V.A. Tatarenko

Effects of nitrogen-doping configurations with vacancies on conductivity in graphene

Abstract We investigate electronic transport in the nitrogen-doped graphene containing different configurations of point defects: singly or doubly substituting N atoms and nitrogen–vacancy complexes. The results are numerically obtained using the quantum-mechanical Kubo–Greenwood formalism. Nitrogen substitutions in graphene lattice are modelled by the scattering potential adopted from the independent self-consistent ab initio calculations. Variety of quantitative and qualitative changes in the conductivity behaviour are revealed for both graphite- and pyridine-type N defects in graphene. For the most common graphite-like configurations in the N-doped graphene, we also consider cases of correlation and ordering of substitutional N atoms. The conductivity is found to be enhanced up to several times for correlated N dopants and tens times for ordered ones as compared to the cases of their random distributions. The presence of vacancies in the complex defects as well as ordering of N dopants suppresses the electron–hole asymmetry of the conductivity in graphene.

On adatomic-configuration-mediated correlation between electrotransport and electrochemical properties of graphene

Abstract The electron-transport properties of adatom–graphene system are investigated for different spatial configurations of adsorbed atoms: when they are randomly-, correlatively-, or orderly-distributed over different types of high symmetry sites with various adsorption heights. The results are obtained numerically using the quantum-mechanical Kubo–Greenwood formalism. A band gap may be opened only if ordered adatoms act as substitutional atoms, while there is no band gap opening for adatoms acting as interstitial atoms. The type of adsorption sites strongly affect the conductivity for random and correlated adatoms, but practically does not change the conductivity when they form ordered superstructures with equal periods. Depending on electron density and type of adsorption sites, the conductivity for correlated and ordered adatoms is found to be enhanced in dozens of times as compared to the cases of their random positions. The correlation and ordering effects manifest weaker or stronger depending on whether adatoms act as substitutional or interstitial atoms. The conductivity approximately linearly scales with adsorption height of random or correlated adatoms, but remains practically unchanged with adequate varying of elevation of ordered adatoms. Correlations between electron transport properties and heterogeneous electron transfer kinetics through potassium-doped graphene and electrolyte interface are investigated as well.

A statistical-thermodynamic analysis of stably ordered substitutional structures in graphene

Ordered distributions of carbon and substitutional dopant (A) atoms over the sites of a graphene lattice, i.e. CmA superstructures with dopant contents c=1/(m+1), and problem of their stability are considered theoretically. The ranges of values of interatomic-interaction parameters providing the low-temperature stability of the graphene-based C7A, C3A, and CA superstructures are determined within the framework of both the third-nearest-neighbor Ising model and, more realistically, the all-coordination-shell interaction model. The first model results in the “omission” (instability) of some predicted superstructures, while the second model shows that all predicted superstructures are stable at certain values of interatomic-interaction energies. Even short-range interatomic interactions provide a stability of some superstructures, while only long-range interactions stabilize others.

The application of radiation diffuse scattering to the calculation of phase diagrams of F.C.C. substitutional alloys

Abstract By using quantitative information about the radiation diffuse-scattering intensity of the disordered f.c.c. substitutional alloy Me ′ 1- c Me ″ c ( c —concentration) the Fourier component, w ∼ k , of mixing energies of Me ′ and Me ″ atoms may be estimated. We have to use the measurement data of the diffuse-scattering intensities at the corresponding reciprocal-space points k of the disordered phase and then determine the parameter w ∼ ( k ). The statistical thermodynamics of the non-ideal solid solution is determined by these energy parameters { w ∼ ( k )}. Therefore, one can obtain the configuration free energy of an alloy, F=U-TS ( U —internal energy, S —entropy), and then determine its fundamental thermodynamic characteristics, including not only its phase diagram, but also the concentration-dependent order–disorder transformation temperature, temperature and concentration long-range order parameter dependences, chemical activity, heat capacity etc. Some thermodynamic properties are calculated within the framework of the statistical-thermodynamic approach for f.c.c.-Ni–Fe alloy. The diffuse-scattering intensity values are taken from data in the literature.

Strain- and Adsorption-Dependent Electronic States and Transport or Localization in Graphene

This chapter generalizes results on the influence of uniaxial strain and adsorption on the electron states and charge transport or localization in graphene with different configurations of imperfections (point defects): resonant (neutral) adsorbed atoms, either oxygen- or hydrogen-containing molecules or functional groups, vacancies or substitutional atoms, charged impurity atoms or molecules, and distortions. To observe the electronic properties of graphene–ad-molecules system, we applied electron paramagnetic resonance technique in a broad temperature range for graphene oxides as a good basis for understanding the electrotransport properties of other active carbons. The applied technique allowed for observation of possible metal–insulator transition and sorption pumping effect as well as discussion of results in relation to the granular metal model. The electronic and transport properties are calculated within the framework of the tight-binding model along with the Kubo–Greenwood quantum-mechanical formalism. Depending on electron density and type of the sites, the conductivity for correlated and ordered adsorbates is found to be enhanced dozens of times as compared to the cases of their random distribution. In case of the uniaxially strained graphene, the presence of point defects counteracts or contributes to the band-gap opening according to their configurations. The band-gap behaviour is found to be non-monotonic with strain in case of a simultaneous action of defect ordering and zigzag deformation. The amount of localized charge carriers (spins) is found to be correlated with the content of adsorbed centres (atoms or molecules) responsible for the formation of potential barriers and, in turn, for the localization effects. Physical and chemical states of graphene edges, especially at a uniaxial strain along one of them, play a crucial role in electrical transport phenomena in graphene-based materials.

Effect of weak impurities on conductivity of uniaxially strained graphene

The main goal of our study was investigation of the influence of the deformations (sufficiently large for the establishing the non-zero gap) on electrotransport properties of impure graphene. To achieve this purpose, we implemented the simulation package that allows to perform numerical calculation of the conductivity and mobility of graphene samples subjected to two types of the uniaxial strain: along zigzag and armchair edges. All numerical calculations are performed within the Kubo-Greenwood methodology along with a tight-binding model. Transport properties are studied in case of a presence of impurity atoms described by the weak short-range scattering potential. Various deformation values are considered. The uniaxial strain acts as an additional source of the electron scattering, herewith, can strongly affect both mobility and conductivity of graphene and introduce anisotropy of its electron transport properties.