Identification of the Au Coverage and Structure of the $\mathrm{Au}/\mathrm{Si}(111)\text{−}(5\times 2)$ Surface

We identify the atomic structure of the $\mathrm{Au}/\mathrm{Si}(111)\text{−}(5\times 2)$ surface by using density functional theory calculations. With seven Au atoms per unit cell, our model forms a bona fide ($5\times 2$) atomic structure, which is energetically favored over the leading model of Erwin et al. [Phys. Rev. B 80, 155409 (2009)], and well reproduces the $Y$-shaped and $V$-shaped ($5\times 2$) STM images. This surface is metallic with a prominent half filled band of surface states, mostly localized around the Au-chain area. The correct identification of the atomic and band structure of the clean surface further clarifies the adsorption structure of Si adatoms and the physical origin of the intriguing metal-to-insulator transition driven by Si adatoms.

Figure 1

Structural models for $\mathrm{Au}/\mathrm{Si}(111)\text{−}(5\times 2)$: (a) EBH model and (b) present model. Large (small) balls represent Au (Si) atoms, and dashed lines represent a ($5\times 2$) unit cell. Three rows of Au atoms are denoted by numbers and the added Au atoms by circles in (b). The simulated STM images represent the surface of constant density with $\rho =2\times {10}^{-6}\mathrm{e}/{\AA }^3$ taken at bias voltages $+0.8\mathrm{V}$ (empty) and $-0.8\mathrm{V}$ (filled). The round, $V$-shaped, and $Y$-shaped features are marked for easy comparison. The experimental images were taken from Ref. [25].

Figure 2

The $\mathrm{Au}/\mathrm{Si}(111)\text{−}(5\times 4)$ surface with 0.05 ML Si adatoms. STM images were taken in the same way as in Fig. 1.

Figure 3

Band structure of the (a) clean, (b) 0.025 ML Si-adatom, and (c) 0.05 ML Si-adatom surfaces. The size of each circle is proportional to the contribution from the surface atoms in the Au-chain area. Shaded areas represent the bulk band structure projected onto the ($5\times 2$) surface [the ($5\times 1$) projection is stressed by darker color]. In the charge plots, the top view represents the charge density in the horizontal plane marked in the side view. The solid lines in (b) and (c) represent the ARPES data (Ref. [4]) obtained for 0.024 and 0.048 ML, respectively.