Publications

In this work, single-phase Te-doped CoSb3 polycrystalline bulk (Indium powder) and nanocomposites (alpha-WC nanopowder) were synthesized via a ball milling, hand-grinding and consolidated by spark plasma sintering technique. The thermoelectric and mechanical characteristics of as-synthesized composites were studied. The electrical resistivity varies between 11.82 and 12.82 mu Omega-m for CoSb2.875Te0.125 + x (x = 0.33% In, 1% In, 2% In, 4% In and 1% In + 0.33% alpha-WC, respectively) composites. At temperature of 300 K, composite with x = 1% In exhibit the lowest resistivity of 11.82 mu Omega-m. Also, negative values of Seebeck coefficients confirm that electrons are the predominant charge carriers. The maximum power factor of 2566 and 2482 mu Wm-1 K-2 are observed from x = 1% In and x = 1% In + 0.33% alpha-WC composites at 673 K, respectively. Notably, the power factor of 1% In and 1% In + 0.33% alpha-WC composites is slightly higher (1.05 times) than the CoSb2.875Te0.125 sample. The composites with lowest weight percent of 1% In and 1% In + 0.33% alpha-WC have a considerably improved power factor. For the composite with x = 1% In + 0.33% alpha-WC, the minimum thermal conductivity of 2.32 W/m-K at 300 K was achieved through a combination of doping and dispersion in the CoSb2.875Te0.125 matrix. It is possible that the multi-scale size distributions of grains will reduce the lattice thermal conductivity by scattering phonons over a large wavelength range. As a result, an increased figure of merit of 0.82 was achieved for CoSb2.875Te0.125 + 1% In + 0.33% alpha-WC composites at 823 K. The results suggest that the doping with composite approach could boost thermoelectric efficiency in n-type CoSb3-based materials.

Blending carbon particles (CPs) and nanoscale bioactive cerium dioxide is a promising approach for designing composites for biomedical applications, combining the sorption and antioxidant potentials of each individual component. To address this issue, it is crucial to assess the correlation between the components' ratio, physicochemical parameters, and biofunctionality of the composites. Thus, the current research was aimed at fabricating C@CeO2 composites with different molar ratios and the examination of how the parameters of the composites affect their bioactivity. XRD, X-ray photoelectron spectroscopy, and electron microscopy data verified the formation of C@CeO2 composites. CeO2 nanoparticles (NPs) of 4-6 nm are highly dispersed on the surfaces of amorphous CPs. The presence of CeO2 NPs on the carbon surface decreased its adsorption potential in a dose-dependent manner. Besides, the coexistence of carbon and CeO2 in a single composite promotes some redox interactions between O-functionalities and Ce3+/Ce4+ species, resulting in changes in the chemical state of the surface of the composites. These observations suggest the strong connection between these parameters and the biofunctionality of the composites. The presence of CeO2 NPs on the surface of carbon led to a significant increase in the stability of the prepared composites in their aqueous suspensions. The enhancement of bioactivity of the newly prepared C@CeO2 compared to bare carbon and CeO2 was validated by testing their pseudomimetic (catalase/peroxidase-like and superoxide dismutase-like), antiamyloid, and radioprotective activities.

Cylindrical magnetic nanowires (NWs) have gained significant interest as building-blocks of spintronics devices and magnetic sensors thanks to their geometry-tunable magnetic properties and anisotropy. While the synthesis and compositional control of NWs have seen major improvements in recent years, considerable challenges remain for the characterization of local magnetic features at the nanoscale. Here, we demonstrate non-perturbative field distribution mapping and minimally invasive magnetic imaging with scanning nitrogen-vacancy magnetometry. This enables a sensitivity down to 3 mu T Hz-1/2 used to localize ultra-scaled magnetic defects with lateral dimensions below 50 nm. The imaging reveals the presence of magnetic inhomogeneities in correspondence of periodical geometrical modulations/anti-notches in axial magnetized nanowires that are largely undetectable with standard metrology. The features induce local fluctuations of the NWs' magnetization orientation that are sensed by SNVM and compared with magnetic force microscopy. Finally, the strong magnetic field confinement in the nanowires is leveraged to study the interaction between the stray magnetic field and the fluorescence generated by two nitrogen-vacancies contained in the probe sensor, thus clarifying the contrast formation mechanisms. We report on magnetic imaging capability with non-perturbative field distribution mapping and minimally invasive magnetic sensing using scanning nitrogen-vacancy magnetometry in axial magnetized nanowires.

The development of thin films of chromium-doped hydroxyapatite (20CrHAp) deposited on silicon substrate by the spin coating method was realized for the first time. A coherent investigation of the physicochemical properties of 20CrHAp thin films was also carried out for the first time. The obtained thin films were studied by various techniques such as, scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) investigations and fractal analysis. By scanning electron microscopy (SEM) studies were obtained valuable information about the surface morphology of the 20CrHAp thin films. The zeta potential (ZP), Dynamic light scattering (DLS) and ultrasound measurements (US) were used in order to evaluate the stability of 20CrHAp suspension. The ratio between the hydrodynamic diameter obtained by DLS and the particle diameter obtained by SEM was 1.6. The SEM results on 20CrHAp thin films suggested that the sample possess a conglomerate of nanoparticles unevenly distributed on their surface. The surface morphology of the 20CrHAp thin films was studied with the aid of atomic force microscopy (AFM). The AFM topography of the 20CrHAp thin film's surface highlighted that the thin films present the morphology of a continuum deposited layer composed of non-uniform particle conglomerates. The presence of hydroxyapatite on the surface of silicium effects on the development of the fungal cells on their surface. Furthermore, our investigation delves into the

Fe, Co and Si powders were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mossbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The room temperature Mossbauer measurements were consistent with the occurrence of FeCo2Si and Fe0.5Co0.5Si crystalline phases. The low temperature Mossbauer spectra confirmed the absence of superparamagnetism up to 44 K in the milled system. XRPD patterns supported the phase sequence derived from Mossbauer spectroscopy. The coercive field was found to increase with the ball milling time (BMT). Zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe in the temperature range 5-300 K evidenced the transition to the skyrmion phase of the Fe0.5Co0.5Si material below the critical temperature of 44 K. The optical absorption in the UV-Vis-NIR region of the spectrum was found to increase with BMT.

The synergistic piezoelectric and osteoconductive properties of barium titanate (BT) and hydroxyapatite (HA) could stir the development of a new generation of synthetic bone graft substitutes, with capability for rapid and safe osseointegration. The research focused on two concurrent approaches for coupling the BT and HA materials: (i) conventional sintering of BT-HA powder mixtures; and (ii) functionalization of pre-sintered BT with HA coatings using magnetron sputtering (MS). Irrespective of the BT/HA ratios ranging from 95/5 to 80/20 wt%, nanocrystalline or highly-crystallized nature of the powders, sub-micron- or micron-sized particle dimensions, and sintering temperature, it was observed that the BT-HA reactivity cannot be prevented above 800 degrees C. At higher temperatures in the range of 1000-1300 degrees C, HA undergoes decomposition and extensively reacts with BT, leading to the formation of several secondary phases such as CaTiO3, Ba2Ca(PO4)2, BaCa6(PO4)4O, BaCa(PO3)4, and beta-Ca2P2O7. As a consequence, the cytocompatibility assessed in fibroblast and osteoblast cell cultures, as well as the piezoelectric response, were significantly altered. Applying HA coatings by MS to the sintered BT ceramics successfully preserved their piezoelectric properties, while also providing an unaltered cytocompatible and osteogenic-prone surface. The HA coatings were fully crystallized at post-deposition annealing temperatures of 550 and 700 degrees C, achieving crystalline qualities comparable to HA powders sintered at 1100 and 1200 degrees C, respectively. No reactivity events between BT and HA were observed. Partial reactivity was only noticeable upon annealing at 1000 degrees C. Therefore, it is suggested that the HA coating of BT is effective in seamlessly coupling the piezoelectric and osteogenic properties of the two constituents without compromise.

Recently, much research has focused on the search for new mixed donor-acceptor layers for applications in organic electronics. Organic heterostructures with layers based on the generation 1 poly(propylene thiophenoimine) (G1PPT) dendrimer, N,N '-diisopropylnaphthalene diimide (MNDI), and a combination of the two were prepared and their electrical properties were investigated. Single layers of G1PPT and MNDI and a mixed layer (G1PPT:MNDI) were obtained via spin coating on quartz glass, silicon, and glass/ITO substrates, using chloroform as a solvent. The absorption mechanism was investigated, the degree of disorder was estimated, and the emission properties of the layers were highlighted using spectroscopic methods (UV-Vis transmission and photoluminescence). The effects of the concentration and surface topographical particularities on the properties of the layers were analyzed via atomic force microscopy. All of the heterostructures realized with ITO and Au electrodes showed good conduction, with currents of the order of mA. Additionally, the heterostructure with a mixed layer exhibited asymmetry in the current-voltage curve between forward and reverse polarization in the lower range of the applied voltages, which was more significant at increased concentrations and could be correlated with rectifier diode behavior. Consequently, the mixed-layer generation 1 poly(propylene thiophenoimine) dendrimer with N,N '-diisopropylnaphthalene diimide can be considered promising for electronic applications.

A series of M(x)CoCeMgAlO mixed oxides with different transition metals (M = Cu, Fe, Mn, and Ni) with an M content x = 3 at. %, and another series of Fe(x)CoCeMgAlO mixed oxides with Fe contents x ranging from 1 to 9 at. % with respect to cations, while keeping constant in both cases 40 at. % Co, 10 at. % Ce and Mg/Al atomic ratio of 3 were prepared via thermal decomposition at 750 degrees C in air of their corresponding layered double hydroxide (LDH) precursors obtained by coprecipitation. They were tested in a fixed bed reactor for complete methane oxidation with a gas feed of 1 vol.% methane in air to evaluate their catalytic performance. The physico-structural properties of the mixed oxide samples were investigated with several techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), elemental mappings, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction under hydrogen (H2-TPR) and nitrogen adsorption-desorption at -196 degrees C. XRD analysis revealed in all the samples the presence of Co3O4 crystallites together with periclase-like and CeO2 phases, with no separate M-based oxide phase. All the cations were distributed homogeneously, as suggested by EDX measurements and elemental mappings of the samples. The metal contents, determined by EDX and ICP-OES, were in accordance with the theoretical values set for the catalysts' preparation. The redox properties studied by H2-TPR, along with the surface composition determined by XPS, provided information to elucidate the catalytic combustion properties of the studied mixed oxide materials. The methane combustion tests showed that all the M-promoted CoCeMgAlO mixed oxides were more active than the M-free counterpart, the highest promoting effect being observed for Fe as the doping transition metal. The Fe(x)CoCeMgAlO mixed oxide sample, with x = 3 at. % Fe displayed the highest catalytic activity for methane combustion with a temperature corresponding to 50% methane conversion, T50, of 489 degrees C, which is ca. 40 degrees C lower than that of the unpromoted catalyst. This was attributed to its superior redox properties and lowest activation energy among the studied catalysts, likely due to a Fe-Co-Ce synergistic interaction. In addition, long-term tests of Fe(3)CoCeMgAlO mixed oxide were performed, showing good stability over 60 h on-stream. On the other hand, the addition of water vapors in the feed led to textural and structural changes in the Fe(3)CoCeMgAlO system, affecting its catalytic performance in methane complete oxidation. At the same time, the catalyst showed relatively good recovery of its catalytic activity as soon as the water vapors were removed from the feed.

The silver/magnesium doped hydroxyapatite (AgMgHAp, Ca10_ x-yAgxMgy(PO4)6(OH)2, xAg=0.05 and yMg=0.02) nanocomposites coatings were deposited on Si substrate using the dip coating technique. The resulting coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR-ATR) spectroscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The EDS analysis highlighted the presence of the constitutive elements of the silver/magnesium doped hydroxyapatite (AgMgHAp) nanocomposites coatings. The surface microtexture of the AgMgHAp was assessed by atomic force microscopy (AFM) technique. The AFM data suggested the obtaining of a uniform deposited layer comprised of equally distributed nanoconglomerates. FT -IR studies highlighted the presence of vibrational modes associated with the phosphate and hydroxyl groups. No bands associated with silver or magnesium were observed. The XPS analysis highlighted the presence of the constituent elements of hydroxyapatite (Ca 2p, P 2 s, O 1 s), as well as dopants (Ag 3d, Mg 1 s and Mg 2p). The antifungal evaluation of AgMgHAp coatings was carried out using the Candida albicans ATCC 10231 fungal strain. The results of the antifungal assay revealed that the AgMgHAp coatings exhibited a strong inhibitory antifungal activity. Furthermore, the data highlighted that the AgMgHAp inhibited the development of biofilm on their surface. The results revealed that the antifungal activity of the coating varied based on the duration of incubation. On the other hand, the data also showed that AgMgHAp nanocomposites coatings inhibited the fungal cell adhesion and development from the early stages of the incubation. In addition to morphological analysis, we additionally take advantage of AFM images to investigate and explore the domain of fractal and multifractal analysis applied to the films under evaluation. Our studies indicates that nanocomposite coatings made from AgMgHAp demonstrate strong antifungal properties. Our studies indicates that nanocomposite coatings made from AgMgHAp demonstrate strong antifungal properties. These results suggest the potential of AgMgHAp nanocomposite coatings as a promising solution for developing innovative antifungal devices in biomedical applications.