$\mathrm{Si}\left(111\right)\text{−}\alpha \text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ phase modified by In adsorption: Stabilization of a homogeneous surface by stress relief

Structural transformations on the $\mathrm{Si}\left(111\right)\text{−}\alpha \text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ surface induced by In adsorption have been studied using scanning tunneling microscopy and first-principles total-energy calculations. It has been found that In adsorption results in the transformation of the $\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ phase to the $\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ phase. At room temperature, the transformation is limited by the interior of the original $\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ domains and does not affect the domain-wall structure. Upon annealing at $600°\mathrm{C}$, the domain walls are eliminated and highly ordered almost defect-free homogeneous $\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ surface develops. The $\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ surface phase contains 1 monolayer (ML) of Au, 1 ML of Si and about 0.15 ML of In. Plausible mechanism of stabilization of the domain-wall-free $\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ surface is the stress relief caused by In adsorption.

Figure 1

STM images of the $\mathrm{Si}\left(111\right)\text{−}\alpha \text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ surface. (a) $50\times 40{\mathrm{nm}}^2$ empty-state $(+2.5\mathrm{V})$ image; (b) $16\times 13{\mathrm{nm}}^2$ empty-state $(+0.8\mathrm{V})$ image; (c) $16\times 13{\mathrm{nm}}^2$ filled-state $(-0.8\mathrm{V})$ image. Images in (b) and (c) were taken from the different surface regions. Unit cells of the $\sqrt{3}\times \sqrt{3}$ commensurate domains and of the $2\times \sqrt{3}$ domain walls are outlined.

Figure 2

STM images of the $\mathrm{Si}\left(111\right)\text{−}\alpha \text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ surface after RT deposition of 0.1 ML of In. (a) $50\times 40{\mathrm{nm}}^2$ empty-state $(+0.7\mathrm{V})$ image; (b) $16\times 13{\mathrm{nm}}^2$ empty-state $(+0.8\mathrm{V})$ image; and (c) $16\times 13{\mathrm{nm}}^2$ filled-state $(-0.8\mathrm{V})$ image. Images in (b) and (c) were taken from the same surface area. The $\sqrt{3}\times \sqrt{3}$ and $2\times \sqrt{3}\text{unit}$ cells are outlined.

Figure 3

Large-scale $(100\times 100{\mathrm{nm}}^2)$ empty-state $(+2.3\mathrm{V})$ STM image of the $\mathrm{Si}\left(111\right)\text{−}\alpha \text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ surface after RT deposition of 0.2 ML of In.

Figure 4

$50\times 40{\mathrm{nm}}^2$ filled-state $(-2.0\mathrm{V})$ STM images of the $\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ prepared by RT deposition of (a) 0.1, (b) 0.2, and (c) 0.4 ML of In, followed by annealing at $600°\mathrm{C}$ for $15\mathrm{s}$.

Figure 5

Large-scale $(400\times 400{\mathrm{nm}}^2)$ filled-state $(-2.3\mathrm{V})$ STM image of the $\mathrm{Si}\left(111\right)\text{−}\alpha \text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Au}$ surface after RT deposition of 0.5 ML of In followed by annealing at $600°\mathrm{C}$.

Figure 6

High-resolution $(12\times 12{\mathrm{nm}}^2)$ dual-polarity $(\pm 0.7\mathrm{V})$ STM image of the $\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ phase. Insets show the corresponding simulated STM images.

Figure 7

Schematic diagram illustrating the location of the STM protrusions of the $\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ phase superposed on the CHCT structure with a domain wall. Location of the STM protrusions coincides with the most stable adsorption sites of In atoms, as determined by calculations.

Figure 8

$25\times 25{\mathrm{nm}}^2$ empty-state $(+1.9\mathrm{V})$ STM image of the $\mathrm{Si}\left(111\right)\sqrt{3}\times \sqrt{3}\text{−}(\mathrm{Au},\mathrm{In})$ surface after cooling to $125\mathrm{K}$.