STM observation of Si(111)-α−3×3-Sn at low temperature

Abstract

We carefully investigated the $\ensuremath{\alpha}\ensuremath{-}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ phase on Si(111) surface covered by 1/3 monolayer of Sn using scanning tunneling microscopy (STM) at room temperature (RT), 70 K, and 6 K, with reflection high-energy electron diffraction (RHEED) at RT and 120 K. While weak streaks of the $3\ifmmode\times\else\texttimes\fi{}3$ periodicity was observed in RHEED at 120 K, STM showed a long-range ordered $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ phase only, without $3\ifmmode\times\else\texttimes\fi{}3$ domains, over the whole temperature range investigated. The $3\ifmmode\times\else\texttimes\fi{}3$ streaks were found to originate from local $3\ifmmode\times\else\texttimes\fi{}3$ modulations around defects. The present result indicates that there is no phase transition from the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ to $3\ifmmode\times\else\texttimes\fi{}3$ on cooling down to 6 K, which contradicts to a prediction from core-level photoemission study and challenges the thermal fluctuation picture for the RT phase.