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

Fe-O thin films were prepared on Al/sub 2/O/sub 3/ 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 /spl alpha/-Fe/sub 2/O/sub 3/ phase was most stable at a deposition temperature around 120/spl deg/C. The Fe/sub 3/O/sub 4/ phase was obtained by the reduction process of /spl alpha/-Fe/sub 2/O/sub 3/ phase in H/sub 2/ ambience or in the deposition range from 200 to 300/spl deg/C. The Fe/sub 3/O/sub 4/ phase could be transformed into a /spl gamma/-Fe/sub 2/O/sub 3/ phase under controlled oxidation conditions at 280/spl sim/300/spl deg/C. The phase transformation phenomenon from Fe/sub 3/O/sub 4/ to /spl gamma/-Fe/sub 2/O/sub 3/ suggests oxidation of Fe/sup 2+/ ions to Fe/sup 3+/ in Fe/sub 3/O/sub 4/. The prepared /spl alpha/-Fe/sub 2/O/sub 3/ and /spl gamma/-Fe/sub 2/O/sub 3/ thin film showed excellent sensitivity to reducing gases of CO and C/sub 4/H/sub 10/.