The Influence of Surface Chemistry on MoS2Transfer Film Formation

Abstract

A variety of MoS₂ films having different initial surface compositions and different degrees of reaction in oxidizing atmospheres have been prepared by sputter deposition onto 440C steel substrates. The compositions of these films, including their degree of oxidation and their molybdenum-sulfur stoichiometry, have been determined by x-ray photoelectron and Auger electron spectroscopy immediately before the films were subjected to sliding wear tests. These tests, which used, an inhouse, “ring-on-disk” apparatus operating in an inert atmosphere, involved rubbing coated specimens against initially uncoated, polished 440C steel coutersurfaces. Films that had approximately 30 to 40 percent of their surface layers oxidized to MoO₃ gave the best wear results. In addition, the presence of elemental sulfur in the film surface layers appears to enhance wear life. These data are interpreted to mean that much better adhesion between the transfer film and he initially bare steel surface is obtained through chemical bonding of the transferred MoS₂ when its surface layers are disrupted by chemical modification.