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The optoelectronic properties of hexagonal boron-nitride and boron-nitride nanotubes (BNNTs) are investigated by using photoconductivity experiments, associated to photoluminescence excitation analysis. By this way, excitations related to the conduction band of hexagonal boron-nitride have been experimentally determined, as well as the free excitonic level. Multiwalled boron-nitride nanotubes have also been lead by using these methods and the first results suggest some hypotheses about the band gap energy and the nature of the various absorptions, which occur under an UV excitation. These experimental results are presented and discussed and some perspectives are finally suggested.

In this paper we report the fabrication and characterization of single wall carbon nanotube film based devices. Carbon nanotubes (CNT) film is deposited on a silica substrate and usual clean room processes have been used to make Pt-electrodes on top of it and to pattern the CNT film. The obtained devices have been used to measure the evolution of the temperature coefficient of resistance (TCR) as a function of temperature. At room temperature the TCR is –0.2%K-1 and becomes even more important as the temperature goes down. Moreover the optical response in atmospheric band II and band III have been investigated at room temperature showing a variation of the device resistance up to 0.2% for an irradiance of ∼100 mW/cm2 in the 3–5 µm range. Such results are very promising for application of CNT films in bolometers for thermal infrared detection (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Optical properties of multiwall boron nitride nanotubes are investigated by means of luminescence and absorption spectroscopies. Cathodoluminescence imaging shows that boron nitride nanotubes are highly UV luminescent materials and that the luminescence is located all along the nanotube. In comparison with the related bulk material, hexagonal boron nitride, luminescence and absorption experiments point out the role of excitonic effects in this nanoobject.

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.

In situ measurements were executed in the continuous wave CO 2 -laser vaporization synthesis of single-walled carbon nanotubes (SWCNTs). The results were compared with the findings of the ex situ analysis of the product. Different catalysts (Co, Ni, Co/Ni, Ni/Y and Co/Y) were used and the temperature of the target surface (T s ) changed to compare the efficiency of the synthesis process. Our main results are related to the SWCNTs diameter which is depending on T, and on the catalysts nature. The targets containing Y with Co or Ni atoms produce more and larger SWCNTs than Co/Ni targets. The SWCNTs' diameter is seen to increase with T s .

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 (∼1 mbar). An optical diagnosticstrategy is demonstrated from these first in situ observations during BNNTs synthesis.

The general expressions for rotationally resolved CARS transitions involving molecular electronic states of arbitrary electronic angular momentum and spin are derived. All possible types of resonances (triple, double, Raman) are considered and the explicit results are presented for Hund's coupling cases (a) and (b) and intermediate (a–b) coupling. The results given are applicable to arbitrary incident laser polarizations. Calculations of practical interest are performed for three diatomics, namely OH, C2 and CH, for the triple resonance. Complete sets of closed formulae are tabulated for Hund's cases (a) and (b) for 3Π ← 3Π and 2Σ ← 2Π type transitions. With minor modifications, these expressions are also applicable to resonant degenerate four wave mixing.

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.

M. G. Silly,1,2 P. Jaffrennou,1,2,4 J. Barjon,3 J.-S. Lauret,4 F. Ducastelle,1,* A. Loiseau,1 E. Obraztsova,5 B. Attal-Tretout,2 and E. Rosencher2 1Laboratoire d’Etude des Microstructures, ONERA-CNRS, Boite Postale 72, 92322 Châtillon Cedex, France 2Departement de Mesures Physiques, ONERA, Chemin de la Huniere, 91761 Palaiseau Cedex, France 3Groupe d’Etude de la Matiere Condensee, Universite de Versailles St. Quentin, CNRS Bellevue, 1 place Aristide Briand, 92195 Meudon Cedex, France 4Laboratoire de Photonique Quantique et Moleculaire, Institut d’Alembert, Ecole Normale Superieure de Cachan, 61 Avenue du President Wilson, 94235 Cachan Cedex, France 5A. M. Prokhorov General Physics Institute of Russian Academy of Sciences, 38 Vavilov Street, 119991 Moscow, Russia Received 27 July 2006; revised manuscript received 21 December 2006; published 12 February 2007

Optical transitions in single-wall boron nitride nanotubes are investigated by means of optical absorption spectroscopy. Three absorption lines are observed. Two of them (at 4.45 and 5.5 eV) result from the quantification involved by the rolling up of the hexagonal boron nitride (h-BN) sheet. The nature of these lines is discussed, and two interpretations are proposed. A comparison with single-wall carbon nanotubes leads one to interpret these lines as transitions between pairs of van Hove singularities in the one-dimensional density of states of boron nitride single-wall nanotubes. But the confinement energy due to the rolling up of the h-BN sheet cannot explain a gap width of the boron nitride nanotubes below the h-BN gap. The low energy line is then attributed to the existence of a Frenkel exciton with a binding energy in the 1 eV range.