Formation of Cu-rich particles on the surface of YBa2Cu3O7−x thin film grown by in situ off-axis sputtering

Abstract

Experiments on the formation of Cu-rich particles on the surface of high quality YBa2Cu3O7−x thin films have been carried out systematically. The films on (001) LaAlO3 were grown using in situ off-axis sputtering. The particle formation observed in our experiment can be described using a classical thin film nucleation and growth model based on the concept of capture zones. In the temperature range from 670 to 750 °C, the nuclei density saturates at the early stage of deposition, and the formation of the Cu-rich particle belongs to the case of initial complete condensation. The saturation nuclei density of the particles N decreases as the temperature increases. It has been also found that N is deposition rate dependent and substrate dependent. Based on the experiments, the activation energy for surface diffusion of the Cu atoms that form the particles is estimated to be 1.5 eV in this temperature range.