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Mark G.I.,Institute of Technical Physics and Materials Science | Mark G.I.,Korean Hungarian Joint Laboratory for Nanosciences | Vancso P.,Institute of Technical Physics and Materials Science | Vancso P.,Korean Hungarian Joint Laboratory for Nanosciences | And 5 more authors.
Journal of Nanophotonics | Year: 2012

If graphene is a promising material in many respects, its remarkable properties may be impaired by unavoidable defects. Chemical vapor deposition-grown graphene samples are polycrystalline in nature, with many grain boundaries. Those extended defects influence the global electronic structure and the transport properties of graphene in a way that remains to be clarified. As a step forward in this direction, we have undertaken quantum mechanical calculations of electron wave-packet dynamics in a multigrain self-supported graphene layer. Our computer simulations show that a grain boundary may act as a reflector at some energies and for some incidences of the Bloch waves. In addition, our calculations reveal that when two grain boundaries run parallel to each other, the graphene ribbon confined between them may behave like a channel for the charge carriers. We emphasize therefore the possibility of creating nanoscale electronic waveguides and nanowires on the graphene surface by a controlled engineering of its grain boundaries. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). Source


Vancso P.,Institute of Technical Physics and Materials Science | Vancso P.,Korean Hungarian Joint Laboratory for Nanosciences | Mark G.I.,Institute of Technical Physics and Materials Science | Mark G.I.,Korean Hungarian Joint Laboratory for Nanosciences | And 6 more authors.
Applied Surface Science | Year: 2014

Chemical vapor deposition (CVD) on Cu foil is one of the most promising methods to produce graphene samples despite of introducing numerous grain boundaries into the perfect graphene lattice. A rich variety of GB structures can be realized experimentally by controlling the parameters in the CVD method. Grain boundaries contain non-hexagonal carbon rings (4, 5, 7, 8 membered rings) and vacancies in various ratios and arrangements. Using wave packet dynamic (WPD) simulations and tight-binding electronic structure calculations, we have studied the effect of the structure of GBs on the transport properties. Three model GBs with increasing disorder were created in the computer: a periodic 5-7 GB, a "serpentine" GB, and a disordered GB containing 4, 8 membered rings and vacancies. It was found that for small energies (E = EF ± 1 eV) the transmission decreases with increasing disorder. Four membered rings and vacancies are identified as the principal scattering centers. Revealing the connection between the properties of GBs and the CVD growth method may open new opportunities in the graphene based nanoelectronics. © 2013 Elsevier B.V. Source


Vancso P.,Research Institute for Technical Physics and Materials Science | Vancso P.,Korean Hungarian Joint Laboratory for Nanosciences | Mark G.I.,Research Institute for Technical Physics and Materials Science | Mark G.I.,Korean Hungarian Joint Laboratory for Nanosciences | And 5 more authors.
European Physical Journal B | Year: 2012

Probability current and probability density of wave packets was calculated by solving the three dimensional time-dependent Schrödinger equation for a local potential model of the scanning tunneling microscope (STM) tip - graphene system. Geometrical and electronic structure effects of the three dimensional tunneling process are identified by studying three models of increasing complexity: a jellium half space, a narrow jellium sheet, and a local one electron pseudopotential. It was found that some of the key characteristics of the STM tip - graphene tunneling process are already present at the simple jellium models. In the STM tip - jellium half space system the direction of the momentum does not change during the tunneling event, hence this setup is characterised by introducing an effective distance. For the STM tip - narrow jellium sheet system the direction of the momentum is changed from vertical to horizontal during the tunneling event. The wave packet preferentially tunnels into the bound state of the jellium sheet. For the atomistic model of the graphene sheet an anisotropic spreading of the wave packet was found for hot electrons. This may open new opportunities to build carbon based nanoelectronic devices. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012. Source


Vancso P.,Institute of Technical Physics and Materials Science | Vancso P.,Korean Hungarian Joint Laboratory for Nanosciences | Mark G.I.,Institute of Technical Physics and Materials Science | Mark G.I.,Korean Hungarian Joint Laboratory for Nanosciences | And 8 more authors.
Carbon | Year: 2013

The evolution of electronic wave packets (WPs) through grain boundaries (GBs) of various structures in graphene was investigated by the numerical solution of the time-dependent Schrödinger equation. WPs were injected from a simulated STM tip placed above one of the grains. Electronic structure of the GBs was calculated by ab-initio and tight-binding methods. Two main factors governing the energy dependence of the transport have been identified: the misorientation angle of the two adjacent graphene grains and the atomic structure of the GB. In case of an ordered GB made of a periodic repetition of pentagon-heptagon pairs, it was found that the transport at high and low energies is mainly determined by the misorientation angle, but the transport around the Fermi energy is correlated with the electronic structure of the GB. A particular line defect with zero misorientation angle Lahiri et al., behaves as a metallic nanowire and shows electron-hole asymmetry for hot electrons or holes. To generate disordered GBs, found experimentally in CVD graphene samples, a Monte-Carlo-like procedure has been developed. Results show a reduced transport for the disordered GBs, primarily attributed to electronic localized states caused by C atoms with only two covalent bonds. © 2013 Elsevier Ltd. All rights reserved. Source


Mark G.I.,Research Institute for Technical Physics and Materials Science | Mark G.I.,Korean Hungarian Joint Laboratory for Nanosciences | Vancso P.,Research Institute for Technical Physics and Materials Science | Vancso P.,Korean Hungarian Joint Laboratory for Nanosciences | And 5 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Computer simulation by numerically solving the time-dependent Schrödinger equation was used to investigate the spreading of electronic wave packets on the graphene surface injected from a local probe. The simulations show a highly anisotropic in-plane dynamics following a 60 + angular periodicity even near the Fermi energy. The wave packet first tunnels onto the small graphene clusters below the tip and the electronic states of these clusters govern the further spreading of the electron on the graphene surface. It was found that in the vicinity of the injection point the molecular physical behavior dominates, but at larger distances the wave propagation is governed by solid-state physical rules. The calculations show complex charge-spreading phenomena at graphene grain boundaries. Our results reveal a new picture of charge propagation in graphene, which has important consequences for nanoelectronic applications. © 2012 American Physical Society. Source

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