Effects of substrate temperature on the film characteristics and gas-sensing properties of copper phthalocyanine films

Copper phthalocyanine thin films were prepared by vacuum deposition at various substrate temperatures onto glass and gold. The effects of substrate temperature and material on film morphology and crystalline structure were studied, and the film characteristics were related to their gas-sensing properties for NO₂. We find that CuPc films have fine-grain morphology and small degree of crystallization at low substrate temperature (T_d = 28 °C). When T_d is elevated to 100 °C, fiber-like morphology was observed on both substrates, with orientation mainly parallel to the substrate. At 150-200 °C, the fibers grow larger without significant change of orientation on glass, but whisker structures with less order were formed on gold. The fiber-like structure prepared at 100 °C has the highest electrical conductivity, which also implies that the stacking axis of the Pc macrocycle is the high conductivity direction. This characteristic also leads to quick response and higher sensitivity of this film to NO₂. The effects of substrate temperature on the film characteristics and gas-sensing properties are compared to the heat-annealing effects observed in our previous work.