Eddy-current anomaly in Fe-based nanocrystalline wires

The circular permeability, μ=μ′−jμ″, of two Fe-based nanocrystalline wires obtained by furnace annealing (S1) and by current annealing (S2) were determined from the measurements of the impedance, Z=R+jωL, as a function of frequency (f=0.1-100 kHz) and DC bias field (H=0-89 kA/m). So the H-dependent low-f eddy-current anomaly factor, η(H), has been investigated. The experimental results indicate that the sample S2 by current annealing has a larger η=4 than the sample S1 by furnace annealing with η=2.8 at H=0. With increasing H, the η(H) of two samples decreases initially until about H=450 A/m, and then increases very quickly. These results have been analyzed by the helical magnetization model considering the contribution of domain wall displacements (DWD) and domain magnetization rotation (DMR).     

Influence of the deposition parameters on the microstructure and opto-electrical properties of hydrogenated nanocrystalline silicon films by HW-CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared at high deposition rates (> 13 Å/s) from pure silane without hydrogen dilution by hot wire deposition method by varying filament-to-substrate distance (d_s-f). In this study we have systematically and carefully investigated the effect of filament-to-substrate distance on structural, optical and electrical properties of the Si:H films. A variety of characterization techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FE-SEM), UV-Visible-NIR spectroscopy and electrical dark and photoconductivity measurement were used to characterize these films. Films deposited at d_s-f > 5 cm are amorphous while those deposited at d_s-f < 5 cm are biphasic; a crystalline phase and an amorphous phase with nano-sized crystallites embedded in it. Low angle X-ray diffraction analysis showed that the crystallites in the films have preferential orientation along (111) directions. Decrease in d_s-f, the crystallinity and crystalline size increases whereas hydrogen bonding shifts from mono-hydride (SiH) to di-hydride (SiH₂) and poly-hydride (SiH₂)_n complexes. The band gaps of nc-Si:H films (~ 1.9-2.0 eV) are high compared to the a-Si:H films, while hydrogen content remains < 10 at.%. We attribute the high band gap to the quantum size effect. A correlation between electrical and structural properties has been established. Finally, from the present study it has been concluded that the filament-to-substrate distance is a key process parameter to induce the crystallinity in the films by hot wire method. The ease of depositing films with variable crystallite size and its volume fraction, and tunable band gap is useful for fabrication of tandem/micro-morph solar cells.     

Zero- and one-dimensional thioindates synthesized under solvothermal conditions yielding α-In2S3, β-In2S3 or MgIn2S4 as thermal decomposition products

The first cationic thioindate with composition [In(en)₂S]₂·2Cl (zero-dimensional) (1) and the first thioindate being charge compensated by a main group metal complex with composition [Mg(en)₃][In₂S₄] (one-dimensional) (2) have been prepared with ethylenediamine under solvothermal conditions. The main structural motif of [In(en)₂S]₂·2Cl is the centro-symmetric rhomboidal [In(en)₂S]₂²⁺ ring which is formed by S-S edge-sharing of two symmetry related [InN₄S₂] octahedra. The structure of [Mg(en)₃][In₂S₄] is composed of a straight one-dimensional {[InS₂]⁻}_∞ chain surrounded by [Mg(en)₃]²⁺ complexes. Both compounds are wide band-gap semiconductors. The thermal decomposition reaction of [In(en)₂S]₂·2Cl stopped at 500 °C yielded cubic α-In₂S₃ and reflections of β-In₂S₃ are seen in the X-ray powder pattern of the residue obtained at 900 °C. In the case of [Mg(en)₃][In₂S₄] the thiospinel MgIn₂S₄ was identified as decomposition product. The size of the MgIn₂S₄ crystals are in the nanometer range as evidenced by a pronounced broadening of the reflections in the powder pattern and with transmission electron microscopy.     

Fabrication and characterization of nanocrystalline n-CdO/p-Si as a solar cell

A nanocrystalline CdO/Si solar cell was fabricated via deposition of a CdO thin film on p-type silicon substrate with approximately 370 nm thickness using solid–vapor deposition for Cd powder at 1274 K with argon and oxygen flow. Scanning electron microscopy revealed that the product was a Cadmium oxide nanocrystalline. X-ray diffraction and energy dispersive X-ray analysis were used to characterize the structural properties of the solar cell. The nanocrystalline thin film had a grain size of 38 nm. The solar cell yielded a minimum effective reflectance that exhibited excellent light-trapping at wavelengths ranging from 400 to 1000 nm. Photoluminescence spectroscopy was conducted to investigate the optical properties. The direct band gap energy of the nanocrystalline CdO thin film was 2.46 eV. CdO/Si solar cell photovoltaic properties were examined under 100 mW/cm² solar radiation. The cell showed an open circuit voltage (V_oc) of 457 mV, a short-circuit current density (J_sc) of 18.5 mA/cm², a fill factor (FF) of 0.652, and a conversion efficiency (η) of 5.51%.     

Magnetic and transport studies on nanocrystalline Fe73.5Si13.5B8CuNb2VAl ribbon

The magnetic and the transport properties of the Fe_73.5Si_13.5B₈CuNb₂VAl nanocrystalline ribbon have been presented. The coercive field was found to increase from 0.24 to 1 Oe on lowering the temperature from 300 to 5 K. The irreversibility in the FC-ZFC was observed and the magnetization was found to follow T^3/2 law. Magnetoresistance measurements were done along the length of the ribbon and the MR of −0.07% was observed at 300 K. Cluster glass behavior was predicted by the power law.     

Surface plasmon resonance (SPR) reflectance imaging: Far-field recognition of near-field phenomena

The surface plasmon resonance (SPR) reflectance imaging technique provides a label-free visualization tool to characterize the near-field fluidic transport properties within 100 nm from the solid surface. The key idea is that the SPR reflectance intensity varies with the near-field refractive index (RI) of the test fluid, which in turn depends on the micro- and nano-fluidic scalar properties such as concentrations, temperatures, and phase changes, occurring in the near-field. As essential knowledge to understand and implement the SPR reflectance imaging technique, this paper presents discussions on the basics of surface plasmon polaritons (SPPs), surface plasmon resonance (SPR), setup of the SPR reflectance imaging system, and the SPR reflectance imaging resolution. The second part of the paper elaborates the applications of the SPR imaging sensor technique in characterizing the near-field fingerprints of nanofluidic evaporative self-assembly.     

Quantum-chemical ab initio study of the crystal-field and charge transfer energies of nanocrystalline Y2O3: Eu

The 4f energy levels and crystal-field parameters for several clusters representing the local coordination surroundings of Eu³⁺ in the bulk and nanocrystalline cubic Y₂O₃: Eu³⁺ crystals are obtained by using a method based on the combination of the DV-X_α calculation and the effective Hamiltonian method initialized by M.F. Reid et al. (J. Phys.: Condens. Matter, 2011, 23: 045501). The results are in reasonable agreement with the measured energy levels and the crystal-field parameters obtained from the least-square fitting. The charge transfer energies are also obtained for all the clusters from the DV-X_α calculation. The results indicate that, compared with the bulk Y₂O₃: Eu³⁺ crystal, the charge transfer band in the excitation spectra is red-shifted in the nanocrystal.     

Nanocrystals and amorphous matrix phase studies of Finemet-like alloys containing Ge

Two simple models were developed in order to determine the chemical composition of both nanocrystals and intergranular amorphous phases in nanocrystallized Fe_73.5Si_13.5B₉Nb₃Cu₁ containing Ge using data from X-ray diffraction and Mössbauer spectroscopy techniques. Saturation magnetization of the amorphous intergranular matrix (M_s^am) was calculated considering the contribution of the α-Fe(Si,Ge) nanocrystals and saturation magnetization of the alloys. The behavior of M_s^am with the iron content of the matrix was obtained and discussed. The exchange stiffness constant for the nanograins and for the amorphous phases was determined. The increment in the coercive field (H_c) with increasing Ge content was evaluated using two theoretical models for the random magnetocrystalline anisotropy constant (〈K₁〉). Results show that the magnetic hardening observed could not be attributed to an increase in 〈K₁〉 but mainly to an important increment of the magnetostriction constant of the α-Fe(Si,Ge) nanocrystals (λ_s^cr). Values for λ_s^cr are proposed.     

High-frequency magnetic properties of soft magnetic cores based on nanocrystalline alloy powder prepared by thermal oxidation

FeSiBNbCu nanocrystalline alloy powder was thermally oxidized in an air atmosphere to enhance an oxide layer formation on the surface of the powder and subsequently toroidal shape FeSiBNbCu nanocrystalline alloy powder cores were prepared by compaction at room temperature. The phase change on the surface of FeSiBNbCu nanocrystalline alloy powder by thermal oxidation was analyzed and its effect on the high frequency magnetic properties of the compacted cores was investigated. By thermal oxidation, the formation of the oxide layer consisting of Fe₂O₃, CuO, and SiO₂ on the surface of FeSiBNbCu nanocrystalline alloy powder was enhanced and the thickness of oxide layer could be controlled by changing the thermal oxidation time. FeSiBNbCu nanocrystalline alloy powder core prepared from the powder treated by thermal oxidation exhibits a stable permeability up to high frequency range over 10 MHz. The core loss could be reduced remarkably and the dc-bias property could be improved significantly, which were due to the formation of oxide layer consisting of Fe₂O₃, CuO, and SiO₂ on the FeSiBNbCu nanocrystalline alloy powder. The improvement in high-frequency magnetic properties of the FeSiBNbCu nanocrystalline alloy powder cores could be attributed to the effective electrical insulation by oxide layer between the FeSiBNbCu nanocrystalline alloy powders.     

Temperature evolution of magnetic susceptibility during devitrification of Cu-free HITPERM alloy

Development of structural and magnetic properties of the Fe_44.5Co_44.5Zr₇B₄ alloy during its successive devitrification from amorphous to nanocrystalline state was investigated. Temperature independence of the initial susceptibility in a wide temperature range (20-600 °C) was observed. The origin of such susceptibility behavior was described through the compensation of lowering exchange interaction between nanocrystalline grains and their magnetization at increased temperatures. The stabilization of the domain structure, due to atom pair directional ordering, was confirmed by measurements of the amplitude dependence of susceptibility in a wide field range, where the initial susceptibility remains constant (Perminvar effect).