thin films prepared by solid state reaction (induced by annealing) between the constituents in thin film form

Abstract

thin films were obtained by solid state reaction (induced by annealing under S pressure) between the W and S constituents in thin film form. The tungsten layers were deposited by RF sputtering, while S layers were evaporated. The thickness of the layers varied between 50 and 100 nm. The films have been investigated using x-ray photoelectron spectroscopy, scanning electron microscopy, x-ray diffraction, optical absorption and conductivity measurements. The effects of annealing conditions (duration and temperature) on the crystallization and composition of the films have been investigated. The films were crystallized in the hexagonal structure. To complete the reaction between W and S, annealing under S pressure at a temperature of at least 820 K for 24 h is required. Under these conditions the films were nearly stoichiometric. The best films present a c-axis length of 1.2500 nm and an a-axis length of 0.3185 nm. All the films were found to be preferentially oriented with the c axis perpendicular to the plane of the substrate. The degree of preferential orientation was found to increase slightly with increasing annealing time and/or temperature. The nearly stoichiometric films present good optical properties, similar to those of single crystals. The conductivity of the films depends strongly on the annealing conditions, i.e. on their composition and on their crystallization state.