Surface morphology and structure of epitaxial yttrium on niobium buffer layers with different orientations

We report temperature- and substrate-dependent growth studies of epitaxial yttrium films. Using three different sapphire orientations and Nb buffers, Y was grown in the (0001), (<10(1)over bar 1>) and (<10(1)over bar 2>) crys tal orientations. Atomic force microscopy and x-ray measurements were used to study the topography and structural properties of the samples. Whereas t he Y(0001) films show a high crystallinity and a small surface roughness, Y (<10(1)over bar 1>) and Y(<10(1)over bar 2>) films have regularly structure d surfaces with a lower crystalline quality. Temperature and thickness stud ies show a strong dependence of the surface morphology on growth temperatur e and film thickness.