Structural phase transitions ofSi(111)−(3×3)R30°−Au: Phase transitions in domain-wall configurations

Abstract

Behaviors of domain walls on the Au-adsorbed $\mathrm{Si}(111)\ensuremath{-}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ and $6\ifmmode\times\else\texttimes\fi{}6$ surfaces have been investigated by spot-profile-analyzing low-energy electron diffraction and scanning tunneling microscopy. A continuous change from the $\ensuremath{\alpha}\ensuremath{-}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ pattern to the $\ensuremath{\beta}\ensuremath{-}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ pattern in diffraction at room temperature has been correlated to the increase in domain-wall density and their characteristic configuration change as a function of Au coverage $\ensuremath{\Theta}=0.76--0.96.$ It has been found that the sharp $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ spikes persists irrespective of the domain-wall morphology. The zigzagging domain walls at $\ensuremath{\Theta}=0.79$ at room temperature are found to transform to roundish ones at 753 K, and finally decompose completely to vanish around 893 K resulting in apparent large domains of $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ structure. Above $\ensuremath{\Theta}=0.96,$ the domain walls are proposed to arrange with a long-range order with $6\ifmmode\times\else\texttimes\fi{}6$ periodicity when the sample is annealed at around 600 K and slowly cooled. On the contrary, metastable amorphous arrangement in the domain walls with average separation of 6a (where a is the substrate lattice period) is formed after annealing followed by quench cooling, which corresponds to the $\ensuremath{\beta}\ensuremath{-}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ structure.