Faculty Profiles - AOKI Takaaki

Papers - AOKI Takaaki

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Recent progress in cluster beam technique Reviewed

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

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

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

MATSUO Jiro, FUJII Makiko, SEKI Toshio, AOKI Takaaki

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

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

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

DOI： 10.3131/jvsj2.59.113

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

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

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

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

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

DOI： 10.1016/j.ijms.2015.04.003

Progress and applications of cluster ion beam technology Reviewed

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

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

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

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

DOI： 10.1016/j.cossms.2014.11.002

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

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

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

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

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

DOI： 10.1002/sia.5528

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

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

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

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

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

DOI： 10.1002/sia.5518

Lipid compounds analysis with MeV-SIMS apparatus for biological applications

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

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

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

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

DOI： 10.1002/sia.5524

Biomaterial imaging with MeV-energy heavy ion beams Reviewed

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

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

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

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

DOI： 10.1016/j.nimb.2014.02.088

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

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

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

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

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

DOI： 10.7567/APEX.7.056602

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

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

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

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

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

DOI： 10.1002/rcm.6867

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

Takaaki Aoki

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

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

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

DOI： 10.1007/s10825-013-0504-5

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

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

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

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

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

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

DOI： 10.1016/j.ijms.2013.12.024

クラスターSIMS法による脂質分子の高感度検出とイメージングへの応用

Takaaki Aoki

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

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

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

DOI： 10.1380/jsssj.35.351

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

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

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

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

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

DOI： 10.14723/tmrsj.39.265

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

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

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

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

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

DOI： 10.1016/j.nimb.2013.05.069

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

Takaaki Aoki, Toshio Seki, Jiro Matsuo

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

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

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

DOI： 10.1016/j.nimb.2012.10.040

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

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

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

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

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

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

DOI： 10.1002/sia.5092

Ion-induced damage evaluation with Ar cluster ion beams Reviewed

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

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

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

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

DOI： 10.1002/sia.5014

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

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

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

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

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

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

DOI： 10.1002/rcm.6599

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

Ultrafine particle removal using gas cluster ion beam technology

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

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

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

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

DOI： 10.1109/TSM.2013.2268871

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