Gas sensing properties of vacuum-deposited titanyl phthalocyanine film

The crystal structure and morphology of vacuum-deposited titanyl phthalocyanine (TiOPc) films can be manipulated by choosing deposition rate and substrate temperature. Five different phases, alpha, beta, gamma, m and amorphous, were found in these experiments. The alpha-phase TiOPc film was prepared at room temperature and slow deposition rate of 0.1-1 nm/s. The gamma-phase was prepared at substrate temperature of 170-230 degrees C and deposition rate of 0.1 or 1 nm/s. The m-phase was prepared at substrate temperature of 70-150 degrees C and deposition rate of 3 nm/s or at substrate temperature of 150-230 degrees C and deposition rate of 5 nm/s. The amorphous film was prepared at room temperature and deposition rate of 1-5 nm/s. The beta-phase was found in two distinct regions covering a wide range of substrate temperatures and deposition rates. The response characteristics of TiOPc films in NO2 gas sensing is also studied. The beta-phase film has the fastest response and slowest recovery, while the gamma-phase film has the slowest response and the fastest recovery. After heat treatment alpha-phase is transformed into beta-phase, and results in faster response and slower recovery. (C) 2000 Elsevier Science S.A. All rights reserved.