Publications

Nd-doped ZnO thin films were grown by pulsed-electron beam deposition (PED) on c-cut sapphire substrates under oblique angle incidence, at 10-2 mbar oxygen pressure and for a substrate temperature of 500 degrees C. The films were smooth, compact and constituted with columnar grains inclined at about 17 degrees +/- 4 degrees from the normal to the substrate surface. From X-ray diffraction and transmission electron microscopy experiments, it was found that the wurtzite phase of Nd-doped ZnO thin films is observed with the c-axis inclined around 35 degrees with respect to the normal axis of the substrate, with a three-fold azimuthal symmetry. Epitaxial relationships between Nd-doped ZnO films and sapphire substrate were determined from the asymmetric X-ray diffraction and are presented compared with those obtained for the films grown by non-oblique PED. The tilt of the ZnO c-axis has been explained by the epitaxy of the (2 2 9) ZnO plane on the (0 0 l) sapphire plane, such particular epitaxial growth having never been reported previously.

Multifunctional materials integrating optical and electric properties into a composite or into a doped single-phase material have attracted much attention from scientists for future optoelectronic devices. In this work, polycrystalline Ba1-xTbxTiO3, x = 0.00, 0.01 and 0.05 materials were synthesized by hydrothermal route and their photoluminescence and dielectric properties were studied. The as-prepared powders showed a microstructure consisting of grains with the shape of cube; and average particle size ranging from 75 nm to 150 nm. The investigated temperature dependence of dielectric permittivity of Ba1-xTbxTiO3 ceramics revealed a decrease of the Curie temperature (Tc) with increasing terbium content, and a more pronounced degree of diffuseness of phase transition. The resistivity at room temperature was discussed in terms of positive temperature coefficient of resistance (PTRC) effect. UV-vis reflectance spectra of Ba1-xTbxTiO3 samples showed a decrease of the band gap energy with the increase of Tb amount, due to the band-gap narrowing effect. The photoluminescence spectra recorded for Tb doped BaTiO3 materials, at 80 K, evidenced the typical f-f luminescence lines of the Tb3+ accompanied the broad luminescence band at about 425 nm due to self-trapped exciton recombination. These results demonstrated that the terbium enhances the dielectric properties and photoluminescence simultaneously, being suitable for electronic applications. (C) 2021 Elsevier B.V. All rights reserved.

Porous multicomponent surface layers consisting of bimetallic oxide nanoparticles, carbon nanomaterials reduced graphene oxide (GO) and multiwall carbon nanotubes (MWCNTs) were prepared by reactive inverse matrix assisted pulsed laser evaporation. The layers were tested as electrodes for supercapacitor devices. Bimetallic oxide nanoparticles were grown through the mixing of simple inorganic oxides and organic compounds in distilled water. A frequency quadrupled Nd:YAG laser was used for the irradiation of the target dispersions consisting of GO platelets, MWCNTs, NiO, and Zn acetate. Besides oxide nanoparticles synthesis, which were present both on the surface of GO platelets and MWCTs and were also encapsulated within the MWCNTs walls, the GO platelets used for the preparation of the target dispersion were reduced under the effect of the laser pulses. An enhancement of the electrochemical performances of the nanohybrid electrodes were obtained as a results of the formation of bimetallic oxide nanoparticles. The electrodes exhibit fast charge-discharge cycling rate and improved storage capacity as compared to compound layer counterparts containing carbon nanomaterials, reduced graphene oxide, carbon nanotubes and simple binary transition metal oxide nanoparticles, 40F/cm3 volumetric capacitance at 10 mV/s scan rate, 1.5 mW/cm3 energy density and 12 W/cm3 power density at 4 mA/cm3 current density.

The discovery of multifunctional properties related to electro-activity of organic systems of biomolecules is important for a variety of applications, especially for devices in the realm of biocompatible sensors and/or bioactuators. A further step towards such applications is to prepare thin films with the required properties. Here, the investigation is focused on the characterization of films of guanine and cytosine nucleobases, prepared by thermal evaporation-an industrial accessible deposition technique. The cytosine films have an orthorhombic non-centrosymmetric structure and grow in two interconnected nanostructured fractal patterns, of nearly equal proportion. Piezoresponse force microscopy images acquired at room temperature on the cytosine films display large zones with antiparallel alignment of the vertical components of the polarization vector. Guanine films have a dense nano-grained morphology. Our studies reveal electrical polarization switching effects which can be related to ferroelectricity in the films of guanine molecules. Characteristic ferroelectric polarization-electric-field hysteresis loops showing large electrical polarization are observed at low temperatures up to 200 K. Above this temperature, the guanine films have a preponderant paraelectric phase containing residual or locally induced nano-scopic ferroelectric domains, as observed by piezoresponse force microscopy at room temperature.

The physico-chemical properties of two anhydrous AZA forms and their interaction with typical pharmaceutical excipients were assessed by applying various methods (such as PXRD, HPLC, TG/DSC, IR, Raman, PL or UV-Vis) in order to highlight new directions for drug formulation. The stability assessment of AZA anhydrous forms I and II was performed in order to determine the risk of degradation of the active ingredient by accidental exposure to nonstandard conditions in the industrial environment, under different storage, transport or processing conditions. The benefits of form II include increased resistance to chemical degradation over a wide range of pH, but further control of storage and processing conditions is necessary to avoid polymorphic transformation into form I. The solubility assessment on the AZA solid forms in different environments that simulate the conditions of the gastrointestinal tract has the advantage of a significantly increased solubility of form II compared with the commercial form I due to the modification of the crystalline structure. In the case of capsules compared to AZA form I or II as powder, an improvement in their solubility was observed, promoted by the presence of one or more excipients in the formulation mixture.

Structural and functional changes induced by TiO2 addition to spherical zinc selenide together with lysozyme adsorption lead to valuable bioinorganic catalysts with enhanced activity. Spherical zinc selenide and its composite with TiO2 were obtained by hydrothermal method and subsequently modified by lysozyme adsorption. Morphological, structural and functional characteristics of zinc selenide based materials (ZnSe, TiO2-ZnSe) and their hybrids with lysozyme (Lys/ZnSe, Lys/TiO2-ZnSe) were investigated. TiO2 addition to ZnSe results in significant changes of surface composition, electrochemical behavior and lysozyme retention capacity. The lysozyme modified ZnSe and TiO2-ZnSe surfaces doubles the biocatalysts efficiency for 4-Methylumbelliferyl p-D-N,N',N ''-triacetylchitotrioside hydrolysis reaction compared to free lysozyme.

TiO2-C (carbon) hybrid materials are promising electrocatalyst supports because the presence of TiO2 results in enhanced stability. Use of new types of carbonaceous materials such as reduced graphene oxide instead of traditional active carbon provides certain benefits. Although the rutile polymorph of TiO2 seems to have the most beneficial properties in these hybrid materials, the anatase type is more frequent in TiO2-rGO composites, especially in graphite oxide (GO) derived ones, as GO has several properties which may interfere with rutile formation. To explore and evaluate these peculiarities and their influence on the composite formation, we compared TiO2-C systems formulated with GO and Black Pearls (BP) carbon. Various physicochemical methods, such as attenuated total reflection infrared (ATR-IR)-, solid state NMR-, Raman- and X-ray photoelectron spectroscopy, X-ray powder diffraction (XRD), electron microscopy, etc. were used to characterize the samples from the different stages of our multistep sol-gel synthesis. Our experiments demonstrated that utilization of GO is indeed feasible for composite preparation, although its sodium contamination has to be removed during the synthesis. On the other hand, high temperature treatment and/or solvothermal treatment during composite synthesis resulted in decomposition of the functional groups of the GO and the functional properties of the final product were similar in case of both composites. However, Pt/TiO2-GO derived sample showed higher oxygen reduction reaction activity than Pt/TiO2-BP derived one. Based on the decrease of electrochemical surface area, the stability order was the following: Pt/C (commercial) < Pt/TiO2-BP derived C < Pt/TiO2-GO derived C.

Basalt fibers were functionalized by ZnO electroless deposition for obtaining a nanostructured interphase for enhancing the interfacial strength with an epoxy resin matrix. The structural, morphological and wetting properties of the pristine basalt fabrics and ZnO-coated basalt fabrics were evaluated. The fabrics were uniformly coated with ZnO nanostructures featuring a wurtzite structure and a twin hexagonal prism morphology. The contact angle measurements revealed that ZnO prisms transformed the hydrophilic basalt fabric into a hydrophobic one (similar to 130 degrees). ZnOs were also grown on the basalt fibers as yarns to evaluate their interfacial adhesion by single fiber pull-out tests. The results emphasize significant improvement in the apparent interfacial shear strength (similar to 42%) with limited degradation of the pristine basalt fiber tensile strength (a reduction of similar to 17%). Therefore, ZnO electroless deposition can be regarded as an effective mute to improve the mechanical performance of basalt/epoxy composites expanding their potential range of applications as structural materials.

One major warning emerging during the first worldwide combat against healthcare-associated infections concerns the key role of the surface in the storage and transfer of the virus. Our study is based on the laser coating of surfaces with an inorganic/organic composite mixture of amorphous calcium phosphate-chitosan-tetracycline that is able to fight against infectious agents, but also capable of preserving its activity for a prolonged time, up to several days. The extended release in simulated fluids of the composite mixture containing the drug (tetracycline) was demonstrated by mass loss and UV-VIS investigations. The drug release profile from our composite coatings proceeds via two stages: an initial burst release (during the first hours), followed by a slower evolution active for the next 72 h, and probably more. Optimized coatings strongly inhibit the growth of tested bacteria (Enterococcus faecalis and Escherichia coli), while the drug incorporation has no impact on the in vitro composite's cytotoxicity, the coatings proving an excellent biocompatibility sustaining the normal development of MG63 bone-like cells. One may, therefore, consider that the proposed coatings' composition can open the prospective of a new generation of antimicrobial coatings for implants, but also for nosocomial and other large area contamination prevention.

Nanocomposites of isotactic polypropylene loaded by various amounts of vapor-grown carbon nanotubes ranging from 0 to 20% wt. were obtained by extrusion. Raman investigations on these nanocomposites are reported. The nanocomposites were irradiated using a Co-60, with an integral dose of 1 kGy/h up to integral doses of 9 kGy, 18 kGy, and 27 kGy, in air, at room temperature. Raman measurements were performed by using a Bruker Senterra confocal Raman spectrometer operating at 785 nm. The research is focused on the information contained within the D and G Raman lines of these nanocomposites as a function of nanotube loading for various integral doses. The experimental data revealed the graduate silencing of the molecular motions assigned to the polymeric matrix due to the nanofiller and ionizing radiation. Based on experimental data, it is concluded that the positions of the D and G lines exhibit faint shifts due to the irradiation and that (on average) these shifts are consistent with the changes of the positions of D and G lines upon the increase of the loading with vapor-grown carbon nanofibers. Raman data suggest that the irradiation relaxes the pressure exerted on the nanofiller by the polymeric matrix, indicating a path to improve the physical features of polymer-carbon nanostructure nanocomposites. The research demonstrates the capability of Raman spectroscopy to sense the modifications of molecular vibrations in polymer-based nanocomposites, for both the polymeric matrix and the nanofiller. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)