TEM and SEM studies of microstructural transformations of thin iron films during annealing

High-temperature induced transformations of the bulk structure as well as the surface and bulk morphology of thin polycrystalline iron films have been investigated using a combination of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The polycrystalline Fe films were evaporated onto a quartz substrate at 78 K under UHV conditions and then annealed in situ within a temperature range 330–1000 K. The morphology of both the surface and bulk Fe films have been observed ex situ after successive annealing steps of the Fe film using SEM and cross-sectional TEM analysis, respectively. An anisotropic polycrystalline bulk morphology accompanied by a fine-grained surface and the formation of microvoids was observed after heating the Fe film at 330 K. The iron films annealed at higher temperatures, exhibit large grain size surface morphology. Polycrystalline Fe film transformation occurred at an annealing temperature of 700–1000 K, resulting in the formation of a columnar microstructure of the bulk phase. The crystallites formed as a result of annealing at 1000 K revealed a monocrystalline structure characterised by low-index Fe bcc diffraction patterns.