Ti vacancies on the (001) surface of TiS2 detected by scanning tunneling microscopy: A combined experimental and theoretical study

Various defects – either bright or dark triangular defects – are observed on the titanium disulfide surface (001) by ultra high vacuum scanning tunneling microscopy. The experimental interpretations of the images available in the literature suggest that a fraction of Ti atoms could be displaced from the octahedral site they occupied to vacant sites of the crystal structure, leading to more or less correlated defects. In this paper, we have performed ab initio periodic LCAO-B3LYP calculations on a (5 × 5) biperiodic supercell to model the electronic and geometrical involvements of Ti vacancies and to generate the theoretical STM images within the Tersoff–Hamann approximation. The relaxed structure of the Ti vacancy shows an inward movement of the neighboring sulfur atoms at the surface. However, the occupied vacancy electronic states at the Fermi level are mainly developed on the atomic orbitals of the first S neighbors at the surface, leading to bright triangular zones on the simulated image.

(a) Experimental zoomed STM image of the defects and (b) [EF − 0.2 eV, EF] charge density map plotted for the (001) plane, 0.5 Å above the top sulfur layer of the (5 × 5) defective supercell. The step between two consecutive lines is 0.001 au.Figure optionsDownload as PowerPoint slide