Growth of Niobium Films at High Temperatures on Sapphire

Abstract

AbstractThe growth and microstructural evolution of Nb thin films on the basal plane of α-Al2O3were studied at different growth temperatures. The influence of island orientation, density, and misfit strain energy on the growth behavior of Nb films on (0001)α-Al2O3at high temperatures has been investigated. The films were grown by MBE at 900°C and 1100°C. At these temperatures the Nb grows in the Volmer-Weber growth mode on the basal plane.In-situreflection high energy electron diffraction (RHEED), Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) investigations revealed that in the initial growth stage, Nb nuclei with different epitaxial orientations were formed. This leads to different orientations of thicker Nb films at different growth temperatures. At a growth temperature of 900°C the Nb{111} planes are parallel to the sapphire basal plane whereas at 1100°C Nb grows with the {110) planes parallel to the basal plane of sapphire. The formation of two different epitaxial orientations of thick Nb films can only be explained by considering both the change in the total density of Nb islands with temperature and the influence of island size on their total energy.