Resistive Gas Sensor Based on Mesoporous MoS\({}_{\mathbf{2}}\) Films

Abstract

Semiconducting mesoporous films with a large specific surface area are of interest for the development of gaseous medium sensors. In this study, such sensors were fabricated using a material synthesized on bulk substrates via a chemical reaction between gaseous H\({}_{2}\)S and Mo vapour obtained by thermal evaporation. X-ray photoelectron spectroscopy confirmed that the obtained layers consist of MoS\({}_{2}\). Scanning electron microscopy (SEM) revealed that the films deposited on different substrates are an array of crystallites with thicknesses of a few nanometers and transversal dimensions of several hundred nanometers. The MoS\({}_{2}\) crystallites are predominantly oriented perpendicular to the substrate surface and are spaced by distances of several tens of nanometers. The surface electrical resistance of the mesoporous MoS\({}_{2}\) layers was measured as a function of water vapour and ammonia vapour concentrations in the surrounding medium. It was discovered that the electrical resistance of MoS\({}_{2}\) decreases with increasing relative humidity and ammonia vapour concentration. The current response profile to changes in the concentration of these components in air exhibits an exponential time dependence with two characteristic time constants. For NH\({}_{3}\) vapour, the characteristic rise times are 0.9 and 17 s, while the fall times are 1.2 and 29 s. In the case of H\({}_{2}\)O vapour, the characteristic rise times are 4 and 45 s, and the fall times are 1.25 and 42 s. The mechanisms underlying the increase in electrical conductivity of MoS\({}_{2}\) films with increasing humidity and ammonia vapour concentration are discussed.