Low friction of a diamond/H-terminated Si [111] sliding system

Hydrogen-terminated Si [111] surfaces have been studied for tribological performance in the sliding of a diamond slider to obtain fundamental information on contact problems between an Si memory disk and the slider. The authors focus on the tribological role of the atoms on the contact surfaces and observe an extraordinarily low coefficient of friction: 0.003 of the relevant sliding surfaces, a coefficient as low as the sliding system of diamond/Ag monolayer/Si [111]. The sliding tests were carried out under ultrahigh vacuum lower than 1.5×10^-7 Pa, with a load of 250 mN and 0.1 mm/s of speed. The Si [111] surface was H-terminated by hydrofluoric acid solution and also by hydrogen gas adsorption, before the sliding tests. By sliding both of the H-terminated Si surfaces, a very low and stable friction coefficient was observed, while the desorbed surface by heating at 600°C showed a very high friction as 0.4 or higher. The observed friction reduction of two orders was attributed to a monolayer of hydrogen atoms terminating the Si [111] dangling bonds. The results are discussed in terms of the sliding mechanism, surface source of friction, and application to reduce memory disk surface damage as the result of probable contact between slider and disk, reduction of the friction of micro-machine sliding system, and design of a sliding system in a vacuum.