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Applied Physics Letters 03/2013; · 3.84 Impact Factor
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ABSTRACT: The presence of hexagonal boron nitride in the initial C:BN:Ni:Y 2 O 3 mixture in the arc-discharge process leads to the modification of carbon nanostructures and to the creation of B x C y N z entities. BN-incorporation into these carbon nanostructures (single-wall nano-tubes and carbon flakes) has been analyzed by high resolution transmission electron micros-copy and electron energy loss spectroscopy. The optical absorption spectroscopy measurements have revealed a monotonous increase of the bandgap value of the synthe-sized nanotubes with the increase of the content of BN phase in the initial mixture of the syn-thesis compounds. Furthermore, a narrowing of the nanotube diameter distribution in favor of small diameters takes place in the presence of BN during the synthesis process.
Carbon 01/2012; 50:791-799. · 5.38 Impact Factor
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L. Museur,
G. Brasse,
A. Pierret,
S. Maine,
B. Attal-Tretout,
F. Ducastelle, A. Loiseau,
J. Barjon,
K. Watanabe,
T. Taniguchi,
A. Kanaev
physica status solidi (RRL) - Rapid Research Letters 05/2011; 5(5‐6):214 - 216. · 2.22 Impact Factor
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H. Lin,
J. Lagoute,
V. Repain,
C. Chacon,
Y. Girard,
F. Ducastelle,
H. Amara, A. Loiseau,
P. Hermet,
L. Henrard,
S. Rousset
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ABSTRACT: Carbon nanotubes have attracted considerable interest for their unique electronic properties. They are fascinating candidates for fundamental studies of one dimensional materials as well as for future molecular electronics applications. The molecular orbitals of nanotubes are of particular importance as they govern the transport properties and the chemical reactivity of the system. Here, we show for the first time a complete experimental investigation of molecular orbitals of single wall carbon nanotubes using atomically resolved scanning tunneling spectroscopy. Local conductance measurements show spectacular carbon-carbon bond asymmetry at the Van Hove singularities for both semiconducting and metallic tubes, demonstrating the symmetry breaking of molecular orbitals in nanotubes. Whatever the tube, only two types of complementary orbitals are alternatively observed. An analytical tight-binding model describing the interference patterns of π orbitals confirmed by ab initio calculations, perfectly reproduces the experimental results.
Phys. Rev. B. 06/2010; 81(23).
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ABSTRACT: Single-walled carbon nanotubes provide an ideal system for studying the properties of one-dimensional (1D) materials, where strong electron-electron interactions are expected. Optical measurements have recently reported the existence of excitons in semiconducting nanotubes, revealing the importance of many-body effects. Surprisingly, pioneering electronic structure calculations and scanning tunnelling spectroscopy (STS) experiments report the same gap values as optical experiments. Here, an experimental STS study of the bandgap of single-walled semiconducting nanotubes, demonstrates a continuous transition from the gap reduced by the screening resulting from the metal substrate to the intrinsic gap dominated by many-body interactions. These results provide a deeper knowledge of many-body interactions in these 1D systems and a better understanding of their electronic properties, which is a prerequisite for any application of nanotubes in the ultimate device miniaturization for molecular electronics, or spintronics.
Nature Material 03/2010; 9(3):235-8. · 32.84 Impact Factor
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ABSTRACT: The boron nitride nanotubes (BNNTs) synthesis, using CO2-laser vaporization of a BN target under nitrogen gas, is investigated by UV-laser induced fluorescence (LIF) of the vapor phase and UV-Rayleigh scattering (RS) of the gas-suspended nanoparticles. The LIF signal from B atoms is mainly detected in the 1.5 mm-thick region above the BN target. It originates from a boron-rich vapor region confined near the hot boron droplet formed at the target surface. Then, recombination between hot boron and N2 gas occurs through a fast condensation process as revealed by both the depletion of B atoms from the vapor phase and the RS signal arising from the grown BN nanoparticles. Fluorescence spectra exhibit a strong peak at 250 nm due to boron fluorescence and mainly to nanoparticles Rayleigh scattering. A narrow peak is observed at 210 nm and a broader peak at 189 nm. These bands are tentatively assigned to fluorescence or photoluminescence (PL) from gaseous or solid BN species respectively since both gas and solid phases coexist in the plume due to the rapid cooling process. Two very weak bands occur at 308 nm and 350 nm. They are related to PL of defects bands from BN nanostructures on the basis of ex situ PL spectra of h-BN crystallites and multi-wall BNNTs. Detection of oxygen impurities is shown feasible through LIF from BO radical which is detected just above the BN target evaporated under vacuum pressure (approximately 1 mbar). An optical diagnostic strategy is demonstrated from these first in situ observations during BNNTs synthesis.
Journal of Nanoscience and Nanotechnology 12/2008; 8(11):6129-40. · 1.56 Impact Factor
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H. Lin,
J. Lagoute,
C. Chacon,
R. Arenal,
O. Stéphan,
V. Repain,
Y. Girard,
S. Enouz,
L. Bresson,
S. Rousset, A. Loiseau
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ABSTRACT: Nitrogen doped single-walled carbon nanotubes (CNx-SWNTs) were successfully synthesized by vaporizing a C:Ni/Y target by a CO2 continuous laser under a nitrogen atmosphere. The as-grown nanotubes were investigated by combining TEM/EELS and STM/STS techniques. According to TEM observations, the tubes are mostly single-walled and few defects are found. Local chemical characterization was performed by EELS analysis, which proves the presence of nitrogen in both individual tubes and SWNTs bundles and indicates a nitrogen concentration around 1 at.%. STM observations of CNx-SWNTs have been then undertaken and atomic resolution images were obtained. First STM analyses of these nanotubes show some defects which have never been observed in pure carbon nanotubes before. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 09/2008; 245(10):1986 - 1989. · 1.32 Impact Factor
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P. Jaffrennou,
J. Barjon,
T. Schmid,
L. Museur,
A. Kanaev,
J.-S. Lauret,
C. Y. Zhi,
C. Tang,
Y. Bando,
D. Golberg,
B. Attal-Tretout,
F. Ducastelle, A. Loiseau
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ABSTRACT: Individual multiwall boron nitride nanotubes with diameters from 30 nm to 110 nm are shown to be efficient UV emitters by cathodoluminescence. Their luminescence does not evolve much in this diameter range, with dominant UV recombinations at about 230 nm. As a result, single nanotube properties can be obtained from experiments performed on ensembles of nanotubes. Such ensembles are studied by photoluminescence as a function of temperature (5 K-300 K) and by photoluminescence excitation experiments at 9 K. The results are discussed and compared with the related bulk material, hexagonal boron nitride. The strong luminescence recorded around 230 nm is attributed to excitonic effects, more precisely to excitons bound to the structural defects: dislocations, facets, which are observed along the walls.
Physical Review B 01/2008; 77:235422. · 3.69 Impact Factor
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ABSTRACT: Continuous laser vaporization of a BN target under N2 atmosphere is up to now the unique route to single-walled boron nitride nanotubes (BN-SWNTs). Although grams of product can be obtained by this technique, the raw material contains in addition to the BN-SWNTs, different by-products made of boron and nitrogen. Since these materials are undesirable for the studying of the intrinsic properties of the nanotubes, we have undertaken a purification process using chemical and physical methods to separate the different components. We show here that most impurities can be removed by successive cycles of washing, sonication, and centrifugation. Furthermore, the two different types of boron nitride nanostructures i.e., BN-SWNTs and BN-cages can be isolated. Efficiency of the separation was monitored by transmission electron microscopy (TEM) at the different steps of the process. Finally, we envisage the further purification of the nanotubes-enriched fraction by functionalizing the nanotubes in a non covalent manner by specific polymers as for carbon nanotubes and BN multi-walled nanotubes.
Journal of Nanoscience and Nanotechnology 11/2007; 7(10):3528-32. · 1.56 Impact Factor
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ABSTRACT: Combined spatially resolved electron-energy loss spectroscopy (EELS) and high resolution near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have been used to investigate the nitrogen doping of multi-walled carbon nanotubes (N-MWNT). EELS indicates that most of the tubes are nitrogen-doped. NEXAFS spectroscopy reveals pyridine-like and nitrile N structures. High resolution NEXAFS experiments show that the main nitrogen concentration originates from a high amount of molecular N2 encapsulated into only a small quantity of tubes.
Journal of Nanoscience and Nanotechnology 11/2007; 7(10):3524-7. · 1.56 Impact Factor
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ABSTRACT: Boron nitride nanotubes nucleation on the catalyst's surface after the formation of metal particle alloys oversaturated with boron and nitrogen atoms is the most important step for any type of the catalytic pro-cesses of BN nanotubes formation. A thermodynamic analysis of the boron-nitride nanotubes nucleation on the catalysts surface was performed. The master equations for the dependence of critical size of BN nucleus on reaction parameters, such as reaction temperature, supersaturation degree of catalyst particles with B and N, work of adhesion of catalyst to BN were obtained. These equations combined with the phase diagram approach can be used for the description of different scenarios of BN deposits formation and for the development of the main principles of catalysts design for BN nanotube production. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 10/2007; 244(11):4165 - 4169. · 1.32 Impact Factor
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Chemical Physics Letters 01/2007; 442:372. · 2.34 Impact Factor
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Journal of Applied Physics 01/2007; 102:116102. · 2.17 Impact Factor
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Physical Review B 01/2007; 75:085205. · 3.69 Impact Factor
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Fullerenes Nanotubes and Carbon Nanostructures 01/2007; Nanotubes(and Carbon Nanostructures):257-266. · 0.77 Impact Factor
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ABSTRACT: The temperature-induced changes in Raman spectra of two BN-based materials: a hexagonal boron nitride and soot with single-wall BN nanotubes, have been measured in temperature range 77–600 K in course of heating in the oven/cryostat cell. A nonlinear temperature dependence of the tangential Raman mode position (being at 1366 cm–1 at room temperature) has been observed for both materials. In the temperature range 350–600 K a linear approximation of the tangential Raman mode shifting was applicable. The measured rates were –0.014 cm–1/K (for h-BN) and –0.027 cm–1/K (for the nanotube-containing sample). The effects of the oven and laser heating have been compared. Under the laser heating with the same power density the nanotube-containing soot demonstrated much bigger shifts (up to 30 cm–1) than h-BN. The data obtained are useful for in-situ diagnostics of different BN-based phases in course of synthesis. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 10/2006; 243(13):3316 - 3319. · 1.32 Impact Factor
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ABSTRACT: We report on the direct synthesis of different kinds of BN–C multi-walled and single-walled nanotubes exhibiting a segregation between BN and C domains. Multi-walled BN–C nanotubes (MW-BN/C-NTs) were synthesized using the aerosol method whereas single-walled BN–C nanotubes (SW-BN/C-NTs) have been for the first time produced using a continuous CO2-laser vaporization process [S. Enouz et al., to be published]. Degrees of purity, homogeneity and yield have been estimated from a systematic inspection of the samples by scanning electron microscopy. Structure of these tubes and spatial distribution of C, B and N as well as their chemical environments have been inspected at the nanometer scale by combining high resolution transmission microscopy and nano-electron energy loss spectroscopy. These analyses provide clear evidence of new kinds of arrangements of C, B and N within the graphene layer, which are due to the segregation properties of h-BN and graphite. Thus, combining BN and C elements into nanotubular systems can open the way to a broad range of new nanodevices. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (b) 10/2006; 243(13):3246 - 3251. · 1.32 Impact Factor
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ABSTRACT: Single-wall boron nitride nanotubes samples synthesized by laser vaporization of a hexagonal BN target under a nitrogen atmosphere are studied by UV and visible Raman spectroscopy. We show that resonant conditions are necessary for investigating phonon modes of BNNTs. Raman excitation in the UV (229 nm) provides preresonant conditions, allowing the identification of the A1 tangential mode at 1370 cm(-1). This is 5 cm(-1) higher than the E(2g) mode in bulk h-BN. Ab initio calculations show that the lower frequency of bulk h-BN with respect to large diameter nanotubes and the single sheet of h-BN is related to a softening of the sp2 bonds in the bulk due to interlayer interaction.
Nano Letters 09/2006; 6(8):1812-6. · 13.20 Impact Factor
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Microscopy and Microanalysis 07/2006; 12:578 - 579. · 3.01 Impact Factor
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Microscopy and Microanalysis 07/2006; 12:1166 - 1167. · 3.01 Impact Factor
