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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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Hydrogen Terminated Germanene for a Robust Selfa??Powered Flexible Photoelectrochemical Photodetector
摘要： As a rising star in the family of graphene analogues, germanene shows great potential for electronic and optical device applications due to its unique structure and electronic properties. It is revealed that the hydrogen terminated germanene not only maintains a high carrier mobility similar to that of germanene, but also exhibits strong light–matter interaction with a direct band gap, exhibiting great potential for photoelectronics. In this work, few-layer germanane (GeH) nanosheets with controllable thickness are successfully synthesized by a solution-based exfoliation–centrifugation route. Instead of complicated microfabrication techniques, a robust photoelectrochemical (PEC)-type photodetector, which can be extended to flexible device, is developed by simply using the GeH nanosheet film as an active electrode. The device exhibits an outstanding photocurrent density of 2.9 μA cm?2 with zero bias potential, excellent responsivity at around 22 μA W?1 under illumination with intensity ranging from 60 to 140 mW cm?2, as well as short response time (with rise and decay times, tr = 0.24 s and td = 0.74 s). This efficient strategy for a constructing GeH-based PEC-type photodetector suggests a path to promising high-performance, self-powered, flexible photodetectors, and it also paves the way to a practical application of germanene.
关键词： photoelectrochemical photodetectors,2D materials,germanene,germanane
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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Electroic and optical properties of germanene/MoS2 heterobilayers: first principles study
摘要： First principles calculations have been performed to investigate the structural, electronic, and optical properties of germanene/MoS2 heterostructures. The results show that a weak van der Waals coupling between germanene and MoS2 layers can lead to a considerable band-gap opening (53 meV) as well as the preserved Dirac cone with a linear band dispersion of germanene. The applied external electric filed can not only enhance the interaction strength between two layers, but also linearly control the charge transfer between germanene and MoS2 layers, and consequently lead to a tunable band gap. Furthermore, the reduction in the optical absorption intensity of the heterostructures with respect to the separated monolayers has been predicted. These findings suggest that the Ge/MoS2 hybrid can be designed as the device where both finite band gap and high carrier mobility are required.
关键词： Heterobilayers,Optical properties,Band gaps,Electric field,Germanene/MoS2
更新于2025-09-23 15:21:01
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The electronic and optical properties of armchair germanene nanoribbons
摘要： The electronic and optical properties of armchair germanene nanoribbons (AGeNRs) are studied using the first principles calculations. The band structure, band-gap size, projected density of states (PDOS), and dielectric function of AGeNRs are calculated. Moreover, the variation of these parameters as a function of various ribbon widths is investigated. By increasing the width of ribbons the band-gap size of pristine AGeNRs is decreased according to three different trends. Based on these trends, it is extracted that the AGeNRs can be divided into three categories named as n=3P, n=3P+1, n=3P+2, here n is the number of germanium atoms in the width and P is an integer. Moreover, all these categories are direct band-gap materials and the order of band-gap size is changed as: EG (3P+2) < EG (3P) < EG (3P+1). Due to the direct band-gap size, it can be extracted that all of AGeNR categories are proper for optical applications. Based on the simulation results of this work, it is demonstrated that the AGeNRs are appropriate for optical devices in the range of infrared applications. In addition, the effect of uniaxial tensile and compressive strain on the band-gap size and the dielectric function of AGeNRs is investigated and it is shown that the electronic and optical properties of AGeNRs can be tuned by strain in a wide range.
关键词： electronic and optical properties,silicene,band gap size,graphene,germanene nanoribbons
更新于2025-09-10 09:29:36
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Molecular adsorption and strain-induced ferromagnetic semiconductor-metal transition in half-hydrogenated germanene
摘要： Very recently, half-hydrogenated germanene has been achieved in an experiment. In this paper, we investigate the effects of tetracyanoquinodimethane (TCNQ) molecular adsorption and strain on the electronic properties of half-hydrogenated germanene through first-principles. As an electron-acceptor molecule, TCNQ is exploited to non-covalently functionalize the half-hydrogenated germanene. However, this physical adsorption induces a ferromagnetic semiconductor–metal transition in half-hydrogenated germanene due to charge transfer from the substrate to the TCNQ molecule. More importantly, the superstructure of half-hydrogenated germanene/TCNQ is extremely sensitive to biaxial tensile strain. Under the biaxial tensile strain of 0.25%, the ferromagnetic semiconductor–metal transition induced by molecular adsorption can surprisingly be overturned. Meanwhile, a strong p-type doping is exhibited. Remarkably, it would return from a ferromagnetic semiconductor to a metal again when the biaxial tensile strain increases to 1.5%. Our analysis based on the structural and electronic properties of half-hydrogenated germanene/TCNQ indicates that such metal–semiconductor–metal transition in half-hydrogenated germanene/TCNQ under biaxial tensile strain may originate from the strong local deformation, resulting in the energy of the valence band maximum decreasing below or increasing above the Fermi level.
关键词： ferromagnetic semiconductor–metal transition,p-type doping,half-hydrogenated germanene,TCNQ molecular adsorption,biaxial tensile strain
更新于2025-09-10 09:29:36
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Spin orbit coupling induced band gap in gemanene modulated by external field
摘要： We investigate the electronic band structure of germanene crystal by using the sixteen band tight-binding calculation. We focus on the modulation of its band gap with spin–orbit coupling (SOC), perpendicular electric ?eld and magnetic ?eld. Our calculation shows that the SOC opens a tunable band gap in the Dirac-type electronic structures, and plays a crucial rule in the formation of the energy band gap. The in?uence of SOC on the gap in germanene is much larger than that in graphene, which makes germanene an ideal candidate to exhibit the quantum spin Hall effect at room temperature. We also ?nd that the electronic structure and topological property of germanene can be tuned by the external ?eld signi?cantly. Thus the electronic structure of germanene can be controlled to produce metallic, semiconducting, or insulating properties by applying an appropriate external ?eld. In addition, the key features of the band structure induced by the electrical ?eld and magnetic ?eld are quite different. For the electric ?eld applied, two spin-up states produce a gap at K point, in contrast, two spin-down states do it at K′ points. While for the magnetic ?eld present, the band gaps are formed by the spin-up states from the conduction band and spin-down state from the valance band at both the K and K′ points. This modulation behavior of the band gap by the external ?eld paves a way to the realization of germanene based spintronic devices.
关键词： topological insulator,electronic structure,tight-binding model,germanene,spin-orbit coupling
更新于2025-09-09 09:28:46
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Vibrational properties of germanane and fluorinated germanene in the chair, boat, and zigzag-line configurations
摘要： The electronic and vibrational properties of germanane and fluorinated germanene are studied within Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) frameworks. Different structural configurations of germanane and fluorinated germanene are investigated. The energy difference between the different configurations are consistently smaller than the energy of thermal fluctuations for all the analyzed DFT functionals LDA, GGA, and hybrid functionals, which implies that, in principle, it is possible to find these different configurations in different regions of the sample as minority phases or local defects. We calculate the Raman and infrared spectra for these configurations by using ab initio calculations and compare it with available experimental spectra for germanane. Our results show the presence of minority phases compatible with the configurations analyzed in this work. As these low energy configurations are metaestable, the present work shows that the synthesis of these energy competing phases is feasible by selectively changing the synthesis conditions, which is an opportunity to expand in this way the availability of new two-dimensional compounds.
关键词： Density Functional Perturbation Theory,germanane,fluorinated germanene
更新于2025-09-09 09:28:46