Publications

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.

The present study demonstrates the effectiveness of hydroxyapatite nanopowders in the adsorption of zinc in aqueous solutions. The synthesized hydroxyapatites before (HAp) and after the adsorption of zinc (at a concentration of 50 mg/L) in solution (HApD) were characterized using X-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM and TEM, respectively). The effectiveness of hydroxyapatite nanopowders in the adsorption of zinc in aqueous solutions was stressed out through ultrasonic measurements. Both Langmuir and Freundlich models properly fitted on a wide range of concentration the equilibrium adsorption isotherms, allowing us to precisely quantify the affinity of zinc to hydroxyapatite nanopowders and to probe the efficacy of hydroxyapatite in removal of zinc ions from aqueous solutions in ultrasonic conditions.

This work is focused on the use of multilayer transparent conductive electrode (TCE) based on ZnO/Ag/ZnO in the fabrication of the organic heterostructures. The ZnO/Ag/ZnO obtained combining sputtering/thermal evaporation/sputtering techniques is featured by a good optical transmittance, a low electrical resistivity and a reduced roughness. All these characteristics recommend it as a viable alternative to indium tin oxide (ITO) for different applications. The organic materials, N,N' - diphenyl N,N' - bis (1 - aphthyl) 1,1' - biphenyl 4,4' - diamine (alpha-NPD), 5,12-Dihydro-5-12-dimethylquino [2,3-b]acridine-7,14dione (DMQA) and 4,7 diphenyl-1,10-phenanthroline (BPhen) were deposited by vacuum thermal evaporation (VTE) method, the properties of the obtained layers being investigated by FTIR, UV-VIS and PL) spectroscopy. The I-V characteristic (recorded in dark) of the organic heterostructure fabricated on the ZnO/Ag/ZriO electrode shows diode behavior, revealing its potential applications in the organic light emitting devices (OLED).

Eggshell membranes were employed as biological scaffolds for developing soft and versatile actuators. A particular architecture, consisting of eggshell membrane coated with polypyrrole, has been fabricated and has been found to be a green, inexpensive, lightweight, and easy to handle class of actuators. The polypyrrole-coated eggshell membrane devices were tested in liquid, ambient atmosphere and controlled humidity environment, with the recorded movements proving their versatility. In 1 M NaCl aqueous solution, by applying successive potential pulses, the actuator contracts/expands owing to the expulsion/insertion of the electrolyte ions out/into polypyrrole film, producing a displacement of similar to 0.1 cm. In air, upon application of voltages from 2 to 5 V on a V-shaped geometry actuator, it bends due to water desorption from its structure induced by Joule heating, generating a displacement which reaches similar to 0.4 cm at 5 V. In a chamber with controlled humidity, the decrease of humidity stimulates a bending/curling motion of the actuator, achieving a displacement of similar to 2.1 cm at 50% relative humidity. Upon modification of the humidity, these actuators move, hold, and release delicate and lightweight objects. Such polypyrrole-coated eggshell membrane actuators which operate in different environments and respond to multiple stimuli can have potential applications in biomimetic micromanipulators or artificial muscle fields.