A tin oxide (SnO2)/arc-discharge single walled carbon nanotubes (SWNTs) hybrid material based sensor was developed for the detection of NH3 and O3 at room temperature. The gas sensitive composite thin films were prepared using sol gel and dip coating techniques, and characterized by transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Overall, the hybrid material based sensor is found to have an enhanced sensitivity as compared to pure SnO2 or pure SWNTs based sensors. An optimum annealing temperature of the composite of 300 °C was determined. The detection limit at room temperature was evaluated at 1 ppm and lower than 20 ppb for NH3 and O3, respectively. Moreover, the hybrid sensor exhibited a fast response (few minutes), a good sensitivity and a full recovery at room temperature. The sensor efficiency has also been demonstrated to strongly depend on the SWNT source used for sensor fabrication (4 different commercial sources have been tested). These results open the way towards further optimized hybrid sensors.

The temperature dependence of the Raman spectrum of a gelatine-based composite material doped with single-walled carbon nanotubes (SWNT@gelatin) is reported. A significant up-shift of the G-mode frequency is observed when the temperature is decreased from room temperature to 20~K. This frequency shift is significantly stronger than the one found for pure thermal effects. In contrast, the features of the radial breathing modes (frequencies and width) display no significant change in the same temperature range. These results are well understood by considering a uniaxial strain on the nanotube induced by the thermal expansitivity mismatch between the nanotube and the surrounding matrix.

The purification of single-walled carbon nanotube (SWCNT) samples was analysed using a multi-technique approach, with structural as well as spectroscopic probes, in order to characterize the samples and to identify important factors for improvement of SWCNT sample quality. The first dry oxidation step (air at 365 degrees C) is shown to have only a weak selectivity for the removal of the amorphous carbon or weakly organized graphitic species as well as resulting in a partial consumption of the SWCNTs. The functionalization of the SWCNTs is highly specific with formation of carboxyl, hydroxyl and carbonyl groups. On the other hand this oxidation step is highly efficient for the oxidation of the catalytic impurities (Ni, Y) which can be easily removed by subsequent acid treatment. A final high temperature treatment indicates some incomplete restoration of the quality of the SWCNT surface. (C) 2009 Elsevier Ltd. All rights reserved.

Fourier transformed infrared microreflectance spectroscopy is used to probe and compare the consequences of thermal quenching or ionic implantation on the structure of silica. A linear change in the main structural feature associated with Si-O-Si vibration with fictive temperature (T-f) is observed up to T-f = 1400 degrees C. Ionic implantation is shown to shift the frequency of the main IR Si-O-Si vibration toward much lower wavenumbers, for all deposited energies, indicating that a comparison can be drawn between fictive temperature and irradiation effects. Extrapolating the linear changes in the IR structural bands obtained as a function of T-f for the implanted samples, we show that two structural (nu(TO)) and (nu(B)) contributions are not affected by ionic implantation, as they would be by a unique very high T-f. In the case of ionic implantation, we also evidence the development of some specific structural contributions indicating a depolymerization of silica network. (C) 2009 American Institute of Physics.

The hydrolysis and condensation of a silylated derivative of ureidopyrimidinone led to nanostructured hybrid silica, such as that depicted, as clearly shown by powder XRD studies. The nanostructuring was directly related to molecular recognition through hydrogen bonding. By combining FTIR, solution and solid-state NMR spectroscopic data, the transcription of the hydrogen-bonding networks from the precursor to the final product was clearly evidenced.

We have investigated and evaluated different TEM sample preparation techniques for studying carbon single-walled nanotube (C-SWNT) nucleation and growth, issued from CVD processes when the catalyst is supported on a substrate. This kind of study requires means to observe individual and isolated tubes. It implies using synthesis conditions able to produce only a low density of tubes and to thin the substrate to electron transparency, to observe the nanotubes and the catalytic particles from which they have grown in their native state. We have tested two approaches, depending if the substrate is thinned after or before the synthesis. The low tube density requirement led us to exclude all the techniques where the substrate is thinned to electron transparency after the synthesis. We have shown, that, with this last approach, all TEM preparation techniques dramatically suffer from a lack of control of thin areas with respect to the location of the tubes, which is unknown. However we have demonstrated that the suitable approach is to perform synthesis directly on transparent substrates presenting several holes. We have tested the capabilities and the potentialities of these supports for studying the size distribution and composition of the catalytic particles, the nucleation mode, the diameter and helicity of the tubes. These results are very promising and represent an important step for performing specific nanoscale TEM analyses necessary for the study of the growth mechanism of nanotubes on substrates. (C) 2009 Elsevier B.V. All rights reserved.

New promising oligo(phenylenethienylene)s have been synthesized to realize suitable materials for improving electronic transport properties, particularly in organic field effect transistors (OFETs). Far-infrared and incoherent neutron scattering measurements have been performed to assign their phonon modes. The assignment of the main low-frequency phonon modes of these materials has been performed experimentally by using a filiation procedure. Assuming a small frequency dispersion of the high-frequency modes, the main intramolecular phonon modes of a model oligomer have been assigned by using first-principles calculations on its isolated molecule. These assignments constitute the preliminary work for a better understanding of these new promising materials in electronic and opto-electronics applications.