Sol-gel growth and structural and optical investigation of manganese-oxide thin films: structural transformation by Zn doping

Using a sol-gel method, Mn2O3, Mn3O4, and MnO thin films have been grown from single precursor solution by varying the post-annealing condition. By annealing the spin-coated precursor films in the air, cubic Mn2O3 films could be prepared in the 600-900degreesC range, while cubic MnO films could only be prepared by annealing in vacuum. When O-2 gas is supplied during the vacuum annealing, the films show tetragonal Mn3O4 structure. Even under the air-annealing condition, Zn doping results in a structural transformation from cubic ZnxMn2-xO3 to tetragonal ZnxMn3-xO4. Optical properties of the Mn2O3 and Mn3O4 films have been investigated by spectroscopic ellipsometry in the 1.5-5 eV photon energy range. Optical absorption structures are observed in the measured optical constants of the oxide films and interpreted in terms of charge-transfer and crystal-field transitions involving the 3d electrons of Mn3+ ions located in the octahedral sites of the oxides. (C) 2004 Elsevier B.V. All rights reserved.