Hydrothermal Growth of Semiconducting Zinc Oxide for Ethanol Sensor Application

Ethanol is a volatile organic compound widely used in various industries. It is commonly found as a colorless, liquid substance. Ethanol has a low flash point of 14–16 °C which brings around a fire hazard. It also poses health risks such as skin, eyes, and respiratory irritation, nausea, vomiting, and intoxication. Ethanol gas sensors have been utilized to mitigate these risks and hazards. The development of ethanol gas sensors has been concentrated on improving sensitivity and selectivity. Zinc Oxide (ZnO) has been one of the most promising active materials for ethanol sensors due to their strong surface interaction. This work aims to fabricate an ethanol sensor based on hydrothermally grown ZnO. Hydrothermal growths were performed using zinc acetate dihydrate (ZAD) and hexamethylenetetramine (HMTA) for 6 hours at 90°C. Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</inf>0<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (001) was employed as the substrate. The silver paste was applied and annealed on the grown ZnO to fabricate a conductivity-based ethanol sensor. The Figaro SR-3 system was utilized to conduct gas sensing tests. The effects of the precursor concentration ratio and its total concentration on the morphology of the grown ZnO were investigated. A shift in growth mode was observed by SEM. FTIR and XRD were used to confirm the formation of hexagonal ZnO on sapphire. The sample grown at a total concentration of 0.3 M, ZAD: HMTA concentration ratios of 3: 1 showed a coalesced island morphology. The gas sensing test indicated a positive correlation between conductivity and ethanol concentration.