Collective dynamics in liquid GeTe was investigated by inelastic x-ray scattering at 2 <= Q <= 31 nm(-1). The dynamic structure factor shows clear inelastic excitations. The excitation energies at low Q disperse with increasing Q, consistent with the behavior of a longitudinal-acoustic excitation. The dispersion curve has a flat-topped region around the pseudo-Brillouin-zone boundary, similar to what is observed in liquid Bi [Inui et al., Phys. Rev. B 92, 054206 (2015)]. The dynamic structure factor shows a low-frequency excitation, and its coupling with the longitudinal-acoustic mode plays an important role for a flat-topped dispersion. From these results, it is inferred that atomic dynamics in liquid GeTe is strongly affected by a Peierls distortion similar to liquid Bi. By comparing the momentum transfer dependence of the excitation energy and quasielastic linewidth to partial structure factors obtained by our own ab initio molecular dynamics simulation for liquid GeTe, the quasielastic and inelastic components were found to be correlated with Te-Te and Ge-(Ge, Te) partial structure factors, respectively.

High-resolution elastic recoil detection analysis (HERDA) has been conducted to quantify outermost OH group on a silica glass surface. The results of HERDA showed that the surface number density of OH groups (silanol number) can be measured with a good reproducibility by heating the sample in vacuum to remove the surface adsorbates. The measured silanol number depends on the temperature and is in good agreement with the result reported for porous silicas. Furthermore, by investigating the relationship between the contact angle of water and the silanol number, it was confirmed that the contact angle increases with decreasing silanol number.

Composition depth profiles of soda-lime silicate glasses were measured using high-resolution Rutherford back-scattering spectroscopy (HRBS) and high-resolution elastic recoil detection analysis (HERDA). Surface enrichment of modifier cations (Na+ and Ca2+) followed by a depletion in the deeper regions was observed using HRBS. The observed surface enrichment was attributed to the effect of radiation damage caused by the He+ irradiation. It was shown that the precise depth profiling of glass surfaces can be performed using HRBS when the fluence is limited below 3 x 10(14) He ions cm(-2). HERDA measurements demonstrated that there is a substantial amount of hydrogen (7.3 +/- 1.3 x 10(21) hydrogen cm(-3)) in the subsurface region as well as on the surface (1.6 +/- 0.2 x 10(15) hydrogen cm(-2)), which is very different from the silica glass surface where no subsurface hydrogen was observed.

Enhancement effect of ionic liquids on analysis of peptides was investigated in mega electron volt secondary ion mass spectrometry (MeV-SIMS). An ionic liquid of tripropylammonium a-hydroxycinnamate (trip-CHCA) was added to Des-Arg(9)-[Leu(8)]-bradykinin (bradykinin) with various molar ratios. The mixtures as well as the neat bradykinin were prepared on Si substrates. The samples were irradiated with 0.84 MeV C+ ions at a grazing angle of 1 degrees. Secondary ions emitted from the sample surface were analyzed using a time of flight mass spectrometer. The yields of both intact peptide ions and fragment ions were enhanced by adding trip-CHCA. The enhancement factor increases almost linearly with the molar ratio R of trip-CHCA to bradykinin for the fragment ions which do not contain arginine while it saturates at R > 1000 for the arginine containing ions. These results are attributed to the strong proton affinity of arginine.

Surface structures of binary mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy and time of flight secondary ion mass spectroscopy. Author(s) Nakajima, Kaoru; Miyashita, Motoki; Suzuki, Motofumi; Kimura, Kenji Citation The Journal of chemical physics (2013), 139(22) Issue Date 2013-12-14 URL http://hdl.handle.net/2433/180089 Right © 2013 AIP Publishing LLC. Type Journal Article Textversion publisher

This thesis is on the study of the characterization of interfaces and surfaces of high-k stacks for the future microelectronics. The changes of the high-k stacks during thermal processing and its mechanism have been experimentally investigated by high-resolution Rutherford Backscattering Spectrometry (HRBS) in combination with isotope tracing. The experimental results are consistent with the theoretical prediction that the silicon will be emitted outward to release the stress which is induced by the interface Si oxidation. Then, we studied the potential method, oxygen-gettering by Ti overlayer, for controlling the interface SiO2 thickness. Furthermore, we proposed a Time-Of-Flight (TOF) detector system for application on crystallographic analysis. TOF-RBS system is capable to analyze the sample’s crystallographic and chemical information even at the near surface of the sample, which is strongly required by the future microelectronics industry. In this chapter, brief introduction to the high-k stacks and the outline of this thesis are described.

We investigate the dynamic structure factor of the melt of the well known glass former, As2Se3, using inelastic x-ray scattering for temperatures, T, [Formula: see text] K and momentum transfers Q from [Formula: see text] nm-1. An anomaly was observed at Q  =  2.7 nm-1 ([Formula: see text] K) with, in the context of a simple model, both an abrupt change in frequency and an increased linewidth reminiscent of an anti-crossing in a solid. Comparison with structural information from reverse Monte Carlo modeling of x-ray diffraction data allows us to associate the disappearance of the anomaly at higher temperatures with a drop in the number of mechanical constraints per atom, n mc, to [Formula: see text] reminiscent of the threshold applicable for glass formation in rigidity theory. It is inferred that the surprising jump in the dispersion in the liquid may be correlated with a stiffness transition in a network glass.

In this study, we developed a particle-based simulation to reproduce the Brownian dynamics of particles on a curved surface, and applied the method to investigate their diffusion on a biological membrane. The mean squared displacement of Brownian particles in a Euclidean space increases with time, but characterizing diffusion in a non-Euclidean space, such as on a curved surface, has remained elusive. In recent years, theoretical studies have shown that the time evolution of the mean squared geodesic distance of a particle diffusing due to Brownian motion on a curved surface depends on its Gaussian curvature. This suggests that the shape of a cellular membrane may change the molecular diffusion kinetics occurring on it. Therefore, in this study, we developed a particle-based simulation of Brownian dynamics in which diffusion depends on the surface's Gaussian curvature, and investigated the molecular diffusion dynamics on a biomembrane with a complicated shape. In this method, during each computational time step, a particle is considered to move by projecting its coordinates onto the nearest curved surface represented by triangular meshes, a key step enabling the simulation. Model results using this method agree well with theoretical predictions. We then applied this method to demonstrate how molecular diffusion on a curved surface is affected by cellular shape in terms of the first passage time of the molecules.

Elemental depth profiles of typical ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethane-sulfonyl) imide ([CnC1Im][Tf2N], n＝2, 6, 10), were measured using high-resolution Rutherford backscattering spectroscopy (HRBS) and high-resolution elastic recoil detection analysis.The obtained depth profiles deviate from the uniform stoichiometric composition in the surface region, showing preferential orientations of ions at the surface.The results were well reproduced by molecular dynamics (MD) simulations, demonstrating that the state-of-the-art MD simulations are a reliable method to study surface structures of ILs.The surface structures of 11 equimolar mixtures were also studied using HRBS.A general tendency that larger IL is enriched at the surface was found.

X-ray Compton scattering measurements have been carried out for fluid rubidium (Rb) from near the melting point up to the critical regions. The electron kinetic energy (KE) was derived from the valence Compton profiles and its relative variation as a function of the fluid density was compared with that of the electron gas model. Reduction in the KE occurs more slowly than that predicted by the model as the fluid density decreases and an apparent deviation in the KE from the model is observed at the densities where the fluid is still metallic. These findings suggest that a fluctuation intrinsic to the low-density electron gas causes charge inhomogeneity in valence electrons in real fluid rubidium, being coupled with ionic density fluctuations. Copyright (C) EPLA, 2017

Surfaces of 11 equimolar mixtures of ionic liquids (ILs) consisting of 1-alkyl-3-methylimidazolium cations (from [C2C1Im] to [C12C1Im]) with anions (Cl, [BF4], [TfO], [PF6], [Tf2N]) were observed using high-resolution Rutherford backscattering spectroscopy (HRBS). The elemental depth profiles of these IL mixtures were derived from the observed HRBS spectra through spectrum modeling. By comparing the observed depth profiles with those of pure ILs, the surface mole fractions of constituent ILs were estimated. We found a general tendency that larger IL is enriched at the surface. The observed surface enrichment can be reasonably well reproduced by a simple thermodynamic calculation based on the Sprow-Prausnitz equation. A slight deviation from the calculated result was ascribed to the nonideal behavior of the IL mixtures, which was neglected in the calculation.

We introduce a novel random walk model that emerges in the event-chain Monte Carlo (ECMC) of spin systems. In the ECMC, the lifting variable specifying the spin to be updated changes its value to one of its interacting neighbor spins. This movement can be regarded as a random walk in a random environment with a feedback. We investigate this random walk numerically in the case of the classical XY model in 1, 2, and 3 dimensions to find that it is superdiffusive near the critical point of the underlying spin system. It is suggested that the performance improvement of the ECMC is related to this anomalous behavior.

Elemental depth profiles of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CnMIM][TFSI], n = 4, 6, 8) are measured using high-resolution Rutherford backscattering spectroscopy (HRBS). The profiles are compared with the results of molecular dynamics (MD) simulations. Both MD simulations and HRBS measurements show that the depth profiles deviate from the uniform stoichiometric composition in the surface region, showing preferential orientations of ions at the surface. The MD simulations qualitatively reproduce the observed HRBS profiles but the agreement is not satisfactory. The observed discrepancy is ascribed to the capillary waves. By taking account of the surface roughness induced by the capillary waves, the agreement becomes almost perfect.

Motivated by the way Japanese tatami mats are placed on the floor, we consider domino tilings with a constraint and estimate the number of such tilings of plane regions. We map the system onto a monomer-dimer model with a novel local interaction on the dual lattice. We make use of a variant of the Hamiltonian replica exchange Monte Carlo method where data for ferromagnetic and anti-ferromagnetic models are combined to make a single family of histograms. The properties of the density of states is studied beyond exact enumeration and combinatorial methods. The logarithm of the number of the tilings is linear in the boundary length of the region for all the regions studied.

In this study, we demonstrate the rapid switching of flow direction in a narrow parallel plate channel filled with water by using the thermoplasmonic Marangoni effect. A gold island film prepared in the channel is used as a thermoplasmonic heater, on which a continuous wave (CW) laser is focused to generate a micro bubble. By displacing the laser spot from the bubble center, Marangoni vortex flows are developed adjacent to the bubble. The direction of the observed flow significantly changes depending on the applied laser power. When the laser power is square-wave modulated at 5 Hz, the flow direction instantaneously switches in response to the power, and polystyrene microspheres dispersed in the water are arranged in a discrete pattern. The flow direction switching is observed for laser power modulation frequency of up to 40 Hz, which indicates that the time constant of the flow direction switching is at least of the order of several milliseconds. This rapid flow direction switching is attributed to the fast response of both the thermoplasmonic effect of the gold nanoparticles and the Marangoni effect on the bubble surface. Consequently, the thermoplasmonic Marangoni flows are useful for the dynamic and flexible flow control and microparticle manipulation in a microfluidic channel.

In order to reveal the surface structures of large molecular ionic liquids (ILs), the near-surface elemental depth distributions of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([CnC1Im][Tf2N], n = 2, 6, 10) were studied using high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with high-resolution elastic recoil detection analysis (HR-ERDA). The elemental depth profiles of all constituent elements, including hydrogen, were derived from HR-ERDA/HRBS measurements, so that the profiles would reproduce both HR-ERDA and HRBS spectra simultaneously. The derived elemental depth profiles agree with state-of-the-art molecular dynamics simulations, indicating the feasibility of this method. A controversy concerning the preferential orientation of [CnC1Im] at the surface has been resolved by this new combination analysis; namely, the [CnC1Im] cation has a preferential orientation with the ethyl chain pointing towards the vacuum in the topmost molecular layer.

Behavior of Li atoms deposited on the surfaces of highly oriented pyrolytic graphite (HOPG) and graphene-based thin films were observed at room temperature using high-resolution elastic recoil detection analysis (ERDA). On the HOPG surface, the deposited Li atoms intercalate into the bulk and no Li was observed in the surface region. The Li atoms were found to stay in the surface region (from the surface down to at least 3nm) when the HOPG was irradiated with 200keV He ions to a fluence of 5×1015ions/cm2 before Li deposition. This indicates that stable Li sites are produced by the ion irradiation. It was also found that Li atoms are accumulated on the surface due to the oxidation by the residual gas. This oxidation occurs only on the surface and not inside HOPG. Graphene-based thin films were prepared on Cu by microwave plasma chemical vapor deposition. The Li atoms deposited on the graphene-based thin films are found to distribute through the film almost uniformly and no accumulation either on the surface or at the interface was observed.

We experimentally investigated the modes of the Marangoni flow around a microbubble in a 50-μm-thick water chamber and found a transition flow mode that enables sheathless particle focusing. A temperature gradient was thermoplasmonically induced around the laser spot on a gold nanoisland film, and Marangoni flows were generated around the microbubble to drive submicron particles dispersed in the water. When the laser spot was slightly displaced from the bubble center, the particles were continuously collected by the bubble underneath and leaked in one direction to form a focused particle stream. The generation of the particle-focusing Marangoni flow was attributed to the appropriate balance of the temperature gradient in the perpendicular and horizontal directions of the chamber, which was controlled by the laser spot position against the bubble center. Temporally controlling this flow mode with laser power caused the periodic emission of clustered particles from the bubble underneath. This particle handling method with a thermoplasmonic Marangoni flow can be useful for improving the efficiency of reaction or sensing processes that take place in a microfluidic chamber.