Studying disorder in graphite-based systems by Raman spectroscopy

Pimenta, M. A.; Dresselhaus, G.; Dresselhaus, M. S.; Cançado, Luiz Gustavo; Jório, Ado; Saito, Riichiro

doi:10.1039/b613962k

Cited by 4,110 publications

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“…Raman spectroscopy is a powerful tool for analyzing carbon materials, including graphite-based systems 31 . A representative Raman spectrum with clearly resolved D and G bands at 1367 cm -1 and 1576 cm -1 is shown in Figure 1.…”

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confidence: 99%

Electrochemical Nanoprobes for Single-Cell Analysis

et al. 2014

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The measurement of key molecules in individual cells with minimal disruption to the biological milieu is the next frontier in single-cell analyses. Nanoscale devices are ideal analytical tools because of their small size and their potential for high spatial and temporal resolution recordings. Here, we report the fabrication of disk-shaped carbon nanoelectrodes whose radius can be precisely tuned within the range 5-200 nm. The functionalization of the nanoelectrode with platinum allowed the monitoring of oxygen consumption outside and inside a brain slice. Furthermore, we show that nanoelectrodes of this type can be used to impale individual cells to perform electrochemical measurements within the cell with minimal disruption to cell function. These nanoelectrodes can be fabricated combined with scanning ion conductance microcopy probes which should allow high resolution electrochemical mapping of species on or in living cells.

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Section: Resultsmentioning

confidence: 99%

Electrochemical Nanoprobes for Single-Cell Analysis

et al. 2014

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“…The 2D band in the Raman spectrum of (monolayer) graphene originates due to a 2 nd order, two-phonon, "double resonance" process, which has been analyzed extensively by various theoretical and experimental techniques 16,[39][40][41][42][43] . Briefly, in this process first an electron-hole pair is created around K valley by a laser photon.…”

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Giant Current-Perpendicular-to-Plane Magnetoresistance in Multilayer Graphene as Grown on Nickel

2014

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Strong magnetoresistance effects are often observed in ferromagnet-nonmagnet multilayers, which are exploited in state-of-the-art magnetic field sensing and data storage technologies. In this work we report a novel current-perpendicular-to-plane magnetoresistance effect in multilayer graphene as-grown on catalytic nickel surface by chemical vapor deposition. A negative magnetoresistance effect of ~10 4 % has been observed, which persists even at room temperature. This effect is correlated with the shape of the 2D peak as well as with the occurrence of D peak in the Raman spectrum of the as-grown multilayer graphene. The observed magnetoresistance is extremely high as compared to other known materials systems for similar temperature and field range, and can be qualitatively explained within the framework of "interlayer magnetoresistance" (ILMR).[Keywords: Graphene, Chemical Vapor Deposition, Raman Spectroscopy, Interlayer Magnetoresistance, Current-Perpendicular-to-Plane Transport] 2 Artificial layered structures often exhibit strong magnetoresistance (MR) effects that are exploited in various data storage and magnetic field sensing technologies 1 . Graphite is a naturally occurring layered material in which single graphitic layers (or "graphene") are stacked on each other. Graphene, epitaxially grown on ferromagnets (such as nickel), is particularly attractive for spintronics because such systems can potentially realize perfect spin filtering 2 and giant Rashba splitting 3 . However, CPP (current-perpendicular-toplane) MR properties of such layered graphene/ferromagnet structures are still largely underexplored. Here we consider multilayer-graphene (MLG) as-grown on nickel by chemical vapor deposition (CVD) and show that these structures exhibit large and nearly temperature-independent CPP-MR of ~ 10 4 % for a small magnetic field of ~ 2 kilogauss. This MR effect is correlated with the shape of the 2D peak and also with the occurrence of the D peak in Raman spectrum of as-grown MLG. These Raman features can be controlled by varying the CVD growth parameters. Such large negative CPP-MR, which persists even at room temperature, has hitherto not been reported in any graphitic system 4-14 . Figure 1a shows the device schematic. CVD growth of MLG is performed on 2 cm × 2 cm nickel (Ni) foils, which act as catalyst for graphene growth as well as bottom electrical contact. To ensure uniform current distribution 6 , the second contact is fabricated at the center of the top MLG surface using silver epoxy. Area of the top contact is ~ 1 mm 2 . As shown in Figure S1 (section I, Supplementary Information), the Ni substrate is polycrystalline with primarily (111) grains. Details of the fabrication process are provided in section I of Supplementary Information. Figure 1b shows a FESEM image of the as-grown large-area MLG on Ni. Raman spectra taken from three representative regions of this sample are shown in the top inset of Figure 1b. The top Raman spectrum (black line) is most commonly observed, with few occurren...

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“…Of the characterization techniques used for layer thickness determination, 13 ,14,15, -16,17,18, 19 Raman spectroscopy is arguably the simplest and fastest, especially for exploring monolayer EG on SiC(0001) (referred to as EG Si )and EG layer stacking on SiC(000-1) (referred to as EG c ). [15][16][17][18][19] Characterization of EG via Raman spectroscopy requires fitting the 2D Raman peak. 15,16,20 Raman spectra of EG Si fit by one or four Lorentzian functions are characteristic of monolayer or bilayer graphene, respectively.…”

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confidence: 99%

“…[15][16][17][18][19] Characterization of EG via Raman spectroscopy requires fitting the 2D Raman peak. 15,16,20 Raman spectra of EG Si fit by one or four Lorentzian functions are characteristic of monolayer or bilayer graphene, respectively.…”

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“…Equally important to layer thickness is layer-stacking, which can also be extracted from the 2D Raman spectra. 17,18,19,23 Multilayer EG C films can exhibit a 2D Raman peak characteristic of turbostratic graphite; 17 however, the layer-stacking may not be completely random. Evidence suggests a mixture of graphene layers rotated by 30° or ±2° (R30 or R2 ± ) with respect to the SiC substrate exist (typically described as R30/R2 ± fault pairs).…”

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Correlating Raman Spectral Signatures with Carrier Mobility in Epitaxial Graphene: A Guide to Achieving High Mobility on the Wafer Scale

et al. 2009

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We report a direct correlation between carrier mobility and Raman topography of epitaxial graphene (EG) grown on silicon carbide (SiC). We show the Hall mobility of material on the Si-face of SiC [SiC(0001)] is not only highly dependent on thickness uniformity but also on monolayer s st tr ra ai in n uniformity. Only when both thickness and strain are uniform over a significant fraction (> 40%) of the device active area does the mobility exceed 1000 cm 2 /V-s. Additionally, we achieve high mobility epitaxial graphene (18,100 cm 2 /V-s at room temperature) on the C-face of SiC [SiC(000-1)] and show that carrier mobility depends strongly on the graphene layer stacking. These findings provide a means to rapidly estimate carrier mobility and provide a guide to achieve very high mobility in epitaxial graphene. Our results suggest that ultra-high mobilities (>50,000 cm 2 /V-s) are achievable via the controlled formation of uniform, rotationally faulted epitaxial graphene.The recent success of graphene transistor operation in the giga-hertz range has solidified the potential of this material for high speed electronic applications. 1,2 Realization of graphene technologies at commercial scales, however, necessitates large-area graphene production, as well as the ability to rapidly characterize its structural and electronic quality. Graphene films can be produced by mechanical exfoliation from bulk graphite, 3,4 reduction of graphite-oxide, 5,6 chemical vapor deposition on catalytic films, 7 or via Si-sublimation from bulk SiC substrates. 8 9, -10,11, 12 The last technique currently appears to hold the most promise for large-area electronic grade graphene, and already shows tremendous potential for high-frequency device technologies. 2 Nevertheless, precise control of the graphene electronic properties (i.e. mobility) over large areas is necessary to enable graphene-based technological applications. Realization of such control will come through an intimate understanding of the process-propertyperformance relationship and the role that graphene thickness, strain, and layer stacking plays in this relationship over very large areas up to full wafers. Of the characterization techniques used for layer thickness determination, 13 ,14,15, -16,17,18, 19 Raman spectroscopy is arguably the simplest and fastest, especially for exploring monolayer EG on SiC(0001) (referred to as EG Si )and EG layer stacking on SiC(000-1) (referred to as EG c ). [15][16][17][18][19] Characterization of EG via Raman spectroscopy requires fitting the 2D Raman peak. 15,16,20 Raman spectra of EG Si fit by one or four Lorentzian functions are characteristic of monolayer or bilayer graphene, respectively. 15 Figure 1a demonstrates layer thickness evaluation for monolayer and bilayer EG Si via Lorentzian fitting of the 2D Raman spectra. To further validate these thickness measurements, cross-sectional transmission electron microscopy (TEM) was performed (Fig. 1b,c). The TEM micrographs in Fig.1b,c include a transition layer (Layer 0), which is in dire...

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Studying disorder in graphite-based systems by Raman spectroscopy

Cited by 4,110 publications

References 67 publications

Electrochemical Nanoprobes for Single-Cell Analysis

Electrochemical Nanoprobes for Single-Cell Analysis

Giant Current-Perpendicular-to-Plane Magnetoresistance in Multilayer Graphene as Grown on Nickel

Correlating Raman Spectral Signatures with Carrier Mobility in Epitaxial Graphene: A Guide to Achieving High Mobility on the Wafer Scale

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