Atomic structure and electronic properties of the In/Si(111)2$\times$2 surface

The Si(111)2$\times$2-In reconstruction can be considered as a precursor phase for the formation of the metallic $\sqrt{7}\times \sqrt{3}$ phases of In overlayers on a Si(111) surface. Using the ab initio random structure searching method, comparison of simulated and experimental scanning tunneling microscopy images, and resemblance of the calculated band structure to the experimental angle-resolved photoelectron spectra, we examined various 2$\times$2 structure models with 0.5, 0.75, 1.0, and 1.25 monolayer In coverage. The only model which fits well all the requirements is the one-monolayer model, where three In atoms in the $T_4$ sites form a trimer centered in the $H_3$ site and the fourth In atom occupies the on-top ($T_1$) site.

Figure 1

The most stable model configurations of the In/Si(111)2$\times$2 surface determined using AIRSS method for In coverage of (a) 0.5 ML, (b) 0.75 ML, (c) 1.0 ML, and (d) 1.25 ML. In atoms are shown by blue circles, Si atoms are shown by open circles, the larger for on-top Si atoms in $T_1$ sites, the smaller for the Si atoms in the $T_4$ site. The 2$\times$2 unit cell is outlined by the red dotted line.

Figure 2

(a) Filled-state (+1.3 V) experimental STM image of the In/Si(111)2$\times$2 surface compared with the simulated STM images (+1.0 V) for (b) 0.75-ML model and (c) 1.0-ML model. To tie the STM images to the surface structure, the schematic of the Si(111) surface structure is superposed on the experimental STM image and model structures on the corresponding simulated STM images. In atoms are shown by blue circles, Si atoms are shown by open circles, the larger for on-top Si atoms in $T_1$ sites, the smaller for the Si atoms in the $T_4$ site.

Figure 3

Calculated band structure for the models (containing eight Si bilayers) of the In/Si(111)2$\times$2 surface with In coverage of (a) 0.5 ML, (b) 0.75 ML, (c) 1.0 ML, and (d) 1.25 ML. The surface state bands are indicated by red, the projected quantum well states are shown in gray. The size of the red symbols reflects the weight of the states in the surface In atoms.

Figure 4

(a) Experimental ARPES spectrum from the In/Si(111)2$\times$2 surface. (b) Calculated surface-state band structure (38 Si bilayers model) superposed with experimental ARPES spectrum. The size of the red symbols reflects the weight of the states in the surface In atoms.