Nicolas Xanthopoulos

Polymer microchips bonded by O2-plasma activation

This paper presents a fabrication of polymer microchips with homogeneous material technique due to surface treatment by plasma before sealing. UV laser photoablation was used for fast prototyping of microstructures, and oxygen plasma was used as a surface treatment for both the microfabricated substrate and the polymer cover. It was found that with an oxidative plasma treatment, successful bonding could be achieved without adhesive material between polymer sheets substantially below the glass transition temperature of the polymer. Homogeneous polyethylene terephthalate (PET) microstructures were characterized by scanning electron microscopy (SEM) and analyzed by X‐ray photoelectron spectroscopy (XPS) surface analyses after different surface treatments. The electroosmotic flow characteristics including the velocity and the stability over 20 days have been tested and compared to composite channels, in which the cover presents a polyethylene (PE) adhesive layer. Capillary zone electrophoresis in both homogeneous and composite microanalytical devices were then performed and compared in order to evaluate the separation efficiency. In preliminary experiments, a plate height of 0.6 νm has been obtained with homogenous microchannels. The surface analysis pointed out that the surface chemistry is of prime importance for the performance of microfluidic separation.

Rare earth cuprates as electrocatalysts for methanol oxidation

A series of rare earth cuprates with overall composition Ln2−xMxCu1−yMy′O4−δ (where Ln=La and Nd; M=Sr, Ca and Ba; M′=Ru and Sb: 0.0≤x≤0.4 and y=0.1) have been tested as anode electrocatalysts for methanol oxidation. The evaluation of electrode kinetic parameters was made galvanostatically. The catalyst characterization was carried out by specific conductivity measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Iodometry. These materials exhibit significant activity for methanol oxidation at higher potentials. The linear correlation between Cu(3+) content and methanol oxidation activity suggests that the active sites for adsorption of methanol is Cu(3+). The methanol oxidation onset potential depends on the ease of Cu(2+)→Cu(3+) oxidation reaction. These materials show better tolerance towards the poisoning by the intermediates of methanol oxidation compared to that of conventional noble metal electrocatalysts (supported and bulk). The lattice oxygen in these oxides could be considered as active oxygen to remove CO intermediates of methanol oxidation reaction.

Nanostructured Conducting Polyaniline Tubules as Catalyst Support for Pt Particles for Possible Fuel Cell Applications

Nanotubules of polyaniline synthesized by template method on commercial carbon cloth have been used as the catalyst support for Pt particles for electro-oxidation of methanol. The ohmic and the charge transfer resistancesof the nanotube-based electrode were considerably lower than the polyaniline electrode synthesized by the conventional route. The Pt incorporated polyaniline nanotube electrode exhibited excellent catalytic activity and stability compared to the 20 wt % Pt supported on the VulcanXC 72R carbon and Pt supported on the conventional polyaniline electrode. The electrode fabrication used in the present investigation is particularly attractive to adopt in the solid polymer electrolyte-based fuel cells, which is usually operated under methanol or hydrogen.

Conducting polymeric nanotubules as high performance methanol oxidation catalyst support

Pt nanoparticle-supported conducting nanotubules of polypyrrole prepared by a template method exhibited excellent catalytic activity and stability for the electrooxidation of methanol in comparison to Pt supported on conventionally synthesised conducting polypyrrole.

Imaging by time-of-flight secondary ion mass spectrometry of plasma patterned metal and oxide thin films

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) imaging is employed to characterize the surface of patterned noble metal (Pt) and titania (TiO2) thin films deposited on oxidized silicon wafers. ToF-SIMS is used to follow the different process steps during the thin films patterning as well as the post-processing cleaning. Both positive and negative ToF-SIMS modes reveal the presence of contaminants, due to the etching processes (Cl- Al-,(+)), but only on the etched surfaces. Elements due to the post-processing cleaning (K+, Na+, Pb+) and photoresist residues are also detected but on the entire wafer surface. The utility of these chemically well-defined titania/platinum patterns is demonstrated for the,selective adsorption of phosphonic acid derivatives. Typical fragments of phosphonic acid groups, i.e. PO2- and PO3- show their preferential adsorption on TiO2