Silicene

/Tag: Silicene

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".

Stable Silicene in Graphene/Silicene Van der Waals Heterostructures

2018-12-13T00:33:36+00:00December 12th, 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".

Collective plasmonic excitations in double-layer silicene at finite temperature. (arXiv:1811.12792v1 [cond-mat.mes-hall])

2018-12-03T04:30:19+00:00December 3rd, 2018|Categories: Publications|Tags: , |

We explore the temperature-dependent plasmonic modes of an n-doped double-layer silicene system which is composed of two spatially separated single layers of silicene with a distance large enough to prevent the interlayer electron tunneling. By applying an externally applied electric field, we numerically obtain the poles of the loss function within the so-called random phase approximation, to investigate the effects of temperature and geometry on the plasmon branches in three different regimes: topological insulator, valley-spin polarized metal, and band insulator. Also, we present the finite-temperature numerical results along with the zero-temperature analytical ones to support a discussion of the distinct effects of the external electric field and temperature on the plasmon dispersion. Our results show that at zero temperature both the acoustic and optical modes decrease by increasing the applied electric field and experience a discontinuity at the valley-spin polarized metal phase as the system transitions from a topological insulator to a band insulator. At finite temperature, the optical plasmons are damped around this discontinuity and the acoustic modes may exhibit a continuous transition. Moreover, while the optical branch of plasmons changes non-monotonically and noticeably with temperature, the acoustic branch dispersion displays a negligible growth with temperature for all phases of silicene. Furthermore, our finite-temperature results indicate that the dependency of two plasmonic branches on the interlayer separation is not affected by temperature at long wavelengths; the acoustic mode energy varies slightly with increasing the interlayer distance, whereas the optical mode remains unchanged.

Published : "arXiv Mesoscale and Nanoscale Physics".

Plasmon-phonon coupling in a valley-spin-polarized two-dimensional electron system: a theoretical study on monolayer silicene. (arXiv:1811.12071v1 [cond-mat.mes-hall])

2018-11-30T04:30:25+00:00November 30th, 2018|Categories: Publications|Tags: , |

We study the hybrid excitations due to the coupling between surface optical phonons of a polar insulator substrate and plasmons in the valley-spin-polarized metal phase of silicene under an exchange field. We perform the calculations within the generalized random-phase approximation where the plasmon-phonon coupling is taken into account by the long-range Fr$ddot{mathrm{o}}$hlich interaction. Our investigation on two hybridized plasmon branches in different spin and valley subbands shows distinct behavior compared to the uncoupled case. Interestingly, in one valley, it is found that while the high energy hybrid branch is totally damped in the spin-up state, it can be well-defined in the the spin-down state. Moreover, we show that the electron-phonon coupling is stronger in both spin-down subbands, regardless of valley index, due to their higher electron densities. In addition, we study the effects of electron-phonon coupling on the quasiparticle scattering rate of four distinct spin-valley locked subbands. The results of our calculations predict a general enhancement in the scattering rate for all subbands, and a jump in the case of spin-down states. This sharp increase associated to the damping of hybrid plasmon modes is almost absent in the uncoupled case. The results suggest an effective way for manipulating collective modes of valley-spin-polarized silicene which may become useful in future valleytronic and spintronic applications.

Published : "arXiv Mesoscale and Nanoscale Physics".

Electrically controlled crossover between $2π$ and $4π$ Josephson effects through topologically confined channels in silicene

2018-11-26T18:33:42+00:00November 26th, 2018|Categories: Publications|Tags: |

Author(s): Daniel Frombach, Sunghun Park, Alexander Schroer, and Patrik RecherWe propose a tunable topological Josephson junction in silicene where electrostatic gates could switch between a trivial and a topological junction. These aspects are a consequence of a tunable phase transition of the topologically confined valley-chiral states from a spin-degenerate to a spin-helic…[Phys. Rev. B 98, 205305] Published Mon Nov 26, 2018

Published in: "Physical Review B".

Structural identification of silicene on the Ag(111) surface by atomic force microscopy

2018-11-21T22:33:19+00:00November 21st, 2018|Categories: Publications|Tags: |

Author(s): Lingyu Feng, Keisuke Yabuoshi, Yoshiaki Sugimoto, Jo Onoda, Masahiro Fukuda, and Taisuke OzakiSilicene is a two-dimensional atomic layer material with buckled honeycomb arrangements of Si atoms. The diversity of those arrangements, which expands its potential applications, makes it difficult to determine its structure in any particular case. In this paper, we show that atomic force microscop…[Phys. Rev. B 98, 195311] Published Wed Nov 21, 2018

Published in: "Physical Review B".

Computational insights and the observation of SiC nanograin assembly: towards 2D silicon carbide. (arXiv:1701.07387v2 [cond-mat.mtrl-sci] UPDATED)

2018-11-16T02:29:21+00:00November 16th, 2018|Categories: Publications|Tags: , , , , |

While an increasing number of two-dimensional (2D) materials, including graphene and silicene, have already been realized, others have only been predicted. An interesting example is the two-dimensional form of silicon carbide (2D-SiC). Here, we present an observation of atomically thin and hexagonally bonded nanosized grains of SiC assembling temporarily in graphene oxide pores during an atomic resolution scanning transmission electron microscopy experiment. Even though these small grains do not fully represent the bulk crystal, simulations indicate that their electronic structure already approaches that of 2D-SiC. This is predicted to be flat, but some doubts have remained regarding the preference of Si for sp$^{3}$ hybridization. Exploring a number of corrugated morphologies, we find completely flat 2D-SiC to have the lowest energy. We further compute its phonon dispersion, with a Raman-active transverse optical mode, and estimate the core level binding energies. Finally, we study the chemical reactivity of 2D-SiC, suggesting it is like silicene unstable against molecular absorption or interlayer linking. Nonetheless, it can form stable van der Waals-bonded bilayers with either graphene or hexagonal boron nitride, promising to further enrich the family of two-dimensional materials once bulk synthesis is achieved.

Published in: "arXiv Material Science".

Composition and Stacking Dependent Topology in Bilayers from the Graphene Family. (arXiv:1811.05525v1 [cond-mat.mtrl-sci])

2018-11-15T02:29:17+00:00November 15th, 2018|Categories: Publications|Tags: , , |

We present a compositional and structural investigation of silicene, germanene, and stanene bilayers from first-principles. Due to the staggering of the individual layers, several stacking patterns are possible, most of which are not available to the bilayer graphene. This structural variety, in conjunction with the presence of the spin-orbit coupling, unveil a diversity of the electronic properties, with the appearance of distinct band features, including orbital hybridization and band inversion. We show that for particular cases, the intrinsic spin Hall response exhibits signatures of non-trivial electronic band topology, making these structures promising candidates to probe Dirac-like physics.

Published in: "arXiv Material Science".

Compelling experimental evidence of a Dirac cone in the electronic structure of a 2D Silicon layer. (arXiv:1811.01291v1 [cond-mat.mtrl-sci])

2018-11-06T05:29:38+00:00November 6th, 2018|Categories: Publications|Tags: , , |

The remarkable properties of graphene stem from its two-dimensional (2D) structure, with a linear dispersion of the electronic states at the corners of the Brillouin zone (BZ) forming a Dirac cone. Since then, other 2D materials have been suggested based on boron, silicon, germanium, phosphorus, tin, and metal di-chalcogenides. Here, we present an experimental investigation of a single silicon layer on Au(111) using low energy electron diffraction (LEED), high resolution angle-resolved photoemission spectroscopy (HR-ARPES), and scanning tunneling microscopy (STM). The HR-ARPES data show compelling evidence that the silicon based 2D overlayer is responsible for the observed linear dispersed feature in the valence band, with a Fermi velocity of v_F ~10^(+6) m.s^(-1) comparable to that of graphene. The STM images show extended and homogeneous domains, offering a viable route to the fabrication of silicene-based opto-electronic devices.

Published in: "arXiv Material Science".

Silicene on IrSi3 crystallites. (arXiv:1810.12373v1 [cond-mat.mtrl-sci])

2018-10-31T02:29:13+00:00October 31st, 2018|Categories: Publications|Tags: , |

Recently, silicene, the graphene equivalent of silicon, has attracted a lot of attention due to its compatibility with Si-based electronics. So far, silicene has been epitaxy grown on various crystalline surfaces such as Ag(110), Ag(111), Ir(111), ZrB2(0001) and Au(110) substrates. Here, we present a new method to grow silicene via high temperature surface reconstruction of hexagonal IrSi3 nanocrystals. The h-IrSi3 nanocrystals are formed by annealing thin Ir layers on Si(111) surface. A detailed analysis of the STM images shows the formation of silicene like domains on the surface of some of the IrSi3 crystallites. We studied both morphology and electronic properties of these domains by using both scanning tunneling microscopy/spectroscopy and first-principles calculation methods.

Published in: "arXiv Material Science".

Shot noise in electrically-gated silicene nanostructures

2018-10-30T14:33:28+00:00October 30th, 2018|Categories: Publications|Tags: , |

We have theoretically studied fundamental shot noise properties in single- and dual-gated silicene nanostructures. It is demonstrated here that due to the intrinsic spin–orbit gap, the Fano factor ( F ) in the biased structures does not coincide with the characteristic value F = 1/3, a value frequently reported for a graphene system. Under gate-field modulations, the F in the gated structure can be efficiently engineered and the specific evolution of the F versus the field strength is symmetric with the center of spectra oppositely shifting away from the zero field condition for the valley or spin-coupled spinor states. This field-dependent hysteretic loop thus offers some flexible methods to distinguish one spinor state from its valley or spin-coupled state via their numerical difference in the F once the incident beam is spin or valley-polarized.

Published in: "Nanotechnology".

Spin and valley control in single and double electrostatic silicene quantum dots

2018-10-10T16:33:09+00:00October 10th, 2018|Categories: Publications|Tags: |

Author(s): Bartłomiej Szafran and Dariusz ŻebrowskiWe study quantum dots defined electrostatically in silicene. We determine the spin-valley structure of confined single- and two-electron systems, and quantify the effects of the intervalley scattering by the electron-electron interaction potential and the crystal edge. The double quantum dots are di…[Phys. Rev. B 98, 155305] Published Wed Oct 10, 2018

Published in: "Physical Review B".

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