Significant surface flattening effect by Au addition for Cu growth on Cu₃Au(001)

To prepare a flat surface of Cu film on Cu₃Au(001), we utilized the effect of Au addition to Cu, and investigated the dependence of the growth mode on the amount of Au added. We grew Cu-x%Au (x = 0-20) films on Cu ₃Au(001) underlayers by co-deposition and observed the surface morphology by scanning tunneling microscopy. For Cu film without Au addition, three-dimensional islands were observed on the surface while flat two-dimensional surfaces were observed for Cu film with only 2.5%Au addition. This difference in the growth mode was found to be due to surface segregation of Au revealed by in situ Auger electron spectroscopy. It was considered that the Au atoms acted like a surfactant and avoided three-dimensional island growth by suppression of the accumulation of epitaxial strain in Cu-x%Au films. However, the terrace size decreased with x. This decrease was thought to be due to an increase in an effective Ehrlich-Schwoebel barrier. The surface flattening effect by addition of another element would be obtained in other systems as well by employing a suitable element.