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

Abstract

The surface of electrodeposited n-Cu2O thin films were modified by sulphidation using aqueous Na2S followed by (NH4)2S vapor treatment. Compared to untreated thin films, the resultant films showed an enhanced response to liquefied petroleum (LP) gas at a relatively low operating temperature (~45 °C), one of the lowest reported for a cuprous oxide based material. X-ray diffraction spectra confirmed that the films were of single phase. Observed by contact angle measurements and energy dispersive x-ray spectroscopy, (NH4)2S vapor treatment converted the highly wetting sulphided films containing both Na and S to a partially wetting surface by forming sulphur on the film surface. This modification on the film surface, enabled the sensor response to recover to an ambient level after stoppage of LP gas flow, which sulphidation alone was inapt. Scanning electron micrographs complemented roughness measurements made by atomic force microscopy and showed a transformation of polycrystalline morphology of bare n-Cu2O film to one having highly porous structures, which thereby increased the surface area of the surface modified films. Therefore, this work demonstrates that the surface of the n-type Cu2O thin films modified by (NH4)2S vapor treatment and sulphidation can alter the surface wetting nature and increase the surface area to enhance LP gas sensing at a relatively low temperature.

Performances of Nano-Structured Cu2O Thin Films Electrochemically Deposited on ITO Substrates in Lactate Bath as Liquid Petroleum Gas Sensors

“…4 In polycrystalline sensing materials, electronic conduction happens via grain-to-grain contacts depending on the potential barrier of adjacent grains called the Schottky barrier. 5 Based on the type of conductivity of the SMO surface layer, carrier concentration gets increased or decreased. A potential barrier induced by the decrease in major carrier (electron) concentration increases n-type SMO resistance.…”

“…This decreases the film sensor resistance. 5 Figure 1 schematically shows this LPG sensing mechanism of p-Cu 2 O thin films deposited on ITO substrates.…”

Substrate Effect on Liquid Petroleum Gas Sensors of Cuprous Oxide Thin Films Electrodeposited in Acetate Bath

“…have been investigated for different target gases with varying degrees of success. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, most of the metal-oxides gas sensors perform at high temperatures, often limits the use of this type of detection.…”

“…By changing deposition parameters or by introducing doping materials, it has the ability to vary the conductivity between n and ptype with high stability in air. 12 The substrate's influence in electrodeposition is one of the crucial parameters, effected on quality of surface morphology, roughness, and wettability of Cu 2 O films. 29 It goes in both ways, with the working electrode and counter electrode.…”

“…On the surface of the grains, 12 oxygen molecules in air are adsorbed by the Cu 2 O surface and remove the surface electrons from the conduction band of Cu 2 O and trap these electrons at the surface as ions, to form O 2 , O − and O 2− at the surface at relevant temperatures. 30…”