Synthesis of p-type semiconducting cupric oxide thin films and their application to hydrogen detection

Nanostructured CuO thin films are synthesized by deposition and thermal oxidation of Cu on SiO2 substrates. The effects of oxidation temperatures on the morphologies and crystallinity of the CuO thin films are investigated by SEM, XRD, and XPS. The electrical and hydrogen sensing properties of CuO are studied by electrical resistance measurements. In addition, the effects of carrier gases on the gas response of CuO are investigated. The results showed that Cu was oxidized into monoclinic cupric oxide in the investigated temperature range from 300 to 800 °C. The p-type semiconducting CuO thin film showed increases in electrical resistance upon exposure to hydrogen. The CuO thin film oxidized at 400 °C showed the highest response as compared to others, and it was 3.72 for 6% H2 at an operating temperature of 250 °C. The carrier gases played very important roles in the hydrogen sensing by CuO. That is, the sensor showed good response-and-recovery with a carrier gas of air but not with nitrogen.