Publications

The aim of this paper was to study the influence of crystallization heat treatments up to 750 degrees C, upon the integrity and structure of hydroxylapatite thin films. Two different types of hydroxylapatite coatings were investigated: abrupt structures prepared by magnetron sputtering and respectively functional graded structures deposited by a co-sputtering technique. A clear dependence was noticed between adherence values and annealing temperature and was correlated with the SEM, XRD and FTIR results. X-ray diffraction and FTIR measurements showed that the hydroxylapatite coatings annealed at 400 degrees C were less crystalline, similar to biological apatites. Over 550 degrees C, the apatite coatings obtained were well crystallized and preferentially oriented on (002) HA crystal plane. The adherence of HA coating increased with annealing the temperature up to 550 degrees C due to diffusion phenomena. At 550 degrees C the adhesion test results indicated better adhesion values in case of functional graded structures (> 85 MPa) in comparison with abrupt ones (similar to 70 MPa). At 750 degrees C an adherence decreasing occurred for both types of structures. This is mainly due to the effect of a significant thermal stress owed to the mismatch of the thermal expansion coefficients between the crystallized HA and Ti substrate. The presence of rutile lines in XRD spectrum suggests an increasing of the diffusion phenomena and a strong substrate oxidation at the HAM interface with annealing temperature.

Ultra fine and homogeneous BaTiO3 doped with 0.5 at% yttrium powder was prepared by sol-precipitation method using barium acetate, titanium (IV) diisopropoxide bis-acetylacetonate and yttrium (III) butoxide as starting precursors. The effect of pH value on the precipitate formation from the sot is pointed out in this paper. The grain size of the precipitate was about 100-200 nm. The structural evolution of the precursor precipitate as function of temperature was investigated. Ba0.995Y0.005TiO3 single phase was obtained at 1300 degrees C. The ceramics manufactured from the as-prepared powder presented good dielectric characteristics (dielectric constant = 2152 and dielectric loss (tan delta) = 4.54% at the Curie temperature of 125 degrees C). These ceramics are expected to be useful in dielectric applications.

Optical techniques allowing observations and spectroscopic investigations of materials at a nanoscale have been recently developed and applied to carbon nanotubes. They are briefly presented, including Scanning near-field optical microscopy, together with the Surface Enhanced or Tip Enhanced Raman Scattering. Even if new physical properties are difficult to extract from observed data, we show that nanostructures can generate non linear phenomena that can be exploited for studying nano-materials and in particular carbon nanotubes. By measuring the anti-Stokes/Stokes ratios of the Raman bands which present strong anomalies with respect to the prediction of the Maxwell-Boltzman law, one can distinguish between semi-conducting and metallic tubes on one hand and between isolated and bundled nanotubes on the other hand.

Lithium ferrites have been obtained by combustion reaction of ureate precursors. Various physico-chemical techniques: IR spectra, XRD, magnetic determinations, Mossbauer spectra have been employed to characterize the precursors and end products. The single spinel phase alpha-Li(0.5)Fe(.2.5)O(4) with saturation magnetization of similar to 56 Am(2)/kg were achieved from ureate precursor with ratio 2.5Fe(3+) : 0.5Li(+) : 7urea after a thermal treatment at 800 degrees C/1h.

In the early days of amorphous research, Romania was deeply involved in the development of the field of amorphous semiconductors within a close collaboration with Boris Kolomiets. The first researches in this field are discussed and further rapid developments up to the present are shown. The latest results in the field of amorphous semiconductor:, with special emphasis on chalcogenide glasses are presented. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Experimental results for the temperature dependence of the density of propyl - cyanobiphenyl (3CB), butyl - cyanobiphenyl (4CB) and hexyl - cyanobiphenyl (6CB) are presented. The results arc compared with previous results for temperature dependence of other members of the alkyl cyanobiphenyl series (nCB). The deviation of the density from linear temperature dependence is discussed in terms of the recently discovered corresponding rule for nematic liquid crystals. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Two soft chemistry routes - complexation and solution combustion - are explored to obtain the zinc gallate spinel ZnGa2O4. Three types of complexes, namely: (NH4)(2)[ZnGa2(C4O6H4)(4)(OH)(2)]center dot 4H(2)O, [ZnGa2(NH2CH2COOH)(4.5)](NO3)(8)center dot 4H(2)O and [ZnGa2(CO(NH2)(2))(7)](NO3)(8)center dot 9H(2)O have been synthesized and characterized by IR and UV-vis spectroscopy. Zinc gallate spinels obtained by decomposition of these compounds have been investigated by XRD spectra, analytic electronic microscopy and photoluminescence spectroscopy. Zinc gallate spinels exhibited blue emission spectra in the wavelength range of 400 nm-450 nm. (C) 2009 Elsevier B.V. All rights reserved.

A multifrequency electron paramagnetic resonance (EPR) investigation of Nd3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (MF) 9.43 GHz, and at the 95, 190, and 285 GHz high frequencies was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective electron spin of one-half and to a tetragonal symmetry. For the magnetic field along the tetragonal axis, the g(-)factor and the hyperfine constant A of the lowest doublet of the ground multiplet decreases with frequency increase. For the magnetic field perpendicular to the tetragonal axis, the g(perpendicular to)-factor exhibits a small azimuthal angular dependence that increases with increasing the frequency due to the S-4 site symmetry. The azimuthal angular dependence allows to clearly distinguish between different local axial symmetries. These properties are interpreted as high field/frequency (HF) effects associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. We show that from the combined analysis of the multifrequency MF- and HF-EPR spectra and of the optical data, an accurate description of the ground multiplet of the Kramers rare earth ions in solid matrices can be derived.

We report measurements of critical current in YBa2Cu3Ox films deposited on SrTiO3 substrates decorated with silver and gold nanodots. An increase in critical current in these films, in comparison with the films deposited on non-decorated substrates, has been achieved. We argue that this increase comes from the c-axis correlated extended defects formed in the films and originated from the nanodots. Additionally to creating extended defects, the nanodots pin them and prevent their exit from the sample during the film growth, thus keeping a high density of defects and providing a lower rate of decrease of the critical current with the thickness of the films. The best pinning is achieved in the samples with silver nanodots by optimising their deposition temperature. The nanodots grown at a temperature of a few hundred degrees C have a small diameter of a few nanometres and a high surface density of 10(11)-10(12) particles/cm(2). We give evidence of c-axis correlated extended defects in YBa2Cu3Ox films by planar and cross-sectional atomic force microscopy, transmission electron microscopy and angle-dependent transport measurements of critical current. (C) 2009 Elsevier B.V. All rights reserved.

Nonstationary and steady-state transport through a mesoscopic sample connected to particle reservoirs via time-dependent barriers is investigated by the reduced density operator method. The generalized master equation is solved via the Crank-Nicolson algorithm by taking into account the memory kernel which embodies the non-Markovian effects that are commonly disregarded. The lead-sample coupling takes into account the match between the energy of the incident electrons and the levels of the isolated sample, as well as their overlap at the contacts. Using a tight-binding description of the system, we investigate the effects induced in the transient current by the spectral structure of the sample and by the localization properties of its eigenfunctions. In strong magnetic fields, the transient currents propagate along edge states. The behavior of populations and coherences is discussed, as well as their connection to the tunneling processes that are relevant for transport.