National Institute Of Materials Physics - Romania

A mathematical approach for describing the influence of the ions dissolved in a liquid crystal on the impedance measurements is presented. New independent variables allow re-formulating the basic coupled differential equations of continuity and Poisson equation as well. The obtained forms are simpler than those used up to now. Illustrative examples are analyzed.

The ecofriendly synthesis of nanoparticles through various biological sources helps in exploring various herbs. Generally, nanoparticles are prepared by a variety of chemical methods which are not environmentally friendly. In this report we use aqueous extracts of Carthamus Tinctorius L. (Safflower) flowers for the synthesis of gold (Au) nanoparticles. A rapid and convenient method was considered for the synthesis of gold nanoparticles by reduction with auric chloride. UV-visible spectroscopy studies were carried out to assess the formation of Au nanoparticles. Transmission electron microscopy (TEM) was used to characterize the Au nanoparticles. TEM image divulges that nano triangle and spherical shaped gold nanoparticles are formed with polydispersed size, and the sizes are in the range of 40 nm to 200 nm. The antimicrobial activity of gold nanoparticles was performed on various gram negative bacteria and fungus. The gold nanoparticles showed more inhibitory activity on pathogenic gram negative bacteria than fungus.

High-peak power, passively Q-switched, composite Nd : YAG/Cr4+ : YAG lasers consisting of all-polycrystalline bonded Nd : YAG and Cr4+ : YAG ceramics are developed, and two applications of such lasers are discussed. A 1.1-at. %-doped Nd : YAG/Cr4+ : YAG ceramic laser is fabricated, which is quasi-cw pumped by a diode laser in the Hz-range, delivering laser pulses of 2.5-mJ energy and 1.9-MW peak power. By frequency doubling the laser output in a LiB3O5 (LBO) nonlinear crystal at room temperature, 0.36-mJ, 0.3-MW green laser pulses with 27% conversion efficiency are produced at 532 nm. Furthermore, a highly doped (1.5-at. %) Nd : YAG/Cr4+ : YAG ceramic laser operates successfully in the range of pulse repetition rates from 50 to 500 Hz, yielding 0.8-to-1.0 mJ pulses with a peak power around 1 MW. The laser output beam is amplified in a master-oscillator-power-amplifier (MOPA) system to generate laser pulses with 11-mJ energy at a 250-Hz repetition rate.

In this paper the electrochemical analysis of new materials, designed to be used as solid electrolytes for intermediate temperature fuel cells (IT-SOFC) was made. The materials are two different composites based on ceria 10YDC + (10%) 150ppm YA and 10ScDC + (10%) 150ppm YA, obtained by sol-gel method and sintered at temperature of 1500 degrees C. The electrochemical investigation was performed by Electrochemical Impedance Spectroscopy technique. According of these analyses the composite 10YDC + (10%) 150ppm YA presents better conductivity than 10ScDC + (10%) 150ppm YA. These results were related with morphological investigation, realized by SEM.

When subjected to a linearly polarized terahertz pulse, a mesoscopic ring endowed with spin-orbit interaction (SOT) of the Rashba-Dresselhaus type exhibits non-uniform azimuthal charge and spin distributions. Both types of SOT couplings are considered linear in the electron momentum. Our results are obtained within a formalism based on the equation of motion satisfied by the density operator which is solved numerically for different values of the angle 0, the angle determining the polarization direction of the laser pulse. Solutions thus obtained are later employed in determining the time-dependent charge and spin currents, whose values are calculated in the stationary limit. Both these currents exhibit an oscillatory behavior complicated in the case of the spin current by a beating pattern. We explain this occurrence on account of the two spin-orbit interactions which force the electron spin to oscillate between the two spin quantization axes corresponding to Rashba and Dresselhaus interactions. The oscillation frequencies are explained using the single particle spectrum.

Magnetic iron oxide nanoparticles (MION) doped dextran thin films for biomedical applications have been deposited onto the glass substrate by spin coating method. To understand the influence of the MION doping dextran on physico-chemical properties was conducted. The particle concentration in the samples defined as the oxide/dextran mass ratio, R was 1 and 5. MION -dextran thin films were charcacterized by various techniques such as X-ray Photoelectron Spectroscopy (XPS), Glow Discharge Optical Emission Spectroscopy (GDOES), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Attachment (EDAX). These techniques have allowed the structural elucidation of polysaccharides thin films. The second derivative FT-IR spectra showed clearly that the polysaccharides bands. The biocompatibility of the maghemite-dextran thin films was demonstrated using MTT test, with the aid of hFOB 1.19 osteoblats cells. To evaluate cell proliferation rate quantitative by the hFOB 1.19 cells on HAp samples were cultured to 4 days. Cellular morphology was investigated using FESEM to obtain qualitative information of osteoblast cells on MION-dextran thin films. The data stronlgy suggest the potential use of iron oxide-dextran nanocomposite as a poetinal marker for or biomedical applications.

The luminescent europium-doped hydroxyapatite (Eu:HAp, Ca10-xEux(PO4)(6)(OH)(2)) with 0 <= x <= 0.2 nanocrystalline powders was synthesized by coprecipitation. The structural, morphological, and textural properties were well characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The vibrational studies were performed by Fourier transform infrared, Raman, and photoluminescence spectroscopies. The X-ray diffraction analysis revealed that hydroxyapatite is the unique crystalline constituent of all the samples, indicating that Eu has been successfully inserted into the HAp lattice. Eu doping inhibits IIAp crystallization, leading to a decrease of the average crystallite size from around 20 nm in the undoped sample to around 7 nm in the sample with the highest Eu concentration. Furthermore, the samples show the characteristic D-5(0) -> F-7(0) transition observed at 578 nm related to Eu3+ ions distributed on Ca2+ sites of the apatitic structure.

A genuine GaAs surface is covered with a relatively thick layer (similar to nm) of native oxide pinning the Surface Fermi level within the band gap of semiconductor. The method presented in this work is related to sulfur passivation by treating n-GaAs in different solutions of alkane thiols. At the surface of GaAs it is developed an adherent layer of sulfur compound as a result of chemical interaction of sulfur ions with GaAs(100) face, that are putted in evidence by scanning electron microscopy (SEM) images and second harmonic generation (SHG) analysis. Using X-ray photoelectron spectroscopy (XPS) is presented a detailed analysis of XPS data at the surface of thiols on GaAs together with the presence of the covalent bond As-S. The electric characteristics of the AuGeNi/Thiol/GaAs structure are presented in I (V) curves recorded in the region of small currents.

Due to the extensive use of new technologies in agricultural and industrial field the soil and groundwater were severely polluted with elements that may pose a serious threat to the environment. For that purpose studies concerning new materials that can be successfully used for removal of heavy metals and other toxic elements from contaminated soil and water were conducted. The attention of the scientific studies were focused on the family of calcium phosphates, with a particular interest in hydroxyapatite (HAp), with general formula Ca-10(PO4)(6)(OH)(2), due to the exquisite ability of adsorbing heavy element ions in aqueous conditions. This study focuses on synthesizing nanocrystalline hydroxyapatite powders with controllable parameters and very good stoechiometry. The structure, morphology and optical properties were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR).

Ba(X1/3Ta2/3)O-3 (X = Zn, Mg) perovskites were prepared by using the solid state reaction method. X-ray diffraction and scanning electron microscopy were employed for structural and morphological characterization of Ba(X1/3Ta2/3)O-3 samples. The dielectric constant of the resonators was 28 for Ba(Zn1/3Ta2/3)O-3 and 24 for Ba(Mg1/3Ta2/3)O-3. A strong influence of the cation ordering on the dielectric loss has been found. The achieved values of Q x f product, ranging from 100 to 200 THz, make Ba(X1/3Ta2/3)O-3 dielectric resonators attractive for microwave and millimetre-wave applications.