Effects of heat annealing on the film characteristics and gas sensing properties of substituted and un-substituted copper phthalocyanine films

Copper phthalocyanine and tetra-tert-butyl copper phthalocyanine were vacuu m deposited onto gold electrode. The effects of substrate materials (glass and gold) and post-deposition annealing on the film morphology and crystall ine structure were studied. The Aim characteristics were related to their s ensing propertied to NO2. The results show that the growth behaviors of CuP c on glass and gold surfaces were different in the early growth stage, but their surface morphologies were similar at the later stage. The CuPc films have structures of amorphous and beta form crystallite, respectively, on go ld and glass surfaces. After heat annealing, the grains grow larger and a b eta form structure were obtained on both surfaces. The films without heat t reatment show a short response time and higher sensitivity to NO2 due to th e higher surface area of their loosely packed fine-grain structure. But thi s characteristic also causes in-diffusion of NO2 deeply into the bulk cryst al and thus, the recovery process is slow and not completely reversible. Co mparing with CuPc films, ttb-CuPc films have smoother morphology both on gl ass and gold and thus, the gas sensitivity is much smaller due to their sma ller exposing area for the adsorption of NO2. The ttb-CuPc films have a dif fraction peak at D = 16.04 Angstrom after heat annealing. The substitution of tetra-tert-butyl group into the phthalocyanine ring leads to a larger la ttice spacing of crystal, which may be the reason for ttb-CuPc films to hav e faster recovery process. Because no apparent variation of the crystal mor phology was found on the heat-treated ttb-CuPc films, the gas sensing prope rties vary little due to the heat treatment, (C) 2001 Elsevier Science B.V. All rights reserved.