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Structural identification of silicene on the Ag(111) surface by atomic force microscopy
摘要： Silicene is a two-dimensional atomic layer material with buckled honeycomb arrangements of Si atoms. The diversity of those arrangements, which expands its potential applications, makes it dif?cult to determine its structure in any particular case. In this paper, we show that atomic force microscopy (AFM) has the capability of structural determination of unknown phases of silicene. We carried out an AFM observation of (√13×√13)R13.9? silicene of unknown structures on Ag(111). Remarkably, it was shown that all constituent Si atoms forming a honeycomb lattice can be resolved by AFM whereas scanning tunneling microscopy (STM) can image only the topmost Si atoms. High-resolution AFM imaging allowed us to identify two types of buckled structure of (√13×√13)R13.9? silicene on Ag(111), which had not been previously discriminated. The structure models obtained by theoretical simulation reproduced AFM images as well as previous STM images. In addition, the mechanism of high-resolution AFM imaging was elucidated by force spectroscopy combined with ?rst-principles calculations. Namely, attractive interaction with the tip pulls up buckled down Si atoms, causing local ?ips of the buckled structures.
关键词： structural determination,buckled structures,Ag(111) surface,silicene,atomic force microscopy
更新于2025-09-23 15:21:21
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Electronic and Topological Properties of Silicene, Germanene and Stanene
摘要： In this chapter, we review the recent progress on electronic and topological properties of monolayer topological insulators including silicene, germanene and stanene. We start with the description of the topological nature of the general Dirac system and then apply it to silicene by introducing the spin and valley degrees of freedom. Based on them, we classify all topological insulators in the general honeycomb system. We discuss topological electronics based on honeycomb systems. We introduce the topological Kirchhoff law, which is a conservation law of topological edge states. Field effect topological transistor is proposed based on the topological edge states. We show that the conductance is quantized even in the presence of random distributed impurities. Monolayer topological insulators will be a key for future topological electronics and spin-valleytronics.
关键词： topological Kirchhoff law,silicene,topological insulators,topological electronics,Dirac system,field effect topological transistor,spin and valley degrees of freedom,stanene,quantized conductance,germanene
更新于2025-09-23 15:21:21
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Optical Properties of Silicene and Related Materials from First Principles
摘要： Slightly buckled, graphene-like honeycomb crystals made by silicon, silicene, or by other group-IV elements such as germanene and stanene represent atomically thin films, i.e., two-dimensional (2D) systems. The theoretical description of their optical properties suffers from three difficulties, (i) a thickness much smaller than the wavelength of light, (ii) their common modeling by superlattice arrangements with sufficiently large layer distances, and (iii) the inclusion of many-body effects. Here, the solutions of all problems are discussed. (i) The optical response of an individual honeycomb crystal is described by a tensor of 2D optical conductivities or dielectric functions, which are related to the optical response of the corresponding superlattice. (ii) The influence of such a sheet crystal on the transmittance, reflectance and absorbance of a layer system is described. (iii) Excitonic and quasiparticle effects are demonstrated to widely cancel each other. Silicene sheets are investigated in detail. As a consequence of the linear bands and Dirac cones the low-frequency absorbance is defined by the Sommerfeld finestructure constant. Van Hove singularities represented by critical points in the interband structure are identified at higher photon energies. Clear chemical trends along the row C → Si → Ge → Sn are derived. The influence of multiple layers is studied for the cases of bilayer silicene and graphene.
关键词： silicene,optical properties,many-body effects,two-dimensional materials,first principles,Van Hove singularities,stanene,Dirac cones,germanene
更新于2025-09-23 15:21:21
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Si Nanoribbons: From 1D to 3D Nanostructures
摘要： In this chapter we give an overview on the theoretical and experimental investigations of one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) Si nanoribbons (SiNRs) formed on the anisotropic Ag(110) substrate surface. We start by introducing briefly free-standing silicene, a silicon layer with Si atoms arranged in honeycomb lattice, with hexagonal Si-rings as structural units. These hexagonal Si units are subsequently discussed as possible candidates to explain the atomic arrangement of the experimentally synthesized Si nanoribbons on Ag(110). This interpretation is supported by properties such as the presence of the 1D projection of the π and π* bands, forming the so-called “Dirac cones” at the K points of the Brillouin zone, the sp2-like nature of the Si valence orbitals, and the strong resistance against oxidation. Besides these results, the atomic structure as well as the origin of the electronic properties of these Si nanoribbons are still controversially debated in the literature. We address this discussion in the last part of the chapter before summarizing it.
关键词： Si nanoribbons,oxidation resistance,silicene,Ag(110) substrate,Dirac cones,sp2 hybridization
更新于2025-09-23 15:21:21
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Properties of Monolayer Silicene on Ag(111)
摘要： The expected properties of silicene and their theoretical background have already been discussed in Chaps. 1–3 and the different ways to synthesize this new 2D material in Chap. 5. It has already been mentioned that such a synthesis requires an adequate substrate material to accommodate the formation of a one-atom-thin silicon layer. Such a material is silver, in particular the Ag(111) surface plane. In this chapter the formation and properties of silicene formed epitaxially on the Ag(111)(1 × 1) surface are discussed. We will see that the properties of these silicene layers are modi?ed with respect to the ones of free-standing silicene, due to the interaction with the substrate. For this reason we will refer to it as epitaxial silicene and look in detail at its two-dimensional (2D) character. A more detailed look at the formation of Si layers on Ag(111) shows that, depending on the speci?c preparation conditions, several 2D Si phase can be formed. Differences and similarities of these structures will be discussed. Furthermore, we will draw the intention on the chemical and temperature stability of these epitaxial silicene layers and unveil the limits for the silicene formation.
关键词： silicene,2D materials,Ag(111),vibrational properties,electronic properties,epitaxial growth
更新于2025-09-23 15:21:21
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Atomic and Electronic Structure of Silicene on Ag: A Theoretical Perspective
摘要： The isolation of graphene sheets from its parent crystal graphites has given the kick to experimental research on its prototypical 2D elemental cousin, silicene [1]. Unlike graphene, silicene lacks a layered parent material from which it could be derived by exfoliation. Hence, the efforts of making the silicene dream a reality were focused on epitaxial growth of silicene on substrates. The first synthesis of epitaxial silicene on silver (111) [27, 46] and zirconium diboride templates [16] and next on an iridium (111) surface [31], has boosted research on other elemental group IV graphene-like materials, namely, germanene and stanene [30, 48]. The boom is motivated by several new possibilities envisaged for future electronics, typically because of the anticipated very high mobilities for silicene and germanene [49], as well as potential optical applications [30]. It is also fuelled by their predicted robust 2D topological insulator characters [14, 28] and potential high temperature superconductor character [5, 50]. One of the most promising candidates as a substrate is Ag because from the studies of the reverse system, where Ag atoms were deposited on silicon substrate, it was known that Ag and silicon make sharp interfaces without making silicide compounds.
关键词： theoretical perspective,electronic structure,silicene,Ag(111),epitaxial growth
更新于2025-09-23 15:21:21
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Optical properties of shortest-width zig-zag Silicene nano-ribbons: effects of local fields
摘要： We have computed from first principles the structural, magnetic and optical properties of zig-zag oriented silicene nanoribbons. The minimal width for structurally stable planar structure having zig-zag edges corresponds to a 4-chains ribbon. Its ground state presents reconstructed and spin polarized edges, coupled antiferromagnetically. For this state, and for the corresponding excited state with ferromagnetically coupled edges, we computed the optical absorption spectra within the independent particle approximation, including local field effect corrections, for light polarized in the directions parallel and perpendicular to the ribbon axis. For the “parallel” light polarization the inclusion of local fields effects is limited to a slight reduction of the intensity of the main peak in the infrared region, as well as that of some minor peaks in the visible-ultraviolet structure. Conversely, the computed optical spectrum for light polarized perpendicularly to the ribbon axis shows that the short-width zig-zag nanoribbons are basically transparent in the infrared and visible region, because of the effect of electronic confinement combined with local fields.
关键词： local fields,silicene nanoribbons,optical properties,zig-zag edges,first principles
更新于2025-09-23 15:21:01
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Surface Functionalization of Silicene
摘要： For two-dimensional (2D) materials, an attractive feature is that all the atoms of the materials are exposed on the surface. Thus tuning the structure and properties by surface treatments becomes straightforward. Similar as graphene, the nearly zero-gap character of silicene hinders its applications in electronic and optoelectronic devices. In the case of graphene, functionalization through hydrogenation, halogenation, oxidation, have been widely explored in order to modify the electronic structure of graphene. However, the stable aromatic π-bond network of graphene makes it very inert and difficult to bond with foreign atoms. For example, hydrogen atoms on graphene usually form clusters instead of an ordered structure. In contrast, silicene possesses hybrid sp2-sp3 bonding, which is more readily to be modified or functionalized. Since the early stage of silicene research, theoretical investigations on the hydrogenation, halogenation, and oxidation of silicene have been widely reported in literature. Recently, increasing experimental successes have been achieved on functionalization of silicene. It is now imperative to review the progresses in the fast-growing field. In this chapter, we will discuss hydrogenation, halogenation oxidization individually. In each section, we first describe those theoretical predictions and then illustrate recent experimental successes. Finally, we will give some overview and outlook of this field.
关键词： electronic structure,silicene,functionalization,halogenation,2D materials,hydrogenation,oxidation
更新于2025-09-23 15:21:01
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Germanene: Silicene’s Twin Sister
摘要： Soon after the discovery of graphene, the first two-dimensional material, many other two-dimensional materials have been developed. Due to their s2 p2 type of electronic structure the elements of the ‘carbon’ column of the periodic system i.e. silicon, germanium and tin have received a lot of attention as potential two-dimensional materials. The silicon, germanium and tin analogues of graphene are coined silicene, germanene and tinene or stanene, respectively, and share many properties with graphene. There are, however, also a few distinct differences with graphene. Here we will give a brief update on the current status of germanene. We briefly review the various routes to synthesize germanene and elaborate on its structural and electronic properties as well as its potential for application in future electronic devices.
关键词： silicene,two-dimensional materials,electronic properties,synthesis,germanene
更新于2025-09-23 15:21:01
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Silicene Quantum Dots Confined in Few-Layer Siloxene Nanosheets for Blue Light-Emitting Diodes
摘要： Two-dimensional silicon-based materials have unique physical and chemical properties due to high surface area and quantum confinement effects. Herein, a topochemical reaction method is used for preparing silicene quantum dots confined in few layer siloxene nanosheets with FeCl3?6H2O as oxidant, which shows thickness less than 2 nm. The experimentally prepared siloxene nanosheets are dispersible, with silicene quantum dots having average diameter less than 5 nm. The silicene quantum dots are self-organized through the oxidation of FeCl3, showing unique optical properties of blue emission. The UV-visible absorption and PL emission spectra indicate the quasi-direct band gap transition to the emission. Besides, the few-layer siloxene nanosheets with silicene quantum dots have a radiative lifetime of 1.098 ns at an emission wavelength of 435 nm, which derives from the quasi-direct band transition of silicene quantum dots. Such two-dimensional nanosheets of silicon possess potential applications for the emitting layer materials of blue light-emitting diodes (LED).
关键词： topochemical reaction,silicene quantum dot,photoluminescence,siloxene,quasi-direct band gap
更新于2025-09-12 10:27:22