M.E. Bijlsma

Surface roughness and height-height correlations dependence on thickness of YBaCuO thin films

For high Tc superconducting multilayer applications, smooth interfaces between the individual layers are required. However, in general, e.g., YBaCuO grows in a 3D screw-dislocation or island nucleation growth mode, introducing a surface roughness. In this contribution we study the surface layer roughness as a function of different deposition techniques as well as deposition parameters. Special attention will be paid to the increase in film roughness with increasing film thickness. For these studies we used scanning probe microscopy. From these experiments, we obtained an island density decreasing with a square root dependence on the film thickness. Furthermore, height-height correlations indicate that the film growth can be described by a ballistic growth process, with very limited effective surface diffusion. The correlation lengths ? are on the order of the island size, inferring that the island size forms the mean diffusion barrier. This results in a representation of non-correlated islands, which can be considered as autonomous systems.

In-situ growth studies of sputtered ybco thin films by spectroscopic ellipsometry

Using spectroscopic ellipsometry we studied in-situ the growth of off-axis sputtered YBa2Cu3O6+x thin films on (001) SrTiO3 as a function of the deposition parameters. Especially in the very first growth stage ( 106A cm?2 @ 77 K) is smooth and homogeneous, except for the first unit cell layer (initial stage regime). The smoothness of the response is indicative for a step-mode like growth mechanism. In contrast, the initial stage regime is governed by a 2D nucleation mechanism. This behaviour changes when the deposition temperature is lowered. Due to increased disorder, the initial stage regime is extended to larger thicknesses and a true 2D growth mode is no longer apparent. Similar behaviour is observed with increasing oxygen partial pressure, where the optical response is shifted from a step-flow mode like mechanism to an island-growth mode.