MoS2−xOx solid solutions in thin films produced by rf-sputter-deposition

Abstract

The chemical composition and structure of MoS2 solid lubricant films are intimately related to their friction and wear characteristics. We have conducted an x-ray photoelectron spectroscopy (XPS) study of 1-μm thick radio frequency (rf)-sputter-deposited MoS2 films to determine the chemical state of the films, focusing on the role of oxygen impurities. Concentrations of chemisorbed and bulk species were determined from the Mo 3d, S 2p, and O 1s peak shapes and intensities after annealing the films to temperatures from 425 to 975 K. Films deposited on substrates that were at ∼345 K [ambient temperature (AT) films] and on substrates heated to ∼525 K [high temperature (HT) films] both had ∼10% oxygen within the bulk of the films. The relative areas and shapes of the XPS peaks for the HT films at all annealing temperatures were consistent with the formation of a MoS2−xOx solid solution, where O atoms were probably substituted into S sites in the 2H–MoS2 crystal lattice. In AT films, this phase composition was stable only for annealing temperatures ≥725 K, in agreement with previous studies of the changes in crystal structure of AT films with annealing. The results are discussed in terms of previous studies of the structure and composition of sputter-deposited MoS2 films.