The impact of the edges and presence of dopants to the work function (WF) of graphene nanoribbons (GNR) and nanoflakes was studied by an ab initio approach. The strong dependence of the WF upon the GNR structure was found and a promising character for the field emission by the donor type impurities was observed. Basing on the predominant impact of the nanostructure edges to the emission properties, the small graphene flakes were investigated as a possible source for the electron emission. The obtained weak dependence of the low WF values of the graphene flakes on their size and shape allows to suggest that the pure carbon medium with high and uniform emission properties can be fabricated by today technology.
This work describes through semiclassical Boltzmann transport theory and simulation a novel nanostructured material design that can lead to unprecedentedly high thermoelectric power factors, with improvements of more than an order of magnitude compared to optimal bulk material power factors. The design is based on a specific grain/grain-boundary (potential well/barrier) engineering such that: i) carrier energy filtering is achieved using potential barriers, combined with ii) higher than usual doping operating conditions such that high carrier velocities and mean-free-paths are utilized, iii) m…
Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range - of over five orders of magnitude - from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon mat…
Hyperfine interactions, magnetic interactions between the spins of electrons and nuclei, in graphene and related carbon nanostructures are studied. By using a combination of accurate first principles calculations on graphene fragments and statistical analysis, I show that both isotropic and dipolar hyperfine interactions can be accurately described in terms of the local electron spin distribution and atomic structure. A complete set of parameters describing the hyperfine interactions of C-13 and other nuclear spins at substitution impurities and edge terminations is determined.
Carbon nanotube field-effect transistors (FETs) with passivated coaxial gate structures have been fabricated after growth of contacted suspended single wall nanotubes (SWNTs) and subsequent coating with gate dielectrics. Electron Fabry-Perot interferences are observed in the FETs indicating ballistic transport in the coated structures. Reliable production of high-performance SWNT FETs has been obtained by combining patterned growth of SWNT arrays with feed-back controlled electrical breakdown to select desired semiconducting SWNTs, making large-scale SWNT FET fabrication achievable. P-type and…
Single-walled carbon nanotubes are a promising material as quantum light sources at room temperature and as nanoscale light sources for integrated photonic circuits on silicon. Here we show that integration of dopant states in carbon nanotubes and silicon microcavities can provide bright and high-purity single photon emitters on silicon photonics platform at room temperature. We perform photoluminescence spectroscopy and observe enhancement of emission from the dopant states by a factor of $\sim$100, and cavity-enhanced radiative decay is confirmed using time-resolved measurements, where $\sim…
The interaction between hydrogen molecules and platinum (Pt)-decorated carbon nanotubes (CNTs) with boron (B)-, nitrogen (N)-dopants or sidewall vacancies is discussed from first-principle calculations. The adsorption patterns of hydrogen molecules on four types of Pt-decorated CNTs are investigated, and the partial density of states projected on the Pt atom is computed to reveal the response to the number of hydrogen molecules, dopants or vacancies. It is found that the B-, N-dopants or sidewall vacancies can adjust the binding energy between the hydrogen molecules and the Pt atom deposited o…
Grain boundaries are commonly observed in carbon nanostructures, but their influence on thermal and electric properties are still not completely understood. Using a combined approach of density functional tight-binding theory and non-equilibrium Green functions we investigate electron and phonon transport in carbon based systems. In this work, quantum transport and thermoelectric properties are summarized for graphene sheets, graphene nanoribbons and carbon nanotubes with a variety of grain boundary types in a wide temperature range. Motivated by previous findings that disorder scatters phonon…
Graphdiyne, atomically-thin 2D carbon nanostructure based on sp-sp2 hybridization, is an appealing system potentially showing outstanding mechanical and optoelectronic properties. Surface-catalyzed coupling of halogenated sp-carbon-based molecular precursors represents a promising bottom-up strategy to fabricate extended 2D carbon systems with engineered structure on metallic substrates. Here, we investigate the atomic-scale structure and electronic and vibrational properties of an extended graphdiyne-like sp-sp2 carbon nanonetwork grown on Au(111) by means of on-surface synthesis. The formati…
High-dose irradiation of nanostructures consisting of multiple graphene shells, such as spherical 'carbon onions' (CO) or cylindrical multi-walled carbon nanotubes (MWNT), induces shell shrinkage by bond reconstruction around irradiation-induced defects. This leads to build-up of internal stresses and to extreme pressures acting on encapsulated materials or on the carbon cores of the nanostructures. We formulate a model which relates the build-up of internal stresses to the point defect dynamics in graphene shells. Calculations are performed for the special case of irradiated CO. The results a…
Emergence of $π$-magnetism in open-shell nanographenes has been theoretically predicted decades ago but their experimental characterization was elusive due to the strong chemical reactivity that makes their synthesis and stabilization difficult. In recent years, on-surface synthesis under vacuum conditions has provided unprecedented opportunities for atomically precise engineering of nanographenes, which in combination with scanning probe techniques have led to a substantial progress in our capabilities to realize localized electron spin states and to control electron spin interactions at the …
Nonlinear electrical properties, such as negative differential resistance (NDR), are essential in numerous electrical circuits, including memristors. Several physical origins have been proposed to lead to the NDR phenomena in semiconductor devices in the last more than half a century. Here, we report NDR behavior formation in randomly oriented graphene-like nanostructures up to 37 K and high on-current density up to 10^5 A/cm^2. Our modeling of the current-voltage characteristics, including the self-heating effects, suggests that strong temperature dependence of the low-bias resistance is resp…
Based on the analysis of the data on the behavior of electric conductivity at the detonation of condensed high explosives (HEs) with the composition CHNO and the carbon mass fraction higher than 0.1, the conclusion was made of the presence of long carbon nanostructures. These structures penetrate all the space of reacting HE. The structures are formed already in the chemical peak region, and they evolve along the detonation wave.
The carbon nanostructures are perspective materials for the future applications. This has two reasons: first, the hexagonal atomic structure which enables a high molecular variability by placing different kinds of the defects and second, good electronic properties which can be modified for the purpose of the concrete applications with the help of the defects and of the chemical ingredients. A lot of kinds of the nanostructures was investigated. Here, the properties of less common forms will be examined - the graphitic nanocone and graphitic wormhole.
The construction of atomically-precise carbon nanostructures holds promise for developing novel materials for scientific study and nanotechnology applications. Here we show that graphene origami is an efficient way to convert graphene into atomically-precise, complex, and novel nanostructures. By scanning-tunneling-microscope manipulation at low temperature, we repeatedly fold and unfold graphene nanoislands (GNIs) along arbitrarily chosen direction. A bilayer graphene stack featuring a tunable twist angle and a tubular edge connection between the layers are formed. Folding single-crystal GNIs…
We report the first observation of trions (charged excitons), three-particle bound states consisting of one electron and two holes, in hole-doped carbon nanotubes at room temperature. When p-type dopants are added to carbon nanotube solutions, the photoluminescence and absorption peaks of the trions appear far below the E11 bright exciton peak, regardless of the dopant species. The unexpectedly large energy separation between the bright excitons and the trions is attributed to the strong electron-hole exchange interaction in carbon nanotubes.
In this paper we investigate from first principles the effect of the electron-phonon interaction in two paradigmatic nanostructures: trans-polyacetylene and polyethylene. We found that the strong electron-phonon interaction leads to the appearance of complex structures in the frequency dependent electronic self-energy. Those structures rule out any quasi-particle picture, and make the adiabatic and static approximations commonly used in the well-established Heine Allen Cardona (HAC) approach inadequate. We propose, instead, a fully ab-initio dynamical formulation of the problem within the Many…
In this work we report new silicon and germanium tubular nanostructures with no corresponding stable carbon analogues. The electronic and mechanical properties of these new tubes were investigated through ab initio methods. Our results show that the structures have lower energy than their corresponding nanoribbon structures and are stable up to high temperatures (500 and 1000 K, for silicon and germanium tubes, respectively). Both tubes are semiconducting with small indirect band gaps, which can be significantly altered by both compressive and tensile strains. Large bandgap variations of almos…
We present a simple way to describe the lowest unoccupied diffuse states in carbon nanostructures in density functional theory (DFT) calculations using a minimal LCAO (linear combination of atomic orbitals) basis set. By comparing plane wave basis calculations, we show how these states can be captured by adding long-range orbitals to the standard LCAO basis sets for the extreme cases of planar <it>sp2</it> (graphene) and curved carbon (C60). In particular, using Bessel functions with a long range as additional basis functions retain a minimal basis size. This provides a smaller and simpler ato…
Based on Monte Carlo (MC) simulations of the interaction of energetic noble gas ions with carbon nanostructures, we have derived the ion-deposited energy formulas and their applications for the above interaction. We also have studied the nuclear point mass effects i.e. the well-known mass ratio effects, and the nuclear point charge effects on the ion-deposited energy then the damage regularities. In particular, we, for first time, find a straight line of the penetrating point threshold energies for energetic noble gas ions. Near this straight line, the nuclear point charge effects dominate the…
Understanding the magnetic properties of graphenic nanostructures is instrumental in future spintronics applications. These magnetic properties are known to depend crucially on the presence of defects. Here we review our recent theoretical studies using density functional calculations on two types of defects in carbon nanostructures: Substitutional doping with transition metals, and sp$^3$-type defects created by covalent functionalization with organic and inorganic molecules. We focus on such defects because they can be used to create and control magnetism in graphene-based materials. Our mai…
We report the observation of Peierls-type metal-insulator transition in carbon nanostructures formed by chemical vapor deposition inside the pore network of the ZSM-5 zeolite. The Raman spectrum of this nanocarbon@ZSM-5 indicates a clear signature of the radial breathing mode (RBM) for (3,0) carbon nanotubes that can constitute the carbon network segments. Electrical transport measurements on multiple few-micron-sized nanocarbon@ZSM-5 crystals showed metallic temperature of resistance dependence down to 30 K, at which point the resistance exhibited a sharp upturn that is accompanied by the ope…
The study of thermal transport in low-dimensional materials has attracted a lot of attention recently after discovery of high thermal conductivity of graphene. Here we study numerically phonon transport in low-dimensional carbon structures being interested in the hydrodynamic regime revealed through the observation of second sound. We demonstrate that correct numerical modeling of such two-dimensional systems requires semi-classical molecular dynamics simulations of temperature waves that take into account quantum statistics of thermalized phonons. We reveal that second sound can be attributed…
The absence of backscattering in metallic nanotubes as well as perfect Klein tunneling in potential barriers in graphene are the prominent electronic characteristics of carbon nanostructures. We show that the phenomena can be explained by a peculiar supersymmetry generated by a first order Hamiltonian and zero order supercharge operators. Like the supersymmetry associated with second order reflectionless finite-gap systems, it relates here the low-energy behavior of the charge carriers with the free particle dynamics.
A new multiscale modeling approach to unravel the influence of interlayer sp3 bonds on the nonlinear large-deformation and fracture behaviors of 2D carbon nanostructures under tension
We investigate the time-dependent electronic transport in single-walled carbon nanotubes (SWCNTs) functionalized with Au clusters on CO gas exposure. Using a tight-binding Hamiltonian and the nonequilibrium Green's function (NEGF) formalism the time-dependent zeroth and first order contributions to the current are calculated. The zeroth order contribution is identified as the time-dependent Landauer formula in terms of the slow time variable, whereas the first order contribution is found to be small. The Green's function for the SWCNT is derived using the equation of motion and Dyson equation …
We demonstrate that 60 keV electron irradiation drives the diffusion of threefold coordinated Si dopants in graphene by one lattice site at a time. First principles simulations reveal that each step is caused by an electron impact on a C atom next to the dopant. Although the atomic motion happens below our experimental time resolution, stochastic analysis of 38 such lattice jumps reveals a probability for their occurrence in a good agreement with the simulations. Conversions from three- to fourfold coordinated dopant structures and the subsequent reverse process are significantly less likely t…
Prompted by recent reports on $\sqrt{3} \times \sqrt{3}$ graphene superlattices with intrinsic inter-valley interactions, we perform first-principles calculations to investigate the electronic properties of periodically nitrogen-doped graphene and carbon nanotube nanostructures. In these structures, nitrogen atoms substitute one-sixth of the carbon atoms in the pristine hexagonal lattices with exact periodicity to form perfect $\sqrt{3} \times \sqrt{3}$ superlattices of graphene and carbon nanotubes. Multiple nanostructures of $\sqrt{3} \times \sqrt{3}$ graphene ribbons and carbon nanotubes ar…
Tomonaga-Luttinger (T-L) theory predicts collective plasmon resonances in 1-D nanostructure conductors of finite length, that vary roughly in inverse proportion to the length of the structure. In-depth quantitative understanding of such resonances which have not been clearly identified in experiments so far, would be invaluable for future generations of nano-photonic and nano-electronic devices that employ 1-D conductors. Here we provide evidence of the plasmon resonances in a number of representative 1-D finite carbon-based nanostructures using first-principle computational electronic spectro…
Single dopants in semiconductor nanostructures have been studied in great details recently as they are good candidates for quantum bits, provided they are coupled to a detector. Here we report coupling of a single As donor atom to a single-electron transistor (SET) in a silicon nanowire field-effect transistor. Both capacitive and tunnel coupling are achieved, the latter resulting in a dramatic increase of the conductance through the SET, by up to one order of magnitude. The experimental results are well explained by the rate equations theory developed in parallel with the experiment.
The main research efforts are aimed at finding inexpensive materials that can be converted into nanostructured carbon-containing materials, such as activated carbon and graphene. Rice husks are one such material, especially in developing countries, where more than 95% of Rice husks are produced worldwide. Although numerous studies have been conducted on the production of activated carbon and graphene structures from Rice husk, the existing scientific information is still widely scattered in the literature. Therefore, this review article provides extensive information on made by various researc…
We report our recent numerical study on the effects of dephasing on a perfectly conducting channel (PCC), its presence believed to be dominant in the transport characteristics of a zigzag graphene nanoribbons (GNR) and of a metallic carbon nanotubes (CNT). Our data confirms an earlier prediction that a PCC in GNR exhibits a peculiar robustness against dephasing, in contrast to that of the CNT. By studying the behavior of the conductance as a function of the system's length we show that dephasing destroys the PCC in CNT, whereas it stabilizes the PCC in GNR. Such opposing responses of the PCC a…
In the majority of cases nanostructures prepared by focused electron beam induced deposition (FEBID) employing an organometallic precursor contain predominantly carbon-based ligand dissociation products. This is unfortunate with regard to using this high-resolution direct-write approach for the preparation of nanostructures for various fields, such as mesoscopic physics, micromagnetism, electronic correlations, spin-dependent transport and numerous applications. Here we present an in-situ cleaning approach to obtain pure Co-FEBID nanostructures. The purification procedure lies in the exposure …
Nonreciprocal plasmons in one-dimensional carbon nanostructures
Max-Born-Institut（马克斯·玻恩研究所）；Center for Nanophotonics, NWO Institute AMOLF（纳米光子学中心，NWO AMOLF研究所）；ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology（ICFO-光子科学研究所，巴塞罗那科学技术研究所）；ICREA-Institució Catalana de Recerca i Estudis Avançats（ICREA-加泰罗尼亚研究高级学院）；POLIMA—Center for Polariton-driven Light–Matter Interactions, University of Southern Denmark（POLIMA-极化激元驱动光物质相互作用中心，南丹麦大学）；Danish Institute for Advanced Study, University of Southern Denmark（丹麦高等研究院，南丹麦大学）
To understand the interaction between nitrogen dopants and native point defects in graphene, we have studied the energetic stability of N-doped graphene with vacancies and Stone-Wales (SW) defect by performing the density functional theory calculations. Our results show that N substitution energetically prefers to occur at the carbon atoms near the defects, especially for those sites with larger bond shortening, indicating that the defect-induced strain plays an important role in the stability of N dopants in defective graphene. In the presence of monovacancy, the most stable position for N do…
Dopants positioned near edges in nanostructured graphene behave differently from bulk dopants. Most notable, the amount of charge transferred to delocalized states (i.e. doping efficiency) depends on position as well as edge chirality. We apply a self-consistent tight-binding model to analyze this problem focusing on substitutional nitrogen and boron doping. Using a Greens function technique, very large structures can be studied and artificial interactions between dopants in periodically repeated simulations cells are avoided. We find pronounced signatures of edges in the local impurity densit…
We introduce a new simplified method for computing the electron field emission current in short carbon nanotubes using ab-initio computation in periodic simulation cells. We computed the evolution of the wave functions using Time-Dependent Density Functional Theory, where we have utilized the Crank-Nicholson propagator. We found that in pristine carbon nanotubes, the emitted charge tends to emerge mostly from electrons that are concentrated at the nanotube tip region. The charge beam concentrates into specific channel structures, showing the utility of carbon nanotubes in precision emission ap…
We show that the energy differences between the lowest optical singlet exciton and the lowest triplet exciton in semiconducting single-walled carbon nanotubes with diameter $\sim 1$ nm and graphene nanoribbons with widths $\sim 2$ nm are an order of magnitude smaller than in the $π$-conjugated polymer poly(para-phenylenevinylene). Our calculated energy gaps between the singlet and triplet excitons are in excellent agreement with the measured values in three different nanotubes with diameters close to 1 nm. The spatial extent of the triplet exciton is nearly the same as that of the singlet exci…
Nanoscrolls (papyrus-like nanostructures) are very attractive structures for a variety of applications, due to their tunable diameter values and large accessible surface area. They have been successfully synthesized from different materials. In this work we have investigated, through fully atomistic molecular dynamics simulations, the dynamics of scroll formation for a series of graphenelike carbon nitride (CN) twodimensional systems: gCN, triazinebased gC3N4, and heptazinebased gC3N4. Our results show that stable nanoscrolls can be formed for all of these structures. Possible synthetic routes…
Carbon fiber and graphene-based nanostructures such as carbon nanotubes (CNTs) and defective structures have extraordinary potential as strong and lightweight materials. A longstanding bottleneck has been lack of understanding and implementation of atomic-scale engineering to harness the theoretical limits of modulus and tensile strength, of which only a fraction is routinely reached today. Here we demonstrate accurate and fast predictions of mechanical properties for CNTs and arbitrary 3D graphitic assemblies based on a training set of over 1000 stress-strain curves from cutting-edge reactive…
A first-principles approach is introduced to calculate electron field emission characteristics of nanostructures, based on the nonequilibrium Green function technique combined with the density functional theory. The method employs atomic-like basis orbitals with large confinement radii and lithium anode to describe the electron density in the vacuum between the nanostructure tip and the anode, so takes the presence of emitted current into account. The simulation results on a capped single-walled carbon nanotube reproduce the experimental trend closely, in particular, the current saturation and…
This work revisits the physics giving rise to the carbon nanotubes phonon bands in the mid- infrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric lineshape and that their effective cross-section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that only the dopant-induced intraband continuum couples to the phonon modes and that defects induced in the sidewall increase the r…
In the last three decades or so, we have witnessed an extraordinary progress in the research and technology of carbon-based nanomaterials. Among the peculiar highlights are the discoveries of fullerene, the carbon nanotubes and the magnificent simple scotch tape exfoliated graphene. The unique photophysical properties of these different allotropic forms of the nanocarbon have opened up vast application possibilities in many fields of science and technology, with particular emphasis on optoelectronics and photonics. A prerequisite for many of these applications is a thorough understanding of th…
A powerful technique is introduced for simulating mechanical and electromechanical properties of one-dimensional nanostructures under arbitrary combinations of bending, twisting, and stretching. The technique is based on a novel control of periodic symmetry, which eliminates artifacts due to deformation constraints and quantum finite-size effects, and allows transparent electronic structure analysis. Via density-functional tight-binding implementation, the technique demonstrates its utility by predicting novel electromechanical properties in carbon nanotubes and abrupt behavior in the structur…
Experimental results from irradiated-carbon nanostructures can be partially explained by selective applications of classical damage theories and ad-hoc thermal models by treating the binary atomic collision cascades and multi-atomic thermal spikes as energy-dissipating mechanisms. An information-theoretic model is developed by treating the irradiated single-walled carbon nanotubes and C60 as entropy-generating dissipative structures. The model is based on evaluating the experimental probability distribution functions of the sputtered constituents and components from the irradiated carbon nanos…
We report on the transport properties of novel carbon nanostructures made of partially unzipped carbon nanotubes, which can be regarded as a seamless junction of a tube and a nanoribbon. We find that graphene nanoribbons act at certain energy ranges as a perfect valley filters for carbon nanotubes, with the maximum possible conductance. Our results show that a partially unzipped carbon nanotube is a magnetoresistive device, with a very large value of the magnetoresistance. We explore the properties of several structures combining nanotubes and graphene nanoribbons, demonstrating that they beha…
We report on the first direct observation of a transition from a Tomonaga-Luttinger liquid to a Fermi liquid behavior in potassium intercalated mats of single wall carbon nanotubes (SWCNT). Using high resolution photoemission spectroscopy an analysis of the spectral shape near the Fermi level reveals a Tomonaga-Luttinger liquid power law scaling in the density of states for the pristine sample and for low dopant concentration. As soon as the doping is high enough to fill bands of the semiconducting tubes a distinct transition to a bundle of only metallic SWCNT with a scaling behavior of a norm…
Based on first-principles approaches, we study the ballistic phonon transport properties of finite monatomic carbon chains stretched between graphene nanoribbons, an $sp$-$sp^2$ hybrid carbon nanostructure that has recently seen significant experimental advances in its synthesis. We find that the lattice thermal conductance anomalously increases with tensile strain for the even-numbered carbon chains that adopt the alternating bond-length polyyne configuration. On the other hand, in the odd-numbered carbon chain cases, which assume the equal bond-length cumulene configuration, phonon conductan…
The magnetic properties of carbon nanotube encapsulated nickel nanowires (C.E. nanowires of diameter ~ 10 nm), and its comparison to other forms of Ni are carried out in this work. The saturation magnetization (M_s) and coercivity (H_c) for C.E. nanowires are 1.0 emu/g and 230 Oe. The temperature dependence of coercivity follows T^0.77 dependence indicating a superparamagnetic behavior. The field-cooled and zero-field-cooled plots indicate that the blocking temperature (T_B) ~ 300 K. These altered magnetic properties of C.E. nanowires are mainly due to the nanoscale confinement effect from car…
Learning and Controlling Silicon Dopant Transitions in Graphene using Scanning Transmission Electron Microscopy
Université de Montréal（蒙特利尔大学）；Mila（米拉研究所）；McGill University（麦吉尔大学）；Reliant AI（Reliant人工智能公司）；Google DeepMind（谷歌DeepMind）；University of Tennessee, Knoxville（田纳西大学诺克斯维尔分校）；Oak Ridge National Laboratory（橡树岭国家实验室）
We investigate spin properties of a Fe2+ dopant, known for having single nondegenerate ground state in bulk host semiconductor. Due to zero magnetic moment such a ground state is of little use for spintronics and solotronics. We show that this well-established picture of Fe2+ spin configuration can be contradicted by subjecting the Fe2+ ion to sufficiently high strain, e.g., resulting from lattice mismatched epitaxial heterostructures. Our analysis reveals that high strain induces qualitative change in the ion energy spectrum and results in doubly degenerate ground state with spin projection S…
We describe the electro-thermal transport in metallic carbon nanotubes (m-CNTs) by a semi-classical approach that takes into account the high-field dynamical interdependence between charge carrier and phonon populations. Our model is based on the self-consistent solution of the Boltzmann transport equation and the heat equation mediated by a phonon rate equation that accounts for the onset of non-equilibrium (optical) phonons in the high-field regime. Given the metallic nature of the nanostructures, a key ingredient of the model is the assumption of local thermalization of charge carriers. Our…
