Publications

Calcium phosphate compounds have been studied for biomedical applications due to chemical and structural similarity to the mineral phase of bone and tooth. The composition, physico-chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparative conditions and sometimes it resulted into non-stoichiometric calcium deficient hydroxyapatite (HAp) powders. The present paper refers to calcinations of hydroxyapatite ceramics at 600, 800 and 1000 degrees C. The effect of heat treatment was previously investigated by X-ray diffraction (XRD). The ultrasonic characterisation of hydroxyapatite powders were performed using the ultrasonic air-coupling technique. Modulated ultrasonic signals of 450 kHz central frequency have been transmitted through the hydroxyapatite ceramics specimens. Correlation between signals allowed to draw some conclusions concerning density, attenuation and influence of the preparation temperature influence on these samples. These comparisons and correlation of methods, allow a better characterization of such important materials.

A THz Time Domain Spectroscopy experimental set-up was built for studying the biomolecules absorption spectra in the THz range and obtaining information on their collective motions. Details on the set-up calibration and performances are presented, together with the used noise and artefacts reduction data processing techniques. Preliminary results on the absorbance spectrum of the solvated Bovine Serum Albumin (BSA) for different water concentration are given.

Two multiphoton absorption processes were revealed in a perylenediimide derivative, at the wavelength of 1064 nm, by using the thermal lens technique. One of the observed multiphoton processes is two photon absorption (TPA) while the second is a four photons process. The value of the measured TPA coefficient is beta = 0.12 x 10(-19) cm W-1.

Poly(styrene-hydroxyethyl methacrylate) [P(ST-HEMA)] latex particles were prepared by surfactant-free emulsion copolymerization. As water-soluble initiator was used potassium persulfate (KPS). The influence of different reactions parameters, such as the reaction temperature, the both monomers (ST and HEMA) concentrations and the KPS concentration on the particles average diameter and particles size dispersion was investigated. Generally monodisperse spherical particles are synthesized, but we also obtained stable large three-dimensional colloidal aggregates. These are formed by the agglomeration of monodispersed spheres in certain polymerization conditions. The P(ST-HEMA) monodispersed spheres with 350 nm average diameter were assembled into colloidal crystals using dip-coating technique. Colloidal crystals with different thickness were obtained by modifying two experimental factors, the colloidal concentration and the substrate lifting speed. The morphologies of copolymer latex particles and colloidal crystals were observed using scanning electron microscopy (SEM). The optical properties of colloidal crystals films were also investigated by transmission spectroscopy.

We investigate the scattering phenomena in two dimensions produced by a general finite-range nonseparable potential. This situation can appear either in a Cartesian geometry or in a heterostructure with cylindrical symmetry. Increasing the dimensionality of the scattering problem, new processes as the scattering between conducting channels and the scattering from conducting to evanescent channels are allowed. For certain values of the energy called resonance energy, the transmission through the scattering region changes dramatically in comparison with an one-dimensional problem. If the potential has an attractive character, even the evanescent channels can be seen as dips of the total transmission. The multi-channel current scattering matrix is determined using its representation in terms of the R-matrix. The resonant transmission peaks are characterized quantitatively through the poles of the current scattering matrix. Detailed maps of the localization probability density sustain the physical interpretation of the resonances. Our formalism is applied to a quantum dot in a two-dimensional electron gas and to a conical quantum dot embedded inside a cylindrical nanowire.

Thin films with nominal composition Fe(78)Si(9)B(13) generated by radio-frequency (rf) sputtering on Si substrates with (100) orientation were irradiated with an eyeliner laser with 130mJ/cm(2) fluence. Information on the induced structural changes were obtained by X-ray diffraction and scanning electron microscopy, while the magnetization curves were determined by the magneto-optical Kerr effect. The effects of the irradiation consist in the growing of crystallites,appearence of melted and ultra-fast frozen zones, surface oxidation and changes in the magnetic properties of the thin films.

The aims of this study are to clarify the effect of different fast sintering techniques on densification behavior, microstructure and mechanical properties of a ZTA type composite obtained with 15 % vol. (Ca-Mg)-ZrO2 nanosized zirconia dispersed in 85% vol. Al2O3 matrix. Three kind of heat consolidation techniques were applied respectively on coprecipitated nanosized alumina-zirconia powders by: 1) conventional sintering; 2) microwaves field sintering at 2.45 GHz and 3) external pulsed electrical field (Spark Plasma Sintering), making possible very high heating rates. Microwave sintering of ceramics can offer certain advantages over conventional firing methods, including fast firing times and improved properties. Heat generated by the interaction of microwaves with the ceramic material results in volumetric heating of the ceramic, thus high heating rates is possible. On the other hand, a newly developed rapid sintering method, the Spark Plasma Sintering (SPS) which involves the application of electrical field and an external pressure is currently used to consolidate ceramic, metal and composite powders. SPSed high density zirconia toughened alumina (ZTA) ceramics show excellent mechanical strengths. Microstructural coarsening within ZTA is found to produce a fracture toughness increment, mainly associated with the effect of zirconia particles phase transformability. The obtained mechanical properties and grain growth kinetics are discussed in terms of microstructural features. The effects of heating technique on the far infrared and Raman spectra were investigated. Additional bands development was observed on spectra as the crystal symmetry is lowered, and certain of these bands are highly sensitive to strain-induced distortions of the crystal lattice.

Vanadium-cerium oxide gels and films obtained by the sot-gel method have been widely studied, due to their catalytic, electrochemical, electronic and ionic properties, a result of their ability to form combinations in more than one valence state. V-Ce oxide powders were synthesized by wet chemical methods, in the presence and absence of polyols. The preparation of an aqueous dispersion of mixed vanadium oxide/CeO2 started from a solution of the corresponding metal oxide and metal salt, V2O5 and Ce(NH4)(NO3)(6), respectively. The powders were characterized by IR-spectroscopy, X-ray photoelectronic spectroscopy, X-ray diffraction, electronic microscopy (TEM, SAED, HRTEM). The influence of the ratio of the components (V/Ce) and of the polyol complexation agent on the structure and morphology of the obtained binary oxide powders was established.

Two-dimensional photonic structure has been imprinted on the surface of arsenic sulphide glass using the pulses of a femtosecond laser. Due to the interaction of the laser beam with the glass, the laser traces were obtained as hillocks of around 150-200 nanometer in height, or holes of depth around 100-300 nm, without the need for a later etching stage as in the usual practice. The calculation of the band structure shows a photonic band gap between 0.9 and 1.0 c/a. By varying the energy of the laser pulse we have the possibility to choose between the two possibilities to produce a photonic structure made-up of hillocks or a photonic structure consisting of holes. The value of the threshold pulse power which controls the resulting surface morphology and the obtained photonic structure has found to be around 15 mW. The surface topography of the structures obtained has been investigated by atomic force microscopy (AFM).

The surface characterization of 304L stainless steel for orthopedic implant applications, unmodified and modified with poly (vinyl) alcohol (PVA) in physiological serum (PS) is discussed according to electrochemical measurements, Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM / EDS) and X-ray Photoelectron Spectroscopy (XPS) techniques. The results obtained through polarization curves indicate that PVA reduces anodic dissolution and also decrease of the corrosion current (i(corr)); decrease of the corrosion current (i(corr)) was associated with a shift of corrosion potential (E-corr) to a less negative values; the polarization resistance(R-p) increases for the surfaces which were treated in physiological serum in the presence of PVA. SEM / EDS and XPS analysis showed that the surface layer which was formed on 304L stainless steel consists of PVA containing of small amount of other elements, such as: Na and Cl.