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ABSTRACT: The ultimate surface exposure provided by graphene monolayer makes it the
ideal sensor platform but also exposes its intrinsic properties to any
environmental perturbations. In this work, we demonstrate that the charge
carrier density of graphene exfoliated on a SiO$_2$/Si substrate can be finely
and reversibly tuned between electron and hole doping with visible photons.
This photo-induced doping happens under moderate laser power conditions but is
significantly affected by the substrate cleaning method. In particular, it is
found to require hydrophilic substrates and to vanish in suspended graphene.
These findings suggest that optically gated graphene devices operating with a
sub-second time scale can be envisioned but also that Raman spectroscopy is not
always as non-invasive as generally assumed.
04/2013;
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ABSTRACT: We report in situ Raman scattering experiments on single layer graphene (SLG) and Bernal bilayer graphene (BLG) during exposure to rubidium vapor. The G and 2D bands evolutions with doping time are presented and analyzed. On SLG, the extended doping range scanned (up to about 1014 electrons/cm²) allows the observation of 3 regimes in the evolution of the G-band frequency: a continuous upshift followed by a plateau and a downshift. Overall the measured evolution is interpreted as the signature of the competition between dynamic and adiabatic effects upon n-doping. Comparison of the obtained results with theoretical predictions indicates however that a substrate pinning effect occurs and inhibits charge-induced lattice expansion of SLG. At low doping, a direct link between electrostatic gating and Rb doping results is presented. For BLG, the added electrons are shown to be first confined in the top layer, but the system evolves with time towards a more symmetric repartition of the added electrons in both layers. The results obtained on BLG also confirm that the slope of the phonon dispersion close to the K point tend to be slightly reduced at low doping but suggest the occurrence of an unexpected increase of the phonon dispersion slope at higher electron concentration.
ACS Nano 11/2012; · 10.77 Impact Factor
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ABSTRACT: In this article, we report the synthesis of ultra-long carbon nanotubes (CNTs) by thermal chemical vapour deposition method. Ultra-long, individual and aligned CNTs were directly grown on a flat silicon substrate. The orientation of the nanotubes was found parallel to the gas flow direction. The ultra-long CNTs were grown with different transition metallic salts, such as nickel chloride, iron (III) chloride, cobalt acetate and ruthenium acetate, as the catalysts. The influence of the growth conditions, such as growth temperature, reactive gas flow on the length and alignment of the CNTs was studied in detail. By using different catalysts, ultra-long single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) were successfully grown. These ultra-long CNTs were transferred to other substrates by two methods. (1) The first method is to use polydimethylsiloxane as a stamp. (2) The second method is to use KOH as an etching agent. The diameter and length of the CNTs were characterised by transmission electron microscope, scanning electron microscope, atomic force microscope and Raman spectroscopy. The results indicate that the length of the CNTs can reach up to 4 mm. The diameter of the SWCNTs is in the range of 0.7–2.1 nm and the diameter of the MWCNTs is approximately 150 nm.
Journal of Experimental Nanoscience 10/2011; 6(5):547-556. · 1.01 Impact Factor
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ABSTRACT: We review the main information that we have obtained from combined Raman spectroscopy and electron diffraction experiments on individual free-standing single-walled carbon nanotubes. This information concerns: the radial breathing mode vs diameter relationship; the dependence of the frequency and lineshape of the G-modes in semiconducting and metallic tubes; the evaluation of the optical transition energies for individual free-standing SWNTs. From these data, we can define Raman criteria allowing the indexing of carbon nanotubes from their Raman features only. We show the efficiency of this approach to assign the (n,m) indices of individual chiral and achiral single-walled carbon nanotubes. These criteria are also applied to identify tubes grown on a substrate from a single wavelength Raman experiments. These results obtained on index-identified individual nanotubes are compared with theoretical predictions
physica status solidi (b) 08/2010; · 1.32 Impact Factor
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ABSTRACT: We demonstrate the use of sequential catalytic growth to encapsulate iron, nickel-iron, and iron-cobalt phosphide catalyst nanoparticles periodically along the entire lengths of carbon nanotubes. Investigations by local electron spectroscopies and electron diffraction reveal the compositions and crystal structures of the encapsulated particles. Significantly, high spatial resolution magnetic characterization using magnetic force microscopy and off-axis electron holography demonstrates that encapsulated iron-cobalt phosphide nanoparticles are ferromagnetic at room temperature, in accordance with the properties of bulk metal phosphides of the same structure and composition.
The Journal of Physical Chemistry B 06/2006; 110(20):9759-63. · 3.70 Impact Factor
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ABSTRACT: We present a detailed electron diffraction study of individual single-walled carbon nanotubes. A novel sample preparation procedure provides well-separated, long and straight individual single-shell nanotubes. Diffraction experiments are carried out at 60 kV, below the threshold for knock-on damage in carbon nanotubes. We describe experimental parameters that allow single-tube electron diffraction experiments with widely available thermal emission transmission electron microscopes. Further, we review the simulation of diffraction patterns for these objects.
Ultramicroscopy 03/2006; 106(3):176-90. · 2.47 Impact Factor
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ABSTRACT: Raman spectra of two isolated single-walled carbon nanotubes with close diameters but different chiral angles are presented
and discussed.
12/2005: pages 121-122;
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ABSTRACT: Using electron diffraction on freestanding single-walled carbon nanotubes, we have determined the structural indices (n,m) of tubes in the diameter range from 1.4 to 3 nm. On the same freestanding tubes, we have recorded Raman spectra of the tangential modes and the radial breathing mode. For the smaller diameters (1.4-1.7 nm), these measurements confirm previously established radial breathing mode frequency versus diameter relations and would be consistent with the theoretically predicted proportionality to the inverse diameter. However, for extending the relation to larger diameters, either a yet unexplained environmental constant has to be assumed, or the linear relation has to be abandoned.
Physical Review Letters 12/2005; 95(21):217401. · 7.37 Impact Factor
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ABSTRACT: We have built a torsional pendulum based on an individual single-walled carbon nanotube, which is used as a torsional spring and mechanical support for the moving part. The moving part can be rotated by an electric field, resulting in large but fully elastic torsional deformations of the nanotube. As a result of the extremely small restoring force associated with the torsional deformation of a single molecule, unusually large oscillations are excited by the thermal energy of the pendulum. By diffraction analysis, we are able to determine the handedness of the molecule in our device. Mechanical devices with molecular-scale components are potential building blocks for nanoelectromechanical systems and may also serve as sensors or actuators.
Science 10/2005; 309(5740):1539-41. · 31.20 Impact Factor
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ABSTRACT: Using electron diffraction on free-standing single-walled carbon nanotubes we have determined the structural indices (n,m) of tubes in the diameter range from 1.4 to 3nm. On the same free-standing tubes we have recorded Raman spectra of the tangential modes and the radial breathing mode. For the smaller diameters (1.4-1.7nm) these measurements confirm previously established radial breathing mode frequency versus diameter relations, and would be consistent with the theoretically predicted proportionality to the inverse diameter. However, for extending the relation to larger diameters, either a yet unexplained environmental constant has to be assumed, or the linear relation has to be abandoned.
07/2005;
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ABSTRACT: Sequential catalytic growth provides an efficient tool for the synthesis of carbon nanotubes periodically inserted with catalyst nanoparticles. Several synthesis parameters were found crucial in order to induce this particular growth mechanism. The presence of phosphorus is required to form metal phosphide particles active for the formation of carbon nanotubes with a matchstick morphology. The metal composition (Ni/Fe ratio) and the carbon supply have no influence on the nanofilament type but strongly affect the nanotube yield. The synthesis temperature induces important changes on both the nanofilament type and yield, which are correlated with important transformations of the catalyst layer in terms of composition, particle size, and physical state.
The Journal of Physical Chemistry B 03/2005; 109(4):1380-6. · 3.70 Impact Factor
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ABSTRACT: We present a procedure for determining independently the lattice structure and the vibrational properties of the same individual nano-object. For the example of an individual single-walled carbon nanotube we demonstrate the determination of the structural indices (n,m) of the nanotube by electron diffraction and of the frequencies of vibrational modes by micro-Raman spectroscopy. The precise and independent determination of both structure and mode frequencies allows for direct and unambiguous verification of molecular dynamical calculations and of conclusions drawn from Raman-only experiments.
02/2005;
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ABSTRACT: Discrete nickel catalyst nanoparticles (NP) have been used to grow isolated single-walled carbon nanotubes by chemical vapor deposition (CVD). Atomic force microscopy (AFM), transmission electron microscopy (TEM) and micro-Raman spectroscopy are used to characterize these as-grown, isolated nanotubes. Using a conventional setup, we are able to produce narrow diameter distribution single-walled carbon nanotubes (SWNTs) (1.45 ± 0.5 nm), showing a clear mismatch with the larger broad size distribution of the catalyst nanoparticles (4.7 ± 1.5 nm). Investigation of the growth conditions allowed us to synthesize, starting with the same catalyst materials, various carbon nanotube (CNT) samples with a wide range of characteristics. The advantages of such a versatile CVD method for the study of physical properties at the single nanotube level are illustrated by means of two prospective studies on SWNTs mechanical and vibrational properties.
10/2004;
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ABSTRACT: We report here on the catalyst features found critical in order to induce the growth of matchstick nanotubes by a sequential catalytic growth mechanism. The presence of phosphorus is required to form metal phosphide particles active for the formation of carbon nanotubes with a matchstick morphology. The metal composition does not influence the nanofilament type but strongly affect the nanotube yield. Original properties of these new periodic nanostructures are also highlighted, such as the preferential breaking at the thin nanomatch interjunctions, giving rise to individual nanomatches in suspension after ultrasonic treatment. The possibility to use this mechanism to insert carbon nanotubes with ferromagnetic nanoparticles is also reported.
MRS Proceedings. 12/2003; 858.
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Christophe Caillier,
Anthony Ayari,
Vincent Gouttenoire,
Jean-Michel Benoit,
Vincent Jourdain,
Matthieu Picher, Matthieu Paillet,
Sylvie Le Floch,
Stephen T Purcell,
Jean-Louis Sauvajol,
Alfonso San Miguel
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ABSTRACT: A transistor based on an individual multiwalled carbon nanotube is studied under high-pressure up to 1 GPa. Dramatic effects are observed, such as the lowering of the Schottky barrier at the gold-nanotube contacts, the enhancement of the intertube conductance, including a discontinuity related to a structural transition, and the decrease of the gate hysteresis of the device.
Advanced Functional Materials.
