Doable resonant Raman scattering in graphite

Institut fur Festkorperphysik, Technische Universitat Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany.
Physical Review Letters (Impact Factor: 7.73). 01/2001; 85(24):5214-7. DOI: 10.1103/PhysRevLett.85.5214
Source: PubMed

ABSTRACT We find that the electronic dispersion in graphite gives rise to double resonant Raman scattering for excitation energies up to 5 eV. As we show, the curious excitation-energy dependence of the graphite D mode is due to this double resonant process resolving a long-standing problem in the literature and invalidating recent attempts to explain this phenomenon. Our calculation for the D-mode frequency shift ( 60 cm(-1)/eV) agrees well with the experimental value.

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    ABSTRACT: Graphene is one of the most promising candidates to build future electronic devices. Its peculiar electronic properties derive from its atomic structure and are characterized by a two-dimensional electron gas at macroscopic scale and molecular states at the nanometer scale. This thesis work aims at patterning graphene monolayer over this entire range of length scales to produce arbitrarily shaped graphene nanoribbons (GNR) continuously connected to graphene pads. The three main objec- tives consist in (i) producing, contacting and patterning graphene monolayer down to features size of about 10 nm for a ribbon length of several hundreds of nanometers, (ii) integrating all steps while minimizing contamination to ultimately reach UHV-compatible samples and (iii) etching GNRs while preserving the high crystallinity of graphene and minimizing its amorphization. The first part will focus on the characterization of the graphene monolayer itself by ambient AFM topography and Raman spectroscopy. We show that these techniques suffer from a poor reproducibility of the height measurement and a limited sensitivity to low defect density. However, the source of AFM instabilities is identified as the presence of a water meniscus. Stable operating conditions are found and yield reproducible height measurements. In order to enhance the Raman signal of defects in graphene, we investigate the intensity evolution near crystalline gold nanorods placed close to graphene edges. The second part describes in detail how GNR can be etched directly in graphene using a low energy (1-20 keV) electron beam in the presence of water vapor. We show that electron beam induced etching (EBIE) can produce < 20 nm-wide GNRs with length of hundreds of nanometers or micrometer-long trenches to isolate the GNR form the graphene sheet. A particu- lar attention is paid to the characterization of the structural quality of the GNR edges. A spherical aberration corrected TEM analysis demonstrates that the graphene lattice is intact at less than 2 nm from the EBIE-cut edges. The last part is dedicated to the application of our promising EBIE method to the fabrication of contacted GNR electronic field-effect devices. We show that graphene devices supported on silica are significantly amorphized by backscattered elec- trons. A new design of devices made of locally suspended graphene is proposed and makes it possible to produce GNRs (typically 30x200 nm) connected to electrodes on a back-gated substrate. This work opens the way to electrical transport measurements of GNR and, beyond, GNR-based complex structures and constitutes the first step towards an integrated atomic technology of molecular graphene devices.
    12/2012, Degree: PhD, Supervisor: Dujardin Erik


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