Figure 1

[(a1)–(c1)] Empty state constant-current STM images of the evolution of Al islands grown on $\mathrm{Si}\left(111\right)\text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Al}$ substrates with increasing Al coverage. (a2)–(c2) show the corresponding island size distributions.Reuse & Permissions

Figure 2

High-resolution empty state (a) STM image and (b) corresponding LEED pattern of Al islands on the $\mathrm{Si}\left(111\right)\text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Al}$ substrate (coverage of 0.49 ML Al). The islands exhibit a moiré pattern (see marked unit cell). (c) Percolating island structures at 0.58 ML coverage. The dashed line indicates the percolation. (d) Periodicity length of the moiré pattern (right scale) and height of the islands relative to the $\mathrm{Si}\left(111\right)\text{−}\sqrt{3}\times \sqrt{3}\text{−}\mathrm{Al}$ substrate (left scale) as a function of the island size (measured at $2\pm 0.1\mathrm{V}$ sample voltage). The data suggest that the islands larger than $2.5{\mathrm{nm}}^2$ have identical Al(111) $1\times 1$ structures. (e) Average island size as a function of the Al coverage. The large error bar of the uppermost data point is due to percolated islands present above about 0.58 ML coverage.Reuse & Permissions

Figure 3

(Color online) Al coverage dependence of electron energy loss spectra. All spectra are normalized by the intensity of the elastic peak. The individual spectra are vertically offset. The respective zero intensities are indicated by small dashes on the right scale. With increasing deposition amount, the band gap of initially about $0.8\mathrm{eV}$ decreases and, at high coverages, a metallic Drude tail appears. Inset: 2D intensity map of the EELS data. The narrowing of the band gap is indicated by the white arrow. The effect of percolation in the EELS data is indicated by the black arrow.Reuse & Permissions

Figure 4

(a) Band gap vs the average area of the islands. Experimental and calculated data points are shown as filled and open circles, respectively. Inset: Electron energy loss intensity at three fixed loss energies as a function of the coverage. The respective threshold coverages are indicated by the arrows. The extracted energy-threshold coverage pairs are used to derive the functional dependence of the band gap on the island size shown in (a) with help of Fig. 2d (see text). (b) Calculated energy levels for several rectangular Al islands with different sizes in the vicinity of the Fermi energy. The band gap is the difference between the highest occupied (labeled HOMO) and lowest unoccupied (LUMO) energy level. Filled and empty energy levels are shown as solid black and dashed gray lines, respectively. The inset shows the selected island geometries used for the calculation of the energy levels.Reuse & Permissions