Publications

The influence of the injection of minority charge carriers on the formation of a divalent bistable defect (DBH) having two energy levels of E-v + 0.44 eV and E-v + 0.53 eV in its metastable configuration is investigated. Using forward current injection, the formation temperature of this defect in p-type silicon can be lowered by about 50 degrees C. The production of such bistable defect is enhanced in materials with a high ratio of boron to carbon concentrations. This allows one to conclude that the boron atom is one of the constituents of the defect under study. There is also a correlation between the behavior of the bistable hole traps and a metastable electron trap observed earlier. It is concluded that these traps are related to metastable and stable configurations of the DBH defect, which has inverse occupancy level ordering in its stable configuration.

In this study, CuxCrFeTiV (x = 0.21, 0.44, 1 and 1.7 M ratio) high entropy alloys have been devised for thermal barriers between the plasma facing tungsten tiles and the copper-based heat sink in the first wall of nuclear fusion reactors. The high entropy alloys were produced by ball milling the elemental powders, followed by consolidation with spark plasma sintering. Irradiation of the equiatomic CuCrFeTiV sample was carried out at room temperature with Ai(+) (300 keV) beams with a fluence of 3 x 10(20) at/m(2). Structural changes prior and after irradiation were investigated by scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy, X-ray diffraction and thermal diffusivity. Preliminary results showed the presence of heterogenous and multiphasic microstructures in all samples. Moreover, with the increase of the Cu content it is possible to observe the formation of Cu-rich structures. The diffractogram of the CuCrFeTiV sample revealed major peaks of a BCC crystal structure and minor peaks of a FCC crystal structure. In addition, after irradiation no modifications in the CuCrFeTiV microstructure or in the diffractogram were observed.

Formation peculiarities of highly-doped (Y(0.86)La(0.09)Vb(0.05))(2)O-3 transparent ceramics have been studied by X-ray diffraction and electron microscopy methods. The phase composition evolution of 1.81Y(2)O(3).0.18La(2)O(3)0.01Yb(2)O(3) powder mixtures annealed at the temperatures of 1100, 1200, 1300, and 1400 degrees C has been studied by XRD. It has been shown that Yb2O3 phase dissolves in Y2O3 matrix in the calcination temperature range of 1300-1400 degrees C. Complete dissolution of La2O3 in Y2O3 matrix occurs at temperatures above 1400 degrees C. La3+ ions enter in Y2O3 and Yb2O3 crystal structures simultaneously in the 1200-1300 degrees C range, which leads to a remarkable increase in the volume of the corresponding crystal lattices. The possible reasons for suppressing the crystalline growth of Y2O3 and Yb2O3 cubic phases have been discussed. Finally, (Y(0.86)La(0.09)Vb(0.05))(2)O-3 transparent ceramics have been obtained by solid-state vacuum sintering at 1650-1750 degrees C. Ceramics synthesized at a temperature of 1750 degrees C have been characterized by an in-line optical transmittance of 60% and a homogeneous distribution of constituent components within the volume and along the grain boundaries.

We reported on three-dimensional (3D) superparamagnetic scaffolds that enhanced the mineralization of magnetic nanoparticle-free osteoblast cells. The scaffolds were fabricated with submicronic resolution by laser direct writing via two photons polymerization of Ormocore/magnetic nanoparticles (MNPs) composites and possessed complex and reproducible architectures. MNPs with a diameter of 4.9 +/- 1.5 nm and saturation magnetization of 30 emu/g were added to Ormocore, in concentrations of 0, 2 and 4 mg/mL. The homogenous distribution and the concentration of the MNPs from the unpolymerized Ormocore/MNPs composite were preserved after the photopolymerization process. The MNPs in the scaffolds retained their superparamagnetic behavior. The specific magnetizations of the scaffolds with 2 and 4 mg/mL MNPs concentrations were of 14 emu/g and 17 emu/g, respectively. The MNPs reduced the shrinkage of the structures from 80.2 +/- 5.3% for scaffolds without MNPs to 20.7 +/- 4.7% for scaffolds with 4 mg/mL MNPs. Osteoblast cells seeded on scaffolds exposed to static magnetic field of 1.3 T deformed the regular architecture of the scaffolds and evoked faster mineralization in comparison to unstimulated samples. Scaffolds deformation and extracellular matrix mineralization under static magnetic field (SMF) exposure increased with increasing MNPs concentration. The results are discussed in the frame of gradient magnetic fields of similar to 3 x 10(-4) T/m generated by MNPs over the cells bodies.

The present work reports on the effect of slow charged ions irradiation on the structural and magnetic properties of zinc ferrite nanoparticles obtained by coprecipitation method. Results from both the x-ray and Fourier Transform Infrared Spectroscopies confirm the formation of the spinel phase. The structural investigation using x-rays reveals no significant impurity peak and a crystallite size of 9 nm. Particle size of pristine sample is determined to be around 9 nm. Crystallinity and magnetic properties of ferrite sample investigated before and after irradiation process show that electronic excitations inside the material alter the magnetic parameters. Mossbauer Spectroscopy measurements indicate that a fluence of 3*10(14) ions cm(-2) Ne8+ ions of 90 keV are sufficient to induce cation redistribution into zinc ferrite nanoparticles.

W-laminates are multi layered composites realized from alternately stacked W and a second metal foils. Such materials are promising candidates for W-based structural materials for fusion reactors like DEMO or beyond concepts, due to the fact that cold-rolled ultrafine-grained thin W foils show exceptional properties in terms of ductility, toughness and ductile to brittle transition (DBT), in contrast to classic bulk W materials. Therefore, different routes to transfer the W foils properties to bulk materials have been investigated. In this work we present the results obtained for W-Cu laminates produced via a FAST (Field Assisted Sintering Technique) joining route. The main advantages of FAST resides in the short processing time, with subsequent lower recrystallization detrimental effects. Structural and thermophysical properties show that the best materials are obtained for about 100 mu m thick W foils and 50-100 mu m thick Cu foils, while tensile and Charpy impact tests results show that the FAST processed W-Cu laminates are similar to the W-Cu laminates obtained by diffusion bonding.

Crystallization processes of bismuth germanate glasses may be evidenced by the optical properties of Eu3+ ions, used as probes because these ions substitute the Bi3+ ions in the glass-ceramic samples. The gradual thermal annealing of these glasses induces rearranging of GeO4 tetrahedra around Bi3+ ions and transforms the red colored glasses in transparent glass-ceramic samples. The red color comes from the light scattering on GeO4 clusters and, after rearranging in Bi4Ge3O12 nanoparticles, convert the glass-ceramic samples in transparent materials. One of the most essential information is given by the phonon side bands investigations which, coupled with the Raman spectra allows the identification of Bi4Ge3O12 lattice vibration but also those of residual GeO4 tetrahedra. The measurements of the luminance and CIE circle have shown a significant increase of the light emission for the glass-ceramic samples, while the Magnetic Circular Dichroism indicate lower symmetry coordination around the Eu3+ ions in the glass sample compared with the glass-ceramic and also a change in the coordination number to the higher values.

Obtaining nanoscale materials has allowed for the miniaturization of components, which has led to the possibility of achieving more efficient devices with faster functions and much lower costs. While hydroxyapatite [HAp, Ca-10(PO4)(6)(OH)(2)] is considered the most widely used material for medical applications in orthopedics, dentistry, and general surgery, the magnesium (Mg) is viewed as a promising biodegradable and biocompatible implant material. Furthermore, Mg is regarded as a strong candidate for developing medical implants due to its biocompatibility and antimicrobial properties against gram-positive and gram-negative bacteria. For this study, magnesium-doped hydroxyapatite (Ca10-xMgx (PO4)(6) (OH)(2), x(Mg) = 0.1), 10MgHAp, suspensions were successfully obtained by an adapted and simple chemical co-precipitation method. The information regarding the stability of the nanosized 10MgHAp particles suspension obtained by zeta-potential analysis were confirmed for the first time by a non-destructive ultrasound-based technique. Structural and morphological studies of synthesized 10MgHAp were conducted by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) mode and scanning electron microscopy (SEM). The XRD analysis of the 10MgHAp samples confirmed that a single crystalline phase associated to HAp with an average grain size about 93.3 nm was obtained. The FTIR-ATR spectra revealed that the 10MgHAp sample presented broader IR bands with less visible peaks when compared to a well-crystallized pure HAp. The SEM results evidenced uniform MgHAp nanoparticles with spherical shape. The antimicrobial activity of the 10MgHAp suspension against gram-positive strains (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212), gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853), as well as a fungal strain (Candida albicans ATCC 90029) were evaluated.

Textile materials can be easily used as a support for the nano-decoration with active particles in order to gain new features such as self-cleaning, antimicrobial efficiency, water repellency, mechanical strength, color change and protection against ultraviolet radiations. In this context, our present research reports the fabrication and characterization (physico-chemical analysis and surface morphology) of cotton fabrics treated with reduced graphene oxide decorated with two types of TiO2 nanoparticles co-doped with 1% iron and nitrogen atoms (TiO2/rGO NPs) and synthesized in different hydrothermal conditions by a simultaneous precipitation of Ti3+ and Fe3+ ions to achieve their uniform distribution or after a sequential precipitation of these two cations for obtaining a higher concentration of iron on the surface of Ti4+ oxyhydroxide. Further, the antimicrobial efficiency of these TiO2/rGO-treated textiles and their influence on human cells were assessed. We demonstrated the successful development of TiO2/rGO coating of cotton fabrics which are harmless for human skin cells and inhibit the growth of Staphylococcus aureus and Enterococcus faecalis. These findings confirm their great potential as novel graphene-based materials for biomedical and photocatalytic applications and this approach could be used for the large-scale fabrication of innovative self-cleaning and antimicrobial textiles.

Novel biomedical composites, based on organically modified vermiculite and montmorillonite with deposited Ca-deficient hydroxyapatite (CDH), were prepared. The monoionic sodium forms of vermiculite and montmorillonite were intercalated with chlorhexidine diacetate (CA). The surfaces of organoclays were used for the precipitation of Ca-deficient hydroxyapatite. The composites with Ca-deficient hydroxyapatite showed very good antibacterial effects, similar to the antimicrobial activity of pure organoclay samples. Better antibacterial activity was shown in the organically modified montmorillonite sample with Ca-deficient hydroxyapatite compared with the vermiculite composite, but, in the case of Staphylococcus aureus, both composites showed the same minimum inhibitory concentration (MIC) value. The antimicrobial effect of composites against bacteria and fungi increased with the time of exposure. The structural characterization of all the prepared materials, performed using X-ray diffraction and FT infrared spectroscopy analysis, detected no changes in the original clay or CDH during the intercalation or precipitation process, therefore we expect the strength of the compounds to be in the original power.