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0 8 Experimental Study of the Intrinsic and Extrinsic Transport Properties of Graphite and Multigraphene Samples J. Barzola-Quiquia, A. Ballestar, S. Dusari and P. Esquinazi Division of Superconductivity and Magnetism, Institute for Experimental Physics II, University of Leipzig Germany 1. Introduction This chapter1 deals with the following basic questions, which sometimes surprise or even irritate the reader, namely: Which are the intrinsic properties of the graphene layers inside the graphite structure? Are their transport properties quasi-two dimensional and are they comparable with those of single layer graphene? Which is the coupling between ideal, i.e. defect free, graphene layers inside graphite? Which is the influence of defects and interfaces within the graphene and graphite structure? These basic questions remain in the literature still unanswered to a large extent mainly because the influence on the transport properties of defects and sample or crystal sizes was not systematically taken into account. A large amount of the published interpretations on the experimental transport data of real graphite samples relied on the assumption that these were intrinsic properties. Let us start with a rather simple example. In the last fifty years scientists flooded the literature with reports on different kinds of electronic measurements on graphite samples, providing evidence for carrier (electron plus hole) densities per graphene layer in graphite2 and at low temperatures n0 > 1010 cm−2 as one can read in the standard book from Kelly (1981) or the old publication from McClure (1964), or from more recent work by Grüneis et al. (2008) (n0 ≃ 1012 cm−2) or Kumar et al. (2010) (n0 ≃ 2.4 × 1011 cm−2). But why this concentration is not a constant and does apparently depend on the measured sample? The reader may ask then why at all is the knowledge of the intrinsic carrier concentration n0 so important? The carrier concentration is one of those basic parameters needed to estimate several others necessary to get a reliable picture of the electronic band structure and from this to understand all intrinsic (or not) transport properties. For example, two-dimensional (2D) calculations 1 This work is supported by the DFG under DFG ES 86/16-1. A.B. is supported by the ESF "Nachwuchsforschergruppe" "Funktionale multiskalige Strukturen" and S.D. by the Graduate school of Natural Sciences of the University of Leipzig "BuildMona". 2 In this chapter and to facilitate a direct comparison between the carrier density of a single graphene layer and that one inside the graphite structure, the carrier density per area will be used. This can be easily obtained multiplying n, the three dimensional carrier density, by the distance between graphene layers in graphite a0 = 0.335 nm. This estimate assume that the coupling between graphene layers inside graphite is very weak and that the electron transport is mainly on the two dimensional graphene layers.PDF Image | GRAPHENE SYNTHESIS CHARACTERIZATION PROPERTIES
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