Further theoretical analyses (2D and 3D) of Ni1/4TiS2 probed by XPS/STM studies

The surface of Ni1/4TiS2 was investigated by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Electronic calculations were performed using the ab initio Hartree-Fock program crystal. The XPS results (chemical shift of core peaks) are satisfactorily accounted for through a Mulliken population analysis. Concerning the STM results, we imaged the top sulfur plane (0 0 1) and interpret the data on the basis of the partial electron density of a slab which consist of seven (0 0 1) Ni1/4TiS2 layers. It was found that the bright spots in experimental STM images correspond to sulfur atoms in a single metallic environment (Ti atoms). Beside higher electronic density, these atoms are highlighted because of their proximity to the tip compared with sulfur atoms in a double environment (Ti and Ni). (C) 2002 Elsevier Science B.V. All rights reserved.