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

High temperature behavior of functional TiAlBSiN nanocomposite coatings

This article reports on the thorough characterization of structural-phase transformation in amorphous TiAlBSiN coating after high temperature annealing at 900 °C in ambient air. The influence of annealing on the tribomechanical behavior of the coating at nano and micro scale was also examined. The research included multiple experimental techniques, i.e. AFM, SEM, TEM, HR-TEM, EDS, XPS and Raman spectroscopy. Experiments showed that the amorphous phase of the TiAlBSiN coating undergoes a structural transformation, evidenced in the changes of parameters such as topological and chemical short-range order after the post-deposition annealing at 900 °C in air. The observed structural transformation, leads to a phase separation with the formation of a three dimensional nc-TiAl3/a-SiBN(O) nanocomposite structure. The relative increase of hardness, reduced elastic modulus, H/Er ratio and H2 /E3 r ratio after high temperature treatment of TiAlBSiN coatings is also reported. The complex interdependency between chemistry, morphology and relative composition of the amorphous TiAlBSiN coating phase, during the high temperature treatment, with the respective change of the tribo-mechanical characteristics, are evidence of the improvement of the coating properties in response to the environmental conditions and high temperature. This work contributes particularly to the development and understanding of flexible nanocomposite protective coatings and their changes at high temperature of operatio

High temperature behavior of functional TiAlBSiN nanocomposite coatings

This article reports on the thorough characterization of structural-phase transformation in amorphous TiAlBSiN coating after high temperature annealing at 900 °C in ambient air. The influence of annealing on the tribomechanical behavior of the coating at nano and micro scale was also examined. The research included multiple experimental techniques, i.e. AFM, SEM, TEM, HR-TEM, EDS, XPS and Raman spectroscopy. Experiments showed that the amorphous phase of the TiAlBSiN coating undergoes a structural transformation, evidenced in the changes of parameters such as topological and chemical short-range order after the post-deposition annealing at 900 °C in air. The observed structural transformation, leads to a phase separation with the formation of a three dimensional nc-TiAl3/a-SiBN(O) nanocomposite structure. The relative increase of hardness, reduced elastic modulus, H/Er ratio and H2 /E3 r ratio after high temperature treatment of TiAlBSiN coatings is also reported. The complex interdependency between chemistry, morphology and relative composition of the amorphous TiAlBSiN coating phase, during the high temperature treatment, with the respective change of the tribo-mechanical characteristics, are evidence of the improvement of the coating properties in response to the environmental conditions and high temperature. This work contributes particularly to the development and understanding of flexible nanocomposite protective coatings and their changes at high temperature of operatio

Localized states in nanocarbons

Localization phenomenon is studied in different modern nanocarbon materials: pristine C60, C60-fullerides, carbon nanotubes and graphene-based structures in the form of activated carbon fibers built of quantum dot-like basic structural units. Two experimental methods are used to define the localization and population control of spins (charge carriers) in the nanocarbon materials – electron paramagnetic resonance (EPR) and direct current (d.c.) electrical conductivity measurements. Results are discussed in the frame of the possible applications of the aforementioned materials in the molecular electronics or spintronics

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$\text{}_{4}$, C$\text{}_{6}$H$\text{}_{5}$NO$\text{}_{2}$, and H$\text{}_{2}$O) 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 Impedance Measurements of Graphene Oxide and Reduced Graphene Oxide

We report the observations of electron paramagnetic resonance and impedance measurements of graphene oxide and reduced graphene oxide performed in the wide temperature range in order to get insight into the electronic properties of graphene-based materials and the role of oxygen functionalities in the charge carrier transport phenomena. In such systems the strong spin localization, hopping charge carrier transport as well as the formation of adsorption layers are observed, all the phenomena changing significantly after the heavily oxidized graphene is reduced

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

Wetting of nanostructurized sapphire and gold surfaces

We present the results of preliminary experiments regarding research on the contact angle measurements of various liquids on solid surfaces with different morphology. The aim was to get insight into the dependence of wetting phenomena on the nanoscale surface roughness. Flat and nanostructurized surfaces of gold and sapphire were used in the experiments. Four liquids - bromobenzene, water, mercury, and gallium - covering a broad range of surface tension values were used to check how varying roughness influences wetting in the systems with different adhesion/cohesion ratio. Structurization was anisotropic, which resulted in the very interesting behaviour of the examined liquids on the selected surfaces. Significant change of the wetting properties was observed as well as a strong dependence on the surface morphology

Characteristics of Laminar Flow in Pipelines of Homogenous Alum Sludge Approximated with use of the Vočadlo Model for Viscoplastic Liquids

The study presents the manners of determination of the Darcy friction factor λ for a homogenous hydromixture of alum sludge of varied hydration and temperature for the laminar flow zone. The rheological evaluation of the hydromixture as a viscoplastic body has been conducted with use of measurements of viscosity. The curves of flow were approximated with use of the generalized Vočadlo model. The Darcy friction factor λ of the pipeline was determined with use of the non-dimensional criterion λ(Regen) and λ(Re, He).Praca przedstawia sposoby określenia współczynnika oporów rurociągu λ, dla jednorodnej hydromieszaniny osadów pokoagulacyjnych o różnym uwodnieniu i różnej temperaturze, dla laminarnej strefy przepływu. Ocenę reologiczną hydromieszaniny, jako ciała plastyczno-lepkiego, wykonano na podstawie pomiarów wiskozymetrycznych, przy zastosowaniu do aproksymacji krzywych płynięcia uogólnionego modelu Vočadli. Określenie współczynnika oporu rurociągu λ przeprowadzono z wykorzystaniem bezwymiarowego kryterium λ(Regen) oraz λ(Re, He)

Charakterystyka laminarnego płynięcia w rurociągach jednorodnych osadów pokoagulacyjnych aproksymowanych modelem cieczy plastyczno-lepkich Vočadli

The study presents the manners of determination of the Darcy friction factor λ for a homogenous hydromixture of alum sludge of varied hydration and temperature for the laminar flow zone. The rheological evaluation of the hydromixture as a viscoplastic body has been conducted with use of measurements of viscosity. The curves of flow were approximated with use of the generalized Vočadlo model. The Darcy friction factor λ of the pipeline was determined with use of the non-dimensional criterion λ(Regen) and λ(Re, He).Praca przedstawia sposoby określenia współczynnika oporów rurociągu λ, dla jednorodnej hydromieszaniny osadów pokoagulacyjnych o różnym uwodnieniu i różnej temperaturze, dla laminarnej strefy przepływu. Ocenę reologiczną hydromieszaniny, jako ciała plastyczno-lepkiego, wykonano na podstawie pomiarów wiskozymetrycznych, przy zastosowaniu do aproksymacji krzywych płynięcia uogólnionego modelu Vočadli. Określenie współczynnika oporu rurociągu λ przeprowadzono z wykorzystaniem bezwymiarowego kryterium λ(Regen) oraz λ(Re, He)