Concentration Of Fe Impurities Research Articles

Numerical and experimental investigation on iron contamination of 200 mm semiconductor-grade CZ-Si by bubble-free layer of quartz crucible

The thickness of bubble-free (BF) layer of the quartz crucible is crucial for heat transfer during the crystal growth process of 200 mm semiconductor-grade CZ silicon. The effect of the BF layer thickness on the contamination of impurity Fe in the wafer was investigated through experimental and numerical simulations. The experimental results demonstrated that a crucible with a 3 mm BF layer (S1) exhibited a lower thermal conductivity (1.37 W/(K• m)) in comparison to a 6 mm BF layer (S2) with a thermal conductivity of 1.72 W/(K• m). Despite the S2 crucible requiring an additional 0.40 kW for thermal compensation, it resulted in a lower concentration of Fe impurities. Compared to S1, S2 crucible offered superior performance in stabilizing the distribution of O and C impurities, resulting in more uniform distribution and improved crystal quality. Simulations indicated that the utilization of S2 quartz crucibles had minimal effect on the velocity field of Ar gas but elevated the melt temperature, strengthened the Taylor-Proudman vortex beneath the crystal-melt interface and altered the flow direction of the secondary vortex. This study highlights the importance of crucible design in controlling the contamination of Fe impurities for the production of high-quality Si wafers.

Purification of Residual Ni and Co Hydroxides from Fe‐Free Alkaline Electrolyte for Electrocatalysis Studies

AbstractIt is critical to control Fe impurity concentrations in oxygen‐evolution‐reaction electrocatalysis experiments so that unambiguous assignments of activity and mechanistic details can be made. An established method to prepare Fe‐free KOH electrolyte is by using particulate Ni(OH)2 or Co(OH)2 as absorbents to remove the Fe from KOH or other neutral‐to‐alkaline electrolytes. However, this method yields residual Ni or Co species in the electrolyte which can be redeposited on the working electrode. Thus, current methods of Fe removal could convolute studies of OER. In this work, we compared two different methods, continuous electrolysis and nano‐filtration, to remove the Ni and/or Co species from Fe‐free alkaline electrolyte. We found the best approach is to pass the Fe‐free electrolyte through a hydrophilic 0.1 μm polyethersulfone filter which decreases the Ni species concentration in 1 M KOH to single ppb levels. This result suggests the remaining Ni or Co species are primarily particulate in nature, consistent with their small solubility as ions. In comparison, extended pre‐electrolysis of the electrolyte removed only a portion of the Ni/Co.

Effects of Fe Impurities on Self-Discharge Performance of Carbon-Based Supercapacitors.

Activated carbon is widely used as an electrode material in supercapacitors due to its superior electrochemical stability, excellent electrical conductivity, and environmental friendliness. In this study, the self-discharge mechanisms of activated carbon electrodes loaded with different contents of Fe impurities (Fe and Fe3O4) were analyzed by multi-stage fitting to explore the tunability of self-discharge. It is was found that a small quantity of Fe impurities on carbon materials improves the self-discharge performance dominated by redox reaction, by adjusting the surface state and pore structure of carbon materials. As the content of Fe impurities increases, the voltage loss of activated carbon with the Fe impurity concentrations of 1.12 wt.% (AF-1.12) decreases by 37.9% of the original, which is attributable to the reduce of ohmic leakage and diffusion, and the increase in Faradic redox at the electrode/electrolyte interface. In summary, self-discharge performance of carbon-based supercapacitors can be adjusted via the surface state and pour structure, which provides insights for the future design of energy storage.

Probing unintentional Fe impurity incorporation in MOCVD homoepitaxy GaN: Toward GaN vertical power devices

Unintentional impurity incorporation in GaN drift layers represents a challenging issue that can limit their potential performance in vertical power devices. In this paper, we focus on studying the origins of Fe impurity incorporation in metal-organic chemical vapor deposition (MOCVD) grown GaN materials. Acting as a compensator in n-type GaN drift layers, Fe impurities can reduce the electron mobility in GaN and limit the lowest controllable doping level. Two sources, the sample cleaning process and growth susceptor, were identified as the main mechanisms of Fe incorporation in the MOCVD GaN growth process. It was found that solvent cleaning of the wafer can introduce significant Fe contamination at the growth interface, which would slowly be incorporated into the GaN epilayer, thus causing background Fe impurity as high as 1017 cm−3 level. Moreover, the Fe impurity in the coating material on the susceptor can introduce additional Fe impurity during the growth process. Our studies revealed that the Fe impurity level could be significantly suppressed by more than two orders when an alternative cleaning process was used and the susceptor surface was fully covered by substrates. Characterization of the Fe impurity concentrations was performed via secondary ion mass spectrometry. The trap level (EC − 0.57) eV from deep-level transient spectroscopy that had previously been attributed to Fe confirmed the carrier compensation effect from Fe. Room temperature Hall mobility as high as 1007 cm2/V s was achieved on the MOCVD grown low-Fe GaN. Results from this work will provide guidance for achieving high purity GaN toward high performance GaN vertical power devices.

Screening of Undesirable Elements Raising the Electrical Resistivity in Very Narrow Cu Wires by Ab Initio Calculation

We estimated segregation energy for compound impurities at the grain boundary in very narrow Cu wires using the ab initio calculation. From the calculation results, we clarified that the impurities such as FeO, Fe(ClO), TiO and Ti(ClO) have a strong segregation tendency at the Cu grain boundaries. The FE-TEM observation results of the Cu wires with Fe impurity atoms confirmed that the impurity atoms led to smaller grain sizes than the impurity-free case. The resistivity was measured as a function of the Cu wire width for various Fe impurity concentrations and the wire resistivity became higher with increased impurity concentration.

High-temperature thermoluminescence of anion-deficient corundum and its connection with Ti impurity

Absract Anion-deficient corundum (α-Al2O3-δ) was studied for a possible correlation between the TL yield in the high-temperature peak at 830 K and the contents and transformation of intrinsic defects and impurities. Only 40–60% of TLD-500 detectors based on α-Al2O3-δ were found to have a 830 K TL peak. Increasing the concentration of the titanium impurity from 7·10−4 to 21·10−4 wt% was found to reduce the TL yield in the 830 K peak to an undetectable level. Similar variations of Mg, Si, Ca, Cr and Fe impurity concentrations did not allow us to reveal correlations with the TL yield at 830 K. Nevertheless, the measurements of active center concentrations at step-annealing from 300 to 1400 K suggest that the anion deficiency and related cation interstitials participate, as well as chromium ions, in the formation of the 830 K TL peak. Presumably, UV emission with a maximum at 4.1 eV observed in the 830 K TL peak may be caused by transitions from higher excited states in F+, F or other centers, including impurities and multi-component centers with intrinsic defects.

The Oxygen Evolution Reaction at Transition Metal Oxide (TMO) Films in Alkaline Media

Alkaline water electrolysis produces H2 gas, which can be used as a fuel in H2/O2 fuel cells to generate power. The most energy intensive step in water electrolysis is the evolution of O2 due to the large anodic overpotential of the Oxygen Evolution Reaction (OER).1 Thus, understanding and optimizing electrocatalysts for OER remains one of the grand challenges for both physical electrochemistry and energy science. For the OER in alkaline media, the best performing electrocatalysts are thermally prepared RuO2 and IrO2, which exhibit the lowest OER overpotentials to date, but these oxides are expensive and somewhat unstable in alkaline media, rendering them impractical and uneconomical.1 First row Transition Metal Oxides (TMO), e.g. Mn, Ni, Co or Fe, show great promise as alternative materials for OER, as they exhibit low overpotentials and high stability at lower costs than those of RuO2 or IrO2. However, mechanistic studies of OER at TMO electrodes in alkaline media have been sparse and the nature of catalytic sites and the mechanism leading to O2 evolution are not well understood.2 In this work, pure and mixed Ni/Fe materials were electrochemically deposited on Ti supports to fabricate inexpensive electrocatalysts. Their potential as OER catalysts was elucidated in NaOH electrolyte with different amounts of Fe impurities; 1 ppb, 5 ppb and 102 ppb, as determined by Inductive Coupled Plasma (ICP) spectroscopy. The results indicate that the electrocatalytic activity of the materials depends on the ratio of Ni/Fe and the concentration of Fe impurities in the electrolyte. Most of the mixed catalysts show improved OER performances compared to the pure Ni and Fe oxide materials with respect to overpotential at 10 mA cm-2, Figure 1(a), Tafel slope values and Turnover Frequencies (TOF) numbers. Interestingly, the pure and mixed Ni/Fe materials in the NaOH electrolyte containing 5 ppb Fe impurities exhibited lower overpotentials at 10mA cm-2 compared to the same material in the NaOH containing 1 ppb and 100 ppb, Figure 1(a). This is thought to be due to the substitution of the Fe ions in the electrolyte for the Ni atoms in the material lattice, improving the OER performance.3 Pure and mixed manganese and ruthenium oxides were also examined in this work. The OER catalytic activity of pure manganese oxide compounds displaying overpotentials between 0.74 - 0.49 V at a current density of 10 mA cm-2. Furthermore, when combined with other compounds this overpotential value further decreases.4 However, mechanistic studies of the OER at thermally prepared DSA® type MnxOy electrodes in alkaline media have been sparse.2 Several of the mixed Mn/Ru electrode materials in this study were found to exhibit significantly improved OER activity and stability when compared with pure RuO2films, Figure 1(b), while lowering the cost of producing the catalyst.5 These Mn/Ru materials could therefore offer a competitive low-cost alternative to the already commercially available OER catalysts. The composition, morphology and structure of all the aforementioned materials are thoroughly characterised by X-Ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and Scanning Electron Microscopy–Energy Dispersive X-Ray (SEM-EDX). Finally, the Ni/Fe and Mn/Ru oxides will be a compared under cost and OER performance, to help identify the most economic and practical OER catalyst in this work. Acknowledgements We would like to thank Science Foundation Ireland (SFI) under the Grant Number SFI/10/IN.1/I2969. References (1) Lyons, M. E. G.; Doyle, R. L.; Fernandez, D.; Godwin, I. J.; Browne, M. P.; Rovetta, A. Electrochem. Commun. 2014, 45, 56-59. (2) Fernández, J. L.; Gennero De Chialvo, M. R.; Chialvo, A. C. J. Appl. Electrochem. 2002, 32, 513-520. (3) Klaus, S.; Louie, M. W.; Trotochaud, L.; Bell, A. T. The Journal of Physical Chemistry C 2015, 119, 18303-18316. (4) Gao, M.-R.; Xu, Y.-F.; Jiang, J.; Zheng, Y.-R.; Yu, S.-H. J. Am. Chem. Soc. 2012, 134, 2930-2933. (5) Browne, M. P.; Nolan, H.; Duesberg, G. S.; Colavita, P. E.; Lyons, M. E. G. ACS Catalysis 2016. Figure 1

The goldilocks electrolyte: examining the performance of iron/nickel oxide thin films as catalysts for electrochemical water splitting in various aqueous NaOH solutions

A rigorous study of electrodeposited Ni/Fe oxides for the OER was performed in three different sodium hydroxide electrolytes with various Fe impurity concentrations.

SIMS Analysis of Fe Impurity Concentration in a PVT-Grown 4H-SiC Bulk Crystal and Source Powders

Iron (Fe) impurity concentrations in a SiC bulk crystal and source powders used for the bulk crystal growth are analyzed by means of secondary ion mass spectrometry and the validity of the obtained data are discussed. The secondary ion signal of 56Fe is found to be affected significantly by the mass interference of 28Si2, and therefore measurements of 54Fe instead of 56Fe offer a better detection limit for the analysis. A high concentration of Fe is found at proximity of the SiC bulk crystal surface. Possible sources of the Fe contamination are discussed based on the depth profile data of Fe in both the bulk crystal and the source powders.

Structural, optical and magnetic properties of polycrystalline BaTi1−xFexO3 ceramics

Polycrystalline BaTi1−xFexO3 ceramics have been prepared by conventional solid-state reaction. Their structural, optical and magnetic properties are then studied by means of x-ray diffraction (XRD), Raman scattering (RS) and absorption spectrometers, and a physical properties measurement system. Detailed analyses of XRD patterns and RS spectra reveal the phase separation of the tetragonal-hexagonal structure at a threshold concentration of x = 0.005. The increase in the Fe-doping content (x) leads to development of the hexagonal phase. Magnetic measurements prove that many BaTi1−xFexO3 samples exhibit the room-temperature ferromagnetic order, excepting the samples with x = 0.02–0.06. The ferromagnetism depends strongly on concentration of Fe impurities. The nature of this ferromagnetism is discussed by means of the results of structural analyses and optical absorption spectra.

Influence of Fe Impurity on Spin Hall Effect in Au

We investigated the influence of Fe impurity on spin Hall effect in Au using multi-terminal devices consisting of an FePt perpendicular spin polarizer and a Au Hall cross with different Fe impurity concentrations. As the Fe impurity concentration was increased in the range of 0-0.95 at.%, the resistivity of Au doped with Fe increased and the spin diffusion length decreased from 35 nm to 27 nm. On the other hand, the spin Hall angle for Au doped with Fe, evaluated from the spin injector-Hall cross distance dependence of spin Hall signals, was approximately 0.07, independent of the Fe concentration. The experimental results provide important information for understanding the mechanism of the large spin Hall effect.

Impurity effects on Fe‐ or MgO‐doped LiNbO3 crystals studied by 7Li and 93Nb NMR relaxation

AbstractThe spin–lattice and spin–spin relaxation times of 7Li and 93Nb nuclei were investigated as a function of the concentration of Fe or MgO species in LiNbO3 crystals using pulse NMR spectrometry. The spin–lattice relaxation times T1 of both nuclei were found to decrease as the number of Fe impurities increased in Fe‐doped LiNbO3 single crystals, because of paramagnetic‐impurity effects. On the other hand, the T1 values of the 7Li and 93Nb nuclei in LiNbO3:MgO crystals remained nearly constant with increasing MgO concentration. The T1 of 7Li was found to be longer than that of 93Nb for both Fe‐ or MgO‐doped single crystals. The spin–spin relaxation times T2 of the 7Li and 93Nb nuclei remained nearly constant with increasing concentration of Fe or MgO. From our results, we can conclude that T1 depends on the concentration of Fe impurities but is independent of the concentration of Mg impurities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Purification of Cu by hydrogen plasma-arc zone melting and characterization of trace impurities by secondary ion mass spectrometry

Purification of 4N (99.99%) and 6N (99.9999%) purity Cu rods by hydrogen plasma-arc zone melting was carried out. Weight loss in the 4N and 6N Cu rods as a function of number of zone refined passes revealed a higher rate of impurity removal by vaporization in 4N Cu when compared to 6N Cu. Purification effect was studied by analyzing major impurities like Mg, Si, Ca, Ti, Cr, Ni and Fe by O 2 + ions and C, O, As, Cl, P and S by Cs + ion sources using secondary ion mass spectrometry. A remarkable decrease of Si, Ti and Fe impurity concentrations in Cu at x/ L = 0.03 after 10 zone passes was observed, but no similar purification effect along the remaining length of the zone refined copper rod was observed. Mg, Se and Ca in the Cu rods were reduced faster by a high evaporation effect due to P i/ P Cu > 10 2. On the other hand, removal of O, C, S and Se was expectedly dominated by vaporization in the form of H 2O, CH 4, H 2S, and H 2Se through thermodynamically favored reactions. The overall segregation rate of the individual impurity elements was decreased with an increase in the purity from 4N to 6N of Cu rods. SIMS analysis of trace impurities was successfully carried out on HPZM Cu for quantitative estimation.

Defect activated infrared multiphonon excitation in iron-doped semi-insulating indium phosphide

Multiphonon excitation induced by long-range order crystal-field and short-range order Jahn–Teller distortion effects is observed in Fe-doped semi-insulating InP in the spectral range from 400 to 1100 cm−1 for infrared light propagating in a slab waveguide geometry. Transmission measurement data are analyzed in terms of phonon energies at critical points in the Brillouin zone. The phonon energies obtained are in excellent agreement with recently reported second order Raman scattering spectra and two-phonon absorption measurements of crystalline InP. The energy differences between the nearly degenerate two phonon transverse optical+longitudinal optical transitions at the Γ, X, and L points are also resolved and shown to be 10 cm−1. No localized mode or vibronic level absorption is observed, consistent with the relatively low concentration of Fe impurities in the samples.

Resonant states in semiconductors: A quantitative study of HgSe:Fe

When the inter-impurity Coulomb interactions dominate over the hybridization between band and resonant impurity states, the spatial correlation of impurity charges may set in. The correlations lead to a reduction of conduction electron scattering and to a modification of the Fermi energy. We show by analytic and Monte-Carlo methods that such a picture enables quantitative description of the electron concentration and mobility dependences on the concentration of Fe impurities as well as on the hydrostatic pressure in HgSe: Fe.

The Influence of Photorefractive Index Change on Raman Scattering Intensities in LiNbO3

The time dependent varying shape of the laser beam within the scattering volume in Raman scattering experiments on LiNbO3 influences the recorded spectra and can be studied spectroscopically by forward-, right angle-, and backward-scattering geometries. The recorded spectra allow a time resolved insight into the microscopic local changes of the refractive index. The decay constant of the scattered phonon intensity is a well defined function of the laser power. It furthermore showed to be characteristic for the individual sample. Raman spectroscopy thus seems to provide a method to determine the concentration of Fe-impurities. We have observed that ordinary photons influence the optically damaged regions of the sample whereas undamaged regions are left almost unchanged. Damped cut-in oscillations recorded when illuminating the sample alternatingly with ordinary and extraordinary laser light seem to originate from local fluctuations of an excited cloud of impurity electrons. The observation of undamped periodic break downs of the scattering intensity from polaritons and back scattered phonons is reported.