Atomic origins of Si $2p$ and Au $4f$ surface core-level shifts on Au/Si(111)-($5\times 2$)

We have performed density functional theory calculations to investigate the core-level shifts on the Au/Si(111)-($5\times 2$) surface. The employed structural model, which was recently proposed as containing seven Au atoms per ($5\times 2$) unit cell [Phys. Rev. Lett. 113, 086101 (2014)], is found to well reproduce the Si $2p$ and Au $4f$ surface core-level shifts reported by previous x-ray photoelectron spectroscopy studies, thereby clarifying their atomic origins.

Figure 1

Atomic structures of (a) the clean Au/Si(111)-($5\times 2$) surface and (b) the Si adsorbed Au/Si(111)-($5\times 4$) surface. Large and small balls represent Au and Si atoms, respectively. Small and large dashed-line boxes represent the ($5\times 2$) and ($5\times 4$) unit cells, respectively. The surface Si (Au) atoms are labeled as $a, b, c$, and $d$ ($\alpha , \beta , \gamma$, and $\delta$) for later core-level resolutions.

Figure 2

Si $2p$ core-level shifts. The labels ($a, b, c$, and $d$) indicate their atomic origins as marked in Fig. 1. The core levels are given relative to the bulk value that is effectively estimated from the atoms in the fifth and sixth Si layers. Experimental data were adapted from the work of Okuda and co-workers [26, 27] and Zhang and co-workers [28].

Figure 3

Electronic-charge analysis of the Si $2p$ CLS. The top panel shows the initial-state Si $2p$ CLS of the clean surface (see Fig. 2). The bottom panel shows the amount of electrons around the surface Si atoms: The total charge and its $s, p$, and $d$ components are given relative to the bulk values. The electron counting was done by using an atomic radius of 1.26 Å, which represents half of the average Au-Si bond length in the clean ($5\times 2$) surface.

Figure 4

Au $4f$ core-level shifts. The labels ($\alpha , \beta , \gamma$, and $\delta$) indicate their atomic origins as marked in Fig. 1. The core levels are given relative to the bulk value of fcc Au. Dashed lines represent the experimental value reported by Okuda and co-workers [26, 27].

Figure 5

Electronic-charge analysis of the Au $4f$ CLS. The top panel shows the initial-state Au $4f$ CLS of the clean surface (see Fig. 4). The bottom panel shows the amount of electrons around the Au atoms: The total charge and its $s, p$, and $d$ components are given relative to the bulk values of fcc Au. The same atomic radius 1.26 Å was used for the electron countings.