Showing papers by "Annick Loiseau published in 2011"

Young modulus, mechanical and electrical properties of isolated individual and bundled single-walled boron nitride nanotubes.

Abstract: The Young modulus of individual single-walled boron nitride nanotubes (SW-BNNTs) was determined using a high-resolution transmission-electron microscope (HRTEM)-atomic force microscope (AFM) set-up. The Young modulus and maximum stress for these NTs were deduced from the analysis of the stress-strain curves, and discussed as a function of the considered value for the shell thickness of an SW-BNNT. The elastic properties of bundles of SW-BNNTs were also investigated. All these experiments revealed that SW-BNNTs are very flexible. Furthermore, the electrical behavior of these SW-BNNTs was also analyzed employing a scanning tunneling microscope (STM) holder integrated with the same HRTEM. I/V curves were measured on individual tubes as well as on bundles of SW-BNNTs.

Nitrogen-Doped Single-Walled Carbon Nanotube Thin Films Exhibiting Anomalous Sheet Resistances

Abstract: Nitrogen-doped single-walled carbon nanotubes (N-SWCNTs) were synthesized using a floating catalyst aerosol chemical vapor deposition method, with carbon monoxide as the carbon source, ammonia as the nitrogen source, and iron particles derived from evaporated iron as the catalyst. The material was deposited on various substrates as grown directly from the gas phase as films and subsequently characterized by Raman and optical absorption spectroscopies, sheet resistance measurements, electron microscopy, energy-loss spectroscopy, and X-ray photoelectron spectroscopy.The sheet resistance measurements revealed that the doped films had unexpectedly high resistances. This stands in contrast to the case of N-MWCNT films, where decreased resistance has been reported with N-doping. To understand this effect, we developed a resistor network model, which allowed us to disentangle the contribution of bundle−bundle contacts when combined with data on undoped films. Assuming doping does not significantly change the con...

Selective differential ammonia gas sensor based on N‐doped SWCNT films

Abstract: The sensing performance of a micro-sensor based on a thick film of nitrogen-doped single-walled carbon nanotube (SWCNTs) is compared to a pristine SWCNTs film. Transfer length method analysis is used to extract the film sheet resistance from electrical measurements and reveals that the gas sensing mechanism is mainly attributed to the charge transfer between gas molecules and SWCNTs. We demonstrate that the sensitivity to NH3 can be improved by using a sensor based N-doped SWCNTs films while the sensitivity to NO2 and water vapour is unmodified. These unique gas-sensing properties can be used to develop a new NH3-selective differential gas sensor.

Exciton and interband optical transitions in hBN single crystal

Abstract: Near band gap photoluminescence (PL) of hBN single crystal has been studied at cryogenic temperatures with synchrotron radiation excitation. The PL signal is dominated by the D-series previously assigned to excitons trapped on structural defects. A much weaker S-series of self-trapped excitons at 5.778 eV and 5.804 eV has been observed using time-window PL technique. The S-series excitation spectrum shows a strong peak at 6.02 eV, assigned to free exciton absorption. Complementary photoconductivity and PL measurements set the band gap transition energy to 6.4 eV and the Frenkel exciton binding energy larger than 380 meV.