Effects of sensing temperature on the gas sensing properties of copper phthalocyanine and copper tetra-tert-butyl phthalocyanine films

Copper phthalocyanine (CuPc) and copper tetra-tert-butyl phthalocyanine (CuTTBPc) were vacuum deposited onto alumina substrates. The surface morphology and crystalline structures of the films prepared by the two compounds were studied first. These films were then used for the experiments of NO₂ sensing. The effects of gas sensing temperature, as well as the NO₂ concentration, on the sensing properties were studied for both films. The experimental results show that both CuPc and CuTTBPc films exhibit fine-grain morphology and low crystallinity. Due to the tetra-tert-butyl (ttb) substitution on the periphery of phthalocyanine, CuTTBPc film has a larger lattice spacing, higher film resistance, and a higher recovery ratio in the NO₂ sensing experiments. On the contrary, the response rate and sensitivity of a CuPc film are superior to that of a CuTTBPc film. By varying the sensing temperature, it was found that the elevation of sensing temperature can improve the sensing response, recovery ratio, and sensitivity of the sensing films. At high concentrations of NO₂, a longer response time is required and the recovery ratio becomes smaller. In addition, the disadvantage caused by the elevation of NO₂ concentration can also be improved by using an elevated sensing temperature.