Publications

The results of the surface morphology studies as well as optical and electrical properties of nano -dimensional vanadium oxide composite structures deposited on various substrates- silica, glass substrates covered by conducting layer of SnO2, pure pyroceramics plates and the same covered by Al(2)O3, SiO2, Ta2O5 layers are presented. According to Raman spectroscopy results the thin film structure obtained on quartz corresponds to the a, -V2O5 orthorhombic phase. In contrast with this the Raman spectra of V2O5 films obtained on pyroceramics substrates, passivated by Al2O3, Ta2O5, SiO2 oxides, do not appear clearly marked narrow lines which indicate their amorphous character. The investigation of the optical properties of the fabricated layers in the spectral range of 200-1000 nm had revealed the presence of both allowed direct and indirect electron transitions. In the frequency range of 10(3)-10(7) Hz the real Z' and imaginary Z '' part of the total impedance of pyroceramics/Al2O3/Al/V2O5/AI structure were studied. The applied direct bias leads to a considerable Z', as well as Z '' decrease. The analysis of the obtained dependencies is carried out by using the method of equivalent circuits.

Capacitance-voltage (C-V) hysteresis of metal-ferroelectric-semiconductor (MFS) structure based on a-In2GaZnO5.5 and Pb0.2Zr0.8TiO3 layers are recorded in the 350-470 K range. The structure is grown on FTO/glass to obtain a transparent MFS. The memory functionality of the heterostructure is proved through C-V and P-V characteristics. The memory window is dependent on the temperature, the largest value of 2.5 V being obtained at 470 K, where the contribution of the ferroelectric-semiconductor interface defect states is minimized. The direction of C-V hysteresis is clockwise at 350 K, and it turns counterclockwise at higher temperatures where the ferroelectric polarization has the main contribution.

Commercial MgB2 powder was loaded into a Fe-tube, by plastic deformation a tape of similar to 0.5 mm in thickness and 6.9 mm in width was obtained. Short pieces were processed by Spark Plasma Sintering (SPS) at 950, 1050 and 1150 degrees C for 3 min. The optimum sintering temperature is 1050 degrees C. From magnetic/electrical measurements, the onset critical temperature and the irreversibility field at 5 K were 38.7 / 38.9 K and 6.2 / 13.5 T, respectively. The pinning-force-related parameters indicate that the dominant flux pinning mechanism is of point pinning type. Contribution of grain boundary pinning is stronger at lower temperatures.

We describe a new concept to encode information in magnetic films that goes beyond the conventional way of digital magnetic recording. In our approach the information is stored via a continuous variable, namely the remanent coupling angle between two magnetic films that are separated by a nonmagnetic spacer layer. Using the technique of nuclear resonant scattering (NRS) [1, 2] we show with good precision, how this coupling angle can be conveniently adjusted with high degree of remanence by shortly applied external magnetic fields. Moreover this effect is explained using a micromagnetic model [3, 4]. Extremely important for future applications of this concept, we demonstrate, that the remanent coupling angles can be read out via magneto-optical or magneto-resistance effects. In principle, this approach allows to design novel memory cells for advance data storage devices, where multiple states per unit cell can be generated and recorded.

The "avalanche" up-conversion properties of the glass-ceramics containing (Ho3+, Yb3+)doped LiYF4 nanocrystals have been studied by comparison to the corresponding nanocrystals and polycrystalline powder samples. Under 810 nm laser light pumping, all the samples showed "green" ((H-2(11/2), 4S(3/2)) -> I-4(15/2)) up-conversion luminescence. The pump power threshold for the avalanche mechanism is about 75mW for the nanocrystalline or polycrystalline powder samples indicating a weak influence of the nanosize related effects is but smaller of about 43mW for the nano-glass ceramic due to the high "local" Yb3+ concentrations.

Two methods were used for the synthesis of composites based on reduced graphene oxide (RGO) and poly(para-phenylene vinylene) (PPV) in un-doped and doped state, respectively, i.e. the annealing conversion (AC) of the PPV precursor solution (PS) at 300 degrees C and the electropolymerization (E) of alpha, alpha, alpha', alpha'-tetrabromo-p-xylene. In the case of the E method, a decrease in the distyrylbenzene (DSB) weight onto the RGO sheet surface in favor of PPV in doped state is demonstrated by the s and p polarized IR spectroscopy. The change of the orientation angle of the transition dipole moment vector for the IR bands at 835 and 964 cm(-1), in the case of the AC of the PPV PS, is a result of the p-p* interactions between the phenyl groups of PPV and the RGO sheets. The photoluminescence (PL) bands at 2.42 and 2.26 eV indicate the formation of PPV macromolecular chains (MCs) with lengths of 5 and 710 repeating units (RUs), respectively. The anisotropic PL studies performed on the composites RGO/PPV in un-doped and doped state, respectively, highlight an increase of the wrapping angle of RGO sheets with PPV MCs with lengths of 5 RUs, when graphene concentration increases.

Thin films of carbon were synthesized by ns pulsed laser deposition in vacuum on silicon substrates, starting from graphite targets. Further on, the films were irradiated with a picosecond laser source emitting in visible at 532 nm. After tuning of laser parameters, we obtained a film surface covered by laser induced periodical surface structures (LIPSS). They were investigated by optical, scanning electron and atomic force microscopy. It was observed that changing the irradiation angle influences the LIPSS covered area. At high magnification it was revealed that the LIPSS pattern was quite complex, being composed of other small LIPSS islands, interconnected by bridges of nanoparticles. Raman spectra for the non-irradiated carbon films were typical for a-C type of diamond-like carbon, while the LIPSS spectra were characteristic to nano-graphite. The pristine carbon film was hydrophilic, while the LIPSS covered film surface was hydrophobic. (C) 2016 Elsevier B.V. All rights reserved.

We report on the selection by combinatorial pulsed laser deposition of Silver-doped Carbon structures with reliable physical-chemical characteristics and high efficiency against microbial biofilms. The investigation of the films was performed by scanning electron microscopy, high resolution atomic force microscopy, energy dispersive X-Ray Spectroscopy, X-ray diffraction, Raman spectroscopy, bonding strength "pull-out" tests, and surface energy measurements. In vitro biological assays were carried out using a large spectrum of bacterial and fungal strains, i.e., Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Enterococcus faecalis and Candida albicans. The biocompatibility of the films obtained was evaluated on MG63 mammalian cell cultures. The optimal combination with reasonable physical-chemical properties, efficient protection against microbial colonization and beneficial effects on human cells was found for Silver-doped Carbon films containing 2 to 7 at.% silver. These mixtures can be used to fabricate safe and efficient coatings of metallic implants, with the goal to decrease the risk of implant associated biofilm infections which are difficult to treat and often responsible for implant failure. (C) 2016 Elsevier B.V. All rights reserved.

Czochralski growth along with linear optical characterizations and near-infrared laser performances of ytterbium doped lanthanum and gadolinium scandium borate crystals (LaxGdYScZYbw(BO3)(4) with x + y + z + w = 4) with acentric huntite-type structure are presented in this paper. Low-temperature spectroscopy analyses reveal two insertion sites for Yb3+ ions: a main one in Sc sites and the other one in lanthanide site. While absorption cross-section spectrum reveals broad bands with a maximum value of 7.8 x 10(-21) cm(2) at 981.5 nm for the s state of polarization, the emission cross-section spectrum presents low anisotropy between the two polarization states over 1060 nm. Best laser performance is obtained in continuous-wave operation mode with 0.94W at 1070 nm for a 12.9-at% doped crystal. (C) 2016 Elsevier B.V. All rights reserved.