Heterocontact type CuO-modified SnO 2 sensor for the detection of a ppm level H 2S gas at room temperature

Abstract

Thick films of SnO 2 were prepared by screen printing technique. The films were modified with Cu 2+ by dipping them into an aqueous solution of copper chloride for different intervals of time and fired at 550 °C for 24 h. The copper chloride would be transformed upon firing into copper oxide. The p-type CuO grains around n-type SnO 2 grains would form n-SnO 2/p-CuO heterojunctions. Upon exposure to H 2S gas, the barrier height of n-SnO 2/p-CuO heterojunctions decreases markedly due to the chemical transformation of p-CuO into well conducting Cu 2S, leading to a drastic change in resistance. These sensors were observed to be operated at room temperature. An exceptional sensitivity was found to low concentrations (below threshold limit value = 10 ppm) of H 2S gas at room temperature, and no cross sensitivity was observed even to high concentrations of other hazardous and polluting gases. The efforts have, therefore, been made to develop the heterocontact type gas sensor based on tin oxide surface-modified with cupric oxide. The effects of microstructure and surfactant concentration on the sensitivity, selectivity, response and recovery of the sensor in the presence of H 2S gas were studied and discussed.