Gas sensing characteristics and transformation phenomena in Fe-O thin film

Fe-O thin films were prepared on Al₂O₃ substrates by PECVD (Plasma-Enhanced Chemical Vapor Deposition). The phase transformation of Fe-O thin films was mainly controlled by the substrate temperature and the reduction-oxidation process. The as deposited α-Fe₂O₃ phase was most stable at a deposition temperature around 120°C. The Fe₃O₄ phase was obtained by the reduction process of α-Fe₂O ₃ phase in H₂ ambience or in the deposition range from 200 to 300°C. The Fe₃O₄ phase could be transformed into a γ-Fe₂O₃ phase under controlled oxidation conditions at 280~300°C. The phase transformation phenomenon from Fe₃O₄ to γ-Fe ₂O₃ suggests oxidation of Fe²⁺ ions to Fe³⁺ in Fe₃O₄. The prepared α-Fe ₂O₃ and γ-Fe₂O₃ thin film showed excellent sensitivity to reducing gases of CO and C₄ H₁₀