.35.0_346

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Language：English   Publisher：Quantum Science and Engineering Center, Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University  

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Language：English   Publisher：Quantum Science and Engineering Center, Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University  

CiNii Books

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Language：English   Publisher：Quantum Science and Engineering Center, Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University  

CiNii Books

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Language：English   Publisher：Quantum Science and Engineering Center, Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University  

CiNii Books

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Publisher：The Surface Science Society of Japan  

&lt;br&gt;脂肪酸や脂質分子は、細胞膜の主要構成分子だけでなく様々なシグナル伝達物質としての役目も負っている興味深い分子である。クラスターSIMS法では多数の脂質分子イオンを同時に高感度に検出でき、その分布を可視化する分子イメージングできるという利点がある。脂質分子の高感度検出とその分子イメージングへの応用について、実サンプルの評価結果交えて議論する。

DOI： 10.14886/sssj2008.33.0_18

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Publisher：The Surface Science Society of Japan  

細胞膜などで普遍的にみられる脂質薄膜をクラスターSIMS法で評価した。ソフトなイオン化法であるクラスターSIMS法は、脂質分子を壊すことなくイオン化でき、構造評価に適した手法である。また、ラットの脳切片などへの応用も示す。

DOI： 10.14886/sssj2008.32.0_262

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Language：Japanese   Publisher：The Surface Science Society of Japan  

二次イオン質量分析法の持つ高い空間分解能を活かし、培養細胞や生体組織切片への応用を進めており、細胞一個を観察することが可能となっている。最新のSIMS法の生命科学への応用を、我々の研究成果を中心に実例を交えながら紹介し、高分解質量イメージング法としての今後の課題や展望について議論する。

DOI： 10.14886/sssj2008.31.0.171.0

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Language：Japanese   Publisher：日本表面科学会  

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Language：English   Publishing type：Research paper, summary (international conference)  

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Language：Japanese   Publisher：砥粒加工学会  

CiNii Books

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Language：Japanese   Publisher：The Surface Science Society of Japan  

A brief overview for recent progress of cluster ion beams is presented in conjunction with atomistic collision dynamics, cluster size effects and nano-process developments. Unique characteristics of cluster ion beam are utilized not only for nano-processing but also metrology for organic materials. Molecular dynamics study on cluster-solid interactions and size dependence of sputtering with Ar or Cl<Sub>2</Sub> cluster ions reveal that both incident energy and chemical potential energy are effectively transfer to the surface to enhance the sputtering yield. In addition to these, less damage was remained on organic surface bombarded with cluster ions. Organic depth profiling of XPS or SIMS are realized with cluster ion beams.

DOI： 10.1380/jsssj.31.564

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Language：Japanese   Publisher：The Surface Science Society of Japan  

二次イオン質量分析法(SIMS)を用いた質量イメージングは工業や医学への応用が期待されている。しかし、従来の数keVのモノマーイオンを用いたSIMS分析では有機試料の分子構造を破壊してしまうという問題がある。我々は低損傷での照射が可能なクラスターイオンを用いたSIMSについて研究しており、今回の研究ではArクラスターSIMSを用いた高面分解能の質量イメージングを取得するための装置開発を行った。

DOI： 10.14886/sssj2008.30.0.308.0

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Language：Japanese   Publisher：The Surface Science Society of Japan  

高速重イオンをプローブとした二次イオン質量分析法(SIMS)は、1μm程度の面分解能で分析可能なことに加え、従来のSIMSに比較し高分子に対して高い感度での分析、および1000 Pa程度の低真空下に保持されたサンプルの分析が可能である。本発表では高速イオンによるSIMSでラットの脳組織内に含まれるリン脂質のイメージングを実施した結果を報告する。

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Language：Japanese   Publisher：The Surface Science Society of Japan  

二次イオン質量分析法を使った細胞や組織切片のイメージング技術についてのべるとともに、実際のアプリケーションに必要な問題点や課題を明らかにする。有機分子分析や質量イメージング法の実現に必要な一次イオンビームの特性、次世代のSIMSに求められているハードウェアーなどについても検討し、新しいSIMS分析法の開発状況を報告する。

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Language：English   Publisher：兵庫県立大学工学研究科イオン光学研究室  

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Language：English   Publisher：MATERIALS RESEARCH SOC  

Ar cluster ions in the size range 1000-16000 atoms/cluster were irradiated onto Si substrates at incident energies of 10 and 20 keV and the sputtering yields were measured. Incident cluster ions were size-selected by using the time-of-flight (TOF) method. The sputtering yield was calculated from the sputtered Si volume and irradiation dose. It was found that the sputtering yields decreased with increasing incident cluster size under the same incident energy conditions. The integrated sputtering yields calculated from the sputtering yields measured for each size of Ar cluster ions, as well as the cluster size distributions, were in good agreement with experimental results obtained with nonselected Ar cluster ion beams.

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DOI： 10.1557/PROC-1181-DD13-25

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Language：Japanese   Publisher：The Surface Science Society of Japan  

近年、生体試料における質量イメージング技術の発展が期待されている。SIMSは高真空下での分析手法であるが、高速重イオンをプローブとすることにより低真空下でのSIMSに成功した。本発表では、数千Pa程度の低真空下で質量イメージングを行うための分析系の開発とその結果について報告する。

DOI： 10.14886/sssj2008.29.0.35.0

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Language：English   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

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Language：English   Publishing type：Research paper, summary (national, other academic conference)  

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Language：English  

Damage accumulation and annihilation processes with low-energy boron implantation were studied by molecular dynamics (MD) simulation. The MD simulation of B atom accelerated with 500eV iteratively implanted into Si(100) target showed that the number of interstitial Si atom saturates at about 1×1015/cm2 of B atomic dose. The results at several implant doses are annealed for about 4ns. When the B implanted dose is as low as 1× or 2×1014/cm2, the annealing simulations showed the re-crystallization of surface damage at 1800K and 2200K. However, very slow re-crystallization ratio was observed at the implant dose of more than 1×1015/cm2. ©2009 IEEE.

DOI： 10.1109/IWJT.2009.5166237

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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

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Language：English   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

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Language：Japanese   Publisher：The Surface Analysis Society of Japan  

&lt;p&gt;  &quot;Non-linear Effect&quot; is one of the unique phenomena in cluster ion impacts, where many atoms are collided each other instantaneously. Novel techniques for Nano-Processing and material analysis have been developed in the last decade, and will give us an opportunity to overcome issues in conventional technique with monomer ions. Recent progress in cluster ion beam is reported from the viewpoint of Nano-Processing and advanced material analysis.&lt;/p&gt;

DOI： 10.1384/jsa.14.196

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.63.1.2.0_165_2

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.63.1.2.0_144_3

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Language：Japanese   Publisher：The Mass Spectrometry Society of Japan  

In this paper, we describe mass spectrometric techniques using swift heavy ions, for biological application. Desorption of large biomolecular ions due to irradiation by swift heavy ions was first observed in 1974, and the time-of-flight mass spectrometry using fission fragments from a ²⁵²Cf source is called plasma desorption mass spectrometry (PDMS). PDMS has been successfully applied in the detection of large biomolecules up to 20 kDa. However, the number of PDMS studies decreased after the emergence of fast atom bombardment (FAB). In recent years, a new mass spectrometric technique, which is called imaging mass spectrometry, has attracted attention, and numerous studies have been conducted on matrix assisted laser desorption/ionization (MALDI) and secondary ion mass spectrometry (SIMS). We have developed a new system for imaging mass spectrometry using MeV-ion beams, which is termed MeV-SIMS. High-resolution MeV-SIMS imaging requires high secondary ion yields, beam focusing, and careful sample preparation. Here, we present our results on MeV-SIMS imaging and future prospects.

DOI： 10.5702/massspec.56.201

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Language：English   Publisher：兵庫県立大学工学研究科イオン光学研究室  

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Language：English   Publisher：兵庫県立大学工学研究科イオン光学研究室  

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

By the recent development of high-performance computing, molecular dynamics method has been a powerful technique for analyzing collisions between cluster and solid target system. In this paper, molecular dynamics simulations of various kinds of clusters impacting on the solid target were demonstrated. The characteristic collisional process of cluster and solid target in penetration depth, dynamic surface morphology deformation and damage formation were examined. ©2008 IEEE.

DOI： 10.1109/IWJT.2008.4540016

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

Cluster ion beam can process targets with shallow damage because of the very low irradiation energy per atom. However. it is needed to investigate the damage with cluster ion beam irradiation, because recent applications demand process targets with ultra low damage. The shallow damage can be investigated from depth profiles of specific species before and after ion irradiation. They can be measured with secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectroscopy (RBS). High resolution Rutherford backscattering spectroscopy (HR-RBS) is a non destructive measurement method and depth profiles can be measured with nano-resolution. The cluster ion beam mixing of thin Ni layer in carbon targets can be investigated with HR-RBS. The mixing depth with cluster ion irradiation at 10 keV was about 10 nm. The mixing depth with cluster ion irradiation at 1 keV and 5 keV were less than 1 nm and 5 nm, respectively. The number of displaced Ni atoms with cluster ion irradiation was very larger than that with monomer ion irradiation of same energy. This result shows that violent mixing occurs with single cluster impact,

DOI： 10.1063/1.3033653

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.62.1.2.0_138_4

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More than ten years have passed since cluster ion implantation was proposed by Kyoto University. Cluster ion implanters equipped with a specially designed ion source are announced for device manufacturing. This technique is now a candidate for ultra shallow junction formation in the ITRS Road Map [1]. It is essential to understand the atomistic mechanism of cluster implantation, because the behavior of damaged atoms during annealing is a very important topic for high-quality shallow junction formation. The damage induced with cluster ions is presented. ©2007 IEEE.

DOI： 10.1109/IWJT.2007.4279945

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The MD simulations of B monomer and small cluster implantation were performed. The non-linear effect for implant range was observed when the incident energy is as low as few hundreds eV/atom, where the B10 or B18 cluster implantation gives deeper implantation energy and so higher implant efficiency of dopants than that of B monomer or dimer. For damage formation, cluster implantation caused large number of collisions at narrow surface region, which results in high-density amorphization of impact area. This amorphization effect was observed at both low and high energy cluster ion implantation, and is expected to reduce enhanced diffusion and show good annihilation process. ©2007 IEEE.

DOI： 10.1109/IWJT.2007.4279937

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Publisher：The Surface Science Society of Japan  

クラスターイオンは単原子イオンと比較して、低速で高エネルギー密度での照射が容易であるため、高精度かつ高効率な表面分析、表面改質が可能とされている。しかし、クラスターと固体表面との相互作用は十分に理解されていない。よって本研究では、クラスターイオン照射によりSi試料から放出される二次イオン収率の入射サイズ依存性を飛行時間型質量分析法を用いて分析し、クラスター照射効果について考察する。

DOI： 10.14886/sssj.26.0.108.0

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Publisher：The Surface Science Society of Japan  

クラスターイオンをプローブとする有機物の二次イオン質量分析は、単原子イオンと比較して収率が高く試料の損傷も少ない。しかしクラスター照射での収率増加機構や最大収率を与えるための入射サイズの最適化については、ほとんど研究されていない。そこで本研究ではサイズ選別したArクラスターをアミノ酸薄膜に照射し、二次イオンを飛行時間型質量分析法を用いて測定することにより収率の入射サイズ依存性について調べた。

DOI： 10.14886/sssj.26.0.106.0

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.61.1.2.0_155_2

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.61.2.2.0_126_3

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Language：English   Publishing type：Research paper, summary (international conference)  

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Language：English   Publishing type：Research paper, summary (international conference)  

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To investigate the size-effect of reactive clusters on sputtering processes, we performed molecular dynamics (MD) simulations of reactive cluster ions with various sizes impacting on solid targets. Various sizes of fluorine clusters, (F2)30, (F2)300 and (F 2)3000, were irradiated on a Si(100) target at the same total incident energy of 6 keV. These clusters were irradiated on the same target one after another in order to reproduce real experimental conditions such as the accumulation of fluorine atoms in the target. The MD simulations of sequential cluster impacts enabled to perform various statistical analyses regarding the sputtered particles. The study of cluster size distributions showed that the sputtering process by reactive cluster ion impact has similarity with the emission from quasi-liquid materials excited to hyper-thermal conditions by ion bombardment. However, the major sputtered particles were different with each other; Si for (F2)30 (100 eV/atom), SiF2 for (F2)300 (10 eV/atom), and SiF 3 for (F2)3000 (1 eV/atom). At the impact of a large size cluster with low incident energy, a large number of Si-F bondings were generated at the cluster-target interface surface, which enhances formation of volatile SiFx compounds with many fluorine atoms. In contrast, a small cluster with high kinetic energy-per-atom could cause the formation of numerous energetic surface atoms at the near surface region, which could be sputtered without being well fluoridated. © 2006 Materials Research Society.

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Language：English   Publisher：ELSEVIER SCIENCE SA  

Energy resolved time of flight (ERTOF) mass spectroscopy has been developed to measure the energy and size distributions in a gas cluster ion beam (GCIB). Gas cluster ions, being aggregates of a few to several thousands of atoms, were generated by the ionization of neutral clusters, which were created by the adiabatic expansion of a high pressure gas into a vacuum. As a result of the large cross section of cluster ions, the cluster size can be easily reduced by collision with fast neutrals and monomer ions.
An ERTOF system consisted of a retarding grid in front of a drift tube with a pair of deflection electrodes that acted as a gate. This system was attached to an ionization chamber, where Ar gas clusters, generated by a nozzle in a source chamber, were ionized by electron impact. Current waveforms were measured with ERTOF as an increasing voltage was applied to the retarding grid. The size distribution of clusters having a particular kinetic energy was calculated from the difference in the current waveform obtained at a corresponding retarding voltage to that at a larger voltage.
Using ERTOF, it was found that the GCIB consisted of two components; small sized clusters with low kinetic energy and large sized clusters with high kinetic energy. It was also noted that the depth to which a substrate, on which the cluster beam impinged, was etched increased with the proportion of large clusters to the GCIB, since the small clusters, resulting from disintegration of large sized clusters by collisions with monomer ions, fast neutrals and residual gas molecules, have too low a kinetic energy to remove atoms from the surface. Note that the etched depth was affected by both the energy and size distribution of cluster ions. Therefore, ERTOF measurement could be utilized to assure the reproducibility of processes for the manufacture of semiconductors and magnetic recording heads. (c) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2004.08.129

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Language：English   Publishing type：Research paper, summary (national, other academic conference)  

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Language：English   Publisher：ELSEVIER SCIENCE BV  

We have measured both secondary neutral and ionized particles from an Irish target under 3.0 MeV Si ion bombardment. Measurements of both ions and neutrals have not been carried out so far in the MeV-energy range. The mass spectra and axial emission energy distributions of secondary particles were investigated. Secondary ions were measured with a linear- and a reflective-type time-of-flight technique, whereas secondary neutral particles were photo-ionized by a UV pulsed laser (ArF: 193 nm) and measured with a reflective-type time-of-flight technique. Different results were obtained for neutral particles in comparison with ionized particles. The mean energy of neutral Sb atoms was much lower than that of neutral In atoms, whereas the mean energies of secondary In and Sb ions were nearly equal. (c) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2004.12.089

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Total sputtering yields have been measured for SiO2 and Cu targets bombarded with Si ions at an incident energy between 500 keV and 5.0 MeV using a quartz crystal microbalance technique. In order to measure total yields accurately, we have developed a beam modulation technique to avoid the effect of thermal drift. In the MeV energy range, an ion penetrates through thin SiO2 and Cu targets and is implanted into a quartz crystal. Therefore, the thickness of these layers deposited on quartz crystals was carefully controlled to avoid damage of quartz crystal by incident ions. As a result, total sputtering yields of SiO2 increased with incident Si ion energy, while those of the Cu target decreased. The total yields of the SiO2 target were represented well by a power low of the electronic stopping power. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2004.12.088

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Molecular dynamics (MD) simulations of cluster and solid target collisions were performed in order to understand the relationship between surface deformation processes and cluster sizes. MD simulations of single impacts of clusters with various sizes showed that, when a cluster size is less than 10000 atoms, a crater-like damage could be caused at 20keV of total energy, while no damage was observed at Ar-10000 and Ar-20000 clusters. The surface morphology change was examined by MID of sequential irradiation of Ar clusters under various conditions. When the initial roughness of the surface was about 10Angstrom in r.m.s. and the total incident energy was 20keV, the surface roughness was reduced with the impact of Ar-13333 or larger cluster. The MD results give information about the final value and decay speed of surface roughness, which are required to optimize the cluster ion irradiation condition for various nano-scale modification processes. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2004.10.021

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.60.2.2.0_56_2

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Language：Japanese   Publisher：The Physical Society of Japan  

CiNii Books

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Language：Japanese   Publisher：The Physical Society of Japan  

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Language：Japanese   Publisher：The Physical Society of Japan  

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Language：English   Publisher：Elsevier  

This chapter reveals the experimental study of cluster size effect with size-selected cluster ion beam. A size-selected gas cluster ion beam (GCIB) system is developed to study the size effects of energetic large cluster ion bombardments on a solid surface for the first time. This system equipped a permanent magnet with a magnetic flux density of 1.2 T. There is a sliding detector and sample holder on a guiding rail perpendicular to the incoming cluster beam axis. By locating a sample at a certain position, particular size of cluster ion can be irradiated continuously with affordable ion current density. When the total acceleration energy of Ar-GCIB is 5keV, both amorphous and oxide thickness on silicon (Si) substrate increased with decreasing cluster size. This result showed good agreement with that obtained from molecular dynamics simulations. © 2005 Elsevier Ltd.

DOI： 10.1016/B978-008044504-5/50044-1

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Language：English   Publisher：Elsevier  

This chapter discusses the surface structure dependence of impact processes of gas cluster ions. The surface modification processes utilizing the impact of large cluster ions is also proposed. One of the unique properties of cluster ion impact is that the low-energy and high-density atomic irradiation can be realized simultaneously. This characteristic impact process causes local heating, large motion, and chemical excitation of the surface atoms. Many experiments proved that cluster irradiation shows remarkable advantages in thin film formation, surface smoothing, and high-rate and high-aspect etching. Surface smoothing is one of the important applications of cluster ion irradiation and is used for industrial applications. Molecular dynamics simulations are performed in order to understand the relationship between surface deformation process and surface structure. It is found that the collisional process of cluster is different depending on local surface morphology where the cluster impacts. When a cluster impacts close to the peak point, the hill structure is made flat and the surface atoms comprising the hill are moved away and deposited on the valley. © 2005 Elsevier Ltd.

DOI： 10.1016/B978-008044504-5/50047-7

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Language：English   Publisher：MATERIALS RESEARCH SOCIETY  

Oblique irradiation using a gas cluster ion beam (GCIB) has been studied in order to achieve low-damage smoothing of magnetic materials. We investigated how the surface morphology and surface roughness depended on the angle of incidence. Quite smooth surfaces could be obtained using both normal and grazing-incidence irradiation. At incident angles larger than 45 degrees, periodic ripples were formed. The orientation of the ripples changed from perpendicular to parallel with respect to the GCIB when the incident angle exceeded a critical value. Surface roughening resulting from the formation of ripples was observed at incident angles between 45 degrees and 65 degrees. Fluctuations in the Ni/Fe component ratio and the intermixing of oxygen from the native oxide were evaluated. As the angle of incidence increased, both the thickness of the layer in which the component ratio was fluctuating and the depth of oxygen intermixing decreased. As a result, it was determined that low-damage smoothing of magnetic materials could be performed by using grazing-incidence irradiation from a GCIB.

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Language：English   Publisher：Elsevier  

This chapter discusses the gas cluster ion beam source for secondary ion emission measurements. When solids are bombarded with cluster ions, collision cascades induced by individual constituent atoms of the cluster overlap each other. Energy density deposited with cluster ions is much higher than that deposited with monomer ions at the same velocity. Thus, subsequent phenomena, such as material modifications or secondary particle emissions, are enhanced under the impact of 'n'- atom clusters compared to the sum over 'n' atomic ions. These enhancements are generally called "nonlinear effects". The feature of secondary ion yield as a function of primary beam energy could be compared for monomer and cluster impacts. For monomer impacts the emission of ionized species has similarities with the emission of neutral species, showing that these processes proceed by a common mechanism. For large cluster impacts, the sputtering yield increases linearly with the primary ion energy. © 2005 Elsevier Ltd.

DOI： 10.1016/B978-008044504-5/50046-5

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Molecular dynamics (MD) simulations of Ar cluster impacts on Si surfaces were performed in order to examine the evolution of surface morphology with cluster irradiations. The MD results revealed that the impact process of cluster is different depending on surface structure around the impact point. When a large cluster, which consists of several thousands atoms and is accelerated with several tens keV, impacts on a plane surface, large number of surface atoms were moved simultaneously and a crater-like shape was left on the surface. On the other hand, the impacts on surface with nano-scale peak and valley structure showed that the impact processes of cluster ions are different depending on the local morphology of the impact points. When a cluster impacts close to a peak, the hill structure is made flat and the surface atoms constitute the hill are moved away and deposited on the valley. At the impact on valley region, however, incident cluster atoms concentrate in the bottom of the valley, which causes a crater-like structure with narrower opening and deeper hole compared with that at plain surface. The change of surface roughness have shown that, when a surface structure has similar scale with the area where the surface is deformed by cluster impact, the surface roughness decreases or increases depending on the impact point. This result indicates that the final state of surfaces roughness and morphology can be estimated. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2003.11.077

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Language：Japanese   Publisher：The Physical Society of Japan  

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Language：English   Publisher：MATERIALS RESEARCH SOCIETY  

A size-selected gas cluster ion beam (GCIB) system has been developed to study the size effects of energetic large cluster ion bombardments on a solid surface for the first time. This system equipped a permanent magnet with a magnetic flux density of 1.2 T. There is a sliding detector and sample holder on a guiding rail perpendicular to the incoming cluster beam axis. By locating a sample at a certain position, particular size of cluster ion can be irradiated continuously with affordable ion current density. When the total acceleration energy of Ar-GCIB was 5keV, both amorphous and oxide thickness on Si substrate increased with decreasing cluster size. This result showed good agreement with that obtained from molecular dynamics simulations.

DOI： 10.1557/proc-792-r10.8

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Language：English   Publisher：MATERIALS RESEARCH SOCIETY  

In order to understand the characteristics of surface modification process with cluster ion irradiation, molecular dynamics simulations of Ar cluster impacting on Si surface with various surface structures were carried out. It was found that the surface morphology is dynamically deformed with only one cluster impact and the impact process of cluster is different depending on the local surface structure. For example, when an Ar-2000 cluster accelerated with 20keV impacted on the convex point of the surface, the hill was compressed and the impact area was smoothed. At the impact on a concave point, a deeper crater was formed compared with the impact on a flat surface. On the other hand, the MD simulations of sequential impacts of large clusters were performed. It was found that the small tip structures on the surface could be removed easily with cluster irradiation. It was shown that surface roughness converges to 15similar to20Angstrom and this value agrees with the result obtained by single impact of cluster.

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Language：English   Publishing type：Research paper, summary (international conference)  

DOI： 10.1557/proc-792-r9.36

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Language：English   Publisher：MATERIALS RESEARCH SOCIETY  

Ar penetration during gas cluster ion beam (GCIB) irradiation has been investigated using secondary ion mass spectroscopy (SIMS). The concentration of Ar rose to a maximum and then decreased gradually with increasing depth. The depth of the Ar penetration peak increased in proportion to the cube root of the acceleration voltage of GCIB and was independent of ion dose. Ar penetration was attributed to fast neutrals in the GCIB and was successfully suppressed by decreasing the pressure of the space downstream of the GCIB or decreasing the monomer ion density in order to suppress charge transfer collisions.

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Language：English   Publishing type：Research paper, summary (international conference)  

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Language：English   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

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Language：English   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

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Language：English   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

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Language：English   Publishing type：Research paper, summary (international conference)  

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Language：English   Publisher：ELSEVIER SCIENCE BV  

Secondary ion mass spectrometry (SIMS) with gas cluster ion beams (GCIB) was studied with experiments and molecular dynamics (MD) simulations to achieve a high-resolution depth profiling. From MD simulations of Ar cluster ion impact on a Si substrate, the ion beam mixing by a cluster ion was heavier than that by Ar+ at the same energy per atom, because the energy density at the impact point by clusters was extremely high. However, the sputtering yield with an Ar cluster ion was one or two orders of magnitude higher than that with Ar+ at the same energy per atom. Comparing at the ion energy where the altered layer thickness was the same by both Ar cluster and Ar+ impact, a cluster ion showed almost 10 times higher sputtering yield than Ar+. Preliminary experiment was performed with a conventional SIMS detector and a mass resolution of several nanometer was achieved with Ar cluster ions as a primary ion beam. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0169-4332(02)00628-1

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

Computer simulation and experiments were performed in order to understand the effect of cluster size on damage formation. Results of molecular dynamics simulations of cluster impact on solid targets derived the model function, which explains the relationship among cluster size, incident energy and number of displacements. On the other hand, time of flight mass measurement system was installed a cluster irradiation system, so that cluster ion beam which cluster size distribution is well known can be irradiated on the target. The damage properties under various cluster irradiation conditions were examined using RBS. The results from computer simulations and experiments showed good agreements with each other, which suggests that irradiation damage by cluster ion beam can be controlled by selecting cluster size distribution and incident energy.

DOI： 10.1063/1.1619820

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Language：English   Publisher：MATERIALS RESEARCH SOCIETY  

Smoothing effect by large gas cluster ion irradiation was studied. Ar cluster ion beams were irradiated on rough Si surface with various ion dosage. 100x100mum(2) AFM image was measured for each surface. These AFM images were treated with fast Fourier transform in order to examine the change of surface morphologies with cluster ion irradiation. Power spectra analysis showed that the intensity at each wave number (the inverse number of wavelength) exponentially decreases with ion dose. The relationship between smoothing rate and wave number was derived. The surface smoothing process was modeled with the use of this wave number dependence on decreasing rate. The calculated and the experimental surface profiles are in good agreements. With this model, roughness of cluster-irradiated surface can be calculated from initial surface images.

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Low energy ion implantation with several hundreds eV of implant energy is one of the important technique for advanced CMOS device fabrication. As the incident energy decreases and the implant range of dopants is reduced, various problems such like the reduction of implant efficiency and dose control becomes more severe. In this study, molecular dynamics simulations of sequential boron implantation on silicon target were performed and the dynamics of accumulation of boron atom and self-sputtering process were discussed.

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Language：English   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Cluster ion implantation using small boron cluster, decaborane (B10H14), has been proposed as the solution for shallow junction formation. Investigation of damage formation process by low-energy ion impact is important issue because diffusion and activation mechanism of dopant depend on the structure of defects in the substrate. In order to study difference of damage characteristics between monomer and cluster implantation, the molecular dynamics simulation of low-energy boron monomer and cluster (such like B4, B8 and B10) implantation into silicon substrate were performed. Additionally damage induced by boron monomer and cluster ion beam implantation is examined using RBS channeling method. From both simulation and experimental results, the amount and structure of defects caused by boron monomer/cluster implantation were discussed.

DOI： 10.1109/IIT.2002.1258066

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Language：English   Publishing type：Research paper, summary (international conference)  

DOI： 10.1557/proc-749-w17.13

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Language：English   Publishing type：Research paper, summary (international conference)  

DOI： 10.1557/PROC-647-O9.4

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DOI： 10.1557/PROC-650-R3.40

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Language：English  

DOI： 10.1557/PROC-669-J20.4

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Formation of precursors and desorption of etching products by fluorine ion irradiation were studied using molecular dynamics simulation. When F atoms impact sequentially on a Si substrate, a mixed layer of F and Si atoms is formed on the surface. The fluorine coverage reaches steady state after 1×10^&lt;16&gt;atoms/cm^2 irradiation. When the incident energy is 30eV, the mixed layer at steady state consists of 6.2 monolayers of fluorine with a depth of 40 A^^○ and the radio of F to Si in the mixed layer is about 1:1 and the main etching products are SiF_2 and SiF_3. At 100eV incident energy, the mixed layer at steady state is 7.7 monolayers with a depth of 50 A^^○ and the main etching products are SiF and SiF_2. It was showed that etching products and the mixed layer at steady state depend on the irradiation energy.

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