Silicene-based Devices Research Articles

Effect of electromagnetic radiation on the electronic and thermoelectric properties of armchair edge silicene nanoribbons

We theoretically investigate the influence of electromagnetic radiation on the electronic and thermoelectric properties of armchair edge silicene nanoribbons. Specifically, we study the effects of varying the polarization (s or p) and incident angle (0, 30, 45, 60, and 90°) of radiation on the band structure, transmission function, density of states, Seebeck coefficient, and electronic figure of merit (ZTe) of the nanoribbons. Our results demonstrate that the electronic properties are highly dependent on radiation conditions due to their influence on electron transport. We find that the transmission function and density of states exhibit distinct polarization-dependent behaviors that highlight the role of the radiation's electric field orientation. Importantly, the ZTe shows significant modulation with the incident angle for both polarizations, achieving optimized values up to 0.18. These findings provide insights into controlling the electronic and thermoelectric properties of silicene nanoribbons using electromagnetic radiation. Our work underscores opportunities for developing silicene-based nanophotonic devices with enhanced performance through all-optical means. The demonstrated tunability via irradiation paves the way for potential applications such as optical switches, sensors, and next-generation optoelectronics using silicene nanoribbons.

All-around encapsulation of silicene.

Silicene or the two-dimensional (2D) graphene-like silicon allotrope has recently emerged as a promising candidate for various applications in nanotechnology. However, concerns on the silicene stability still persist to date and need to be addressed aiming at the fabrication of competing and durable silicene-based devices. Here, we present an all-around encapsulation methodology beyond the current state-of-the-art silicene configuration, namely silicene sandwiched in between a capping layer (e.g., Al2O3) and the supporting substrate (e.g., Ag). In this framework, the insertion of one or two sacrificial 2D Sn layers enables the realization of different atomically thin encapsulation schemes, preserving the pristine properties of silicene while decoupling it from the growth template. On one hand, the epitaxy of a 2D Sn layer before silicene allows for the removal of the Ag substrate with no effect on silicene which in turn can be easily gated, for example, with an oxide layer on its top face. On the other hand, a full 2D encapsulation scheme, where top and bottom faces of silicene are protected by 2D Sn layers, gives rise to an atomically thin and cm2-scaled membrane preventing degradation of silicene for months. Both schemes thus constitute an advancement for the silicene stability and encapsulation in ambient conditions, paving the way to further exploitation in flexible electronics and photonics.

Revealing the hydrogenated structure of silicene- (√13×√13)R13.9∘ by tip-induced dehydrogenation

The application of voltage pulse in a scanning tunneling microscope has been demonstrated to induce dehydrogenation on hydrogenated silicene/Ag(111), recovering intact silicene phases. This manipulation provides us a method to build a relationship between various silicene phases and their hydrogenated structures. Combining with density-functional theory calculations, hydrogenation of silicene-$(\ensuremath{\surd}13\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}13)R13.{9}^{\ensuremath{\circ}}$ is found to produce the same half silicane as hydrogenated silicene-$(2\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{}2\ensuremath{\surd}3)R{30}^{\ensuremath{\circ}}$. These two silicene phases are suggested to be the same monolayer silicene on Ag(111), albeit with different Si buckling configurations and lattice strains. Our study not only reveals the hydrogenated structure of silicene-$(\ensuremath{\surd}13\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}13)R13.{9}^{\ensuremath{\circ}}$, but also offers significant potential for lithography and modification of hydrogenated silicene at atomic scale for future design of silicene-based electronic devices.

Multifunctional silicene/CeO2 heterojunctions: Desirable electronic material and promising water-splitting photocatalyst

The first-principles calculations demonstrate that covalently bonded (cb) heterojunction and van der Waals (vdW) heterojunction can coexist in silicene/CeO2 heterojunctions, due to the different stacking patterns. Especially, the cb heterojunction with band gap of 1.97 eV, forms a type-II heterojunction, exhibits good redox performance and has high-effective optical absorption spectra, thus it is a promising photocatalyst for overall water splitting. Besides, for the vdW heterojunction, the Dirac cone of silicene is well kept on CeO2 semiconducting substrate, with a considerable energy gap of 0.43 eV, which can be an ideal material in building silicene-based electronic device. These results may open a new gateway in both of nanoelectronic device and energy conversion for silicene/CeO2 nanocomposites.

Role of line defect in the bandgap and transport properties of silicene nanoribbons

By using the tight-binding model and non-equilibrium Green's function method (NEGF), we study the band structures and transport properties of a silicene nanoribbon with a line defect where a bulk energy gap is opened due to the sublattice symmetry breaking. The flat subband bends downwards or upwards due to the effect of the line defect. The spin-orbit coupling induces quantum spin Hall states. Especially, the energy band depends on the distance between the line defect and the edge of the nanoribbon. The effects of the on-site energies on the band spectra of the two defect configurations are different. There always exists one band gap for different on-site energies for the defect configuration of case 1. However, a gapless state and a band gap can be modulated by changing the on-site energy, the sublattice potential and spin-orbit couplings for the defect configuration of case 2. Accordingly, the variation trends of the conductance including zero conductance can be well understood in terms of the combined effect of the sublattice potential, the on-site energy and spin-orbit couplings on the band structures. Thus it is easy and effective to modulate the transport property of the silicene nanoribbon with the defect configuration of case 2 by utilizing the sublattice potential, the on-site energy and spin-orbit couplings. This study is of great significance for the fabrication and the modulation of the transport property of silicene-based devices.

Topological phases in few-layer silicene nanoribbon induced by normally applied electric field and Rashba spin-orbit coupling

Edge states of a few-layer silicene nanoribbon (FSNR) have potential applications in spintronic and nanodevices. Quantum transport properties of zigzag superlattice FSNR exposed to vertical electric field and Rashba spin-orbit coupling (RSOC) are studied within the tight-binding based non-equilibrium Green's function approach. In addition, the topological insulator-band insulator phase transition of FSNR and the influence of adding a new layer on edge states of conduction electrons have been investigated. Calculations demonstrate that the external electric field applied perpendicularly to the FSNR device, results in gap opening and metal-semiconductor and metal-semimetal phase transition. Further, we found that different topological phase transitions, quasi-topological insulator-band insulator and topological insulator-band insulator by applying a vertical electric field. Meanwhile, results reveal that by tuning the RSOC strength, we can control the spin current. This controllability of spin and quantum transport in FSNR may contribute to potential applications in silicene-based devices and the development of spintronic.

Optical properties of silicene-dielectric interfaces from IR to far UV

Since the growth of single layer of Si has emerged, silicene became a potential candidate material to make up the disadvantage of graphene. In this paper, the complex surface conductivity is applied to characterize the properties of silicene and we investigate the optical characterization of silicene-dielectric interfaces from IR to far UV range. The silicene-Si and silicene-Ge interfaces along both parallel and perpendicular polarization directions of electromagnetic field with normal incidence are considered in this work. The optical properties of the silicene-dielectric systems proposed in this paper lay a foundation for the performance of complex silicene-based optoelectronic devices such as sensors, detectors, filters, UV absorbers and so on.

Correction: Largely enhanced thermoelectric effect and pure spin current in silicene-based devices under hydrogen modification

Correction for 'Largely enhanced thermoelectric effect and pure spin current in silicene-based devices under hydrogen modification' by G. Qiao et al., Nanoscale, 2020, 12, 277-288, DOI: 10.1039/C9NR07541K.

Tunable electronic properties of silicene based heterojunctions with ultrathin high-к La2O3 gate dielectric

The silicene/La 2 O 3 heterojunctions envision promising applications in novel integrated functional nanodevices . The electronic properties of silicene , La 2 O 3 , and silicene/La 2 O 3 heterojunctions are investigated by first-principles calculations. The silicene/La-terminated La 2 O 3 heterojunction presents a 1.753 eV band gap, which is desired for silicene-based semiconductor devices. The effects of biaxial strain and external electric field are studied for the band structure of silicene/La 2 O 3 heterojunction. The band gap values of silicene/La 2 O 3 heterojunction could be effectively modulated. These findings indicate the potential application prospects of silicene-based field effect transistor with La 2 O 3 gate dielectric in nanoscale devices. • The silicene/La-terminated La 2 O 3 heterojunction presents a desired 1.753 eV band gap. • External electric field induces semiconductor–metal transitions. • The band gap values of silicene/La 2 O 3 heterojunction could be effectively modulated by biaxial strains. • The silicene/La 2 O 3 heterojunction has a potential application in silicene-based MOSFETs.

Largely enhanced thermoelectric effect and pure spin current in silicene-based devices under hydrogen modification.

Based on the density functional theory and nonequilibrium Green's function methods, we launch a systematic study of the magnetic properties and thermoelectric effects in silicene-based devices constructed by using zigzag silicene nanoribbons (ZSiNRs). By modulating the adsorption site, it is found that the ground state of ZSiNRs varies from an antiferromagnetic state to a ferromagnetic state. Meanwhile, a spin-degenerate semiconductor evolves into a spin semiconductor. The spin and charge thermoelectric figure of merits have an almost equal value of about 60 in the narrow device, which originates from the spin-dependent conductance dips and high spin-filtering effects. Moreover, a thermally-driven pure spin current in the silicene-based devices is obtained in the absence of the gate voltage, and its magnitude is effectively enhanced as the device width increases. Our results suggest that the silicene-based devices have very good prospects for spin caloritronics.

Effects of heteroatom (B or N)-doping on the electronic and transport properties of armchair silicene nanoribbon

We investigate the effects of heteroatom (boron or nitrogen atom)-doping on the electronic and transport properties of armchair silicene nanoribbon by means of the First-principles method. The calculated results show that the bandgap of armchair silicene nanoribbons (ASiNRs) can be modulated by changing the distance between two doping sites. The ASiNRs appear the semi-metallic property with two boron atoms doping, while the ASiNRs transform from semiconducting to metallic property with two nitrogen atoms doping. It can be found that the bandgaps of ASiNRs are decreasing with the increasing distance between boron atom and nitrogen atom. The transport properties of ASiNRs with B/N codoping are also investigated, the differential conductance appears an oscillatory behavior, it is hoped that it may be useful for designing the silicene-based electronic devices.

Computational study of silicene nanoribbon tunnel field-effect transistor

Stable room temperature operation of field-effect transistor (FET) based on two-dimensional silicon (silicene) has recently been reported. Like graphene, silicene is a Dirac cone material. Silicene-based devices provide high off-state leakage current due to lack of a significant bandgap. However, quantum confined silicene nanoribbon (SiNR) shows observable bandgap which can be used for making switching transistors for digital integrated circuit design. Contrary to metal oxide semiconductor FET (MOSFET), tunnel field-effect transistor (TFET) overcomes the physical limit of scaling of supply voltage. In this work, we present structure and characteristics of SiNR TFET using atomistic simulation based on self-consistent solution of 3D Poisson and Schrodinger equations within the non-equilibrium Green’s function formalism. Performances are also compared with the International Technology Roadmap for Semiconductors projected high performance requirements of 2026 nMOSFETs.

Fracture characteristics of silicene nanosheet with a crack under tension estimated using molecular dynamics simulation

Abstract By conducting molecular dynamics (MD) simulations, we investigated the fracture behavior of a silicene nanosheet that had a pre-existing crack and was subjected to tensile loading. The effects of the crack length and crack angle were also examined under different tensile strains at different temperatures of 0, 100, 200, 400, and 500 K. According to the simulation results, the ultimate stresses and the corresponding strains decreased as the temperature increased. At 0, 100, 200, 400, and 500 K, the ultimate stresses on the silicene nanosheet with a crack length L of 3 nm and crack angle θ of 0° were 10.2, 9.8, 8.8, 7.9, and 7.4 N/m, respectively, and the corresponding strains were 0.35, 0.32, 0.28, 0.23, and 0.22, respectively. This study is crucial for the future design and application of silicene-based devices.

Generation of valley pump currents in silicene**Project supported by the National Natural Science Foundation of China (Grant Nos. 11274059, 11574045, and 11704165).

We propose a workable scheme for generating a bulk valley pump current in a silicene-based device which consists of two pumping regions characterized by time-dependent strain and staggered potentials, respectively. In a one-dimension model, we show that a pure valley current can be generated, in which the two valley currents have the same magnitude but flow in opposite directions. Besides, the pumped valley current is quantized and maximized when the Fermi energy of the system locates in the bandgap opened by the two pumping potentials. Furthermore, the valley current can be finely controlled by tuning the device parameters. Our results are useful for the development of valleytronic devices based on two-dimensional materials.

Emergence of magnetism in silicene by introducing carbon atom as foreign atom in all possible ways

In spite of the unique properties of graphene and considerable efforts by various researchers in last two decades to functionalize it for tailored applications, its limitations have spurred much interest in the search of alternate two-dimensional (2D) materials beyond graphene. A new crystalline form of silicon namely ‘‘silicene’’ which is the silicon-based counterpart of grapheme has emerged out as a substitute of graphene. Motivated by novel properties of this nanomaterial, we have explored the emergence of magnetism in Silicene via introducing a C-atom as foreign atom in almost all possible ways using first principles approach. The case we have investigated are (1) pristine silicene (2) vacancy in silicene (3) C lies at adsorption site (4) C lies at adsorption site with vacancy consideration (5) C is adsorbed in the middle of two Si atoms surrounding vacancy (6) C is present as an adatom (7) C acts as substitutional dopant in silicene. Among all these, the case in which the C lies at adsorption site with vacancy consideration is found to be most stable. All cases show the ferromagnetic behavior and transition from semi conducting to metallic state; generation of magnetic moment of 2.0–2.8 µB on it by surface modifications. The Fermi level (EF) is manipulated by intermixing of p-states of Si with p-states of foreign C atom are major cause of generation of magnetism inside the channel. The magnetism in silicene via C adsorption increases its potential in more compatible with current Si-based technology in comparison with graphene. These results provide better understanding for manufacturing the silicene-based nanoelectronic devices and expect to open new horizons in spintronic applications.

Spin-current pump in silicene**Project supported by the National Natural Science Foundation of China (Grant Nos. 11274059, 11574045, and 11704165).

We report a theoretical study of pumped spin currents in a silicene-based pump device, where two time-dependent staggered potentials are introduced through the perpendicular electric fields and a magnetic insulator is considered in between the two pumping potentials to magnetize the Dirac electrons. It is shown that giant spin currents can be generated in the pump device because the pumping can be optimal for each transport mode, the pumping current is quantized. By controlling the relevant parameters of the device, both pure spin currents and fully spin-polarized currents can be obtained. Our results may shed a new light on the generation of pumped spin currents in Dirac-electron systems.

Width-Dependent Optical Properties for Zigzag-Edge Silicene Nanoribbons**Supported by the National Natural Science Foundation of China under Grant Nos 11664010 and 11264013, the Hunan Provincial Natural Science Foundation of China under Grant Nos 2017JJ2217 and 12JJ4003, the Scientific Research Fund of Hunan Provincial Education Department of China under Grant No 14B148, the Science and Technology Innovative Research Team in Higher Educational

We study theoretically the optical response for perfect zigzag-edge silicene nanoribbons with N silicon atoms of the A and B sublattices (N-ZSiNRs) under the irradiation of an external electromagnetic field at low temperatures. The 8- and 16-ZSiNRs are demonstrated to exhibit a broad energy regime of absorption coefficient, refractive index, extinction coefficient, and reflectivity from infrared to ultraviolet, utilizing the dipole-transition theorem for semiconductors. The optical spectra for 8- and 16-ZSiNRs may be classified into two types of the transitions, one between valence and conduction subbands with the same parity, and the other among the edge state and bulk state subbands. With the increase of the ribbon width, the optical spectra for ZSiNRs are proved to exhibit red shift and blue shift at the lower and higher energy regimes, respectively. The obtained novel features are believed to be of significance in designs of silicene-based optoelectronic devices.

Infrared to near-ultraviolet optical response for zigzag-edge silicene nanoribbons under the irradiation of an external electromagnetic field

We investigate theoretically the width-dependent electronic structure and optical spectrum for intrinsic zigzag-edge silicene nanoribbons with N silicon atoms of the A and B sublattice (N-ZSiNRs) under the irradiation of an external electromagnetic field at low temperatures. Based on the method of the tight-binding approximation, we have derived a width-dependent dispersion relation and wave function for N-ZSiNRs under the hard-wall boundary condition. By way of the dipole-transition theorem for semiconductors, both the 8- and 16-ZSiNRs have been observed to exhibit broad values (0.30–3.20 eV) of optical conductivity, dielectric function and electron energy loss spectrum in the range of infrared to near-ultraviolet. The optical spectra for 8- and 16-ZSiNRs have been manifested to be transitions between the valence and conduction bands with the same subband indices, as well as the resonances between the edge state and bulk state subbands, while the optical transitions among the different indexed bulk subbands should be forbidden owing to the non-conserved momentum. The obtained results are believed to be of importance in exploring new effects and optoelectronic applications of the silicene-based electron devices.

Guided modes in silicene-based waveguides

Silicene is a new Dirac-type electron system similar to graphene. A monolayer silicene sheet forms a quantum well induced by an electrostatic potential, which acts as an electron waveguide. The guided modes in the silicene waveguide have been investigated. Electron waves can propagate in the silicene-based waveguide in the cases of Klein tunneling and classical motion. The behavior of the wave function depends on the spin and valley indices. The amplitude of the electron wave function in the silicene waveguide can be controlled by the external electric field. These phenomena may be helpful for the potential applications of silicene-based electronic devices.

Robust and controllable electronic local transports in armchair silicene nanoribbons under a perpendicular electric field

We study the electronic local distribution and transports in pristine armchair-edge silicene nanoribbons (ASiNRs) based on the tight-binding approximation. By calculating the local densities of states at different sites and the bond current between two adjacent sites, we show that comparing to the pristine armchair-edge graphene nanoribbons, a similar “[Formula: see text]” rule and multiple low-electron transport channels exist in the pristine [Formula: see text]-ASiNRs. However, differently, they are controllable to appear and disappear by applying an electric field perpendicular to the ribbon plane. Therefore, one can manipulate the semiconducting channels and realize the current switch “on/off,” unchanging their structures. Moreover, the results are robust against the edge-passivation and a few structural defects, which ensures their stability for the practical application in the silicene-based device.