Various defects –bright or dark triangular defects – were observed on the titanium disulfide surface (001) by ultra-high vacuum scanning tunnelling microscopy. The experimental interpretations of the images available in the literature suggested that a fraction of Ti atoms could be displaced from the octahedral site, to vacant sites of the crystal structure, leading to more or less correlated defects. Here, ab initio periodic LCAO-B3LYP calculations were performed on a (5x5) bi-periodic super-cell in order to model the electronic and geometrical involvements of Ti vacancies and to generate the theoretical scanning tunnelling microscopy images within the Tersoff–Hamann approximation. The relaxed structure of the Ti vacancy exhibited an inward movement of the neighboring S atoms at the surface. However, the occupied vacancy electronic states at the Fermi level were mainly developed on the atomic orbitals of the first S neighbors at the surface, leading to bright triangular zones in the simulated image.

Ti Vacancies on the (001) Surface of TiS2 Detected by Scanning Tunneling Microscopy - a Combined Experimental and Theoretical Study. E.Amzallag, H.Martinez, I.Baraille, M.Rérat, M.Loudet, D.Gonbeau: Solid State Sciences, 2007, 9[7], 594-9