荒川 一郎

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.

We have studied electron stimulated desorption (ESD) and photon stimulated desorption (PSD) of positive ions from water absorbed on a surface of solid rare gases. In TOF spectrum, a series of ionized clusters are observed, which were thought to be protonated water clusters, (H₂O) _nH⁺. In both PSD experiments of H₂O/Ar, the desorption threshold of (H₂O) _nH⁺ was found to be coincide to 2p core ionization of Ar.

Luminescent phenomena during sliding friction between a diamond micro sphere and a flat quartz single-crystal disk under controlled ambient gas pressure of N<SUB>2</SUB>, Ar, and Kr were investigated. Spectra of the luminescence clearly indicated the gas discharge of each gas around the frictional contact. Spatial distributions of the gas-discharge luminescence were measured. The distributions at different sliding speeds were almost identical. The distributions depend strongly on the gas species and the pressure; the area of the discharge becomes larger with decrease of the gas pressure.

An innovative technique to evaluate electric potential difference of triboelectricity between both dielectric surfaces was developed. Electric-discharge luminescence due to electrification during friction between a spherical diamond surface and a flat quartz one was observed using a microscope under various pressures of N₂ gas. Two-dimensional spatial distribution of the luminescence around a contact shows a strong luminescence immediately after the friction and ring pattern of luminescence outside of friction area. The distribution of the strong luminescence along sliding direction, i.e., breakdown characteristics depending on gap distance, was well explained by a semi-empirical equation of discharge-current and gap distance. The potential difference between the both sides was also evaluated. Using the relation between a potential difference and a charge density in parallel-plate capacitor, surface charge density in the discharge area was calculated.

The layering transition of a physisorption system on a metal single crystal has been investigated by means of an ellipsometry and an eXtremely-low-current LEED (XLEED). Our XLEED system is operated at the primary electron current of about 0.1 pA, which minimizes the effect of desorption, defect formation, and charging. We observed the surface structure of Xe/Ag (111) by XLEED while monitoring the layer growth by the ellipsometry from a submonolayer film to a thick one. An equilibrium between the Xe film and coexisting three-dimensional Xe gas has been maintained throughout the experiment. From a monolayer film to a sufficiently thick film, the Xe overlayer has clear hexagonal structure whose directions of the unit vectors are coincident with those of the substrate. The Xe-Xe spacing in the monolayer film on Ag (111) is known to be a few per cent larger than that of bulk. Our interest is how the Xe-Xe spacing varies in the process of layer growth. We have made a systematic observation of the change of the Xe-Xe spacing in one and two monolayer films at pressures between 10^-7 and 10^-2 Pa and at temperatures between 50 and 100 K.

We have developed an eXtremely-low-current Low Energy Electron Diffraction (XLEED) apparatus equipped with a micro-channel plate and a position-sensitive detector which reduces electron beam damage and charge-up effects and makes it possible to study the structure of physisorbed films. This XLEED system is combined with the ellipsometer system which monitors the thickness of a physisorbed film. We observed Xe overlayer on Ag (111) and grahpite (0001) surfaces. We found that a thick Xe films on Ag (111) showed a single crystal structure which keeps relative orientation to the substrate.

We have developed an eXtremely-low-current Low Energy Electron Diffraction (XLEED) apparatus equipped with a micro-channel plate and a position-sensitive detector which reduces electron beam damage and charge-up effects and makes it possible to study the structure of physisorbed films. This XLEED system is combined with the ellipsometer system which monitors the thickness of a physisorbed film. We observed Xe overlayer on Ag (111) and grahpite (0001) surfaces. We found that a thick Xe films on Ag (111) showed a single crystal structure which keeps relative orientation to the substrate.

The characteristics of a new ionization gauge for pressure measurement in XHV were examined by experiments and computer simulations. The new gauge (axial-symmetric transmission gauge : AT gauge) has a Bessel-Box type energy filter between a B-A gauge type ionizer and a secondary electron multiplier as an ion collector to eliminate the limiting factors of pressure measurement in XHV, such as the X-ray effect and electron stimulated desorption (ESD) ions. The lower limit of the pressure measurement at present is estimated to be about 10^-12 Pa. The sensitivity factor of the AT gauge, which was further corrected for the effect of outgassing by the conductance modulation method (CMM), is almost constant in the pressure range from 10^-10 to 10^-6 Pa and is (2.3±0.1) ×10^-3 Pa^-1 for hydrogen.