Experimental evidence for kinetically determined intermixed Volmer-Weber growth in thin-film deposition of Au on Ag(110)

Abstract

Au films, from the submonolayer range up to 11 ML, have been deposited in situ at 300 K. The geometrical structures of these films have been investigated combining full-hemispherical x-ray photoelectron diffraction, low-energy electron diffraction (LEED), low-energy ion-scattering spectroscopy, and scanning tunneling microscopy leading to an intermixed Volmer-Weber growth model. The results demonstrate that below 0.5 ML most Au atoms are buried within the second substrate layer, forming inverted Ag/Au areas on the surface. The ejected Ag atoms and vacancies created during the Au-Ag exchange nucleate into elongated two-dimensional Ag islands and vacancy clusters, respectively, quickly breaking up the surface into smaller terraces. Above about 0.5-ML coverage, the Au-Ag exchange mechanism continues to be active. In addition, due to the reduced mobility of Au atoms deposited on inverted Ag/Au areas, one-dimensional Au stripes as well as elongated three-dimensional (1\ifmmode\times\else\texttimes\fi{}3)-symmetric Au islands are observed already at submonolayer coverages on inverted Ag/Au areas. Only after the deposition of more than 8-ML Au is the Ag substrate completely covered, and missing-row reconstructed terraces extend over regions large enough to yield a well-defined 1\ifmmode\times\else\texttimes\fi{}2 LEED pattern. The growth model is compared to both, published thermodynamic equilibrium predictions and molecular-dynamics simulations, revealing that the Au/Ag(110) growth system is kinetically determined.