Detection of reducing gases by SnO2 thin films: an impedance spectroscopy study

Impedance spectroscopy studies were carried out on SnO2 thin films after exposure to H2S and NH3 gases in frequency range of 0.1 Hz to 1 MHz. The results showed that the impedance is mainly contributed by potential barrier at grain boundaries. Cole-cole plots showed a reduction in real part of impedance at low frequencies on exposure to both gases. Analysis of data revealed that this arises due to reduction in real part of grain boundary impedance and not due to negative capacitance (inductance) effect. The effect has been attributed to formation of ions on interaction of reducing gases and their drift to grain boundary region in the presence of applied field.