Optical Fingerprints of Si Honeycomb Chains and Atomic Gold Wires on the Si(111)-($5\mathbf{\times }2$)-Au Surface

The intensively studied Si(111)-($5\times 2$)-Au surface is reexamined using reflectance anisotropy spectroscopy and density functional theory simulations. We identify distinctive spectral features relating directly to local structural motifs such as Si honeycomb chains and atomic gold wires that are commonly found on Au-reconstructed vicinal Si(111) surfaces. Optical signatures of chain dimerization, responsible for the observed ($\times 2$) periodicity, are identified. The optical response, together with STM simulations and first-principles total-energy calculations, exclude the new structure proposed very recently based on the reflection high-energy electron diffraction technique analysis of Abukawa and Nishigaya [Phys. Rev. Lett. 110, 036102 (2013)] and provide strong support for the Si honeycomb chain with the triple Au chain model of Erwin et al. [Phys. Rev. B 80, 155409 (2009)]. This is a promising approach for screening possible models of complex anisotropic surface structures.

Figure 1

Structures (top layers only) and simulated STM images of proposed models for Si(111)-($5\times 2$)-Au at a 0.6 ML Au coverage. Surface unit cells are indicated by the solid (white) lines, except for model $E$ (dashed line), which is shown as a subsection of model $D$. The single-chain model of Si(557)-($5\times 2$)-Au is also shown ($F$). Constant current STM images are calculated at a bias of $-1.0\mathrm{eV}$. Partial experimental images extracted from (a) Ref. 5 and (b) Ref. 4 at biases of $-0.4$ and $-1.5\mathrm{eV}$, respectively.

Figure 2

Measured (solid black dots) and computed (lines) RAS response for Si(111)-($5\times 2$)-Au (left panel) and Si(557)-($5\times 2$)-Au (right panel). The experimental data are taken from Ref. 12. Labels refer to structural models in Fig. 1. Note the rigid shift in the energy axis between theory and experiment.

Figure 3

Optical signatures of chain dimerization in Si(111)-Au. Square brackets indicate artificial doping of the simulation cell [$A$, ($5\times 2$); $B$, ($5\times 4$)]. $A^{[1-]}+B^{[2+]}$ represents a mixed-domain signal. ${\theta }_{\mathrm{Si}}$ denotes the adatom coverage.