Metallic Nanoribbons Research Articles

Broadband optical waveguide modulators based on strongly coupled hybrid graphene and metal nanoribbons for near-infrared applications

In this paper, we numerically demonstrate a variety of broadband optical waveguide modulators based on the hybrid surface plasmon polariton (HSPP) concept for near-infrared applications. The modulator is composed of strongly coupled double-layer graphene and double rectangle cross-sectional metal nanoribbons separated by three Al2O3 spacers, which are interpolated in a SiO2 waveguide. Owing to the unique strong coupling of HSPPs between metal nanoribbons, the subwavelength confinement, the in-plane electric field component, the light-graphene interaction, and the modulation effect of the modulator are significantly enhanced. The results show the proposed modulator achieves an outstanding performance with a modulation depth (MD) over 2.3 dB μm-1 and a small normalized mode area of ∼10-5 in a wide range of wavelength from 1.3 to 1.8 μm. By optimizing the separation of the double rectangle metal nanoribbons at the telecommunication wavelength of 1.55 μm, the modulator exhibits a high MD of 3.12 dB μm-1, a small footprint of 1.8 μm2, an ultra-wide 3 dB modulation bandwidth of 380.23 GHz, and an ultra-low energy consumption of 29.39 fJ per bit. Furthermore, we also demonstrate a modulator based on two properly apart semicircular (rhombus) metal nanoribbons with a drastically enhanced MD of 11.3 (6.32) dB μm-1 at 1.55 μm. Benefitting from the strong subwavelength confinement and excellent broadband modulation performance, the proposed optical waveguide modulators offer a significant potential to realize various long-wave near-infrared integrated modulators, interconnects and optoelectronic devices.

Crystal Orbital Study on one-dimensional β-graphyne and its BN-substituted derivatives

In this study, one-dimensional (1D) β-graphyne (βGY) Nanoribbons (NRs) and its three types of BN-substituted derivatives are investigated by the self-consistent-field Crystal Orbital (SCF-CO) method. To the authors’ knowledge, little information about the structural, electronic and transport properties of the 1D βGY NRs and BN-substituted βGY derivatives has been reported before. The phonon analysis shows that these 1D NRs should be dynamically stable. The structures with more BN pairs are believed to be more stable. The BN substituted positions and the edge structures have great impact on the electronic properties of the studied NRs. These NRs can be conductors, semiconductors or insulators. It is found that the metallic NR with sp2 hybridized C atoms substituted by BN units has high superconducting transition temperature which is even higher than those of alkali-doped C60 complexes. The mobilities of charge carriers for these NRs are also calculated. The band structures and the mobilities of 1D NRs are compared with those of the corresponding two-dimensional (2D) slabs.

An efficient mechanism for enhancing the thermoelectricity of nanoribbons by blocking phonon transport in 2D materials

Inspired by the novel mechanism of reducing thermal conductivity by local phonon resonance instead of by inducing structural defects, we investigate the effect of side branching on the thermoelectric properties of nanoribbons, and prove that side branching is a highly efficient mechanism for enhancing the thermoelectricity of different kinds of nanoribbons. For both armchair and zigzag nanoribbons, the side branches result in not only significant blocking of phonon transport but also notable increase of the Seebeck coefficient. Consequently, the thermoelectric figure of merit of the armchair nanoribbon is boosted from 0.72 to as high as 1.93, and the originally non-thermoelectric metallic zigzag nanoribbon is turned into a thermoelectric material due to the appearance of the band gap induced by the side branches. These results mean that the mechanism of branching is not only very efficient, but also takes effect regardless of the original properties of the nanoribbons, and thus will hold great promise for its application in the thermoelectric field.

Zigzag graphene nanoribbons separated by hydrogenation

As the integrated circuits continue to miniaturize, the narrower interconnect matched is needed. Using density functional theory combined with non-equilibrium Green's function, we try to adopt a row or a column of hydrogen atoms adsorbed on the zigzag graphene nanoribbons, which are in the middle parallel or perpendicular to the axial direction to limit the movement of π electron. The utilization of the adsorbed hydrogen row blocks the transport of electrons, zigzag graphene nanoribbons are divided into conductive and non-current part. Physically, the nanoribbons are separated laterally or longitudinally to two strips that contain fewer atoms, preserving the structural integrity of zigzag graphene nanoribbons. According to the transmission pathways after hydrogenation, there is almost no current flowing through the intermediate hydrogenated carbon chains when hydrogenated in the direction of the ribbon axis; while perpendicular to the ribbon axis, except for the loop current among the two edge carbon atoms and the hydrogenated carbon atoms, only a small part of the current flows along the zigzag axial direction. In the application of graphene nanoribbons, we usually want to use semiconductor nanoribbons as devices, and metal nanoribbons for interconnects. Our results indicate that zigzag graphene nanoribbons can be qualitatively separated into two narrower strips by regular adsorption of hydrogen to connect smaller devices.

Symmetrical metallic and magnetic edge states of nanoribbon from semiconductive monolayer PtS2

Transition metal dichalcogenides (TMD) MoS2 or graphene could be designed to metallic nanoribbons, which always have only one edge show metallic properties due to symmetric protection. In present work, a nanoribbon with two parallel metallic and magnetic edges was designed from a noble TMD PtS2 by employing first-principles calculations based on density functional theory (DFT). Edge energy, bonding charge density, band structure, density of states (DOS) and simulated scanning tunneling microscopy (STM) of four possible edge states of monolayer semiconductive PtS2 were systematically studied. Detailed calculations show that only Pt-terminated edge state among four edge states was relatively stable, metallic and magnetic. Those metallic and magnetic properties mainly contributed from 5d orbits of Pt atoms located at edges. What's more, two of those central symmetric edges coexist in one zigzag nanoribbon, which providing two atomic metallic wires thus may have promising application for the realization of quantum effects, such as Aharanov–Bohm effect and atomic power transmission lines in single nanoribbon.

Hybridization induced metallic and magnetic edge states in noble transition-metal-dichalcogenides of PtX2(X = S, Se) nanoribbons

The semiconducting transition metal dichalcogenide (TMD) 2H-MoS2 zigzag nanoribbon has two different edges, and only one edge shows metallic properties due to symmetric protection. In the present work, a nanoribbon with two parallel metallic and magnetic edges was designed from a noble TMD 1T-PtX2 (X = S, Se) by employing first-principles calculations based on density functional theory (DFT). The band structure, density of states (DOS), and simulated scanning tunneling microscopy (STM) of three possible zigzag edge states of monolayer semiconducting PtX2 were systematically studied. Detailed calculations showed that the Pt-terminated edge state among the three zigzag edge states was metallic. The Pt-terminated edge state designed from monolayer PtS2 showed both metallic and magnetic properties. These metallic and magnetic properties were mainly contributed to by the hybridization of the 5d orbitals of Pt atoms and the 3p orbitals of S atoms located at the edges. However, hybridization of the 5d orbitals of Pt atoms and the 4p orbitals of Se atoms located at the edges does not bring magnetic properties to the zigzag metallic PtSe2 nanoribbon. The interesting electronic and magnetic properties of 1T-PtX2 nanoribbons indicate that they may have promising applications as zigzag nanoribbons in spin electronics and photovoltaic cells.

Single-band negative differential resistance in metallic armchair MoS2 nanoribbons

Semiconductor armchair MoS2 nanoribbons can be converted into conductors by edge functionalization of H atoms or OH groups. Those metallic nanoribbons exhibit I–V characteristics of a single half-filled band with strong negative differential resistance (NDR) under a voltage bias less than 1 V. This originates from the spatial separation between electrons in the conduction and valence bands. The NDR becomes spin dependent if the H atoms or OH groups are not uniformly adsorbed on the edge. Furthermore, the spin polarization can be greatly enhanced in heterojunctions of H- and OH-passivated nanoribbons.

Combined Effect of External Periodic and Constant Electric Fields on Electron Transport in Carbon Nanotubes and Nanoribbons with Metallic Conductivity

We review the simultaneous effect of AC and DC fields on metallic and semiconductor nanoribbons and nanoribbons with hexagonal structure nanoribbons. Moreover, we define the density of the nonlinear surface current. We find that the amplitude of oscillation in zigzag nanoribbons is exponentially dependent on width and does not depend on width in armchair nanoribbons. The absolute negative conductivity in the nanoribbons was revealed. We define the magnitude of the nonlinear current in the conduction band, taking into account the approaches of dispersion law, based on the first-principle approach.

Quantum Size Effects in the Terahertz Nonlinear Response of Metallic Armchair Graphene Nanoribbons

We use time dependent perturbation theory to study quantum size effects on the terahertz nonlinear response of metallic graphene armchair nanoribbons of finite length under an applied electric field. Our work shows that quantization due to the finite length of the nanoribbon, the applied field profile, and the broadening of the graphene spectrum all play a significant role in the resulting nonlinear conductances. In certain cases, these effects can significantly enhance the nonlinearity over that for infinitely-long metallic armchair graphene nanoribbon.

How to realize a spin-dependent Seebeck diode effect in metallic zigzag γ-graphyne nanoribbons?

The spin-dependent Seebeck effect (SDSE) is one of the core topics of spin caloritronics. In the traditional device designs of spin-dependent Seebeck rectifiers and diodes, finite spin-dependent band gaps of materials are required to realize the on-off characteristic in thermal spin currents, and nearly zero charge current should be achieved to reduce energy dissipation. Here, we propose that two ferromagnetic zigzag γ-graphyne nanoribbons (ZγGNRs) without any spin-dependent band gaps around the Fermi level can not only exhibit the SDSE, but also display rectifier and diode effects in thermal spin currents characterized by threshold temperatures, which originates from the compensation effect occurring in spin-dependent transmissions but not from the spin-splitting band gaps in materials. The metallic characteristics of ZγGNRs bring about an advantage that the gate voltage is an effective route to adjust the symmetry of spin-splitting bands to obtain pure thermal spin currents. The results provide a new mechanism to realize spin-Seebeck rectifier and diode effects in 2D materials and expand material candidates towards spin-Seebeck device applications.

Tunable angle-independent refractive index sensor based on Fano resonance in integrated metal and graphene nanoribbons.

We propose a novel mechanism to construct a tunable and ultracompact refractive index sensor by using the Fano resonance in metal-graphene hybrid nanostructure. Plasmon modes in graphene nanoribbons and waveguide resonance modes in the slits of metal strip array coexist in this system. Strong interference between the two different modes occurs when they are spectrally overlapped, resulting in a Fano-type asymmetrically spectral lineshape which can be used for detecting the variations of ambient refractive index. The proposed sensor has a relatively high figure of merit (FOM) over 20 and its sensing performance shows a good tolerance to roughness. In addition to the wide range measurement enabled by the electrical tuning of graphene plasmon modes, such ultracompact system also provides an angle-independent operation and therefore, it can efficiently work for the detection of gas, liquid, or solids. Such optical nanostructure may also be applied to diverse fields such as temperature/pressure metering, medical detection, and mechanical precision measurement.

Charge susceptibilities of armchair graphene nanoribbon in the presence of magnetic field

We present the behaviors of both dynamical and static charge susceptibilities of undoped armchair graphene nanoribbon using the Green’s function approach in the context of tight binding model Hamiltonian. Specifically, the effects of magnetic field on the the plasmon modes of armchair graphene nanoribbon are investigated via calculating the correlation function of charge density operators. Our results show that the increase of magnetic field makes the high-frequency plasmon mode for both metallic and insulating cases disappear. We also show that low-frequency plasmon mode for metallic nanoribbon appears due to increase of magnetic field. Furthermore, the number of collective excitation modes increases with ribbon width at zero magnetic field. Finally, the temperature dependence of the static charge structure factor of armchair graphene nanoribbon is studied. The effects of both magnetic field and ribbon width on the static charge structure factor are discussed in detail.

Perfect narrow band absorber for sensing applications.

We design and numerically investigate a perfect narrow band absorber based on a metal-metal-dielectric-metal structure which consists of periodic metallic nanoribbon arrays. The absorber presents an ultra narrow absorption band of 1.11 nm with a nearly perfect absorption of over 99.9% in the infrared region. For oblique incidence, the absorber shows an absorption more than 95% for a wide range of incident angles from 0 to 50°. Structure parameters to the influence of the performance are investigated. The structure shows high sensing performance with a high sensitivity of 1170 nm/RIU and a large figure of merit of 1054. The proposed structure has great potential as a biosensor.

A theoretical investigation on the transport properties of armchair biphenylene nanoribbons

Armchair biphenylene nanoribbons are investigated by using density functional theory. The nanoribbon that contains one biphenylene subunit in a unit cell is a semiconductor with a direct band gap larger than 1eV, while that containing four biphenylene subunits is a metal. The semiconducting nanoribbon has high electron mobility of 57174cm2V−1s−1, superior to armchair graphene nanoribbons. Negative differential resistance behavior is observed in two electronic devices composed of the semiconducting and metallic nanoribbons. The on/off ratios are in the order of 103. All these indicate that armchair biphenylene nanoribbons are potential candidates for ultra-small logic devices.

Stable and metallic borophene nanoribbons from first-principles calculations

The high electronic conductance and structural stabilities enable the edge-reconstructed borophene nanoribbons to be promising electrical connections in nanoscale circuits.

Simulating periodic trends in the structure and catalytic activity of coinage metal nanoribbons

We present a systematic density functional theory (DFT) study of the structure and catalytic activity of group 10 (Ni, Pd, Pt) and group 11 (Cu, Ag, Au) coinage metal nanoribbons. These infinite, periodic, quasi-one-dimensional structures are conceptually important as intermediates between small metal clusters and close-packed metal surfaces, and have been shown experimentally to be practical catalysts. We find that nanoribbons have significantly higher predicted H2 dissociation activity than close-packed metal surfaces consistent with their lower coordination numbers. Computed periodic trends are reasonable, with late transition states and low barriers for H2 dissociation over late group 10 nanoribbons, suggesting their promise as practical catalysts. These trends are consistent with the isolated nanoribbons' computed molecular electrostatic potentials. Calculations also predict nearly linear Bronsted–Evans–Polanyi relationships between the nanoribbons' H2 dissociation energies and dissociation barriers. We also test new meta-generalized gradient approximation (GGA) and hybrid DFT approximations for H2 dissociation over these nanoribbons. These new functionals increase the (generally underestimated) dissociation barriers predicted by standard GGAs, motivating their continued application in surface chemistry. © 2015 Wiley Periodicals, Inc.

Stable Metallic 1T-WS2 Nanoribbons Intercalated with Ammonia Ions: The Correlation between Structure and Electrical/Optical Properties.

Stable metallic 1T-WS2 nanoribbons with zigzag chain superlattices, highly stabilized by ammonia-ion intercalation, are produced using a facile bottom-up process. The atomic structure of the nanoribbons, including W-W reconstruction and W-S distorted octahedral coordination, results in distinctive electrical transport and optical Raman scattering properties that are very different from semiconducting 2H-WS2 . The correlations between structure and properties are further confirmed by theory calculations.

Electronic properties of armchair graphene nanoribbons doped with Cobalt atoms

We have investigated the electronic properties of Co doped armchair graphene nanoribbons (AGNR) within the framework of density functional theory. We have considered Co as an adsorbed atom as well as substitutional dopant in AGNR. Adsorption is found energetically favorable over substitutional doping. The calculated formation energy suggests edge as the most energetically favorable site for Co atoms in AGNR. It is observed that for all the considered sites, Co atoms effectively modify the electronic band structures of AGNR and introduce metallicity. Moreover, substitutional Co-doping induces a large number of conducting channels crossing the Fermi energy and thereby enhancing the metallicity in AGNR as compared to Co-adsorption. The observed highly metallic nanoribbons are crucial for nano interconnects and other technological applications.

Broadband absorption enhancement in ultrathin-film solar cells by combining dielectric nanogratings and metallic nanoribbons

Optical absorption improvement and cost reduction of thin-film solar cells have been long-time issues. These two aims are achieved simultaneously by combining metallic nanoribbons and dielectric gratings at the front side of ultrathin-film amorphous silicon solar cells. Surface-plasmon-polariton waves excited by the nanoribbons at the long wavelength co-operates with Uller-Zenneck waves and cavity resonances excited by the gratings at the short wavelength with little cross-effect, leading to a complementary absorption enhancement of 31% when compared to planar structure. In addition, this design exhibits wide-angle absorption as well as a high fabrication tolerance. Compared to the previous work combining different mechanisms, this design provides fewer fabrication steps and an easier approach. Moreover, the nanoribbons can be used as a transparent conducting electrode for a low-cost alternative to expensive indium tin oxide thin-film.

Electronic, magnetic, optical, and edge-reactivity properties of semiconducting and metallic WS2 nanoribbons

First-principles density functional theory calculations are performed in one-dimensional single-layer WS2 nanoribbons with zigzag- and armchair-edges. Magnetic ordering, optical response, and chemical reactivity are investigated. Our results demonstrated that WS2 zigzag nanoribbons exhibit a ferromagnetic-metallic behavior that is attributed to the edges; the resulting magnetic moments are mainly localized in S and W edge atoms. Furthermore, the magnetic ordering along the edges depends on the zigzag nanoribbon’s width. Armchair nanoribbons exhibit semiconducting behavior. Optical response results demonstrated that there exists a strong optical polarization anisotropy enhancing a well defined absorption intensity peak, with polarization along the nanoribbons axis. Regarding chemical reactivity, ribbons are exposed to water (H2O), thiophene (C4H4S), and carbon monoxide (CO) molecules. Results reveal that H2O can be covalently joined to the edges via the W-atoms in the ribbons with zigzag-edges, whereas in ribbons with armchair edges, H2O is dissociated in OH and H, and these species are joined to W and S atoms respectively. Results for thiophene on zigzag nanoribbons demonstrated that C4H4S molecules are absorbed by W-terminated edges, whereas in armchair ribbons, the C4H4S is linked to the edges by binding to the sulfur. Interestingly, CO molecules give rise to half-metallicity and surprising ferromagnetism in zigzag and armchair nanoribbons, respectively. The results discussed here could help to understand the physical and chemical properties of edges in transition metal dichalcogenides materials.