Electronic Conduction through Monolayer Amorphous Carbon Nanojunctions (original) (raw)
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Electronic properties of disordered two-dimensional carbon
Physical Review B, 2006
Two-dimensional carbon, or graphene, is a semi-metal that presents unusual low-energy electronic excitations described in terms of Dirac fermions. We analyze in a self-consistent way the effects of localized (impurities or vacancies) and extended (edges or grain boundaries) defects on the electronic and transport properties of graphene. On the one hand, point defects induce a finite elastic lifetime at low energies with the enhancement of the electronic density of states close to the Fermi level. Localized disorder leads to a universal, disorder independent, electrical conductivity at low temperatures, of the order of the quantum of conductance. The static conductivity increases with temperature and shows oscillations in the presence of a magnetic field. The graphene magnetic susceptibility is temperature dependent (unlike an ordinary metal) and also increases with the amount of defects. Optical transport properties are also calculated in detail. On the other hand, extended defects induce localized states near the Fermi level. In the absence of electron-hole symmetry, these states lead to a transfer of charge between the defects and the bulk, the phenomenon we call selfdoping. The role of electron-electron interactions in controlling self-doping is also analyzed. We also discuss the integer and fractional quantum Hall effect in graphene, the role played by the edge states induced by a magnetic field, and their relation to the almost field independent surface states induced at boundaries. The possibility of magnetism in graphene, in the presence of short-range electron-electron interactions and disorder is also analyzed.
Victoria University of Wellington, 2015
This thesis is cited by: 3. Zambrzycki, M. et al. (2021). "Structure and electrical transport properties of carbon nanofibres/carbon nanotubes 3D hierarchical nanocomposites: Impact of the concentration of acetylacetonate catalyst", Ceramics International, 47 (3), 4020-4033. https://doi.org/10.1016/j.ceramint.2020.09.269 2. Αρετή, Θ. Κ. [Areti, T. K.] (2017). Diploma Thesis, Department of Physics, University of Athens. Available at https://pergamos.lib.uoa.gr/uoa/dl/frontend/file/lib/default/data/1702786/theFile 1. Hang, S. (2015). Irradiation-based defect engineering of graphene devices. PhD Thesis, University of Southampton, UK. Available at http://eprints.soton.ac.uk/388184/ Graphene, consisting of a single layer of carbon atoms, is being widely studied for its interesting fundamental physics and potential applications. The presence and extent of disorder play important roles in determining the electronic conduction mechanism of a conducting material. This thesis presents work on data analysis and modelling of electronic transport mechanisms in disordered carbon materials such as graphene. Based on experimental data of conductance of partially disordered graphene as measured by Gómez-Navarro et al., we propose a model of variable-range hopping (VRH) – defined as quantum tunnelling of charge carriers between localized states – consisting of a crossover from the two-dimensional (2D) electric field-assisted, temperature-driven (Pollak-Riess) VRH to 2D electric field-driven (Skhlovskii) VRH. The novelty of our model is that the temperature-dependent and field-dependent regimes of VRH are unified by a smooth crossover where the slopes of the curves equal at a given temperature. We then derive an analytical expression which allows exact numerical calculation of the crossover fields or voltages. We further extend our crossover model to apply to disordered carbon materials of dimensionalities other than two, namely to the 3D self-assembled carbon networks by Govor et al. and quasi-1D highly-doped conducting polymers by Wang et al. Thus we illustrate the wide applicability of our crossover model to disordered carbon materials of various dimensionalities. We further predict, in analogy to the work of Pollak and Riess, a temperature-assisted, field-driven VRH which aims to extend the field-driven expression of Shklovskii to cases wherein the temperatures are increased. We discover that such an expression gives a good fit to the data until certain limits wherein the temperatures are too high or the applied field too low. In such cases the electronic transport mechanism crosses over to Mott VRH, as expected and analogous to our crossover model described in the previous paragraph. The second part of this thesis details a systematic data analysis and modelling of experimental data of conductance of single-wall carbon nanotube (SWNT) networks prepared by several different chemical-vapour deposition (CVD) methods by Ansaldo et al. and Lima et al. Based on our analysis, we identify and categorize the SWNT networks based on their electronic conduction mechanisms, using various theoretical models which are temperature-dependent and field-dependent. The electronic transport mechanisms of the SWNT networks can be classed into either VRH in one- and two-dimensions or fluctuation-assisted tunnelling (FAT, i.e. interrupted metallic conduction), some with additional resistance from scattering by lattice vibrations. Most notably, for a selected network, we find further evidence for our novel VRH crossover model previously described. We further correlate the electronic transport mechanisms with the morphology of each network based on scanning electron microscopy (SEM) images. We find that SWNT networks which consist of very dense tubes show conduction behaviour consistent with the FAT model, in that they retain a finite and significant fraction of room-temperature conductance as temperatures tend toward absolute zero. On the other hand, SWNT networks which are relatively sparser show conduction behaviour consistent with the VRH model, in that conductance tends to zero as temperatures tend toward absolute zero. We complete our analysis by estimating the average hopping distance for SWNT networks exhibiting VRH conduction, and estimate an indication of the strength of barrier energies and quantum tunnelling for SWNT networks exhibiting FAT conduction.
Quantum transport in disordered graphene: A theoretical perspective
Solid State Communications, 2012
The present theoretical review puts into perspective simulations of quantum transport properties in disordered graphene-based materials. In particular, specific effects induced by short versus long range scattering on the minimum conductivity, weak (anti-)localization, and strongly insulating regimes are discussed in depth. Using various types of disorder profiles (random fluctuations of the local impurity potential, long range Coulomb scatterers or more intrusive chemical functionalizations), universal aspects of transport as well as novel features in chemically modified graphene-based materials are depicted, especially in the cases of oxygen and hydrogen atoms adsorption. Finally, our theoretical results are compared to experimental measurements.
Disorder and electronic transport in graphene
Journal of Physics: Condensed Matter, 2010
In this review, we provide an account of the recent progress in understanding electronic transport in disordered graphene systems. Starting from a theoretical description that emphasizes the role played by band structure properties and lattice symmetries, we describe the nature of disorder in these systems and its relation to transport properties. While the focus is primarily on theoretical and conceptual aspects, connections to experiments are also included. Issues such as short versus long-range disorder, localization (strong and weak), the carrier density dependence of the conductivity, and conductance fluctuations are considered and some open problems are pointed out.
C Y Cheah et al 2013 J. Phys.: Condens. Matter 25 (46), 465303 doi:10.1088/0953-8984/25/46/465303 (pre-print arXiv:1305.0315)
This paper is cited by: 15. Muhin, A. (2024). PhD Thesis, Technischen Universität Berlin. 14. Ruiz, E. (2023). PhD Thesis, Université Clermont Auvergne. 13. Lemesh, N. V. et al. (2023). Low Temp. Phys. 49, 1050–1057. https://doi.org/10.1063/10.0020598 12. Berlin. V. (2022). Graphene oxide reduction and decoration with lead sulphide nanoparticles for gas sensing application. Master's Thesis, Politecnico di Milano. 11. C¸ınar, M. N. et al. (2022). Nano Lett., 22, 2202. https://doi.org/10.1021/acs.nanolett.1c03883 10. Kovtun, A. et al. (2021). ACS Nano, 15, 2654. https://doi.org/10.1021/acsnano.0c07771 9. Leardini, F. et al. (2019). 2D Mater., 6, 035015. https://doi.org/10.1088/2053-1583/ab175c 8. Turmaud, J. P. (2018). Variable range hopping conduction in the epitaxial graphene buffer layer on SiC (0001). PhD Thesis, Georgia Institute of Technology. 7. Gómez, J. et al. (2017). Mater. Res. Express, 4, 105020. Available at doi.org/10.1088/2053-1591/aa8e11 6. Matis, B. R. et al. (2017). Electronic transport in bilayer MoS2 encapsulated in HfO2. ACS Appl. Mater. Interfaces, 9, 27995–28001. 5. Kusiak-Nejman, E. et al. (2017). Catal. Today, 287, 189–195. 4. Gillgren, N. A. (2017). Quantum Transport Properties of Atomically Thin Black Phosphorus. PhD Thesis, Uni California Riverside. https://escholarship.org/content/qt48k9x0s3/qt48k9x0s3\_noSplash\_134d8a6348e785ef6fa76c7c838d847f.pdf 3. Liu, C.-I. et al. (2016). Semicond. Sci. Technol., 31, 105008. 2. Hang, S. (2015). Irradiation-based defect engineering of graphene devices. PhD Thesis, University of Southampton, UK. 1. Lippert, G. et al. (2014). Carbon, 75, 104-112. _______________________________________________________________________________________ We report an analysis of low-temperature measurements of the conductance of partially disordered reduced graphene oxide, finding that the data follow a simple crossover scenario. At room temperature, conductance is dominated by two-dimensional (2D) electric field-assisted, thermally-driven (Pollak-Riess) variable-range hopping (VRH) through highly-disordered regions. However, at lower temperatures T, we find a smooth crossover to follow the exp(-E_0/E)^(1/3) field-driven (Shklovskii) 2D VRH conductance behaviour when the electric field E exceeds a specific crossover value E_C (T)_2D = (E_a E_0^(1/3) /3)^(3/4) determined by the scale factors E_0 and E_a for the high-field and intermediate field regimes respectively. Our crossover scenario also accounts well for experimental data reported by other authors for three-dimensional disordered carbon networks, suggesting wide applicability.
Electron transport in disordered graphene
Physical Review B, 2006
We study electron transport properties of a monoatomic graphite layer (graphene) with different types of disorder. We show that the transport properties of the system depend strongly on the character of disorder. Away from the half filling, the concentration dependence of conductivity is linear in the case of strong scatterers, in line with recent experimental observations, and logarithmic for weak scatterers. At half filling the conductivity is of the order of e 2 /h if the randomness preserves one of the chiral symmetries of the clean Hamiltonian; otherwise, the conductivity is strongly affected by localization effects.
Physical Review B, 2011
An efficient computational methodology is used to explore charge transport properties in chemically modified (and randomly disordered) graphene-based materials. The Hamiltonians of various complex forms of graphene are constructed using tight-binding models enriched by first-principles calculations. These atomistic models are further implemented into a real-space order-N Kubo-Greenwood approach, giving access to the main transport length scales (mean free paths, localization lengths) as a function of defect density and charge carrier energy. An extensive investigation is performed for epoxide impurities with specific discussions on both the existence of a minimum semiclassical conductivity and a crossover between weak to strong localization regime. The 2D generalization of the Thouless relationship linking transport length scales is here illustrated based on a realistic disorder model.
Electronic properties and quantum transport in Graphene-based nanostructures
European Physical Journal B, 2009
Carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) represent a novel class of low-dimensional materials. All these graphene-based nanostructures are expected to display the extraordinary electronic, thermal and mechanical properties of graphene and are thus promising candidates for a wide range of nanoscience and nanotechnology applications. In this paper, the electronic and quantum transport properties of these carbon nanomaterials are reviewed. Although these systems share the similar graphene electronic structure, confinement effects are playing a crucial role. Indeed, the lateral confinement of charge carriers could create an energy gap near the charge neutrality point, depending on the width of the ribbon, the nanotube diameter, the stacking of the carbon layers regarding the different crystallographic orientations involved. After reviewing the transport properties of defect-free systems, doping and topological defects (including edge disorder) are also proposed as tools to taylor the quantum conductance in these materials. Their unusual electronic and transport properties promote these carbon nanomaterials as promising candidates for new building blocks in a future carbon-based nanoelectronics, thus opening alternatives to present silicon-based electronics devices.
Peculiar electronic transport properties of disordered nanographene ribbons
Journal of Physics and Chemistry of Solids, 2008
The band structure of graphene ribbons with zigzag edges have two valleys well separated in momentum space, related to the two Dirac points of the graphene spectrum. The propagating modes in each valley contain a single chiral mode originating from a partially flat band at band center. This feature gives rise to a perfectly conducting channel in the disordered system, if the impurity scattering does not connect the two valleys, i.e. for long-range impurity potentials. Ribbons with short-range impurity potentials, however, through inter-valley scattering display ordinary localization behavior. r