Effects of Surface Modification of n-Cu₂O/p-Cu_xS 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-* Correspondance should be addressed to Ms.

Surface properties of sulphur based surface modified n-Cu2O thin films for enhanced liquefied petroleum gas sensing

“…Jayathilaka et al further demonstrated that (NH 4 ) 2 S vapor treatment of electrodeposited pCu 2 O films reduces resistivity by at least four orders of magnitude, while preserving structural integrity [27] and Jayathilaka et al also reported that (NH 4 ) 2 S vapor treatment of sulphided electrode posited nCu 2 O films improved photovoltaic efficiency from 0.11% to 0.54% [28]. Similar surface treated electrodeposited nCu 2 O thin films have also shown improved LP gas sensing ability in our previous work [29]. Here it was observed that both an optimal treatment of the films with (NH 4 ) 2 S vapor as well as having a minimum Cu 2 O thin film thickness was crit ical in introducing optimal response at a relatively lower oper ating temperature (~45 °C) in the presence of LP gas, while being able to recover response to ambient level in the absence of LP gas.…”