Magnetotransport Properties and Electronic Structure of Ni 8 1 Fe 1 9 /W 9 0 Ti 1 0 Multilayers

The magnetotransport properties of Ni₈₁Fe₁₉/W₉₀Ti₁₀ multilayers are investigated. The effect of the thicknesses of magnetic (Ni₈₁Fe₁₉) and nonmagnetic (WTi) layers on the magnetoresistance (MR) is theoretically discussed in the framework of the Johnson–Camley semiclassical approach based on the Boltzmann transport equation. A comparison between the calculated and measured MR ratios is obtained. The observed MR ratio oscillates for WTi layer thickness with an average period of 10 Å. A weak MR(t_NiFe) ratio for a fixed t_WTi is obtained, and it presents a maximum peak of the MR with a value of 0.8 % located at t_NiFe = 50 Å. In addition, electronic and magnetic properties of multilayers are investigated by self-consistent ab initio calculations based on the Korringa–Kohn–Rostocker (KKR) approximation. Spin polarized within the framework of the coherent potential approximation (CPA) is considered for calculations.     

Improvement of multicrystalline silicon solar cell performance via chemical vapor etching method-based porous silicon nanostructures

In this paper, we report on the effect of chemical vapor etching-based porous silicon (PS) on the performance of multicrystalline silicon solar cells performed via deep n⁺/p junction-type structures. Chemical vapor etching of silicon leads to the formation of porous silicon (PS) nanostructures that dramatically decrease the surface reflectivity from 30% to about 8%, and increase the minority carrier diffusion lengths from 90 μm to 170 μm. As a result, the short-circuit current density was improved by more than 20% and the fill factor (FF) by about a 10%. An enhancement of the photovoltaic conversion energy efficiency of the solar cells from 7% to 10% was observed. This low-cost PS formation process can be applied in the photovoltaic cell technology as a standard procedure.     

Formation,rapid thermal oxidation and passivation of solar grade silicon nanowires for advanced photovoltaic applications

Uniform and regular silicon nanowires (SiNWs) arrays are fabricated on both sides of solar grade silicons (SiGS) by silver assist-electrochemical etching. SiNWs arrays exhibit an excellent antireflection character with an overall reflectance of 2% in the range from 300 to 1000 nm. More importantly, the effective lifetimes of the symmetric SiNWs/Si structures decreased due to the high densities of dangling bonds and surface defects. Surface passivation to overcome lifetime degradation is realized by means of rapid thermal oxidation (RTO). Following rapid oxidation, Fourier Transform Infrared spectroscopy reveals that oxygen diffusion is enhanced inside silicon nanowires where the morphological structure is preserved during RTO. Moreover, it is shown that even the rapid thermal oxidation process is not effective to recover initial τ_eff due to the high density of imperfections involved during nanowires formation and the contamination level induced by silver. The interdiffusion between residual silver and metal contaminants in the core of the nanowire can probably limit the passivation effect due to the segregation of metal atoms at SiO₂ and to the redistribution of both impurities across the wire.     

Monocrystalline silicon surface passivation by Al2O3/porous silicon combined treatment

In this paper, we report on the effect of Al₂O₃/porous silicon combined treatment on the surface passivation of monocrystalline silicon (c-Si). Al₂O₃ films with a thickness of 5, 20 and 80 nm are deposited by pulsed laser deposition (PLD). It was demonstrated that Al₂O₃ coating is a very interesting low temperature solution for surface passivation. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 2 μs to 7 μs at a minority carrier density (Δn) of 1 × 10¹⁵ cm^?3 and the reflectivity reduce from 28% to about 7% after Al₂O₃/PS coating.     

Experimental Investigation of the Isothermal Section at 800 °C of the Nd-Fe-Co Ternary System

The phase equilibrium of the ternary Nd-Fe-Co system at 800 °C was investigated by means of powder x-ray diffraction and scanning electron microscopy–energy dispersive x-ray spectroscopy. Seven binary compounds, i.e., Nd₂Co₁₇, NdCo₅, Nd₅Co₁₉, Nd₂Co₇, NdCo₃, NdCo₂, Nd₂Fe₁₇ were identified to exist at this isothermal section. This isothermal section consists of ten single-phase, ten two-phase and six three-phase regions. All measured compositions and unit-cell refinements were performed at room temperature from quenched samples annealed at 800 °C for one week. The maximum solubility at 800 °C of Fe in NdCo_2?x Fe _x (MgCu₂-type structure, Fd-3 m), NdCo_3?x Fe _x (PuNi₃-type structure, R-3 m space group), Nd₂Co_7?x Fe _x (Ce₂Ni₇-type structure, R-3 m), Nd₅Co_19?x Fe _x (CeCo₁₉-type structure, R-3 m space group), NdCo_5?x Fe _x (CaCu₅-type structure, P6/mmm), Nd₂Co_17?x Fe _x (Th₂Zn₁₇ type structure, R-3 m) and Nd₂Fe_17?x Co _x (Th₂Zn₁₇ type structure, R-3 m) are about 31.6 at.% Fe, 47.9 at.% Fe, 13.3 at.% Fe, 8.6 at.% Fe, 10.37 at.%, 36.35 at.% Fe, and 58.23 at.% Fe respectively. The solid solubility range of Co in Nd₂Fe₁₇ form discontinuous series of 2 ranges is about 0-30.14 at.% Co, and 51.9-100 at.% Co and the solid solubility range of Fe in Nd₂Co₁₇ is about 0-48.1 at.% Fe, and 69.86-100 at.% Fe.     

High Purity Porous Silicon Powder Synthesis by Magnesiothermic Reduction of Tunisian Silica Sand

Silicon - Crystalline metallurgical silicon nanopowder was successfully produced from Tunisian silica sand by magnesiothermic reduction. Silica sand was first transformed into silica powder via a...     

Correlation between Morphological Structure and Optoelectronic Properties of Al2O3 thin layer coated silicon nanowires

Silicon - This study reports on correlation between morphological structure and optoelectronic properties of Al2O3/silicon nanowires (SiNWs). The SiNWs were prepared from etching a silicon...     

Novel silicon surface passivation by porous silicon combined with an ultrathin Al2O3 film

We report on a dual passivation approach of monocrystalline-silicon (c-Si), which combines porous silicon (PS) treatment and pulsed laser deposition (PLD) of Al₂O₃ ultrathin layer. Al₂O₃ ultrathin films were deposited, under an oxygen background pressure of 10 mTorr. In this work we demonstrate that the dual treatment Al₂O₃/PS provide excellent passivation quality of c-Si surfaces. Surface passivation and reflectivity properties are investigated before and after heat treatment at 700 °C. The level of surface passivation is quantified using photoconductance and Fourier-transform infra-red absorption techniques. X-ray diffraction analysis suggested that the heat treatment leads to an average crystallite size decrease which help the diffusion of the Al₂O₃ NPs along the wafer surface. As a result, the effective minority carrier lifetime increases from 2 to 7 μs. Our results demonstrate that this dual treatment not only provides strong passivation of the c-Si substrate but decreases also the total surface reflectivity at 500 nm (from 28 % for untreated c-Si samples to ～7 % for Al₂O₃/PS treated ones).     

X-ray and intrinsic magnetic properties of nanocrystalline Sm2(Fe,M)17 (M = Si,Ga, Co,Cr, Zr or Mo)

The structure and magnetic properties of ball-milled and subsequently annealed Sm₂Fe_17–xM_x compounds (M = Si, Ga, Co, Cr, Zr, Mo, for x = 2) were investigated by X-ray diffraction coupled with magnetic measurements and Mössbauer spectroscopy. Rietveld analysis have shown that all these samples crystallize in the Th₂Zn₁₇ type rhombohedral structure. The substituting elements Si, Ga, Co occupy the 18h atom site, while Cr, Zr, Mo prefer the 6c site. Mössbauer studies corroborate these results. The X-ray analysis cannot solve the possible M atom distribution over Fe atom sites when atomic factors of Fe and M are close. Mössbauer spectroscopy appears as the efficient tool to raise this ambiguity. The Curie temperature increases upon Zr and Cr substitution reaching a maximum for x = 1, then decreases because of magnetic dilution.