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See detailSpatially resolved raman spectroscopy of single- and few-layer graphene
Graf, D.; Molitor, F.; Ensslin, K. et al

in Nano Letters (2007), 7(2), 238-242

We present Raman spectroscopy measurements on single- and few-layer graphene flakes. By using a scanning confocal approach, we collect spectral data with spatial resolution, which allows us to directly ... [more ▼]

We present Raman spectroscopy measurements on single- and few-layer graphene flakes. By using a scanning confocal approach, we collect spectral data with spatial resolution, which allows us to directly compare Raman images with scanning force micrographs. Single-layer graphene can be distinguished from double- and few-layer by the width of the D' line: the single peak for single-layer graphene splits into different peaks for the double-layer. These findings are explained using the double-resonant Raman model based on ab initio calculations of the electronic structure and of the phonon dispersion. We investigate the D line intensity and find no defects within the flake. A finite D line response originating from the edges can be attributed either to defects or to the breakdown of translational symmetry. [less ▲]

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See detailRaman imaging of graphene
Graf, D.; Molitor, F.; Ensslin, K. et al

in Solid State Communications (2007), 143(1-2), 44-46

A Raman spectrum of a solid contains information about its vibrational and electronic properties. Collecting spectral data with spatial resolution and encoding it in a 2D plot generates images with ... [more ▼]

A Raman spectrum of a solid contains information about its vibrational and electronic properties. Collecting spectral data with spatial resolution and encoding it in a 2D plot generates images with information complementary to optical and scanning force imaging. In the case of few-layer graphene the frequency of the G line and especially the width of the D ' line turn out to be sensitive to single layers. The thickness of the few-layer graphene flake is reflected in the intensity of the G line and in the reduced intensity of the dominant peak of the underlying silicon oxide. (c) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailRaman mapping of a single-layer to double-layer graphene transition
Graf, D.; Molitor, F.; Ensslin, K. et al

in European Physical Journal. Special Topics (2007), 148

We report on confocal Raman spectroscopy on a few-layer graphene flake. Adjacent single- and double-layer graphene sections allow mapping the transition in vibrational and electronic properties to a ... [more ▼]

We report on confocal Raman spectroscopy on a few-layer graphene flake. Adjacent single- and double-layer graphene sections allow mapping the transition in vibrational and electronic properties to a second stacked graphene sheet and with it a weak interlayer coupling. Most prominently the width of the D' peak doubles upon going from a single to a double layer, which can be explained within the double-resonant Raman model. The intensities of the G and G' lines decrease at the crossover to a single layer. Contrary to the G' line the G peak position shifts to higher wave numbers, however, not uniformly over the entire section: its frequency fluctuates spatially. The Raman map of the D line intensity shows a non-zero contribution at the boundaries of the flake and the individual sections, which can be attributed either to defects and disorder or to the breakdown of translational symmetry, whereas within the flake no D line signal is detected. [less ▲]

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See detailRaman imaging of doping domains in graphene on SiO(2)
Stampfer, C.; Molitor, F.; Graf, D. et al

in Applied Physics Letters (2007), 91(24),

We present spatially resolved Raman images of the G and 2D lines of single-layer graphene flakes. The spatial fluctuations of G and 2D lines are correlated and are thus shown to be affiliated with local ... [more ▼]

We present spatially resolved Raman images of the G and 2D lines of single-layer graphene flakes. The spatial fluctuations of G and 2D lines are correlated and are thus shown to be affiliated with local doping domains. We investigate the position of the 2D line-the most significant Raman peak to identify single-layer graphene-as a function of charging up to vertical bar n vertical bar approximate to 4x10(12) cm(-2). Contrary to the G line which exhibits a strong and symmetric stiffening with respect to electron and hole doping, the 2D line shows a weak and slightly asymmetric stiffening for low doping. Additionally, the linewidth of the 2D line is, in contrast to the G line, doping independent making this quantity a reliable measure for identifying single-layer graphene. (C) 2007 American Institute of Physics. [less ▲]

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