Texture Evolution of Lithium Fluoride Thin Films by Nucleation

Abstract

We have used a transmission electron microscope (TEM)-based method to extract grain size information for <111> surface normal grains in lithium fluoride (LiF) thin films, and applied this to analyze textures as a function of substrate temperature and annealing time. The size distributions of grains diffracting into the (111)+(200) and (220) rings were measured separately using dark field (DF) TEM images. From these data, we deduce the size distribution of <111> surface normal grains based on the assumption that only 3 principal textures (100), (110) and (111) exist in films. The (111) texture formation was also observed by x-ray diffraction (XRD). For all deposition and annealing conditions, the grain size data can be matched to lognormal distributions within an acceptable error, but at longer annealing times the distribution becomes bimodal. A novel feature of the LiF films is that the (111) texture component strengthens with annealing and substrate temperature, through the nucleation of new grains rather than the growth of existing ones.