Paweł Szroeder

On adatomic-configuration-mediated correlation between electrotransport and electrochemical properties of graphene

Abstract The electron-transport properties of adatom–graphene system are investigated for different spatial configurations of adsorbed atoms: when they are randomly-, correlatively-, or orderly-distributed over different types of high symmetry sites with various adsorption heights. The results are obtained numerically using the quantum-mechanical Kubo–Greenwood formalism. A band gap may be opened only if ordered adatoms act as substitutional atoms, while there is no band gap opening for adatoms acting as interstitial atoms. The type of adsorption sites strongly affect the conductivity for random and correlated adatoms, but practically does not change the conductivity when they form ordered superstructures with equal periods. Depending on electron density and type of adsorption sites, the conductivity for correlated and ordered adatoms is found to be enhanced in dozens of times as compared to the cases of their random positions. The correlation and ordering effects manifest weaker or stronger depending on whether adatoms act as substitutional or interstitial atoms. The conductivity approximately linearly scales with adsorption height of random or correlated adatoms, but remains practically unchanged with adequate varying of elevation of ordered adatoms. Correlations between electron transport properties and heterogeneous electron transfer kinetics through potassium-doped graphene and electrolyte interface are investigated as well.

Application of Films Consisting of Carbon Nanoparticles for Electrochemical Detection of Redox Systems in Organic Solvent Media

In the present article, the electrochemical sensitivity and response of films consisting of carbon nanoparticles were examined to test their potential applications as electrode materials for the construction of electrochemical sensors. For this purpose, a film of vertically aligned multi-walled carbon nanotubes (MWCNTs) on silicon dioxide substrate was synthesized by means of catalytic chemical vapor deposition (CVD) at 900oC using ferrocene (FeCp2) as catalyst and acetonitrile (ACN) as a carbon source. Furthermore, bucky-paper (BP) film was produced upon ultrasonic treatment of aqueous solution of single-walled carbon nanotubes (SWCNTs) in the presence of sodium dodecyl sulfate (SDS) micelle. In order to examine the electrochemical activity of the fabricated films, electrochemical studies of the oxidation of ferrocene (FeCp2) to ferrocenium cation (FeCp2 +) (where Cp denotes cyclopentadienyl anion) in ACN containing n-tetrabutylammonium hexafluorophosphat (NBu4PF6) as supporting electrolyte were performed. For the electrochemical experiments the techniques of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed. The electrochemical parameters of the FeCp2 +/0 redox couple in ACN on the fabricated films were determined and compared with those obtained using conventional glassy carbon (GC) electrode. The results demonstrate that the FeCp2 +/0 redox couple exposes Nernstian response on either MWCNT or GC electrodes while its response on BP film can be recognized as near Nernstian. The findings verify that the synthesized MWCNT and BP films hold promising and important applications in electro-analytical chemistry.

Effects of Dispersion and Ultraviolet/Ozonolysis Functionalization of Graphite Nanoplatelets on the Electrical Properties of Epoxy Nanocomposites

The influence of liquid dispersive mediums used in the fabrication of graphite nanoplatelets (GNPs) on their morphology as well as the surface state and electrical conductivity of GNPs/epoxy nanocomposites (NCs) was studied in detail. Ultrasonic dispersion of thermally expanded graphite (TEG) in alcohol medium has been found to be the most effective by the time parameter and allows fabrication of GNPs with rather high aspect ratio (102) and low level of defects. Ultrasonic dispersion of TEG in water medium requires a long time (up to 20 h) of ultrasonic action, but the resulting GNPs are characterized by large lateral size and, therefore, a higher aspect ratio (104). The effects of different ultraviolet (UV)/ozone treatment time on GNPs/epoxy NCs morphology and electrical properties were investigated by optical microscopy, scanning electron microscopy (SEM), infrared (IR) spectrometry, and Raman spectroscopy. The NCs with GNPs subjected to UV/ozone treatment have shown the increase of electrical conductivity with the increase of UV/ozone treatment time, which can be associated with the improved dispersion and distribution of GNPs within the epoxy matrix as well as decreased contact resistance between individual GNPs in conductive network due to chemical functionalization of GNPs during UV/ozone treatment.

Strain- and Adsorption-Dependent Electronic States and Transport or Localization in Graphene

This chapter generalizes results on the 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 the electronic properties of graphene–ad-molecules 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. The applied technique allowed for 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 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 or contributes to the band-gap opening according to their configurations. The band-gap behaviour is found to be non-monotonic 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 (atoms or molecules) 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.