Ribbon Edges Research Articles

Investigating geometries and electronic states of boron and nitrogen Co-doping graphene nanoribbons from a DFTB algorithm

Self consistent charge-density functional tight binding simulations are used to investigate the effects of doping B and N atoms on structures and electronic states of armchair graphene nanoribbons passivated by H atoms at the ribbon edges. We considered ten different doping configurations of the doping ribbons, which are categorized into two groups based on whether B and N atoms are in the same carbon ring. The geometric configurations, energy, charge density differences, and Mulliken charges are characterized. The co-doping of B and N atoms in the ribbons significantly affects band structures for different doping arrangements. As covalent bonds form between B and C atoms, the Mulliken population on B atoms changes significantly when B and N atoms are located at different positions of the nanoribbons. The electrical information helps us understand how doping can adjust the electronic states of the graphene nanoribbons to meet the various requirements of electronic devices based on these nanoribbons.

Quantum discord in zigzag graphene nanoribbons

Based on Hubbard model with the Hartree-Fock approximation, we study the properties of quantum discord (QD) between the nearest-neighbor sites A and B in zigzag graphene nanoribbons thermalized with a reservoir at temperature T. Several influences of the site position, on-site Coulomb repulsion U, temperature, and ribbon width on QD are discussed in detail. The results show that QD is robust against thermal fluctuations, and QD for the leg pairs along the zigzag chain near ribbon edges is always larger than that for the rung pairs linking two adjacent zigzag chains. QD for the rung pairs increases and then approaches to saturation as the ribbon width increases, where the velocity of saturation is strongly correlated to U. Moreover, for rung pairs the values of U at the QD peaks perform the scaling behaviors with increasing ribbon width.

Terahertz and Infrared Plasmon Polaritons in PtTe2 Type-II Dirac Topological Semimetal.

Surface plasmon polaritons (SPPs) are electromagnetic excitations existing at the interface between a metal and a dielectric. SPPs provide a promising path in nanophotonic devicesforlight manipulation at the micro and nanoscale with applications in optoelectronics, biomedicine, and energy harvesting. Recently, SPPs are extended to unconventional materials like graphene, transparent oxides, superconductors, and topological systems characterized by linearly dispersive electronic bands. In this respect, 3D Dirac and Weyl semimetals offer a promising frontier for infrared (IR) and terahertz (THz) radiation tuning by topologically-protected SPPs.In this work, the THz-IR optical response of platinum ditelluride (PtTe2) type-II Dirac topological semimetal films grown on Si substrates is investigated. SPPs generated on microscale ribbon arrays of PtTe2are detected in the far-field limit,finding an excellent agreement among measurements, theoretical models, and electromagnetic simulation data.The far-field measurements are further supported by near-field IR data which indicate a strong electric field enhancement due to the SPP excitation near the ribbon edges. The present findings indicate that the PtTe2ribbon array appears an idealactive layout for geometrically tunable SPPs thus inspiring a new fashion of optically tunable materials in the technologically demanding THz and IR spectrum.

Grain boundary diffusion behaviors of hot-deformed magnets in different directions with additional pressure

The diffusion behaviors of hot-deformed magnets were investigated in two different directions with additional pressure. For magnets diffusion along the direction parallel to the C-axis (∥C magnets) and magnets diffused perpendicular to the C-axis (⊥C magnets), the coercivity increased by 3.66 kOe and 4.94 kOe, while the remanence decreased by 1.39 kGs and 1.04 kGs, respectively. The coercivity and remanence are both higher in ⊥C magnets as compared to ∥C magnets. SEM indicates that the orientation in ⊥C magnets is better than in ∥C magnets, which contributes to the more excellent remanence. The SEM also suggests the distribution of the rare-earth-rich phase was more uniform in ⊥C magnets. EPMA shows that the diffusion depth of ⊥C magnets reaches around 1500 μm, while ∥C magnets is less than 1250 μm. Both the homogeneous distribution of the rare-earth-rich phase and deeper diffusion depth are responsible for the improved coercivity of ⊥C magnets. EDS shows that the Nd70Cu30 preferentially entered the interior of the magnets through the interface formed by the fine grains of melt-spun ribbon edges for ∥C magnet during grain boundary diffusion process. But the ⊥C magnet did not show this preference during diffusion. The grain morphology and diffusion resistance of magnets in different directions is the fundamental cause for the difference of Cu distribution in ∥C magnet and ⊥C magnet. The initial magnetization curves suggests that the coercivity mechanism of the initial magnets combines nucleation and domain wall pinning, while the domain wall pinning is enhanced for the diffused magnets. The optimum performances with Br = 13.21 kGs, Hcj = 18.23 kOe, and (BH)max = 43.01 MGOe were achieved in ⊥C magnets.

Inducing abundant magnetic phases and enhancing magnetic stability by edge modifications and physical regulations for NiI2 nanoribbons.

Recently, a magnetic semiconducting NiI2 monolayer was successfully fabricated. To obtain richer magneto-electronic properties and find new physics for NiI2, we studied the zigzag-type NiI2 nanoribbon (ZNiI2NR) with edges modified by different concentrations of H and/or O atoms. Results show that these ribbons hold a higher energy stability, thermal stability, and magnetic stability, and the Curie temperature can be increased to 143 from 15 K for the bare-edged ribbons. They feature a half-semiconductor, bipolar magnetic semiconductor, or half-metal, depending on the edge-terminated atomic species and concentrations, and are closely related to the ribbon edge states, impurity bands or hybridized bands. By applying strain or an electric field, ribbons can achieve a reversible multi-magnetic phase transition among a bipolar magnetic semiconductor, half-semiconductor, half-metal, and magnetic metal. This is because strain changes the Ni-I bond length, resulting in a variation of bond configurations (weight of ionic and covalent bonds) and the number of unpaired electrons. The compressive strain can increase the Curie temperature because it makes the edged Ni-I-Ni bond angle closer to 90°, leading to the FM d-p-d superexchange interaction being increased. The electric field varies the magnetic phase because it alters the electrostatic potential of the ribbon edges, and the Curie temperature is enhanced under the electric field because the ribbon is changed to a metallic state (half-metal or magnetic metal), in which the magnetic Ni atoms satisfy the Stoner criterion and hold a large magnetic exchange coefficient and electron state density at the Fermi surface.

Role of 1D edge in the elasticity and fracture of h-BN doped graphene nanoribbons

Recent achievement of BN-graphene alloy material has enabled the potential of bandgap tuning through both sub-10 nm width control and BN concentration variation. However, its mechanics, which is necessary for prediction of stability in functional applications, is not well studied. Here, molecular dynamics simulation is performed to conduct uniaxial tensile test for BN-doped graphene nanoribbons (BN-GNR) with varying widths and BN atom fractions. Efforts are made to study the constitutive relations for the edges and the whole BN-GNR and explore the fracture mechanisms of the hybrid nanoribbons. The substantial softening effect of the edges induced by wrinkling alters the impact of BN concentration on the stiffness in the sub-20 nm regime deviating from the linear behaviour observed in the bulk case. Fracture properties are unexpectedly independent of BN concentrations unlike in the bulk and the failure behaviour is rather decided by the graphene ribbon edge structure. Here the armchair edges serve as the source of crack nucleation at an early stage leading to weakened strength and reduced stretchability, whereas zigzag edges do not promote early crack nucleation and leads to the size dependence of fracture properties.

Water-Mediated Hydrogen Bond Network Drives Highly Crystalline Structure Formation of Crown Ether-Based Covalent Organic Framework for Sr Adsorption.

Covalent organic frameworks (COFs) with crown ether units have drawn great attention due to their potential applications in adsorption, catalysis, and sensing. However, employing crown ethers to construct COFs is still challenging in light of the flexible nature of macrocycles. Here, a highly crystalline one-dimensional covalent organic framework (1D-18C6-COF) with crown ether units on the ribbon edge was synthesized. The water-mediated hydrogen bond network and π-π stacking hold the 1D COF ribbons together. The combination of experimental and DFT studies demonstrated that the hydrogen bond network plays a crucial role in the structure crystallinity. The 1D-18C6-COF was applied as an adsorbent for strontium, and it exhibited rapid kinetics with good selectivity. In the competitive adsorption experiment, a separation factor of 1900 was achieved, representing one of the largest values for cesium/strontium separation. This work provides new insights into the design and functional exploration of crystalline COFs with flexible units.

Effects of divacancies on the electronic properties of zigzag-edge buckling silicene nanoribbons

In this study, we explore the influence of divacancies (DVs) on the electronic structure and thermoelectric properties of zigzag buckling silicene nanoribbons (ZBSiNRs). We employ the tight-binding approach and determine the electronic structure by numerically diagonalizing a tight-binding Hamiltonian with various configurations of hopping parameters. We investigate impacts of an external electric field perpendicular to the material surface on the band gap's width and the Seebeck coefficient's maximal value. Our results reveal that ZBSiNRs retain their metallic nature even in divacancies. However, the dispersion curves of the flat bands transform into upward-sloping bands. Additionally, our calculations indicate that introducing DVs near the ribbon edges can enhance the conductance of the ribbons. Notably, the width of the band gap and the Seebeck coefficient of the ZBSiNRs exhibit an almost linear increase in response to an applied electric field.

Stabilizing High-Frequency Magnetic Properties of Stretchable CoFeB Films by Ribbon-Patterned Periodic Wrinkles.

The intrinsic nonstretchable feature of magnetic films has significantly limited its applications on wearable high-frequency devices. Recent studies have proved that the wrinkling surface structure based on the growth on polydimethylsiloxane (PDMS) is an effective route to obtain stretchable magnetic films. However, it is still a great challenge to simultaneously achieve a desired stretchability and stretching-insensitive high-frequency properties of magnetic films. Herein, we reported a convenient method to stabilize the high-frequency properties of stretchable magnetic films by depositing magnetic ribbon-patterned films on prestrain PDMS membranes. The ribbon-patterned wrinkling CoFeB films have far fewer cracks than the continuous film, which indicates a nice strain-relief effect and thus confers the stability of high-frequency properties for the films under stretching. However, the wrinkle bifurcation and the uneven thickness at the ribbon edge could adversely affect the stability of its high-frequency properties. The 200 μm wide ribbon-patterned film shows the best stretching-insensitive behaviors and maintains a constant resonance frequency of 3.17 GHz at strain from 10% to 25%. Moreover, a good repeatability has been demonstrated by performing thousands of stretch-release cycles, which did not significantly deteriorate its performances. The ribbon-patterned wrinkling CoFeB films with excellent stretching-insensitive high-frequency properties are promising for application in flexible microwave devices.

Issue Information

International Journal of Applied Glass ScienceVolume 14, Issue 2 p. 165-166 ISSUE INFORMATIONFree Access Issue Information First published: 10 March 2023 https://doi.org/10.1111/ijag.16587AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Cover Photograph: Top) Optimization of the electric heatings for the annealing lehr's zones bottom left and bottom right; (Bottom left) Original and optimized temperature distribution in the UTG ribbon's side at 400 mm to the edge; (Bottom right) Original and optimized residual stresses calculated from FEM and measured via VI at different distances to the UTG ribbon edge. Residual stress seriously affects the quality of ultra-thin glass (UTG); therefore, it is of great scientific interest and technological significance to precisely regulate the annealing process for controlling residual stress. In the past, many studies point out that the residual stress formation process is the comprehensive result of the stress accumulation and release of viscoelastic in the macro. However, we consider that it is caused by the glass atoms structure relaxation process in the micro based on our molecular dynamics (MD) calculation results. The precise regulation of UTG residual stress is realized by revealing the relationship between residual stress with annealing temperature schedule from the micro-scale and combining it with the relevant measurement and calculation means. Volume14, Issue2April 2023Pages 165-166 RelatedInformation

Structural stability, electronic properties, and physical modulation effects of armchair-edged C<sub>3</sub>B nanoribbons

C<sub>3</sub>B monolayer is a typical graphene-like two-dimensional material, which has been successfully prepared experimentally. Here, we use the density functional theory to study the structural stability, electronic properties and physical regulation effects of its armchair-edged nanoribbons. The results show that for the bare-edged nanoribbons, if the ribbon edges are composed of C atoms completely (AA-type), their electronic phase is a semiconductor; when both ribbons edges consist of C and B atoms (BB-type) jointly, their electronic phase is a metal; if one edge of the ribbon is composed of C atoms and the other edge is comprised of B and C atoms (AB-type), their electronic phase is also a metal. This suggests that the B atom located at the ribbon edge plays an important role in determining whether nanoribbons is a metal or semiconductor. While for the H-terminated nanoribbons, they are all direct or indirect band-gap semiconductors. The carrier mobility of H-terminated nanoribbons is generally lower than that of bare-edged nanoribbon, which is closely related to their larger effective mass and higher deformation potential values. Meanwhile, it is found that the semiconducting nanoribbons are very sensitive to physical regulation, especially under applied compressive strain and external electric field, the band gap of the nanoribbons becomes very smaller, which is favorable for the absorption of light energy and development of novel optical devices.

Precise Structural Regulation and Band-Gap Engineering of Curved Graphene Nanoribbons.

Graphene nanoribbons (GNRs)─quasi-one-dimensional graphene cutouts─have drawn growing attention as promising candidates for next-generation electronic and spintronic materials. Theoretical and experimental studies have demonstrated that the electronic and magnetic properties of GNRs critically depend on their widths and edge topologies. Thus, the preparation of structurally defined GNRs is highly desirable not only for their fundamental physicochemical studies but also for their future technological development in carbon-based nanoelectronics. In the past decade, significant efforts have been made to construct a wide variety of GNRs with well-defined widths and edge structures via bottom-up synthesis. In addition to extensively studied planar GNRs consisting of armchair, zigzag, or gulf edges, curved GNRs (cGNRs) bearing cove ([4]helicene unit) or fjord ([5]helicene unit) regions along the ribbon edges have received increasing interest after we presented the first attempt to synthesize the fully cove-edged GNRs in 2015. Profiting from their novel edge topologies, cGNRs usually exhibit an unprecedented narrow band gap and high carrier transport mobility in comparison to the planar GNRs with similar widths. Moreover, cGNRs with particular out-of-plane-distorted structures are expected to provide further opportunities in nonlinear optics and asymmetric catalysis. However, the synthesis of cGNRs bearing cove or fjord edges remains underdeveloped due to the absence of efficient synthetic strategies/methods and suitable molecular precursor design.In this Account, we present the recent advances in the bottom-up synthesis and characterization of structurally defined cGNRs containing cove or fjord edges, mainly from our research group. First, the synthetic strategies toward cGNRs bearing cove edges are described, including the design of molecular monomers and polymer precursors as well as the corresponding polymerization methods, such as Ullmann coupling, Yamamoto coupling, A2B2-type Diels-Alder polymerization, followed by Scholl-type cyclodehydrogenation. The synthesis of typical model compounds is also described to support the understanding of the related cGNRs. In addition, the synthesis of cGNRs containing fjord edges from other research groups via the regioselective Scholl reaction, Hopf cyclization or regioselective photochemical cyclodehydrochlorination approach is presented. Second, we discuss the optoelectronic properties of the as-synthesized cGNRs and reveal the design principle to obtain cGNRs with high charge carrier mobilities. Finally, the challenges and prospects in the design and synthesis of cGNRs are offered. We anticipate that this Account will further stimulate the development of cGNRs through a collaborative effort between different disciplines.

Enhanced Spin Thermopower in Phosphorene Nanoribbons via Edge-State Modifications.

We investigated spin-dependent thermoelectric transport in zigzag phosphorene nanoribbons with a ferromagnetic stripe. We explored the possibility to enhance the spin thermopower via modifications of the edge states in zigzag ribbons. Two methods are proposed to modulate the edge transport: one is applying gate voltages on the edges; the other is including notches on the ribbon edges. The transport gap is enlarged by the edge-state modifications, which enhance the charge and spin Seebeck coefficients almost twofold. Our results suggest phosphorene to be a promising material for thermoelectric applications and open a possibility to design a tunable spin-thermoelectric device.

Investigating arrangements of doping B atoms affecting electrical structures of graphene nanoribbons from DFTB simulations

Self-consistent charge-density functional tight binding simulations are performed to study the effects of different doping positions for B atoms on electrical structures in armchair graphene nanoribbons passivated with H atoms at ribbon edges. Fourteen different doping modes of the two B atoms in the ribbon matrix are demonstrated. The variations of the structural, thermal stability and electrical structures of the fourteen modes are elucidated. The band gap of the B atoms doped in armchair graphene nanoribbons (B-AGNRs) decreases significantly. In the meanwhile, with doping the B atoms at different positions, the B-AGNRs present metallicity or semi-conductivity. Band structures and density of states are also affected by the arrangements of these doping atoms. The molecular orbitals on HOMO and LUMO energy levels show that the B atoms and their surrounding C atoms forms the Π bond, and the size and directivity of the Π bond change corresponding to different doping positions of the B atoms. Accompany with the formation of covalent bonds between the B and C atoms, Mulliken populations on the B atoms change significantly when they are located at the edge and the bulk positions of the B-AGNRs. These findings on electrical level provide us understanding in adjusting the electronic states of the graphene nanoribbons through doping to meet various requirements for electronic devices based on those nanoribbons.

Infrared plasmons in ultrahigh conductive PdCoO2 metallic oxide

PdCoO2 layered delafossite is the most conductive compound among metallic oxides, with a room-temperature resistivity of nearly 2,mu Omega ,{{{{{rm{cm}}}}}}, corresponding to a mean free path of about 600 Å. These values represent a record considering that the charge density of PdCoO2 is three times lower than copper. Although its notable electronic transport properties, PdCoO2 collective charge density modes (i.e. surface plasmons) have never been investigated, at least to our knowledge. In this paper, we study surface plasmons in high-quality PdCoO2 thin films, patterned in the form of micro-ribbon arrays. By changing their width W and period 2W, we select suitable values of the plasmon wavevector q, experimentally sampling the surface plasmon dispersion in the mid-infrared electromagnetic region. Near the ribbon edge, we observe a strong field enhancement due to the plasmon confinement, indicating PdCoO2 as a promising infrared plasmonic material.

Three-dimensional temperature and stress field simulation with all-hexahedral element mesh in a high efficiency cooling structure for the fabrication of amorphous ribbons

Planar flow casting is an advanced technology to produce amorphous and nanocrystalline ribbons in electrical application. At present, the utilization rate of roller surface is generally under 20% in industrial production. This work reports a new cooling structure that is designed to produce ribbons width 65 mm with the utilization rate of roller surface up to 65%. The cooling structure is simulated with the software ANSYS by employing three-dimensional temperature and stress field mathematic model incorporating actual production conditions with all-hexahedral element mesh. It is shown that the liquid velocity is uniform with consistent distribution of convective heat transfer coefficient in width direction between cooling water and rotating roller. The thermal expansion difference in the new cooling structure is only 0.0042 mm at the ribbon edge. In this case, it is unnecessary to make the slit with an upward bend. The new cooling structure is expected to be applied for industrial production at an ideal level.

Functionalized MoS2 Nanoribbons for Intrinsic Cold-Source Transistors: A Computational Study

Power dissipation is a great challenge for continuous size scaling in CMOS technology because of the thermal limitation on the switching rate of conventional transistors. Here, to break the thermal tyranny, we propose a series of intrinsic cold-source field-effect transistors (CS-FETs) with steep slopes based on armchair transition-metal dichalcogenides (TMD) nanoribbons (NRs) (MX2NRs, M = Mo, W; X = S, Se, Te). The edge states of the TMD NRs can filter out the high-energy electrons and break the “Boltzmann tyranny” at room temperature. First-principles calculations unveil the electronic properties of −H, −F, and −H–O terminated MX2NRs with different ribbon widths. Based on quantum transport simulation, −F and −H–O terminated MoS2NRs present FET performance better than that of the −H terminated MoS2NR. A steep subthreshold swing (28 mV/decade) and a large ON/OFF ratio (4 × 105) are obtained for the 12-MoS2NR–F FET with a 5 nm channel length. Moreover, the effects of the ribbon width, channel length, bias voltage, edge roughness, and defects on MoS2NR–F FET performance are also investigated. This work demonstrates edge functionalization as an effective approach to modulate the TMD NRs and guides the design of intrinsic cold-source transistors.

Strain-induced switching in field effect transistor based on zigzag graphene nanoribbons

In this paper, we investigate the effects of uniaxial and oblique strain on Non-linear transport of zigzag graphene nanoribbons using non-equilibrium Green's function formalism. The current-voltage characteristics and especially negative differential resistance (NDR) are affected by the type, strength, and direction of the applied strain. For the tensile strain along the ribbon axis, the on-off current ratio increases, while for the compressive strain, NDR gradually disappears. In the oblique strain, the on-off current ratio drastically decreases compared to the un-strained case. In context, we demonstrate how strain can affect band structure and transition rules as well as transmission coefficients. Also in our calculations, we consider Coulomb interaction as long-range electrostatic potential at mean-field approximation. Coulomb interaction decreases off current and leads to the increased on-off current ratio in the oblique strain. Here, we observe under the influence of the oblique strain, the geometrical symmetry is broken, so the symmetry of charge profile and local currents are broken across ZGNR. We show an imbalanced accumulated charge located on the nanoribbon edges that as a consequence, appear some transverse local currents between the upper and lower edges. These transverse local currents are increased by the strain strength. The minimum (maximum) imbalanced charge accumulated on the ribbon edges occurs exactly at the on (off)-state of longitudinal bias where the transverse current is decreasing (increasing). Finally, we strongly suggest the strain can operate as a nanoelectromechanical switch.

Electronic properties of edge functionalized S-graphene nanoribbons

The structural and electronic properties of edge functionalized S-graphene nanoribbons are studied based on density functional theory. The C atoms of both edges of S-graphene nanoribbons are saturated with –H, –F, –OH, –S, and –Cl groups. It is shown that these edge functionalized nanoribbons are thermally stable. Their electronic properties are strongly dependent on the ribbon width and edge functionalization. The –S and –Cl edge functionalized S-graphene nanoribbons show metallic properties, while S-graphene nanoribbons functionalized by –H, –F, and –OH are semiconductors. Increasing the ribbon width –H, –F, and –OH edge functionalized S-graphene nanoribbons leads to semiconducting-metal transition. Our results indicate that functionalization is a proper way to tune the electronic properties of S-graphene nanoribbons towards various devices and sensing applications.

First-principle investigations of zigzag III-V nitride nanoribbons as CS2 scavengers

We performed density functional theory (DFT) based first-principle calculations to study the CS2 scavenger characteristics of zigzag nitride nanoribbons (ZXNNR, X = Ga/Al/B). The sensing capabilities of Ga, Al and B based nitride nanoribbons have been systematically compared to reveal the optimum host and adsorption sites. The adsorption of CS2 on the edges is mediated via formation of stable chemical bonds while the same at the middle of ribbon is regarded to be physisorbed one. Various possible geometries have been investigated and the CS2 adsorption on considered materials is found to be energetically feasible. It is revealed that interaction with CS2 has a significant impact on the electronic and transport properties of the considered family of III-V nitride nanoribbons. A semiconductor to metallic transition is witnessed for adsorption on the edges. The observed metallic nature is also confirmed by the corresponding current–voltage (I-V) characteristics which further exhibit typical negative differential resistance (NDR) phenomenon in selective configurations. Our analysis shows that recovery time is significantly higher for adsorption at the ribbon edges. On the other hand, adsorption at the center of ribbon is favorable for re-usable sensors with significantly lower recovery time. Present findings are useful for selecting the active adsorption sites and designing the efficient CS2 scavengers.