Using atomic resolved scanning tunneling microscopy, we present here the experimental evidence of a silicene sheet (graphenelike structure) epitaxially grown on a close-packed silver surface [Ag(111)]. This has been achieved via direct condensation of a silicon atomic flux onto the single-crystal substrate in ultrahigh vacuum conditions. A highly ordered silicon structure, arranged within a honeycomb lattice, is synthesized and present two silicon sublattices occupying positions at different heights (0.02 nm) indicating possible sp2-sp3 hybridizations.

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Epitaxial growth of a silicene sheet

Recent studies have revealed that single-layer transition-metal oxides and dichalcogenides (MX2) might offer properties superior to those of graphene. So far, only very few MX2 compounds have been synthesized as suspended single layers, and some of them have been exfoliated as thin sheets. Using first-principles structure optimization and phonon calculations based on density functional theory, we predict that, out of 88 different combinations of MX2 compounds, several of them can be stable in free-standing, single-layer honeycomb-like structures. These materials have two-dimensional hexagonal lattices and have top-view appearances as if they consisted of either honeycombs or centered honeycombs. However, their bonding is different from that of graphene; they can be viewed as a positively charged plane of transition-metal atoms sandwiched between two planes of negatively charged oxygen or chalcogen atoms. Electron correlation in transition-metal oxides was treated by including Coulomb repulsion through LDA...

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Stable, Single-Layer MX2 Transition-Metal Oxides and Dichalcogenides in a Honeycomb-Like Structure

Silicene, a two-dimensional (2D) honeycomb structure similar to graphene, has been successfully fabricated on an Ir(111) substrate. It is characterized as a (√7×√7) superstructure with respect to the substrate lattice, as revealed by low energy electron diffraction and scanning tunneling microscopy. Such a superstructure coincides with the (√3×√3) superlattice of silicene. First-principles calculations confirm that this is a (√3×√3)silicene/(√7×√7)Ir(111) configuration and that it has a buckled conformation. Importantly, the calculated electron localization function shows that the silicon adlayer on the Ir(111) substrate has 2D continuity. This work provides a method to fabricate high-quality silicene and an explanation for the formation of the buckled silicene sheet.

/pdf/buckled-silicene-formation-on-ir-111-3z4m59418z.pdf

Buckled silicene formation on Ir(111).

Scanning tunneling microscopy (STM) and ab initio calculations based on density functional theory (DFT) were used to study the self-aligned silicon nanoribbons on Ag(110) with honeycomb, graphene-like structure. The silicon honeycombs structure on top of the silver substrate is clearly observed by STM, while the DFT calculations confirm that the Si atoms adopt spontaneously this new silicon structure.

/pdf/graphene-like-silicon-nanoribbons-on-ag-110-a-possible-30q3iai5qc.pdf

Graphene-like silicon nanoribbons on Ag(110): A possible formation of silicene

Molecular Semiconductors in Organic Photovoltaic Cells

Physics of ultra-thin phthalocyanine films on semiconductors

In the quest of nano-objects for future electronics, silicon nanowires could possibly take over carbon nanotubes. Here we show the growth by self-organization of straight, massively parallel silicon nanowires having a width of 1.6 nm, which are atomically perfect and highly metallic conductors. Surprisingly, these silicon nanowires display a strong symmetry breaking across their widths with two chiral species that self-assemble in large left-handed and right-handed magnetic-like domains.

Growth of straight, atomically perfect, highly metallic silicon nanowires with chiral asymmetry.

Silicene, the new allotropic form of silicon, represents an interesting promise for future new nanostructured materials. Here, we investigate the room temperature oxidation of a one-dimensional grating of silicene nanoribbons grown on a Ag(1?1?0) surface by high-resolution Si 2p core level photoemission spectroscopy and low-energy electron diffraction observations. The oxidation process starts at very high oxygen exposures, about 104 times higher than on the clean Si(1?1?1)7 ? 7 surface, which demonstrates the low reactivity of silicene to molecular oxygen. Ar+sputtering produces defects, which enhance the oxidation uptake.

https://iopscience.iop.org/article/10.1088/0022-3727/44/31/312001/pdf

Strong resistance of silicene nanoribbons towards oxidation

Silicon oxide nanowires hold great promise for functional nanoscale electronics. Here, we investigate the oxidation of straight, massively parallel, metallic Si nanowires. We show that the oxidation process starts at the Si NW terminations and develops like a burning match. While the spectroscopic signatures on the virgin, metallic part, are unaltered we identify four new oxidation states on the oxidized part, which show a gap opening, thus revealing the formation of a transverse internal nanojunction.

Burning Match Oxidation Process of Silicon Nanowires Screened at the Atomic Scale

In this paper we report a Scanning Tunneling Microscopy (STM) and Spectroscopy (STS) study as a function of temperature (ranging from room to liquid helium temperature) of the Si/Ag(110) surface at different silicon coverage. In particular, partially and fully covered surfaces, both characterized by the presence of highly ordered nanowires, are examined by STM imaging and by STS spectroscopy in order to study the temperature dependence of both the nanowires structure and their peculiar metallic behavior. No evident variation was observed upon cooling from room to liquid helium temperature, both in the STM images and in the STS spectroscopy, suggesting that such nanowires maintain the same structure in the investigated temperature range. Empty states differential conductance images show a dramatic evolution as the bias voltage is increased, suggesting that electrons are confined along the direction perpendicular to the nanowires (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Guy Le Lay

Papers

Physics of ultra-thin phthalocyanine films on semiconductors

Growth of straight, atomically perfect, highly metallic silicon nanowires with chiral asymmetry.

Strong resistance of silicene nanoribbons towards oxidation

Burning Match Oxidation Process of Silicon Nanowires Screened at the Atomic Scale

Low temperature STM/STS study of silicon nanowires grown on the Ag(110) surface