X-ray photoelectron spectroscopy and scanning tunneling microscopy investigations of the solid solutions TixTa1−xS2 (0⩽x⩽1)

The surface of mixed transition metal sulfur TixTa1−xS2 has been studied both by X-ray photoelectron spectroscopy and scanning tunneling microscopy over the entire range of stoichiometry 0⩽x⩽1. For compositions close to the native materials, we highlight according to x an evolution between the existence of a charge density wave (TaS2) and the existence of structural defects (TiS2), interpreted as metal atoms vacancies or migration within the vacant sites of the structure. The results obtained by XPS and scanning probe microscopy for intermediate compositions (0.4⩽x⩽0.6) lead us to propose a model in ordered domains, separated by frontier zones where the metal distribution is random. These various interpretations, supported by our experimental results, find their origin from the different electronic characteristics of native materials and their evolution according to the composition. On the basis of model systems, we have undertaken band structure calculations (FP-LAPW method) in order to highlight specific interactions occurred in TixTa1−xS2 when x varies between 0.4 and 0.6. Those make it possible to rationalize some of our experimental data.