Robert Cortes

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.

Extended X-ray absorption fine structure studies of zinc hydroxo-sulphide thin films chemically deposited from aqueous solution

Abstract Thin films of zinc hydroxo-sulphide were prepared by chemical bath deposition (CBD) in alkaline ammonia solutions containing a zinc salt, thiourea as sulphur precursor and different amine additives. The films were characterized by extended X-ray absorption fine structure (EXAFS) and infrared spectroscopy. A detailed simulation of ZnS, Zn(OH) 2 and ZnO EXAFS functions showed that the composition corresponded to zinc hydroxo-sulphide and that the ratio between the hydroxyl and sulphur concentrations depended on the bath composition.

Relationship between short-range order and ease of nucleation in Na2Ca2Si3O9, CaSiO3 and PbSiO3 glasses

Abstract A relationship between the short-range order around the modifier cations and the crystal nucleation tendency in silicate glasses is demonstrated. New extended X-ray absorption fine spectroscopy (EXAFS) results on the local structure around calcium and lead atoms were obtained and analyzed for both vitreous and crystalline samples. Three different silicate systems were studied: wollastonite (CaSiO3) and soda-lime–silica (Na2Ca2Si3O9), for which volume nucleation is easily observed and lead metasilicate (PbSiO3) for which nucleation occurs only on the sample surfaces in typical laboratory conditions. In the glasses that have a high nucleation tendency (Na2Ca2Si3O9 and CaSiO3), the local structures of these modifier cations are similar to their short-range order in the isochemical crystalline phases, whereas the local structure in the glass that presents a low nucleation tendency (PbSiO3) is quite different from that of its isochemical crystal phase.

Development of a new energy scanned (4–20 keV) ESAFS-II spectrometer at lure

The new energy scanned EXAFS spectrometer (EXAFS-II) which has been recently installed on beam line D2 at LURE (Orsay) is described in this paper. The key component of the spectrometer is a versatile monochromator operating in a vacuum of ∼10−3 Torr. It uses a vertically dispersing two separated crystal design in the (+, −) arrangement which offers an exit beam of constant offset and direction relative to the incident beam, optional sagittal focusing and order sorting. Also optional is the energy modulation provifed by a piezoelectric transducer capable of small angular oscillations of up to 1 kHz. Conventional gas filled ion chambers are used as detectors — even for fluorescence EXAFS — but each detector is incorporating a home-made, ultralow noise, fast preamplifier capable of detecting weak signals even at a high modulation frequency (1 kHz). Glitch-free spectra have been recorded over the whole energy range covered by DCI in standard operating conditions.

Electrodeposition of PbSe epitaxial films on (111) InP

Epitaxial growth of PbSe is addressed on (111) InP single crystals by electrodeposition from aqueous solutions containing Se(IV), Pb(II) and Cd(II). The structure of the deposits is studied by reflection high-energy electron diffraction and X-ray diffraction. It is shown that an epitaxial growth is only observed in the presence of cadmium in the electrolyte. The best epitaxy is obtained for an optimal 0.5 M cadmium concentration.

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.

XANES spectroscopy sensitivity to small electronic changes Case of carp azidomethemoglobin

Spin states equilibrium of hemoglobin‐iron varies with external conditions: pH, allosteric effectors, temperature. The small electronic reorganization of the iron caused by the spin state changes has been detected by X‐ray absorption near edge structure (XANES) spectroscopy at room temperature. The iron K‐edge region which is sensitive to spin state is located in 7110–7130 eV. Here are presented the 100% high spin and 100% low spin XANES spectra of carp azido ferric hemoglobin.

Epitaxial CdSe Films Chemically Deposited on InP Single Crystals Influence of the Growth Mechanism

Epitaxial growth of cadmium selenide on (111) InP single crystals is achieved by chemical bath deposition in cadmium sulfate and sodium selenosulfate solutions complexed by sodium nitrilotriacetate. Correlations are established between the growth mechanism, studied by means of a quartz crystal microbalance, and the CdSe epitaxial quality evaluated by means of x-ray diffraction and electron microscopy. It is shown that the formation of CdSe films can be described by a layer-by-layer mechanism. Correlatively the epitaxy of CdSe on InP substrates occurs when the thickness of each layer is close to one lattice unit. Epitaxial CdSe layers present a cubic blende structure with a density of twins which deDends on the growth conditions.

DNA adsorption at liquid/solid interfaces.

DNA adsorption on solid or liquid surfaces is a topic of broad fundamental and applied interest. Here, we study by X-ray reflectivity the adsorption of monodisperse double-stranded DNA molecules on a positively charged surface, obtained through chemical grafting of a homogeneous organic monomolecular layer of N-(2-aminoethyl) dodecanamide on an oxide-free monocrystalline Si(111) wafer. The adsorbed dsDNA is found to embed into the soft monolayer, which is deformed in the process. The surface coverage is very high, and this adsorbed layer is expected to display 2D nematic ordering.

XANES spectroscopy of carp hemoglobin-iron in correlation with the affinity changes of the protein for ligand

The strong variation of ligand‐binding properties with pH for carp hemoglobin is not reflected in the electronic distribution of the heme‐iron. Thus, we can suppose that hemoglobin affinity is directly controlled by the protein and not by some particular changes of the iron atom.