Influence of the ion energy on the structure of Bi and Fe₂O₃ thin films

Abstract

Compounds containing bismuth, iron and oxygen (BFO) can result in materials with important magnetic and electrical properties for high-technology applications. We plan to prepare such compounds using the simultaneous ablation of bismuth and iron oxide targets. For that reason in the first part of this work we study the plasmas and the materials produced by ablation of bismuth or Fe₂O₃ targets, and then the two plasmas are combined in order to deposit the BFO compounds. The individual plasmas were characterized using a Langmuir probe, in order to measure the mean kinetic ion energy (E _p) and plasma density (N _p). Bismuth and magnetite-Fe₃O₄ thin films were obtained in high vacuum (2.7×10⁻⁴ Pa). Meanwhile for the deposition of α-Fe₂O₃ (hematite) or amorphous bismuth oxide thin films a reactive atmosphere (Ar/O₂=80/20) was used. All depositions were made at room temperature. The bismuth thin films crystallized in the rhombohedral metallic system with preferential orientations that depended on the Bi-ion energy used. Bismuth oxide phases were only obtained after annealing of the Bi thin films at different temperatures. Iron oxide thin films reproducing the target stoichiometry were obtained at a certain value of iron-ion energy. Preliminary structural results of the BFO thin films obtained by the combination of the individual plasmas are presented.