荒川 一郎

The infrared absorption spectra of D2O monomers and clusters isolated in rare-gas matrices were systematically reinvestigated under the control of the following factors: the D2O concentration, deposition rate, heating temperature, and rare-gas species. We clearly show that the cluster-size distribution is dependent on not only the D2O concentration but also the deposition rate of a sample as the rate got higher, smaller clusters were preferentially formed. Under the heating procedures at different temperatures, the cluster-size growth was successfully observed. Since the monomer diffusion was not enough to balance the changes in the column densities of the clusters, the dimer diffusion was likely to contribute the cluster growth. The frequencies of the bonded-OD stretches of (D2O)k with k = 2-6 were almost linearly correlated with the square root of the critical temperature of the matrix material. Additional absorption peaks of (D2O)2 and (D2O)3 in a Xe matrix were assigned to the species trapped in tight accommodation sites.

Abstract: Nuclear spin relaxation of methane in solid xenon has been studied by infrared spectroscopy. From the analysis of the temporal changes of the rovibrational peaks, the rates of the nuclear spin relaxation of I = 2 ← 1 correlated to the rotational relaxation of J = 0 ← 1 were obtained at temperatures of 5.1–11.5 K. On the basis of the temperature dependence of the relaxation rate, the activation energy of the indirect two-phonon process was determined to be 50 ± 6 K, which is in good agreement with the rotational transition energies of J = 2 ← 1 and J = 3 ← 1. Taking into account this result and the spin degeneracy, we argue that the lowest J = 3 level in which the I = 1 and I = 2 states are degenerate acts as the intermediate point of the indirect process. Graphical abstract: [Figure not available: see fulltext.].

<p>An apparatus for terahertz spectroscopy in an ultrahigh vacuum has been developed. We used broadband Mylar for the beam splitter in a Fourier transform spectrometer, diamond for optical windows, and a liquid-helium-cooled Si bolometer for the terahertz detector to achieve the spectral range of 50–650 cm<sup>−1</sup>. For the purpose of keeping the ultrahigh vacuum in a sample chamber, we evacuated the whole optical path by turbo molecular pumps and made its pressure down to 10<sup>−4</sup> Pa. Using this apparatus, we measured temperature dependence of the terahertz spectrum of D<sub>2</sub>O ice vapor-deposited at 10 K. The spectral changes due to the structural transformation from amorphous ice to cubic crystalline ice I<sub>c</sub> were successfully observed in the range of 140–160 K. We report the spectral difference between low-density and high-density amorphous ice as well as that between hexagonal crystalline ice I<sub>h</sub> and cubic one.</p>

<p>An experimental system was developed for the physisorption study of hydrogen at substrate temperatures between 1.8 K and 10 K and at pressures down to 10<sup>－10</sup> Pa. The vaccum system was separated into two rooms by a bulkhead ; the upper chamber contained a cryostat equipped with a 4 K mechanical refrigerator and the lower one a substrate kept in an extremely high vacuum. Helium was liquefied at the refrigerator in the upper chamber and was stored in a pot in the lower one. The substrate was directly attached to the helium pot. The substrate temperature was controlled with an accuracy of 0.1 K by a heater located in the helium pot. The adsorption density of hydrogen physisorbed on the copper surface was measured with use of the electron stimulated desorption method. The mean residence time of hydrogen was directly determined by applying this technique to the transient state of adsorption. The adsorption isotherms were obtained by monitoring the hydrogen ion yield as a function of the pressure in the adsorption equilibrium state.</p>

A theoretical model of the phonon-mediated nuclear spin relaxation in H2O trapped by cryomatrices has been established for the first time. In order to test the validity of this model, we measured infrared spectra of H2O trapped in solid Ar, which showed absorption peaks due to rovibrational transitions of ortho-and para-H2O in the spectral region of the bending vibration. We monitored the time evolution of the spectra and analyzed the rotational relaxation associated with the nuclear spin flip to obtain the relaxation rates of H2O at temperatures of 5-15 K. Temperature dependence of the rate is discussed in terms of the devised model.

Using infrared-active solvents of CH4 and CD4 for matrix isolation, we measured infrared spectra of H2O and D2O clusters at 7 K. The solute-concentration dependence of the spectrum of H2O clusters in a CH4 matrix was investigated and was used for the peak assignment. Annealing procedures were found to promote the size growth of water clusters in methane matrices for all the combinations of (H2O, CH4), (H2O, CD4), (D2O, CH4), and (D2O, CD4). We also monitored the nu(3) absorption due to methane to find the annealing-induced structural change only of solid CH4. The matrix effects on the vibrations of the clusters are discussed on the basis of "T-c plots", where their frequencies are plotted as a function of the square root of the matrix critical temperature, T-c. The obtained plots assure the validity of the assignment of the cluster peaks. (C) 2016 Author(s).

Infrared spectra of solid CH4 were studied in the nu(3) and nu(4) vibrational regions. The phase I crystal around 30 K showed broad absorption bands, whereas the phase II crystal at 6.9-10.3 K exhibited splitting of these bands after annealing above 20 K. The split peaks were assigned to the librating and almost freely rotating molecules in phase II on the basis of the peak spacings and time evolution of the peak intensities. From the quantitative analysis of the temporal changes of the R(0) and R(1) peak intensities, the relaxation rates of the numbers of molecules with J = 0 (I = 2) and J = 1 (I = 1) were determined in the temperature range of 6.9-10.3 K. We fitted the function resulting from a combination of direct and indirect relaxation processes mediated by phonons to the temperature dependence of these rates and obtained the activation energies of the indirect process: C similar or equal to 36 K. Since this value is higher than the energies of perturbed J = 2 states relative to the J = 1 state, we argue that the nuclear spin conversion through the J = 3 state also takes place. (C) 2015 AIP Publishing LTC.

Electron stimulated desorption techniques were applied to probe the density of H-2 physisorbed on a cold surface. The adsorption isotherm of H-2 on a copper surface was measured in the equilibrium pressure range between 10(-9) and 10(-4) Pa at surface temperatures of 6.5 and 4.2 K. The mean residence times of H-2 on copper were obtained from the observation of the time development of the surface density in a transitional state approaching equilibrium, and are 50-500 s for the coverage between 1 and 0.18 at 4.2K of the substrate temperature. The adsorption energies of 1.18-1.27 kJ/mol, and the condensation coefficient of 0.074-0.018 were also deduced. (C) 2014 American Vacuum Society.

&nbsp;&nbsp;Triboluminescence spectra were measured by means of pin-on-disk method for several samples of natural diamond and a synthetic quartz disk in Ne or N₂ gas at pressures between 10 and 10⁵ Pa. At the gas pressure between 10 and 1000 Pa, a blue luminescence was observed besides the gas discharge luminescence due to triboelectricity. The spectrum of cathode-ray luminescence, which was measured by electron bombardment on the same diamond sample, was identical with that of the blue luminescence. The gas pressure dependence of the blue luminescence intensity also supports the model that the blue luminescence was induced by electron impact on the diamond surface in the gas discharge.<br>

To understand physico-chemical processes at real contacts (asperities) on fault surfaces, we conducted pin-on-disk friction experiments at room temperature, using single crystalline quartz disks and quartz pins. Velocity weakening from friction coefficient mu similar to 0.6 to 0.4 was observed under apparent normal stresses of 8-19 (18 &gt; 19), when the slip rate was increased from 0.003 to 2.6 m/s. Frictional surfaces revealed ductile deformation of wear materials. The Raman spectra of frictional tracks showed blue shifts and broadening of quartz main bands, and appearance of new peaks at 490-520 and 610 cm(-1). All these features are indicative of pressure-and strain-induced amorphization of quartz. The mapping analyses of Fourier transform infrared (FT-IR) spectroscopy at room dry conditions suggest selective hydration of wear materials. It is possible that the strained Si-O-Si bridges in amorphous silica preferentially react with water to form silica-gel. In natural fault systems, amorphous materials would be produced at real fault contacts and accumulate over the fault surfaces with displacements. Subsequent hydration would lead to significant reduction of fault strength during slip. Citation: Nakamura, Y., J. Muto, H. Nagahama, I. Shimizu, T. Miura, and I. Arakawa (2012), Amorphization of quartz by friction: Implication to silica-gel lubrication of fault surfaces, Geophys. Res. Lett., 39, L21303, doi:10.1029/2012GL053228.

Photo-stimulated desorption of ions from methane and water heteroclusters on the surface of solid neon was studied. The desorption yields of various photo-desorbed species showed strong dependence on the composition and size of the mother cluster. It was found that presence of a water molecule in the cluster significantly enhanced, or was almost essential for, desorption of all species observed. Systematic investigation of the correlation between the cluster size and desorption yield of each ion revealed the corresponding mother cluster for each species of the desorbed ions. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742182]

We carried out quartz-crystal microbalance (QCM) experiments for Xe films adsorbed on an exfoliated single-crystalline graphite substrate (Xe/Gr) and Kr films adsorbed on a synthetic mica substrate (Kr/mica) around LN2 temperature. For Xe/Gr, it was found that the resonance frequency decreases greatly around the first layer completion, while it does not decrease at low coverages. The observed behavior is similar to that of Kr films on a graphite substrate (Kr/Gr). This demonstrates that the layer completion strongly affects the sliding motion of noble gas films on graphite.

We have developed a quartz-crystal microbalance (QCM) using a quartz tuning fork resonator, and have carried out experiments for Kr films adsorbed on a single crystalline graphite at LN2 temperature. For the monolayer film, the coupled mass to the oscillating substrate is significantly small until the film enters the commensurate (C) phase. It starts to increase at the C phase, and the increase in the coupled mass with respect to the coverage decreases at the coexistence phase between the C and the incommensurate (IC) phases. It is enhanced again when the film enters the IC phase. We compared the observed behavior with that of 5 MHz QCM experiments, and found that the sliding motion does not depend on oscillation frequency.

We have carried Out quartz crystal microbalance (QCM) experiments for Kr films adsorbed on exfoliated graphite from a single crystal, and have examined the coverage dependence of the sliding friction and the depinning transition up to the bilayer film. For the monolayer film, the coupled mass density appears at the commensurate and fluid (C+F) phase. An increase of this density starts at the commensurate (C) phase and continues at the incommensurate (IC) phase after the C-IC transition. It was found that the monolayer film slides not uniformly but partly on the substrate, and that the slip time is 60 ns at the C phase. On the other hand, the film around the layer completion slides almost uniformly, and its slip time is about 10 ns. For the bilayer film, the experimental data are reasonably explained by a model in which the slip occurs at the boundary between the first and second atomic layers, in addition to the boundary between the film and the substrate. For the oscillation amplitude sweep at a constant coverage, a rapid change in frequency was observed for the monolayer and bilayer films, which is attributed to the depinning transition. This magnitude takes the minimum value around the layer completion.

We have measured spectra of the light emission from the frictional contact between the pin of natural diamond, synthetic fused silica, MgO, or NaCl and the disk of quartz or synthetic sapphire in a vacuum in the wavelength range between 380 and 1000 nm. Each spectrum shows the relaxation of electronic excited vacancies, which are thought to be produced at the solid surface by mechanical abrasion. (C) 2009 Elsevier Ltd. All rights reserved.

We have performed a quartz crystal microbalance (QCM) experiment for Kr films adsorbed on a single-crystalline graphite substrate at various temperatures. The substrate enables us to study the oscillation direction dependence of the sliding friction. In the present experiment, the direction is parallel to the a-axis of graphite. It was found that the resonance frequency at 85 K does not change greatly until the film enters the commensurate phase. At the commensurate phase, the resonance frequency starts to decrease. In addition, at the transition from the commensurate phase to the incommensurate phase, the coverage dependence of frequency changes slightly.

&nbsp;&nbsp;The pressure dependence of the electron stimulated desorption (ESD) ions were investigated by the quadrupole mass spectrometer with a Bessel-box type energy analyzer. The mass spectra of the ESD ions were measured under introduction of H₂O, CO, O₂ and CO₂. The ESD ion peaks for those gasses were observed at O⁺ (m/z=16). The mass spectra of the gas phase ions were also measured and compared with those of ESD ions during the pumping down process. The origin of the main species in ESD ions, O⁺, was the adsorbed H₂O on the grid surfaces.<br>

&nbsp;&nbsp;The isotherms and the isobars of krypton and xenon physisorbed on a silver single crystal surface were investigated by ellipsometric observation of the amount of adsorption. It was found that they showed a hysteresis in an adsorption-desorption loop for both the first and the second layer condensations. Careful examination of the effect of instability of an equilibrium pressure and a substrate temperature during the measurement revealed that they were not responsible for hysteresis. The observed hysteresis is very likely to be intrinsic one though its origin and mechanism are unknown.<br>

&nbsp;&nbsp;The deviation of the sensitivity factors for the axial-symmetric transmission gauge (AT gauge) were examined and compared with those for the B-A gauges and the extractor gauges. The calibrations were performed against nitrogen. The deviations for three types of gauges were about &plusmn;10%, nearly the same one another. The long-term variation of the sensitivity factor for two AT gauges was also examined. For one sensor, the sensitivity factor decreased 10% during initial two years operation while the factor stabilized within &plusmn;3% for the successive three years. The temperature dependence of the sensitivity factor is discussed for the data obtained in the stabilized period.<br>

Although several mechanisms of precursory electromagnetic emissions of earthquakes have been proposed, there has been no in situ observation of electromagnetic phenomena occurring at the frictional contacts during rock frictions. From an experiment simulating the motion of an asperity on a fault surface, we report the generation of photon emissions around frictional contacts between natural rock minerals. Spectroscopic analysis clarified that the photon emissions are caused by dielectric breakdown of ambient gases (electric-discharge plasma) due to frictional electrification. The plasmas were found to occur under normal stress of 4 MPa and sliding speed of 10(-2) m/s. This indicates that plasma generations do not require high-normal stresses needed to fracture rocks and sliding speeds as high as seismic rates (similar to 1 m/s). Thus, frictional discharges could occur at microscopic asperities at the onset of the slips of earthquakes, and might be one of the sources of the seismo-electromagnetic emission. (c) 2008 Elsevier B.V. All rights reserved.

Gas breakdown caused by triboelectricity during friction between two insulators was observed in measuring two-dimensional spatial distributions of luminescence from gas discharge plasma. The insulators were chosen among diamond, quartz, sapphire, MgO single crystal, and quartz glass. The discharge between identical materials was also observed. The patterns of the gas discharge luminescence had a shape of a ring for all frictions between insulators. By using a gold-coated diamond pin for friction with a quartz disk, the discharge pattern differed from the ring pattern. In the case of insulator pin, electric field induced by a localized charge at the off-track area near the tip of the pin during friction accounts for formation of the ring shape of the gas discharge. The gold coating makes it possible to monitor an amount of charge transferred from the quartz surface during friction. The negative charge density at the frictional track on the quartz disk is calculated to be -2.2x10(-4) C/m(2), which leads the gas discharge in a micro-gap near the contact between the diamond pin and the quartz disk.

To investigate the relation between the rock friction and the fractal electromagnetic radiation before the main-shock of earthquakes, we conducted a friction experiment simulating the motion of an asperity on a fault plane, and observed photon emissions due to electric discharge by dielectric breakdown of ambient gases from friction contacts between rock minerals. This indicates that frictional discharges (plasma generations) could occur locally at microscopic asperities on fault surfaces. From concepts on the fractal size-distribution and temporal evolution of fault asperities, the frictional discharge occurring at asperities on the fault plane can be one of origins of the fractal electromagnetic radiation (Benioff electromagnetic radiation) prior to earthquakes. (c) 2006 Elsevier B.V. All rights reserved.

Electron or photon irradiation of H2O adsorbed on the surface of rare gas solids induces the desorption of protonated water clusters, (H2O)(n)H+. The yield and the size n distribution of cluster ions depend on the coverage, the deposition temperature of the water, and the thickness of the rare gas film. These results indicate that the (H2O)(n)H+ ions originate from the isolated water clusters, and the most important factor determining the size n distribution of desorbed (H2O)(n)H+ is the sizes of water islands on the rare gas solid. The measurement of kinetic energy distributions indicated that the desorbing energy of clusters depend on the rare gas species of the substrates and the cluster size. It is suggested that the (H2O)(n)H+ desorption is due to Coulomb repulsion between the ionic water cluster and the rare gas ion. (c) 2006 American Institute of Physics.

This paper reviews our progress on the desorption induced by electronic transitions ( DIET) in rare gas solids by selective excitation of valence excitons. Observation of metastable atoms desorbed by excitonic excitation gives us direct information on the exciton-induced desorption processes in rare gas solids. The validity of three desorption mechanisms, cavity ejection, excimer dissociation, and internal sputtering, is demonstrated by systematic measurements of kinetic energies and angular distributions of desorbed particles. The absolute yield of total and partial desorption was measured, which can lead us to the quantitative understanding of exciton-induced desorption processes.

To clarify the fractal natures of electromagnetic radiations prior to earthquakes, we conducted a friction experiment simulating the essential elements of the motion of an asperity on a fault plane, and observed the generation of photon emissions around frictional contacts due to the dielectric breakdown of ambient gases by frictional electrification. According to the fractal distribution of fault asperities, we show that the frictional discharge (plasma generation) at asperities on the fault plane can be one of origins of the fractal seismo-electromagnetic radiation prior to earthquakes.

Adsorption isobars of Xe and Kr oil Ag(111) and Ag(100) Nvere observed Simultaneously by an extremely-low-current low energy electron diffraction and an ellipsometry in the temperature range between 60 K and 90 K and in the equilibrium pressure range between g X 10(-6) Pa and 2 x 10(-4) Pa. Two dimensional condensation of the first layer of Xe on Ag(111) occurred at the temperature 0.3 +/- 0.1 K higher than that on Ag(100). In the case of Kr oil Ag(111) and Ag(100) the temperature difference was 0.2 +/- 0.1 K. This temperature difference was discussed oil the assumption that it is caused by the repulsive interaction between the dipoles induced in rare gas atoms. We estimated the difference of the induced dipole moment p: p of Xe atom on Ag(100) is 6% larger than that on Ag(111) and p of Kr atom on Ag(100) is 14% larger than that oil Ag(111). (c) 2006 Elsevier B.V. All rights reserved.

Gas breakdown caused by triboelectricity during friction between two insulators was observed in measuring two-dimensional spatial distributions of luminescence from gas discharge plasma. The insulators were chosen among diamond, quartz, sapphire, MgO single crystal, and quartz-glass. The discharge between identical materials was also observed. The patterns of the gas discharge luminescence had a shape of a ring for all frictions between insulators. By using a gold-coated diamond pin for friction with a quartz disk, the discharge pattern differed from the ring pattern. © 2006 IEEE.

By a pin-on-disk frictional experiment simulating the motion of an asperity on a fault plane, we observed photon emissions from the gap between the quartz disk and pins made of natural semiconductor or insulator minerals during friction. The patterns and intensities of photon emissions depended significantly on the gas pressure, on the normal stress and on the shape and material of the pins. The frictional contacts made of different grain sets or ore veins can be regarded as natural semiconductor/insulator junctions arising from the difference in electron states or work functions between the contacts. During seismic activities, such semiconductor/insulator junctions in natural fault zones would generate discharge plasmas that could be one of origins of seismo-electromagnetic phenomena. Finally, in addition to its effect on the geoelectromagnetic perturbations, the significances of the discovery of discharge plasmas on geochemical reactions on a fault zone arising from tectonic activities are discussed. (c) 2006 Elsevier Ltd. All rights reserved.

The photon-stimulated desorption of (H2O)(n)H+ from water physisorbed on a rare gas solid (Ne, Ar, Kr, and Xe) has been investigated. From the measurements of the desorption yield as a function of the incident photon energy, the (H2O)(n)H+ desorption is effectively and indirectly induced by the multiple-excitation and -ionization of rare gas substrates. The direct excitation of the water molecule does not induce noticeable desorption of (H2O)(n)H+. (c) 2005 Elsevier B.V. All rights reserved.

We measured spectra of light-emissions during sliding friction between diamond and quartz in ambient gases of He, Ne, and Ar at 10-10³ Pa. Two types of the light emission were observed; one has a band spectrum specific to each gas and the other has a continuous spectrum from 300 to 600 nm. The shape of the latter spectrum was almost the same for all the ambient gases while the pressure dependence of the intensity differed from gas to gas. The continuous spectrum is highly similar to that of photoluminescence caused by the oxygen vacancy in quartz. Microscopic spectroscopy revealed that the source of the continuous spectrum was on the friction track in the electric discharge region. Experimental results suggest that electrons or ions in the gas discharge stimulate the oxygen vacancy in quartz.

The basic characteristics of the axial-symmetric transmission gauge (AT gauge), that were modified for measurement over a wide pressure range, are reported. A Faraday cup ion collector is used instead of a secondary electron multiplier to extend the measurable pressure range to 10(-3) Pa. The sensitivity of the gauge was determined by a conductance modulation method, and by direct comparison against an extractor gauge and a spinning rotor gauge as well. When operating in O-2, there was systematic disagreement between pressure readings with the AT gauge and the extractor gauge. This is due to the difference in the elimination efficiency of the electron stimulated desorption ion. &COPY; 2005 American Vacuum Society.

We have developed a miniature cylindrical mirror analyzer (CMA) for ion kinetic energy measurements. The CMA consists of a shield for electric field, inner and outer cylinders, a pinhole, and microchannel plates. We have applied it for the measurements of kinetic energy distribution of H⁺ desorbed by O 1s transitions of condensed H₂O.

We investigate static electrification due to asymmetric rubbing. Eight different plastic materials, for which self-consistent electrostatic series can be obtained, are investigated here. Two rotating disc samples whose edges brought into contact are rubbed each other. The surface voltages of the rubbed surfaces are measured systematically changing the degree of asymmetry of the rubbing by varying the rotation speeds of the two discs. It is found that the tendency of the charge separation depends on the species of materials. This might indicate there are two or more mechanism of charge separation. (C) 2004 Elsevier B.V. All rights reserved.

We performed spectral measurements of gas discharge luminescence caused by triboelectricity during sliding friction between a diamond spherical surface and a quartz plate in N-2. As the gas pressure decreased, luminescence of negative glow intensely appeared and vibrational temperature of electronic excited N-2 increased. The spatially resolved spectral measurements made it clear that the spectrum of N-2 discharge differs from position to position; emission from negative glow was relatively strong on the frictional track where is far from the contact. This result implies that the diamond tip was charged to positive and the frictional track on the quartz to negative. (C) 2004 Published by Elsevier B.V.

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A two-parameter auto-null ellipsometer system was constructed and applied for precise observation of the growth of rare gas films physisorbed on a metal surface in quasi equilibrium condition. We obtained the adsorption isobar of Xe/Ag (111) at P = 2.5&times;10^-6Pa, which shows the layer by layer growth of the Xe film up to the third layer. The relative of polarizability of a Xe atom in the second and the third layer to that of the first layer are 0.94 and 0.91, respectively.

The effect of disturbances induced by the injection of the electrons and ions from outside of the gauge on the axial-symmetric transmission gauge (AT gauge) was examined. There were less sign of disturbance in comparison to a BA gauge and an extractor gauge. The energy analyzer in the AT gauge works as a cut off filter for the charged particles and reduces the disturbances from the external source as well as the effects of the soft x-rays and ESD (electron stimulated desorption) ion generated in the ionizer.

We have developed a laser-plasma vacuum ultraviolet light source (LPLS) for the purpose of using it as an excitation light source in experimental studies of Desorption Induced by Electronic Transitions (DIET). In comparison with the synchrotron light source, LPLS has an advantage of being intense in short duration. The pulse width of the order of 10 ns makes it possible to obtain higher time resolution in a time-of-flight measurement of desorbed particles.

The growth and the structure of a Xe film physisorbed on a Ag(l 11) substrate have been investigated by means of ellipsometry and extremely low current low-energy electron diffraction (XLEED). Equilibrium between the Xe film and the coexisting three-dimensional Xe gas was maintained throughout the film growth. From a monolayer to a sufficiently thick film, the Xe film has a clear hexagonal structure whose directions of the unit vectors are coincident with those of the substrate. We have made a systematic observation of the change of the Xe-Xe spacing in the process of film growth. The Xe-Xe spacing just after the first layer condensation is a few percent larger than that of the bulk. While the pressure is increased or the temperature is lowered, the Xe-Xe spacing decreases gradually and reaches the bulk value before the second layer condensation. The second layer adatom density has been determined from ellipsometric and XLEED data. It was found that the compression in the first layer precedes the second layer adsorption. Using a simple model, we calculated the densities of the first and the second layer, which are consistent with our experimental results.