Morphological transformations in the crystallization of TeSe-halide thin films

Abstract

Amorphous Te3Se4X (X = Br,I) thin films were prepared by RF sputter deposition where the halide is used to stabilize the amorphous structure. Crystallization in the films was induced by heating with pulsed laser irradiation, with an electron beam, and in a furnace. Crystallization was achieved when the halide was depleted which became more difficult the higher its mass and concentration. As a consequence, crystallization was highly anisotropic and confined to a thin surface layer with a lateral size to thickness ratio of up to 104. We observed various stages of the process. At low temperature, a spherulitic-type growth produced a low-dimensional branching morphology by non diffusive processes such as rotation. Increasing temperature favored the formation of higher dimensions with patterns typical for aggregation processes. At the highest temperatures material flow enabled the formation of three-dimensional structures. In case of the films with Iodine, facetted single crystals grew out of the surface to sizes many times larger than the original film thickness.