25 research outputs found
Strain- and Adsorption-Dependent Electronic States and Transport or Localization in Graphene
The chapter generalizes results on 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 electronic properties
of graphene-admolecules 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. Applied
technique allowed 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 in 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 against or contributes to the band-gap opening
according to their configurations. The band-gap behaviour is found to be
nonmonotonic 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 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.Comment: 16 pages, 10 figure
Size Modification of Nanographite System of Activated Carbon Fibers Studied by EPR
We report results of EPR measurements of activated carbon fibers. Experiments made for pristine activated carbon fibers and activated carbon fibers with adsorbed molecules (CCl, CHNO, and HO) confirmed the localized character of paramagnetic centers observed in the system. Pristine activated carbon fibers are characterized by single Lorentzian line. Broader component of EPR signal appears when guest molecules are adsorbed in nanopores. The strongest localization is observed for water-filled activated carbon fibers nanopores (with hydrophobic pore walls) where changes in distance between nanographite particles were monitored by the g-shift to higher values. This process is related to stronger spin-orbit interaction of electrons trapped at nanographite particles compressed by guest molecules
EPR and MMMA Study of C upon K-Doping
EPR and ΜΜMΑ studies of C upon K-doping have been performed. Two different and well separated EPR narrow lines were detected for C and C at temperatures below 100 K. Time dependent changes in the intensities of both and C lines were observed when the system undergoes an eutectoid transformation. The evolution of superconductivity with two T related to different valences (v) of C ion radicals have been found
Electric Conductivity of Carbon Nanoparticles Stimulated by Electric Field
Host-guest interactions can be the unique method of spin manipulation in nanoscale. Strong changes in spin localization are generated when potential barriers between nanographitic units of activated carbon fibers are modified by interaction with adsorbed molecules. Stronger modifications occur when dipolar guest molecules are stimulated with external electric field. We report experimental results which show the influence of electric field on the spin localization in activated carbon fibers
Effect of Ultrasound Irradiation on Graphite Crystals Dimension
International audienc
Pseudorotational Averaging of EPR Spectrum of Cu(II)O Complex in YBaCuO in Low Temperatures
In low temperatures the condensation of oxygen was found to occur at 05 site in an elementary cell of YBaCuO being the fifth ligand forming the CuO complex around Cul copper in chain. This change of coordinantion from CuO to CuO is the origin of a pseudorotation related to a strong vibronic coupling of two distorted configurations: a tetragonal pyramid C and a trigonal bipyramid D, which yields a pseudocubic EPR spectrum in low temperatures. The averaged spectroscopic splitting coefficient is related to a superposition of vibronically coupled orbital states |x - y〉 and |3z - r〉. The averaged spectrum was for the first time observed in low temperatures since the oxygen condensation in YBaCuO at 05 site of the chain occur only when oxygen undergoing fast diffusion among the chains, gets localized with decreasing temperature. The activation energy of oxygen desorption from the 05 site is 36 K
Impedance Spectroscopy as a detailed method to characterize electrochemical performance of porous carbon
International audienc
Effect of ultrasounds irradiation on graphite crystals dimensio
International audienc
Free Radicals in K and Rb Admixtured Fullerene C
Molecules of C form Van der Waals type crystals. The observations reported here concern EPR investigations of such C samples with only a slight amount of Rb or K. Detected defects are (C) or (C) ion-radicals. A hole (h) or trapped electron (t) are localized on one fullerene ball. In the case of potassium fullerites C:K the line shape of EPR signal was of the Dysonian form which is characteristic of conducting electrons in metal. The EPR lines of holes (C) are characterized by g ≥ g whereas for electrons g is below the value g = 2.0023 characteristic of a free electron (g ≤ g). The EPR linewidth 2ΔB of the (C) weakly increased with decreasing temperature whereas the EPR linewidth attributed to the electron 2ΔB significantly decreases with decreasing temperature. The C:K sample reached superconducting phase below T = 11 K which is significantly less than T = 16.5 K observed for KC where 2 ≤ x ≤ 4