About the preferential sputtering of chalcogen from transition metal dichalcogenide compounds and the determination of compound stoichiometry from XPS peak positions

We use the fact that for 2 keV Ar+ ion bombardment the sputtering yield of the chalcogen X is higher than that of the transition metal M in transition metal dichalcogenide compounds MX2 (M = W, Mo; X = Te, Se, S) to obtain variations of stoichiometry in these materials. While the binding energy of the chalcogen is independent of the MXx, stoichiometry (2 greater than or equal to x greater than or equal to 0.7), we find a correlation between the stoichiometry decrease and the reduction of the M binding energy, which can be used to estimate the compound composition. For binding energies of BEM and BEX in a MXx compound we find a linear dependence of(BEM - BEX) on x. However, a simple correlation does not exist between the chemical shift of the metal and the electronegativity difference Delta(chi (X) - chi (M)) between chalcogen and metal. (C) 2001 Elsevier Science B.V. All rights reserved.