Structural phase transitions of Si(111)-(root 3x root 3)R30 degrees-Au: Phase transitions in domain-wall configurations

摘要

Behaviors of domain walls on the Au-adsorbed Si(111)-root 3 x root 3 and 6 x 6 surfaces have been investigated by spot-profile-analyzing low-energy electron diffraction and scanning tunneling microscopy. A continuous change from the alpha-root 3 x root 3 pattern to the beta-root 3 x root 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 Theta = 0.76-0.96. It has been found that the sharp root 3 x root 3 spikes persists irrespective of the domain-wall morphology. The zigzagging domain walls at 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 root 3 x root 3 structure. Above Theta = 0.96, the domain walls are proposed to arrange with a long-range order with 6 x 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 beta-root 3 x root 3 structure. [References: 34]