Effects of substrate shape, curvature and roughness on thin heteroepitaxial films of Pt on Au(1Â 1Â 1)

The growth of thin (1-10 nm) films of Pt on Au(1 1 1) was studied in order to understand and clarify differences in growth mode observed in ultra-high vacuum (UHV) studies and in electrochemical deposition studies. It was found that on flat Au(1 1 1), Pt grows in a layer-by-layer growth mode, but if the gold substrate is exposed to an acidic environment prior to Pt deposition, then the substrate becomes nanoscopically rough (islanded) and Pt growth follows a pseudo-Stranski-Krastanov (SK) growth mode in which an initially thin wetting layer becomes rougher with increasing film thickness. An analysis of curvature effects on epitaxial growth mode shows that thermodynamic curvature effects involving surface stress are negligible for the Pt/Au(1 1 1) system. Rather, the apparent SK growth is linked to kinetic effects associated with inhomogeneous in-plane elastic relaxation of Pt films on rough surfaces that drive Pt atoms from pits to the tops of islands in the early stages of growth. Implications for the control of epitaxial film roughness are discussed.