5 research outputs found
Dirac point resonances due to atoms and molecules adsorbed on graphene and transport gaps and conductance quantization in graphene nanoribbons with covalently bonded adsorbates
We present a tight binding theory of the Dirac point resonances due to
adsorbed atoms and molecules on an infinite 2D graphene sheet based on the
standard tight binding model of the graphene p-band electronic structure and
the extended Huckel model of the adsorbate and nearby graphene carbon atoms.
The relaxed atomic geometries of the adsorbates and graphene are calculated
using density functional theory. Our model includes the effects of the local
rehybridization of the graphene from the sp^2 to sp^3 electronic structure that
occurs when adsorbed atoms or molecules bond covalently to the graphene. Unlike
in previous tight-binding models of Dirac point resonances, adsorbed species
with multiple extended molecular orbitals and bonding to more than one graphene
carbon atom are treated. More accurate and more general analytic expressions
for the Green's function matrix elements that enter the T-matrix theory of
Dirac point resonances than have been available previously are obtained. We
study H, F, OH and O adsorbates on graphene and for each we find a strong
scattering resonance (two resonances for O) near the Dirac point of graphene,
by far the strongest and closest to the Dirac point being the resonance for H.
We extract a minimal set of tight binding parameters that can be used to model
resonant electron scattering and electron transport in graphene and graphene
nanostructures with adsorbed H, F, OH and O accurately and efficiently. We also
compare our results for the properties of Dirac point resonances due to
adsorbates on graphene with those obtained by others using density functional
theory-based electronic structure calculations, and discuss their relative
merits. We then present calculations of electronic quantum transport in
graphene nanoribbons with these adsorbed species...Comment: 21 pages, 9 figure
Π‘ΠΎΡΡΠ°Π»ΡΠ½ΠΎ-ΠΊΠΎΠΌΡΠ½ΡΠΊΠ°ΡΠΈΠ²Π½ΠΈΠΉ Π°ΡΠΏΠ΅ΠΊΡ Π·ΠΌΡΡΡΠ²Π°Π½Π½Ρ ΠΌΠΎΠ²Π½ΠΈΡ ΠΊΠΎΠ΄ΡΠ² (Π½Π° ΠΌΠ°ΡΠ΅ΡΡΠ°Π»Ρ ΠΏΠΎΠ΅ΡΠΈΡΠ½ΠΈΡ ΡΠ²ΠΎΡΡΠ²)
(UA) Π‘ΡΠ°ΡΡΡ ΠΏΡΠΈΡΠ²ΡΡΠ΅Π½Π° Π°ΠΊΡΡΠ°Π»ΡΠ½ΠΈΠΌ ΠΏΠΈΡΠ°Π½Π½ΡΠΌ Π±ΡΠ»ΡΠ½Π³Π²ΡΠ·ΠΌΡ. ΠΠ΄ΡΠΉΡΠ½Π΅Π½Π΅ Π²ΠΈΠ²ΡΠ΅Π½Π½Ρ ΠΎΡΠΎΠ±Π»ΠΈΠ²ΠΎΡΡΠ΅ΠΉ Π²ΠΈΠΊΠΎΡΠΈΡΡΠ°Π½Π½Ρ ΡΠ½ΡΠΎΠΌΠΎΠ²Π½ΠΈΡ
Π΅Π»Π΅ΠΌΠ΅Π½ΡΡΠ² Π² ΡΠΊΡΠ°ΡΠ½ΡΡΠΊΠΈΡ
ΠΏΠΎΠ΅ΡΠΈΡΠ½ΠΈΡ
ΡΠ²ΠΎΡΠ°Ρ
.(EN) The article is devoted to the questions of bilingualism. The analysis of the bilingual units usage in the Ukrainian poetry is done in the paper
Effect of Coulomb interaction on transport gap in ideal graphene nanoribbons
Quantum-mechanical calculations of electron transport in ideal graphene nanoribbons show that the transport gap that is predicted by noninteracting theories vanishes if the long-range Coulomb interaction between electrons is taken into account. This is a result of charge screening with the lowest subband edge being pinned to the chemical potential. However, the transport gap reappears if a ribbon is connected to wider leads, which is typically realized in an experimental setup that is based on lithographically patterned graphene ribbons. The gap is determined by scattering at the lead-to-ribbon interface, which can already be captured by the noninteracting theory.& nbsp;(C) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Funding Agencies|SNIC [2020/13-95]</p
Understanding hopping transport and thermoelectric properties of conducting polymers
We calculate the conductivity sigma and the Seebeck coefficient S for the phonon-assisted hopping transport in conducting polymers poly(3,4-ethylenedioxythiophene) or PEDOT, experimentally studied by Bubnova et al. [J. Am. Chem. Soc. 134, 16456 (2012)]. We use the Monte Carlo technique as well as the semianalytical approach based on the transport energy concept. We demonstrate that both approaches show a good qualitative agreement for the concentration dependence of sigma and S. At the same time, we find that the semianalytical approach is not in a position to describe the temperature dependence of the conductivity. We find that both Gaussian and exponential density of states (DOS) reproduce rather well the experimental data for the concentration dependence of sigma and S giving similar fitting parameters of the theory. The obtained parameters correspond to a hopping model of localized quasiparticles extending over 2-3 monomer units with typical jumps over a distance of 3-4 units. The energetic disorder (broadening of the DOS) is estimated to be 0.1 eV. Using the Monte Carlo calculation we reproduce the activation behavior of the conductivity with the calculated activation energy close to the experimentally observed one. We find that for a low carrier concentration a number of free carriers contributing to the transport deviates strongly from the measured oxidation level. Possible reasons for this behavior are discussed. We also study the effect of the dimensionality on the charge transport by calculating the Seebeck coefficient and the conductivity for the cases of three-, two-, and one-dimensional motion.Funding Agencies|Energimyndigheten; European Research Council (ERC-starting-grant) [307596]; Knut and Alice Wallenberg Foundation (The Tail of the Sun)</p
Spin polarization in modulation-doped GaAs quantum wires
We study spin polarization in a split-gate quantum wire focusing on the effect of a realistic smooth potential due to remote donors. Electron interaction and spin effects are included within the density functional theory in the local spin density approximation. We find that depending on the electron density, the spin polarization exhibits qualitatively different features. For the case of relatively high electron density, when the Fermi energy EF exceeds a characteristic strength of a long-range impurity potential Vdonors, the density spin polarization inside the wire is practically negligible and the wire conductance is spin-degenerate. When the density is decreased such that EF approaches Vdonors, the electron density and conductance quickly become spin polarized. With further decrease of the density the electrons are trapped inside the lakes (droplets) formed by the impurity potential and the wire conductance approaches the pinch-off regime. We discuss the limitations of the density functional theory in the local spin density approximation in this regime and compare the obtained results with available experimental data.Original publication: M. Evaldsson, S. Ihnatsenka, and I. V. Zozoulenko, Spin polarization in modulation-doped GaAs quantum wires, 2008, Physical Review B, (77), 165306. http://dx.doi.org/10.1103/PhysRevB.77.165306. Copyright: The America Physical Society, http://prb.aps.org/</p