Ichiro Arakawa

<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>

&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>

&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>

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.

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.

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.

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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.