National Institute Of Materials Physics - Romania

NiO-loaded SnO2 powders were prepared involving two chemical procedures. The mesoporous SnO2 support was synthesized by a hydrothermal route using Brij 35 non-ionic surfactant as a template. The nickel loadings of 1 and 10 wt.%. NiO were deposited by the wet impregnation method. The H2S sensing properties of xNiO-(1-x)SnO2 (x = 0, 1, 10%) thick layers deposited onto commercial substrates have been investigated with respect to different potential interfering gases (NO2, CO, CO2, CH4, NH3 and SO2) over a wide range of operating temperatures and relative humidity specific for in-field conditions. Following the correlation of the sensing results with the morphological ones, 1wt.% NiO/SnO2 was selected for simultaneous electrical resistance and work function investigations. The purpose was to depict the sensing mechanism by splitting between specific changes over the electron affinity induced by the surface coverage with hydroxyl dipoles and over the band bending induced by the variable surface charge under H2S exposure. Thus, it was found that different gas-interaction partners are dependent upon the amount of H2S, mirrored through the threshold value of 5 ppm H2S, which from an applicative point of view, represents the lower limit of health effects, an eight-hour TWA.

Gold nanoparticles (similar to 10 nm) were deposited on titanium dioxide nanoparticles (similar to 21 nm) and the material obtained was characterized using IR, UV-Vis, N-2 adsorption-desorption isotherm, DLS, EDS (EDX), TEM, XPS, and XRD techniques. It was found that the methylene blue dye is degraded in the presence of this material when using hydrogen peroxide as the oxidant. Tests were performed at 2, 4, 6, and 24 h, with hydrogen peroxide contents varying from 1 to 5 mg/mL. Longer exposure time and a higher content of oxidant led to the degradation of methylene blue dye at up to 90%. The material can be reused several times with no loss of activity.

Tuning the intrinsic structural and stoichiometric properties by different means is used for increasing the green energy production efficiency of complex oxide materials. Here, we report on the formation of self-assembled nanodomains and their effects on the photoelectrochemical (PEC) properties of LaFeO3 (LFO) epitaxial thin films as a function of layer's thickness. The variation with the film's thickness of the structural parameters such as in-plane and out-of-plane crystalline coherence length and the coexistence of different epitaxial orientation-SrTiO3// LFO, SrTiO3// LFO and [110] LFO//[10] STO, as well as the appearance of self-assembled nanodomains for film's thicknesses higher than 14 nm, is presented. LFO thin films exhibit different epitaxial orientations depending on their thickness, and the appearance of self-assembled nanopyramids-like domains after a thickness threshold value has proven to have a detrimental effect on the PEC functional properties. Using Nb:SrTiO3 as conductive substrate and 0.5 M NaOH aqueous solution for PEC measurements, the dependence of the photocurrent density and the onset potential vs. RHE on the structural and stoichiometric features exhibited by the LFO photoelectrodes are unveiled by the X-ray diffraction, high-resolution transmission electron microscopy, ellipsometry, and Rutherford backscattering spectroscopy results. The potentiodynamic PEC analysis has revealed the highest photocurrent density J(photocurrent) values (up to 1.2 mA/cm(2)) with excellent stability over time, for the thinnest LFO/Nb:SrTiO3 sample, both cathodic and anodic behavior being noticed. Noticeably, the LFO thin film shows unbiased hydrogen evolution from water, as determined by gas chromatography in aqueous 0.5 M NaOH solution under constant illumination.

Amorphous metal chalcogenides have good switching properties for resistive memories, but have low thermal stability. In this work, the response to rapid thermal stress, as high as 550 degrees C, of amorphous Cu-GeSe, Ag-GeSe, Cu-GeTe, Ag-GeTe thin films, is investigated. Metal-GeTe films, which are amorphous up to 280 degrees C, are the most stable. Metal-GeSe films start to crystallize at 190 degrees C and a Cu1.59Se phase, with 20.5% Cu vacancies and a structure similar to the c-Cu2-xSe superionic conductor, is formed. This might boost the performance of memory devices. Silver atoms migration is facilitated in Ag-GeSe by poor crystallization (below 5%, at all temperatures). Difussion of Ag is enhanced in Ag-GeTe, due to the crystallization of the cubic (Ag2Te)(4)-GeTe2 (Ag8GeTe6) phase, which has Ag+ vacancies. In Cu-GeTe, the formation of stoichiometric polycrystalline Cu0.67Ge0.33 Te might hinder diffusion. An unusual anisotropic behaviour (increase in thickness, simultaneously with contraction of surface) is observed at 100 degrees C in Cu-GeSe and Cu-GeTe thin films, which suggests the orientation of the amorphous clusters package along a preferential direction.

Structural and electrical properties of epitaxial Pb(Zr0.2Ti0.8)O-3 films grown by pulsed laser deposition from targets with different purities are investigated in this study. One target was produced in-house by using high purity precursor oxides (at least 99.99%), and the other target was a commercial product (99.9% purity). It was found that the out-of-plane lattice constant is about 0.15% larger and the a domains amount is lower for the film grown from the commercial target. The polarization value is slightly lower, the dielectric constant is larger, and the height of the potential barrier at the electrode interfaces is larger for the film deposited from the pure target. The differences are attributed to the accidental impurities, with a larger amount in the commercial target as revealed by composition analysis using inductive coupling plasma-mass spectrometry. The heterovalent impurities can act as donors or acceptors, modifying the electronic characteristics. Thus, mastering impurities is a prerequisite for obtaining reliable and reproducible properties and advancing towards all ferroelectric devices.

Resveratrol (RES) is a naturally occurring product with numerous biological activities. Despite its potential benefits, its use is limited due to its low aqueous stability and solubility in its native form. The porous sol-gel silica materials which are able to entrap different organic molecules represent new studied release carriers. The aim of this work was to generate a solid matrix to encapsulate RES ensuring protection, increased solubility and release in solutions. A non-toxic ingredient, namely beta-cyclodextrin (beta-CD), able to form inclusion complexes (ICs) with RES has been used. Ecological formulations have been processed by entrapping the RES containing ICs in silica matrices obtained from a silica colloidal sol by the aqueous route of the sol-gel method. Characterization methods (DSC, FTIR, UV-Vis, fluorescence studies, SEM) have evidenced the presence of RES-beta-CD inclusion complex in the silica powder, RES stability in the matrix and its release in aqueous and organic solutions, and the morphology of the carrier. An evaluation of the antioxidant activity of RES in the present formulation was performed by the chemiluminescence assay and RES release profile in aqueous solutions was obtained by HPLC-MS. The resulted materials can find applications in different domains. Graphic abstract

In this work, amorphous tin oxide thin films were deposited by non-reactive radio frequency magnetron sputtering. A ceramic SnO2 target was used, while different working pressures were employed. The target to substrate distance was fixed to 17 cm, and the substrate was not intentionally heated. The properties of SnO2 (thickness, refractive index dispersion, optical band gap, resistivity, free carriers concentration, carriers mobility, carriers majority type and their scattering time) have been inferred from spectroscopic ellipsometry, conventional UV-Vis spectroscopy and specific Hall electrical measurements. Thickness and refractive index are slightly dependent on the deposition conditions, while the optical band gap, free carriers concentration and their mobilities are changing from sample to sample. The evolution of the optical band gap and carriers concentration is correlated to the active defects concentration. Amorphous SnO2 films grown at 0.4 Pa have the lowest resistivity of 0.86 Omega cm, a carrier concentration of 1.05x10(18)cm(-3) Vs. The average optical transmittance in visible spectrum is 76%.

In this study, nano-BaTiO3 (BTO) powders were obtained via the solvothermal method at different reaction times and were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results were compared with those obtained for a larger crystallite size BTO powder (BTO-m). The sizes of the cuboid crystallites (as determined by XRD and TEM) ranged from about 18 to 24 nm, depending on the reaction time. The evolution with temperature of the structure parameters of nano-BTO was monitored by means of X-ray diffraction and Raman spectroscopy and no signs of phase transition were found up to 170 degrees C. Careful monitoring of the dependence of the XRD peak widths on the hkl indices showed that the effect of the cubic crystallite shape upon the XRD peak widths was buried by the effect of hidden tetragonal line splits and by anisotropic microstrain. The good correlation of the line widths with the tetragonal split amplitudes, observed especially for BTO-m above the transition temperature, indicates tetragonal deformations, as also revealed by Raman spectroscopy. The large anisotropic microstrain shown by the nano-powders, which had a maximum value in the directions, was considered evidence of the phenomenon of surface relaxation of cubic crystallites edged by {100} faces. The observed behavior of the nano-BTO structures with increasing temperature may suggest a correlation between the surface relaxation and tetragonal deformation in the nano-cubes. The experimental results for both nano-BTO and mezoscale-BTO are in agreement with the core-shell model.

We report the obtaining of a new composite starting from pyrene thiazole, a compound certified by nuclear magnetic resonance and its covalent grafting on the surface of graphene oxide. Novel material was synthesized in two stages: the first involving transformation of carboxyl groups of graphene oxide into acid chlorides and the second the amide reaction between acid chloride and amine group of pyrene thiazole (PTC). Numerous characterization methods have been used to certify this material, such as: Raman spectroscopy, fluorescence, infrared spectroscopy and X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Their results show the successful covalent functionalization of graphene oxide with pyrene thiazole through the formation of amide bonds. The electrochemical investigation consisted of evaluating the redox behavior of the carbon screen printed electrodes modified with the new composite (GO-PTC) using caffeic acid, as analyte. From analytical point of view, it is relevant to be able to quantify the presence of caffeic acid and for such reason we used as analytical method the square wave voltammetry. The results showed that the GO-PTC modified carbon screen printed electrodes were able to detect the caffeic acid over more than one order of magnitude (linear working range: 0.005-0.1 mM) and GO-PTC modified electrodes can be considered promising for other analytical investigations.

Six compounds of the types [M(dmbg)(2)]center dot nH(2)O ((1) M: Ni, n = 0; (4) M: Cu, n = 1; Hdmbg: N,N '-dimethylbiguanide) and, respectively, [ML]center dot nH(2)O (where (2) M: Ni, L: L-1, n = 0; (3) M: Ni, L: L-2, n = 0; (5) M: Cu, L: L-1, n = 0 and (6) M: Cu, L: L-2, n = 3, H2L1: ligand resulted from the condensation of (1) with ammonia and formaldehyde and H2L2: ligand resulted from the condensation of (4) with hydrazine and formaldehyde) were characterized as mononuclear species through information provided by NMR, electronic paramagnetic resonance (EPR) and UV-Vis spectroscopy as well as cyclic voltammetry. All data are consistent with macrocyclic formation by condensation. The complexes adopt a distorted square planar geometry resulting from the chelating behaviour of the corresponding ligands. The EPR spectra recorded after the addition of Cu(II) complexes into the corresponding Ni(II) complexes show a well resolved hyperfine structure with the superhyperfine pattern corresponding to four nitrogen atom donors. The cathodically shift of E-pc2 for both series can be correlated with the increased stability of the M(I) species through macrocyclic ligands. Geometry optimization studies for complexes (2), (3), (5) and (6) have further confirmed the experimental data. The pharmacokinetic computational results indicate that the complexes exhibit medium to low intestinal absorption and slow blood-brain barrier permeability but low toxicity. Their predictive pharmacodynamic profiles show that the compounds present the ability to inhibit protease activity. By corroborating the results of the in silico analysis with the experimental ones, the most promising complexes for antimicrobial applications are (1) and (2) and, respectively, (4) and (6) for the development of novel antitumour strategies.