EFFECT OF AIR HUMIDITY ON THE ANALYTICAL SIGNAL OF A SEMICONDUCTOR ETHANOL SENSOR

Abstract

The effect of ambient relative humidity on the analytical characteristics of a semiconductor ethanol sensor based on a nanostructured SnO₂–ZnO sensing layer was investigated. Particular attention was paid to changes in baseline resistance, chemiresistive response, response and recovery times, and reproducibility under controlled humidity conditions. The SnO₂–ZnO nanocomposite was prepared by a hydrothermal method followed by thermal treatment at 500 °C. Its phase composition, morphology, elemental composition, and surface characteristics were evaluated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and low-temperature nitrogen adsorption. The material contained tetragonal SnO₂ and hexagonal ZnO phases with an average crystallite size of approximately 19–26 nm and a specific surface area of 45.7 m² g⁻¹. Gas-sensing measurements were performed at 250 °C using 100 ppm ethanol in air at relative humidity levels ranging from 10 to 80% RH. The sensor response, expressed as Ra/Rg, decreased from 30.6 at 10% RH to 16.7 at 80% RH. Simultaneously, baseline resistance decreased because of competitive adsorption of water molecules and formation of surface hydroxyl groups.