Crystallization and atomic scale structure of sputtered amorphous Fe-B films

Abstract

We have used electron microscopy, electron diffraction and structure modelling techniques to investigate crystallization behavior and structure of sputtered Fe 100-x B x films (X = 16. - 24 at.%) of 100 A - 300 A thickness. Electron micrographs of most as deposited films showed a network of voids and low density regions. Areas of crystalline iron oxides were present on surfaces of most films, monoclinic e-Fe 2 O 3 as thin platelets ∼ 4000 A in diameter and cubic Fe 3 O 4 with 100A-200A granular morphology. Crystallization phenomena depended on heating rate and on whether oxide was present. Diffraction patterns and radial distribution functions of as-deposited films showed little dependence on B-content and were similar to those reported for liquid quenched Fe-B alloys. The average nearest neighbor distance for X = 24, at.% was 2.574A and increased by only 1.% with decreasing B content. The average nearest neighbor coordination number varied between 11.2 and 11.5. Binary dense random packing models for Fe-B alloys were generated using sphere diameters of 2.55A and 1.70A for Fe and B. No B-B nearest neighbor pairs were allowed, of the Fe configurations was controlled, and structures were relaxed with Lennard-Jones potentials. Models reproduced peak positions and relative peak heights of experimentally observed diffraction patterns and distribution functions only when different levels of tetrahedron perfection were used for model structures of different B content, indicating that the simple binary dense random packing algorithm does not adequately simulate effects of B on arrangements of Fe atoms in the amorphous alloys. Agreement achieved between experimental and model results became poorer with decreasing B content. Coordination numbers of the model structures were about 20% smaller than those obtained experimentally.