Showing papers on "Graphene published in 1990"
TL;DR: Le phenomene de localisation faible des systemes electroniques a deux dimensions explique la magnetoresistance negative ainsi que la dependance, vis-a-vis des basses temperatures, de the resistivite des echantillons de pyrocarbone chauffes entre 2000 et 2600°C.
Abstract: The weak-localization phenomenon for two-dimensional (2D) electronic systems is invoked to explain the negative magnetoresistance as well as the low-temperature dependence of the resistivity of pyrocarbon samples heat treated between 2000 and 2600 \ifmmode^\circ\else\textdegree\fi{}C. The 2D character is found to originate from the random stacking of the graphene layers (turbostratic structure) characteristic of pregraphitic carbon materials. For a heat-treatment temperature (HTT) lower than 2200 \ifmmode^\circ\else\textdegree\fi{}C, x-ray analysis reveals that the structure is almost turbostratic, while the material exhibits a pronounced negative magnetoresistance. For higher HTT, 3D order typical of crystalline graphite increases, leading to a 2D-to-3D crossover and to a vanishing negative magnetoresistance.
62 citations
TL;DR: In this article, the topography of polyacrylonitrile (PAN)-based carbon fibres in air at ambient pressure has been studied using scanning tunnelling microscopy.
31 citations
TL;DR: In this paper, the authors model the charging of pure stage graphite hydrogenosulfate with expulsion of H + from the intercalate layer by transmission lines which agree quite well with A.C Impedance measurements.
Abstract: "Overcharging" of pure stage graphite hydrogenosulfate i.e charging of graphene layers with expulsion of H + from the intercalate layer is modelized by transmission lines which agree quite well with A.C Impedance measurements. The meaning of the apparent Diffusivity D a = 1 2 /3 R 1 C 1 is discussed as significant of the displacement of H + /e− holes pairs along the blocking interface separating graphene and intercalate layers.
1 citations
TL;DR: In this paper, the authors used scanning tunneling microscopy (STM) to visualize the structure of copper chloride and cobalt chloride graphite intercalation compounds (GICs).
Abstract: Scanning tunneling microscopy (STM) is used to visualize the structure of copper chloride and cobalt chloride graphite intercalation compounds (GICs). When the samples are biased negatively with respect to the tip, the images show details of the structure of the intercalant layers, and of its effects on the surface graphene layer. When the sample is under positive bias, symmetry properties of the uppermost graphite planes are revealed. Images of the CuCl2 stage 1 GIC display a hexagonal symmetry in which all the atoms of the graphite surface plane appear. This is in contrast to the three-fold symmetry usually seen in atomic resolution STM images of highly oriented pyrolytic graphite (HOPG), which we also observe on a reference sample of HOPG. The three-fold symmetry is attributed to the ABAB stacking of the atomic layers in HOPG. In GICs, this stacking sequence is interrupted by the layer of intercalate, so that for the stage 1 compound all carbon atoms in the plane become equivalent, and six-fold symmetry develops. For a stage 2 (CuCl2 or CoCl2) GIC three-fold symmetry is expected to persist. Images of the CoCl2 stage 1 GIC, taken with the sample bias is positive with respect to the tip, display a mixed trigonal and hexagonal symmetry, and may be attributable to the fact that the surface of sample is of mixed stage.