National Institute Of Materials Physics - Romania

TiO2-based photocatalysts were obtained during previous years in order to limit pollution and to ease human daily living conditions due to their special properties. However, obtaining biocompatible photocatalysts is still a key problem, and the mechanism of their toxicity recently received increased attention. Two types of TiO2 nanoparticles co-doped with 1% of iron and nitrogen (TiO2-1% Fe-N) atoms were synthesized in hydrothermal conditions at pH of 8.5 (HT1) and 5.5 (HT2), and their antimicrobial activity and cytotoxic effects exerted on human pulmonary and dermal fibroblasts were assessed. These particles exhibited significant microbicidal and anti-biofilm activity, suggesting their potential application for microbial decontamination of different environments. In addition, our results demonstrated the biocompatibility of TiO2-1% Fe-N nanoparticles at low doses on lung and dermal cells, which may initiate oxidative stress through dose accumulation. Although no significant changes were observed between the two tested photocatalysts, the biological response was cell type specific and time- and dose-dependent; the lung cells proved to be more sensitive to nanoparticle exposure. Taken together, these experimental data provide useful information for future photocatalytic applications in the industrial, food, pharmaceutical, and medical fields.

We report the synthesis of dextran-coated iron oxide magnetic nanoparticles (DIO-NPs) with spherical shape and uniform size distribution as well as their accumulation and toxic effects on Jurkat cells up to 72 h. The characterization of dextran-coated maghemite nanoparticles was done by X-ray diffraction and dynamic light scattering analyses, transmission electron microscopy imaging, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, magnetic hysteresis, and relaxometry measurements. The quantification of DIO-NPs intracellular uptake showed a progressive accumulation of iron as a function of time and dose accompanied by additional lysosome formation and an increasing darkening exhibited by a magnetic resonance imaging (MRI) scanner. The cytotoxicity assays revealed a decrease of cell viability and a loss of membrane integrity in a time-and dose-dependent manner. Exposure to DIO-NPs determined an increase in reactive oxygen species level up to 72 h. In the first two days of exposure, the level of reduced glutathione decreased and the amount of malondyaldehyde increased, but at the end of the experiment, their concentrations returned to control values. These nanoparticles could be used as contrast agents for MRI but several parameters concerning their interaction with the cells should be taken into consideration for a safe utilization.

Electrochemical impedance spectroscopy (EIS), X-ray spectroscopy (XPS), and atomic force microscopy (AFM) have been used to investigate the effects of the sodium dodecyl sulfate (SDS) interaction with the L-cysteine-thiolate covered p- and n-GaAs(100) electrodes in H2SO4 solution. The potential-induced reversible proton transfer found to occur within the L-cysteine-thiolate layer in the simple acid solution during the cathodic as well as the anodic potential scans at the p-doped semiconductor electrode and only in the anodic scan at the n-doped one is suppressed in both cases. XPS data revealed that the anionic surfactant has a complex interaction with the L-cysteine-thiolate covered GaAs(100) electrodes, which implicates both electrostatic and chemical forces. The SO42 head group interacts electrostatically with the NH3+ group of the cysteine-thiolate but it is also chemically involved in a chemisorption bond with the available Ga atoms. The amount of Ga-bound SDS species is much more pronounced at the L-cysteine-thiolate/p-GaAs(100) than at the L-cysteine thiolate/n-doped GaAs(100) electrodes meaning that cysteine-thiolate is mainly formed at As sites in the first case and at Ga sites in the latter one. This outcome strengthens the previous conclusions concerning the role of the dopant in determining the bonding way of the L-cysteine on GaAs(100) surfaces. (C) 2016 Elsevier Ltd. All rights reserved.

A new method based on transformation of magnetron sputtered platinum thin films into platinum nanostructures enclosed by high-index facets, using electrochemical potential cycling in a twin working electrode system is reported. The controllable formation of various Pt nanostructures, described in this paper, indicates that this method can be used to control a selective growth of high purity Pt nanostructures with specific shapes (facets or edges). The method opens up new possibilities for electrochemical preparation of nanostructured Pt catalysts at high yield. (C) 2016 Elsevier B.V. All rights reserved.

We study Coulomb interacting electrons confined in polygonal quantum rings. We focus on the interplay of localization at the polygon corners and Coulomb repulsion. Remarkably, the Coulomb repulsion allows the formation of in-gap states, i.e., corner-localized states of electron pairs or clusters shifted to energies that were forbidden for non-interacting electrons, but below the energies of corner-side-localized states. We specify conditions allowing optical excitation to those states.

Different aspects related to the sol-gel preparation and structural investigation of silico-phosphate glasses (SiO2-P2O5 system) doped with Fe ions are reported. During the preparation process, tetraethoxysilane was used as a precursor for SiO2 and phosphoric acid (H3PO4-HP) for P2O5. Ferric chloride was used as precursor for Fe ions, water as reagent for hydrolysis reaction and ethylic alcohol as solvent. The pH of the sols was modified by adding hydrochloric acid and ammonia. It was observed that a slight increase of the solution temperature (up to 40 degrees C) allows a drastic decrease of the gelation time (from days to hours). The structure of the obtained powders dried in air at room temperature and at 100 degrees C for 10 h and subsequently thermally treated at different temperatures was investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy. Vibration modes specific to Si-O-Et, Si-OH, PO-P, P-O-Si, hydrogen bonds and H2O, as well as combined modes have been observed. The local structure and electron configurations of the doping Fe ions have been investigated by Fe-57 Mossbauer spectroscopy.

Epitaxial thin films of NiFe2O4 are fabricated by pulsed laser deposition on SrTiO3 substrate. Symmetrical capacitor-like structures are formed using SrRuO3 as bottom and top electrodes. Electrical characterizations, including current-voltage, capacitance-voltage and capacitance-frequency measurement, reveal a hysteresis-like behaviour for current and capacitance as function of voltage. This could be assigned to a resistive and/or capacitive switching. A "degradation" process takes place after repeated voltage cycling or after heating the sample to 400 K, leading to the stabilization of different resistive states. These features can be related to the changes observed in the capacitance-frequency characteristics, suggesting the presence of a relaxation mechanism at low frequencies, and can be associated with the presence of a deep donor-type level in the band-gap of the NiFe2O4 layer.

A dynamic electrical model is introduced to investigate the hysteretic effects in the J-V characteristics of perovskite based solar cells. By making a simple ansatz for the polarization relaxation, our model is able to reproduce qualitatively and quantitatively detailed features of measured J-V characteristics. Pre-poling effects are discussed, pointing out the differences between initially over- and under-polarized samples. In particular, the presence of the current overshoot observed in the reverse characteristics is correlated with the solar cell pre-conditioning. Furthermore, the dynamic hysteresis is analyzed with respect to changing the bias scan rate, the obtained results being consistent with experimentally reported data: the hysteresis amplitude is maximum at intermediate scan rates, while at very slow and very fast ones it becomes negligible. The effects induced by different relaxation time scales are assessed. The proposed dynamic electrical model offers a comprehensive view of the solar cell operation, being a practical tool for future calibration of tentative microscopic descriptions. (C) 2016 Elsevier B.V. All rights reserved.

Additives to MgB2 can improve the superconducting functional characteristics, such as critical current density (J (c)) and irreversibility field (H (irr)). Recently, we have shown that repagermanium (C6H10Ge2O7) is an effective additive, enhancing both J (c) and H (irr). To look into details of the processes taking place during the reactive sintering, a thermal analysis study (0.167 K s(-1), in Ar) is reported. We used differential scanning calorimetry between 298 and 863 K and simultaneous thermogravimetric-differential thermal analysis between 298 and 1233 K. Samples were mixtures of powders with composition 97 mol% MgB2 and 3 mol% C6H10Ge2O7. Up to 863 K, repagermanium decomposes by multiple steps and forms amorphous phases. A reaction with MgB2 is not observed. Above this temperature, partial decomposition of MgB2 occurs. Crystalline Ge and MgO are detected before formation of Mg2Ge and MgB4, when temperature approaches the melting point of Ge (1211 K). Carbon substitution for boron in the crystal lattice of MgB2 is observed for samples heated above 863 K. The amount of substitutional C does not significantly change with temperature.