Controlling the Bi content, phase formation, and epitaxial nature of BiMnO_3 thin films fabricated using conventional pulsed laser deposition, hybrid pulsed laser deposition, and solid state epitaxy

摘要

Loss of Bi during thin film growth of bismuth-based compounds is a major challenge to obtaining stoichiometric films. Three approaches to BiMnO_3 film growth were investigated to understand and to control the loss of Bi. First, a systematic study was carried out using a conventional pulsed laser deposition (PLD) approach, using targets of different Bi compositions. Conventional PLD was plagued with high re-evaporation and slow reaction kinetics, which led to Bi-deficient multiphase films. A phenomenological model was developed to describe Bi loss in conventional PLD and demonstrated that the film composition was dependent on both the rate of reaction between the constituent oxides and the rate of desorption of bismuth species from the substrate surface. To overcome the problems of conventional PLD, two different growth approaches were developed: a solid state epitaxy approach, in which stoichiometric but amorphous films deposited at low temperatures (T ＜ 500 ℃) were annealed to generate crystalline films, and a hybrid PLD approach, in which conventional PLD is supplemented with an effusion cell to provide a background flux of Bi. Both of these approaches produced stoichiometric, epitaxial films of BiMnO_3 in a straightforward fashion since the local composition was maintained to the overall stoichiometry during crystallization.