乾 徳夫

Squared deviations from the equilibrium positions of one-dimensional coupled harmonic oscillators with fixed and free endpoints are calculated, and the time averages are expressed as a function of the initial displacements and velocities. Furthermore, we consider the averages of squared deviations over an ensemble of initial displacements and velocities, which distribute based on a product of the same distribution functions with variances of the initial coordinates σ x 2 and velocities σ v 2 , respectively. We demonstrate that the mean squared deviation linearly increases as the oscillator separates further from the fixed endpoint because of the asymmetrical boundary conditions, and that the increase rate depends only on σ v 2 and not on σ x 2 . This simple statistical property of harmonic oscillation is similarly observed in the oscillations of a graphene sheet and carbon nanotube in molecular dynamics simulations, in which the interacting forces are nonlinear.

Graphene exhibits diamagnetism, and its origin is the orbital electric currents induced on the surface by an applied magnetic field. The magnetic response of a graphene cantilever in the presence of a magnetic field is mainly determined by the diamagnetic electric current, and spin paramagnetism, which suppresses the diamagnetism. We elucidate the change in the electric current distribution caused by the large bending of the graphene cantilever using the tight-binding model. The electric current almost disappears when the position of the graphene cantilever transitions from perpendicular to parallel to the magnetic field and reverses when the graphene cantilever is folded in half. Furthermore, the temporal change in the magnetic energy of the vibrating graphene cantilever is calculated using the molecular dynamics simulation. The strong dependence of the magnetization of a graphene cantilever on its position relative to the magnetic field can be utilized for actuating and controlling the cantilever.

This study considers the energy level of a charged particle on a large hexagonal lattice in a magnetic field. The discretized Schrödinger equation on a hexagonal lattice, which can be expressed as a special case of a tight-binding model is derived, and its energy level is numerically calculated. The size dependence of the energy level near zero for large radii is considered by analyzing the asymptotic behavior of the zeros of the Laguerre function, which is the radical wavefunction of the continuous Schrödinger equation. Additionally, the splitting of the Landau level due to the finite size of a hexagonal disk is discussed.

Graphene exhibits diamagnetism, enabling it to be lifted by the repulsive force produced in an inhomogeneous magnetic field. However, the stable levitation of a graphene flake perpendicular to the magnetic field is impeded by its strong anisotropic of magnetic susceptibility that induces rotation. A method to suppress this rotation by applying the Casimir force to the graphene flake is presented in this paper. As a result, the graphene flake can archive stable levitation on a silicon plate when the gravitational force is small.

This study considers the dependence of the force caused by the dipolar interaction between small low-dimensional magnets such as single-molecule magnets and two-dimensional magnets on the distance between them within the framework of the dipolar Ising model with nearest-neighbor exchange interactions and long-range dipolar interactions. In particular, we focus on the rapid change in the force between ferromagnetic and antiferromagnetic plates, which arise from the transition of the spin states and explain that this behavior originates from the spin frustrations between magnetic plates. Furthermore, the size and temperature dependence of the interaction energy are investigated using a Monte Carlo simulation.

The application of a magnetic field perpendicular to the surface of a graphene cantilever generates a bending force owing to the strong anisotropy of the magnetic susceptibility. We calculate the mechanically stable equilibrium shape of a graphene cantilever in the presence of a magnetic field by minimizing the magnetic and bending energies, which are calculated using the tight-binding model and the Tersoff-Brenner potential, respectively. Furthermore, the introduction of a continuous model enables the size-dependence of the displacement by bending to be considered.

A graphene disk can be levitated above a magnet by a repulsive force arising from their diamagnetic interaction if the product of the magnetic field and its gradient is sufficiently large. The diamagnetic force also causes the rotation of the graphene disk because of the strong anisotropy of the magnetic permeability of graphene; thus a motion of centroid and rotation are considered by solving simultaneous Langevin equations. Furthermore, the dependence of a fluctuations of the position and angle of the levitated graphene disk on the size and temperature is also explained.

The Casimir effect between type-II superconducting plates in the coexisting phase of a superconducting phase and a normal phase is investigated. The dependence of the optical con-ductivity of the superconducting plates on the external magnetic field is described in terms of the penetration depth of the incident electromagnetic field, and the permittivity along the imaginary axis is represented by a linear combination of the permittivities for the plasma model and Drude models. The characteristic frequency in each model is determined using the force parameters for the motion of the magnetic field vortices. The Casimir force between parallel YBCO plates in the mixed state is calculated, and the dependence on the applied magnetic field and temperature is considered.

Strong diamagnetic interactions enable carbon materials such as graphite plates and organisms to levitate stably in the atmosphere without active control. Although the repulsive force caused by diamagnetism becomes weak as the size of the object decreases, the necessary force against gravity also decreases. Thus, a nanocarbon material such as a single-layer graphene sheet may be levitated by the diamagnetic force. However, the stability worsens as the dimensions of the sheet decrease. The dominant factors affecting the stability of the diamagnetic levitation of nanomaterials are the Brownian motion and attractive surface forces such as the Casimir interactions. We calculate the potential energy of a square graphene sheet in two states, vertical and horizontal to a magnet, and considered the transition rate between these states based on Kramers' theory for the escape problem. Furthermore, the stiction of a single-layer graphene sheet onto a substrate caused by the Casimir force, which discontinues the levitation, is examined.

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.

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.

The recoil of a neutral atom irradiated by counter-propagating light with the same frequency and intensity is studied. The expectation value of the momentum transferred from the light to the atom with spherical symmetry at rest is usually zero because of symmetry. However, if the optical absorption coefficient of the atom depends on the incident light direction due to the magnetoelectric effect, as is the case in materials with nonreciprocal directional dichroism, the momentum transfer between the atom and photons depends on the incident direction. This allows even a standing electromagnetic wave to break the symmetry of the recoil of an atom.

© 2020 American Physical Society. The van der Waals potential energy of a linear dipole array is calculated based on a formula using a determinant of a matrix determining the dipole interactions, which includes all orders of the coupling strength and can be applied to a system with an arbitrary number of dipoles. To consider the nonadditivity of the van der Waals interactions, the van der Waals potential energy is expressed as a series of ratios of the susceptibility of the dipole to a cubic root of the distance between the nearest-neighboring dipoles, up to the fourth order for different numbers of dipoles. We show that the contribution of the terms including nonadditive interactions between four dipoles increases with the total number of dipoles and exceeds that between two dipoles. Furthermore, the error in the series expansion is evaluated by comparing the exact potential energy, including all orders of the coupling strength for a small number of dipoles.

The van der Waals force between a single atom and a rod-like molecule is investigated by introducing a one-dimensional dipole dipole interaction atomic model. The force between a single atom and its nearest neighbor atom in a rod-like molecule is related to the correlation between them, which is obtained by solving the problem of coupled quantum oscillators. The dependence of the correlation on the coupling constant between the single atom and atoms in the molecule are presented for different molecular weight. Furthermore, the transition of the force from attractive to repulsive in the excited state is considered with regard to the correlation.

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.

© 2020 The Institute of Electrical Engineers of Japan. We propose the system to analyze water permeability through the lipid bilayer. The lipid bilayer suspended over microwells changes its shape when the difference of osmotic pressure is formed by solution exchange. When the solution concentration outside the microwell is lower than the inside, water permeates through the lipid bilayer membrane and bulges outward. The interference fringes observed in the suspended lipid bilayer allowed us to accurately analyze its structural changes. Water permeability through the lipid bilayer could be accurately estimated based on analysis of the changes in the interference fringes observed in the suspended lipid bilayer caused by the solution exchange.

We calculate the Casimir force acting on randomly stacked graphene layers and investigate the impact of diamagnetism on the Casimir force. The randomly stacked graphene layers are predicted to have a much smaller permeability than regularly stacked graphene layers such as graphite. We show that the Casimir force between randomly stacked graphene layers and a conducting plate is enhanced as the permeability of the randomly stacked graphene layers decreases from 1 to 0, especially for large separations. Conversely, the magnitude of the Casimir force between the randomly stacked graphene layers and a magnet ic-dielectric plate such as yttrium-iron-garnet decreases as the permeability of the randomly stacked graphene layers decreases, and the force can be repulsive if the permittivity of the magnetic-dielectric plate contains a permeability much smaller than its permeability.

We investigate changes in the layered structure of particles confined between flat and step-shaped substrates. Using the Monte Carlo method, the density profiles of argon atoms interacting through a Lennard-Jones potential near a silicon step are calculated for different separation distances. Two different layered structures parallel to the surface of the substrate are observed far from the edge; the transition between the structure takes place within an interval of approximately 1 nm from the edge of the step. The particle distribution in the transition region reflects the formation of additional layers parallel to the contour of the Lennard-Jones potential generated near the edge. Although spatial changes in the layered structure of the nearest layer to the flat substrate across the step edge are small, they induce a non-uniform force on the substrate. If the substrate is flexible, the generated force acts to bend the substrate near the edge. The dependence of the layered structure on the temperature and the density is also evaluated.

The distribution of particles interacting with Lennard-Jones potentials and confined between parallel graphene sheets is investigated by molecular dynamics simulations. For small separation distances, the particles are densely localized in the central region between the graphene sheets. However, two high-density layers appear as the separation distance increases. The particle distribution also depends on the temperature, tensile force of the graphene sheets, and the initial configuration, and various configurations are observed for large separation. For example, an argon cluster initially located between the graphene sheets changes shape, and a bridge between the parallel walls is formed at low temperature. In contrast to the Lennard-Jones system sandwiched between rigid walls, the flexibility of the graphene sheets strongly affects the distribution of particles in the direction perpendicular to the graphene sheets.

The infinite pairwise summation of the potential energy between an atom above a graphene sheet and carbon atoms arranged in a hexagonal lattice is considered. Its magnitude depends on the minimum distance between the atom and the graphene sheet, as well as the number of carbon atoms on concentric circles, whose center exists under the atom. Using an analytical expression for an upper bound on the number of carbon atoms on a circle, which is the number of solutions to a Diophantine equation, an upperbound on the magnitude of the interaction potential energy between a carbon atom and a graphene sheet is obtained. Upper and lower bounds on the van der Waals interaction potential are calculated as a specific example.

We theoretically investigate the desorption process of an argon atom from a vibrating nanographene sheet. A high eigenfrequency of a graphene membrane owing to a small mass density per area and a large Young's modulus of graphene enable increasing the velocity of an atom enough to escape from the attractive interaction between the atom and graphene in a short time by accelerating the graphene sheet. We present the dependence of the velocity of ejected atom on the frequency and amplitude of the graphene membrane and consider an application to heating gas in small cavity.

© 2018 IOP Publishing Ltd. The equilibrium shape of a graphene sheet suspended over a silicon substrate with a narrow gap is investigated by introducing a continuum model. The displacement of the suspended graphene sheet, subject to electrostatic and van der Waals forces, was obtained by solving the equation of motion including the dissipation terms. The van der Waals force was calculated based on the quantum theory by considering the unique optical properties of graphene and their temperature dependence. The van der Waals force has a large effect on the equilibrium shape near the threshold value, below which a pull-in phenomenon occurs.

© 2017 Author(s). We propose a method to control a graphene-based mechanical switch with light. By positioning a self-supporting graphene sheet parallel to a doped silicon membrane, irradiation of the membrane with light can bring the graphene into contact with the membrane. This operation is based on the enhancement of the Casimir force between the graphene sheet and a doped silicon membrane that results from photoionization; therefore, pull-in phenomena can occur even without applying any voltage. We theoretically investigated the dependence of the maximum displacement of a graphene sheet on the power of the irradiation light. Furthermore, the switching time is estimated by analyzing the time-evolution of the carrier density in a doped silicon membrane.

© 2017 Elsevier B.V. The van der Waals force between dielectric plates comprising ultrathin conducting films was calculated by employing two models. In the first model, the ultrathin dielectric film was modeled as a dielectric plate of a small thickness, and the Lifshitz theory was applied. In the second model, an ultrathin dielectric film was modeled as a plasma sheet, which is an infinitesimally thin fluid carrying mass and charge. For each model, the interacting force was considered to be a function of the separation gap between the films, and the difference in the force-distance relationships of two was discussed.

© 2016 Elsevier B.V. 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.

© 2016 IEEE. 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.

© 2016 World Scientific Publishing Company. 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 4km/s dissociates in approximately 1ps 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.

© 2016 AIP Publishing LLC. We theoretically investigated the influence of the Casimir effect on mechanical properties of a graphene resonator, where a graphene sheet is located in parallel with a perfectly conducting plate. The Casimir force arising from this effect strongly attracts a graphene sheet to a perfectly conducting plate and increases the tension of a graphene sheet as the separation distance between them decreases. The maximum vertical displacement of a graphene sheet to the substrate increases obeying a power law of a separation distance with an exponent of 4/3 as the separation distance decreases. For small separation distances, the Casimir force is excessively strong for the graphene sheet to maintain a free-standing shape, consequently resulting in the adhesion of the sheet to the substrate below a critical separation distance. The resonant frequency increases over a wide range as the separation distance decreases for large separation distances. However, it then rapidly decreases for small separations and converges to zero at a critical separation. These various behaviors enable the control of a graphene resonator.

<p>自立したグラフェンと基板間距離が近い場合，グラフェンは基板との間に生じるカシミール力で変形する．またそれに伴い，グラフェンの共振周波数は張力の増加により高周波数側にシフトする．これらグラフェンの機械的特性が基板との距離によりどのように変化するかについてディラックモデルを用いて理論的に考察する.</p>

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.

©2015 The Physical Society of Japan. The thermal fluctuations in the tilt angles of a disk levitated above a liquid-liquid interface by a repulsive Casimir force are compared with those of a disk suspended by surface tension at the interface. By using a proximity force approximation, the probability density function of the tilt angle of a copper disk immersed in cyclohexane in contact with water is calculated. We show that the tilt angle of the levitated disk of micron-order radius exhibits comparatively large fluctuations. Observance of the difference in the amplitude of the fluctuations could be helpful in determining the position of the disk relative to the liquid-liquid interface.

サイズを選別した水およびメタノールクラスターイオンビームをアスパラギン酸薄膜に照射し、表面から放出された二次イオンを質量分析した。水およびメタノールの巨大クラスター照射による有機分子のイオン化には、試料中の残留水素からのプロトン付加反応の他に、クラスターと試料分子間でのプロトン交換反応が寄与していることがわかった。また、この反応は低エネルギー領域（～3.3eV）で促進されていることがわかった。

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 similar to 5 eV/atom dissociate into smaller cluster ions such as Ar-2(+) or Ar-3(+), 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.

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.

By counteracting gravity, the repulsive Casimir force enables stable levitation of a perfectly conducting particle near a liquid-air interface if the particle exists inside the liquid. In the present study, we examine the levitation of a gold particle near a bromobenzene-air interface and calculate the levitation height using the scattering-matrix formulation. In addition, we consider the Casimir force acting on a gold sphere near the interface between bromobenzene and water. At asymptotically large separations, the Casimir force is attractive because of the large static dielectric permittivity of water. However, the Casimir force changes from attractive to repulsive as the separation decreases. We also found that the gold particle can be levitated in bromobenzene above water. © 2014 American Physical Society.

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

構成原子数が数千個であるArクラスターイオンを金属に衝突させた結果、その衝撃により構成原子数がより少ないクラスターイオンに解離した。この解離特性が、クラスターイオンと金属の接触面に作用する衝撃応力と相関関係があることを見出した。今回の報告では、ターゲットとして異なる種類の金属、および金属にグラフェンを積層させた場合について検討したところ、興味深い知見が得られたので報告する。

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+ ion projectile and X-ray photoelectron spectroscopy (XPS). All three samples were contaminated by poly (dimethylsiloxane) (PDMS) on the surface. Compared to the Ar+ SIMS spectra, the fragments in the PS and DDB SIMS spectra for Ar 1550+, 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 ešectively 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. The shallow volume sputtering by GCIB is responsible for the preferential enhancement of the surface contaminants.

We study the vertical Brownian motion of a gold particle levitated by a repulsive Casimir force to a silica plate immersed in bromobenzene. The time evolution of the particle distribution starting from an equilibrium position, where the Casimir force and gravitational force are balanced, is considered by solving the Langevin equation using the Monte Carlo method. When the gold particle is very close to the silica plate, the Casimir force changes from repulsive to attractive, and the particle eventually sticks to the surface. The escape rate from a metastable position is calculated by solving the Fokker-Plank equation; it agrees with the value obtained by Kramers' escape theory. The duration of levitation increases as the particle radius increases up to around 2.3 μm. As an example, we show that a 1-μm-diameter gold particle can be levitated for a significantly long time by the repulsive Casimir force at room temperature. © 2013 American Physical Society.

Brownian motion of a gold particle levitated by a repulsive Casimir force at short distances from a silica plate in bromobenzene is studied. By using a proximity force approximation, the distribution function of the levitation height is calculated. Taking account for the effect of hindered diffusion near a wall, the diffusion constant of a gold particle is expressed as a function of the particle radius. © 2013 The Physical Society of Japan.

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.

Using the dipole scattering theory, we study the dependence of the Casimir force on the separation between arrays of planar scatterers. The reflection amplitude near zero frequency is computed by taking into account the interaction between scatterers that are organized in an array. The absolute values of amplitude can be described as linearly increasing functions of frequency that cross the origin, with their slopes depending on the values of incidence angle and polarization. The argument value of the reflection amplitude is determined from the absolute value of the reflection amplitude, on the basis of the assumption that the reflection amplitude is analytical in the upper half of a complex frequency plane. The numerical results show that, for a large separation between the arrays, the strength of the Casimir force between arrays of metal disks is inversely proportional to the sixth power of the separation between the arrays. © 2013 The Physical Society of Japan.

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 similar to 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 (E-atom) of the Ar cluster projectile decreases from similar to 8 to similar to 4 eV. These results indicate that tuning E-atom can maximize the surface sensitivity and the sensitivity for intact ions. Copyright (C) 2012 John Wiley & Sons, Ltd.