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Jing Kong - One of the best experts on this subject based on the ideXlab platform.

  • raman spectroscopy as a tool to address individual Graphene layers in few layer Graphene
    Journal of Physical Chemistry C, 2012
    Co-Authors: Martin Kalbac, Jing Kong, Mildred S. Dresselhaus
    Abstract:

    We developed a new general approach to address individual Graphene sheets in Few-Layer Graphene by Raman spectroscopy. Our method is based on isotope labeling of individual layers during their synthesis and subsequent transfer to form multilayered Graphene. The power of the procedure is demonstrated in the analysis of the interactions of individual layers with the substrate and with the environment. In addition, we measured Raman spectra of individual Graphene layers in 3-LG during electrochemical doping. We show that they do not exhibit the same level of doping as one another and the doping level is dependent on layer position with respect to the substrate.

  • large area few layer Graphene films on arbitrary substrates by chemical vapor deposition
    Nano Letters, 2009
    Co-Authors: Alfonso Reina, Mildred S. Dresselhaus, John Ho, Daniel Nezich, Vladimir Bulovic, Jing Kong
    Abstract:

    In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area (∼cm2) films of single- to Few-Layer Graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to ∼12 Graphene layers. Single- or bilayer regions can be up to 20 μm in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications.

  • Transferring and identification of single- and Few-Layer Graphene on arbitrary substrates
    Journal of Physical Chemistry C, 2008
    Co-Authors: Alfonso Reina, Hyungbin Son, Living Jiao, Ben Fan, Zhong Fan Liu, Mildred S. Dresselhaus, Jing Kong
    Abstract:

    The transferring and identification of single- and few- layer Graphene sheets from SiO2/Si substrates to other types of substrates is presented. Features across large areas (~cm2) having single and Few-Layer Graphene flakes, obtained by the microcleaving of highly oriented pyrolytic graphite (HOPG), can be transferred reliably. This method enables the fast localization of Graphene sheets on substrates on which optical microscopy does not allow direct and fast visualization of the thin Graphene sheets. No major morphological deformations, corrugations, or defects are induced on the Graphene films when transferred to the target surface. Moreover, the differentiation between single and bilayer Graphene via the G′ (~2700 cm-1) Raman peak is demonstrated on various substrates. This approach opens up possibilities for the fabrication of Graphene devices on a substrate material other than SiO2/Si.

Mildred S. Dresselhaus - One of the best experts on this subject based on the ideXlab platform.

  • raman spectroscopy as a tool to address individual Graphene layers in few layer Graphene
    Journal of Physical Chemistry C, 2012
    Co-Authors: Martin Kalbac, Jing Kong, Mildred S. Dresselhaus
    Abstract:

    We developed a new general approach to address individual Graphene sheets in Few-Layer Graphene by Raman spectroscopy. Our method is based on isotope labeling of individual layers during their synthesis and subsequent transfer to form multilayered Graphene. The power of the procedure is demonstrated in the analysis of the interactions of individual layers with the substrate and with the environment. In addition, we measured Raman spectra of individual Graphene layers in 3-LG during electrochemical doping. We show that they do not exhibit the same level of doping as one another and the doping level is dependent on layer position with respect to the substrate.

  • large area few layer Graphene films on arbitrary substrates by chemical vapor deposition
    Nano Letters, 2009
    Co-Authors: Alfonso Reina, Mildred S. Dresselhaus, John Ho, Daniel Nezich, Vladimir Bulovic, Jing Kong
    Abstract:

    In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area (∼cm2) films of single- to Few-Layer Graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to ∼12 Graphene layers. Single- or bilayer regions can be up to 20 μm in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications.

  • Transferring and identification of single- and Few-Layer Graphene on arbitrary substrates
    Journal of Physical Chemistry C, 2008
    Co-Authors: Alfonso Reina, Hyungbin Son, Living Jiao, Ben Fan, Zhong Fan Liu, Mildred S. Dresselhaus, Jing Kong
    Abstract:

    The transferring and identification of single- and few- layer Graphene sheets from SiO2/Si substrates to other types of substrates is presented. Features across large areas (~cm2) having single and Few-Layer Graphene flakes, obtained by the microcleaving of highly oriented pyrolytic graphite (HOPG), can be transferred reliably. This method enables the fast localization of Graphene sheets on substrates on which optical microscopy does not allow direct and fast visualization of the thin Graphene sheets. No major morphological deformations, corrugations, or defects are induced on the Graphene films when transferred to the target surface. Moreover, the differentiation between single and bilayer Graphene via the G′ (~2700 cm-1) Raman peak is demonstrated on various substrates. This approach opens up possibilities for the fabrication of Graphene devices on a substrate material other than SiO2/Si.

Tony F Heinz - One of the best experts on this subject based on the ideXlab platform.

  • observation of out of plane vibrations in few layer Graphene
    arXiv: Mesoscale and Nanoscale Physics, 2012
    Co-Authors: Chun Hung Lui, Leandro M Malard, Sukhyun Kim, Gabriel Lantz, Francois E Laverge, Riichiro Saito, Tony F Heinz
    Abstract:

    We report the observation of layer breathing mode (LBM) vibrations in Few-Layer Graphene (FLG) samples of thickness from 2 to 6 layers, exhibiting both Bernal (AB) and rhombohedral (ABC) stacking order. The LBM vibrations are identified using a Raman combination band lying around 1720 cm-1. From double resonance theory, we identify the feature as the LOZO' combination mode of the out-of-plane LBM (ZO') and the in-plane longitudinal optical mode (LO). The LOZO' Raman band is found to exhibit multiple peaks, with a unique line shape for each layer thickness and stacking order. These complex line shapes of the LOZO'-mode arise both from the material-dependent selection of different phonons in the double-resonance Raman process and from the detailed structure of the different branches of LBM in FLG.

  • Imaging stacking order in Few-Layer Graphene
    Nano Letters, 2011
    Co-Authors: Chun Hung Lui, L. E. Brus, Paul V. Klimov, Zheyuan Chen, Zhiqiang Li, Tony F Heinz
    Abstract:

    Few-Layer Graphene (FLG) has been predicted to exist in various crystallographic stacking sequences, which can strongly influence the material's electronic properties. We demonstrate an accurate and efficient method to characterize stacking order in FLG using the distinctive features of the Raman 2D-mode. Raman imaging allows us to visualize directly the spatial distribution of Bernal (ABA) and rhombohedral (ABC) stacking in tri- and tetralayer Graphene. We find that 15% of exfoliated Graphene tri- and tetralayers is composed of micrometer-sized domains of rhombohedral stacking, rather than of usual Bernal stacking. These domains are stable and remain unchanged for temperatures exceeding 800 °C.

  • the evolution of electronic structure in few layer Graphene revealed by optical spectroscopy
    Proceedings of the National Academy of Sciences of the United States of America, 2010
    Co-Authors: Kin Fai Mak, Matthew Y Sfeir, J A Misewich, Tony F Heinz
    Abstract:

    The massless Dirac spectrum of electrons in single-layer Graphene has been thoroughly studied both theoretically and experimentally. Although a subject of considerable theoretical interest, experimental investigations of the richer electronic structure of Few-Layer Graphene (FLG) have been limited. Here we examine FLG Graphene crystals with Bernal stacking of layer thicknesses N = 1,2,3,...8 prepared using the mechanical exfoliation technique. For each layer thickness N, infrared conductivity measurements over the spectral range of 0.2-1.0 eV have been performed and reveal a distinctive band structure, with different conductivity peaks present below 0.5 eV and a relatively flat spectrum at higher photon energies. The principal transitions exhibit a systematic energy-scaling behavior with N. These observations are explained within a unified zone-folding scheme that generates the electronic states for all FLG materials from that of the bulk 3D graphite crystal through imposition of appropriate boundary conditions. Using the Kubo formula, we find that the complete infrared conductivity spectra for the different FLG crystals can be reproduced reasonably well within the framework a tight-binding model.

  • electronic structure of few layer Graphene experimental demonstration of strong dependence on stacking sequence
    Physical Review Letters, 2010
    Co-Authors: Jie Shan, Tony F Heinz
    Abstract:

    The electronic structure of Few-Layer Graphene (FLG) samples with crystalline order was investigated experimentally by infrared absorption spectroscopy for photon energies ranging from 0.2-1 eV. Distinct optical conductivity spectra were observed for different samples having precisely the same number of layers. The different spectra arise from the existence of two stable polytypes of FLG, namely, Bernal (AB) stacking and rhombohedral (ABC) stacking. The observed absorption features, reflecting the underlying symmetry of the two polytypes and the nature of the associated van Hone singularities, were reproduced by explicit calculations within a tight-binding model. The findings demonstrate the pronounced effect of stacking order on the electronic structure of FLG.

Min Qian - One of the best experts on this subject based on the ideXlab platform.

  • production of few layer Graphene through liquid phase pulsed laser exfoliation of highly ordered pyrolytic graphite
    Applied Surface Science, 2012
    Co-Authors: Min Qian, Y S Zhou, Tao Feng, Lan Jiang, Yongfeng Lu
    Abstract:

    Abstract Graphene suspension was obtained through liquid-phase pulsed laser exfoliation of highly ordered pyrolytic graphite (HOPG). The liquid-phase pulsed laser process leaded to the compression and expansion of HOPG surface, resulting in the exfoliation of Graphene sheets. Graphene sheets of ∼1 nm in thickness and micrometers in size were obtained. Transparent conductive Graphene films were fabricated by vacuum filtration, showing an electrical conductivity of ∼1000 S/m and an optical transparency of ∼75% at 550 nm. This study demonstrated the growth of Few-Layer Graphene by pulsed laser exfoliation of HOPG in liquid and explored its applications in transparent conductive films.

Alfonso Reina - One of the best experts on this subject based on the ideXlab platform.

  • large area few layer Graphene films on arbitrary substrates by chemical vapor deposition
    Nano Letters, 2009
    Co-Authors: Alfonso Reina, Mildred S. Dresselhaus, John Ho, Daniel Nezich, Vladimir Bulovic, Jing Kong
    Abstract:

    In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area (∼cm2) films of single- to Few-Layer Graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to ∼12 Graphene layers. Single- or bilayer regions can be up to 20 μm in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications.

  • Transferring and identification of single- and Few-Layer Graphene on arbitrary substrates
    Journal of Physical Chemistry C, 2008
    Co-Authors: Alfonso Reina, Hyungbin Son, Living Jiao, Ben Fan, Zhong Fan Liu, Mildred S. Dresselhaus, Jing Kong
    Abstract:

    The transferring and identification of single- and few- layer Graphene sheets from SiO2/Si substrates to other types of substrates is presented. Features across large areas (~cm2) having single and Few-Layer Graphene flakes, obtained by the microcleaving of highly oriented pyrolytic graphite (HOPG), can be transferred reliably. This method enables the fast localization of Graphene sheets on substrates on which optical microscopy does not allow direct and fast visualization of the thin Graphene sheets. No major morphological deformations, corrugations, or defects are induced on the Graphene films when transferred to the target surface. Moreover, the differentiation between single and bilayer Graphene via the G′ (~2700 cm-1) Raman peak is demonstrated on various substrates. This approach opens up possibilities for the fabrication of Graphene devices on a substrate material other than SiO2/Si.