Synthesis of CuO thin films by a direct current reactive sputtering process for CO gas sensing application
Debashrita Mahana, Amit Kumar Mauraya, Somu Kumaragurubaran, Preetam Singh, M. Senthil Kumar
Abstract
Abstract A direct current magnetron reactive sputtering, one of the well-known physical vapour deposition (PVD) techniques, was employed for the preparation of CuO thin films at room temperature for CO gas sensing application. The effect of the O 2 gas flow ratio on the phase formation of copper oxide was studied by varying the O 2 flow rate in the total flow of Ar/O 2 gas mixture. Cu 2 O phase was found to form at a low O 2 flow ratio of 10% and gradually converted into stable CuO phase with an increase in O 2 flow ratio through the intermediate phase of Cu 4 O 3 . The films exhibited a granular morphology, and the average grain size increased with an increase in the O 2 partial flow. Single-phase CuO thin film has been obtained with 40% of O 2 gas flow ratio. The evolution of the copper oxide phases with increasing O 2 partial flow was also confirmed using the Cu 2p and O 1s core-levels of X-ray photoelectron spectroscopy. The CO gas sensing characteristics of the CuO thin film were examined by varying the operating temperature in the range of 200 °C–400 °C. An optimized CO sensing response of 127% has been obtained at 375 °C towards 91 ppm concentration with a response/recovery time of 161 s/99 s.