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ABSTRACT: We exfoliate graphite in both aqueous and non-aqueous environments through mild sonication followed by centrifugation. The dispersions are enriched with monolayers. We mix them with polymers, followed by slow evaporation to produce optical quality composites. Nonlinear optical measurements show ∼5% saturable absorption. The composites are then integrated into fiber laser cavities to generate 630 fs pulses at 1.56 µm. This shows the viability of solution phase processing for graphene based photonic devices.
physica status solidi (b) 09/2010; 247(11‐12):2953 - 2957. · 1.32 Impact Factor
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ABSTRACT: One dimensional nanostructures such as organic and inorganic nanotubes, nanowires and graphene have generated much excitement among materials scientists in recent years. However difficulties associated with their lack of processability have seriously hampered the number of possible applications. Poor dispersability in most common solvents and tendency to bundle forming larger aggregates has been a hurdle in the way of real exploitation. The recent development of techniques able to disperse and exfoliate these 1D objects have captured much attention, strongly re-launching these materials towards the applicative scene. It is mandatory to understand at what extent these techniques are efficient and whether the atomic structures of these nanomaterials are damaged or remain pristine after dispersion and exfoliation in liquid media. Aberration-corrected electron microscopy becomes in this context a very attractive and unique tool to investigate these structures at atomic scale.
Journal of Physics Conference Series 08/2010; 241(1):012100.
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O. M. Marago,
F. Bonaccorso,
R. Saija,
G. Privitera,
P. G. Gucciardi,
M. A. Iati,
G. Calogero,
P. H. Jones,
F. Borghese,
P. Denti, V. Nicolosi,
A. C. Ferrari
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ABSTRACT: We study the Brownian motion (BM) of optically trapped graphene flakes. These
orient orthogonal to the light polarization, due to the optical constants
anisotropy. We explain the flake dynamics, measure force and torque constants
and derive a full electromagnetic theory of optical trapping. The understanding
of two dimensional BM paves the way to light-controlled manipulation and
all-optical sorting of biological membranes and anisotropic macromolecules.
06/2010;
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ABSTRACT: We have demonstrated a method to disperse and exfoliate graphite to give graphene suspended in water-surfactant solutions. Optical characterisation of these suspensions allowed the partial optimisation of the dispersion process. Transmission electron microscopy showed the dispersed phase to consist of small graphitic flakes. More than 40% of these flakes had <5 layers with ~3% of flakes consisting of monolayers. These flakes are stabilised against reaggregation by Coulomb repulsion due to the adsorbed surfactant. However, the larger flakes tend to sediment out over ~6 weeks, leaving only small flakes dispersed. It is possible to form thin films by vacuum filtration of these dispersions. Raman and IR spectroscopic analysis of these films suggests the flakes to be largely free of defects and oxides. The deposited films are reasonably conductive and are semi-transparent. Further improvements may result in the development of cheap transparent conductors.
10/2008;
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Y. Hernandez, V. Nicolosi,
M. Lotya,
F. Blighe,
Z Sun,
S. De,
I. T. McGovern,
B. Holland,
M. Byrne,
Y. Gunko,
J. Boland,
P. Niraj,
G. Duesberg,
S. Krishnamurti,
R. Goodhue,
J. Hutchison,
V. Scardaci,
A. C. Ferrari,
J. N. Coleman
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ABSTRACT: Graphene is at the centre of nanotechnology research. In order to fully exploit its outstanding properties, a mass production method is necessary. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to ~0.01 mg/ml by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This occurs because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energy matches that of graphene. We confirm the presence of individual graphene sheets with yields of up to 12% by mass, using absorption spectroscopy, transmission electron microscopy and electron diffraction. The absence of defects or oxides is confirmed by X-ray photoelectron, infra-red and Raman spectroscopies. We can produce conductive, semi-transparent films and conductive composites. Solution processing of graphene opens up a whole range of potential large-scale applications from device or sensor fabrication to liquid phase chemistry.
05/2008;
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ABSTRACT: Stable dispersions of single-walled carbon nanotubes in deionized water were prepared using six common surfactants: sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl sulfate (SDS), lithium dodecyl sulfate (LDS), tetradecyl trimethyl ammonium bromide (TTAB), sodium cholate (SC), and Fairy liquid (FL). For all nanotube dispersions (C-NT = 1 mg/mL), the optimum concentration of surfactant was found to be close to C-Surf = 10 mg/mL by measuring the fraction of nanotubes remaining after centrifugation for a range of surfactant concentrations. The aggregation state of each nanotube-surfactant dispersion was characterized as a function of nanotube concentration by AFM analysis of large numbers of nanotubes/bundles deposited onto substrates. The dispersion quality could then be quantified by four parameters: the saturation value (at low concentration) of the root-mean-square bundle diameter, the maximum value of the total number of dispersed objects (individuals and bundles) per unit volume of dispersion, the saturation value (at low concentration) of the number fraction of individual nanotubes, and the maximum value of the number of individual nanotubes per unit volume of dispersion. According to these metrics, the dispersion quality of the six surfactant-nanotube dispersions varied as SDS > LDS > SDBS > TTAB > SC > Fairy liquid. It was found that each of these dispersion-quality metrics scaled very well with the measured zeta-potential of the surfactant-nanotube dispersion. This confirms that dispersion quality is controlled by the magnitude of electrostatic repulsive forces between coated nanotubes.
Journal of Physical Chemistry C. 01/2008; 112(29):10692-10699.
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ABSTRACT: We have demonstrated debundling of molydenym-sulphur-iodine nanowires simply
by diluting nanowire dispersions in isopropanol. Using
atomic-force-microscopy we observe the bundle diameter distribution to
decrease dramatically with concentration. Detailed analysis of the data
suggests the presence of an equilibrium bundle number density. The
population of individual nanowires increases with decreasing concentration
until almost half of all dispersed objects are individual nanowires at a
concentration of 4 × 10−3 mg/ml. The partial concentration of
individual nanowires peaks at a concentration of ~7 × 10−3 mg/ml. This debundling also occurs spontaneously without the input of sonic
energy, suggesting thermodynamic solubility. The absorbance of the nanowire
dispersions, measured in the visible region increases linearly with
concentration indicating a concentration independent absorption coefficient.
However, for the infra-red feature that has been associated with band edge
transitions, the absorption coefficient increases with increasing
concentration for both stoichiometries. This suggests that this transition
may be quenched by the inter-nanowire interactions associated with bundling.
Finally, nanowire re-aggregation can be induced by the addition of small
quantities of non-solvents.
The European Physical Journal Applied Physics 01/2007; 37(02):149 - 159. · 0.77 Impact Factor
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ABSTRACT: Molybdenum chalcogenide nanowires have potential applications in some of the same areas as carbon nanotubes but are, as yet, not as well understood structurally. Previous investigations to determine atomic structure using x-ray diffraction and high-resolution transmission electron microscopy have been inconclusive. Images obtained using an annular darkfield detector in an aberration corrected scanning transmission electron microscope have provided an additional means of structure determination. Simulations of the electron scattering within the sample were performed by including thermal diffuse scattering into a multislice routine. Such simulations allow insight into the location of certain atomic species and the nature of the packing into bundles of the wires. It is also shown that for structure refinement, a simple object function approach is sufficient, rather than a full dynamical calculation.
Journal of Physics Conference Series 02/2006; 26(1):280.
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ABSTRACT: In this work, we have demonstrated debundling of Molydenum-sulphur-iodine nanowires simply by diluting dispersions of nanowires in isopropanol. Using atomic force microscopy, we observe the bundle diameter distribution to decrease dramatically as a function of concentration. In addition, a significant population of individual nanowires is present at all concentrations. This population increases with decreasing concentration until one quarter of all dispersed objects are individual nanowires at a concentration of 4 x 10(-3) Mg/ml. The partial concentration of individual nanowires also increases with decreasing concentration but actually peaks at a concentration of similar to 4x 10(-3) mg/ml. This represents an optimum concentration for finding individual nanowires. (c) 2006 Elsevier B.V. All rights reserved.
CHEMICAL PHYSICS LETTERS. 425(1-3):89-93.
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T Hasan,
Z Sun,
D Popa,
E J R Kelleher,
F Bonaccorso,
E Flahaut,
F Torrisi,
O Trushkevych,
G Privitera, V Nicolosi,
J R Taylor,
A C Ferrari
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ABSTRACT: Materials with nonlinear optical properties are much sought after for ultrafast photonic applications. Mode-locked lasers can generate ultrafast pulses using saturable absorbers[1]. Currently, the dominant technology is based on semiconductor saturable absorber mirrors (SESAMs). However, narrow tuning range (tens of nm), complex fabrication and packaging limit their applications[2]. Single wall nanotubes (SWNTs) and graphene offer simpler and cost-effective solutions[1]. Broadband operation can be achieved in SWNTs using a distribution of tube diameters[1,3], or by using graphene[4-8], due to the gapless linear dispersion of Dirac electrons[8,9]. © 2011 IEEE.
2011 Conference on Lasers and Electro-Optics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011;
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ABSTRACT: Applications of single-wall carbon nanotubes (SAINT) are severely restricted, as they exist in rope-like bundles. Many methods have been suggested to de-bundle SWNTs, including both covalent and noncovalent funtionalisation with surfactants, acids, polymers and macromolecules. However, these strategies are unsatisfactory because they result in either the chemical modification of the nanotube or the presence of residual dispersion agents. What is required is the demonstration of stable, exfoliated SWNT dispersions in common solvents. In. this work we have demonstrated debundling of single-wall nanotubes by diluting nanotubes dispersions in the solvent N-methyl-2-pyrrolidinone (NMP). Atomic-force-microscopy measurements show a steady decrease in bundle diameter distribution as the concentration is decreased. Photoluminescence and Raman spectroscopy confirmed the presence of individual nanotubes in NMP dispersion.
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS. 243(13):3058-3062.
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ABSTRACT: We have demonstrated debundling of molydenym-sulphur-iodine nanowires simply by diluting nanowire dispersions in isopropanol. Using atomic-force-microscopy we observe the bundle diameter distribution to decrease dramatically with concentration. Detailed analysis of the data suggests the presence of an equilibrium bundle number density. The population of individual nanowires increases with decreasing concentration until almost half of all dispersed objects are individual nanowires at a concentration of $4\times 10^{-3}$ mg/ml. The partial concentration of individual nanowires peaks at a concentration of $\sim $$7\times 10^{-3}$ mg/ml. This debundling also occurs spontaneously without the input of sonic energy, suggesting thermodynamic solubility. The absorbance of the nanowire dispersions, measured in the visible region increases linearly with concentration indicating a concentration independent absorption coefficient. However, for the infra-red feature that has been associated with band edge transitions, the absorption coefficient increases with increasing concentration for both stoichiometries. This suggests that this transition may be quenched by the inter-nanowire interactions associated with bundling. Finally, nanowire re-aggregation can be induced by the addition of small quantities of non-solvents.
http://dx.doi.org/10.1051/epjap:2007029.
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ABSTRACT: The processing of one-dimensional nanomaterials, such as carbon-nanotubes, is generally hampered by the fact that they are insoluble. By conducting sedimentation experiments on Mo6S4.5I4.5 nanowires in isopropanol we show that a significant portion (approximate to12wt%) of the as-produced material is soluble as small diameter nanowire bundles. Using this technique, as a purification procedure, high purity Mo6S4.5I4.5 nanowire dispersions can be produced with concentrations as high as 0.34 mg/ml. (C) 2004 Elsevier B.V. All rights reserved.
CHEMICAL PHYSICS LETTERS. 401(1-3):13-18.
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ABSTRACT: Homogenous composite films were fabricated from a polymer doped with Mo6S4.5I4.5 nanowires. Alternating current and direct current electrical testing revealed percolative behavior characterized by an extremely low percolation threshold, p(c) = 1.3 x 10(-5) and a maximum conductivity of 4 x 10(-3) S/m. The low value of the percolation threshold can be explained by debundling of the nanowires at low concentration during sample preparation. This results in a homogenous dispersion of individual nanowires at low loading level. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
SCRIPTA MATERIALIA. 54(3):417-420.
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ABSTRACT: We have demonstrated debundling of molydenym-sulphur-iodine nanowires simply by diluting nanowire dispersions in isopropanol. Using atomic-force-microscopy we observe the bundle diameter distribution to decrease dramatically with concentration. Detailed analysis of the data suggests the presence of an equilibrium bundle number density. The population of individual nanowires increases with decreasing concentration until almost half of all dispersed objects are individual nanowires at a concentration of 4 x 10(-3) mg/ml. The partial concentration of individual nanowires peaks at a concentration of similar to 7 x 10(-3) mg/ml. This debundling also occurs spontaneously without the input of sonic energy, suggesting thermodynamic solubility. The absorbance of the nanowire dispersions, measured in the visible region increases linearly with concentration indicating a concentration independent absorption coefficient. However, for the infra-red feature that has been associated with band edge transitions, the absorption coefficient increases with increasing concentration for both stoichiometries. This suggests that this transition may be quenched by the inter-nanowire interactions associated with bundling. Finally, nanowire re-aggregation can be induced by the addition of small quantities of non-solvents.
EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS. 37(2):149-159.
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ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY. 227(Part 1):184-IEC.
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ABSTRACT: Optical reflectivity and absorbance measurements of oriented Mo6S3I6 nanowire thin films and dispersions in different solvents are presented extending from the far infrared to the ultraviolet. In spite of the highly one-dimensional character of the nanowire material and narrow electronic valence and conduction subbands, as predicted by the density-functional theory calculations, sharp Van Hove features in the optical absorption spectra are not observed, partly because of the large density of interpenetrating electron subbands and partly due to damping and disorder. The optically measured electrical conductivity extrapolated to zero frequency σ1(ω→0) and the calculated conductivity are significantly higher than the typical dc value from resistance measurements, indicating that disorder limits electron transport, a feature characteristic of strongly one-dimensional systems.
Phys. Rev. B. 76(7).
