Surface Development of (As₂S₃)_1–x (AgI)_x Thin Films for Gas Sensor Applications

Abstract

Thin (As₂S₃)_100−x(AgI)_x (x = 0–40) films were deposited by thermal vacuum evaporation from the respective bulk glasses; their structure and morphology before and after illumination with light have been studied by scanning electron microscopy (SEM). As-deposited films show fractional evaporation and surface inhomogeneities but after illumination they become uniform on the surface and in the depth as revealed by SEM top-view and cross-section images. Mechanical parameters like stress and microhardness of as-prepared and illuminated films were also investigated. The results from the stress measurements show variation in both the sign and the magnitude of the values with increasing AgI content and with time. Pure As₂S₃ layers possess a low tensile stress. The addition of AgI initially reduces the tensile stress and turns it to compressive for higher AgI concentrations. The exposure to light does not affect significantly the magnitude of the stress. The microhardness of the thin films decreases when the content of AgI increases. Furthermore, the microhardness in the surface region of the films is higher than in depth; it increases after the exposure to light.