National Institute Of Materials Physics - Romania

The acceptor removal process is the most detrimental effect encountered in irradiated boron-doped silicon. This process is caused by a radiation-induced boron-containing donor (BCD) defect with bistable properties that are reflected in the electrical measurements performed in usual ambient laboratory conditions. In this work, the electronic properties of the BCD defect in its two different configurations (A and B) and the kinetics behind transformations are determined from the variations in the capacitance-voltage characteristics in the 243-308 K temperature range. The changes in the depletion voltage are consistent with the variations in the BCD defect concentration in the A configuration, as measured with the thermally stimulated current technique. The A & RARR;B transformation takes place in non-equilibrium conditions when free carriers in excess are injected into the device. B & RARR;A reverse transformation occurs when the non-equilibrium free carriers are removed. Energy barriers of 0.36 eV and 0.94 eV are determined for the A & RARR;B and B & RARR;A configurational transformations, respectively. The determined transformation rates indicate that the defect conversions are accompanied by electron capture for the A & RARR;B conversion and by electron emission for the B & RARR;A transformation. A configuration coordinate diagram of the BCD defect transformations is proposed.

Grazing incidence X-ray scattering (GIXRS) patterns of thin solid films based on non-stoichiometric chalcogenide glasses (ChG) from the pseudo - binary system (GeS4)x(AsS3)1-x were studied with a focus on the First Sharp Diffraction Peak (FSDP), assigned to the middle range order (MRO) of the glassy material. The films were grown using explosive thermal evaporation in vacuum (10-4 Pa) of pulverized ChG, prepared from previously synthesized bulk glasses, onto mono-crystalline silicon substrates. Scanning Electron Microscopy (SEM) and EnergyDispersive X-ray (EDX) spectroscopy were used to examine the morphology and elemental composition of the films, which were found to have similar composition to the bulk glasses. However, it was revealed that the molecular structure of the grown amorphous films differs from that of the initial ChG bulk material, as indicated by changes in the composition-dependent position and width of the FSDP. Additionally, the intensities of the FSDP in the films were higher compared to those of the bulk samples, suggesting that the molecular-like structure of ChGs is more pronounced in the form of thin films grown from the vapor phase.

The phosphate KCoCr-(PO4)(2) and iron-substitutedvariants KCoCr1-x Fe x (PO4)(2) (x =0.25, 0.5, and 0.75) were synthesized by a solid-state reaction route,while a high substitution level of Fe was achieved. Their structureswere refined using powder X-ray diffraction and indexed in a monoclinicsystem with a P2(1)/n spacegroup. A 3D framework with six-sided tunnels parallel to the [101]direction was formed in which the K atoms are located. Mo''ssbauerspectroscopy confirms the exclusive presence of octahedral paramagneticFe(3+) ions, with isomer shifts increasing slightly with x substitution. Electron paramagnetic resonance spectroscopyconfirmed the presence of paramagnetic Cr3+ ions. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present higher ionic activity. Relative to the electrochemicalactivity of K, these materials could be good candidates for positiveand/or negative electrode materials for energy storage applications. The synthesized phosphate KCoCr-(PO4)(2) and Fe-substituted variants KCoCr1-x Fe x (PO4)(2) (x = 0.25, 0.5, and 0.75) present a 3D frameworkwith six-sided tunnels in which the K atoms are located. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present improved ionic activity, making these materials goodcandidates for positive and/or negative electrode materials for energystorage applications.

We simulated numerically and demonstrated experimentally that the thermal emittance of a metasurface consisting of an array of rectangular metallic meta-atoms patterned on a layered periodic dielectric structure grown on top of a metallic layer can be tuned by changing several parameters. The resonance frequency, designed to be in the near-infrared spectral region, can be tuned by modifying the number of dielectric periods, and the polarization and incidence angle of the incoming radiation. In addition, the absorbance/emittance value at the resonant wavelength can be tuned by modifying the orientation of meta-atoms with respect to the illumination direction.

Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8-xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard's law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8-xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan d) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxation. Rise in Zinc concentration leads to a decrease in dielectric constant (e (r)) due to the declining of Fe3+-O-M2+ conducting network (M is Co or Ni). Here, we report a low loss tangent factor of the order of 8x10-3 0.6Zn(0.2)Co(0.2)Fe(2)O(4) make this composition suitable for high frequency-applications at room temperature. The activation energy is calculated from electric modulus formalism and DC electrical conductivity and found to increase with further substitution of Zn2+ concentration.

Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8-xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard's law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8-xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan d) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxation. Rise in Zinc concentration leads to a decrease in dielectric constant (e (r)) due to the declining of Fe3+-O-M2+ conducting network (M is Co or Ni). Here, we report a low loss tangent factor of the order of 8x10-3 0.6Zn(0.2)Co(0.2)Fe(2)O(4) make this composition suitable for high frequency-applications at room temperature. The activation energy is calculated from electric modulus formalism and DC electrical conductivity and found to increase with further substitution of Zn2+ concentration.

The phosphate KCoCr-(PO4)(2) and iron-substitutedvariants KCoCr1-x Fe x (PO4)(2) (x =0.25, 0.5, and 0.75) were synthesized by a solid-state reaction route,while a high substitution level of Fe was achieved. Their structureswere refined using powder X-ray diffraction and indexed in a monoclinicsystem with a P2(1)/n spacegroup. A 3D framework with six-sided tunnels parallel to the [101]direction was formed in which the K atoms are located. Mo''ssbauerspectroscopy confirms the exclusive presence of octahedral paramagneticFe(3+) ions, with isomer shifts increasing slightly with x substitution. Electron paramagnetic resonance spectroscopyconfirmed the presence of paramagnetic Cr3+ ions. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present higher ionic activity. Relative to the electrochemicalactivity of K, these materials could be good candidates for positiveand/or negative electrode materials for energy storage applications. The synthesized phosphate KCoCr-(PO4)(2) and Fe-substituted variants KCoCr1-x Fe x (PO4)(2) (x = 0.25, 0.5, and 0.75) present a 3D frameworkwith six-sided tunnels in which the K atoms are located. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present improved ionic activity, making these materials goodcandidates for positive and/or negative electrode materials for energystorage applications.

This work evaluates the effects of manganese (Mn) doping on the morpho-structural features, mechanical performance, and in vitro biological response of beta-tricalcium phosphate (beta-TCP) derived bioceramics for bone tissue engineering applications. Five different Mn doping levels (i.e., 0.01%, 0.05%, 0.1%, 0.5%, and 1 wt.%) were investigated, with the beta-TCP-based bioceramics being sintered at four temperatures (i.e., 1000, 1100, 1200, and 1300 degrees C). A densification improvement was induced when using Mn in excess of 0.05 wt.%; the densification remained stationary in the sintering temperature range of 1200 - 1300 degrees C. The structural analyses evidenced that all samples sintered at 1000 and 1100 degrees C were composed of beta-TCP as major phase and hydroxyapatite (HA) as a minor constituent (similar to 4-6 wt.%). At the higher temperatures (1200 and 1300 degrees C), the formation of alpha-TCP was signalled at the expense of both beta-TCP and HA. The Mn doping was evidenced by lattice parameters changes. The evolution of the phase weights is linked to a complex inter-play between the capacity of the compounds to incorporate Mn and the thermal decomposition kinetics. The Mn doping induced a reduction in the mechanical performance (in terms of compressive strength, Vickers hardness and elastic modulus) of the beta-TCP-based ceramics. The metabolic activity and viability of osteoblastic cells (MC3T3-E1) for the ceramics were studied in both powder and compacted pellet form. Ceramics with Mn doping levels lower than 0.1 wt.% yielded a more favorable microenvironment for the osteoblast cells with respect to the undoped beta-TCP. No cytotoxic effects were recorded up to 21 days. The Mn-doped beta-TCPs showed a significant increase (p < 0.01) in alkaline phosphatase activity with respect to pure beta-TCP.

Sub-stochiometric nickel oxide (NiOx) films were investigated as a hole selective contact option in silicon (Si) heterojunction solar cells. Numerical simulations were carried out to evaluate the impacts of the NiOx electronic properties variations and the NiOx/Si interface defect density (D-it) on device performance. Simulation data suggest that the best performance is achievable for wide bandgaps (E-g) and corresponding high valence band edge (E-VB) positions in the NiOx films. Overall, in simulations, the performance remains practically unchanged for the nickel vacancy concentrations [V-Ni] = 10(17)-10(21 )cm(-3), assuming high E-VB and low D-it. The experimental data measured using NiOx films prepared by radio-frequency magnetron sputtering reveal that the increase in [V-Ni] lifts the conductivity, concurrently decreasing E-g and E-VB. As a result, we concluded that the performance of the fabricated sputtered NiOx/Si heterojunction solar cell is limited by high D-it as well as narrow E-g and low E-VB.

The attraction towards Ti and its alloys reside in their superior mechanical and tribological features, as compared to CaPs, which are renowned for their compositional and structural features similar to those of natural bones. However, Ti-based materials suffer from limited biocompatibility and inertness when implanted for extended periods. As such, surface modification with ceramic coatings is required in order to achieve proper biomedical features and enhance their overall behavior in the human body. Hence, this study outlined for the first time the prospect of coating several Ti6Al4V substrates (disks) with bovine-bone derived hydroxyapatite (HA) by laser cladding technique with pre-placed slurry. During laser processing the input materials merge depending on the heating rate/temperature and clad materials. The proposed sample preparation set-up, followed for the first time in this study, involved the concomitant modulation of two parameters: the natural HA ratio (100 wt%, and 50 wt % HA + 50 wt% Ti blends) and laser beam power (500-1000 W range). The laser beam was applied after the ceramic slurries (prepared HA/HA-based blends mixed with polyvinyl alcohol) were placed inside the priorly machined channels on the metallic Ti disks. Partially overlapped cladding tracks (similar to 30% overlapping ratio) resulted and the investigations were further performed in cross-section view. The structural analyses confirmed the formation of calcium titanate as main phase for all samples and the arrest of HA only for those prepared with 100% HA ratio at low to medium laser powers. In addition, the morpho-compositional evaluation revealed the formation of a fully ceramic coating only for the latter sample sets. Further, the surface wettability (contact angle and surface free energy) and Vickers micro-hardness results led to the selection of the optimal technological parameters for the development of ceramic cladded layers with prospect compatibility with regenerative med-icine applications.