Publications

Growth of Ag films of up to 30 nm thickness on Si(1 1 1) 7 x 7 at room temperature is investigated by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). LEED revealed the coexistence of Ag and Si spots starting with 1 monolayer (ML) of Ag deposited. The Ag lattice constant, starting with 25 ML, is slightly higher than for bulk Ag and increase linearly with Ag thickness, reaching about 4.2 nm for the thickest films. The average terrace widths detected from LEED spot profile analysis are about 30 nm for clean Si(1 1 1) 7 x 7 and about 5.5 nm for the thickest Ag(1 1 1) film, in agreement with STM observations. The intensity variation of core levels analyzed by XPS is taken into account by a model assuming the initial formation of Ag islands with linear variation of coverage vs. the amount of Ag deposited, followed by growth in a quasi layer-by-layer mode. The interface barrier is in the range of 0.4 eV, lower than all values reported previously. Ag deposited on Si(1 1 1) 7 x 7 at room temperature provides flat Ag(1 1 1) for synthesis of 2D materials, and may be used for low barrier Schottky diodes.

Co-sputtering of tungsten-aluminum fusion relevant materials in a dual-High Power Impulse Magnetron Sputtering discharge, operated in different Ar-D-2 gas mixtures, was investigated in gas phase by means of energy-resolving mass spectrometry. Experimental results indicate that the total ion flux and its composition are strongly dependent on sputtering gas composition and the average power applied to the targets. During single HiPIMS operation with W target, the D- ions are the most abundant species. The measured D- ion flux shows an increase with the rising of D-2 content in Ar-D-2 gas mixture and a linear increase with the power applied to the W target. In contrast, during dual-HiPIMS operation, a decrease of D- ion flux was observed when the input power applied to the Al target was increased. The origin of different deuterium ion species and retention mechanisms are discussed. The surface morphology, microstructure and chemical composition of the W-Al coatings obtained in Ar-D-2, were investigated by means of, Atomic Force Microscopy, X-ray diffraction and Glow Discharge Optical Emission Spectroscopy. GDOES depth profiles show the presence of a large amount of deuterium (up to 21 at.%) in the mixed W-Al layers and indicate that the D retention in the mixed W-Al layers is mainly related to the W in-depth concentration and less dependent on the Al one. The intense and energetic bombardment of the growing film with D- ions seems to be responsible for the large amount of D retained in the W-Al layers.

The development of coenzyme Q(10) (CoQ(10)) based electrochemical sensor for the detection of oxidative stress initiators is described for the first time. The sensor relies on CoQ(10) redox properties. CoQ(10) was immobilized at the surface of glassy carbon electrodes (GCE) in combination with cyclodextrins (CD), alpha-CD or beta-CD, that ensure the formation of a well dispersed CoQ(10) film. Nanostructured thin films of CoQ(10) alone and in complexes with alpha-CD or beta-CD at the electrode surface were characterized by scanning electron microscopy (SEM) and Fourier-transformed infrared spectroscopy (FTIR), enabling to identify the morphology of the films and the interactions between the CoQ(10) and CD. Nafion (R) was used to ensure sensor stability. The optimization of the CoQ(10) sensor configuration was made by assessing CoQ(10) redox properties through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), correlated with the results obtained from SEM and FTIR characterization. Next, the sensor in the optimized configuration, GCE/alpha-CD + CoQ(10)/Nafion (R), was applied for the detection of oxidant molecules, hydrogen peroxide and the superoxide radical, through the evaluation of the CoQ(10) redox properties monitored by fixed potential chronoamperometry and square wave voltammetry (SWV). (C) 2019 Elsevier Ltd. All rights reserved.

Thin films of (117) Bi2Sr2Ca2CuO8+ (Bi-2212) were grown by Molecular Organic Chemical Vapor Deposition (MOCVD) on (110) SrTiO3 and (110) LaAlO3 substrates. Substrates were vicinal with off angles up to 20 degrees. Films are 3D epitaxial and X-ray diffraction phi- scans demonstrate that, while the films grown on a flat substrate are composed of twinned grains, the films on vicinal substrate are twin-free. A higher quality is obtained if growth is performed at two temperatures: Growth starts at 550-600 degrees C and continues at 700-750 degrees C. The twin-free film grown by the two-temperature method shows a zero-resistance critical temperature of 37 and 32 K when the measuring current is applied in-plane parallel and perpendicular to [001] direction of the substrate. Twin-free non c-axis thin films are promising for fabrication of novel planar THz devices.

ZnO-CuxO core-shell radial heterojunction nanowire arrays were fabricated by a straightforward approach which combine two simple, cost effective and large-scale preparation methods: (i) thermal oxidation in air of a zinc foil for obtaining ZnO nanowire arrays and (ii) radio frequency magnetron sputtering for covering the surface of the ZnO nanowires with a CuxO thin film. The structural, compositional, morphological and optical properties of the high aspect ratio ZnO-CuxO core-shell nanowire arrays were investigated. Individual ZnO-CuxO core-shell nanowires were contacted with Pt electrodes by means of electron beam lithography technique, diode behaviour being demonstrated. Further it was found that these n-p radial heterojunction diodes based on single ZnO-CuxO nanowires exhibit a change in the current under UV light illumination and therefore behaving as photodetectors.

Fe-14Cr-0.4Ti-0.25Y(2)O(3) ferritic steels were produced by varying the amount of residual process control agent, PCA (ethanol), in the ball-milled powders and changing the spark-plasma-sintering, SPS, temperature. Near the-oretical density (99.3%), high Vickers hardness (501-920 HV, measured by applying a load of 100 g for 5 s) and fine grain size (26-36 nm), very stable against heating, can be achieved on ODS ferritic steels, consolidated from powders with a low amount of PCA and processing temperature in the range of 1000 degrees C-1100 degrees C. Additional grain refinement occurs near alpha -> gamma transition which is generated by the reaction of the traces of PCA with the ferritic matrix upon heating. High local temperatures and the evolved thermally activated processes, at the contact points between particles/at the particle surfaces during SPS-consolidation, were demonstrated to be the main factors responsible for improved densities and hardness. The role of PCA in the sintering, thermal and microstructure particularities and its impact on the quality of the final steel was thoroughly analysed throughout the work. (C) 2019 Elsevier B.V. All rights reserved.

Previous electron spin resonance investigations correlated with data from cathodoluminscence and photoluminescence measurements have shown that impurity ions consisting mainly of isotopes with zero nuclear moments are involved in the structure of the observed paramagnetic point defects. In the present microstructural and compositional investigation we demonstrate that oxygen, carbon and silicon impurity atoms exhibiting low natural content of isotopes with non-zero nuclear spin are indeed present in cBN crystallites selected from amber coloured BORAZON CBN400 and CBN 500 super abrasive powders, as well as in the black coloured BORAZON CBN1000 and CBN Type 1. It is also shown that aggregates of impurity atoms are present next to the extended cBN lattice defects, which could explain the non-uniform distribution of the electro- and opto-active impurities reported in a spectroscopy investigation.

This study proves that the new developed zinc-doped hydroxyapatite (ZnHAp) colloids by an adapted sol-gel method can be widely used in the pharmaceutical, medical, and environmental industries. ZnHAp nanoparticles were stabilized in an aqueous solution, and their colloidal dispersions have been characterized by different techniques. Scanning Electron Microscopy (SEM) was used to get information on the morphology and composition of the investigated samples. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the elemental compositions of ZnHAp colloidal dispersions. The homogeneous and uniform distribution of constituent elements (zinc, calcium, phosphorus, oxygen) was highlighted by the obtained elemental mapping results. The X-ray diffraction (XRD) results of the obtained samples showed a single phase corresponding to the hexagonal hydroxyapatite. The characteristic bands of the hydroxyapatite structure were also evidenced by Fourier-transform infrared spectroscopy (FTIR) analysis. For a stability assessment of the colloidal system, -potential for the ZnHAp dispersions was estimated. Dynamic light scattering (DLS) was used to determine particles dispersion and hydrodynamic diameter (D-HYD). The goal of this study was to provide for the first time information on the stability of ZnHAp particles in solutions evaluated by non-destructive ultrasound-based technique. In this work, the influence of the ZnHAp colloidal solutions stability on the development of bacteria, such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), was also established for the first time. The antimicrobial activity of ZnHAp solutions was strongly influenced by both the stability of the solutions and the amount of Zn.

The results of the present Q-band electron spin resonance (ESR) investigation on amber colored cubic boron nitride (cBN) crystalline superabrasive powder (BORAZON CBN400) offer further support to the hypothesis that impurity ions with high natural abundant zero nuclear spin isotopes, distributed non-uniformly, are involved in the structure of the observed paramagnetic centers. One could thus explain the absence of any hyperfine structure in the multifrequency electron spin resonance spectra of both presently and previously investigated cBN crystalline powders and single crystals. The scanning electron microscopy, cathodoluminescence and photoluminescence studies performed on single crystallites selected from the same cBN400 batch further confirm the presence of electro- and photo-luminescent active impurity related centers, non-uniformly distributed in the cBN crystallite host lattice. The observation of an intense and reproducible thermoluminescence spectrum, up to high radiation doses, attributed to several trapping centers involving impurities, is also reported here.

In analogy with equilibrium phase transitions, we address the problem of the instability to symmetry-breaking perturbations of systems undergoing a laser transition. The symmetry in question is the U(1) invariance with respect to a phase factor, and the perturbation is a coherent field E, coupled to the exciton. At the rate-equation level we analyze first the case of a cavity containing a single, two-level emitter, and then a chain of such cavities interacting by photon-hopping processes. In both cases, spontaneous symmetry breaking takes place when the system is in the lasing phase. For the laser transition, the analog of the thermodynamic limit is the scaling limit of vanishing cavity loss and light-matter coupling, kappa -> 0, g -> 0, so that g(2)/kappa remains finite. We show that in the lasing regime, anomalous averages persist in the E -> 0 limit, provided that the scaling limit is performed first. Lasing diagnosis based on robust anomalous averages is compared numerically with the familiar coherence criterion g((2))(0) = 1, and the advantages of the former are discussed.