Effects of substrate temperature on the ®lm characteristics and gas-sensing properties of copper phthalocyanine ®lms

Copper phthalocyanine thin ®lms were prepared by vacuum deposition at various substrate temperatures onto glass and gold. The effects of substrate temperature and material on ®lm morphology and crystalline structure were studied, and the ®lm characteristics were related to their gas-sensing properties for NO2. We ®nd that CuPc ®lms have ®ne-grain morphology and small degree of crystallization at low substrate temperature (Td ˆ 28 C). When Td is elevated to 1008C, ®ber-like morphology was observed on both substrates, with orientation mainly parallel to the substrate. At 150±2008C, the ®bers grow larger without signi®cant change of orientation on glass, but whisker structures with less order were formed on gold. The ®ber-like structure prepared at 1008C 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 ®lm to NO2. The effects of substrate temperature on the ®lm characteristics and gas-sensing properties are compared to the heat-annealing effects observed in our previous work. # 2001 Elsevier Science B.V. All rights reserved