Publications

The low-energy electron irradiation improves the electrical properties of the Ti-doped chromium thin films obtained by Laser-assisted Thermionic Vacuum Arc (LTVA). The irradiation doses, between 0.6 C/m(2) and 326.4 C/m(2), operate as a nanozonal melting effect, decreasing the metallic alloy's roughness, and increasing the electrical conductivity at a depth up to 8 nm. Therefore, the grain sizes of the surface nanostructures are increased after irradiation, but the surface roughness is substantially improved. By tailoring the surface parameters like crystallinity and roughness of the metallic thin films used as electrodes in the OLED technologies, a reduction of the Schottky contacts between the metal and semiconductor contact is expected. This fact minimizes the contact resistance between the metallic and semiconductor thin films and increases the charge injection across the OLED sandwich structures.

The aim of this work is the development of a cylindrical dielectric resonator antenna with multimodal operation. In order to use modes with different radiation patterns, the field distributions were investigated. Using a feeding solution with the resonator placed asymmetrically above a wide microstrip feeding line, we managed to excite and identify 17 operating modes in the 1.8-4.5 GHz frequency band. In dissimilarity with the symmetric configuration, the proposed feeding allows excitation of new modes, which exhibit a magnetic dipole radiation pattern. The new added modes enhance the antenna pattern diversity and increase the antenna capacity to mitigate the multipath effects.

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

Nano-nitride reinforcement of Fe-Cr alloys are under intense investigations, e.g., along with oxide-strengthened, nitride-strengthened reduced activation steels with superior high temperature mechanical properties are developed as materials for nuclear energy applications. Fe14Cr alloy powders were produced by mechanical milling for up to 170 h under a nitrogen atmosphere followed by heating under an Ar5%H-2 atmosphere to 600 degrees C-1120 degrees C. The samples were investigated by means of X-ray diffraction, DTA/TG and magnetic measurements. CrN, detected after milling for 58 h, reached 39 wt % (5.3 wt.% total N) at 170 h milling. The ferrite supersaturated with nitrogen shows a strong decrease in grain size and saturation magnetization, an increase in lattice constant, microstrain and coercivity, H-c. Upon heating, the metastable ultrafine alpha-ferrite and CrN in the as-milled samples undergo transformations and recrystallization into ferrite grains free of super-saturation, whose microstructure follows a continuous relaxation. The supersaturation with nitrogen was retained upon heating in the relatively stable ferrite crystalized at the milling stage. This microstructure undergoes a discontinuous relaxation in the 800 degrees C-1120 degrees C region: a pronounced decrease of grain size (down to similar to 25 nm), an increase of lattice constant, microstrain and H-c. These improvements were associated with features of discontinuous precipitation reaction of coherent nitride precipitates (involving a new alpha ''-phase with expanded lattice), in connection with the heating in the austenite phase field. Such microstructure refinement or (nitride) strengthening of Fe14Cr alloys can be achieved on powders milled for much less time as compared to previously reported (oxide dispersion) strengthening of Fe14Cr-W-Ti ferritic steels. (C) 2022 The Authors. Published by Elsevier B.V.

Zr0.8Sn0.2TiO4 powders synthesized by solid state reaction route have been consolidated by conventional and spark plasma sintering methods. Single-phase ceramics with various microstructures and, consequently, different extrinsic absorption were investigated by terahertz time-domain spectroscopy. The results showed that the terahertz spectroscopy can be used for tailoring in the " synthesis - microstructure - properties" cycle.

Exchange coupling in a SrFe12O19 - Fe3O4 nanocomposite magnet was explored in this study. The composition, microstructure, local structure and magnetic properties were investigated by XRD, SEM, Mossbauer spectroscopy, and SQUID magnetometry. The magnetoplumbite SrFe12O19 and spinel Fe3O4 structures were verified by X-ray diffraction. The morphology of the composite reveals the characteristics of the two components. The hyperfine parameters allowed the identification of the Wyckoff positions of the iron ions corresponding to the involved phases. The magnetic measurements of the composite, showing a single-phase-like magnetic hysteresis loop, confirmed the exchange coupling between the hard and soft magnetic phases.

Bulk high density MgB2 and a composite material made of a PLA matrix and MgB2 powder inclusions were in vivo tested as candidates for biodegradable materials for orthopedic implants. A rat model was used. Implants were introduced into femoral bone, in transversal and longitudinal directions. Assessment of the implant-tissue interaction was performed by X-ray imaging, X-ray computer tomography, electron microscopy, cytology, and histopathology on samples at 40 and 90 days after surgery. Both materials are biocompatible, bone and adjacent soft tissue showing good tolerance of implants. Biodegradation of MgB2 is faster than for PLA-MgB2 composite, but in both cases, it is accompanied by bone regeneration. Results suggest that use of MgB2-containing composites can promote space and time control of degradation and promotes MgB2 as a promising material for fracture repair. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

NiTi cylindrical materials were obtained by spark plasma sintering at 850??C or 900??C from high purity Ni and Ti powders. These mixtures were previously processed by mechanical alloying for 8 and 15 hours. In order to increase the alloy homogeneity, the NiTi materials were subjected to post aging treatment in protective atmosphere at constant temperature 400??C and cooling in water with ice. All samples were characterized by optical microscopy, differential calorimetry (DSC), X-ray measurements (XRD) and micro/nanoindentation measurements. The results demonstrate that the NiTi materials obtained by this preparation route have good mechanical properties and can serve as a quantitative reference for the microstructure design of shape memory materials for various applications, such as the biomedical ones.

The dielectric and electric properties of a core-shell SrFe12O19 - BNT-BT nanocomposite were explored in this study. The desired composition and the existence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. The dielectric constant values approached the case of BNT-BT due to the small amount of hexaferrite content. The electric properties were also derived.

A consistent quantitative description of radiation-induced degradation on p-type Silicon detectors is conducted within CERN RD50 collaboration. The present contribution summarizes the first obtained results for epitaxial 50 mu m thin pad diodes irradiated with protons, neutrons and gamma rays. Microscopic and Macroscopic damage-driven effects are analyzed.