Silicene Nanoribbons Research Articles

Diverse structural and electronic properties of carbon-substituted armchair silicene nanoribbons: A first-principles study

The structural and electronic properties of the armchair silicene nanoribbons (ASiNRs) under various C substitutions are investigated using the first-principles calculations. The C substitution-diversified structural and electronic properties are fully identified by the developed first-principles quantities, including the formation energies, phonon calculations, optimal structural parameters, orbital- and atom-projected density of states, and direction-projected spatial charge density distributions. The C substitutions at various adatom concentrations and distributions form the typical C substitution configurations of the single C, ortho-2C, meta-2C, para-2C, and 100% C, whereas the lower buckling height is found at the higher concentrations that become the flat 1D structure at 100% C substitution. The reshaped bandgaps are larger under shorter Si–C bond lengths. The largest opened bandgap of 2.37 eV is found at the highest adatom concentration of the 100% C configuration. The C substitutions generate the quasi σ bonds of the Si-(3s, 3p x , and 3p y ) and C-(2s, 2p x , and 2p y ) orbitals and the quasi π bonds of the Si-3p z and C-2p z orbitals, in which the quasi π orbitals create the long-range quasi π bands that determine the reshaped bandgaps. The quasi σ and π orbitals are hybridized at the middle valence energies that only separate at the deeper valence energies. The weak separation of the σ and π orbitals is responsible for the hybridization mechanism of the mixed sp 2 /sp 3 quasi in the C-substituted systems. The diverse electronic properties of the C-substituted ASiNRs will be very compatible with electronic and optoelectronic applications.

Band Polarization Effect on the Kondo State in a Zigzag Silicene Nanoribbon.

Using the Numerical Renormalization Group method, we study the properties of a quantum impurity coupled to a zigzag silicene nanoribbon (ZSNR) that is subjected to the action of a magnetic field applied in a generic direction. We propose a simulation of what a scanning tunneling microscope will see when investigating the Kondo peak of a magnetic impurity coupled to the metallic edge of this topologically non-trivial nanoribbon. This system is subjected to an external magnetic field that polarizes the host much more strongly than the impurity. Thus, we are indirectly analyzing the ZSNR polarization through the STM analysis of the fate of the Kondo state subjected to the influence of the polarized conduction electron band. Our numerical simulations demonstrate that the spin-orbit-coupling-generated band polarization anisotropy is strong enough to have a qualitative effect on the Kondo peak for magnetic fields applied along different directions, suggesting that this contrast could be experimentally detected.

Doping of two thallium atoms in silicene nanoribbons in the electric field

Abstract The low-dimensional material that revolutionizes technology, silicene is a monolayer of silicon molecules, which is a potential material. Silicene nanoribbons (SNRs) are one-system silicene ribbons with two hydrogen-modified edges. Two thallium atoms will be doped in each unit cell of the SNRs, the electric field acting on the doped system has a magnitude of 0.1V/angstrom. The configurations studied here all exhibit stability because of the bonds between atoms. The configurations studied here all exhibit stability because of the bonds between atoms. Density functional theory (DFT) and VASP software are used to study and simulate materials.

Investigating magneto-resistance in transition metals doped silicene nanoribbons

The Magneto Resistance (MR) is investigated in magnetic impurity-doped Zigzag Silicene Nano-Ribbons (ZSiNR) through Density Functional Theory (DFT) and Non-Equilibrium Green's Functions (NEGF) formalism using different spin configurations (Ferromagnetic (FM) and Antiferromagnetic (AFM)) in electrodes. The MR is calculated, and results show a GMR of about 2 ​× ​104% at 0.01V bias voltage for up-spin electrons in Co@ZSiNR structure and a total GMR of 2.6 ​× ​104% at 0.02V, which makes the proposed structures as possible candidates in spintronic device applications. The structures are modified by adding the impurities to the electrodes region, and removing the Hydrogen passivation. The GMR effect is investigated in these structures with different widths, which improves GMR ratios in certain widths.

Inner-edge states in silicene nanoribbons and related applications to novel device design

We study the quantum transport in hybrid silicene nanoribbons in the presence of a spatially alternative electric field. We found that valley resolved inner-edge states can be obtained in zigzag nanoribbons with opposite electric fields applied in the upper and lower half-nanoribbons, and pure valley current is obtained. A dissipationless transistor is designed based on the inner-edge states. It is found that the inner-edge states are not robust, and defects on the interface between the upper and lower half-nanoribbons can change the conductance to zero. To improve the performance of the device, we consider a region without electric field between two regions with opposite electric fields. Electrons is not confined at the interface of the upper and lower half-nanoribbons, and they can transport in the region without electric field. Defects can also affect the conductance, but the conductance can not be changed to zero easily. Armchair nanoribbons are also considered in this study to design a dissipationless transistor, and the difference is that we do not consider the degree of freedom valley in the device based armchair ribbons. Our findings open the possibility of the dissipationless transistor design based on inner-edge states in silicene nanoribbons.

Thermoelectric performance of biased silicene nanoribbon in the presence of magnetic field

In this study with the tight binding model, we investigated the electronic and thermal properties of biased Armchair Silicene nanoribbon (AN-SiNR) in the presence of the perpendicular magnetic field. The band gap of AN-SiNRs decreases and increases with applying the vertical magnetic field and bias voltage, respectively. In the presence of magnetic field the DOS spectrum shows significant modifications such as splitting the DOS peak and changing the number of DOS peaks. The thermal properties of unbiased A16-SiNR in absence of external fields is negligible in low temperature and increases rapidly with temperature because the thermal energy increases with T. The bias voltage and magnetic field have opposite effects on the electronic and thermal properties of SiNRs. The increasing rate of thermal properties in terms of temperature decreases (increases) with bias voltage U (magnetic field Π) and the stronger U (Π) has smaller (larger) thermal properties due to increasing (decreasing) the band gap. The Lorenz coefficient has peak for each AN-SiNRs and it decreases by increasing the magnetic field and their peak positions move to lower temperature range. By comparing the thermal properties of A16-SiNR and A19-SiNR, we found that A19-SiNR has higher thermal properties because it has a smaller band gap in the present magnetic field and bias voltage and its charge carriers can be excited to conduction bands by lower thermal energy.

Computational Study of Metal-Free Magnetism and Spin-Dependent Seebeck Effect in Silicene Nanoribbons with Zigzag and Klein Edges

Nanoribbons based on low-dimensional materials are potential candidates for nanoscale spintronics devices. Here, some ferromagnetic silicene nanoribbons with zigzag and Klein edges (N-ZKSiNRs) are constructed. It is demonstrated that the N-ZKSiNRs with various widths (N) are placed in various spin-resolved electronic situations. With the increase of the width parameter N from 4 to 19, the N-ZKSiNRs pass from the indirect-gap bipolar magnetic semiconducting state (BMS) to the bipolar spin-gapless semiconductor (BSGS) and eventually to half-metallicity (HM). Moreover, applying a temperature gradient through the nanoribbons leads to spin-dependent current with the opposite flowing and spin orientations, demonstrating the spin-dependent Seebeck effect (SDSE). Besides, it was found that the BSGS phase is superior to the BMS and HM for generating SDSE. These findings confirm that the ZKSiNRs are promising choices for spin caloritronics devices.

Structural and electronic properties of silver-adsorbed silicene nanoribbons: A first-principles study

The geometrical and electrical features of Ag adsorption armchair silicene nanoribbons structure have been investigated using first-principles calculations. The findings reveal that the bandgap of doped Ag has changed, as it does for chemical adsorption on the surface of ASiNRs; this material became metallic at the valance band contact fermi level, with a mean bandgap of 0 eV. Furthermore, the survey to discover the best height 6.39 of Ag and 2.26 bond length Si-Si and Si-Si-Si bond angle 115015’ with structural stability near to the pristine situation has shown promising results for developing novel spintronic and optoelectronic materials in the future.

The spectral detectivity analysis of intrinsic, n-type and p-type A-SiNRs IR-photodetectors

In the present paper, the results of the performance of armchair silicene nanoribbons (A-SiNR) based Infrared (IR) photodetector using density functional theory (DFT) method are presented. A-SiNRs in different widths of group NA = 3 m in pure state and in the state applied by aluminum (Al) and phosphorus (P) atoms in optimize position as impurities have been studied. The results show that with increasing width and increasing temperature in the presence of impurity atoms, the spectral responsivity increases but the specific detectivity (D*) decreases due to increasing dark current. The maximum specific detectivity for the group NA = 3 m is observed in pure state, which the maximum specific detectivity value is related to the width NA = 6 and is equal to 3.7 × 1010 (cmHz1/2/W). The maximum spectral responsivity is observed in the width NA = 12 and the state in which the impurity Al atoms are applied, that is equal to 0.045 A/W.

Effects of hydrogen/halogen –edge termination on structural, electronic, and optical properties of planar silicene nanoribbons SiNRs

The effects of (hydrogen/halogen)–edge termination on the structural, electronic, and optical properties of planar SiNRs with either zigzag (ZSiNRs) and armchair (ASiNRs) edges are investigated by means of DFT calculations . The obtained results show that X-edge termination is a new approach to tune and open the band gap in planar SiNRs, and exhibiting a metallic character. The density of states (DOS) analysis reveals a strong hybridization between halogen- p and edges Si- p states, which is not the case of H- s and edges Si- p states. The calculated charge density contours manifest the ionic nature of Si–X (X = H, F, Cl, Br, and I) bonds. However, the Si–Si bonds display a typical covalent bonding feature. The investigation of the optical properties for both polarizations indicates that 7-ASiNR-X and 5-ZSiNR-X exhibit strong optical anisotropy in infrared (IR), visible (VIS), and ultraviolet (UV) regions under both polarizations, making them promising candidates for optoelectronics and optical nanodevices such as polarization-sensitive photodetectors. Besides, for perfect planar ASiNR and ZSiNR, the strong absorbance peak of ε 2 y y ( ω ) has been found to occur at 0.32 (0.36) eV, respectively, suggesting that these compounds may be candidates for IR optoelectronic devices . The most dominant absorption peaks centred at 5.17 and 4.5 eV for ASiNR-H and ZSiNR-H systems, respectively, indicate a high absorbance in the UV range, making them prospective nanomaterials for photovoltaic devices . • The X-edge terminated planar ZSiNRs exhibit a metallic character. • Si–X (X = H, F, Cl, Br, I) bonds manifest an ionic nature whereas Si–Si bonds display a typical covalent bonding. • 7-ASiNR and 5-ZSiNR exhibit a strong optical anisotropy (IR, VIS, UV), hence promising candidates for optoelectronics. • Perfect planar ASiNR/ZSiNR exhibit a strong absorbance peak at 0.32/0.36 eV hence can be used for IR optoelectronic devices. • The high absorbance in UV range makes them prospective nanomaterials for photovoltaic devices.

First-Principles Investigations of Al/P Co-doping Effect on Disconnected Armchair Silicene Nanoribbon for Switching Device Applications

First-Principles Investigations of Al/P Co-doping Effect on Disconnected Armchair Silicene Nanoribbon for Switching Device Applications

The effects of Co/Ni-vacancy complex defects on the electronic and transport properties of armchair silicene nanoribbon

The effects of Co/Ni-vacancy complex defects on the electronic and transport properties of armchair silicene nanoribbon

Study on doping of two zinc atoms in silicene nanoribbons in the presence of an external electric field

One low-dimensional material with many favorable properties that promise potential future applications is silicene. By modifying the edges, it is possible to create a one-dimensional material from silicene that is silicene nanoribbons. This study deals with SNRs material with a width of 6Si atoms and modified edges by H atoms. In this work, Zn atoms will be doped instead in SNRs, an external electric field. magnitude 0.35 V/Angstrom will act on the system during the research. Density functional theory (DFT) and VASP software will be used to study and simulate the doped structures. The study shows that the band gap in the meta configuration is extended to 0.643 eV, and multi-orbital hybridizations are evident in the energy region from −3eV to −6eV. Research results will suggest future applications in the field of microelectronics.

Study of doping a thallium atom in silicene nanoribbons in an electrical field

Silicene is a two-dimensional material made up of silicon atoms, the silicene nanoribbons (SNRs) studied here are made of silicene with edges modified by hydrogen atoms. The work doped a thallium atom into the unit cell of SNRs, the electric field acting on the system has a constant magnitude: 0.15V/Å. There are two doped structures studied, top structure and valley structure. Density functional theory (DFT) is used in this study, the bands of energy and states of the configurations will be plotted, investigated, and analysed. The partial states (s, p) will be studied.

Silicene Nanoribbon Based Spin-Field Effect Transistor With Spin Filtering and Spin Seebeck Effects

The present work reports the application of density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism based framework to investigate the voltage-dependent spin transport properties for a Z-shaped silicene nanoribbon (SiNR) based spin-field effect transistor (spin-FET). The structural and magnetic properties of transition metal passivated zigzag-SiNR with symmetric and asymmetric hydrogenation at other ends have been analyzed to identify the suitability of these materials as a potential source and drain electrodes for the proposed spin-FET model. The analysis reveals that the device displays an excellent spin filtering effect and oscillatory transfer characteristics in the parallel configuration (PC) mode. Also, a high drive current and I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ _{ON}$</tex-math></inline-formula> /I <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ _{OFF}$</tex-math></inline-formula> ratio and both positive and negative transconductance are achieved. Additionally, the device generates a highly spin-polarized thermal current with the spin Seebeck effect and high spin filtration efficiency under the influence of temperature gradient. These findings defend that the proposed device model can be treated as multifunctional spintronic and spin caloritronic devices.

Ag-doped silicene nanoribbons in the electric field

Silicene nanoribbons (SNRs) will be doped with Ag atoms, silver atoms will be substituted at several positions in the structure of SNRs to create doped configurations. An external electric field of 0.1 V/Å will be applied to the doped systems. The theory used in this study is density functional theory (DFT). The doping profiles are optimized and they are all stable in the external electric field. The formation energies of the doped configurations will be calculated, the structure of energy bands and state densities of the systems will be plotted, investigated, and discussed. The study shows that the top configuration is a semi-metal, while the meta configuration is a semiconductor. Depending on the application, the system can use a semi-metal or a semiconductor, which creates a wide range of applications in electronic technology.

Several semiconducting two-dimensional silicon nanosheets assembled from zigzag silicene nanoribbons.

Semiconducting two-dimensional intrinsic silicon nanosheets are ideal materials for many applications in modern industry, since they are the only ones that can match well with previous silicon components. However, such materials are still lacking, especially those with moderate band gaps. In this work, by using first-principles theory, a series of two-dimensional intrinsic silicon nanosheets are assembled from zigzag silicene nanoribbons with different widths. The result shows that all the nanosheets behave as semiconductors, although some of them possess small band gaps of dozens of meV. Two of them, individually assembled from the two narrowest zigzag silicene nanoribbons, possess the largest indirect band gaps of 0.20 and 0.26 eV, respectively. Under low compressive strain, these two nanosheets would turn into quasi-direct or direct band gap semiconductors, and the gaps increase up to 0.62 or 0.54 eV, respectively. Due to the electron transfer from three-fold to four-fold coordinated Si atoms, the charge carriers prefer to transport along the zigzag direction, and electrons and holes transport in the respective Si chains. Interestingly, the investigation of Poisson's ratio reveals that the assembled silicon nanosheets have a negative Poisson's ratio in certain strain ranges if the width n of zigzag silicene nanoribbons is even. This work provides a new approach to design semiconducting silicon nanosheets and benefits to the applications of two-dimensional silicon nanosheets in many electronic and mechanical fields.

Electronic and Thermoelectric Properties of Armchair Edge Silicene Nanoribbons: Role of Quantum Antidot Arrays

Electronic and Thermoelectric Properties of Armchair Edge Silicene Nanoribbons: Role of Quantum Antidot Arrays

Applying first principles to study the structural, electronic, and magnetic properties of Pr adsorbed ASiNRs

Applying first-principles calculations, the investigation of the geometrical and electronic properties of Pr adsorption armchair silicene nanoribbons structure has been established. The results show that the bandgap doped Pr has been changed, which is the case for chemical adsorption on the surface of ASiNRs; this material became metallic with the peak of valance band contact fermi level. Moreover, the survey to find the optimal height 1.82 Å of Pr and 2.24 Å bond length Si-Si, and Si-Si-Si bond angle 108005’, energy adsorption is -7.65 eV, buckling is 0.43 Å with structure stability close to the pristine case, has brought good results for actively creating newly applied materials for the spintronic and optoelectronics field in the future.

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.