Journal of Crystal Growth, Vol.519, 46-53, 2019
Preferred orientations and microstructures of lanthanum phosphate films prepared via laser chemical vapor deposition
In this study, the vapor-phase growth of lanthanum phosphate (LaPO4 monazite) films having preferred orientations on polycrystalline alumina substrates was demonstrated via laser chemical vapor deposition using metal-organic precursors. The effects of the laser power densities and oxygen (O-2) partial pressure on the crystal orientations, microstructures, and textures of the LaPO4 films were investigated. Monoclinic LaPO4 monazite was grown at laser power densities of 62-96 W cm(-2) (deposition temperatures of 1075-1120 K) and an O-2 partial pressure of 257 Pa. The (11 (1) over bar)-oriented LaPO4 films with small pyramidal facets of less than 1 mu m in sizes and large platelets were grown at laser power densities lower than 85 W cm(-2). The preferred orientation of the monoclinic LaPO4 changed from (11 (1) over bar) to (10 (1) over bar) as the laser power density was increased to 95 W cm(-2), at which large platelets inclined from the substrate surface were formed. Deposition with a reduced O-2 partial pressure of 200 Pa induced the growth of highly (11 (1) over bar)-oriented LaPO4 films with small pyramidal facets, which comprised (001), (100), and (010) faceted planes. At a low O-2 partial pressure of 133 Pa, (100)-oriented LaPO4 films with platelet grains vertically grown from the substrate were formed. The deposition rates of the LaPO4 films were as high as 58.6 mu m h(-1).
Keywords:Chemical vapor deposition processes;Phosphates;Crystal morphology;Surface structure;Texture;Preferred orientation