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The energy dispersion of fermions or bosons vanishes in momentum space if destructive quantum interference occurs in a frustrated Kagome lattice with only nearest-neighbor hopping. A discrete flat band (FB) without any dispersion is consequently formed, promising the emergence of fractional quantum Hall states at high temperatures. Here, we report the experimental realization of an FB with possible nontrivial topology in an electronic Kagome lattice on twisted multilayer silicene. Because of the unique low-buckled two-dimensional structure of silicene, a robust electronic Kagome lattice has been successfully induced by moiré patterns after twisting the silicene multilayers. The electrons are localized in the Kagome lattice because of quantum destructive interference, and thus, their kinetic energy is quenched, which gives rise to an FB peak in the density of states. A robust and pronounced one-dimensional edge state has been revealed at the Kagome edge, which resides at higher energy than the FB. Our observations of the FB and the exotic edge state in electronic Kagome lattice open up the possibility that fractional Chern insulators could be realized in two-dimensional materials.

Silicene, a counterpart of graphene, has achieved rapid development due to its exotic electronic properties and excellent compatibility with the mature silicon-based semiconductor technology. Its low room-temperature mobility of ~100 cm2 V−1 s−1, however, inhibits device applications such as in field-effect transistors. Generally, defects and grain boundaries would act as scattering centers and thus reduce the carrier mobility. In this paper, the morphologies of various point defects in epitaxial silicene on Ag(111) surfaces have been systematically investigated using first-principles calculations combined with experimental scanning tunneling microscope (STM) observations. The STM signatures for various defects in epitaxial silicene on Ag(111) surface are identified. In particular, the formation energies of point defects in Ag(111)-supported silicene sheets show an interesting dependence on the superstructures, which, in turn, may have implications for controlling the defect density during the synthesis of silicene. Through estimating the concentrations of various point defects in different silicene superstructures, the mystery of the defective appearance of $\sqrt{13}\times \sqrt{13}$ and $2\sqrt{3}\times 2\sqrt{3}$ silicene in experiments is revealed, and 4 x 4 silicene sheet is thought to be the most suitable structure for future device applications.

The " multilayer silicene" films were grown on Ag(111), with increasing thickness above 30 monolayers (ML). Scanning tunneling microscopy (STM) observations suggest that the " multilayer silicene" is indeed a bulk-like Si(111) film with a (√ 3 x √ 3)R30° honeycomb superstructure on surface. The possibility for formation of Si(111)(√ 3 x √ 3)R30°-Ag reconstruction on the surface can be distinctively ruled out by peeling off the surface layer with the STM tip. On this surface, delocalized surface state as well as linear energy-momentum dispersion was observed from quasiparticle interference patterns. Our results indicate that a bulklike silicon film with diamondlike structure can also host delocalized surface state, which is even more attractive for potential applications, such as new generation of nanodevices based on Si.

We report on the epitaxial growth mechanism of silicene layers fabricated on a Ag(111) surface by molecular beam epitaxial deposition. The coverage effect and the structural defects have been characterized using scanning tunneling microscopy (STM). It is found that substrate temperature plays an important role in the formation of silicene in different structures. Several kinds of defects are observed in different phases of silicene, which are most likely induced by the low coverage effect and the structural mismatch between the silicene and the Ag(111) surface. The Silicene sheet prefers to first emerge at the terrace edge of the substrate. Our results indicate that the growth mechanism of silicene follows the Stranski-Krastanov growth mode for all structures.