Publications

One of the most fundamental aspects of the heterogeneous catalysis field is the manipulation of the catalysts' activity. In photocatalysis this is carried out by maximizing the right crystal plane of a semiconductor oxide. Until now, most of the papers have achieved this by a combination of different oxides, with noble metals and sometimes with carbon nanomaterials. In this work MWCNTs (multiwalled carbon nanotubes) were applied as "crystallization promoters" in a very simple, safe, one-step hydrothermal method. By this method TiO2 nano/micro crystals with exposed {001} facets were obtained in the first step. The next episode in the crystal manipulation "saga" was the modification of the (001) crystallographic plane's structure by creating ordered/own faceted "crystallographic holes". These elements are capable of further enhancing the obtained activity of titania microcrystals to a higher extent, as shown by the UV driven photocatalytic phenol degradation experiments. The appearance of the holes was "provoked" by simple calcination and their presence and influence were demonstrated by XPS and HRTEM.

Titanium films sputtered on FTO glass were used for obtaining highly oriented titania nanotubes via anodization technique. Then, pulsed laser deposition of CdS was carried out for sensitizing of similar to 60 nm wide titania nanotubes by applying 50, 100, 150 or 200 subsequent laser pulses. Scanning electron microscopy was used to indicate which samples had the open nanotubular structure of titania preserved after the deposition of CdS. Energy dispersive spectroscopy showed that a higher number of applied laser pulses results in the increase of Cd and S quantity within samples. Pulsed laser deposition technique was also employed for the fabrication of PbS counter electrode. I-V characteristics of the photovoltaic cells consisting the obtained electrodes were measured and compared under one-sun illumination. The photovoltaic cell with photoanode sensitized with CdS by applying 150 laser pulses showed the highest current density and voltage among the investigated cell.

Influence of Nd substitution for Ni on the magnetic properties and the martensitic transformation (MT) characteristics are investigated on Ni57-xNdxFe18Ga25 (x=0 divided by 4) ferromagnetic shape memory alloys (FSMAs) in bulk and also in ribbons prepared by melt spinning method and subjected to different thermal treatments. Increasing the Nd content induces a decrease of both the Curie and the MT temperatures. (C) 2015 The Authors. Published by Elsevier Ltd.

Ge and Si nanocrystals (NCs), quantum dots (QDs), and amorphous nanoparticles (NPs) have a significant role in the developement of micro- and nanoelectronic devices due to capability to tune their electrical and photoconductive properties by tailoring the morphology and structure parameters. Ge and Si NCs/QDs/NPs are zero-dimensional (0D) systems and the SiO2 films containing them are percolative systems. In this review, the role of deposition and annealing conditions in the morphology and structure of Ge and Si NCs/QDs/NPs embedded in amorphous SiO2 matrix is discussed for a wide variety of films and multilayered structures. The electrical and photoconductive properties of nanostructures deposited by different techniques as magnetron sputtering, ion implantation, chemical vapour deposition, sol-gel and molecular beam epitaxy, and subsequently annealed in conventional furnace or by rapid thermal annealing under different conditions are analised. We demonstrate how the electrical and photoconductive properties of nanostructures can be tuned by varying the deposition and annealing parameters. The role of Si-rich oxide and defects in the formation of Ge and Si NCs is shown and the role of defects in improving electrical properties and enhancing the photoconductivity of films and multilayered structures is highlighted. We evidence the contribution of quantum confinement effect and show that the most probable transport mechanisms in these percolative systems are tunnelling and hopping.

Zinc silicate ceramics have been prepared by using conventional ceramic technology. Morphological, structural, and dielectric characterizations of the samples were performed using scanning electron microscopy, X-ray diffraction, and terahertz time-domain spectroscopy. The achieved absorption properties of zinc silicates make them very attractive solutions for submillimeter-wave applications.

SERS studies were performed on films of two families of multi-wall carbon nanotubes (MWCNTs) under an excitation light of 514.5 nm and 647.1 nm. These included Aldrich-MWCNTs, which alternate semiconducting and metallic tubes and M-MWCNTs that contain only metallic tubes obtained by water assisted catalytic chemical vapour deposition (CCVD). The two families of MWCNTs reveal similar spectra in the Stokes branch, which feature an increasing Raman intensity when the glass substrate is replaced with an Au or Ag substrate, indicating a (surface enhanced Raman scattering) SERS mechanism. In the anti-Stokes branch, despite an enhancement of approximately 100 times compared to the predictions of the Boltzmann law, only Aldrich-MWCNTs exhibit a Raman spectrum with an intensity that increases as a result of the change in the glass substrate to Au or Ag, a fact that is revealed by the signature of the SERS process. The invariance of the Raman intensity in the anti-Stokes branch as a result of the change of the substrate is characteristic of M-MWCNTs and results from a Raman light scattering process that takes place only within the skin depth of the metallic structure.

The synthesis routes for polycrystalline bulk Sr2FeMoO6 (SFMO), offer various possibilities, but in all the cases it is difficult to obtain a single phase of this compound. A new challenge in the field is to achieve mono-crystals using different growing routes and the Bridgman method represents one of them. In order to establish the optimal conditions of mono-crystals growing process, a complex thermal investigation of bulk double perovskite has been performed. Differential thermal analysis investigation in argon inert atmosphere, starting from room temperature up to 1650 degrees C provided information about melting and re-crystallization temperature range. Both, the activation energy of Sr2FeMoO6 re-crystallization process and the re-crystallization mechanism were comparatively analyzed by two free-model estimations (Friedman and Ozawa-Flynn-Wall analysis). The resulted data are very important in order to set up the heating program of Bridgman furnace.

The electrical behavior of layered double hydroxides containing Al or Ga as the trivalent ions and Mg or Zn as bivalent ions was evaluated using broadband dielectric spectroscopy in a wide temperature range. Besides conduction effects a relaxation peak is observable at high frequencies which is assigned to the reorientational fluctuations of water molecules adsorbed on the oxide surface or in the interlayer voids. The Maxwell-Wagner-Sillars peak, superimposed to the conductivity phenomenon is observable at low frequencies. A non-monotonous temperature dependence of the relaxation rates of the relaxation process has been found. A quantitative description of this dependence was possible based on a model assuming two competing processes: rotational fluctuation of water molecules and formation of additional defects. Reasonable values for the characteristic parameters were obtained. Thus the water behavior in the studied layered oxides is similar to that observed for water in other porous materials. However, the activation energy of the rotational fluctuation, the pre exponential factor and the number of defects are higher whereas the value of the energy of defect formation is lower in the layered oxide materials than for water confined to nanoporous molecular sieves, porous glasses or in bulk ice.

In this paper we show that the possibility of obtaining the high values of efficiency of relief-phase holographic gratings formed in the photo-thermoplastic recording process holds not only due to the non-sinusoidal profile form, but also due to the effect of optical coating that appears in the two-layer system of photo-semiconductor deformed thermoplastic. Analyzed are the conditions, under which takes place the antireflection optical coating, reducing unwanted reflections from surfaces and thereby enhancing efficiency. It is shown that by careful choice of the thicknesses and refractive indices of the layers materials the efficiency of holographic gratings can be improved by 2-5 %.

Dense MgB2 samples with La2O3 addition were obtained by spark plasma sintering. We used two different La2O3 raw powders showing different particle sizes and shapes. The as-obtained composite samples have significant differences in microstructure and Vickers hardness. A deposited phosphate layer was obtained by immersing the samples in PBS, and drying. Formation of phosphate needles, gathered in bouquets, show a possible bioactive behavior of MgB2.