A Surface science investigation of ZnS (001) single crystal

This work present a surface science investigation on the properties of the ZnS (001) single-crystal by X-ray Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED). Besides the experimental results, which are the heart of this thesis, we performed some first-principles calculations based on the Density Functional Theory (DFT) in view to rationalize some speculations derived by the experiments. We aim to convert the insulating behavior of the ZnS surface into a semiconducting structure. In this regard, we perform several cycles of sputtering followed by thermal annealing. The experimental findings reveal that this methodology leads the formation of a s-richer structure. Then we speculated that the surface treatment favors the removal of zinc atoms. Based on this finding, we purposed a empirical model consisting of a (1 x 2) surface reconstruction characterized by alternating missing row of Zn atoms. In view of the correction on the binding energies positions in XPS experiments and the LEED patterns, one can speculate that this scenario (reconstructed and s-richer surface) might increase the surface conductivity of the ZnS system. An indirect assignment of such an hypothesis was derived by band structure calculations, which revealed several surface states with a semi-metallic like character filling the forbidden zone.