Effects of Surface Modification of n-Cu2O/p-CuxS Thin Film Heterostructures for Enhanced Liquefied Petroleum Gas Sensing Properties

Abstract

We report a novel mechanism to effectively detect LP gas based on surface modification through sulphidation followed by passivation of electrodeposited n-type cuprous oxide (Cu2O), forming a thin film n Cu2O/p-CuxS semiconducting heterostructure. Electrochemically deposited n-type cuprous oxide (n-Cu2O) thin films on Ti substrates in acetate bath were sulphided using Na2S to fabricate n-Cu2O/p CuxS heterostructures. Subsequent passivation of these thin film structures using (NH4)2S vapor enhanced the sensitivity (fractional change in thin film resistance) when exposed to liquefied petroleum (LP) gas. Scanning electron micrographs (SEM) confirmed that typical unsulphided n-type Cu2O thin films exhibit polycrystalline surface morphology, while SEM of both sulphided and passivated thin films revealed micro/nano-crystalline surface morphological features with porous structures. As expected, the thin film structures obtained through sulphidation followed by passivation of n-type Cu2O films decreased the resistance (100 kΩ) in comparison to the resistance (1 MΩ) of the unsulphided n-type Cu2O thin films. Upon exposure to LP gas, the resistance of these thin film structures increased while, sensitivity to LP gas depended on the sensing temperature. Exposure of thin film structures fabricated by electrodepositing n-type Cu2O thin films for 45 min, sulphided and passivated for 5 s and maintained at a sensing temperature of 45 ºC to LP gas with a flow rate of 2.5 ml/min recorded the highest sensitivity of 48 %.