Silicene, the considered equivalent of graphene for silicon, has been recently synthesized on Ag(111) surfaces. Following the tremendous success of graphene, silicene might further widen the horizon of two-dimensional materials with new allotropes artificially created. Due to stronger spin-orbit coupling, lower group symmetry and different chemistry compared to graphene, silicene presents many new interesting features. Here, we focus on very important aspects of silicene layers on Ag(111): First, we present scanning tunneling microscopy (STM) and non-contact Atomic Force Microscopy (nc-AFM) observations of the major structures of single layer and bi-layer silicene in epitaxy with Ag(111). For the (3 × 3) reconstructed first silicene layer nc-AFM represents the same lateral arrangement of silicene atoms as STM and therefore provides a timely experimental confirmation of the current picture of the atomic silicene structure. Furthermore, both nc-AFM and STM give a unifying interpretation of the second layer (√3 × √3)R ± 30° structure. Finally, we give support to the conjectured possible existence of less stable, ~2% stressed, (√7 × √7)R ± 19.1° rotated silicene domains in the first layer.

The interaction of oxygen with the ordered Ni3Al (111) surface has been investigated in the temperature range from 300 to 1000 K using high-resolution electron-energy-loss spectroscopy (HREELS) and low-energy electron diffraction (LEED). The “2×2” LEED pattern of the clean Ni3Al (111) surface indicates a bulklike termination. After oxygen adsorption at 300 K the LEED pattern is diffuse suggesting the formation of an amorphous overlayer. The HREELS spectra show evidence for oxygen interaction with both aluminum and nickel atoms. At 600 K adsorption temperature the fcc surface order is restored, however, the observed (1×1) LEED pattern indicates the loss of chemical order. Again HREELS spectra suggest interaction of oxygen with both aluminum and nickel. For an adsorption temperature of 800 K LEED shows an unrotated oxygen induced superstructure with a lattice spacing of 2.93 Å in addition to the (1×1) substrate spots. The HREELS spectra exhibit an intense loss at 81.9 meV, which is also known from oxygen in threefold hollow sites on Al (111). Since such sites are not available on the Ni3Al (111) surface, we conclude the buildup of an oxygen covered aluminum overlayer. Finally, during oxygen exposure at 1000 K we observe the growth of a γ′-Al2O3 structure on the reordered Ni3Al (111) substrate surface. This structure has been identified by means of the characteristic vibrational losses in HREELS at 54.6, 80.3, and 112.8 meV together with the emergence of overlayer spots in LEED exhibiting the lattice spacing of γ′-Al2O3 (3.02 Å). For oxygen exposures at 800 and 1000 K an island growth of the overlayer has been found.

The growth of vapor deposited palladium on a well-ordered thin alumina film grown on a Ni₃Al(111) surface was studied as a function of the sample temperature during deposition and the palladium flux. The superstructure of the oxide film turns out to be an excellent template for the growth of nanostructured palladium cluster arrays. By taking advantage of the growth steering properties of the alumina film we were able to prepare nearly perfectly ordered hexagonal arrays of palladium clusters with a uniform distance of 4.5 nm between the particles. Furthermore the dependence of the cluster height and diameter on the sample voltage as measured by STM has been investigated. In the range between 0.7 V and 2.0 V the measured cluster heights are nearly independent of the sample voltage whereas at voltages higher than 2 V they are continuously decreasing.