Phase transformation phenomena from alpha type to gamma type one of Fe2O3 thin film deposited by PECVD

Fe-O thin films were prepared on an Al2O3 substrate by a plasma-enhanced ch emical vapor deposition (PECVD) technique. The phase transformation of Fe-O thin films was mainly controlled by the substrate temperature and the redu ction-oxidation process. The as deposited alpha-Fe2O3 phase was most stable at a deposition temperature of around 120 degrees C. The Fe3O4 phase was o btained by the reduction process of cu Fe2O3 phase in a H-2 ambiance or in the deposition range from 150-350 degrees C. The Fe3O4 phase could be trans formed into a gamma-Fe2O3 phase under controlled oxidation conditions at 28 0-300 degrees C. The phase transformation phenomenon from Fe3O4 to gamma-Fe 2O3 suggests oxidation of the Fe2+ ions to Fe3+ in Fe3O4, Fe3O4 and gamma-F e3O4 phases had the same spinal structure and were coexisted. (C) 1999 Else vier Science S.A. All rights reserved.