Das, A. et al. Monitoring dopants by Raman scattering in an electrochemically top-gated graphene transistor. Nature Nanotech. 3, 210-215

Department of Physics, Indian Institute of Science, Bangalore 560012, India.
Nature Nanotechnology (Impact Factor: 34.05). 04/2008; 3(4):210-5. DOI: 10.1038/nnano.2008.67
Source: PubMed


The recent discovery of graphene has led to many advances in two-dimensional physics and devices. The graphene devices fabricated so far have relied on SiO(2) back gating. Electrochemical top gating is widely used for polymer transistors, and has also been successfully applied to carbon nanotubes. Here we demonstrate a top-gated graphene transistor that is able to reach doping levels of up to 5x1013 cm-2, which is much higher than those previously reported. Such high doping levels are possible because the nanometre-thick Debye layer in the solid polymer electrolyte gate provides a much higher gate capacitance than the commonly used SiO(2) back gate, which is usually about 300 nm thick. In situ Raman measurements monitor the doping. The G peak stiffens and sharpens for both electron and hole doping, but the 2D peak shows a different response to holes and electrons. The ratio of the intensities of the G and 2D peaks shows a strong dependence on doping, making it a sensitive parameter to monitor the doping.

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    • "The main Raman features of nanocarbons – the G band (≈1590cm −1 ), the G' or 2D band (≈2700cm −1 ), and the defect-induced D band, (≈1350cm −1 ) [15] are sensitive to doping. Small amounts of substitutional dopants in SWCNTs and graphene can be tracked by changes in the G and G' bands [16] [17] [18]. In bulk SWCNT samples, one generally observes two G' bands: the G' P band (P standing for pristine), which is related to undoped regions of the tubes, and the G' D band (D standing for defect or doping), which emerges near the dopant sites of the sample [16]. "
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    • "upshift of the G band frequency, (b) upshift or downshift of the 2D band frequency, for p-type or n-type doping, respectively , (c) decrease of the 2D band intensity [13] [14]. The G and 2D bands can be found in the Raman spectra of undoped suspended graphene at %1580 cm À1 and at %2680 cm À1 , at 2.41 eV, respectively [34]. "
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    • "We found that the reduced graphene oxide in Fig. 5, labelled (b) gave a similar Raman spectrum in terms of the shapes and positions of Raman peaks as can be seen in Fig. 5. These results agreed very well with that obtained by Ferrari et al. [54] and the studies by Das et al. [55]. Raman spectrum obtained from the synthesised antimony nanoparticles (labelled (a)), indicated that the main features of the wavenumber are observed at about 110; 140; 578; 624; 655; 681 and 764 cm −1 . "
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