J.-J. Pireaux

Gold clusters on oxygen plasma functionalized carbon nanotubes: XPS and TEM studies

Oxygen plasma treated multi-walled carbon nanotubes (MWCNTs) have been decorated with gold nanoclusters by thermal evaporation. Transmission electron microscopy (TEM) shows that the nature and extent of gold coverage can be varied by simultaneously changing the parameters used for the plasma treatment and the gold evaporation time. The evaporated gold clusters on oxygen plasma treated MWCNTs have a more dense distribution than the clusters evaporated on as-synthesized MWCNTs. Analyses of the valence band and the core levels by x-ray photoelectron spectroscopy (XPS) suggest poor charge transfer between the gold clusters and the MWCNTs.

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).

Influence of the doping method on the sensitivity of Pt-doped screen-printed SnO2 sensors

Abstract In this work, we study the influence of the introduction method of Pt atoms on the sensitivity to traces of ethanol of Pt-doped SnO2 sensors. The tin oxide films were obtained by a screen-printing process. Two different methods were employed to introduce Pt atoms on SnO2 films. In the first one, the Pt atoms were added to the screen-printed tin oxide layer by using RF magnetron sputtering and a subsequent thermal treatment. The second method consisted of mixing SnO2 and Pt pastes before the screen-printing process. The different active layers (including un-doped tin oxide) were carefully examined relative to their sensitivity to ethanol at different working temperatures. Sensors prepared by the second method showed sensitivity to ethanol four times higher than one of the sensors prepared by the first method and 12 times higher than un-doped sensors. XPS and scanning electron microscopy (SEM) measurements showed that this behaviour could be associated with the spatial distribution of the doping elements within the tin oxide film. While in Pt-sputtered sensors most of the Pt atoms were found at the surface of the active layer, for the sensors made by mixing Pt and SnO2 pastes, a homogeneous distribution of the Pt atoms was observed. These sensors show high sensitivity and fast response time to ethanol vapours, with a detection limit in the ppb range.

Scanning transmission x-ray microscopy of isolated multiwall carbon nanotubes

Scanning transmission x-ray microscopy (STXM) has been used to study isolated carbon nanotubes for the first time. STXM and transmission electron microscopy were applied to the same type of nanotubes, providing unique information about their composition, and electronic and structural properties. The carbon 1s near-edge x-ray absorption fine structure spectra show significant differences between multiwall carbon nanotube and carbon nanoparticle contaminants. Pristine and acid treated multiwall carbon nanotubes were also compared, highlighting the potential of the technique to differentiate surface functional groups at the nanoscale.

Ag induced modifications on WO3 films studied by AFM, Raman and x-ray photoelectron spectroscopy

In this paper, the morphology, vibrational spectra and electronic properties of WO3 films loaded with different levels of Ag, prepared by screen printing onto Si substrates and annealed in air at 600°C were investigated. AFM micrography showed that the films are grain-like, and the grain size increases with an increase in the Ag loading level. Raman spectroscopy results showed the formation of a AgWO3 bronze structure that results in a more stable film. X-ray photoelectron spectroscopy results showed that the Ag concentration is 1.8 times higher than the nominal concentration indicating that Ag diffuses to the WO3 grain surface. No strong electronic interaction between the Ag clusters and the WO3 grains was found. Sensors fabricated with the WO3 : Ag films exhibited a significant increase in their sensitivity and selectivity towards NO2 detection.

Highly Selective NO2 Gas Sensors Made of MWCNTs and WO3 Hybrid Layers

Hybrid gas sensors were fabricated by means of multiwalled carbon nanotubes (MWCNTs) covered by W O3 deposited by an advanced reactive gas deposition method. In order to increase the dispersion of ...

Structural defects and epitaxial rotation of C60 and C70(111) films on GeS(001)

A transmission electron microscopy study of epitaxial C60 and C70 films grown on a GeS (001) surface is presented. The relationship between the orientation of the substrate and the films and structural defects in the films, such as grain boundaries, unknown in bulk C60 and C70 crystals, are studied. Small misalignments of the overlayers with respect to the orientation of the substrate, so‐called epitaxial rotations, exist mainly in C70 films, but also sporadically in the C60 overlayers. A simple symmetry model, previously used to predict the rotation of hexagonal overlayers on hexagonal substrates, is numerically tested and applied to the present situation. Some qualitative conclusions concerning the substrate‐film interaction are deduced.

New TiO2 and Carbon Nanotube Hybrid Microsensors for Detecting Traces of O2 in Beverage Grade CO2

We report on the development, fabrication and testing of an oxygen microsensor conceived for detecting traces of oxygen in beverage grade carbon dioxide. The microsensor is based on a titanium oxide and carbon nanotube hybrid gas sensitive layer obtained by a modified sol-gel process. The hybrid films show a high responsiveness towards traces of oxygen (~ 6) when operated at moderate temperatures (350degC). This sensitivity compares very favourably to the one shown by similar microsensors based on titanium oxide with no carbon nanotubes.

Gas sensing using CNT-doped WO/sub 3/

WO/sub 3/, multiwall carbon nanotubes (MWNT) and WO/sub 3/+MWNT were employed as sensitive materials for gas sensors. Morphological studies of the fabricated films were performed by scanning electron microscopy. Gas sensing properties were investigated for NO/sub 2/, CO and NH/sub 3/ at ambient temperature. It is shown that all these gases can be detected at room temperature.

Thick film sensor for heavy metals detection

This work covers an area of electrochemical detection of heavy metals that are dissolved in water solutions. This perspective and ecological way of heavy metals detection could be achieved using our prepared thick film sensor with suitable material of working electrode. This sensor should ensure reproducible and reliable detection of heavy metals with sufficient limit of detection. Various graphite materials for sensors working electrodes were prepared, screen-printed, measured and compared with a classical graphite electrode and thick film gold electrode, in this work.