Edge Of Ribbon Research Articles

Continuous Template Growth of Large-Scale Tellurene Films on 1T'-MoTe2.

Use of a template triggers an epitaxial interaction with the depositing material during synthesis. Recent studies have demonstrated that two-dimensional tellurium (tellurene) can be directionally oriented when grown on transition metal dichalcogenide (TMD) templates. Specifically, employing a T-phase TMD, such as WTe2, restricts the growth direction even further due to its anisotropic nature, which allows for the synthesis of well-oriented tellurene films. Despite this, producing large-area epitaxial films still remains a significant challenge. Here, we report the continuous synthesis of a 1T'-MoTe2 template via chemical vapor deposition and tellurene via vapor transport. The interaction between helical Te and the 1T'-MoTe2 template facilitates the Te chains to collapse into ribbon shapes, enhancing lateral growth at a rate approximately 6 times higher than in the vertical direction, as confirmed by scanning electron microscopy and atomic force microscopy. Interestingly, despite the predominance of the lateral growth, cross-sectional transmission electron microscopy analysis of the tellurene ribbons revealed a consistent 60-degree incline at the edges. This suggests that the edges of the tellurene ribbons, where they contact the template surface, are favorable sites for additional Te absorption, which then stacks along the incline angle to expand. Furthermore, controlling the synthesis temperature, duration, and preheating time has facilitated the successful synthesis of tellurene films. The resultant tellurene exhibited hole mobility as high as ∼400 cm2/V s. After removing the underlying metallic template with plasma treatment, the film showed a current on/off ratio of ∼103. This ratio was confirmed by two-terminal field-effect transistor measurements and supported by near-field terahertz (THz) spectroscopy mapping.

The impact of electron phonon scattering on transport properties of topological insulators: A first principles quantum transport study

Using first-principles calculations and non-equilibrium Green’s function, we study the topologically-protected carrier transport in the edges of topological insulator ribbons. We investigate the effects of electron–phonon interactions on the edge state transport. We observed that in topological insulator with small bulk gaps, electron–phonon scattering results in the bulk states broadening into the bulk gap. This leads to the destruction of the dissipationless transport. However, if the transport is restricted to the protected states, a higher immunity to electron–phonon scattering can be achieved. This can lead to the design of topological insulator field effect transistors operating based on scattering modulation, benefiting from a channel material with strong electron–phonon coupling.

Electron-scattering-induced entanglement between two atoms placed near the zigzag edge of a phosphorene ribbon

Electron-scattering-induced entanglement between two atoms placed near the zigzag edge of a phosphorene ribbon

Nanoporous Vesicular Membranes of Amphiphilic Polymers Containing Trans / Cis Isomers

Nanoporous Vesicular Membranes of Amphiphilic Polymers Containing <i>Trans</i> / <i>Cis</i> Isomers

Spontaneous spin polarization at the edge of the chiral superconducting states in a spin Hall metal

We discuss the chiral superconducting state in a square lattice system with an intrinsic spin-orbit coupling causing the spin Hall effect. We estimate the spontaneous spin polarization (local moment) 〈mi 〉 at the i-th site and its sum M = ∑ i 〈mi 〉 in ribbons. In the zigzag ribbon, we see 〈mi 〉 ≠ 0 near the edge. The energy spectra of the chiral edge states show the spin splitting and then we have non-zero M. Moreover, we find that M is enhanced significantly at a topological phase transition point, where the energy gap is closing. We also have non-zero 〈mi 〉 near the edge of the straight ribbon, but in contrast, there is no spin splitting in the spectra and M vanishes.

Interactions Between Epitaxial Graphene Grown on the Si- and C-Faces of 4H-SiC Investigated Using Raman Imaging and Tip-Enhanced Raman Scattering.

Interactions between epitaxial graphene grown on Si- and C-faces were investigated using Raman imaging and tip-enhanced Raman scattering (TERS). In the TERS spectrum, which has a spatial resolution exceeding the diffraction limit, a D band was observed not from graphene surface, but from the edges of the epitaxial graphene ribbons without a buffer layer, which interacts with SiC on the Si-face. In contrast, for a graphene micro-island on the C-face, the D band disappeared even on the edges where the C atoms were arranged in armchair configurations. The disappearance of the edge chirality via combination between the C atoms and SiC on the C-face is responsible for this phenomenon. The TERS signals from the C-face were weaker than those from the Si-face without the buffer layer. On the Si-face with a buffer layer, the graphene TERS signal was hardly observed. TERS enhancement was suppressed by interactions on the edges or by the buffer layer between the SiC and graphene on the C- or Si-face, respectively.

Development of a Confined Circular-Cum-Parallel Ribbon Flare and Associated Pre-Flare Activity

We study a complex GOES M1.1 circular ribbon flare and related pre-flare activity on 26 January 2015 [SOL26-01-2015] in solar active region NOAA 12268. This flare activity was observed by the AIA on board SDO and the RHESSI. The examination of photospheric magnetograms during the extended period, prior to the event, suggests the successive development of a so-called 'anemone' type magnetic configuration. NLFFF extrapolation reveals a fan-spine magnetic configuration with the presence of a coronal null-point. We found that the pre-flare activity in the active region starts ~15 min prior to the main flare in the form of localized bright patches at two locations. A comparison of locations and spatial structures of the pre-flare activity with magnetic configuration of the corresponding region suggests onset of magnetic reconnection at the null-point along with the low-atmosphere magnetic reconnection caused by the emergence and the cancellation of the magnetic flux. The main flare of M1.1 class is characterized by the formation of a well-developed circular ribbon along with a region of remote brightening. Remarkably, a set of relatively compact parallel ribbons formed inside the periphery of the circular ribbon which developed lateral to the brightest part of the circular ribbon. During the peak phase of the flare, a coronal jet is observed at the north-east edge of the circular ribbon which suggests interchange reconnection between large-scale field lines and low-lying closed field lines. Our investigation suggests a combination of two distinct processes in which ongoing pre-flare null-point reconnection gets further intensified as the confined eruption along with jet activity proceeded from within the circular ribbon region which results to the formation of inner parallel ribbons and corresponding post-reconnection arcade.

Numerical analysis of surface and edge states in slabs, stripes, rods and surface steps of topological insulators

By numerically solving the effective continuous model of a topological insulator with parameters corresponding to the band structure of the topological insulator Bi2Se3, we analyze possible appearance of one-dimensional states in various geometries. Massless Dirac fermions are found at the edges of thin ribbons with surface oriented not only along the van der Waals gap but also in the perpendicular direction. Thick rods and slabs with surface steps host massive modes localized on surface faces. We argue that the the origin of the massive modes is due to the difference in the Dirac point energy of adjacent faces. The absence of one-dimensional states near edges of a large rectangular rod and surface steps is demonstrated.

Tunable rectification and negative differential resistance induced by asymmetric doping in phosphorene nanoribbon

By using first-principles calculations based on density functional theory and non-equilibrium Green's function, we present the electronic transport properties of two kinds of devices based on armchair phosphorene nanoribbons, namely, A device, and B device. In A device, the phosphorus atoms in the center of armchair phosphorene nanoribbon have been replaced by impurity atoms of the S and Si, whereas in the B device, the impurity atoms are at the edge of ribbon. The results show that the current–voltage characteristics for both devices have striking nonlinear features and the rectifying behaviors strongly depend on the positions of impurity atoms. The highest rectification ratio is obtained about 125992 at 0.8 V bias for B device. Moreover, only for A device, robust negative differential resistance is observed with a high peak–valley ratio 27500 in the bias range [−0.2,−0.6] V. The mechanism of the rectification behavior is analyzed in terms of the evolution of energy levels of the related electrodes and transmission spectra as well as the projected self-consistent Hamiltonian eigenvalues with the applied bias voltage. The results indicate that the asymmetric doping of the impurity atoms can lead to a robust rectification which can be utilized to design phosphorene-base rectifier with good performance.

Kondo effect in a two-dimensional topological insulator: Exact results for adatom impurities

The Lanczos transformation [Phys. Rev. B 91, 085101 (2015)] combined with density matrix renormalization group calculations is used to obtain exact real space properties of a model for a magnetic adatom impurity coupled to the edge of a zigzag stanene ribbon, which, given stanene's sizable spin-orbit interaction, has non-trivial topological properties. We consider an impurity coupled to a site from either sublattice A or B (where a zigzag edge can be pictured as ⋯/∖/∖⋯, or ⋯ABABA⋯, where a B-site, dubbed a crest site, is an outermost one, while an A-site is dubbed a trough site). Our real space resolution allows us to conclude that the two possible ground states are qualitatively very different: in both cases, the introduction of spin-orbit interaction greatly increases the range of the spin correlations between the impurity and the electron spins in the metallic edge-state; however, for the trough-site-coupled impurity the spin correlations show very strong anisotropy (〈Simp,zsz〉≠〈Simp,xsx〉, where Simp denotes the impurity spin and s denotes the spin of an electron in the lattice), while the spin correlations for the crest-coupled impurity are almost isotropic. These results suggest that for either type of site (crest or through) the problem can be mapped onto an Anderson impurity problem, with the adatom side-coupled to a one-dimensional channel. For the crest-coupled case this channel has practically trivial character, while for a trough site the spin-orbit interaction introduces a strong Dzyaloshinskii-Moriya interaction.

Influence of spout lip set-height on flow behavior during the glass float process

One of the most widely employed procedures for flat glass manufacture is float process proposed by Pilkington. Nowadays, there is great demand for thinner float glass of high optical quality. The most important stage of float process is the glass forming in tin bath. In this study, the ANSYS Fluent 14.0 software is adopted to develop a multiphase numerical model and simulate the flow phenomena of molten glass when it is spouted over a lip onto the tin bath under protective atmosphere. The influence of spout lip set-height on flow behavior of molten glass and tin at tin bath entrance is investigated. The results of 2D simulation indicate that the velocity at the vertex of spout lip, the depth where glass dips into tin bath as well as wetback flow increase with the set-height. From results of 3D simulation, the expansion of glass ribbon and velocity gradient along lateral direction of tin bath occurs as molten glass floats on molten tin. The velocity components of Vy and Vx of wetback flow are significant at the edge while are extremely low near symmetry plane. The larger velocity components of Vy and Vx of wetback flow are achieved with increase of spout lip set-height, which would facilitate more glass containing impurities to flow towards the edge of glass ribbon and improve the glass forming quality. The simulation results are supposed to guide the optimization design of spout lip.

A multifilar helical antenna on a sphere and the limits of broadbandness

An antenna in form of a dense multifilar helix of thin metal ribbons on a spherical surface with lower order transverse-electric and transverse-magnetic modes is considered. Averaged boundary conditions taking into account the capacitances between the edges of ribbons are formulated. Formulas for calculating the angle of inclination of ribbons and the required inter-edge capacitance from a given resonance frequency and approximate ellipticity coefficient are obtained. The inclination of the axes of the polarization ellipse and an improved ellipticity coefficient are determined. The fractional bandwidth of the antenna is expressed via the improved limits of the fractional bandwidth of linearly polarized antennas. The limits of the fractional bandwidth of circularly polarized antennas are found. It is established that the maximum fractional bandwidth is reached if the ellipticity coefficient is slightly different from unity.

Self-assembly of a nanotube from a black phosphorus nanoribbon on a string of fullerenes at low temperature.

A string of fullerenes is used for generating a nanotube by self-assembly of a black phosphorus (BP) nanoribbon at a temperature of 8 K. Among the fullerenes in the string, there are at least two fixed fullerenes placed along the edge of the BP ribbon for keeping its configuration stability during winding. By way of molecular dynamics simulations, it is found that successful generation of a BP nanotube depends on the bending stiffness of the ribbon and the attraction between the fullerenes and the ribbon. When the attraction is strong enough, the two edges (along the zigzag direction) of the BP ribbon will be able to bond covalently to form a nanotube. By the molecular dynamics approach, the maximum width of the BP ribbon capable of forming a nanotube with a perfect length is investigated in three typical models. The maximum width of the BP ribbon becomes larger with the string containing more fullerenes. This finding reveals a way to control the width of the BP ribbon which forms a nanotube. It provides guidance for fabricating a BP nanotube with a specified length, the same as to the width of the ribbon.

Topological insulator on honeycomb lattices and ribbons without inversion symmetry

We study the Kane-Mele-Hubbard model with an additional inversion-symmetry-breaking term. Using the topological Hamiltonian approach, we calculate the $\mathbb{Z}_2$ invariant of the system as function of spin-orbit coupling, Hubbard interaction $U$, and inversion-symmetry-breaking on-site potential. The phase diagram calculated in that way shows that, on the one hand, a large term of the latter kind destroys the topological non-trivial state. On the other hand, however, this inversion-symmetry-breaking field can enhance the topological state, since for moderate values the transition from the non-trivial topological to the trivial Mott insulator is pushed to larger values of interaction $U$. This feature of an enhanced topological state is also found on honeycomb ribbons. With inversion symmetry, the edge of the zigzag ribbon is magnetic for any value of $U$. This magnetic moment destroys the gapless edge mode. Lifting inversion symmetry allows for a finite region in interaction strength $U$ below which gapless edge modes exist.

Two-point Green functions of free Dirac fermions in single-layer graphene ribbons with zigzag and armchair edges

Green function technique is a very efficient theoretical tool for the study of dynamical quantum processes in many-body systems. For the study of dynamical quantum processes in graphene ribbons it is necessary to know two-point Green functions of free Dirac fermions in these materials. The purpose of present work is to establish explicit expressions of two-point Green functions of free Dirac fermions in single-layer graphene ribbons with zigzag and armchair edges. By exactly solving the system of Dirac equations with appropriate boundary conditions on the edges of graphene ribbons we derive formulae determining wave functions of free Dirac fermions in above-mentioned materials. Then the quantum fields of free Dirac fermions are introduced, and explicit expressions of two-point Green functions of free Dirac fermions in single-layer graphene ribbons with zigzag and armchair edges are established.

Self-organised formation of nanotubes from graphene ribbons. A molecular dynamics study

The conditions for self-organised formations of carbon nanotubes from two parallel graphene ribbons were studied in a density functional adjusted tight binding molecular dynamics simulation. We have found that the seemingly trivial process is significantly limited by the thermal motion of the carbon atoms. There are further difficulties as well, primarily the unfavourable position of the atoms at the edges of the zigzag graphene ribbons. In repeated molecular dynamics runs we analysed the conditions of perfect coalescences, the influence of the substrate and the impact of the zigzag graphene ribbon positions. We have obtained that contrary to the abovementioned unfavourable conditions perfect nanotube production can be obtained using substrates. As the positioning of the substrate can be made with piezoelectric devices, this can significantly help the experimental realisation of the nanotube formation as well.

Oxygen Vacancy Formation on α-MoO3 Slabs and Ribbons

MoO3 is a versatile catalyst for oxidation reactions that consists of bilayers connected by van der Waals interaction. In principle, a MoO3 nanocrystal can be exfoliated to create two-dimensional ribbons. For this article, we study the difference between the chemistry of slabs having a variety of crystal faces and that of the edges of ribbons cut from a two-dimensional bilayer. As a descriptor of chemical reactivity we use the energy of oxygen-vacancy formation: the easier it is to form an oxygen vacancy, the better oxidant the face of a slab or the edge of a two-dimensional ribbon is. We find that the properties of ribbon edges are different from those of the corresponding slab surfaces. The surface energies of slabs are in the order (010)s < (100)s < (101)s < (001)s, whereas the edge energies of ribbons are in the order ⟨100⟩r ≈ ⟨101⟩r < ⟨001⟩r (the subscript s indicates a slab, and r, a ribbon). Among the surfaces studied, we have found that (001)s and (101)s faces have the lowest oxygen-vacancy formation energies, and (010)s has the highest. In contrast, among the edges studied, ⟨101⟩r has the lowest vacancy formation energies. Our calculations suggest that no benefit is obtained by creating ⟨100⟩r or ⟨001⟩r ribbon edges. However, a significant decrease of oxygen-vacancy formation energies is observed on formation of ⟨101⟩r edge by exfoliating (101)s slabs. Also, among the structures studied, we found ⟨101⟩r edges to be the most reactive and (010)s surfaces to be the least reactive.

Finite-width effects for the localized edge modes in zigzag graphene nanoribbons

A matrix formalism is used to derive the analytical Green's functions describing correlations between any two atomic sites on a zigzag (ZZ) graphene nanoribbon, incorporating modified electronic hopping values between edge sites that may be distinct from the hopping between interior sites. An analysis of the poles of our Green's functions shows two distinct types of localized edge modes in the electronic spectrum. The first of these, the ``zero'' mode, is a topologically induced mode arising from the bipartite honeycomb lattice structure of graphene and is always present along ZZ edges. The second type of localized edge mode is present at edges when the edge-to-bulk hopping ratio deviates significantly from unity. The correlations between edge sites are found to exhibit strikingly different features when mediated by the zero edge mode compared with mediation by the ``modified'' edge mode. In particular, the zero-mode spectral intensity for correlations between two atomic sites along opposite edges can be comparable in strength with that between two sites on the same edge of a finite-width ribbon, before it eventually tends to zero as the ribbon width tends to infinity. This remarkable behavior shows a strong dependence on the sublattice labels of the sites and is in contrast with properties of the modified hopping edge modes. The explicit form of our analytical expressions for the electronic spectrum enables us to predict the zero-mode properties (including frequency, spatial attenuation, and intensity) when the hopping values along ZZ edges are modified.

First principles study of Li terminated armchair graphene nanoribbons

We have investigated the consequences of Li termination on the electronic and structural properties of armchair graphene nanoribbons (AGNR) by employing first-principles calculations. We considered the effect of Li termination on one edge as well as on both the edges of ribbons and revealed their potential applications. It is observed that Li termination has a profound effect on the electronic structure of AGNR. The analysis of binding energy suggests that all the structures are energetically feasible to obtain. Further, AGNR with larger widths are comparatively more stable than the narrow width nanoribbons. A semiconducting to metallic transition can be observed depending upon the ribbon width. Our results indicate that Li termination could be a potential way to tailor the electronic and transport properties of AGNR.

Simulation of Molten‐Glass Evolution from Spout Lip to Tin Bath

Viscous molten glass with a high temperature flows into a tin bath through a complicated three‐phase flow during the production of glass. It is very important to understand the characteristics of evolution for optimizing float‐glass design as well as preparing high‐quality flat glass. A three‐phase flow system containing molten glass, molten tin under N2/H2 atmosphere in a 600 t/day tin bath from the spout lip to the end of restrictor tile, was simulated and analyzed using ANSYS Fluent 14.0 software. The glass velocity field at the vertical section of the end of restrictor tiles, the relative position of glass material point between the entrance of tin bath and the vertical section of the restrictor tiles end, and the glass flow trend at the wetback area were analyzed. The edge of glass ribbon was formed by the bottom molten glass flow in the spout lip in contact with refractories, and greater proximity to the spout lip edge corresponded with greater proportion was supplied. The simulation indicates that the middle section of the glass cross‐section stria image can reflect the real glass location state at the canal vertical section and has little relationship with the tin bath.