Publications

Human society's demand for energy has increased faster in the last few decades due to the world's population growth and economy development. Solar power can be a part of a sustainable solution to this world's energy need, taking into account that the cost of the renewable energy recently dropped owed to the remarkable progress achieved in the solar panels field. Thus, this inexhaustible source of energy can produce cheap and clean energy with a beneficial impact on the climate change. The considerable potential of the organic photovoltaic (OPV) cells was recently emphasized, with efficiencies exceeding 18% being achieved for OPV devices with various architectures. The challenges regarding the improvement in the OPV performance consist of the selection of the adequate raw organic compounds and manufacturing techniques, both strongly influencing the electrical parameters of the fabricated OPV devices. At the laboratory level, the solution-based techniques are used in the preparation of the active films based on polymers, while the vacuum evaporation is usually involved in the deposition of small molecule organic compounds. The major breakthrough in the OPV field was the implementation of the bulk heterojunction concept but the deposition of mixed films from the same solvent is not always possible. Therefore, this review provides a survey on the development attained in the deposition of organic layers based on small molecules compounds, oligomers and polymers using matrix-assisted pulsed laser evaporation (MAPLE)-based deposition techniques (MAPLE, RIR-MAPLE and emulsion-based RIR-MAPLE). An overview of the influence of various experimental parameters involved in these laser deposition methods on the properties of the fabricated layers is given in order to identify, in the forthcoming years, new strategies for enhancing the OPV cells performance.

Novel complexes of type [Cu(N-N)(dmtp)(2)(OH2)](ClO4)(2)& BULL;dmtp ((1) N-N: 2,2 & PRIME;-bipyridine; (2) L: 1,10-phenantroline and dmtp: 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine) were designed in order to obtain biologically active compounds. Complexes were characterized as mononuclear species that crystallized in the space group P-1 of the triclinic system with a square pyramidal geometry around the copper (II). In addition to the antiproliferative effect on murine melanoma B16 cells, complex (1) exhibited low toxicity on normal BJ cells and did not affect membrane integrity. Complex (2) proved to be a more potent antimicrobial in comparison with (1), but both compounds were more active in comparison with dmtp-both against planktonic cells and biofilms. A stronger antimicrobial and antibiofilm effect was noticed against the Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA). Both electron paramagnetic resonance (EPR) and Saccharomyces cerevisiae studies indicated that the complexes were scavengers rather than reactive oxygen species promoters. Their DNA intercalating capacity was evidenced by modifications in both absorption and fluorescence spectra. Furthermore, both complexes exhibited nuclease-like activity, which increased in the presence of hydrogen peroxide.

Polarization P(T) of triglycine sulfate (TGS) crystal shows distinct properties versus temperature, between 28 degrees C and the Curie point Tc. Carefully measured polarization versus temperature on several ranges is presented. The slopes on the curve P(T) on three temperature ranges between 28 divided by 46 degrees C appear quite normal, while near the Curie point (47 degrees C divided by Tc) behave abnormally, due to the domain walls. The relaxation time LOW, MIDDLE and HIGH appear very interesting. The MIDDLE relaxation time tau(M), between 40 divided by 46 degrees C behave like the HIGH relaxation time tau (H) between 47 and 48 degrees C and between -20 divided by 10 degrees C (25 KBT) similar to LOW relaxation time tau(L) (28K(B)T). The diagrams Cole-Cole of TGS are analyzed here for the first time. Roughly, several parameters change their slopes at 30, 42, and 47 degrees C. The values of epsilon '(H) and epsilon"(H) show about the same slope on the zones 42-47 degrees C and 30-42 degrees C. For the same zones, epsilon '(L) shows several increasing activation energies toward Curie point, except epsilon"(L) and R (L) whose activation energy decreases. Finally, we mention the opposite variation of the negative ordinate Y (CH), Y (CL) of both arcs Cole-Cole and of the radius R (H) and R (L).

Ferroelectric alpha-Fe2O3/BaTiO3 photoanodes (hematite/BT) were fabricated on FTO and FTO/TiO2 substrates using a hydrothermal process and spin coating along with thermal treatments. The prepared hematite nanowires had length under 1 mu m and the BT film was about 18 nm thick. SEM, TEM and XPS investigations prove the formation of alpha-Fe2O3/BaTiO3 heterojunction structure. The ferroelectric poling of hematite/BT heterojunction was conducted both in propylene carbonate and in air. The photoelectrochemical performance of hematite/BT photoanodes is strongly influenced by the direction of ferroelectric polarization. The positive poling of the hematite/BT prepared on FTO/TiO2 substrate produces a 40.4% photocurrent density enhancement, in comparison with not poled version of the sample. Electrochemical impedance spectroscopy measurements provided usefull information regarding the effect of ferroelectric polarization on the charge transfer kinetics at the photoanode/electrolyte interface. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

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.