Publications

Chemical growth of calcium phosphate films on top of apatite structures is an essential step for promoting implants integration in human bones. We used for chemical growth silicon wafers either covered with crystalline and amorphous hydroxyapatite films or uncoated. To promote growing, the structures have been immersed in simulated body fluids for 21 days at 37degreesC. The growth stages were monitored by atomic spectroscopy of Ca and P ions in solution. The calcium phosphate deposits were investigated by X-ray diffraction, optical and atomic force microscopy and FTIR spectroscopy. The grown structures onto sputtered hydroxyapatite were amorphous and smooth. The depositions performed directly on silicon substrates are mild. (C) 2004 Elsevier B.V. All rights reserved.

NdNiSnD and PrNiSnD monodeuterides have been studied by Sn-119 Mossbauer spectroscopy at variable temperatures between 4.2 and 300 K. Deuterium insertion into the RE3Ni sites induces at low temperatures a magnetic splitting of the tin nuclear levels. Slightly different magnetic ordering temperatures, 25(1) and 20(1) K, were evidenced for the Nd- and Pr-containing deuterides, respectively. The Mossbauer spectra suggest a similar type of local structures for both compounds, with a mutual substitution of Sn and Ni atoms. The magnetic behaviour is discussed in relation to the different spin waves mechanisms. (C) 2003 Elsevier B.V. All rights reserved.

Hydrogenated and nitrogenated carbon films were obtained by PECVD with carbon species supplied by acetylene gas injected into an argon or argon/nitrogen remote plasma generated by an expanding radiofrequency discharge. The properties of carbon material like the nature of bonds, morphology, surface topography, crystallinity are presented. The reaction pathways linking the precursors with the depositing species, as revealed by emission spectroscopy, are discussed. (C) 2003 Elsevier B.V. All rights reserved.

A chalcogenide material of composition Se42S58, doped by 10 wt.% paraffins has been prepared as thin films by pulsed laser deposition. The structural properties of the films have been investigated by X-ray diffraction. Sample stabilization was carried out by annealing at temperatures around 100degreesC.

Electron spin resonance and DC electrical investigations on the effect of chlorine doping on emeraldine base polyaniline are reported. From the experimental data it is concluded that the chlorine doping of polyanilines increases the conductivity and that the charge transport is well described by an one dimensional variable range hopping, up to a doping level of 15% Cl/N. The characteristic temperature rises as the doping level is increased. Electron spin resonance investigations revealed the contribution of polarons to the charge transport. The absence of high spin bipolarons was proved by electron spin resonance data within the experimental errors. At high doping levels, the mesoscopic nature of charge transport in polyanilines is confirmed by the Dysonian shape of the resonance lines.

Electrical conduction mechanisms in Si-SiO2 nanocomposite films were experimentally investigated and theoretically modelled. The films with silicon volume concentration varying from 0% to 100% were deposited on rectangular quartz substrates. They were prepared by co-sputtering CVD from two targets, one of silicon and one of silicon dioxide. Their middle part is formed by Si nanodots embedded in SiO2. 50 parallel aluminium electrodes were deposited, forming 49 coplanar samples, centred around x = 45% Si concentration. The microstructure investigations proved that the silicon nanodots have diameters between 4 nm (x = 23%) and 36 nm (x = 81%). The current-voltage characteristics were measured at room temperature, in the -25 divided by +25 V interval. The obtained curves are symmetric and superlinear. As the current - voltage characteristic is determined by the maximum resistance met by the carriers in their path, the experimental curve is modelled by the field-assisted tunnelling under Coulomb blockade. The used parameters are correlated with previous results obtained on nanocrystalline porous silicon. The correlation coefficient between the theoretical formula and the experimental data is greater than 99.95%.

Thallium related paramagnetic centers of Tl2+ (6s(1)) and Tl-0 (6p(1)) type were produced by low temperature x-ray irradiation in ferroelectric Rb2ZnCl4:Tl single crystals. Extensive EPR investigations have been performed in order to elucidate their intrinsic properties and sensitivity as paramagnetic probes for structural phase transitions studies. Compared to the s-type Tl2+ centers, already used in many such studies, it was found that the p-type Tl-0 centers are much more sensitive to the small variations in the local crystal field associated with these transformations. Their EPR spectra provided information about the unit cell tripling in the P2(1)cn phase, as well as the symmetry lowering and lattice dynamics in the C1c1 phase. The temperature induced, continuous changes observed in the EPR spectra of both Tl-0 and Tl2+ centers were explained by the influence of the soft modes responsible for the 74-K structural phase transition.

Structural and electrical properties of polycrystalline CdSe thin films irradiated with high-energy electrons are analyzed. The samples were prepared by vacuum deposition onto optical glass substrate. Their structure and the temperature dependence of the electrical resistance were determined, both before and after irradiation with 6 MeV electrons and fluencies up to 10(16) electronS/cm(2). There were no measurable changes in the crystalline structure of the films after irradiation. Electrical properties are controlled by a defect level of donor type, possibly a selenium vacancy, with two charge states having ionization energies of about 0.40 eV, respectively 0.22 eV. Irradiation increases significantly the concentration of those defects.

In a planar oriented sample of a calamitic nematic lyotropic system ( mixture of sodium lauryl sulphate/water/decanol), isotropic pretransitional domains appear at the nematic to isotropic transition. The domains are oblong in shape with the long axis along the orientational direction. We show experimental evidence that this oblong shape is determined by the nematic-isotropic interfacial tension anisotropy. Two uniparametric models of simple angular dependences for the interfacial tension are tested. Using the differential system obtained from the Young-Laplace condition at the nematic-isotropic interface, the domain shape can be numerically calculated for each value of the interfacial tension anisotropy. By processing the values of the transmitted light through both an isolated isotropic domain and its surrounding nematic zone, we obtain the anisotropy of the interfacial tension as the main fitting parameter. An estimation of the ratio of the extreme values for the interfacial tension is given.

(Cu, C)Ba2Ca3Cu4Ox superconductor with addition of y mol LiF has been synthesized by a high-pressure method. For the same synthesis conditions it was found that (almost) single-phase Cu, C-1234 samples can be synthesized for y(LiF) = 0-0.1 if the amount of z mol AgO oxidizer is increased linearly from Z(AgO) = 0.45 to 0.73 and for y(LiF) = 0 - 1-0.2 if ZAgO = 0.73 = constant. Transport measurements (rho(T) and room-temperature Seebeck coefficient) have shown that these samples are overdoped: LiF is an effective addition for synthesis of overdoped Cu, C-1234 with a controlled level of carriers. LiF addition continuously decreases T-c. The critical point at y(LiF) = 0.1 is discussed as the solubility limit of LiF and/or the point where the doping mechanism changes. It is proposed that the reason is the reaction of extra Li with C and O to form Li2CO3, inducing a lower concentration of C in Cu, C-1234/LiF crystals, and at the same time a possible substitution of Li not only for the Cu site but also for the Ca site, resulting in formation of a higher amount of residual Ca0.828CuO2 (for y(LiF) > 0.1). LiF induces the formation of a liquid phase and acts as a flux promoting the formation of Cu, C-12(n - 1)n with n greater than or equal to 4. LiF modifies to some degree the grain growth from a 3D to a 2D type (thinner platelike grains have been observed in the LiF added samples).