Masao Uemura

A Mechanism of Vapor Effect on Friction Coefficient of Molybdenum Disulfide

Molybdenum disulfide single crystals, compressed single crystals and pellets were friction tested in vacuum, air and water. The friction coefficient of MoS2 single crystal was hardly affected by air or water. In the case of the compressed MoS2 single crystals or MoS2 pellets, the friction coefficient became higher in the order of vacuum, air and water. When a large quantity of water was charged into compressed MoS2 single crystals or MoS2 pellets, the friction coefficient decreased to that obtained in a vacuum. These phenomena were explained by the surface tension of the condensed water in wedge-shaped cavities. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989

Segregation of As on GaAs(100) Surface during Abrasion Process Studied by X-Ray Photoelectron Spectroscopy and Auger Electron Spectroscopy

When a GaAs(100) surface was mechanically scribed by a diamond tip in an ultrahigh vacuum (UHV), surface segregation of As was observed using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The same phenomenon was also seen when the surface was abraded in air using emery paper. In the latter case, angle-resolved XPS analysis of As3d and Ga3d spectra showed the formation of As-As bonds on the abraded surface. Ga-Ga bonds existed beneath the layer of As-As bonds isolated from Ga-As bonds. The mechanism of the surface segregation of As is discussed.

Low friction force of diamond sliding on Ag thin films deposited on Si(111) plate

The tribological properties between subnanometer thick Ag films, which were prepared on cleaned Si(lll) substrate by electron bombardment type evaorator, and diamond(111) were studied using a pin-on-plate type tribometer. The preparation of the substrate with Ag ultralhin films and the tribotest were performed successively in an ultrahigh vaccum (UHV) chamber In the UHV condition, an extremely low friction coefficient (β < 0.004) was obtained when the pin slid on Ag film at a restricted sliding speed. By exposing to N2 gas (99.9995 % pure) atmosphere, however, the extreme low friction coefficient disappeared at the same sliding condition. The mechanism of the extremely low friction coefficients and the patterns of observed friction coefficient transitions were discussed in terms of chemical interaction force between atoms of topmost layers, and of Ag coverage on Si surface.

Clean surfaces of metals prepared by scribing with a diamond tip

Abstract Atomically clean surfaces of various metals prepared by scribing with a diamond tip are studied, using quantitative Auger analysis. For metals immiscible with carbon, atomically clean surfaces are prepared easily and quickly, and surface compositions are in good agreement with the bulks. For metals miscible with carbon, carbide-like layers are observed at the top of the surfaces prepared by scribing without heating. Atomically clean surfaces, however, are prepared by scribing at room temperature just after heating.

The friction behavior of Ni−-, SiO−2- and mica sodium silicate-based solid lubrication composites

The friction behavior of Ni - -, SiO - 2 - and mica sodium silicate-based lubricant composites, which included BN, WS 2 and graphite as lubricants, were examined. A ring-on-disk apparatus, in which a solid lubricant composite disk was held against a rotating stainless ring, was used as the test configuration. The tests were run with a load from 62 to 250 N in temperatures from 20 to 800°C in the laboratory environment. The wear surface was characterized by scanning electron microscope and X-ray photo spectroscopy. The major findings were that both mica sodium silicate- and SiO - 2 -based composites failed at above 500°C due to severe wear and surface damage; in contrast, Ni - -based composite showed a stable friction coefficient and low wear from 20 to 800°C.