X-ray diffraction study of theSi(111)−3×3−Agsurface structure

Abstract

In-plane structures of a $\mathrm{Si}(111)\ensuremath{-}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}\mathrm{Ag}$ surface at both room temperature (RT) and 50 K are determined by x-ray diffraction. The honeycomb-chained triangle model with strongly anisotropic thermal vibrations of Ag atoms is preferred over the inequivalent triangle (IET) model at RT. On the other hand, at 50 K, the IET model better explains the experimental results. The phase transition temperature of ${T}_{\mathrm{C}}=150\ifmmode\pm\else\textpm\fi{}4\mathrm{K}$ is obtained from the temperature dependence of the fractional-order reflection intensity. The critical exponent $\ensuremath{\beta}$ is also found to be $0.27\ifmmode\pm\else\textpm\fi{}0.03.$