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Raman imaging of graphene ; ; 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 ▲] Detailed reference viewed: 56 (1 UL)On the visibility of electron--electron interaction effects in field emission spectra Schmidt, Thomas ; in Solid State Communications (2005), 135 One of the most convenient methods to obtain information about the energy distribution function of electrons in conducting materials is the measurement of the energy resolved current $j(\omega)$ in field ... [more ▼] One of the most convenient methods to obtain information about the energy distribution function of electrons in conducting materials is the measurement of the energy resolved current $j(\omega)$ in field emission (FE) experiments. Its high energy tail $j_>(\omega)$ (above the Fermi edge) contains invaluable information about the nature of the electron--electron interactions inside the emitter. Thus far, $j_>(\omega)$ has been calculated to second order in the tunnelling probability, and it turns out to be divergent toward the Fermi edge for a wide variety of emitters. The extraction of the correlation properties from real experiments can potentially be obscured by the eventually more divergent contributions of higher orders as well as by thermal smearing around $E_F$. We present an analysis of both factors and make predictions for the energy window where only the second order tunnelling events dominate the behaviour of $j_>(\omega)$. We apply our results to the FE from Luttinger liquids and single-wall carbon nanotubes. [less ▲] Detailed reference viewed: 78 (1 UL)The phonon dispersion of graphite revisited Wirtz, Ludger ; in Solid State Communications (2004), 131(3-4), 141-152 We review calculations and measurements of the phonon dispersion relation of graphite. First-principles calculations using density-functional theory are generally in good agreement with the experimental ... [more ▼] We review calculations and measurements of the phonon dispersion relation of graphite. First-principles calculations using density-functional theory are generally in good agreement with the experimental data since the long-range character of the dynamical matrix is properly taken into account. Calculations with a plane-wave basis demonstrate that for the in-plane optical modes, the generalized-gradient approximation (GGA) yields frequencies lower by 2% than the local-density approximation (LDA) and is thus in better agreement with experiment. The long-range character of the dynamical matrix limits the validity of force-constant approaches that take only interaction with few neighboring atoms into account. However, by fitting the force-constants to the ab initio dispersion relation, we show that the popular 4th-nearest-neighbor force-constant approach yields an excellent fit for the low frequency modes and a moderately good fit (with a maximum deviation of 6%) for the high-frequency modes. If, in addition, the non-diagonal force-constant for the second-nearest neighbor interaction is taken into account, all the qualitative features of the high-frequency dispersion can be reproduced and the maximum deviation reduces to 4%. We present the new parameters as a reliable basis for empirical model calculations of phonons in graphitic nanostructures, in particular carbon nanotubes. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲] Detailed reference viewed: 84 (0 UL)Evidence for low temperature phase transition in Rb2ZnCl4 from dielectric constant and birefringence measurements ; Sanctuary, Roland ; et al in Solid State Communications (1981), 37(11), 883-888 Temperature dependences of the dielectric constants [epsilon]i and of the birefringences [Delta]ni for light propagation directions along all the three crystallographic axes (i = a, b, c) have been ... [more ▼] Temperature dependences of the dielectric constants [epsilon]i and of the birefringences [Delta]ni for light propagation directions along all the three crystallographic axes (i = a, b, c) have been measured between 5 and 350 K. The optical measurements clearly reveal a new phase transition at TL = 75 K, below which the crystal structure is transformed from the ferroelectric Pna21 phase into an unknown low temperature phase, possibly the monoclinic space group P1121. Small peaks in the dielectric constants [epsilon]a and [epsilon]b have been observed at this transition temperature. [less ▲] Detailed reference viewed: 141 (0 UL) |
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