Understanding the ethanol and acetone sensing behaviour of CuO thin films through elements of gas diffusion theory

A general gas diffusion equation was used to predict the variation of sensor response with operating temperature and thickness for p-type CuO thin films for ethanol and acetone vapours. Assuming Langmuir-Hinshelwood mechanism and non-linear variation of sensor conductance with gas concentration, the response transients were modelled for a wide concentration range under isothermal conditions and fitted with extended Freundlich and Langmuir isotherms for ethanol and acetone respectively. Maximum responses of 144% and 168% were obtained for 300 ppm ethanol and acetone respectively at 300 degrees C for 240 nm CuO thin films. For CuO thin films of thickness 120-240 nm, response (5) versus temperature (T) exhibited a bell-shaped dependence with peak maxima of ethanol and acetone varying only slightly. Irreversible type gas response was obtained for a concentration range of 300-50 ppm for both ethanol and acetone vapours wherein response time systematically decreases with an increase in target gas concentration.

Automated summary

The response of p-type CuO thin films to ethanol and acetone vapours was investigated using a gas diffusion equation, Langmuir-Hinshelwood mechanism, and nonlinear sensor conductance variations with gas concentration. The maximum response rates were achieved at 300 degrees C for 240 nm CuO thin films, with a bell-shaped dependence of response on temperature for different film thicknesses. Additionally, irreversible gas responses were observed for both ethanol and acetone vapours within a certain concentration range.