CHEMICAL BONDING IN RESTACKED SINGLE-LAYER MOS(2) BY X-RAY-ABSORPTION SPECTROSCOPY

Restacked single-layer MoS2 films have been studied by polarized X-ray absorption spectroscopy at the S K and Mo L(III) edges. These restacked single-layer MoS2 films were obtained by exfoliation Of MoS2 powder and subsequent collection of the single molecular layer of MoS2 onto a glass substrate. Films with and without tetrachloroethylene (TCE) included between the layers were obtained. The interlayer spacing of the film without tetrachloroethylene is 6.2 angstrom, and there is a 4.0-angstrom interlayer expansion on introducing TCE molecules between layers of MoS2. The S K-edge X-ray absorption spectra of restacked single-layer MoS2 films with and without TCE included between the layers have been compared with that Of MoS2 powder. A few percent of sulfate anion was found in the restacked single-layer MoS2 films; it may originate from the partial decomposition of the molybdenum disulfide. Apart from that, the S K-edge absorption spectra of restacked single-layer MoS2 films with and without TCE are similar to that of MoS2 powder. This suggests that the chemical bonding of the S atom in the restacked MoS2 filMS is identical with that found in crystalline MoS2. In particular, we found no evidence for the presence of a new axial ligand on the S atom that should have manifest itself by introducing a new absorption band below the ionization threshold. Also, no difference was observed at the Mo L(III) edge between the restacked single-layer MoS2 films and the MoS2 powder.