Temperature-dependent coverage of the √3 × √3<i>R</i>30° structure of Ag/Si(111)

Abstract

The coverage \ensuremath{\Theta} of the \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 R30\ifmmode^\circ\else\textdegree\fi{} Ag/Si(111) interface has been measured by micro-Auger electron spectroscopy. With a dose of 5 monolayer (ML), we find \ensuremath{\Theta}\ensuremath{\approxeq}1 ML for deposition temperature ${\mathit{T}}_{\mathit{d}}$\ensuremath{\ge}700 K and \ensuremath{\Theta}\ensuremath{\approxeq}2/3 ML for ${\mathit{T}}_{\mathit{d}}$\ensuremath{\le}620 K. Much smaller changes (\ensuremath{\approxeq}0.05 ML) were observed during annealing. These effects are explained by a simple kinetic model in which \ensuremath{\sim}2 Ag atoms are readily incorporated into the structure, but a third atom must overcome an activation energy ${\mathit{E}}_{\mathit{r}}$ to become embedded, with a gain in energy ${\mathit{E}}_{\mathit{e}}$. We find ${\mathit{E}}_{\mathit{r}}$=1.90, ${\mathit{E}}_{\mathit{e}}$=0.60, and ${\mathit{E}}_{\mathit{a}}$=2.45, all \ifmmode\pm\else\textpm\fi{}0.05 eV, where ${\mathit{E}}_{\mathit{a}}$ is the adatom adsorption energy. Possible structural and microstructural models and the interpretation of the energy ${\mathit{E}}_{\mathit{r}}$ are discussed.