Takashi Miura

Gas discharge caused by triboelectricity around a contact during friction between insulators

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 -2.2times10-4 C/m2, which leads the gas discharge in a micro-gap near the contact between the diamond pin and the quartz disk.

Desorption of water cluster ions from the surface of solid rare gases

Electron or photon irradiation of H2O adsorbed on the surface of rare gas solids induces the desorption of protonated water clusters, (H2O)nH+. 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)nH+ ions originate from the isolated water clusters, and the most important factor determining the size n distribution of desorbed (H2O)nH+ 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)nH+ desorption is due to Coulomb repulsion between the ionic water cluster and the rare gas ion.

At What Age Is the Occupational Accident Risk High? Analysis of the Occurrence Rate of Occupational Accidents by Age

This study aims to analyze changes in the annual occurrence rate of occupational accidents by industry and by accident type, and to clarify the risk of occupational accidents by age. Based on the published number of casualties and number of employees, the annual number of casualties per 1000 workers was calculated. Although the occurrence rate of occupational accidents in the manufacturing industry and in the construction industry exhibited similar tendencies, risk for construction workers in their late teens was extremely high. The distributions of risk of falls and of cuts and abrasions differed greatly by age. In the future, we plan to make use of these data for safety management of sites and for improvement of workers’ safety awareness.

Absolute measurements of the total PSD and ESD yields at the surface of solid krypton

Abstract Absolute total desorption yields from the surface of solid krypton were measured by photo excitation at excitonic excitation energies and by electron excitation in the energy range between 70 and 320 eV. The absolute desorption yields and their dependence on the film thickness and on the excitation energy were quantitatively reproduced by a simulation based on the desorption model of excimer dissociation followed by internal sputtering.

Observation of growth and structure of Kr films physisorbed on Ag(111) and Ag(100)

The structure and growth of two-dimensional crystals of Kr on Ag(111) and Ag(100) have been investigated by means of ellipsometry and eXtremely-low-current Low Energy Electron Diffraction (XLEED) under the quasi-equilibrium condition. The layered growth of a Kr film was observed up to the third layer by ellipsometry and the crystal geometry by XLEED. The Kr overlayer on Ag(100) has two types of alignment. In the predominant alignment, one of the unit vectors aligns with the 〈001〉 direction of the Ag substrate, while in the other it aligns with 〈011〉. The Kr–Kr spacing in a monolayer on Ag is 10% larger than that of the bulk.

Application of electron stimulated desorption techniques to measure the isotherm and the mean residence time of hydrogen physisorbed on a metal surface

Electron stimulated desorption techniques were applied to probe the density of H2 physisorbed on a cold surface. The adsorption isotherm of H2 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 H2 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 4.2 K 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.

Measurement of Charge Separation during Metal-Insulator Friction and Charge Relaxation due to Micro-gap Discharge

We developed an experimental setup to measure in real time the charge generated during friction between a metal and a plastic material in a vacuum chamber in order to reveal the absolute quantity of the initial charge separation in a vacuum and the relaxation processes, e.g., micro-gap discharge, in a gas ambience. In this paper, the static electricity generated by friction between stainless steel or gold metal and polyethylene terephthalate (PET) was measured. The density of the separated charge on the PET-rubbed surface was evaluated. The two-dimensional spatial distribution of light emission from the gas discharge was recorded with a CCD camera, and the voltage of the discharge was estimated.

Photo-stimulated desorption from water and methane clusters on the surface of solid neon

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.