Eric Irissou

Influence of the expansion dynamics of laser-produced gold plasmas on thin film structure grown in various atmospheres

The expansion dynamics of plasma produced by excimer laser ablation of a gold target was measured by means of spatially resolved real time emission spectroscopy. The emission line of the Au(I) neutral gold species at 267.65 nm was used to monitor the expansion dynamics of the plasma in several background gases (He, N2, O2, and Ar). The measurements were performed as a function of the gas pressure (from 4×10−5 to 4 Torr) and target-to-substrate distance (from 1.5 to 11 cm). Gold thin films were prepared in the same conditions and their structure was analyzed by x-ray diffraction. All films prepared fall into one of three categories: highly (111) oriented, mixed, or polycrystalline. All the films prepared herein show a transition from highly (111) oriented to mixed and then to polycrystalline as the velocity of the Au(I) neutral gold species decreases. In the case of inert background gases (He, N2, and Ar), the velocity at which the transition between the various types of structure occurs is remarkably cons...

Influence of an inert background gas on bimetallic cross-beam pulsed laser deposition

A cross-beam pulsed laser deposition (CBPLD) system operated at variable pressure in an inert (He) background atmosphere was used to deposit films from two dissimilar targets (Pt–Ru and Pt–Au). Using this setup, we showed that films with mixed Pt–Au and Pt–Ru composition can be prepared over the whole compositional range, from [Pt] = 0 to 100at.%. Films deposited at He pressure higher than 1.6Torr are fairly homogeneous and the standard deviation of the Pt concentration over the whole area of the deposit is less than 1at.%. Using a diaphragm located at the interaction zone between the two plasmas, a drastic reduction of the normalized droplet density was observed, from about 700×102cm−2nm−1 in conventional PLD to 6×102cm−2nm−1 in CBPLD. The deposition rate increases as the pressure is increased from vacuum to an optimal He pressure. The deposition rate decreases again for higher He pressure. The optimal operating conditions are P(He)=2Torr for Pt–Ru and P(He)=4Torr for Pt–Au. In these conditions, the depo...

Correlation between plasma expansion dynamics and gold-thin film structure during pulsed-laser deposition

Pulsed-laser deposition of Au thin films has been achieved by ablating a gold target with a KrF excimer Laser in various conditions of ambient Ar gas pressure (from 10−5 to 4 Torr) and target-to-substrate distance (from 1.0 to 11 cm). The dynamics of the plasma plume were measured in the same conditions. Highly oriented Au (111) thin films are obtained for pressure-distance deposition conditions such that the neutral Au species have a typical velocity larger than 2u2002kmu200as−1, while a polycrystalline powder is obtained when the typical velocity is smaller than 0.8u2002kmu200as−1.

Influence of pressure on the Pt nanoparticle growth modes during pulsed laser ablation

Pulsed laser deposition of a platinum target was performed in solution and in a He background gas atmosphere at pressures ranging from 10−5 to 11 Torr. The influence of the plasma dynamics on the structural properties of the nanostructured Pt films was investigated by time-of-flight and space-resolved emission spectroscopy (velocity measurements). It is shown that two different growth modes exist. In the first, formation of nanoparticle is occurring in the surrounding media (gas or solution), while in the second one, diffusion and reorganization of atomic species at the substrate surface is favored. In a gaseous environment, the transition between both modes is occurring at He pressure of ∼0.5u2002Torr, which corresponds to a velocity of ∼5.8×103u2002mu2009s−1.Pulsed laser deposition of a platinum target was performed in solution and in a He background gas atmosphere at pressures ranging from 10−5 to 11 Torr. The influence of the plasma dynamics on the structural properties of the nanostructured Pt films was investigated by time-of-flight and space-resolved emission spectroscopy (velocity measurements). It is shown that two different growth modes exist. In the first, formation of nanoparticle is occurring in the surrounding media (gas or solution), while in the second one, diffusion and reorganization of atomic species at the substrate surface is favored. In a gaseous environment, the transition between both modes is occurring at He pressure of ∼0.5u2002Torr, which corresponds to a velocity of ∼5.8×103u2002mu2009s−1.

Hydrogen absorption in thermally prepared RuO2 electrode

Electrochemical in situ X-ray diffraction measurements were performed in 1 N H 2 SO 4 electrolyte on a thermally prepared RuO 2 thin layer deposited on a Ti substrate. As evidenced by a shift of the characteristic diffraction peaks of RuO 2 , a volume increase of the tetragonal unit cell occurs when the electrode is polarized in the potential region where hydrogen evolution occurs. These changes in the lattice parameter are thought to occur as a result of hydrogen absorption in the oxide layer. These modifications are not totally reversible, as the positions of the diffraction peaks of the used electrode do not coincide with that of pristine material.

Comparative study of nanocrystalline Ti2RuFe and Ti2RuFeO2 electrocatalysts for hydrogen evolution in long-term chlorate electrolysis conditions

Ti2RuFe and Ti2RuFeO2 nanocrystalline alloys were prepared by high energy ball-milling and used as cathodes for the hydrogen evolution reaction (HER) in the process of sodium chlorate synthesis. Ti2RuFe is almost single phase with the B2 structure. In contrast, Ti2RuFeO2 is made of a mixture of Ti2RuFe and TiOx phases. Tests in chlorate electrolysis conditions did not show any sign of degradation of Ti2RuFeO2 over a 300 h period, while Ti2RuFe breaks down after less than 100 h. The degradation of Ti2RuFe occurs because of hydrogen absorption and desorption during alternating hydrogen discharge and open-circuit conditions. Various hypotheses to explain the increase stability of the O containing alloy are considered.

Plasma-sprayed nanocrystalline Ti-Ru-Fe-O coatings for the electrocatalysis of hydrogen evolution reaction

Abstract Nanocrystalline Ti–Ru–Fe–O (2-1-1-2) was prepared by mechanical alloying in a ZOZ attritor. Vacuum plasma spray (VPS) was then used to deposit coatings of this material on a substrate. Energy dispersive X-ray fluorescence and X-ray diffraction analysis was used to follow the change in the chemical composition and crystalline structure of the powder upon deposition by VPS. Nanocrystalline Ti–Ru–Fe–O (2-1-1-2) prepared by the ZOZ attritor contains more than 50 wt.% of hexagonal Fe 2 Ti and a smaller amount ( 2 Ti and Ru results in the formation of several cubic phases with lattice parameters ranging from 2.96 to 3.02 A. This reflects a change in the Ru content on the 1 a ( 1 2 , 1 2 , 1 2 ) site of the cubic lattice. The deposition process also results in the formation of Ti 2 O 3 . This phase is present in excess at the surface of the coating but can be efficiently dissolved through etching in an acid solution. The cathodic overpotential for hydrogen evolution of such activated coatings in typical chlorate electrolysis conditions is η 250 =−550 mV.

Laser-Assisted Cold Spray (LACS)

Resume du livre : nDiscovered almost fifty years ago at Bell Labs (1964), the Nd:YAG laser has undergone an enormous evolution in the years, being now widely used in both basic research and technological applications. Nd:YAG Laser covers a wide range of topics, from new systems (diode pumping, short pulse generation) and components (a new semiorganic nonlinear crystal) to applications in material processing (coating, welding, polishing, drilling, processing of metallic thin films), medicine (treatment, drug administration) and other various fields (semiconductor nanotechnology, plasma spectroscopy, laser induced breakdown spectroscopy).