Thermal diffusion of Co into atomically flat ZnO(000-1) surfaces investigated by scanning probe microscopies and low energy electron diffraction

Abstract

In this study, we established a cleaning procedure to obtain atomically flat (000-1) surfaces from pressurized melt grown ZnO. Ex situ chemical cleaning removes fluid layer and trapped contaminants from the surface. This was followed by cycles of sputtering and annealing in ultrahigh vacuum. It is critical that the ion energy be high enough to produce small and highly mobile molecular fragments. On the other hand, annealing must be done at moderate temperatures to avoid segregation of potassium to the surface. Secondly, the interaction of Co thin films on atomically flat ZnO(000-1) has been investigated by low energy electron diffraction, scanning tunneling microscopy, and Auger electron spectroscopy. A high density of islands nucleates at the earliest stages of the growth and a subsequent Volmer-Weber growth of these islands is observed. Upon annealing at 550°C, an atomically flat surface (Zn,Co)O(000-1) is restored due to the diffusion of the Co into the semiconductor.