An XPS study of the surface modification of natural MoS2 following treatment in an RF-oxygen plasma

The surface modification of natural MoS2 treated in an RF-oxygen plasma has been studied by X-ray photoelectron microscopy (XPS). The depth distribution of the component elements and their different possible combinations at or in the surfaces of the plasma etched samples is determined, The actual oxidation by the RF-oxygen plasma used was found to be confined to the surface whereas the physical effects of the etching regime extend to much thicker surface volumes. The higher oxidation states of the constituent elements, S6+, MO5+ and Mo6+, were detected in the surfaces of the samples after plasma etching. These are assigned, variously, to the presence molybdenum sulphate, molybdenum oxysulphides and a smaller number of O-Mo and O=Mo containing species present within the surface region of the samples involved. Loss of sulphur was also found to occur during plasma etching. The extent of this depends on the plasma conditions used and on the sub-surface depth. Aging the plasma-etched samples leads to further oxidation of S and Mo centres by the excess oxygen found to be present in the surface volume of the specimens after plasma processing. (C) 1998 Elsevier Science B.V. All rights reserved.