Atmospheric effects of friction, friction noise and wear with silicon and diamond. Part II. SEM tribometry of silicon in vacuum and hydrogen

Scanning electron microscope (SEM) tribometric data on polycrystalline sili con (poly-Si) vs. poly-Si, Si(100) vs. Si(100) and Si(111) vs. Si(111) inte rfaces, obtained in similar to 1 x 10(-5) Torr and in 0.2 Torr partial pres sure of hydrogen gas (P-H2) from room temperature to 850 degrees C, were pe rformed under standard and much slower thermal ramping rates. The friction data were analyzed per the methodology described in part I of this paper se ries. The results indicate a highly beneficial friction- and wear-reducing regime within a relatively narrow thermal region. This desirable region coi ncides with some chemisorption of excited species of molecular hydrogen jus t before the mass thermal desorption of surface hydrides. These data repres ent the tribochemical equivalent of a method routinely used in electronics, whereby deep electron traps (dangling Si bonds) are passivated by baking i n molecular hydrogen. The P-H2 also exerts a moderating influence on the si ze of the friction noise at all test temperatures. However, the general lev el of friction beyond the beneficial thermal region is high. In parallel, t he general wear rate of Si representative of the entire range of standard t hermal ramping in both atmospheric environments is in the extremely high 10 (-12) m(3)/(N m) range. Operating strictly in the beneficial, low-friction thermal regime resulted in a several orders-of-magnitude reduction in the w ear rate over those measured under standard thermal ramping conditions. Alt hough the results confirm previous findings that Si is not a good material of construction for miniaturized moving mechanical assemblies (e.g., microb earings and gears), there seems to be some limited possibility of gas-phase lubrication of Si micromechanisms with rarefied hydrogen at surface temper atures between 100 and 300 degrees C.