National Institute Of Materials Physics - Romania

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.

Pottery vessels made of kaolin clay from the Roman Period (2nd, 3rd centuries CE) found in Romula (Re?ca village, Olt County, Romania) from Dacia Inferior (Malvensis) were investigated by petrographic, X-ray diffraction, X-ray fluorescence, thermal analysis, electron microscopy, and mechanical tests. Our results are compared with available data on kaolin clays and pottery vessels from other sites located along the lower course of Danube river and near the Black Sea, namely in Moesia Superior, Moesia Inferior, and Thracia. Archeological and geographical contexts are addressed. Results of our analysis suggest a local production of ceramics in Romula, by using raw materials from the north of Lower Danube, in opposition to the idea that kaolin ware was imported from the provinces south of the Danube.

Properties of epitaxial PbZr0.2Ti0.8O3 (PZT) films deposited on Si substrates were investigated for integration in the present CMOS technology. Polarization is downward oriented, in association with the presence of an internal electric field, and has a lower value compared to the PZT films deposited on single crystal perovskite SrTiO3 (STO) substrates (40 mu C/cm(2) versus 80 mu C/cm(2)), while the dielectric constant is larger (180 versus 120). Large value for the pyroelectric coefficient was also found, 1.22 x 10(-3)C/m(2)K, as for PZT grown on single crystal STO. The macroscopic ferroelectric and pyroelectric properties appear to be affected by the structural quality and stoichiometry of the PZT film. The changes in the electric properties are an effect of the strain gradients induced by the large difference between the thermal expansion coefficients of PZT and Si substrate, leading in turn to Pb oxidation and antisite defect formation compared to PZT films deposited on STO substrates.

Photodegradation of the aqueous solutions of acetylsalicylic acid, in the absence (ASA) and the presence of excipients (ASE), is demonstrated by the photoluminescence (PL). A shift of the PL bands from 342 and 338 nm to 358 and 361-397 nm for ASA and ASE in solid state and as aqueous solutions was reported. By exposure of the solution of ASA 0.3 M to UV light, a decrease in the PL band intensity was highlighted. This behavior was revealed for ASA in the presence of phosphate buffer (PB) having the pH equal to 6.4, 7, and 8 or by the interaction with NaOH 0.3 M. A different behavior was reported in the case of ASE. In the presence of PB, an increase in the intensity of the PL band of ASE simultaneously with a change of the ratio between the intensities of the bands at 361-364 and 394-397 nm was highlighted. The differences between PL spectra of ASA and ASE have their origin in the presence of salicylic acid (SAL). The interaction of ASE with NaOH induces a shift of the PL band at 405-407 nm. Arguments for the reaction of ASA with NaOH are shown by Raman scattering and FTIR spectroscopy.