Electron transport properties of graphene with charged impurities and vacancy defects
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Nano-structured graphene has recently attracted extraordinary attention due to its potential use as an electronic or spintronic material. We investigated the electrical conductivities of antidot and Ar-sputtered graphene samples under a magnetic field in terms of the carrier density. Antidot samples exhibit conductivity that is well explained by charged impurity scattering, which is associated with intravalley scattering. This suggestion is supported by the low intensity of the Raman D band, which is related to intervalley scattering induced by structural defects. In contrast, Ar-sputtered samples show a strong D band and conductivity that is affected by defect scattering. The difference in the main scattering mechanism between the two types of samples appears as Shubnikov-de Haas oscillations at high magnetic fields, which are observed in antidot samples but not in Ar-sputtered samples. Furthermore, an analysis of weak localization effects in both samples at low fields reveals that intra- and intervalley scatterings play significant roles in antidot and Ar-sputtered samples, respectively.
I. INTRODUCTION
Graphene, a single sheet of graphite, is a twodimensional (2D) crystal of carbon atoms arranged in a honeycomb structure. Since macroscopic flakes of monoor multilayer graphene were first isolated by micromechanical exfoliation of graphite, followed by the discovery of the anomalous quantum Hall effect,1–3 many studies have been performed to elucidate the electron behavior described by the massless Dirac equation. The electron transport properties of graphene, in which carrier mobility reaches as high as 200,000 cm2/V/s,4 are highly attractive topics and the electron scattering mechanisms have been studied experimentally and theoretically. The electrostatic potentials of charged impurities, which are inevitably introduced during device fabrication, act as long-range scattering sources.5,6 The gentle decay of the potential created by these charged impurities is closely related to the intravalley process, in which electrons are scattered within a valley in the first Brillouin zone. Here, the effect of the scattering potential depends strongly on the electrostatic screening effect, which is modulated by the charge carrier density. On the other hand, a steep potential induced by structural defects, such as vacancies and grain boundaries in graphene, causes larger changes in the electron momentum, including
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] c) e-mail: [email protected] DOI: 10.1557/jmr.2013.62 J. Mater. Res., Vol. 28, No. 8, Apr 28, 2013
backscattering, which corresponds to the K-to-K9 transition (i.e., intervalley scattering). Such defects form midgap states in graphene, which reportedly contribute to the conductivity.7,8 In addition, these structural defects have been experimentally and theoretically examined as the origin of localized magnetic moments in various carbon materials as well as graphene.9,10 Chen et al.11 recently re
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