Showing papers on "Zigzag published in 2013"
TL;DR: The phase diagram of spin-orbit Mott insulators on a honeycomb lattice is explored, within the Kitaev-Heisenberg model extended to its full parameter space, and Zigzag-type magnetic order is found to occupy a large part of the phase diagram.
Abstract: We explore the phase diagram of spin-orbit Mott insulators on a honeycomb lattice, within the Kitaev-Heisenberg model extended to its full parameter space. Zigzag-type magnetic order is found to occupy a large part of the phase diagram of the model, and its physical origin is explained as due to interorbital t(2g)-e(g) hopping. The magnetic susceptibility, spin wave spectra, and zigzag order parameter are calculated and compared to the experimental data, obtaining thereby the spin coupling constants in Na(2)IrO(3) and Li(2)IrO(3).
376 citations
TL;DR: A topological transition in photonic graphene is experimentally and theoretically demonstrated by applying a uniaxial strain to transform the system from one that supports states localized on the edge to one that does not.
Abstract: We experimentally demonstrate a topological transition of classical light in ``photonic graphene'': an array of waveguides arranged in the honeycomb geometry. As the system is uniaxially strained (compressed), the two unique Dirac points (present in the spectrum of conventional graphene) merge and annihilate each other, and a band gap forms. As a result, edge states are created on the zigzag edge and destroyed on the bearded edge. These results are applicable for any 2D honeycomb-type structure, from carbon-based graphene to photonic lattices and crystals.
259 citations
TL;DR: This work has successfully grown a perfect single-layer h-BN-graphene (BNC) patchwork on a selected Rh(111) substrate, via a two-step patching growth approach and found that zigzag linking edges were preferably formed, as demonstrated by atomic-scale scanning tunneling microscopy images and theoretically verified using density functional theory calculations.
Abstract: The atomic layer of hybridized hexagonal boron nitride (h-BN) and graphene has attracted a great deal of attention after the pioneering work of P. M. Ajayan et al. on Cu foils because of their unusual electronic properties (Ci, L. J.; et al. Nat. Mater. 2010, 9, 430−435). However, many fundamental issues are still not clear, including the in-plane atomic continuity as well as the edge type at the boundary of hybridized h-BN and graphene domains. To clarify these issues, we have successfully grown a perfect single-layer h-BN-graphene (BNC) patchwork on a selected Rh(111) substrate, via a two-step patching growth approach. With the ideal sample, we convinced that at the in-plane linking interface, graphene and h-BN can be linked perfectly at an atomic scale. More importantly, we found that zigzag linking edges were preferably formed, as demonstrated by atomic-scale scanning tunneling microscopy images, which was also theoretically verified using density functional theory calculations. We believe the experim...
236 citations
TL;DR: In this article, the authors apply the recursive Green's function method to the computation of electronic transport properties of graphene sheets and nanoribbons in the linear response regime, allowing for an amenable inclusion of several disorder mechanisms at the microscopic level, as well as inhomogeneous gating, finite temperature, and dephasing.
Abstract: We describe how to apply the recursive Green's function method to the computation of electronic transport properties of graphene sheets and nanoribbons in the linear response regime. This method allows for an amenable inclusion of several disorder mechanisms at the microscopic level, as well as inhomogeneous gating, finite temperature, and, to some extend, dephasing. We present algorithms for computing the conductance, density of states, and current densities for armchair and zigzag atomic edge alignments. Several numerical results are presented to illustrate the usefulness of the method.
189 citations
TL;DR: A comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (α, β, γ, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method is reported.
Abstract: Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (α, β, γ, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the α-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag α-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current–voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between π* and π subbands. Unlike α- and 6,6,12-GyNRs, both zigzag β-GyNRs and zigzag γ-GyNRs exhibit NDR behavior regardless of the symmetry.
166 citations
TL;DR: It is demonstrated for the first time that the graphene etching mode can deviate significantly from simple anisotropic etching, leading to complex fractal geometric patterns with sixfold symmetry.
Abstract: An anisotropic etching mode is commonly known for perfect crystalline materials, generally leading to simple Euclidean geometric patterns. This principle has also proved to apply to the etching of the thinnest crystalline material, graphene, resulting in hexagonal holes with zigzag edge structures. Here we demonstrate for the first time that the graphene etching mode can deviate significantly from simple anisotropic etching. Using an as-grown graphene film on a liquid copper surface as a model system, we show that the etched graphene pattern can be modulated from a simple hexagonal pattern to complex fractal geometric patterns with sixfold symmetry by varying the Ar/H2 flow rate ratio. The etched fractal patterns are formed by the repeated construction of a basic identical motif, and the physical origin of the pattern formation is consistent with a diffusion-controlled process. The fractal etching mode of graphene presents an intriguing case for the fundamental study of material etching.
145 citations
TL;DR: An algorithm for WSN coverage based on Zigzag Pattern Scheme Deployment Algorithm expresses a very high coverage efficiency 91%, as well as, it expands and covers the whole interest area with minimum number of nodes, while it generates a very little coverage redundancy.
Abstract: The problem of having sufficient coverage is an essential issue in wireless sensor network (WSN). A high coverage rate delivers a higher quality of service. The aim of coverage problem is to ensure a minimum number of nodes (at least one sensor) with little redundant data cover every point inside the interest area. In this paper, we provided an algorithm for WSN coverage based on Zigzag Pattern. The interest area divided into multiple Zigzag Patterns with multiple corners and lines segments, each node is deployed in a corner of Zigzag Pattern. Zigzag Pattern Scheme Deployment Algorithm expresses a very high coverage efficiency 91%, as well as, it expands and covers the whole interest area with minimum number of nodes, while it generates a very little coverage redundancy. We provided geometrical analysis to illustrate when the algorithm reaches the maximal and optimal coverage efficiency. The algorithm reaches the maximal and optimal coverage efficiency when the circumference of sensing range for each node is equal to the sum of its vertical Arcs length and horizontal Arcs length, while the optimal length of each line segment in Zigzag Pattern is approximatey root of three per r and the optimal angle of each corner is 60o.
140 citations
TL;DR: In this article, a combination of high-resolution scanning tunneling microscopy and first-principles calculations is used to determine the exact atomic structure of plasma-etched GNR edges and establish the chemical nature of terminating functional groups for zigzag, armchair and chiral edge orientations.
Abstract: The edges of graphene nanoribbons (GNRs) have attracted much interest due to their potentially strong influence on GNR electronic and magnetic properties. Here we report the ability to engineer the microscopic edge termination of high-quality GNRs via hydrogen plasma etching. Using a combination of high-resolution scanning tunneling microscopy and first-principles calculations, we have determined the exact atomic structure of plasma-etched GNR edges and established the chemical nature of terminating functional groups for zigzag, armchair, and chiral edge orientations. We find that the edges of hydrogen-plasma-etched GNRs are generally flat, free of structural reconstructions, and terminated by hydrogen atoms with no rehybridization of the outermost carbon edge atoms. Both zigzag and chiral edges show the presence of edge states.
135 citations
TL;DR: Graphene edges fabricated by electron beam-initiated mechanical rupture or tearing in high vacuum are clean and largely atomically perfect, oriented in either the armchair or zigzag direction, providing a valuable tool for realizing atomically tailored graphene and facilitating meaningful experimental study.
Abstract: The atomic structure of graphene edges is critical in determining the electrical, magnetic and chemical properties of truncated graphene structures, notably nanoribbons. Unfortunately, graphene edges are typically far from ideal and suffer from atomic-scale defects, structural distortion and unintended chemical functionalization, leading to unpredictable properties. Here we report that graphene edges fabricated by electron beam-initiated mechanical rupture or tearing in high vacuum are clean and largely atomically perfect, oriented in either the armchair or zigzag direction. We demonstrate, via aberration-corrected transmission electron microscopy, reversible and extended pentagon-heptagon (5-7) reconstruction at zigzag edges, and explore experimentally and theoretically the dynamics of the transitions between configuration states. Good theoretical-experimental agreement is found for the flipping rates between 5-7 and 6-6 zigzag edge states. Our study demonstrates that simple ripping is remarkably effective in producing atomically clean, ideal terminations, thus providing a valuable tool for realizing atomically tailored graphene and facilitating meaningful experimental study.
119 citations
TL;DR: The armchair-edged nanographene is found to have an energetically stable electronic pattern and the zigzag-edgednanographene shows a nonbonding (π radical) pattern, which is the source of the material's electronic and magnetic properties and its chemical activity.
Abstract: Graphene can be referred to as an infinite polycyclic aromatic hydrocarbon (PAH) consisting of an infinite number of benzene rings fused together. However, at the nanoscale, nanographene’s properties lie in between those of bulk graphene and large PAH molecules, and its electronic properties depend on the influence of the edges, which disrupt the infinite π-electron system. The resulting modulation of the electronic states depends on whether the nanographene edge is the armchair or zigzag type, corresponding to the two fundamental crystal axes. In this Account, we report the results of fabricating both types of edges in the nanographene system and characterizing their electronic properties using a scanning probe microscope.We first introduce the theoretical background to understand the two types of finite size effects on the electronic states of nanographene (i) the standing wave state and (ii) the edge state which correspond to the armchair and zigzag edges, respectively. Most importantly, characterizing...
119 citations
TL;DR: In this article, the URANS computations of standard maneuvers are performed for a surface combatant at model and full scale using CFDShip-Iowa v4, a free surface solver designed for 6DOF motions in free and semi-captive problems.
Abstract: Unsteady Reynolds averaged Navier–Stokes (URANS) computations of standard maneuvers are performed for a surface combatant at model and full scale. The computations are performed using CFDShip-Iowa v4, a free surface solver designed for 6DOF motions in free and semi-captive problems. Overset grids and a hierarchy of bodies allow the deflection of the rudders while the ship undergoes 6DOF motions. Two types of maneuvers are simulated: steady turn and zigzag. Simulations of steady turn at 35° rudder deflection and zigzag 20/20 maneuvers for Fr = 0.25 and 0.41 using constant RPM propulsion are benchmarked against experimental time histories of yaw, yaw rate and roll, and trajectories, and also compared against available integral variables. Differences between CFD and experiments are mostly within 10 % for both maneuvers, highly satisfactory given the degree of complexity of these computations. Simulations are performed also with waves, and with propulsion at either constant RPM or torque. 20/20 zigzag maneuvers are simulated at model and full scale for Fr = 0.41. The full scale case produces a thinner boundary layer profile compared to the model scale with different reaction times and handling needed for maneuvering. Results indicate that URANS computations of maneuvers are feasible, though issues regarding adequate modeling of propellers remain to be solved.
TL;DR: Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.
Abstract: The feasibility of using π-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of π-conjugated polymers by covering the π-conjugated chain with macrocycles and regularly localizing π-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, insulated wires containing meta-junctioned poly(phenylene-ethynylene) as the backbone units were designed and synthesized. The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires. When the length of the linear region of the zigzag wires was increased to 10 phenylene-ethynylene units, the intramolecular charge mobility increased to 8.5 cm(2) V(-1) s(-1). Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.
TL;DR: In this article, a three-dimensional Reynolds-averaged Navier-Stokes equations and heat transfer equations are solved to analyze conjugate heat transfer in the zigzag channels.
Abstract: Comparative study has been performed with various channel cross-sectional shapes and channel configurations of a zigzag printed circuit heat exchanger (PCHE), which has been considered as a heat exchanging device for the gas turbine based generation systems. Three-dimensional Reynolds-averaged Navier–Stokes equations and heat transfer equations are solved to analyze conjugate heat transfer in the zigzag channels. The shear stress transport model with a low Reynolds number wall treatment is used as a turbulence closure. The global Nusselt number, Colburn j-factor, effectiveness, and friction factor are used to estimate the thermal–hydraulic performance of the PCHE. Four different shapes of channel cross section (semicircular, rectangular, trapezoidal, and circular) and four different channel configurations are tested to determine their effects on thermal–hydraulic performance. The rectangular channel shows the best thermal performance but the worst hydraulic performance, while the circular channel shows the worst thermal performance. The Colburn j-factor and friction factor are found to be inversely proportional to the Reynolds number in cold channels, while the effectiveness and global Nusselt number are proportional to the Reynolds number.
Patent•
17 Jan 2013
TL;DR: In this paper, a display and control logic are coupled to the display and the control logic is configured to receive display data and render the display data into control signals for driving the display.
Abstract: An apparatus including a display and control logic is provided. In one example, the display includes an array of subpixels having a plurality of zigzag subpixel groups. Each zigzag subpixel group includes at least three zigzag subpixel units arranged adjacently along a horizontal or vertical direction. Each zigzag subpixel unit includes a plurality of subpixels of the same color arranged in a zigzag pattern. In each zigzag subpixel unit, a first plurality of subpixels are arranged along one diagonal direction from a turning subpixel disposed at a turning corner of the zigzag pattern, and a second plurality of subpixels are arranged along another diagonal direction from the turning subpixel. In another example, the display includes an array of subpixels having a novel subpixel repeating group. The control logic is operatively coupled to the display and configured to receive display data and render the display data into control signals for driving the display.
TL;DR: The Refined Zigzag Theory (RZT) belongs to the zigzag class of approximations for the analysis of laminated composite and sandwich structures as discussed by the authors, and it can be used to derive reliable and computationally efficient finite elements suited for large-scale analyses of sandwich structures.
TL;DR: In this article, a new iron-based superconductor (Ca,Pr)FeAs2 was discovered and plate-like crystals of the new phase were obtained and crystal structure was investigated by single-crystal X-ray diffraction analysis.
Abstract: A new iron-based superconductor (Ca,Pr)FeAs2 was discovered. Plate-like crystals of the new phase were obtained and crystal structure was investigated by single-crystal X-ray diffraction analysis. The structure was identified as the monoclinic system with space group P21/m, and is composed of two Ca(Pr) planes, anti-fluorite Fe2As2 layers, and As2 zigzag chain layers. Plate-like crystals composed of the new phase showed superconductivity with Tc ~20 K in both magnetization and resistivity measurements.
TL;DR: Refined Zigzag Theory (RZT) has been recently developed for the analysis of homogeneous, multilayer composite and sandwich laminates as mentioned in this paper, which has a number of practical and theoretical advantages over the widely used First-order Shear Deformation Theory (FSDT) and other types of higher order and zigzag theories.
Abstract: The Refined Zigzag Theory (RZT) has been recently developed for the analysis of homogeneous, multilayer composite and sandwich plates. The theory has a number of practical and theoretical advantages over the widely used First-order Shear Deformation Theory (FSDT) and other types of higher-order and zigzag theories. Using FSDT as a baseline, RZT takes into account the stretching, bending, and transverse shear deformations. Unlike FSDT, this novel theory does not require shear correction factors to yield accurate results for a wide range of material systems including homogeneous, laminated composite, and sandwich laminates. The inplane zigzag kinematic assumptions, which compared to FSDT add two additional rotation-type kinematic variables, give rise to two types of transverse shear strain measures – the classical average shear strain (as in FSDT) and another one related to the cross-sectional distortions enabled by the zigzag kinematic terms. Consequently, with a fixed number of kinematic variables, the theory enables a highly accurate modeling of multilayer composite and sandwich plates even when the laminate stacking sequence exhibits a high degree of transverse heterogeneity. Unlike most zigzag formulations, this theory is not affected by such theoretical anomalies as the vanishing of transverse shear stresses and forces along clamped boundaries. In this paper, six- and three-node, C 0 -continuous, RZT-based triangular plate finite elements are developed; they provide the best compromise between computational efficiency and accuracy. The element shape functions are based on anisoparametric (aka interdependent) interpolations that ensure proper element behavior even when very thin plates are modeled. Continuous edge constraints are imposed on the transverse shear strain measures to derive coupled-field deflection shape functions, resulting in a simple and efficient three-node element. The elements are implemented in ABAQUS – a widely used commercial finite element code – by way of a user-element subroutine. The predictive capabilities of the new elements are assessed on several elasto-static problems, which include simply supported and cantilevered laminated composite and sandwich plates. The numerical results demonstrate that the new RZT-based elements provide superior predictions for modeling a wide range of laminates including highly heterogeneous sandwich laminations. They also offer substantial improvements over the existing plate elements based on FSDT as well as other higher-order and zigzag-type elements.
TL;DR: Wang et al. as mentioned in this paper reported the zigzag silicene nanoribbons (ZSiNRs) with asymmetric sp2−sp3 edges are bipolar magnetic semiconductors due to the incorporation of Klein and Zigzag edge states, which can be altered to half-metals with opposite conductive spin channels by p-type and n-type dopings.
Abstract: The nanomaterials with peculiar spintronic characteristics, such as half-metals, spin gapless semiconductors [X. L. Wang, Phys. Rev. Lett. 100, 156404 (2008)], and bipolar magnetic semiconductors [Li et al., Nanoscale 4, 5680 (2012)], play the crucial role in nano-electronics and spintronics. Here, we report the zigzag silicene nanoribbons (ZSiNRs) with asymmetric sp2−sp3 edges are bipolar magnetic semiconductors due to the incorporation of Klein and zigzag edge states. With the bipolar feature, these asymmetric ZSiNRs can be altered to half-metals with opposite conductive spin channels by p-type and n-type dopings. Moreover, the semiconducting properties can also be tailored by the strain, which makes the nanoribbons into spin gapless semiconductors or ferromagnetic metals.
TL;DR: The intrinsic magnetism of graphene edge states revealed based on unidirectional aligned graphene sheets derived from completely carbonized SiC crystals is revealed and ferromagnetic ordering curie-temperature of the fundamental magnetic order unit (FMOU) is 820 ± 80 K.
Abstract: The magnetism of graphene has remained divergent and controversial due to absence of reliable experimental results. Here we show the intrinsic magnetism of graphene edge states revealed based on unidirectional aligned graphene sheets derived from completely carbonized SiC crystals. It is found that ferromagnetism, antiferromagnetism and diamagnetism along with a probable superconductivity exist in the graphene with irregular zigzag edges. A phase diagram is constructed to show the evolution of the magnetism. The ferromagnetic ordering curie-temperature of the fundamental magnetic order unit (FMOU) is 820 ± 80 K. The antiferromagnetic ordering Neel temperature of the FMOUs belonging to different sublattices is about 54 ± 2 K. The diamagnetism is similar to that of graphite and can be well described by the Kotosonov's equation. Our experimental results provide new evidences to clarify the controversial experimental phenomena observed in graphene and contribute to a deeper insight into the nature of magnetism in graphene based system.
TL;DR: In this paper, a new Inverse Hyperbolic Zigzag Theory (IHZZT) is proposed for the analysis of laminated and sandwich plates, which considers an inverse hyperbolic function as shear strain shape function, which represents the non-linear distribution of inplane displacement across the thickness as compared to a third order polynomial term in conventional theories.
TL;DR: Through the scaling of the phonon dispersion, it is illustrated that the thermal conductivity calculated for the MoS2 nanoribbon is esentially in consistent with the superior thermal Conductivity found for graphene.
Abstract: We investigate the thermal conductivity in the armchair and zigzag MoS2 nanoribbons, by combining the non-equilibrium Green's function approach and the first-principles method. A strong orientation dependence is observed in the thermal conductivity. Particularly, the thermal conductivity for the armchair MoS2 nanoribbon is about 673.6 Wm−1 K−1 in the armchair nanoribbon and 841.1 Wm−1 K−1 in the zigzag nanoribbon at room temperature. By calculating the Caroli transmission, we disclose the underlying mechanism for this strong orientation dependence to be the fewer phonon transport channels in the armchair MoS2 nanoribbon in the frequency range of [150, 200] cm−1. Through the scaling of the phonon dispersion, we further illustrate that the thermal conductivity calculated for the MoS2 nanoribbon is esentially in consistent with the superior thermal conductivity found for graphene.
TL;DR: In this article, a comparison between two existing zigzag functions that are used to improve Equivalent Single Layer (ESL) theories for the analysis of multilayered composite and sandwich beams is presented.
Abstract: The paper presents a comparison between two existing zigzag functions that are used to improve Equivalent Single Layer (ESL) theories for the analysis of multilayered composite and sandwich beams. ESL theories are easy to implement and computationally affordable but, in order to correctly describe the mechanical behavior of laminated structures (especially those exhibiting high transverse anisotropy or high thickness-to-side length ratios), the displacement field needs to be enriched by a through-the-thickness piecewise linear contribution denoted as "zigzag". The zigzag term of the displacement field is used to model the local distortion of the cross section in each lamina of multilayered structures and is related to the continuity of transverse stresses. The paper considers two zigzag functions that have been proposed in the open literature (namely Murakami's zigzag function and the Refined zigzag function) and compares their performances when they are used to improve the classical Timoshenko beam theory; both displacement-based and mixed formulations are considered. To the best of the author's knowledge, such a comparative study has never been published. The problem of a simply supported beam subjected to a transverse distributed load is considered as a test case. Several stacking sequences, ranging from monolithic to sandwich-like and from symmetric to arbitrary, are considered. The special case of laminates with external weak layers is also investigated and the effects of these lay-ups on the derivation of the Refined zigzag function are analyzed for the first time. The capability of the tested zigzag functions to help evaluate the overall deflection and model the through-the-thickness distribution of the axial displacement and stress is investigated. It has been recognized that the Refined zigzag function is more accurate, especially for unsymmetric and arbitrary lay-ups, and can be adopted to efficiently introduce zigzag kinematics into any ESL theory
TL;DR: In this paper, the electronic structures and Seebeck coefficients of the graphene/h-BN superlattices which consist of zigzag graphene nanoribbons (ZGNRs) and zigerzag BN nanoribrbs (ZBNNRs) have been investigated using ab initio calculations based on the density functional theory.
Abstract: The electronic structures and Seebeck coefficients of the graphene/h-BN superlattices which consist of zigzag graphene nanoribbons (ZGNRs) and zigzag BN nanoribbons (ZBNNRs) have been investigated using ab initio calculations based on the density functional theory. It has been shown that a ZGNR/ZBNNR marks up to 20 times larger in the Seebeck coefficient than graphene. The Seebeck coefficients of the superlattices increase with decreasing width of the constituent ZGNR. It has been revealed that the giant Seebeck coefficients of the superlattices stem from the so-called pudding mold band with a finite energy gap.
TL;DR: In this article, the authors show that the penetration depth of the helical edge channel is antiproportional to the spin-orbit gap for the armchair edge, while it remains as short as the lattice constant for the zigzag edge.
Abstract: Silicene is a graphene-like honeycomb structure made of silicon atoms. It is a two-dimensional quantum spin-Hall insulator due to the spin-orbit interaction. According to the bulk-edge correspondence we expect zero-energy edge channels to appear in silicene nanoribbons. The behaviors of the helical edge channels are completely different between the armchair and the zigzag edges. Zero-energy states disappear in armchair nanoribbons despite the bulk-edge correspondence, while they appear as zigzag nanoribbons even if the width is quite narrow. The difference originates in the penetration depth of the helical edge channel, which is antiproportional to the spin-orbit gap for the armchair edge, while it remains as short as the lattice constant for the zigzag edge. These properties make clear distinctions between silicene and graphene nanoribbons, especially for armchair edges: In silicene edge states emerge as required by its topology, though the zero-energy states disappear from the energy spectrum, whereas in graphene no edge states exist. The emergence of edge states in armchair nanoribbons must be experimentally detectable by scanning tunneling microscopy, and may well serve as an experimental signal that silicene is a topological insulator.
TL;DR: In this paper, the authors studied the electron transmission through the domain boundary on bilayer graphene separating the AB and BA stacking regions using the effective continuum model and calculated the transmission probability as a function of the electron energy and the incident angle for several specific boundary structures.
Abstract: We study the electron transmission through the domain boundary on bilayer graphene separating $\mathit{AB}$ and $\mathit{BA}$ stacking regions. Using the effective continuum model, we calculate the electron transmission probability as a function of the electron energy and the incident angle, for several specific boundary structures. The transmission strongly depends on the crystallographic direction of the boundary and also on the atomic configuration inside. At low energy, the boundary is either insulating or highly transparent depending on the structure. In insulating cases, the transmission sharply rises when the Fermi energy is increased to a certain level, suggesting that the electric current through the boundary can be controlled by the field effect. The boundary parallel to the zigzag direction generally has different transmission properties between the two different valleys, and this enables one to generate the valley polarized current in a certain configuration. We show that those characteristic features can be qualitatively explained by the transverse momentum conservation in the position-dependent band structure in the intermediate region.
TL;DR: In this paper, a 2D finite element model based on higher order zigzag theory (HOZT) was proposed to solve the vibration problem of shells incorporating all three radii of curvatures including the effect of cross curvature.
TL;DR: In this article, the authors show that the zigzag edge is not the most stable fully hydrogenated edge structure along the ⟨21⎯⎲ 1⎵⎾⎫ 0⟩ direction, and instead hydrogenated Klein and reconstructed Klein based edges are more favorable, with stabilities approaching that of armchair edges.
Abstract: Hydrogenated graphene edges are assumed to be either armchair, zigzag, or a combination of the two. We show that the zigzag is not the most stable fully hydrogenated edge structure along the ⟨21⎯⎯1⎯⎯0⟩ direction. Instead hydrogenated Klein and reconstructed Klein based edges are found to be energetically more favorable, with stabilities approaching that of armchair edges. These new structures “unify” graphene edge topology, the most stable flat hydrogenated graphene edges always consisting of pairwise bonded C2H4 edge groups, irrespective of the edge orientation. When edge rippling is included, CH3 edge groups are most stable. These new fundamental hydrogen-terminated edges have important implications for graphene edge imaging and spectroscopy, as well as mechanisms for graphene growth, nanotube cutting, and nanoribbon formation and behavior.
TL;DR: In this paper, the electronic and magnetic properties of edge-hydrogenated and edge-doped zigzag silicene nanoribbons (ZSiNRs) were investigated.
Abstract: We have performed density-functional-theory calculations to study the electronic and magnetic properties of edge-hydrogenated and edge-doped zigzag silicene nanoribbons (ZSiNRs). The formation energies of monohydrogenated and dihydrogenated edges slightly depend on the width of ZSiNRs, whereas the electronic and magnetic properties of ZSiNRs can be tuned by the different forms of edge hydrogenation. The dihydrogenated edges can effectively stabilize the antiferromagnetic semiconducting ground state of ZSiNRs. Moreover, nitrogen- or phosphorus-doped monohydrogenated ZSiNR is a magnetic semiconductor, and becomes a half-metal under a transverse electric field. Owing to the compelling electronic and magnetic properties, silicene nanoribbons hold great promise for application in nanodevices.
TL;DR: In this article, a series of 3D graphene monoliths using zigzag or armchair graphene nanoribbons as building blocks and sp3 carbon chains as junction nodes are constructed, and calculations based on first principles are performed in order to predict their mechanical and electronic properties.
Abstract: One of the biggest challenges in graphene applications is how one can fabricate 3D architectures comprising graphene sheets in which the resulting architectures have inherited graphene's excellent intrinsic properties but have overcome its shortcomings. Two series of 3D graphene monoliths (GMs) using zigzag or armchair graphene nanoribbons as building blocks and sp3 carbon chains as junction nodes are constructued, and calculations based on first principles are performed in order to predict their mechanical and electronic properties. The perfect match between sp2 nanoribbons and sp3 linkers results in favorable energy and mechanical/dynamic stability. Owing to their tailored motifs, wine-rack-like pores, and rigid sp3 linkers, these GMs possess high surface areas, appreciable mechanical strength, and tunable band gaps. Negative linear compressibilities in a wide range are found for the zigzag GMs. By solving the problems of zero gap and dimensionality of graphene sheets simultaneously, these GMs offer a viable strategy towards many applications, e.g., microelectronic devices, energy storage, molecular sieves, sensitive pressure detectors, and telecommunication line systems.
TL;DR: Li et al. as discussed by the authors proposed several kinds of simple nano-structures constructed by BP and SiC nanoribbons, which show peculiar electronic properties and might have promising applications in nano-electronics.
Abstract: First-principles density functional theory and non-equilibrium Green function calculations provide theoretical support for the promising applications of multi-functional nano-electronics constructed using zigzag boron phosphide (BP) nanoribbons (zBPNRs) and silicon carbide nanoribbons (zSiCNRs). The results indicate that zBPNRs are non-magnetic direct bandgap semiconductors with bandgaps of ∼1 eV. Devices constructed using hybrid zSiC-BP-SiC nanoribbon structures are found to exhibit not only significant field-effect characteristics but also tunable negative differential resistance. Moreover, ‘Y’- and ‘Δ’-shaped nano-structures composed of zBPNRs and zSiCNRs exhibit pronounced spin polarization properties at their edges, suggesting their potential use in spintronic applications. Interestingly, a transverse electric field can convert zBPNRs to non-magnetic indirect bandgap semiconductors, ferrimagnetic semiconductors or half-metals depending on the strength and direction of the field. This study may provide a new path for the exploration of nano-electronics. Graphene has sparked such interest among the scientific and technology community that it has been called a ‘wonder material’. The one-dimensional, atom-thick sheet of carbon holds particular promise for nanoelectronics — in field-effect transitors for example — but its zero bandgap hinders practical application. Strategies to circumvent this issue include cutting graphene into nanoribbons or turning to materials that feature boron, nitrogen, silicon or phosphorus — all elements that neighbour carbon in the periodic table. Through first-principles density functional theory and nonequilibrium Green's function calculations, Hui Li from Shandong University, China, and co-workers have predicted interesting electron transport properties for a peculiar material consisting of two zigzag silicon carbide (SiC) nanoribbons connected by a central zigzag boron phosphide (BP) nanoribbon. A variety of configurations were investigated, and the hybrid SiC-BP nanostructures were found to exhibit versatile electronic properties that may be suitable for the construction of multifunctional optoelectronic or spintronic devices. In this article, we propose several kinds of simple nano-structures constructed by BP and SiC nanoribbons, which show peculiar electronic properties and might have promising applications in nano-electronics. SiC-BP-SiC nanoribbons are found to exhibit not only significant field-effect characteristics but also tunable negative differential resistance. ‘Y’- and ‘Δ’-shaped SiC-BP structures show significant spin polarization at their edges. Under the transverse electric field, the non-magnetic direct bandgap zigzag BP nanoribbons can change to non-magnetic indirect bandgap semiconductors, ferrimagnetic semiconductors or half-metals depending on the field strength and direction. These findings reveal the possibility of using SiC-BP nano-structures to construct multi-functional electronics.