Michel Froment

Study of CdS Epitaxial Films Chemically Deposited from Aqueous Solutions on InP Single Crystals

Epitaxial growth of cadmium sulfide on InP single crystals is achieved by chemical bath deposition (CBD) in ammonia solutions at near room temperature. A better understanding of the correlations between the deposition parameters (temperature, bath composition) and the epitaxial quality is obtained by using electron diffraction and transmission techniques, x-ray diffraction, in combination with Raman spectroscopy. They are supplemented by electrochemical impedance and photocurrent experiments which give information on energetic structures between InP and CBD-CdS. Direct relations between the substrate properties and the growth habits of the CdS film (hexagonal vs. cubic, epitaxial vs. polycrystalline) are found.

Inhibition of lead electrocrystallization by organic additives

Abstract Lignin sulphonate and an extract of horse chestnut are added to a lead fluorosilicate electrolyte in order to improve the levelling of cathodic lead electrodeposits. By inducing a strong overpotential, these additives suppress totally the various forms of dendritic growth. The resulting smooth layers present weak fibre textures with characteristic morphologies. An original and simple method based on X-ray diffraction was developed in order to evaluate the texture quality. These levellers have different dependence on potential and rotation rate of the disk electrode. In particular, electrolyte agitation tends to increase the inhibition efficiency for one compound and to decrease it for the other. The conjoint use of the two additives ensures a good levelling, even for very thick lead electrodeposits.

Epitaxial electrodeposition of CdTe films on InP from aqueous solutions: Role of a chemically deposited CdS intermediate layer

Epitaxial (111) CdTe films have been grown on (1u20091u20091) InP single crystals by one step electrodeposition in aqueous acidic solution, at a temperature of 85u2009°C, and a growth rate of about 0.7 μm h−1. Reflexion high‐energy electron diffraction and five‐circle x‐ray diffraction techniques have been used to characterize the interface structure and epitaxial quality. The epitaxy of CdTe (fcc a=6.49 A) takes place with a direct continuation of the InP lattice (fcc a=5.87 A), with no rotation of the respective crystallographic directions. The epitaxy is markedly improved when the InP substrate is covered with a thin film (20–30 nm) of epitaxial CdS grown by chemical bath deposition which acts as an interfacial buffer layer.

Exafs from measurements of X-ray reflectivity on passivated electrodes☆

Abstract Quite recently, it has been found that X-ray absorption spectroscopy may be used as a probe for passive films. We measured the reflectivity vs. the incident energy from bulk samples and now report the preliminary results obtained from in situ measurements on passivated nickel.

Chemical bath deposition of CdSe layers from Cd(II)-selenosulfite solutions

Abstract The chemical bath deposition of CdSe layers from cadmium acetate + sodium selenosulfite solutions was studied by means of quartz crystal microbalance (QCM) experiments, combined with electron microscopy observations and energy-dispersive X-ray analysis. Nanocrystalline deposits with the cubic blende structure are obtained showing confinement effects. From mass vs. time measurements and modeling of the time derivative, it is established that the nucleation and growth process occurs via two steps: the first corresponds to an instantaneous nucleation of cylindrical nuclei, with two-dimensional growth until complete coverage of the substrate; the second consists of a three-dimensional instantaneous nucleation and growth process occurring on sites randomly distributed on the evolving surface. The addition of silicotungstic acid to the deposition bath is shown to influence the growth kinetics of the CdSe deposit. From analysis of the kinetic data, and from the transmission and scanning electron microscope images, it is suggested that the chemical deposition of CdSe occurs through the aggregation of colloids and not according to an atom-by-atom mechanism.

Selective Metal Deposition on Silicon Substrates

In order to delineate n/p junctions at (100) or cleaved Si faces, different plating processes (electroless in the dark or under illumination with photons of different energy) have been investigated. The effects of metal cation concentration, of illumination upon the formation of deposits onto n- or p-type silicon substrates, and p/n Si junctions have been studied. The role of an interfacial oxide layer has been emphasized. it is shown that platinum or palladium electroless deposition can be carried out on p-Si under ultraviolet illumination, in solutions free of HF

Role of Cadmium on Epitaxial Growth of PbSe on InP Single Crystals

Epitaxial PbSe layers were electrodeposited onto InP(111) single crystals, from solutions containing Pb 2+ and Cd 2+ ions, the latter being largely in excess. It is demonstrated that underpotential deposition of Pb and Cd takes place on InP and PbSe epitaxial electrodeposits. Cd acts by inhibiting superficial sites and is incorporated both at the InP/PbSe interface (2-4%) but also in the bulk of the PbSe layers (1%). The cadmium concentration is maintained at a low level by a chemical displacement of Cd 0 by Pb 2+ .

Epitaxial growth of electrodeposited cadmium selenide on (111) gallium arsenide

Epitaxial growth of CdSe has been achieved on (111) GaAs by electrodeposition from an aqueous electrolyte. The structure of the film corresponds to the cubic modification of CdSe. The quality of epitaxy has been investigated by reflection high-energy electron diffraction, transmission electron microscopy and X-ray diffraction techniques.

Sur l'etude potentiocinetique de la transpassivite du fer et des aciers

Resume Des methodes de mesure recentes utilisant des potentiostats electroniques permettent dimposer an potential dune electrode une loi de variation determinee en fonction du temps. Nous donnerons ici quelques resultats dune etude de la transpassivite du fer et de differents aciers effectuee avec ces methodes, la vitesse de variation de la tension pouvant etre comprise entre 10 −2 et 150 V/min. La courbe I-U est tracee en fonction de la tension a lelectrode prise comme variable independante. Dans le domaine de la transpassivite des aciers inoxydables 18-8 austeniques, on observe une chute du courant qui correspond a une diminution de la vitesse de dissolution de lalliage (passivite secondaire). Nous avons constate que lapparition de ce phenomene est liee a la teneur en carbone et, si celle-ci est suffisamment faible, a la vitesse de variation de la tension anodique. Une etude similaire effectuee sur du fer pur et sur des aciers dont la teneur en carbone est comprise entre 0,001 et 0,3 pour cent montre que le phenomene depend encore etroitement de la vitesse de variation de la tension et que, de plus, il est lie a letat de surface de lelectrode.

Photoinduced metal deposition on sprayed SnO2 films

La photodeposition de palladium ou de platine par rayonnement UV sur une couche mince doxyde detain est examinee