COMPOSITIONAL CHANGE OF (0001) WS2 SURFACES INDUCED BY ION-BEAM BOMBARDMENT WITH ENERGIES BETWEEN 100 AND 1500-EV

Ion beam bombardment at low ion energies is of interest in both surfac e analysis and thin film deposition, however, concerns exist regarding preferential sputtering and chemical reduction at the surface. In thi s study, the rate of reduction and extent of alteration of (0001) WS2 was examined with respect to type of ion beam (Ne+, Ar+, and Kr+), inc ident ion energy and ion beam dosage using x-ray photoelectron spectro scopy. At saturation, the surface stoichiometry was reduced to approxi mately WS0.4, in general agreement with preferential sputtering models . By decreasing the atomic mass of the ion or the energy of the ion be am, the resolution of the surface species formed was enhanced. With io n bombardment, the W(4f) spectrum shows the formation of a reduced W s pecies representing metallic W. In addition, the enhanced W concentrat ion at the surface causes an increased density of states up to the Fer mi level as well as a 0.5 eV band bending due to pinning at surface de fects. The corresponding S(2p) spectrum shows the formation of a reduc ed S species. This reduced S species is associated with S surrounded b y metallic W, which causes a final state polarization effect, decreasi ng the binding energy.