Morphology and texture evolution of nanostructuredCaF2 films on amorphous substrates under oblique incidence flux

Abstract

The morphology and biaxial texture of vacuum evaporatedCaF2 films on amorphous substrates as a function of vapour incident angle, substratetemperature and film thickness were investigated by scanning electron microscopy,x-ray pole figure and reflection high energy electron diffraction surface pole figureanalyses. Results show that an anomalous [220] out-of-plane texture was preferred inCaF2 films deposited onSi substrates at < 200 °C with normal vapour incidence. With an increase of the vapour incident angle, theout-of-plane orientation changed from [220] to [111] at a substrate temperature of100 °C. Infilms deposited with normal vapour incidence, the out-of-plane orientation changed from [220] at100 °C to [111]at 400 °C. In films deposited with an oblique vapour incidence at100 °C, the texture changed from random at small thickness (5 nm) to biaxial at larger thickness(20 nm or more). Using first principles density functional theory calculation, it was shownthat [220] texture formation is a consequence of energetically favourable adsorption ofCaF2 moleculesonto the CaF2(110) facet.