盛谷 浩右

Stable structures of a rolled seamless belt of atoms arranged in a two-dimensional honeycomb lattice such as a carbon nano-belt, transit from a ring-shaped structure with a rotational invariance to folded structures as the circumference of the belt increases. Using molecular mechanics, we consider the size dependence of the structures obtained by simulated annealing. In addition, the relationship between the variety of metastable structures and the rate of temperature decrease during annealing is also examined. Furthermore, we investigate the effects of the van der Waals interaction between the surfaces on the structural transitions.

Since molecular cluster ion beams are expected to have various chemical effects, they are promising candidates for improving the secondary ion yield of Tof-SIMS. However, in order to clarify the effect and its mechanism, it is necessary to generate molecular cluster ion beams with various chemical properties and systematically examine it. In this study, we have established a method to stably form various molecular cluster ion beams from relatively small amounts of liquid materials for a long time by the bubbling method. Furthermore, we applied the cluster ion beams of water, methanol, methane, and benzene to the primary beam of SIMS and compared the molecular ion yields of aspartic acid. The effect of enhancing the yields of [M+H](+) ion of aspartic acid was found to be the largest for the water cluster and small for the methane and benzene clusters. These results indicate that the chemical effect contributes to the desorption/ionization process of organic molecules by the molecular cluster ion beam.

In contrast to a convex droplet, the particles contained in a suspended droplet accumulate near its bottom and can reflect light passing through it. The intensity of the light scattered by the particles near the bottom depends on the radius of curvature of the droplet at the bottom, and therefore this enables the detection of the shape change of the droplet with high sensitivity. We show that during the evaporation of a water droplet containing gold particles, the intensity of the scattered light initially increases gradually, after which it decreases rapidly immediately before the droplet evaporates completely. This change elucidates that the suspended droplet is rapidly flattened after its radius of curvature decreases, and the particles contained in it strongly affect its evaporation process, particularly for small droplets. This phenomenon can be used to more brightly illuminate the surface of a droplet relative to the interior.

We developed a gas cluster ion beam (GCIB) source in conjunction with a two rotating electric fields (REFs)-type mass filter. The REFs method is suitable for a mass filter of a massive cluster ion beam because masses can be separated from a continuous ion beam with a constant mass resolution in all mass ranges. In principle, the mass range is unlimited. Using this apparatus, we measured the size distribution of an Ar cluster ion beam. The REFs method has a wide mass range of at least 40 similar to 160,000 Da. The peak cluster size of the Ar cluster ion beam generated in this apparatus is 900. The annular patterns projected onto a fluorescent screen by Ar+ indicate that the maximum estimated mass resolution (M/Delta M) for the REFs mass filter is 86 for the full width at half maximum (FWHM) at a beam diameter of 0.12 mm (empty set). This mass filter should realize new applications of size-selected massive cluster ion beams as well as the study of cluster physics.

The Brownian motion of two particles confined near the bottom of a suspended droplet was considered in order to examine the electrical double-layer interaction between them. The mean distance between the particles was expressed as a function of the Debye screening length. We report the application of Brownian particle trajectories for the experimental determination of the Debye screening length between gold particles trapped within a water droplet. This was computed through a comparison of the mean distance measured by observing the Brownian motion with its theoretical value. (C) 2016 Elsevier B.V. All rights reserved.

The impact of an argon (Ar)-cluster ion on a thin film is evaluated in order to investigate a new method for probing the mechanical properties of the thin metallic film. Using a molecular dynamic (MD) method, we show that an Ar nanocluster ion with an incident velocity of 4 km/s dissociates in approximately 1 ps without sputtering the atoms of a target sample. After the impact, the Ar ion is scattered from the target surface with several neutral Ar atoms. The number of neutral atoms combining with the Ar ion and the velocity of the Ar ion depend on the mass density and Young's modulus of the target. Analyzing these dependencies, we find that the mass density and Young's modulus of thin films can be simultaneously determined by measuring the mass and velocity of the Ar-cluster ion scattered from the sample surface.

We present a method of determining the mass of a single picogram particle by observing its Brownian motion near the bottom of a droplet of water. The motion of the particle caused by thermal fluctuation is restricted within a narrow region because of gravity, and the vertical displacement of the particle from the bottom of the droplet depends on its mass. Since the particle is trapped inside the droplet, the mean horizontal displacement decreases as the mass of the particle increases. Hence, the mass can be determined by observing displacement. Although a modeling error arises from neglecting the electrical double-layer interaction between a particle and water surface, we show that its influence on the mass is very small.

The Brownian motion of a single small particle trapped on the surface of a suspended liquid droplet is studied and used to measure its mass. On the basis of the Ornstein-Uhlenbeck theory, the time dependence of the distance between the particle and the bottom of the suspended droplet is considered. The mass of the particle is determined from this time-averaged distance independently of the size and shape of the particle. The uncertainty of the estimation depends mainly on the measurement time of the trajectory, and it can be evaluated by Monte Carlo simulations. We experimentally demonstrate that the mass of a single gold particle 0.3 mu m in radius can be measured using an optical microscope.

We demonstrate a method to clean and probe a graphene layer on copper by using cluster ions consisting of thousands of argon (Ar) atoms. Ar cluster ions colliding with a solid at kinetic energies below ∼5 eV/atom dissociate into smaller cluster ions such as Ar&lt inf&gt 2&lt /inf&gt &lt sup&gt +&lt /sup&gt orAr&lt inf&gt 3&lt /inf&gt &lt sup&gt +&lt /sup&gt , and the dissociation rate (ease of dissociation) depends on the physical property of the solid. We apply this phenomenon to probe a graphene layer on copper. Contaminants at the graphene surface are removed without damage to the surface by Ar cluster ion bombardment and the cleanliness of the surface is simultaneously probed by measuring the dissociation rate. This rate gradually approaches the value for a clean surface. After cleaning, the dissociation rate for pristine graphene on copper is five times lower than that for bare copper, indicating that the graphene layer acts as a buffer against the impact force of the cluster ion upon collision. Accordingly, the method can probe the quality of graphene, such as carbon coverage, by comparing the dissociation rate with that for bare copper. Furthermore, the method can probe the interface between graphene and copper, showing that the dissociation rate increases with increasing copper oxidation. The obtained experimental results are compared with simulated results obtained by molecular dynamics simulation for the collisions of an Ar cluster ion with graphene on copper. The combined results are discussed with respect to the utility of the proposed method for controlling the quality of graphene in the manufacture of electronic or mechanical devices.

A pre-coated steel sheet for household electrical appliances needs to be highly formable and stain resistant. In recent years, secondary ion mass spectrometry (SIMS) with a time-of-flight (TOF) mass analyzer with an Ar gas cluster ion beam (Ar-GCIB) has been widely used as a structure analysis technology of organic molecules. In this paper, we looked into the effectiveness of Ar-GCIB-TOF-SIMS as a structure analysis technique of paint film. As a result, we could detect the trimer fragment ions of hexamethoxymethylmelamine in the range of m/z=400-800 for the first time for the spin-coating of HMMM on a Si wafer. By evaluation of characteristic monomer fragment ions, we could find out the different surface distributions of melamine-formaldehyde resin with the different formulations of paint films. Copyright (c) 2014 John Wiley & Sons, Ltd.

RATIONALE: Collisions of clusters with solids have become important, especially in the fields of thin film growth or surface processing such as etching or topography smoothing. However, it is not clear how much of the theory or model used in macroscopic collisions is appropriate for the consideration of microscopic collisions. METHODS: We considered a cluster ion consisting of thousands of argon atoms as a continuum and examined the possibility that classical mechanics could analyze its collision with metals. A mass spectrometric analysis of the dissociated ions of argon cluster ions (Ar-1500(+)) in collision with five different metals was performed. RESULTS: In the mass spectra at an incident kinetic energy per atom of less than 10 eV, no monatomic argon ions (Ar+) were observed regardless of the prominence of Ar-2(+) or Ar-3(+). The branching ratio for the ion yield Ar-2(+)/ Sigma Ar-n(+) (n >= 2), representing the dissociation rate, was found to be significantly different for each metal. The relationship between the branching ratio and the impulsive stress caused by the collision of the cluster ion with metal was investigated. The impulsive stress was calculated based on the Young's modulus and density of the clusters and metal, under the assumption that the collision was initially elastic. As a result, the magnitude correlation in the branching ratio corresponded well with that in the impulsive stress. CONCLUSIONS: This result is important in that it indicates that collision of nano-sized clusters with solids at low energies can be modeled using elastic theory. Furthermore, the result suggests a new method for evaluating a physical property of a material such as its Young's modulus. Copyright (C) 2014 John Wiley & Sons, Ltd.

We study the surface-roughness dependence of the Casimir force between fractal surfaces, which is represented by theWeierstrass-Mandelbrot function. When compared the Casimir force in the case of smooth surfaces, the Casimir force between fractal surfaces rapidly increases as the separation distance decreases. We express this deviation as a simple analytical function that is composed of three parameters including fractal dimension, and compare it with the deviation obtained from Monte Carlo simulations. © 2014 The Surface Science Society of Japan.

Using molecular dynamics (MD) simulation, we consider the stable structure of a partially unzipped carbon nanotube, in which a graphene nanoribbon is formed at the tip. We characterize the shape of the junction between a single carbon nanotube and a graphene nanoribbon using three parameters: the radius of curvature, bend, and twist-rotation. The increase in the radius of curvature is proportional to the square of the distance from the boundary between the carbon nanotube and the graphene nanoribbon, and this can be explained by using continuous mechanics for a thin plate. The oscillations of the graphene nanoribbon at room temperature are also taken into consideration. (C) 2014 The Japan Society of Applied Physics

A size-selected Ar gas cluster ion beam (GCIB) was applied to secondary ion mass spectrometry (SIMS) of a polystyrene (PS) thin film, a 1,4-didodecylbenzene (DDB) thin film, and an ITO glass sample. Additionally, the samples were analyzed by SIMS using an atomic Ar<sup>+</sup> ion projectile and X-ray photoelectron spectroscopy (XPS). All three samples were contaminated by poly(dimethylsiloxane) (PDMS) on the surface. Compared to the Ar<sup>+</sup> SIMS spectra, the fragments in the PS and DDB SIMS spectra for Ar<sub>1550</sub><sup>+</sup>, including siloxane, were enhanced more than ∼100-fold, while the hydrocarbon fragments were enhanced 10-20-fold. XPS spectra during beam irradiation indicate that Ar-GCIB sputters contaminants on the surface more effectively than the atomic Ar<sup>+</sup> ion beam. These results indicate that a large gas cluster projectile can sputter a much shallower volume of organic material than small projectiles, resulting in an extremely surface-sensitive analysis of organic thin films. The shallow volume sputtering by GCIB is responsible for the preferential enhancement of the surface contaminants.<br>

Recent advances in large cluster projectiles for secondary ion mass spectrometry (SIMS) allow the intact ions of some protein molecules to be detected without a matrix. However, detailed mechanisms of soft-sputtering and ionization of biomolecules remain unknown. Herein we investigate the secondary ion emission from insulin films under argon, krypton, and methane cluster ion bombardment. The intact insulin ion intensity significantly decreases for (CH4)(1500)(+) ion bombardment compared with Ar-1500(+), ion bombardment at the same energy range of 3.3 eV/atom (or molecule), even though collisions with energetic methane clusters should generate numerous protons on the surface, which would enhance the ionization probability through proton attachment. In contrast, the intact ion intensity is almost the same for Ar-2500(+) and Kr-2500(+) cluster ion bombardment at the same energy range of 2 eV/atom. These observations suggest that detailed mechanisms for the ionization and sputtering by gas cluster ions should be investigated to enhance the intact ion intensity. (C) 2013 Elsevier B.V. All rights reserved.

The Casimir interaction between a torsion balance and flat plate is considered using proximity force approximation (PFA) and geometric optics approximation (GOA). Both approximations predict that the parallel configuration becomes unstable as the distance between a torsion balance and flat plate decreases. However, the dependence of the tilt angle at the stable position on the separation is significantly different. The tilt angle obtained by PFA continuously changes over the entire range however, the discontinuous transition is predicted in GOA. © 2013 The Surface Science Society of Japan.

A size-selected Ar gas cluster ion beam (GCIB) is applied to secondary ion mass spectrometry (SIMS) of a polystyrene (PS) thin film, a 1,4-didodecylbenzene (DDB) thin film, and an ITO glass sample. All three samples are contaminated by poly(dimethylsiloxane) (PDMS) on the surface. Compared with the Ar+ SIMS spectra, the fragments in the PS and DDB SIMS spectra for Ar 1550+, including siloxane, are enhanced more than ∼100-fold, whereas the hydrocarbon fragments are enhanced 10- to 20-fold. The shallow volume sputtering by GCIB is responsible for the preferential enhancement of the surface contaminants. The intensities of the fragment PDMS ions and the intact DDB ion increase, but the hydrocarbon fragment ions from PS and DDB decrease as the energy per atom (Eatom) of the Ar cluster projectile decreases from ∼8 to ∼4 eV. These results indicate that tuning Eatom can maximize the surface sensitivity and the sensitivity for intact ions. Copyright © 2012 John Wiley &amp Sons, Ltd. Copyright © 2012 John Wiley &amp Sons, Ltd.

The gigantic Buddha of Nara, in Japan, is one of the greatest examples in the world where a scientific approach based on modern experimental paradigms succeeds to shed light on ancient realizations of mankind. Copper-gilded statues worldwide belong to cultural heritage, and gilding technologies involve some common expertise procedures which allow us to establish a close connection with present sophisticated nanotechnology techniques. To unveil the old mystery of Great Buddha of Nara gives us an excellent example how corrosion protection technology is performed using copper/gold amalgam gilding. The experiments of oxidation of Cu3Au modeling the surface of Buddha, using modern surface science techniques, demonstrates the protective nature against the bulk oxidation, induced by Au atoms. Thus, art and knowledge have been always interconnected and scientific analysis by experiment can successfully test archeological hypothesis.

We investigated defects produced on a graphite surface by bombardment with gas cluster ions consisting of hundreds or thousands of argon atoms, and examined the structural changes of these defects by heat treatment. Two types of defects, craters and dots, were observed in STM images of the ion-bombarded surfaces. The production of these defects depends on the average kinetic energy per constituent atom of the cluster ion, and the threshold energy for the production of the crater and dot are 5 eV and 1.5 eV, respectively. After heating an ion-bombarded sample to 560 °C in air, the craters changed to hexagonal pits and most of the dots disappeared, although a few (∼10%) dots changed to irregularly shaped pits. We describe the formation mechanisms of the two pit types on the basis of the oxidative etching of ion-induced defects. © 2012 The Surface Science Society of Japan.

We have investigated the converging behavior of argon gas cluster ion beam passed through a glass capillary. The gas cluster ions are attractive as a projectile for SIMS from the view point of minimization of the damages. The cluster ion beam of 5 keV consisting of 500∼3000 argon atoms was injected in the capillary. The inner diameters of the capillary at the inlet and outlet were 0.8 mm and 9.6∼140 μm, respectively. Ion current from the outlet of the all the capillaries were detected. We obtained the converging factor of 2∼7, which depended on the incident ion current. The kinetic energy of the incident ions was found to be reduced by 20∼30% by passing through the capillary. Contrary, the velocity of the ions was not changed. These facts suggest that the cluster becomes 20∼30% smaller in mass by passing through the capillary. As far as we know, this is the first report on the study of the converging of cluster ions by using a glass capillary.<br>

We study theoretically the trapping of a nanoparticle by a rotational motion around another nanoparticle caused by surface forces comprising electrostatic and Casimir forces. We introduce a local power exponent of the surface force as a function of the separation distance and show that it strongly depends on the electric charges carried by the nanoparticles. The stability of circular motions depends mainly on the local power exponent, and if the electric charges are not zero and the mass of the nanoparticle is small, then the stable tapping is possible in the Earth's gravity field. © 2011 The Surface Science Society of Japan.

A new cluster time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed, using a size-selected gas cluster ion as a projectile. Because a large gas cluster ion can generate numerous low-energy constituent atoms during a collision with the surface, multiple and ultralow-energy sputterings are induced. Dividing the acceleration energy of a gas cluster ion by the number of constituent atoms provides the mean kinetic energy of the constituent atoms. Hence, sputtering can be controlled to minimize decomposition of the sample molecules by precisely adjusting the number of constituent atoms (the cluster size) and/or the acceleration energy of the gas cluster ions. The cluster size was selected by the time-of-flight method using two ion deflectors attached along the ion-beam line. A high resolution of 11.7 was achieved for the cluster size/size width (m/Delta m) of the Ar-cluster ions. The SIM spectra of poly(methyl methacrylate) (PMMA) were measured using the size-selected gas-cluster SIMS machine. The large fragment ions emitted from PMMA are enhanced as the cluster size increases. This result suggests that a large cluster ion projectile in which each constituent atom within the cluster has decreased kinetic energy inhibits the decomposition of the polymer structure. (C) 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(3): 52-58, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21159

In secondary ion mass spectrometry (SIMS) of organic substances, the dissociation of the sample molecules is crucial. We have developed SIMS equipment capable of bombardment, where the primary ions are argon cluster ions with kinetic energy per atom controllable down to 1 eV. We previously reported the detection of intact ions of insulin and cytochrome C using this equipment. In this paper, we present a detailed characterization of the emission of secondary ions from insulin, focusing on the difference in secondary ion yield between intact ions and fragment ions by varying the incident angle of the cluster ions. The emission intensity of the intact ions was changed drastically due to the exposed dosage and incident angle of the cluster ions in contrast to the fragment ions. We discuss these results based on the manner in which the argon-cluster ions collide with the organic solid. Copyright (C) 2011 John Wiley & Sons, Ltd.

A size-selected Ar gas cluster ion beam (GCIB) was applied to the SIMS of a polystyrene thin film. The size of Ar cluster ions are selected between 5000 to 500 atoms at an acceleration voltage of 5 and 10 kV using time-of-flight technique. Under this condition, the kinetic energy per constituent atom (E-atom) of the GCIB projectile was estimated to be 1 similar to 20 eV. The E-atom dependence of secondary ion yield of fragment species of polystyrene can be essentially classified into three types which are attributable to the relationship between the E-atom and the dissociation energy of the specified bonding site of the molecule. These results indicate that the site-specific bond breaking of molecules could be possible by adjusting the E-atom of size-selected GCIB. Copyright (C) 2010 John Wiley & Sons, Ltd.

Gas cluster (GC) ion sources, such as an argon cluster source, have been employed in SIMS of organic or biomaterials due to their low-energy projectile effect. Recently, it was found that GC-SIMS reportedly provides intact ion detection of proteins with molecular weights of 10000 or higher. Since GC-SIMS enables control of the gas cluster size and collision energy per atom, it is considered sensitive for the detection of very small differences in the monolayers of polypeptides such as leu-enkephalin (H-Tyr-Gly-Gly-Phe-Leu-OH) and met-enkephalin (H-Tyr-Gly-Gly-Phe-Met-OH). In this study, both enkephalins were measured with GC-SIMS and their spectra were compared to evaluate GC-SIMS sensitivity to small chemical structure differences. The polypeptides, leu-enkephalin and met-enkephalin, were immobilized on indium-and tin oxide (ITO)-coated glass plates, respectively, by binding their N terminal residues to glutaraldehyde-activated aminosilanized-ITO plates. An aminosilanized-ITO plate without polypeptide was also prepared as the control sample. After freeze-drying, the samples were measured with TOF-SIMS with the argon cluster ion source, and then TOF-SIMS spectra were analyzed to select peaks specific to the polypeptides. As a result, fragment ions related to the polypeptide without recombination were detected using the argon GC-SIMS. Copyright (C) 2010 John Wiley & Sons, Ltd.

A size-selected argon (Ar) gas-cluster ion beam (GCIB) was applied to the secondary ion mass spectrometry (SIMS) of a 1,4-didodecylbenzene (DDB) thin film. The samples were also analyzed by SIMS using an atomic Ar(+) ion projectile and X-ray photoelectron spectroscopy (XPS). Compared with those in the atomic-Ar(+) SIMS spectrum, the fragment species, including siloxane contaminants present on the sample surface, were enhanced several hundred times in the Ar gas-cluster SIMS spectrum. XPS spectra during beam irradiation indicate that the Ar GCIB sputters contaminants on the surface more effectively than the atomic Ar(+) ion beam. These results indicate that a large gas-cluster projectile can sputter a much shallower volume of organic material than small projectiles, resulting in an extremely surface-sensitive analysis of organic thin films. Copyright (C) 2010 John Wiley & Sons, Ltd.

The formation of a nanopore in a graphene sheet by collision with an argon cluster is simulated using molecular dynamics method. The number of removed carbon atoms and the size of the nanopore are obtained as a function of the kinetic energy of the cluster. In contrast to nanosculpting with a monomer ion beam, the size of the nanopore that is created by one shot of the cluster varies because of the variety of atom configuration. However, the mean size of the nanopore can be controlled over a wide range only by changing the kinetic energy of the cluster. This implies that the cleaning and processing of the graphene sheet may be realized simultaneously by changing the acceleration energy of the cluster.

Oxygen adsorption and subsequent oxide formation on Cu(110) using a hyperthermal oxygen molecular beam (HOMB) were investigated using X-ray photoelectron spectrometry. The O-uptake curves, which were determined from the evolution of the O-1s peaks, indicate that simple Langmuir type kinetics can describe dissociative adsorption of O-2 with an incident energy (E-i) below 0.5 eV under Theta <= 0.5 ML. The reaction order dependence oil E-i implies two competing dissociation mechanisms, trapping-mediated and directly activated adsorption. Oxidation at Theta <= 0.5 ML proceeds rather effectively using highly energetic HOMB at E-i >= 1.0 eV. The azimuthal dependence of the sticking probability during the effective oxidation using HOMB incidence Suggests that the added rows, which consist of the Cu-O structure, shade the reactive hollow sites in the trough where oxygen penetrates into the subsurface. The surface Cu-2 formed with highly energetic HOMB incidence decomposes with desorbing subsurface oxygen even at room temperature, demonstrating that HOMB can induce a metastable surface Structure that cannot be produced in the thermal equilibrium process.

The secondary ion mass spectrum (SIMS) of a polystyrene thin film was investigated using a size-selected Ar gas cluster ion beam (GCIB). The fragmentation in the SIM spectrum varied by kinetic energy per atom (E(atom)); the E(atom) dependence of the secondary ion intensity of the fragment species of polystyrene can be essentially classified into three types based on the relationship between E(atom) and the dissociation energy of a specific bonding site in the molecule. These results indicate that adjusting E(atom) of size-selected GCIB may realize site-specific bond breaking within a molecule. (C) 2009 The Japan Society of Applied Physics

In the secondary ion mass spectrometry (SIMS) of organic substances, the molecular weight of the intact ions currently detectable is at best only as high as 1000 Da, which for all practical purposes prevents the technique from being applied to biomaterials of higher mass. We have developed SIMS instrumentation in which the primary ions were argon cluster ions having a kinetic energy per atom, controlled down to 1 eV. On applying this instrumentation to several peptides and proteins, the signal intensity of fragment ions was decreased by a factor of 102 when the kinetic energy per atom was decreased below 5 eV; moreover, intact ions of insulin (molecular weight (MW): 5808) and cytochrome C (MW: 12 327) were detected without using any matrix. These results indicate that fragmentation can be substantially suppressed without sacrificing the sputter yield of intact ions when the kinetic energy per atom is decreased to the level of the target's dissociation energy. This principle is fully applicable to other biomolecules, and it can thus be expected to contribute to applications of SIMS to biomaterials in the future. Copyright (C) 2009 John Wiley & Sons, Ltd.

A new cluster time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using a size-selected gas cluster ion as a projectile. Since a large gas cluster ion can generate many low-energy constituent atoms in a collision with the surface, it causes multiple and ultra low energy sputtering. The mean kinetic energy of constituent atoms is provided by dividing the acceleration energy of the gas cluster ion by the number of constituent atoms. Therefore, the sputtering can be controlled to minimize the decomposition of sample molecules and substrate material by precisely adjusting the number of constituent atoms (the cluster size) and/or acceleration energy of the gas cluster ion. The cluster size was selected by the time-of-flight method using two ion deflectors attached along the ion-beam line. A high resolution of 11.7 was achieved for the cluster size/size width (m/Δm) of Ar-cluster ions. SIMS spectra of polymethyl methacrylate (PMMA) was measured using the size-selected gas cluster SIMS machine. As increasing the cluster size, large fragment ions emitted from PMMA were enhanced. This result suggested that the decomposition of the polymer structure was suppressed by the larger cluster ion projectile which decreased the kinetic energy per constituent atom of a cluster ion. © 2009 The Institute of Electrical Engineers of Japan.

A new cluster time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using a size-selected gas cluster ion as a projectile. Since a large gas cluster ion can generate many low-energy constituent atoms in a collision with the surface, it causes multiple and ultra low energy sputtering. The mean kinetic energy of constituent atoms is provided by dividing the acceleration energy of the gas cluster ion by the number of constituent atoms. Therefore, the sputtering can be controlled to minimize the decomposition of sample molecules and substrate material by precisely adjusting the number of constituent atoms (the cluster size) and/or acceleration energy of the gas cluster ion. The cluster size was selected by the time-of-flight method using two ion deflectors attached along the ion-beam line. A high resolution of 11.7 was achieved for the cluster size/size width (<i>m</i>/<i>Δm</i>) of Ar-cluster ions. SIMS spectra of polymethyl methacrylate (PMMA) was measured using the size-selected gas cluster SIMS machine. As increasing the cluster size, large fragment ions emitted from PMMA were enhanced. This result suggested that the decomposition of the polymer structure was suppressed by the larger cluster ion projectile which decreased the kinetic energy per constituent atom of a cluster ion.

A new cluster time-of-flight secondary ion mass spectrometry (TOF-SIMS) was developed using a size-selected gas cluster ion as a projectile. Since a large gas cluster ion can generate many low-energy constituent atoms in a collision with the surface, it causes multiple and ultra low-energy sputtering. The mean kinetic energy of constituent atoms is provided by dividing the acceleration energy of the gas cluster ion by the number of constituent atoms. Therefore, the sputtering can be controlled to minimize the decomposition of sample molecules and substrate material by precisely adjusting the number of constituent atoms (the cluster size) and/or acceleration energy of the gas cluster ion. The cluster size was selected on the basis of the time-of-flight method using two ion deflectors attached along the ion-beam line. A high resolution of 11.7 was achieved for the cluster size/size width (M/Delta M) of Ar-cluster ions. (C) 2008 Elsevier B. V. All rights reserved.

Using a molecular dynamics simulation, we examine the actuation of nanodrums consisting of a single graphene sheet. The membrane of the nanodrum, which contains 190 carbon atoms, is bent by collision with a cluster consisting of 10 argon atoms. The choice of an appropriate cluster velocity enables nanometre deformation of the membrane in sub-picosecond time without rupturing the graphene sheet. Theoretical results predict that, if an adsorbed molecule exists on the graphene sheet, the quick deformation due to the impact with the cluster can break the weak bonding between the adsorbed molecule and the graphene sheet and release the molecule from the surface; this suggests that this system has attractive potential applications for purposes of molecular ejection.

Oxidation reactions at Si(001) surfaces have been studied via real-time in situ photoemission spectroscopy with synchrotron radiation for chemical bonding states of Si and O atoms and mass spectrometry for desorption of SiO molecules with supersonic O-2 molecular beams in a temperature region from 900 K to 1300 K. In our previous studies, the SiO desorption yield decreased with increasing incident energy in a temperature region from 900 K to 1000 K. In that case, the time evolutions of Si 2p photoemission spectra showed that SiO2 structure on the surface was easily formed by the action of larger incident energy and the increased SiO2 coverage correlated with the decreased SiO desorption yield. In this study, simultaneous measurements of Si 2p photoemission spectra and SiO desorption yield revealed that the decrease of SiO correlated with the increase of Si2+ component, and the SiO desorption was terminated at the oxide thickness of 0.22 nm. These facts suggest that the SiO desorption takes place at the topmost Si dimcrs and a precursor for SiO desorption is a so-called T site, in which O atoms are bonding with the dangling bonds of the dimers. Consequently, M1 and M2 in the Dual-Oxide-Species (DOS) model have been clarified to be a T site and a Si2+ state, respectively. (c) 2008 Wiley Periodicals, Inc.

We present here a supersonic molecular beam investigation of the initial sticking probability (SO) for the O-2/Cu(410) system. Over the temperature range between 130 and 800 K adsorption occurs dissociatively and So increases up to similar to 0.7 with beam energy, indicating that the process is activated. So is larger for angles corresponding to molecules impinging on the step rises, implying that defects are more reactive than terrace atoms. The saturation value of S-0 is however lower than for the parent low Miller index surfaces; this indicates that the reactivity at nanosized terraces is reduced compared to extended Cu(100) faces. A precursor mediated adsorption path is observed at the lowest translational energy (E-i) below 150 K, as in the case of O-2/Cu(110) and at variance with O-2/Cu(100). At low T and higher energy and for all E-i at T > 150 K, adsorption occurs directly, yielding a sticking probability independent of surface temperature. (C) 2008 Elsevier B.V. All rights reserved.

The process of sputtering by bombardment with gas cluster ions was investigated from the perspective of the kinetic energy per constituent atom (E-atom) of an incident cluster ion, which determines the threshold for the formation of craterlike defects by irradiation of an argon gas cluster ion beam (Ar-GCIB) onto a graphite surface. Furthermore, DNA molecules adsorbed on a graphite surface were preferentially sputtered by adjusting E-atom of the Ar-GCIB down to this threshold, while the substrate graphite surface retained its carbon lattice structure without the formation of craterlike defects These results indicate that a GCIB could be used as a primary ion beam for secondary ion mass spectrometry (SIMS), which would enable the preferential analysis of an adsorbed layer on a substrate without causing damage to the substrate.

We report results of our study on the surface-temperature dependence of the steric effect in the dissociative adsorption of NO on Si(111)-(7 x 7). Data presented here show that, at an incident energy of 58 meV, the reactive sticking probability for the N-end collision is larger than that for the O-end collision. Furthermore, this steric preference is quite sensitive to the surface temperature and the surface coverage. This study shows that the transient surface trapping into a shallow precursor well plays a key role in the stereodynamics of the dissociative adsorption at the low energy region.

This paper reports a study on the surface reconstruction on Cu(l 11) induced by a hyperthermal oxygen molecular beam (HOMB) at room temperature (RT). HOMB incidence at translational energies (E-i) >= 0.5 eV induced surface reconstruction to the I--1(3) I-2(2) structure for an O coverage (Theta) >= 0.27 monolayer (ML). On the other hand, long-range-ordered structures were not formed even at Theta approximate to 0.4 ML for the backfilling of thermal O-2 at RT. No surface reconstruction was induced at E-i <= 0.23 eV where the attainable Theta value was 0.27 ML for the O-2 exposures below 10(18) molecules/cm(2). Translational energy above 0.5 eV is required for the dissociative adsorption of O-2 and the resulting surface reconstruction at Theta >= 0.27 ML. The O-1s XPS peak for HOMB incidence at RT was resolved into two components, 529.4 and 528.9 eV, at Theta >=.27 ML, which can be assigned to the O atoms occupying the three-fold hollow sites on unreconstructed Cu(111) and four-coordinated sites on the I--1(3) I-2(2) structure, respectively. Annealing the I--1(3) I-2(2) reconstructed surface at 620 K decreased Theta to similar to 0.27 ML and induced (root 13R46.1 degrees X 7R21.8 degrees), the so-called "29" superstructure.

The stereochemical control of surface reactions is one of the ultimate goals of surface scientists. An oriented-molecular-beam technique based on the Stark effect of a molecule in an inhomogeneous hexapole electrostatic field is a potential tool for achieving this goal. This technique allows us to select a specific rotational quantum state and also an orientation of a reagent molecule. We have designed, built, and tuned a new UHV-compatible oriented-molecular-beam machine for the elucidation of surface chemical reactions and their related surface modifications. This apparatus is equipped with the components for Xray photoemission spectroscopy (XPS) in order to detect the surface-reaction products. In the dissociative adsorption of NO on a Si{111} surface, we found a steric effect in the reactivity by monitoring the products on the surface with the new machine. The N-end collision is more reactive than the O-end collision at an incident energy of 58 meV. To our knowledge, this is the first measurement of the steric effect appearing in the reaction products on a surface. [DOI: 10.1143/JJAP.47.3686]

The dissociative adsorption of nitric oxide (NO) on a Si(111)-(7 x 7) surface between 330 and 600 K was investigated using X-ray photoelectron spectroscopy (XPS). The uptake curves of both the N and O atoms as functions of NO exposure revealed a prominent temperature dependence for the dissociative adsorption of NO on a Si(111)-(7 x 7) surface. The decrease in the rates of the dissociative adsorption of NO with an increase in surface temperature (T(s)) suggests that a precursor exists. Additionally, the number ratio of N atoms to O atoms on the surface (N/O ratio) changed from 1.0 (T(s) = 330 K) to 1.2 (T(s) = 600 K). This increase in N/O ratio with an increase in T(s) suggests that an additional reaction path becomes available at higher T(s).

We studied the oxidation of Cu(410) using high-resolution electron energy loss spectroscopy and X-ray photoemission spectroscopy performed with synchrotron radiation. Cu2O formation starts above half a monolayer oxygen coverage, and the oxidation rate is larger,than for the parent low Miller index Cu(100) surface. Open steps favor therefore the process by opening pathways for subsurface migration and oxygen incorporation. Oxidation occurs only above 500 K when dosing O-2 by backfilling, but the ignition temperature can be lowered to room temperature by dosing O-2 Via a supersonic molecular beam at hyperthermal energy indicating the opening of a different pathway. The oxidation rate is maximal at normal incidence; at grazing incidence, it is higher when O-2 impinges nearly normal to the (100) nanofacets than when it hits the surface close to the normal to the step rises. A collision induced absorption mechanism can explain the experimental findings.