Reconstruction and growth of Ag on the Si(111)- sqrt 3 x sqrt 3 -Ag surface at low temperature.

Abstract

Surface reconstruction structures and epitaxial growth of Ag on the Si(111)-\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 -Ag structure at low temperature (160-K order) have been investigated by reflection high-energy electron diffraction (RHEED). When Ag was deposited on a \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 -Ag surface at 160 K, reconstruction structures \ensuremath{\surd}21 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}21 and 6\ifmmode\times\else\texttimes\fi{}6 were observed in addition to the \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 structures. The \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 and \ensuremath{\surd}21 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}21 structures were observed for a thickness range between 0.19 and 2.6 ML, and the 6\ifmmode\times\else\texttimes\fi{}6 structures appeared and coexisted with the \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 and \ensuremath{\surd}21 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}21 structure between 0.7 and 1.7 ML. From RHEED patterns analysis, a 6\ifmmode\times\else\texttimes\fi{}6 model was proposed. Beyond Ag growth of 3 ML, three-dimensional (3D) Ag islands were formed at the temperature range from 160 K to RT. These results imply that the mean free path of Ag atoms on the \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 -Ag surface is large enough even at 160 K that 2D nuclei cannot be formed on the terrace in spite of decreasing substrate temperature.