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, α, β, γ, m and amorphous, were found in these experiments. The α-phase TiOPc film was prepared at room temperature and slow deposition rate of 0.1–1 nm/s. The γ-phase was prepared at substrate temperature of 170–230°C and deposition rate of 0.1 or 1 nm/s. The m-phase was prepared at substrate temperature of 70–150°C and deposition rate of 3 nm/s or at substrate temperature of 150–230°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 β-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 β-phase film has the fastest response and slowest recovery, while the γ-phase film has the slowest response and the fastest recovery. After heat treatment α-phase is transformed into β-phase, and results in faster response and slower recovery.