One-dimensional Graphene Research Articles

Sequential BN-doping induced tuning of electronic properties in zigzag-edged graphene nanoribbons: a computational approach.

We employed first-principles methods to elaborate doping induced electronic and magnetic perturbations in one-dimensional zigzag graphene nanoribbon (ZGNR) superlattices. Consequently, the incorporation of alternate boron and nitrogen (hole–electron) centers into the hexagonal network instituted substantial modulations to electronic and magnetic properties of ZGNR. Our theoretical analysis manifested some controlled changes to electronic and magnetic properties of the ZGNR by tuning the positions (array) of impurity centers in the carbon network. Subsequent DFT based calculations also suggested that the site-specific alternate electron–hole (B/N) doping could regulate the band-gaps of the superlattices within a broad range of energy. The consequence of variation in the width of ZGNR in the electronic environment of the system was also tested. The systematic analysis of various parameters such as the structural orientations, spin-arrangements, the density of states (DOS), band structures, and local density of states envisioned a basis for the band-gap engineering in ZGNR and attributed to its feasible applications in next generation electronic device fabrication.

Rectifying performances of oligo phenylene ethynylene molecular devices based on graphene electrodes

With the experimental advances in microscale fabrication technology, the designing of functional devices by using single molecules has become one of the most promising methods for the next generation of electronic devices. Molecular rectifier, as a basic component almost for any electronic device, has become a research hotspot in molecular electronics. Recently, one-dimensional graphene nanoribbons (GNRs) which cut off from the novel two-dimensional material-graphene were used as the electrodes for several molecular devices due to their unique electronic structures and transport characteristics. The GNRs have less serious contact problems than metallic electrode materials like gold. In this paper, we investigate the rectifying performances of oligo phenylene ethynylene molecular devices based on graphene electrodes by using the density-functional theory and the non-equilibrium Green's function method. The effect of functional group on the rectifying performances of molecular device is discussed. The results show that the functional group plays a significant role in determining the rectifying performances of oligo phenylene ethynylene molecular device. The rectifying ratio can be effectively tuned by the functional group: adding the donor group (NH2) can lead to the positive rectifying phenomenon, adding the acceptor group (NO2) can trigger the negative rectifying phenomenon, and simultaneously adding NH2 and NO2 groups can bring about an alternate phenomenon between positive and reverse rectifying . The physical mechanism of the rectifying behavior is explained based on the transmission spectra and molecular projected self-consistent Hamiltonian. The transmission spectra of four models (M1-M4) bias voltages in range from-1.0 V to 1.0 V are given. The main transmission peak of M1 for positive bias is similar to that for negative bias, resulting in a weak rectification ratio. However, for M2 and M3, the main transmission peaks for positive and negative bias are significantly different from each other, which shows obviously a rectifying behavior. For M4, the main transmission peak is higher for the bias of (0.44-0.83 V) and also for the bias (0.95-1.00 V), showing an alternate phenomenon between positive and reverse rectifying. The maximum rectification ratio reaches 2.71 by adding an acceptor group (NO2), which suggests that this system has attractive potential applications in future molecular circuit.

The Oxygen Reduction Reaction on Graphene from Quantum Mechanics: Comparing Armchair and Zigzag Carbon Edges

Using density functional theory (PBE-D2 flavor), we report the mechanism for the oxygen reduction reaction (ORR) on graphene sheets. We find that ORR starts with OO chemisorbing onto the carbon edges, rather than the basal plane face, which is not energetically favorable. The carbon edges were described as one-dimensional periodic graphene ribbons with both armchair and zigzag edges. We calculated the binding energies of the ORR products (OO, OOH, O, OH, HOH, HOOH) for the zigzag and armchair edges, examining both the Langmuir–Hinshelwood (LH) and Eley–Rideal (ER), to understand how OO is reduced. For the armchair edge, we calculate an onset potential of 0.55 V vs reversible hydrogen electrode (RHE), which corresponds to −0.22 V at pH 13 in agreement with experiments. We find that the rate-determining step (RDS) to form peroxide (a 2e– process) is hydrogenation of adsorbed OO with a barrier of 0.92 eV. The process to make water (a 4e– process) was found to be unfavorable at the onset potential but becomes...

Plasmonic thermal transport in graphene nanodisk waveguides

The thermal radiation properties of guided surface plasmons in one-dimensional co-planar graphene nanodisk arrays are predicted using a semi-analytical electrostatic model. The plasmonic band structure contains nonlocalized dispersion bands that are well-described by the electrostatic model for disk diameters smaller than 200 nm. A nondimensional model is proposed that enables systematic analysis of the waveguiding properties based on scaling laws. The thermal transport is dominated by the lowest-order radial modes and can be controlled by tuning the disk size, the substrate optical properties, and graphene's doping concentration and electron mobility. The maximum predicted thermal conductivity and thermal diffusivity are 4.$5{\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and $1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{4pt}{0ex}}{\mathrm{m}}^{2}$/s, orders of magnitude larger than predictions of thermal transport by guided surface plasmon- or phonon-polaritons in other materials. The results suggest that graphene surface plasmons, which can be thermally-activated at room temperature, are a suitable platform for tunable and fast thermal transport, with potential application as photon-based thermotronic interconnects.

(Invited) Graphene Nanostructure By Molten Salt Process for Supercapacitor Applications

Graphene has a two-dimensional honeycomb structure consisting of a single layer of carbon atoms with a sp2-bonding configuration and has recently attracted significant attention owing to its unique properties, which include an exceptionally high specific surface area and high electrical and thermal conductivities as well as mechanical and chemical stability. However, graphene sheets exhibit an extreme tendency to agglomerate or restack. This leads to a surface that is electrochemically less effective, low electrical conductivity, and an interlayer spacing that hinders access to electrolyte ions, thus limiting the use of the sheets in supercapacitor applications. Introducing spacer materials such as metal oxide, carbonaceous between the graphene sheets is a viable strategy for preventing the sheets from agglomerating. In this study, we report the scalable fabrication of a high-quality hierarchical interconnected carbon nanostructure, combining two-dimensional graphene nanosheets and one-dimensional graphene nanoscrolls from graphite by a simple high temperature molten salt method. The electrode using the prepared material exhibited high reversible specific capacitance, excellent rate capability, and good cyclability because of their unique interconnected networks of carbon nanostructures with high electrochemically active surface area and high electrical conductivity. More details on the synthetic procedure, electrochemical and structural properties will be presented at the meeting.

One-dimensional multiband terahertz graphene photonic crystal filters

Properties of one-dimensional graphene photonic crystals with dual-layer defects are studied. Results show that two defect modes appear within the gaps, and the defect modes shift to the lower frequencies with the chemical potential increasing, the physical mechanism are also given based on the relative dielectric constant of the graphene. It is also found that the frequency, magnitude, and numbers of the defect modes can vary with the symmetrical changes of the dual-defect layers. For oblique incidence, the defect modes of the TE polarization follow a similar trend with the TM polarization, and all the defect modes shift to the higher frequencies and disappear while new defect modes appear at the larger incident angles. These properties of graphene photonic crystals with dual-layer defects have potential applications in tunable terahertz narrow multiband filters.

Van-der-Waals-gap tunneling spectroscopy for single-wall carbon nanotubes

As a consequence of their unique electronic band structures, low-dimensional materials such as one-dimensional (1D) single-wall carbon nanotubes (SWCNTs), 2D graphene and various 2D transition-metal dichalcogenides have exhibited intriguing electrical transport properties when incorporated into field-effect transistors. Meanwhile, the van-der-Waals (vdW) interfaces between top-contacted metals and low-dimensional materials have become a challenging issue for future high-performance electronics. Here, we report a new aspect of vdW interface that offers vdW-gap tunneling spectroscopy by adopting indium (In) as a top-contacted metal on SWCNTs without an artificial insulating tunnel barrier. We show that multiple differential conductance peaks for varying bias voltages correspond to the van Hove singularities existing in the electronic density of states of SWCNTs. Our first-principles calculations reveal that In forms a physisorption interface with a considerable vdW gap, which causes little disruption to the density of states of the SWCNTs near the metal interface and which thus allows vdW-gap tunneling spectroscopy.

Modeling the excitation of graphene plasmons in periodic grids of graphene ribbons: An analytical approach

We study electromagnetic scattering and subsequent plasmonic excitations in periodic grids of graphene ribbons. To address this problem, we develop an analytical method to describe the plasmon-assisted absorption of electromagnetic radiation by a periodic structure of graphene ribbons forming a diffraction grating for THz and mid-IR light. The major advantage of this method lies in its ability to accurately describe the excitation of graphene surface plasmons (GSPs) in one-dimensional (1D) graphene gratings without the use of both time-consuming, and computationally-demanding full-wave numerical simulations. We thus provide analytical expressions for the reflectance, transmittance and plasmon-enhanced absorbance spectra, which can be readily evaluated in any personal laptop with little-to-none programming. We also introduce a semi-analytical method to benchmark our previous results and further compare the theoretical data with spectra taken from experiments, to which we observe a very good agreement. These theoretical tools may therefore be applied to design new experiments and cutting-edge nanophotonic devices based on graphene plasmonics.

Interconnected Carbon Nanostructures for High Performance Supercapacitor Applications

Graphene has a two-dimensional honeycomb structure consisting of a single layer of carbon atoms with a sp2-bonding configuration and has recently attracted significant attention owing to its unique properties, which include an exceptionally high specific surface area and high electrical and thermal conductivities as well as mechanical and chemical stability. However, graphene sheets exhibit an extreme tendency to agglomerate or restack. This leads to a surface that is electrochemically less effective, low electrical conductivity, and an interlayer spacing that hinders access to electrolyte ions, thus limiting the use of the sheets in supercapacitor applications. Introducing carbonaceous materials such as metal oxide, carbon nanotubes (CNTs) between the graphene sheets is a viable strategy for preventing the sheets from agglomerating.In this study, we report the scalable fabrication of a high-quality hierarchical interconnected carbon nanostructure, combining two-dimensional graphene nanosheets and one-dimensional graphene nanoscrolls from graphite by a simple hightemperature molten salt method. The electrode using the prepared material exhibited high reversible specific capacitance, excellent rate capability, and good cyclability because of their unique interconnected networks of carbon nanostructures with high electrochemically active surface area and high electrical conductivity. More details on the synthetic procedure, electrochemical and structural properties will be presented at the meeting.

Erratum to: Analytical investigation of carrier concentration effect on one-dimensional graphene nanoscroll

Erratum to: Analytical investigation of carrier concentration effect on one-dimensional graphene nanoscroll

Quasi-Dirac points in one-dimensional graphene superlattices

Quasi-Dirac points (QDPs) with energy different from the traditional Dirac points (TDPs) have been found for the first time in one-dimensional graphene superlattices. The angular-averaged conductance reaches a minimum value at the QDPs, at which the Fano factor approaches 1/3. Surprisingly, the minimum conductance at these QDPs may be lower than that at the TDPs under certain conditions. This is remarkable as the minimum conductance attainable in graphene superlattices was believed to appear at TDPs.

Phonon transport effects in one-dimensional width-modulated graphene nanoribbons

We investigate the thermal conductance of one-dimensional periodic width-modulated graphene nanoribbons using lattice dynamics for the phonon spectrum and the Landauer formalism for phonon transport. We conduct a full investigation considering all relevant geometrical features, i.e., the various lengths and widths of the narrow and wide regions that form the channel. In all cases that we examine, we find that width-modulation suppresses the thermal conductance at values even up to ∼70% below those of the corresponding uniform narrow nanoribbon. We show that this can be explained by the fact that the phonon spectrum of the width-modulated channels acquires less dispersive bands with lower group velocities and several narrow bandgaps, which reduce the phonon transmission function significantly. The largest degradation in thermal conductance is determined by the geometry of the narrow regions. The geometry of the wider regions also influences thermal conductance, although modestly. Our results add to the ongoing efforts in understanding the details of phonon transport at the nanoscale, and our conclusions are generic and could also apply to other one-dimensional channel materials.

(Invited) Direct Template-Less Synthesis of Oriented Sub-10 Nm Semiconducting Graphene Nanoribbons with Smooth Armchair Edges on Ge(001)

The rational synthesis of graphene nanoribbons that are semiconducting with sub-10 nm width, controlled crystallographic orientation, and well-defined edges on non-metallic substrates has been a significant challenge. The growth of nanoribbons on metal substrates precludes their direct use in semiconducting electronics due to the conductive substrate, and the direct synthesis of nanoribbons in solution is complicated by challenges of their post-synthetic assembly. In this talk, we demonstrate the direct, scalable synthesis of graphene nanoribbons via chemical vapor deposition (CVD) on Ge(001).[1] Low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) show that the ribbons are self-orienting ±2.9° from the Ge[110] directions and are self-defining. The nanoribbons have predominately smooth armchair edges that give rise to electron interference patterns indicative of high quality edges. By tuning the precursor flux, growth time, and growth temperature, the ribbon anisotropy and growth kinetics can be tailored to yield ribbons with controlled width < 10 nm and aspect ratio > 60. Compared to previous low aspect ratio crystals of graphene obtained on Ge, we find that in order to realize high aspect ratio nanoribbons, it is critical to operate in a regime in which the growth rate is especially slow, on the order of 5 nm/h in the width direction. This work is important because unlike continuous two-dimensional graphene, which is semimetallic, one-dimensional graphene nanoribbons can be semiconducting, allowing for the substantial modulation of their conductance and enabling their application in semiconductor logic, optoelectronics, photonics, and sensors. Moreover, the direct synthesis of ultranarrow and smooth graphene nanoribbons on Ge demonstrated here provides a scalable, high throughput pathway for integrating semiconducting graphene directly on conventional large-area semiconductor wafer platforms that are compatible with planar processing. [1] Jacobberger RM, Kiraly B, Fortin-Deschenes M, Levesque PL, McElhinny KM, Brady GJ, Rojas Delgado R, Singha Roy S, Mannix A, Lagally MG, Evans PG, Desjardins P, Martel R, Hersam MC, Guisinger NP, Arnold MS, Direct Oriented Growth of Armchair Graphene Nanoribbons on Germanium, NATURE COMMUNICATIONS, 6, 8006 (2015)

Two-color light-emitting diodes with polarization-sensitive high extraction efficiency based on graphene

In the present study, graphene photonic crystals are employed to enhance the light extraction efficiency (LEE) of two-color, red and blue, light-emitting diode (LED). The transmission characteristics of one-dimensional (1D) Fibonacci graphene photonic crystal LED (FGPC-LED) are investigated by using the transfer matrix method and the scaling study is presented. We analyzed the influence of period, thickness, and permittivity in the structure to enhance the LEE. The transmission spectrum of 1D FGPC has been optimized in detail. In addition, the effects of the angle of incidence and the state of polarization are investigated. As the main result, we found the optimum values of relevant parameters to enhance the extraction of red and blue light from an LED as well as provide perfect omnidirectional and high peak transmission filters for the TE and TM modes.

Investigation and comparison of bare-dihydrogenated junction rectifiers of graphene and silicene nanoribbons

Although silicon and similar bulk materials are widely used in today's integrated circuits, the transition to lower dimensional structures such as two-dimensional graphene, one-dimensional graphene nanoribbons (GNRs) and silicene nanoribbons (SiNRs) seems inescapable due to the increment of inelastic scattering and related performance degrading effects in bulk circuit components. In this context, GNRs and SiNRs provide advantages such as low area consumption and the adjustment of their electronic behaviours by edge states and widths. On the other hand, rectifiers together with their static and dynamic behaviours constitute the basics of the electronics technology. In this paper, rectifier characteristics of bare-dihydrogenated junctions of GNR and SiNR structures are investigated and compared utilizing first-principles approach. Density functional theory in combination with non-equilibrium Green's function formalism are used to obtain current---voltage characteristics, transmission eigenstates and dynamic electron densities of the considered GNR and SiNR rectifiers and then these quantities are processed to obtain the dynamical resistance, junction capacitance and time constants of these structures, which is essential for graphene and silicene based electronics design. The paper is concluded with the discussion of the large-signal and small-signal performances of the considered GNR and SiNR rectifiers for commercial integrated circuit applications.

Analytical investigation of carrier concentration effect on one-dimensional graphene nanoscroll

In recent years, carbon nanoscrolls (CNSs) that have a tubular structure similar to that of the open multi-wall carbon nanotube have received significant attention. Graphene nanoscrolls (GNSs) have also attracted significant attention, owing to their unique properties. These nanoscrolls are obtained by systematically winding graphene sheets into a spiral, and are expected to have high mechanical strength, high carrier mobility, and high thermal conductivity. In the present work, an analytical model was used to determine the band energy of (16,0) GNS, and the normalized Fermi energies in the degenerate and non-degenerate regimes are modeled. The model revealed that degenerate and non-degenerate approximations can be used for normalized Fermi energies higher than 3 and lower than −3, respectively.

In situ growth of porphyrinic metal–organic framework nanocrystals on graphene nanoribbons for the electrocatalytic oxidation of nitrite

A nanocomposite of MOF-525 nanocrystals interconnected by numerous one-dimensional graphene nanoribbons serves as a promising electrocatalyst for nitrite oxidation.

Transmission property of one-dimensional multilayer graphene–dielectric stack

The transmission property and field distribution of one-dimensional multilayer containing graphene sheets separated by dielectric slabs are theoretically studied in terahertz. It is shown that the multilayer graphene–dielectric stack supports a series of passband and stopband whose number increases with the dielectric thickness. The field distributions show that the transmission resonances in the passband are attributed to Fabry–Perot resonances in the dielectric layer and the node numbers that appear in the field distribution in each graphene–dielectric–graphene cavity can be quantitatively given. It is also noticed that these resonances lie within a certain characteristic frequency bands which are independent of the number of unit cells making up the structure. The low frequency edge of the passband is highly tunable by the Fermi energy and the layer number of graphene sheets, while the high frequency edge is just determined by the dielectric slab. When an impurity is introduced, a defect mode can appear inside the stopband and it can be adjusted by Fermi energy of graphene controlled via a gate voltage.

Phonon-limited carrier mobility and resistivity from carbon nanotubes to graphene

Under which conditions do the electrical transport properties of one-dimensional (1D) carbon nanotubes (CNTs) and 2D graphene become equivalent? We have performed atomistic calculations of the phonon-limited electrical mobility in graphene and in a wide range of CNTs of different types to address this issue. The theoretical study is based on a tight-binding method and a force-constant model from which all possible electron-phonon couplings are computed. The electrical resistivity of graphene is found in very good agreement with experiments performed at high carrier density. A common methodology is applied to study the transition from one to two dimensions by considering CNTs with diameter up to 16 nm. It is found that the mobility in CNTs of increasing diameter converges to the same value, i.e., the mobility in graphene. This convergence is much faster at high temperature and high carrier density. For small-diameter CNTs, the mobility depends strongly on chirality, diameter, and the existence of a band gap.

Velocity renormalization and Dirac cone multiplication in graphene superlattices with various barrier-edge geometries

The electronic properties of one-dimensional graphene superlattices strongly depend on the atomic size and orientation of the 1D external periodic potential. Using a tight-binding approach, we show that the armchair and zigzag directions in these superlattices have a different impact on the renormalization of the anisotropic velocity of the charge carriers. For symmetric potential barriers, the velocity perpendicular to the barrier is modified for the armchair direction while remaining unchanged in the zigzag case. For asymmetric barriers, the initial symmetry between the forward and backward momentum with respect to the Dirac cone symmetry is broken for the velocity perpendicular (armchair case) or parallel (zigzag case) to the barriers. At last, Dirac cone multiplication at the charge neutrality point occurs only for the zigzag geometry. In contrast, band gaps appear in the electronic structure of the graphene superlattice with barrier in the armchair direction.