/Tag: Silicene

Substrate-induced half-metallic property in epitaxial silicene. (arXiv:1903.03230v1 [cond-mat.mtrl-sci])

2019-03-11T02:29:24+00:00March 11th, 2019|Categories: Publications|Tags: , |

For most practical applications in electronic devices, two-dimensional materials should be transferred onto semiconducting or insulating substrates, since they are usually generated on metallic substrates. However, the transfer often leads to wrinkles, damages, contaminations and so on which would destroy the previous properties of samples. Thus, generating two-dimensional materials directly on nonmetallic substrates has been a desirable goal for a long time. Here, via a swarm structure search method and density functional theory, we employed an insulating cubic boron nitride (c-BN) as a substrate for the generation of silicene. The result shows that the silicene behaves as ferromagnetic half-metal because of the strong interaction between silicon and nitrogen atoms on c-BN(111) surface. The magnetic moments are mostly located on nitrogen sites without bonding silicon atoms on surface and the value is 0.12 uB. In spin-up channel, it behaves as a direct band gap semiconductor with a gap of 1.35 eV, while it exhibits metallic characteristic in spin-down channel. The half-metallic band gap is 0.11 eV. Besides, both the magnetic and electronic properties are not sensitive to the external compressive strain. This work maybe open a way for the utility of silicene in spintronic field.

Published in: "arXiv Material Science".

Higher harmonic generation by massive carriers in buckled two-dimensional hexagonal nanostructures

2019-02-20T14:38:59+00:00February 20th, 2019|Categories: Publications|Tags: , |

Author(s): H. K. Avetissian and G. F. MkrtchianGeneration of high harmonics in novel two-dimensional (2D) nanostructures such as silicene, germanene, and stanene initiated by strong coherent electromagnetic radiation of arbitrary polarization, taking into account the spin-orbit coupling and the buckling of two Bravais lattices, is investigated. …[Phys. Rev. B 99, 085432] Published Wed Feb 20, 2019

Published in: "Physical Review B".

Giant Seebeck magnetoresistance triggered by electric field and assisted by a valley through a ferromagnetic/antiferromagnetic junction in heavy group-IV monolayers

2019-02-19T14:43:49+00:00February 19th, 2019|Categories: Publications|Tags: , |

Author(s): Xuechao Zhai, Junwei Gu, Rui Wen, Ruo-Wen Liu, Min Zhu, Xingfei Zhou, L.-Y. Gong, and Xing’ao LiElectrons in heavy group-IV monolayers, including silicene, germanene, and stanene, have the ability to exhibit rich physics due to the compatibility of the spin and valley degrees of freedom. We propose here that a valley-mediated giant Seebeck magnetoresistance (MR) effect, triggered and controlle…[Phys. Rev. B 99, 085421] Published Tue Feb 19, 2019

Published in: "Physical Review B".

Searching for the optimum conditions for silicene growth by calculations of the free energy. (arXiv:1902.06248v1 [cond-mat.mtrl-sci])

2019-02-19T02:29:24+00:00February 19th, 2019|Categories: Publications|Tags: , , |

Very recently we developed an efficient method to calculate the free energy of 2D materials on substrates and achieved high calculation precision for graphene or $gamma$-graphyne on copper substrates. In the present work, the method was further confirmed to be accurate by molecular dynamic simulations of silicene on Ag substrate using empirical potential and was applied to predict the optimum conditions based on emph{ab initio} calculations for silicene growth on Ag (110) and Ag (111) surface, which are in good agreement with previous experimental observations.

Published in: "arXiv Material Science".

Magneto-optical effects in the Landau level manifold of 2D lattices with spin-orbit interaction. (arXiv:1902.05359v1 [cond-mat.mes-hall])

2019-02-15T04:30:31+00:00February 15th, 2019|Categories: Publications|Tags: , |

Silicene is a competitive and promising 2D material, possessing interesting topological, electronic and optical properties. The presence of strong spin orbit interaction in silicene and its analogues, germanene and tinene, leads to the opening of a gap in the energy spectrum and spin-splitting of the bands in each valley. We develop a general method to determine the magneto-optic response of silicene, when a Gaussian beam is incident on silicene grown on a dielectric substrate in the presence of a static magnetic field. We use a semiclassical treatment of silicene monolayer to describe the Faraday rotation (FR) and Magneto-optical Kerr effect (MOKE) using a general model for beam propagation. The response can be modulated both electrically and magnetically. We derive analytic expressions for valley and spin polarized FR and MOKE for arbitrary polarization of incident light in the terahertz regime. We demonstrate that large FR and MOKE can be achieved by tuning the electric field, magnetic fields and chemical potential in these fascinating 2D materials. Implications for novel valleytronic experiments are also discussed.

Published : "arXiv Mesoscale and Nanoscale Physics".

<i>Ab initio</i> study of the structural, electronic, magnetic, and optical properties of silicene nanoribbons

2019-02-11T14:35:29+00:00February 11th, 2019|Categories: Publications|Tags: |

Author(s): Matteo Ferri, Guido Fratesi, Giovanni Onida, and Alberto DebernardiWe present first-principles calculations of structural, electronic, magnetic, and optical properties of zigzag-oriented silicene nanoribbons, which, being endowed with spin-polarized edge states, are promising candidates as building blocks of future spintronic devices. The minimal width for a struct…[Phys. Rev. B 99, 085414] Published Mon Feb 11, 2019

Published in: "Physical Review B".

All-electron fully relativistic Kohn-Sham theory for solids based on the Dirac-Coulomb Hamiltonian and Gaussian-type functions. (arXiv:1902.02828v1 [physics.chem-ph])

2019-02-11T02:29:26+00:00February 11th, 2019|Categories: Publications|Tags: |

We present the first full-potential method that solves the fully relativistic 4-component Dirac-Kohn-Sham equation for materials in the solid state within the framework of atom-centered Gaussian-type orbitals (GTOs). Our GTO-based method treats one-, two-, and three-dimensional periodic systems on an equal footing, and allows for a seamless transition to the methodology commonly used in studies of molecules with heavy elements. The scalar relativistic effects and spin-orbit interaction are handled variationally. The full description of the electron-nuclear potential in the core region of heavy nuclei is straightforward due to the local nature of the GTOs and does not pose any computational difficulties. We show how the time-reversal symmetry and a quaternion algebra-based formalism can be exploited to significantly reduce the increased methodological complexity and computational cost associated with multiple wave-function components coupled by the spin-orbit interaction. We provide a description of how to employ the matrix form of the multipole expansion and an iterative renormalization procedure to evaluate the conditionally convergent lattice sums arising for periodic systems. We investigate the problem of inverse variational collapse that arises if the Dirac operator containing a repulsive periodic potential is expressed in a basis containing diffuse functions, and suggest a possible solution. We demonstrate the validity of the method on silver halide crystals with large relativistic effects, and two-dimensional honeycomb structures (silicene and germanene) exhibiting the spin-orbit-driven quantum spin Hall effect. Our results are well-converged with respect to the basis limit using standard bases developed for molecular calculations, and indicate that the rule of

Published in: "arXiv Material Science".

Concentration-Dependent Diverse Magnetic and Electronic Properties of Halogen-Adsorbed Silicene. (arXiv:1901.11202v1 [cond-mat.mtrl-sci])

2019-02-01T02:29:32+00:00February 1st, 2019|Categories: Publications|Tags: , |

Concentration-dependent diverse magnetic and electronic properties of halogen-doped silicene are investigated using the first-principles method. The optimal buckled geometric structures, atom-related energy bands, spin density distributions, spatial charge densities, and spin- and orbital-decomposed density of states strongly depend on the double-side and single-side adsorptions. The two-dimensional electronic structures are enriched by the competition between the significant halogen-Si bonds and weak sp^3 hybridizations. Such critical halogen-Si bonding is formed by the high charge transfer from Si atoms to halogen adatoms. The double-side adsorptions belong to the middle-gap semiconductors that become a p-type metal at the 11% concentration, while the single-side adsorptions fully lead to the p-type metallic behaviors, in which the magnetism vanishes at the 5.6% concentration. The predicted results in the optimal buckled geometries, atom-related energy bands, and density of states could be verified by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and scanning tunneling spectroscopy experiments, respectively.

Published in: "arXiv Material Science".

Superstructure-induced splitting of Dirac cones in silicene. (arXiv:1901.11329v1 [cond-mat.mtrl-sci])

2019-02-01T02:29:26+00:00February 1st, 2019|Categories: Publications|Tags: |

Atomic scale engineering of two-dimensional materials could create devices with rich physical and chemical properties. External periodic potentials can enable the manipulation of the electronic band structures of materials. A prototypical system is 3×3-silicene/Ag(111), which has substrate-induced periodic modulations. Recent angle-resolved photoemission spectroscopy measurements revealed six Dirac cone pairs at the Brillouin zone boundary of Ag(111), but their origin remains unclear [Proc. Natl. Acad. Sci. USA 113, 14656 (2016)]. We used linear dichroism angle-resolved photoemission spectroscopy, the tight-binding model, and first-principles calculations to reveal that these Dirac cones mainly derive from the original cones at the K (K’) points of free-standing silicene. The Dirac cones of free-standing silicene are split by external periodic potentials that originate from the substrate-overlayer interaction. Our results not only confirm the origin of the Dirac cones in the 3×3-silicene/Ag(111) system, but also provide a powerful route to manipulate the electronic structures of two-dimensional materials.

Published in: "arXiv Material Science".

Electron interferometry and quantum spin Hall phase in silicene. (arXiv:1901.10161v1 [cond-mat.mes-hall])

2019-01-30T04:30:31+00:00January 30th, 2019|Categories: Publications|Tags: , |

We discuss devices for detection of the topological insulator phase based on the two-path electron interference. For that purpose we consider buckled silicene for which a local energy gap can be opened by vertical electric field to close one of the paths and for which the quantum spin Hall insulator conditions are controlled by the Fermi energy. In quantum spin Hall phase the interference is absent due to the separation of the spin currents and the conductance of the devices include sharp features related to localized resonances. In the normal transport conditions the two-path interference produces a regular Aharonov-Bohm oscillations in the external magnetic field.

Published : "arXiv Mesoscale and Nanoscale Physics".

Coulomb excitations and decays in graphene-related systems. (arXiv:1901.04160v1 [physics.comp-ph])

2019-01-15T04:31:01+00:00January 15th, 2019|Categories: Publications|Tags: , |

The layered graphene systems exhibit the rich and unique excitation spectra arising from the electron-electron Coulomb interactions. The generalized tight-binding model is developed to cover the planar/buckled/cylindrical structures, specific lattice symmetries, different layer numbers, distinct configurations, one-three dimensions, complicated intralayer and interlayer hopping integrals, electric field, magnetic quantization; any temperatures and dopings simultaneously. Furthermore, we modify the random-phase approximation to agree with the layer-dependent Coulomb potentials with the Dyson equation, so that these two methods can match with other under various external fields. The electron-hole excitations and plasmon modes are greatly diversified by the above-mentioned critical factors; that is, there exist the diverse (momentum. frequency)-related phase diagrams. They provide very effective deexcitation scatterings and thus dominate the Coulomb decay rates. Graphene, silicene and germanene might quite differ from one another in Coulomb excitations and decays because of the strength of spin-orbital coupling. Part of theoretical predictions have confirmed the experimental measurements, and most of them require the further examinations. Comparisons with the other models are also made in detail.

Published : "arXiv Mesoscale and Nanoscale Physics".

Thermal transport in silicene nanotubes: Effects of length, grain boundary and strain. (arXiv:1901.00625v1 [physics.comp-ph])

2019-01-04T04:30:26+00:00January 4th, 2019|Categories: Publications|Tags: |

Thermal transport behavior in silicene nanotubes has become more important due to the application of these promising nanostructures in the engineering of next-generation nanoelectronic devices. We apply non-equilibrium molecular dynamics (NEMD) simulations to study the thermal conductivity of silicene nanotubes with different lengths and diameters. We further explore the effects of grain boundary, strain, vacancy defect, and temperature in the range of 300-700 K on the thermal conductivity. Our results indicate that the thermal conductivity varies with the length approximately in the range of 24-34 W/m.K but exhibits insensitivity to the diameter and chirality. Besides, silicene nanotubes consisting of the grain boundary exhibit nearly 30% lower thermal conductivity compared with pristine ones. We discuss the underlying mechanism for the conductivity suppression of the system consisting of the grain boundary by calculating the phonon power spectral density. We find that by increasing the defect concentration and temperature, the thermal conductivity of the system decreases desirably. Moreover, for strained nanotubes, we observe unexpected changes in the thermal conductivity, so that the conductivity first increases significantly with tensile strain and then starts to decrease. The maximum thermal conductivity for the armchair and zigzag edge tubes appears at the strains about 3% and 5%, respectively, which is about 28% more than that of the unstrained structure.

Published : "arXiv Mesoscale and Nanoscale Physics".

Thermal transport across grain boundaries in polycrystalline silicene: a multiscale modeling. (arXiv:1901.00639v1 [physics.comp-ph])

2019-01-04T04:30:23+00:00January 4th, 2019|Categories: Publications|Tags: |

During the fabrication process of large scale silicene through common chemical vapor deposition (CVD) technique, polycrystalline films are quite likely to be produced, and the existence of Kapitza thermal resistance along grain boundaries could result in substantial changes of their thermal properties. In the present study, the thermal transport along polycrystalline silicene was evaluated by performing a multiscale method. Non-equilibrium molecular dynamics simulations (NEMD) was carried out to assess the interfacial thermal resistance of various constructed grain boundaries in silicene as well as to examine the effects of tensile strain and the mean temperature on the interfacial thermal resistance. In the following stage, the effective thermal conductivity of polycrystalline silicene was investigated considering the effects of grain size and tensile strain. Our results indicate that the average values of Kapitza conductance at grain boundaries at room temperature were estimated nearly 2.56*10^9 W/m2K and 2.46*10^9 W/m2K through utilizing Tersoff and Stillinger-Weber interatomic potentials, respectively. Also, in spite of the mean temperature whose increment does not change Kapitza resistance, the interfacial thermal resistance can be controlled by applying strain. Furthermore, it was found that, by tuning the grain size of polycrystalline silicene, its thermal conductivity can be modulated up to one order of magnitude.

Published : "arXiv Mesoscale and Nanoscale Physics".

Carrier Transport and Thermoelectric Properties of Differently Shaped Germanene (Ge) and Silicene (Si) Nanoribbon Interconnects

2018-12-25T00:33:42+00:00December 24th, 2018|Categories: Publications|Tags: |

Here, we report a study of carrier transport and thermoelectric properties of silicene/germanene nanoribbon (SiNR/GeNR) interconnects of varying shapes (namely, “V,” “L,” “U,” and “S” shaped) with empirical tight binding—nonequilibrium Green’s function approach. Our simulation shows that a significant reduction in both electron and phonon transmission in such differently shaped NRs compared to perfect ones. In terms of thermoelectric properties, Seebeck coefficient ($mathbb {S}$ ) variation in the range of −72.3 to $3.52~mu text{V}$ /K at 300 K for SiNR and −176 to $-textsf {95.5},,mu text{V}$ /K at 300 K for GeNR is observed in different pattern conditions. For Peltier coefficient ($pi $ ), these ranges are −0.23 to 0.001 V for SiNR and −0.053 to −0.011 V for GeNR at 300 K. Simulation also shows significant change in thermoelectric figure of merit ($textit {ZT}$ ) for a different pattern and temperature with peak $textit {ZT}~0.09$ at 800 K for “U”-shaped SiNR and 0.80 at 400 K for “L”-shaped GeNR.

Published in: "IEEE Transactions on Electron Devices".

Band Modulation for Silicene and Graphene Quantum Dots: A First-Principles Calculation. (arXiv:1812.08931v1 [cond-mat.mes-hall])

2018-12-24T04:30:23+00:00December 24th, 2018|Categories: Publications|Tags: , , |

The band modulation of the silicene and graphene quantum dots is investigated by a first-principles method. This study includes the ordinary silicene and graphene quantum dots and the embedded quantum dots in the hydrogenated silicene and graphene. The shapes and sizes of quantum dots are recognized as important factors for the electronic properties. We studied several types of quantum dots: triangular, parallelogram, rectangular, hexagonal dots. It demonstrates the energy gap of the quantum dot can be tuned by the dot size, the larger of the dot the smaller the energy gap. Moreover, the shapes affect the magnetism of the quantum dots. The triangular dot exhibits as magnetic semiconductor; the parallelogram dot shows antiferromagnetic characteristics; while the hexagonal dot is non-magnetic. Control the size and shape of a silicene or graphene quantum dot can manipulate its magnetism and electronic properties.

Published : "arXiv Mesoscale and Nanoscale Physics".

Stable Silicene in Graphene/Silicene Van der Waals Heterostructures

2018-12-15T22:33:23+00:00December 15th, 2018|Categories: Publications|Tags: , , |

Graphene/silicene van der Waals heterostructures are fabricated by intercalating Si atoms between graphene and a Ru substrate. By adjusting the Si dosage, silicene nanoflakes, monolayers, and multilayers are observed to form beneath the graphene. These heterostructures show good air stability for extended periods. The I–V characteristics of the vertical heterostructures show rectification behavior. Abstract Silicene‐based van der Waals heterostructures are theoretically predicted to have interesting physical properties, but their experimental fabrication has remained a challenge because of the easy oxidation of silicene in air. Here, the fabrication of graphene/silicene van der Waals heterostructures by silicon intercalation is reported. Density functional theory calculations show weak interactions between graphene and silicene layers, confirming the formation of van der Waals heterostructures. The heterostructures show no observable damage after air exposure for extended periods, indicating good air stability. The I–V characteristics of the vertical graphene/silicene/Ru heterostructures show rectification behavior.

Published in: "Advanced Materials".

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