Synthesis and Electrophysical Properties of Copper Oxide Films for Gas Sensors

Abstract

Thin films of copper oxide were fabricated by sol-gel method. For the preparation of CuO thin films, a sol-gel method based on copper acetate (Cu(CH3COO)2•H2O), isopropyl alcohol (C3H8O) and diethylamine ((CH3CH2 )2NH) was used. The film was applied by centrifugation at a speed of 1500 rpm for 75 seconds. The films were applied in 2, 4, 8 layers with drying between layers for 10 minutes at 250 °C. The thermal probe method was used to determine the p-type of conductivity of the films. The films were annealed at temperatures of 300, 400, 500, 600 °C. By method of X-ray phase analysis, it was found that the main phase in the films is CuO. On films without additional annealing, a single reflex corresponding to CuO (110) 31.7° is observed. After annealing the films at 400 and 500 °C, crystallization occurs and reflexes manifest: (110) by 31.7°, (–111) by 35.5°, (111) by 38.8°, corresponding to CuO. It was found that with an increase in the annealing temperature, the grain size decreases, which indicates the crystallization of the film and contributes to the improvement of gas-sensitive properties. The transparency of the films in the visible range has values T = 30—67 %. The width of the gap is estimated to be 1.9 eV. According to AFM data, the films have a fine-grained structure and with an increase in the annealing temperature from 300 °C to 400 °C, the size of the roughness decreases. The films have high gas sensitivity values (resistance change of 30 %) and low temperature values of maximum gas sensitivity (180—190) °C to ethanol, acetone, ammonia vapors in the air.