Publications

Arrays of magnetic Ni-Cu alloy nanowires with different compositions were prepared by a template-replication technique using electrochemical deposition into polycarbonate nanoporous membranes. Photolithography was employed for obtaining interdigitated metallic electrode systems of Ti/Au onto SiO2/Si substrates and subsequent electron beam lithography was used for contacting single nanowires in order to investigate their galvano-magnetic properties. The results of the magnetoresistance measurements made on single Ni-Cu alloy nanowires of different compositions have been reported and discussed in detail. A direct methodology for transforming the magnetoresistance data into the corresponding magnetic hysteresis loops was proposed, opening new possibilities for an easy magnetic investigation of single magnetic nanowires in the peculiar cases of Stoner-Wohlfarth-like magnetization reversal mechanisms. The magnetic parameters of single Ni-Cu nanowires of different Ni content have been estimated and discussed by the interpretation of the as derived magnetic hysteresis loops via micromagnetic modeling. It has been theoretically proven that the proposed methodology can be applied over a large range of nanowire diameters if the measurement geometry is suitably chosen.

In this work, the ferroelectric characteristics of 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) thin films grown on 0.7 wt. % Nb-doped (001)-SrTiO3 (Nb:STO) single-crystal have been investigated. High-resolution transmission electron microscopy and electron energy loss spectroscopy revealed a very sharp Nb:STO/BCZT interface, while selected area electron diffraction revealed the epitaxial growth of the BCZT layer on the Nb:STO substrate. The ferroelectric nature of the BCZT films have been investigated by piezoresponse force microscopy and hysteresis loops. The effect of electric field on polarization switching kinetics has been investigated and has been analyzed by the nucleation limited switching model with a Lorentzian distribution function. The local field variation was found to decrease with the increase in the electric field, and thus, the switching process becomes faster. The peak value of the polarization current and the logarithmic characteristic switching time exhibited an exponential dependence on the inverse of electric field. This model gave an excellent agreement with the experimental polarization reversal transients throughout the whole time range. Published by AIP Publishing.

Bio-waste eggshell membranes (ESM) present a unique micro-architecture consisting in an interwoven fibrous network which can be functionalized with metal oxides resulting in hybrid materials. ESM were covered with ZnO nanostructures by electroless deposition using Au as catalyst. The structural, optical, morphological and wetting properties of the pristine ESM and ESM/ZnO were evaluated. The ESM fibers were uniformly coated by ZnO hexagonal prisms, the hybrid ESM/ZnO preserving the water absorption characteristic of the pristine ESM. Combining an abundant bio-waste with a simple wet chemical synthesis method, flexible organic/inorganic hybrid networks based on ZnO-functionalized ESM can be designed for various applications. (C) 2018 Elsevier B.V. All rights reserved.

The production and thermal stability of the irradiation paramagnetic point defects (IPPDs) in the as-grown, standard float-zone silicon (STFZ) and oxygen doped float-zone silicon (DOFZ) irradiated at room temperature with high fluence 3.5 MeV (1 x 10(17) cm(-2)) low energy and 27 MeV (2 x 10(16) cm(-2)) high energy electrons were investigated by Electron Spin Resonance (ESR). The nature and concentration of the IPPDs identified in the as-irradiated and isochronally annealed up to 300 degrees C samples by ESR measurements under intense above the gap 1.06 mu m in-situ laser illumination, were found to depend on oxygen concentration and electrons energy. While irradiation of STFZ with electrons produced as main IPPDs, besides divacancies, larger tetravacancy and pentavacancy cluster defects, irradiation of DOFZ resulted mainly in divacancies, vacancy-oxygen and interstitial oxygen-carbon impurity pairs. The observed variation in the nature of the main resulting IPPDs with the concentration of incorporated oxygen is explained by differences in the dominant defects production mechanisms. Thus in STFZ with lower oxygen concentration (1 x 10 16 cm(-3)) the dominant production mechanisms are the direct defects formation from a chain of neighboring vacancies by a cascade of secondary recoils across the path of the high energy irradiating particle and the divacancies diffusion and trapping/aggregation. Meanwhile, in DOFZ with larger oxygen content (1.2 x 10(17) cm(-3)) the primary vacancy and interstitial trapping by the oxygen and carbon impurities is the dominant defect production mechanism. Variations in the concentration and nature of the IPPDs observed during isochronal annealing are discussed in terms of defects thermal activated diffusion and recombination processes.

Ce3+ and Tb3+-doped silico-phosphate films were obtained by using the sol-gel method, followed by the spin-coating deposition on silicon substrate. The homogeneity of the films was investigated by the conoscopy method. It was observed that the analysed films are isotropic but relatively inhomogeneous due to the specificity of the deposition technique. The morphology of the sol-gel films was investigated by Scanning Electron Microscopy and Atomic Force Microscopy. The elemental composition was determined by Energy Dispersive X-ray analysis. The magneto-optical investigations evidenced the capability of Ce and Tb-doped films of less than 2 mu m thickness to produce measurable Kerr rotations of 1 mdeg/T and 0.28 mdeg/T, respectively. (C) 2018 Elsevier B.V. All rights reserved.

InGeNi ohmic contacts on n-type semi-insulating GaAs(110) cleaved surfaces were fabricated. Cleaving semiconductor single crystal ensures the obtaining of semiconductor surfaces almost ideal in terms of chemical purity and stoichiometry. The chemical depth profile of metallic layer was investigated and revealed through multiple alternating steps of Ar+ etchings and XPS (x-ray photoelectron spectroscopy) measurements. The metallic layers made of alloy of Ge, In and Ni (60 nm Ge, 60 nm In and 10 nm Ni), were obtained by thermal evaporation on cleaved surfaces in a high vacuum facility, followed by a thermal annealing at 430-450 degrees C for 5 min. Twelve etching sessions were required until the metal/semiconductor interface has been reached. A total of 14 etchings steps were performed during the experiment, a layer with a thickness of 140 nm being removed from the surface. The atomic concentrations of the constituent chemical elements were determined. In3d, In4d, Ga3d, Ga2p, As3d, As2p, Ni2p(3/2), Ge3d, O1s and C1s spectral lines were recorded and chemical bonds within the layer were analyzed from the fittings. The formation of InxGa1-xAs type compounds and of an intermediate semiconductor layer rich in Ge atoms at the interface was highlighted. X-ray detectors InGeNi/GaAs/Al and InGeNi/GaAs/Ti were fabricated with ohmic contacts based on this contacting scheme and Schottky interfaces prepared also by evaporation on cleaved edges. Electrical characteristics have been investigated and key diode parameters determined - ideality factor, Schottky barrier height, series resistance. Detection capabilities of these devices were studied in an x-rays flux, provided by a Co anode x-ray source.

Non-ionising energy loss of radiation produces point defects and defect clusters in silicon, which result in a significant degradation of sensor performance. In this contribution results from TSC (Thermally Stimulated Current) defect spectroscopy for silicon pad diodes irradiated by electrons to fluences of a few 10(14) cm(-2) and energies between 3.5 and 27 MeV for isochronal annealing between 80 and 280 degrees C, are presented. A method based on SRH (Shockley-Read-Hall) statistics is introduced, which assumes that the ionisation energy of the defects in a cluster depends on the fraction of occupied traps. The difference of ionisation energy of an isolated point defect and a fully occupied cluster, Delta E-a is extracted from the TSC data. For the VOt (vacancy-oxygen interstitial) defect Delta E-a = 0 is found, which confirms that it is a point defect, and validates the method for point defects. For clusters made of deep acceptors the Delta E-a values for different defects are determined after annealing at 80 degrees C as a function of electron energy, and for the irradiation with 15 MeV electrons as a function of annealing temperature. For the irradiation with 3.5 MeV electrons the value Delta E-a = 0 is found, whereas for the electron energies of 6-27 MeV Delta E-a > 0. This agrees with the expected threshold of about 5 MeV for cluster formation by electrons. The Delta E-a values determined as a function of annealing temperature show that the annealing rate is different for different defects. A naive diffusion model is used to estimate the temperature dependencies of the diffusion of the defects in the clusters.

We have prepared Eu2+ (1%) doped BaCl2 nanopowders by using a hybrid sol-gel/thermal decomposition route using barium acetate and trichloracetic acid as in situ chlorination agent. Structural and thermal analysis data have shown that orthorhombic BaCl2 phase crystallization occurs at 260 degrees C. BaCl2:Eu2+ nanocrystals of about 100-200 nm in size were produced after annealing (in air) at 500 degrees C and they displayed Eu2+ d -> f type luminescence at 396 nm. X-ray photoelectron spectroscopy indicated the presence of both Eu2+, Eu3+ ions species and a BaO passivating layer at the surface of the nanocrystals. A polymer nanocomposite (PVP@BaCl2:Eu2+) was also processed and its optical response under x-ray irradiation was found to be similar to that of the nanopowder. X-ray excited luminescence showed Eu2+ luminescence at 396 nm, whereas the thermoluminescence peak at 130 degrees C was assigned to the F(Cl)-center recombination with Eu2+ related hole centers.

The nature of the second magnetization peak (SMP) appearing on the dc magnetic hysteresis curves of superconducting single crystals with random pinning is still under debate. Many interesting SMP models and mechanisms were proposed and considered so far, and it is believed at present that this effect is system dependent. We analyzed the dc magnetization curves and the magnetic relaxation in the SMP domain for various single-crystal specimens (superconducting cuprates and iron-based superconductors), of different pinning strengths, with the external magnetic field H oriented along the crystallographic c axis or perpendicular to it. The sample independent aspects revealed by the relaxation results are the absence of single-vortex collective pinning around the SMP onset field and the sign changing of the vortex creep exponent between the onset field and the peak field. This general behavior supports strongly the pinning-induced disordering of the low-H quasi-ordered vortex solid as the actual scenario for the SMP.

The sol-gel method was used to synthesize the silver doped hydroxyapatite (Ag:HAp) gels in order to produce the antifungal composite layers. The pure Ti disks were used as the substrate for the composite layers. Important information about suspensions used to make Ag:HAp composite layers were obtained from an ultrasonic technique. The identification of the phase composition of the Ag:HAp composite layers was accomplished X-ray diffraction (XRD). The morphology and the thickness of the layers was evaluated using scanning electron microscopy (SEM). The uniform distribution of the constituent elements (Ag, Ca, P, and O) in both analyzed samples was observed. The antifungal activity of the samples against Candida albicans ATCC 10231 microbial strain were investigated immediately after their preparation and six months later. SEM and confocal laser scanning microscopy (CLSM) images showed that the composite layers at the two time intervals exhibited a strong antifungal activity against Candida albicans ATCC 10231 and completely inhibited the biofilm formation.