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Phase diagram of silicene on four different surfaces and the Ca(0.5ML)/Si(111)2 × 1 substrate without silicene versus the chemical potentials of Si and Ca. The energy zeros correspond to the chemical potentials of bulk Si and Ca. The trends of preparation conditions are also indicated.
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The deposition of silicene on several metals is investigated. For fcc crystals the (111) surfaces while for hexagonal ones the (0001) surfaces are used. The Ca(111)1 × 1 substrate is found to be the most promising candidate. The silicene adsorption on Ca-functionalized Si(111)1 × 1 and 2 × 1 surfaces is also studied. The 1 × 1 substrates lead to ov...
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... 20−22 Among others, Au(111) was proposed to be a promising candidate for the stabilization of silicene. 23 Scanning tunneling microscopy investigations revealed the hexagonal silicene structure on top of Au(111), however, with an increased lattice constant compared to that of freestanding silicene. 24 Further, low interaction of the Si atoms with the Au substrate was demonstrated. ...
The allotropic affinity for bulk silicon and unique electronic and optical properties make silicene a promising candidate for future high-performance devices compatible with mature complementary metal–oxide–semiconductor technology. However, silicene’s outstanding properties are not preserved on its most prominent growth templates, due to strong substrate interactions and hybridization effects. In this letter, we report the optical properties of silicene epitaxially grown on Au(111). A novel in situ passivation methodology with few-layer hexagonal boron nitride enables detailed ex situ characterization at ambient conditions via μ-Raman spectroscopy and reflectance measurements. The optical properties of silicene on Au(111) appeared to be in accordance with the characteristics predicted theoretically for freestanding silicene, allowing the conclusion that its prominent electronic properties are preserved. The absorption features are, however, modified by many-body effects induced by the Au substrate due to an increased screening of electron–hole interactions.
... The Fermi level is used to define the energy zero and, therefore, the position of the Dirac points. Adapted and reproduced from Ref.[207].The treatment of the electron spins in the noncollinear approximation and the inclusion of relativistic effects including the SOC in the framework of the Pauli equation mainly modify the bands inFig. 16near high-symmetry and crossing points. ...
... The two 1 × 1 BZs together with the small 2D BZs of the overlayer system. Adapted from Ref.[207]. ...
The fascinating electronic and optoelectronic properties of freestanding graphene and the possible inclusion of novel two-dimensional (2D) systems in silicon-based electronics have driven the search for atomic layers consisting of other group-IV elements Si, Ge, Sn, and Pb, which form similar hexagonal lattices and are isoelectronic to graphene. The resulting 2D crystals silicene, germanene, stanene and plumbene, referred as Xenes, but also their functionalized counterparts, e.g. the hydrogenated sheet crystals, named as Xanes, silicane, germanane, and stanane, are in the focus of this review article. In addition, halogenated Xenes are investigated. The consequences of the larger atomic radii on the atomic geometry, the energetic stability, and possible epitaxial preparations are discussed. In the case of honeycomb atomic arrangements, the low-energy electronic excitations are ruled by almost linear bands. Spin–orbit coupling opens small gaps leading to Dirac fermions with finite effective masses. The linear bands give rise to an absorbance of the Xenes determined by the finestructure constant in the long-wavelength regime. While for vanishing photon energies the excitonic influence is still an open question, saddle-point excitons and excitons at M0 van Hove singularities appear at higher frequencies. After opening substantial fundamental gaps by hydrogenation, the absorption edges of the Xanes, silicane, germanane, and stanane, are dominated by bound excitons with extremely large binding energies. Other chemical functionalizations, but also vertical electric fields, yield electronic structures ranging from topological to trivial insulators. Even a quantum spin Hall phase is predicted at room temperature. The topological character and the possible quantization of the spin Hall conductivity are studied versus gap inversion, chemical functionalization, and Rashba spin–orbit interaction. The drastic changes of the electronic properties of Xenes with chemical functionalization, interaction with the substrate, and external perturbations, open future opportunities for tailoring fundamental properties and, therefore, interesting applications in novel electronic and optoelectronic nanodevices.
... The optimized lattice parameters calculated in this study as well as the experimental lattice parameters from previous studies are listed in Table III, [47][48][49][50] and the visualizations of the 2D monolayers can be seen in Fig. 1. Based on the table, we can see that the lattice parameters obtained in this study closely resemble the experimental values. ...
In this study, we conducted density functional theory calculations comparing the binding energy of the copper-amyloid-β complex to the binding energies of potential chelation materials. We used the first-coordination sphere of the truncated high-pH amyloid-β protein subject to computational limits. Binding energy and charge transfer calculations were evaluated for copper’s interaction with potential chelators: monolayer boron nitride, monolayer molybdenum disulfide, and monolayer silicene. Silicene produced the highest binding energies to copper, and the evidence of charge transfer between copper and the monolayer proves that a strong ionic bond is present. Although our three monolayers did not directly present chelation potential, the absolute differences between the binding energies of the silicene binding sites and the amyloid-β binding sites were minimal, proving that further research in silicene chelators may be useful for therapy in Alzheimer’s disease.
... More importantly, ruling out completely the formation of alloys between metals and Si/Ge/Sn is not trivial, and controversial reports indeed question the successful synthesis on metal substrates. [45][46][47][48][49][50] In addition, conductive substrates jeopardize integration into microelectronic devices as they do not allow modulating the 2D material's Fermi level by electric gating. For this reason, and because of their instability in air, there are presently only a few reports on electric devices based on this class of materials. ...
The family of two-dimensional materials has been expanding rapidly over the last few years. Within it, a special place is occupied by silicene, germanene, and stanene due to their inherent compatibility with the existing semiconductor technology (notably for the case of silicene and germanene). Although obtaining them is not trivial due to the lack of layered bulk counterparts from which they could be mechanically exfoliated, they have been recently synthesized on a number of metallic substrates. The remarkable interaction between metals and these puckered materials, however, strongly modifies their intrinsic electronic properties, and also jeopardizes their integration into functional devices. In this context, first experimental efforts are now being devoted to the synthesis of silicene, germanene, and stanene on nonmetal substrates. Here, we review these pioneering works, present the ongoing debate, analyze, and discuss the major technical challenges and finally suggest possible novel solutions worth exploring.
... [7] Since it is doubtful that silicene can exist in freestanding form, the search for appropriate substrates is key from an application point of view. Several candidate substrates have been identified in theoretical studies, ranging from insulators (such as hexagonal boron nitride, hBN [8,9] ) to semiconductors (such as MoS 2 [10] and GaAs [11] ) and metals (such as Ag, [12] Ca, [13] and Ir [14] ). The binding energy on these substrates varies from a few ten to several hundred meV per Si atom. ...
The stacking effects on the electronic structure of van der Waals heterostructures consisting of silicene and hexagonal boron nitride are investigated by first‐principles calculations. It is shown that the stacking is fundamental for the details of the dispersion relation in the vicinity of the Fermi energy (gapped, non‐gapped, linear, parabolic) despite small differences in the total energy. It is also demonstrated that the tight‐binding model of bilayer graphene is able to capture most of these features of the van der Waals heterostructures, and the limitations of the model are identified.
... Promising substrates of this kind include insulators, 33 semiconductors, [34][35][36][37][38] and metals. 39 ...
Silicene, the ultimate scaling of a silicon atomic sheet in a buckled honeycomb lattice, represents a monoelemental class of two-dimensional (2D) materials similar to graphene but with unique potential for a host of exotic electronic properties. Nonetheless, there is a lack of experimental studies largely due to the interplay between material degradation and process portability issues. This review highlights the state-of-the-art experimental progress and future opportunities in the synthesis, characterization, stabilization, processing and experimental device examples of monolayer silicene and its derivatives. The electrostatic characteristics of the Ag-removal silicene field-effect transistor exhibit ambipolar charge transport, corroborating with theoretical predictions on Dirac fermions and Dirac cone in the band structure. The electronic structure of silicene is expected to be sensitive to substrate interaction, surface chemistry, and spin–orbit coupling, holding great promise for a variety of novel applications, such as topological bits, quantum sensing, and energy devices. Moreover, the unique allotropic affinity of silicene with single-crystalline bulk silicon suggests a more direct path for the integration with or revolution to ubiquitous semiconductor technology. Both the materials and process aspects of silicene research also provide transferable knowledge to other Xenes like stanene, germanene, phosphorene, and so forth.
... Covalent bonding exists in reconstructed silicene on (0 0 0 1) surfaces of ZrB 2 and ZrC and on Ir (1 1 1), where strong hybridization of the Si sp 2 and p z orbitals with corresponding d orbitals of Zr or Ir destroys the DC [238,[294][295][296]. Many other metallic substrates have been extensively explored by DFT calculations searching for suitable surfaces to host silicene, addressing the interaction issue [297][298][299][300]. Among them only Ca(1 1 1) and Pb(1 1 1) appear as promising substrates to host Dirac fermions [299,300]. ...
... Many other metallic substrates have been extensively explored by DFT calculations searching for suitable surfaces to host silicene, addressing the interaction issue [297][298][299][300]. Among them only Ca(1 1 1) and Pb(1 1 1) appear as promising substrates to host Dirac fermions [299,300]. Silicene on Ca(1 1 1) surface does not form any reconstruction, and Si 3p z orbitals can be identified in the band structure [299]. The gapped DC (E g = 574 meV) is shifted below the E F and the whole structure becomes metallic. ...
... Among them only Ca(1 1 1) and Pb(1 1 1) appear as promising substrates to host Dirac fermions [299,300]. Silicene on Ca(1 1 1) surface does not form any reconstruction, and Si 3p z orbitals can be identified in the band structure [299]. The gapped DC (E g = 574 meV) is shifted below the E F and the whole structure becomes metallic. ...
The great success of graphene has boosted intensive search for other single-layer thick materials, mainly composed of group-14 atoms arranged in a honeycomb lattice. This new class of two-dimensional (2D) crystals, known as 2D-Xenes, becomes an emerging field of intensive research due to their remarkable electronic properties and the promise for a future generation of nanoelectronics. In contrast to graphene, Xenes are not completely planar, and feature a low buckled geometry with two sublattices displaced vertically as a result of the interplay between sp2 and sp3 orbital hybridization. In spite of the buckling, the outstanding electronic properties characteristic of graphene governed by the Dirac physics, are preserved in Xenes too. The buckled structure has also several advantages over graphene. Together with the spin-orbit interaction it may lead to the emergence of various experimentally accessible topological phases, like quantum spin Hall effect. This in turn would lead to designing and building new electronic and spintronic devices, like topological field effect transistor. In this regard the important issue concerns the electron energy gap, which for Xenes naturally exists owing to the buckling and spin-orbit interaction. The electronic properties, including the magnitude of the energy gap, can further be tuned and controlled by external means. Xenes can easily be functionalized by substrate, chemical adsorption, defects, charge doping, external electric field, periodic potential, in-plane uniaxial and biaxial stress, and out-of-plane long-range structural deformation, to name a few. This topical review explores structural, electronic and magnetic properties of Xenes and addresses the question of their functionalization in various ways, including external factors acting simultaneously. It also points to future directions to be explored in functionalization of Xenes. The results of experimental and theoretical studies obtained so far have many promising features making the 2D-Xene materials important players in the field of future nanoelectronics and spintronics.
... Thus, in practice either silicene is directly integrated with a substrate 19,20 or forms stacks of alternating silicene and metal monolayers, as in CaSi 2 which is experimentally shown to host Dirac fermions 25 . The borderline case is integration with the Si(111) substrate which is predicted to be possible by the 1 × 1 metal passivation leading to overlayer silicene preserving its Dirac cones 26 . Recently, we managed to produce epitaxial films on Si(111) of multilayer silicene stoichiometrically intercalated with active metals 27,28 , which could serve as parent compounds for 2D layer structures. ...
The appeal of ultra-compact spintronics drives intense research on magnetism in low-dimensional materials. Recent years have witnessed remarkable progress in engineering two-dimensional (2D) magnetism via defects, edges, adatoms, and magnetic proximity. However, intrinsic 2D ferromagnetism remained elusive until recent discovery of out-of-plane magneto-optical response in Cr-based layers, stimulating the search for 2D magnets with tunable and diverse properties. Here we employ a bottom-up approach to produce layered structures of silicene (a Si counterpart of graphene) functionalized by rare-earth atoms, ranging from the bulk down to one monolayer. We track the evolution from the antiferromagnetism of the bulk to intrinsic 2D in-plane ferromagnetism of ultrathin layers, with its characteristic dependence of the transition temperature on low magnetic fields. The emerging ferromagnetism manifests itself in the electron transport. The discovery of a class of robust 2D magnets, compatible with the mature Si technology, is instrumental for engineering new devices and understanding spin phenomena.
... We carry out the first-principle (FP) density functional theory (DFT) calculations using the QUANTUM ESPRESSO package [36] with the local-density approximation (LDA) the plane wave energy cutoff is setted as 250 eV in our calculation, and the Hellmann-Feynman force on the atoms was relaxed to below 0.01 eV/Å . For silicene which is one kind of the heavy boson superconductors with the crystal constant a = b = 3.86Åand c = 15.31Åwhich are close to the result of Ref. [33], the band structure with the pairing symmetry open the door to modulating the SC, which is essentially because the different hoppings in r-direction and r ′ -direction, e.g., from the d 1 + id 2 chiral symmetry SC to the f -wave symmetry SC. As the interaction U increase with the spin fluctuation under low-doping which keep the electron and hole pockets comparable [31], the susceptibility will diverging from the peak Γ-point which is related to the antiferromagnetic SDW instability due to the RPA, and get close to the FS which may be slightly modified by the electron-doping. ...
We carry out both the tight-binding model and the $ab\ initio$ to study the layered silicene, the spin, valley, sublattice degrees of freedom are taken into consider and the effects of electric field, magnetic field, and even the light in finite frequency together with its interesting optical propertice, which are all closely related to the spin-orbit coupling and Rashba coupling and lead to the tunable phase transitions (between the nontrivial topological phase which has nonzero Chern number or nonzero spin Chern number and the trivial phase). An exotic quantum anomalous Hall insulator phase are found which has nonzero spin Chern number and nonzero valley Chern number and as a giant-application-potential spintronic and valleytronics in the two-ternimate devices based on the monolayer silicene for the information transmission. In fact, the gap-out action can be understanded by analyse the Dirac mass as well as the Zeeman splitting or the external-field-induced symmetry-broken, and the changes of gap has a general nonmonotone-variation characteristic under both the effects of electron filed-induced Rashba-coupling $R_{2}(E_{\perp})$ and the electron field-induced band gap, and the band inversion related to the spin-orbit coupling which absorbs both the spin and orbital angular of momentum may happen during this process. The quantized Hall/longitudinal conductivity together with the optical conductivity are also explored, we see that even in the quantum spin Hall phase without any magnetic field, the two-terminate conductivity can be reduced to the value $e^{2}/h$ by controlling the helical edge model, and it can be further reduced to $e^{2}/2h$ by applying the magnetic field which similar to the graphene.
... Unfortunately, a free-standing silicene layer has not been produced so far. However, silicene has been formed, mainly by epitaxy, on a few substrates [7][8][9][10][11], and is predicted to be stable on other templates [12][13][14][15] or fabricated by other means [16][17][18]. In any case, the substrate may introduce external factors influencing the properties of silicene. ...
Effects of strain, charge doping and external electric field on kinetic and magnetic properties of hydrogen atoms on a free-standing silicene layer are investigated by first-principles density functional theory. It was found that the charge doping and strain are the most effective ways of changing the hydrogen-silicene binding energy, but they can only raise its value. The perpendicular external electric field can also lower it albeit in a narrower range. The strain has also the strongest impact on diffusion processes, and the diffusion barrier can be modified up to 50% of its unstrained value. The adsorption of hydrogen atoms results in a locally antiferromagnetic ground state with the effective exchange constant of approximately 1 eV. The system can easily be driven into a nonmagnetic phase by the charge doping and strain. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in fields of modern nanoelectronics and spintronics.
