Jérôme Guillot

Carbon nanotubes randomly decorated with gold clusters: from nano2hybrid atomic structures to gas sensing prototypes.

Carbon nanotube surfaces, activated and randomly decorated with metal nanoclusters, have been studied in uniquely combined theoretical and experimental approaches as prototypes for molecular recognition. The key concept is to shape metallic clusters that donate or accept a fractional charge upon adsorption of a target molecule, and modify the electron transport in the nanotube. The present work focuses on a simple system, carbon nanotubes with gold clusters. The nature of the gold-nanotube interaction is studied using first-principles techniques. The numerical simulations predict the binding and diffusion energies of gold atoms at the tube surface, including realistic atomic models for defects potentially present at the nanotube surface. The atomic structure of the gold nanoclusters and their effect on the intrinsic electronic quantum transport properties of the nanotube are also predicted. Experimentally, multi-wall CNTs are decorated with gold clusters using (1) vacuum evaporation, after activation with an RF oxygen plasma and (2) colloid solution injected into an RF atmospheric plasma; the hybrid systems are accurately characterized using XPS and TEM techniques. The response of gas sensors based on these nano(2)hybrids is quantified for the detection of toxic species like NO(2), CO, C(2)H(5)OH and C(2)H(4).

Carbon nanotubes decorated with gold, platinum and rhodium clusters by injection of colloidal solutions into the post-discharge of an RF atmospheric plasma

In this paper, we present a new, simple, robust and efficient technique to decorate multi-wall carbon nanotubes (MWCNT) with metal nanoparticles. As case studies, Au, Pt and Rh nanoparticles are grafted onto MWCNTs by spraying a colloidal solution into the post-discharge of an atmospheric argon or argon/oxygen RF plasma. The method that we introduce here is different from those usually described in the literature, since the treatment is operated at atmospheric pressure, allowing the realization in only one step of the surface activation and the deposition processes. We demonstrate experimentally that the addition of oxygen gas in the plasma increases significantly the amount of grafted metal nanoparticles. Moreover, TEM pictures clearly show that the grafted nanoparticles are well controlled in size.

Elaboration of a wide range of TiO2 micro/nanostructures by high power impulse inverted cylindrical magnetron sputtering

An inverted cylindrical magnetron sputtering reactor mode was used for TiO2 thin films deposition. The high voltage was delivered to the target in dc mode and in pulsed mode at low frequency (250?Hz) to reach high power impulse magnetron sputtering (HiPIMS) regimes and obtain subsequent higher plasma ionization rates. Time-resolved electrical and optical characterizations of the discharge were performed and the layers chemistry, morphology and microstructure were characterized using x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis. In accordance to the conclusions described in the literature for TiO2 HiPIMS deposition in planar configuration, it is shown that the increase of peak target current (induced by the decrease of the duty cycle at constant average power) leads to smoothening and densification of the layers. The microstructure of the coatings is also strongly influenced by the energy and the flux of the incoming species to the substrate. XRD experiments show that passing from dc to HiPIMS mode leads to a transition from anatase to rutile formation, but HRTEM analyses allows one to highlight that the proportion of amorphous domains is also increased when increasing the energy delivered to the growing film. It results in the obtaining of layers with globular structure composed of rutile nano-crystallites embedded in an amorphous matrix.

LiFePO4 Cathode Nanocomposite with PPy/PEG Conductive Network

The polypyrrole-LiFePO4 composites were synthesized by simple chemical oxidative polymerization of pyrrole (Py) monomer directly on the surface of LiFePO4 particles. Properties of resulting polypyrrole-LiFePO4 (PPy-LiFePO4) samples (especially conductivity) are strongly affected by the preparation technique, polymer additives and conditions during synthesis. The polyethylene glycol (PEG) as additive during polymerization was used to increase the PPy-LiFePO4 conductivity. The electrochemical behaviour of samples was examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and the chemical stability was evaluated using X-ray photoelectron spectrometry (XPS). It was found that PPy-PEG composite polymer decrease particle to particle contact resistance. Impedance measurements showed that the coating of PPy-PEG significantly decreases the charge transfer resistance of LiFePO4 electrodes. Addition of polyethylene glycol (PEG) during PPy polymerisation leads to enhanced electronic conductivities.