MOS2 THIN-FILMS OBTAINED BY A NEW TECHNIQUE - SOLID-STATE REACTION BETWEEN THE CONSTITUENTS IN THIN-FILM FORM

MoS2 thin films have been obtained by solid state reaction, induced by annealing, between the constituents sequentially deposited in thin fi lm form. Multilayer Mo/S/Mo/.../Mo/S samples were annealed under sulph ur pressure at 853 K for 6-144 h. Then the samples were annealed for 3 h at 670 K under dynamic vacuum. At the end of the process the films are crystallized in the 2H-MoS2 structure. They are polycrystalline wi th the c axis of the crystallites preferentially oriented perpendicula rly to the plane of the substrate. The grain size stays small, always smaller than 10 nm. The micrograph of the cross section obtained by sc anning electron microscopy shows the good adhesion of the films to the substrate. Quantitative analysis-X-ray photoelectron spectroscopy and microprobe analysis-show that the films are stoichiometric and homoge neous. The optical band gap measured (1.2-1.35 eV) is in good accordan ce with that of MoS2 single crystal. However, the conductivity of the films is smaller, which can be understood by using a grain boundary mo del. The grain boundary model, which gives the best fit between experi mental and theoretical curves, is the one which proposed fluctuations of the barrier height at the grain boundaries.