Kagome-like structure of germanene on Al(111)

The structure of a 3 × 3 reconstruction formed by Ge deposition onto Al(111) [Al(111)3 × 3-Ge] was investigated by coaxial impact collision ion scattering spectroscopy, which is one of the most surface-sensitive structural analysis techniques. It has been revealed that Al(111)3 × 3-Ge forms a structure with 10 Ge atoms in a unit cell, similar to the recently reported “kagome-like” silicene on Al(111) rather than the previously reported honeycomb lattice. A surface band structure of the Al(111)3 × 3-Ge has also been investigated by angle-resolved photoemission spectroscopy (ARPES). The calculated band structure of our proposed model based on a density functional theory well reproduces ARPES spectra, which also indicates that Al(111)3 × 3-Ge forms a kagome-like structure.

Figure 1

CAICISS spectra for Al(111) clean surface (a) and surface after Ge deposition (b). The LEED pattern obtained at each stage is also shown in the right of each spectrum.

Figure 2

(a) Experimentally obtained azimuth angle φ dependence of Ge intensity for Al(111)3 × 3-Ge at various ion incidence angles α (left: $\alpha ={10}^{\circ }$; center: $\alpha ={15}^{\circ }$; right: $\alpha ={20}^{\circ }$). (b) and (c) Simulated φ dependencies of Ge intensity built upon 2 × 2 honeycomb models proposed by Derivaz et al. [15] (b) and Fukaya et al. [16] (c). Schematic illustrations show side views of corresponding models.

Figure 3

(a) Azimuth angle φ dependence of experimentally obtained Ge intensity for Al(111)3 × 3-Ge [same as Fig. 2]. The optimal simulation curve based on our proposed model (see Fig. 4) is shown in (b).

Figure 4

(a) Structural model of Al(111)3 × 3-Ge proposed in this study. The simulated STM image at $V_s=0.10\mathrm{V}$ and the experimentally obtained image ($V_s=0.10\mathrm{V}, I_t=1.0\mathrm{nA}$) are shown in (b) and (c), respectively.

Figure 5

(a) ARPES intensity distribution obtained on clean Al(111). The obtained direction in the Brillouin zone is shown on the right, in which the relationship between 1 × 1 and 3 × 3 lattices are shown. (b) ARPES intensity distribution obtained on Al(111)3 × 3-Ge. (c) Calculated band structure of Al(111)3 × 3-Ge shown in Fig. 4. In the band calculation, the number of Al layers is set at 20. The color indicates the contribution of the Ge layer.