STM observation of Si(111)-α-√3x√3-Sn at low temperature -: art. no. 201308

We carefully investigated the alpha-root3 x root3 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 3x3 periodicity was observed in RHEED at 120 K, STM showed a long-range ordered 3 x 3 phase only, without 3x3 domains, over the whole temperature range investigated. The root3xroot3 streaks were found to originate from local 3x3 modulations around defects. The present result indicates that there is no phase transition from the root3 x root3 to 3x3 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.