bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier Recombination Dynamics of AlxGa1−xN Epilayers Grown by MOCVD
Authors: Cho Yong-Hoon , Gainer G. H. , Lam J. B. , Song J. J. , Yang W. , McPherson S. A.
Published: April 2011

We present a comprehensive study of the optical characteristics of AlxGa1−xN epilayers by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. All AlxGa1−xN epilayers were grown by metalorganic chemical vapor deposition and the Al mole fraction (x) was varied from 0 to 0.6. We observed that (i) the full width at half maximum of the PL emission, (ii) the energy difference between the PL emission peak energy and the PLE absorption edge, and (iii) the effective lifetime increase with increasing x. These facts indicate that degree of band-gap fluctuation due to a spatially inhomogeneous Al alloy content distribution increases with increasing x. We observed anomalous temperature-induced emission shift behavior for AlxGa1−xN epilayers, specifically, an S-shaped (decrease-increase-decrease) temperature dependence of the peak energy with increasing temperature. This anomalous temperature-dependent emission behavior was enhanced as the Al mole fraction was increased. Since the band-gap fluctuation in AlxGa1−xN epilayers due to inhomogeneous spatial variations of the Al content increases with increasing Al content, we believe that band-gap fluctuation causes the PL peak energy to deviate from the typical temperature dependence of the energy gap shrinkage. Therefore, the anomalous temperature-induced emission shift can be attributed to energy tail states due to alloy potential inhomogeneities in the AlxGa1−xN epilayers with large Al content.
Recessed gate GaN MESFETs fabricated by the photoelectrochemical etching process
Authors: Lee Won Sang , Choi Yoon Ho , Chung Ki Woong , Shin Moo Whan , Moon Dong Chan
Published: April 2011

A new photo-electrochemical etching method was developed and used to fabricate GaN MESFETs. The etching process uses photoresist for masking illumination and the etchant is KOH based. The etching rate with 1.0 mol% of KOH for n-GaN is as high as 1600 Å/min under the Hg illumination of 35 mW/cm/2. The MESFET saturates at VDS = 4 V and pinches off at VGS = −3 V. The maximum drain current of the device is 230 mA/mmn at 300 K and the value is remained almost same for 500 K operation. The characteristic frequencies, fT and fmax, are 6.35 GHz and 10.25 GHz, respectively. Insensitivity of the device performance to temperature was attributed to the defect-related high activation energy of dopants for ionization and band-bending at the subgrain boundaries in GaN thin films.
High Barrier Height n-GaN Schottky diodes with a barrier height of 1.3 eV by using sputtered copper metal
Authors: Lai W. C. , Yokoyama M. , Chang C. Y. , Guo J. D. , Tsang J. S. , Chan S. H. , Sze S. M.
Published: April 2011

Copper Schottky diodes on n-type GaN grown by metal-organic chemical vapor deposition were achieved and investigated. Ti/Al was used as the ohmic contact. The copper metal is deposited by the Sputter system. The barrier height was determined to be as high as (ΦB =1.13eV by current-voltage (I-V) method and corrected to be ΦB =1.35eV as considered the ideality factor, n, with the value of 1.2. By the capacitance-voltage (C-V) method, the barrier height is determined to be ΦB =1.41eV. Both results indicate that the sputtered copper metal is a high barrier height Schottky metal for n-type GaN.
Photoionization Spectra of Traps Responsible for Current Collapse in GaN MESFETs
Authors: Klein P. B. , FreitasJr J. A. , Binari S. C.
Published: April 2011

Current collapse in GaN MESFETS is believed to result from the trapping of carriers in the high resistivity GaN layer, and can be reversed by the application of light. Light photoionizes (or photoneutralizes) the carriers, releasing them from the traps and restoring all or part of the original I-V characteristics of the device. In these investigations we have taken advantage of this effect to characterize the traps responsible for current collapse in an n-channel GaN MESFET. At fixed source-drain voltage, the incremental light-induced drain current, above that measured in the dark, and normalized per incident photon, is measured as a function of wavelength. The resulting photoionization spectrum reflects two absorption thresholds corresponding to two distinct electron traps. Because of the nature of the measurement, these traps can be identified as those responsible for current collapse in the device.
Carbon and Silicon Related Surface Compounds of Palladium Ultrathin Films on SiC After Different Annealing Temperatures
Authors: Lu W. J. , Shi D. T. , Crenshaw T. , Burger A. , Collins W. E.
Published: April 2011

Pd/SiC Schottky diode has triggered interest as a chemical sensor to be operated at high temperatures. Various surface compounds formed at high temperatures are known to alter the device performance. In this work, the carbon and silicon related compounds and morphology of Pd ultra-thin film on 6H-SiC and 4H-SiC are investigated after thermal annealing using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The Pd ultra-thin films of about 3 nm in thickness are deposited by RF sputtering. The XPS analysis reveals the presence of silicon oxycarbides (SiCxOy) as deposited. After being annealed above 300°C, the atomic ratio of C to 0 in SiCxOy decreases with increasing the annealing temperatures, and the Pd film becomes a Pd silicide nanofeatured layer on SiC. When the annealing temperature is at 500°C, the majority of the SiCxOy is converted into SiO2. An amorphous Si phase exists after annealing at 200 to 400°C, which indicates that the Si-C bonds in SiC are broken at lower temperatures due to the presence of Pd. Graphite and C=O are found on the as deposited samples and also after annealing at temperatures up to 600°C. The formations of the carbon and silicon related compounds on Pd/4H-SiC are very similar to those on Pd/6H-SiC.
Production of InSb Thin Films Through Annealing Sb2S3-In Thin Films
Authors: Nair M. T. S. , Rodríguez-Lazcano Y. , Nair P. K.
Published: April 2011

A method to produce large area indium antimonide thin films through a reaction, Sb2S3 + 2 In → 2 InSb + 3 S↑ is presented. A thin film of Sb2S3 with typically 0.2 μm thickness is produced on glass substrate by chemical bath deposition (CBD) at 10°C using thiosulfatoantimonate(III) complex. Subsequently, a thin film of indium is deposited on the Sb2S3 film by thermal evaporation. Annealing the thin film stack of Sb2S3-In at 300°C in a nitrogen atmosphere produces the InSb thin film. The formation of this film is confirmed by x-ray diffraction studies. We would discuss the optimization of the individual film thickness in the Sb2S3-In stack to produce a thin film of single phase InSb or a heterostructure, Sb2S3-InSb. The electrical and optical properties of the films are presented.
Low Energy, High Density Plasma (ICP) for Low Defect Etching and Deposition Applications on Compound Semiconductors
Authors: Etrillard J. , Maher H. , Medjdoub M. , Courant J. L. , Nissim Y. I.
Published: April 2011

The use of a low ion energy of an extremely dense plasma has been studied as a dry etching as well as a thin film deposition tool (same source, two different reactors) for InP and GaAs device processing. Under these working conditions it is expected to control well the etch depth or in the case of deposition to obtain high deposition rates. In all cases minimun ion damages are induced on the processed substrate. Both technologies are presented here from the point of view of material analysis as well as device processing demonstration. For etching, the gate recess of an InP-based HEMT has been addressed as one of the key technological step that requires such properties for good device performances. InGaAs/InAlAs HEMT like structures have been grown and the recess of the InGaAs layer has been conducted with a 13eV SiCl4 inductively coupled plasma (ICP). DLTS and AFM measurements made on the exposed AlinAs surface after InGaAs removal indicate that device quality on its electrical and structural properties are achieved. Passivation of fully processed HEMT devices with a ICP enhanced chemical vapor deposition (ICPECVD) silicon nitride film is being studied.
Wet and Dry Etching Characteristics of Electron Beam Deposited SiO and SiO2
Authors: LaRoche J. R. , Ren F. , Lothian J. R. , Hong J. , Pearton S. J. , Lambers E.
Published: April 2011

We have studied the thermal stability and etching characteristics of E-beam deposited SiO and SiO2. Dry etch rates were studied using SF6 and NF3 discharges in a Plasma Therm inductively coupled plasma system. Wet etch rates were assessed with buffered HF and HF/H2O solutions. SiO2 etched faster than SiO under all etch conditions. Dry etch rate of SiO2 was comparable with PECVD SiO2. Auger analysis indicated that SiO2 maintained excellent thermal stability after annealing to 700°C. The Si/O ratio of SiO in the film increased when annealed to 700°C. Ellipsometry also revealed greater refractive index variance across the sample for SiO, as compared to SiO2. However, thickness variation of both films was ≤ 2% across the wafer. Ellipsometry data also showed great thermal stability of SiO and SiO2. There was <4% change after 700°C annealing.
Structure of Chemically Passivated Semiconductor Surfaces Determined Using X-Ray Absorption Spectroscopy
Authors: Hitchcock A. P. , Tyliszczak T. , Lu Z. H. , Brodersen P. , Dharmawardana M. W. C.
Published: April 2011

The structure of monolayer-passivated single crystal semiconductor surfaces has been studied using synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS). The near edge and extended fine structure signals, supported in some cases by first-principles calculations, have been used to investigate Ge(111)-Cl; GaAs(111)-Cl; GaAs(111)A-S, GaAs(111)B-S and GaAs(001)-S. The use of a solid state Ge X-ray fluorescence array detector has led to significant improvements in data quality and thus structural accuracy. The relationship between the derived surface structures and the development of improved passivated surfaces is discussed.
Li Ion diffusion measurements in crystalline and amorphous V2O5 thin-film battery cathodes
Authors: McGraw Jeanne M. , Bahn Christian S. , Parilla Philip A. , Perkins John D. , Readey Dennis W. , Ginley David S.
Published: April 2011

Thin films of crystalline and amorphous V2O5 were deposited by pulsed laser deposition (PLD) and the chemical diffusion coefficients, , were measured by the potentiostatic intermittent titration technique (PITT). In crystalline V2O5 films, the maximum and minimum were found to be 1.7 × 10−2 cm2/s and 5.8 × 10−15 cm2/s respectively, with a general trend for to rise in single-phase regions. The changes in correlated well to the known phases in LiV2O5. In amorphous V2O5 films, exhibited a smooth, continuous decrease as the Li concentration increased.
Structural study of lithium insertion in vanadium oxides used as cathode materials
Authors: Rozier Patrick , Savariault Jean Michel , Galy Jean
Published: April 2011

Combined soft and solid state chemistry followed by precise XRD investigations allow us to determine the Li-V-O system as well as the structural modifications induced by Li insertion in silver vanadates. On the base of these studies we propose an interpretation of both Li//V2O5 and Li//Ag2V4O11 batteries electrochemical behavior. In the I<x<3 domain, disproportionation of V4+, occurs leading to the formation of different mixtures between lithium vanadates and vanadium oxides. The different domains are related to the different steps observed in the Li//V2O5 discharge curve. It is also demonstrated that the sprouting phenomenon occurring in the Ag1+xV3O8 vanadate induces the formation of a new phase Ag2V4O11 instead of the oxygen deficient form Ag2V4O11-y. According single crystal XRD structural determination this phase is shown to be isostructural with Li1+xV3O8. Electrochemical Li insertion starts with the reduction of Ag+ leading to the lithiated phase meaning that whatever the starting phase used, the main insertion process occurs in Li1+xV3O8.
High Performance Zr-based Metal Hydride Alloys For Nickel Metal Hydride Batteries
Authors: Young R. C. , OVSHINSKY S. R. , HUANG B. , CHAO B S. , LI Y.
Published: April 2011

Based upon Ovonic's multi-element, atomic engineering approach, two families of alloys are being used in commercial Nickel Metal Hydride (NiMH) rechargeable batteries, i.e. the mischmetal (Mm) based AB5 and Zr based AB2 alloys. While Mm based alloys are faster to activate, are limited by a discharge capacity of only 320–340 mAh/g. The Zr based alloy, although slightly slower to activate, provides a much higher discharge capacity. In this paper, we first discuss the use of Ovonic's multi-element approach to generate a spectrum of disordered local environments. We then present experimental data to illustrate that through these atomically engineered local environments, we are able to control the hydrogen site occupancy, discharge capacity, kinetics, and surface states. The Zr based alloy with a specific discharge capacity of 465 mAh/g and excellent rate capability has been demonstrated.
Development of Composite Materials for Pefc bipolar Plates
Authors: Busick Deanna , Wilson Mahlon
Published: April 2011

The most costly and problematic components of fuel cell stacks may be bipolar plates. Besides meeting cost constraints, bipolar plates must possess a host of other properties including low gas permeability, corrosion resistance, low weight, high strength, and manufacturability. While we have developed a baseline composite material that meets these requirements, further optimization and development have resulted in significant improvements in properties and processability.
Heat-Resistant, Electrically Conducting Joint Between Ceramic end Plates and Metallic Conductors in Solid Oxide Fuel Cell
Authors: Wilkenhoener R. , Buchkremer H. P. , Stoever D. , Stolten D. , Koch A.
Published: April 2011

Ceramic parts made of doped lanthanum chromite are used as interconnects and end plates
in stacks for several solid oxide fuel cell (SOFC) designs. Metallic conductors have to be
attached to enable a low-resistance connection between individual stacks in each SOFC unit and
to permit power to be drawn from the SOFC. The resistances of the metal-ceramic bond and the
metallic conductors have to be stable under operating conditions, i.e., 1000°C in air.
Consequently, heat-resistant materials have to be used.
A two-step process has been developed to connect commercially available, Ni- or Febased
metallic conductors to ceramic SOFC end plates by vacuum furnace brazing. In the first
step, a metallic sheet, which acts as the current collector, is brazed onto the ceramic end plate.
Thereby, the much lower electrical conductivity of the ceramic part is compensated by that of
the metal. The chromium alloy CrFe5Y2O31 is suitable because it is heat-resistant, and its
thermal expansion coefficient is close to that of lanthanum chromite. In the second step, metallic
wires or strips are brazed on the current collector. Since this joint area is significantly smaller
than that of the first joint, materials with a different thermal expansion coefficient can be used,
such as conventional heat-resistant nickel alloys (Inconel 617) and ferritic stainless steels
(FeCrAl 25 5). Filler alloys for both brazing steps with matching melting points have been
found. Hence, both brazing steps can be performed cost-effectively in one heating step.
Suitable parameters for vacuum furnace brazing of both joints are presented, and the
composition of the filler alloys is given. Data concerning the long-term behavior of the joint
resistances in air at 1000'C are discussed.
Phase Relations and Conductivity in Ba2 (In2. xMx)O5, System
Authors: Yamaji Akihiko , Kawakami Kazuya , Arai Masahiro , Adachi Tadaharu
Published: April 2011

The high temperature cubic phase of Ba2 nr2O5 shows large ion conductivity. It is interestingto examine, if the cubic phase can be stabilized in the low temperature region (920 C) by making solid solution of another element. In the present study, we investigated the ion conductivity and the crystal structure of Ba2(In2-x.Mx)O5 system by substituting In site for element M such as Sc, Y, La, Ce, Nb, Ta etc. By substituting 3 mole % Nb for In, the transition temperature decreased by about 300 C. High temperature X-ray diffraction analysis shows the crystal structure changes from orthorhombic to cubic at this transition temperature. The effective elements which decreased the transition temperature were pentavalent or tetra valent elements such as Nb or Si ,Ce. The substitution In site for 20 mole percentage Nb stabilizes the cubic structure down to room temperature. Considering the transport number, the tetravalent element doping is very effective to stabilize the cubic phase of Ba2In2O5 without lose of excellent characteristic of pure Ba2ln2O5.
Nanostructure Material for Supercapacitor Application
Authors: Huang Yuhong , Chu C. T. , Wei Qiang , Zheng Haixing
Published: April 2011

Transition metal nitrides and carbonitride materials were fabricated via sol-gel technology. The transition metal amides were sythesized by two methods: chemical route and electrolysis. The transition metal amides were then further polymerized, sintering to high temperature in an inert or reduced atmosphere. Transition metal nitrides and carbonitrides powders with surface area up to 160 m2/g were obtained. The resultant electrode material showed high specific capacitance as crystalline ruthenium oxide.
Dielectric Properties of Pd/Y8Z Composites
Authors: Hendriks Mark G.H.M. , Verwei Henk , Timmerman Manon P.
Published: April 2011

Impedance measurements are performed on Pd/Y8Z composites. At 500 'C a 2- 108 times enhancement of the permittivity of the composite at a Pd composition near the percolation threshold for electronic conductivity relative to Y8Z at room temperature is obtained. At high frequencies, the enhancement decreases to a value comparable to geometric capacity of the composite as the double-layer capacity diminishes. At relatively low temperatures the capacity of Y8Z, due to ionic polarisability, increases with temperature.
Synthesis and properties of a vanadium oxide based lithium ion Cathode
Authors: Chaloner-Gill Benjamin , Shackle Dale R.
Published: April 2011

The development of high capacity cathode materials for lithium ion batteries has resulted in three materials dominating the market, lithiated manganese, cobalt and nickel oxides and mixtures thereof. In the search for greater energy storage, we have examined a number of vanadium oxides.

Comparing the ratio of lithium to metal atom in the three compounds listed above allows for the extraction of one lithium atom per two metal atoms. If the cathode is vanadium based, the number of cycleable lithiums increases to a value closer to 0.75–1.00.

Despite the fact that vanadium oxides operate at lower voltages, a net gain in energy is observed from the use of LixVyOz over the currently available materials. Lithiation of LiV3O7.9 for use in a lithium ion cell is the focus of this paper. Chemical lithiation by reducing lithium salt will be described.
Melt Intercalation of PMMA into Organically-Modified Layered Silicate
Authors: Shen Z. , Simon G. P. , Cheng Y-B.
Published: April 2011

Organic-inorganic hybrid nanocomposite materials of poly(methyl methacrylate) (PMMA) and organically-modified silicate (B34) systems have been prepared via melt intercalation with variation of tacticity and molecular weight as the main molecular variables. Only two of the PMMA samples (with the lowest glass transition temperatures) were able to undergo large-scale intercalation into B34, as seen by X-ray diffraction (XRD) and Infrared spectroscopy. The saturation weight ratio of PMMA to B34 was about 25:75 (wt%), deduced by a controlled differential scanning calorimetry (DSC) experiment. Two new absorption bands of PMMA-B34 hybrid in Fourier transform-infrared spectrometry (FTIR) were demonstrated for first time in this system and show a change in molecular interaction of bulk and intercalated PMMA. The degradation temperature of the PMMA-B34 hybrid is higher than that of PMMA alone, or a physical mixture of PMMA and silicate under an air or a nitrogen flow.
Calculating Phase Diagrams of Polymer-Clay Mixtures by Combining Density Functional and Self-Consistent Field Theory
Authors: Balazs Anna C. , Singh Chandralekha , Ginzburg Valeriy V.
Published: April 2011

We analyze the thermodynamics of polymer-clay mixtures within the framework of density functional theory (DFT). The interaction potential between clay particles is calculated using the self-consistent field (SCF) method and is strongly dependent on the length and density of grafted short-chain organic modifiers. By combining the DFT and SCF techniques, we determine the role of the grafted chains on the equilibrium phase behavior of the mixtures.
Formation of Mesoscopic Polymer Dots by Rubbing Transfer
Authors: Sano M. , Okamura J. , Shinkai S.
Published: April 2011

Regularly spaced polymer dots are formed on a silicon surface by rubbing a thin polymer plate against the silicon substrate. Typically, the disk-shaped dots are 10 nm in height and 160 nm in diameter, and are separated by 340 nm from each other. It is found that the substrate temperature, the rubbing rate, the polymer viscoelasticity, and wettability against a substrate surface must be within a certain range to produce the aligned dots.
Covalent Attachment of a Single Dextran Polymer Between the Tip of an Atomic Force Microscope and a Gold Surface
Authors: Grandbois M. , Décor R. , Rief M. , Wagner A. , Mioskowski C. , Gaub Hermann
Published: April 2011

A method for covalent immobilization of a single dextran polymer between a gold surface and the tip of an atomic force microscope (AFM) is presented. Carboxymethylated dextran immobilized on gold by epoxythiol chemistry was activated with N-hydroxysuccinimide (NHS) and N-ethyl-N'-(dimethylaminopropyl) carbodiimide hydrochloride (EDC) in order to make the dextran polymer reactive for the amino groups present on the previously aminosilanized AFM tip. By measuring force vs extension curves we have shown that it is possible to catch such an activated dextran polymer with an AFM tip through the formation of a covalent bond. Dextran polymers were attached even without any detectable indentation of the tip in the dextran-coated gold surface. In this so-called fly-fishing mode, attachment of multiple dextran polymers, which typically occurs when the tip is indented into the surface, are efficiently avoided.
Integrating Organic Molecules to Silicon Surfaces
Authors: Zhu X.-Y. , Mulder J. A. , Hsung R. P. , Bergerson W. F. , Gasser A. , Nguyen A.
Published: April 2011

We present a general strategy for the efficient assembly of organic molecules directly onto the silicon surface via Si-N and Si-O linkages. This is achieved from the reaction between an amine or an alcohol functional group and a chlorinated Si surface. The resulting organic monolayers are thermally stable. These methods are applicable for the assembly of a variety of functional organic molecules in both vacuum environment and solution phases.
Deposition of Nanocrystalline Tin (IV) Oxide Films on Organic Self-Assembled Monolayers
Authors: Supothina S. , Guire M. R. De , Niesen T. P. , Bill J. , Aldinger F. , Heuer A. H.
Published: April 2011

Nanocrystalline thin films of tin (IV) oxide (cassiterite) have been deposited from aqueous solutions of tin (IV) chloride and hydrochloric acid at 80°C. Substrates were {100} single-crystal silicon wafers, with and without silanol-anchored, sulfonate-terminated organic self-assembled monolayers (SAMs). Using flowing solutions, films with thicknesses of up to 1 μtm have been grown, whereas the thickness of the films from static solutions is limited to about 80 nm. The films were characterized using transmission electron microscopy and Rutherford backscattering spectroscopy. The role of the flow rate and configuration of the deposition chamber is discussed.
Sol-Gel Synthesis And Characterization Of Molybdenum Oxide/Polypyrrole Hybrids
Authors: Dong W. , Dunn B.
Published: April 2011

Monolithic Mo oxide/polypyrrole hybrid aerogels and xerogels were successfully synthesized through sol-gel methods. The PPy formed appears to be β-substituted. A 100 fold increase in electrical conductivity was observed for the hybrids (4× 10–3 S/cm) as compared to the pristine MoO3 gels (2× 10–5 S/cm). An initial increase in Li+ intercalation capacity is also observed for the hybrid. The electrical conductivity and Li+ intercalation depend greatly on the concentration of Motrichloro alkoxide precursor and sol aging conditions. The hybrid aerogels have a density of 0.5 g/cc and a surface area of 120 m2/g. The as-formed gels are amorphous and crystallize to the orthorhombic MoO3 phase at 375°C.
Modifications Of Preceramic Polymers Suitable For Corrosion Resistant And High Temperature Coatings
Authors: Blum Y. D. , Chen H. P. , Macqueen D. B. , Johnson S. M.
Published: April 2011

Low-cost preceramic polymers have been developed and used for various coating and composite applications. These siloxane-based polymers can be tailored to be precursors to ceramics or remain as polymeric materials. Polyhydridomethylsiloxane (PHMS) serves as the base polymer, and it can be cured or modified by dehydrocoupling or a combination of hydrosilylation-dehydrocoupling reactions, both catalyzed by transition metal catalysts (Pt and Ru). The base polymer filled with various powders is used primarily for thick ceramic coatings. Modified polymers are used for low-temperature paint-like applications, especially where ambient curing is desirable. Both organic and inorganic modifications of PHMS for coating applications are discussed in this article. Paints containing such polymers and fillers are being evaluated for corrosion resistance and high-temperature applications.
Host-Guest Systems in the Development of Anticorrosive Polymeric Films
Authors: Estevão L. R. M. , Nascimento R. S. V.
Published: April 2011

Interactive dispersion-type LDPE/EVA films with anticorrosive properties were produced using host-guest systems of thermally stable volatile corrosion inhibitors (VCI) dicyclohexylammonium p-nitrobenzoate and phosphate, adsorbed on NaY zeolites and diatomaceous earths. Carbon steel specimens were either directly exposed to the inhibiting systems studied or wrapped with the additivated films. Accelerated corrosion tests were carried out where the inhibitive properties of the systems being studied were determined by mass loss of the test coupons. The influence of the mineral support on the volatility of the corrosion inhibitors was evaluated by TG/DTG techniques. The obtained results may be regarded as a confirmation of the hypothesis that VCI volatility may be controlled by their deposition on determined supports. Also, both VCIs had their efficiency enhanced by zeolites, and the phosphate greatly benefited from the use of diatomaceous earth.
Nanoscaled Filled Sol-Gel Hybrid Materials for Powder Coatings
Authors: Seneur S , Dutfurth C. , Muhle J. , Poppe A. , Schmidt H.
Published: April 2011

The sol-gel process has been applied for the synthesis of inorganic-organic powder materials. For this purpose, low reactivity and, for reasons of comparison, nanoscaled sol-gel precursors and nanoscaled silica filler were used to synthesize a low molecular weight inorganic-organic composite which was meltable between 85°C and 100°C and curable at temperatures of 150°C - 200°C. The powders were used for electrostatic coating of aluminum sheets. The resulting coatings of the unfilled system exhibited excellent mechanical properties, e. g. a high abrasion resistance (weight losses between 6 mg and 10 mg per 1000 cycles by taber abrader test (ASTM D1044)) and high values for hardness (universal hardness (DIN 55676): 150 N/mm2). The hardness of the materials was increased up to 210 N/mm2 by the addition of silica, while the abrasion resistance remained unaffected.
High Surface Area Substrates for DNA Arrays
Authors: Glazer M. , Frank C. , Vinci R. P. , Mcgallo G. , Fidanza J. , Beecher J.
Published: April 2011

High-density, spatially addressable arrays of DNA probes offer a high-throughput approach to DNA sequence analysis that is likely to have a major impact on biological and genetic research. These arrays are comprised of short strands of immobilized DNA (“probe”) sequences prepared synthetically on a planar glass support. Samples of unknown, fluorescentlylabeled strands of “target' DNA can be analyzed by sequence-specific binding (“hybridization”) to the arrays in order to extract detailed sequence information. The detection sensitivity of these arrays is dependent on quantity and density of immobilized probe molecules on the surface, as well as the thermodynamics of nucleic acid hybridization. In this report, substrates with a porous, “3-dimensional” surface layer were investigated as a means of increasing the number of available probes, and therefore the amount of detectable bound target per unit area. Two methods for creating porous silica layers were investigated - a “subtractive” method and an “additive” method. For the systems investigated, the additive method, sol-gel processing, offered the most promising route for high density DNA arrays.
Lowering The Percolation Threshold In Carbon Blackfilled Polymer Composites
Authors: Grujnlan J. C. , Gerberich W. W. , Francis L. F.
Published: April 2011

In an effort to lower the percolation threshold of carbon black-filled polymer composites, various polymer microstructures were examined. Composites prepared with a polyvinyl acetate (PVAc) latex and a poly(vinyl acetate – ethylene) water-dispersible powder showed a significantly lowered percolation threshold relative to an equivalently prepared composite that used a polyvinyl alcohol (PVA) solution to form the matrix phase. The percolation threshold of the dispersion-based composites occurred at 5 vol.% carbon black, while the equivalent solutionbased composite produced a threshold at 14 vol.%. By excluding the carbon black from regions occupied by polymeric particles, the dispersion-based composites lead to preferential aggregation of carbon black, as evidenced by SEM, and a lowered percolation threshold.
Dialkylenecarbonate-Bridged Polysilsesquioxanes: Hybrid Organic-Inorganic Sol-Gels with a Thermally Labile Bridging Group
Authors: Loy Douglas A. , Beach James V. , Baugher Brigitta M. , Assink Roger A. , Shea Kenneth J. , Tran Joseph , Small James H.
Published: April 2011

In this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane xerogels using post-processing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or by chemical means after the gel has been processed to a xerogel. These modifications can produce changes in density, solubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic-inorganic materials. Dialkylenecarbonate-bridged polysilsesquioxane gels were prepared by the sol-gel polymerization of bis(triethoxysilylpropyl)carbonate (1) and bis(triethoxysilylisobutyl)-carbonate (2). Thermal treatment of the resulting non-porous xerogels and aerogels at 300–350°C resulted in quantitative decarboxylation of the dialkylenecarbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic xerogels and aerogels that can not be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.
A Study on The Phase Transformation and Exchange-Coupling of (Nd0 95La0 05)9 5FebalCo5Nb2B10.5 Nanocomposites
Authors: Chen Q. , Ma B. M. , Lu B. , Huang M. Q. , Laughlin D. E.
Published: April 2011

The phase transformation and the exchange coupling in (Ndo095Lao005)9.5FebaICOsNb 2BI05 have been investigated. Nanocomposites were obtained by treating amorphous precursors at temperatures ranging from 650TC to 9500C for 10 minutes. The magnetic properties were characterized via the vibrating sample magnetometer (VSM). X-ray diffraction (XRD), thermomagnetic analysis (TMA), and transmission electron microscopy (TEM) were used to perform phase identification, measure grain size, and analyze phase distribution. The strength of the exchange coupling between the magnetically hard and soft phases in the corresponding nanocomposite was analyzed via the AM-versus-H plot. It was found that the remanence (Br), coercivity (Hci), and maximum energy product (BHmax) obtained were affected by the magnetic phases present as well as the grain size of constituent phases and their distribution. The optimal magnetic performance, BHm, occurred between 700°C to 750°C, where the crystallization has completed without excessive grain growth. TMA and TEM indicated that the system was composed of three phases at this point, Nd2(Fe Co) 14B, ca-Fe, and Fe3B. The exchange coupling interaction among these phases was consistently described via the AM-versus-H plot up to 750°C. The Br, Hci, and BHmax degraded severely when the thermal treatment temperature increased from 750°C. This degradation may be attributed to the grain growth of the main phases, from 45 to 68nm, and the development of precipitates, which grew from 5nm at 750°C to 12nm at 850°C. Moreover, the amount of the precipitates was found to increase with the thermal treatment temperatures. The precipitates, presumably borides, may cause a decrease in the amount of the a-Fe and Fe 3B and result in a redistribution of the Co in the nanocomposites. The increase of the Co content in the Nd 2(Fe Co) 14B may explain the increase of its Curie temperature with the thermal treatment temperatures. In this paper, we examine the impacts of these factors on the magnetic properties of (Ndo 95Lao 05)9 5FebaICosNb2B10.5 nanocomposite.
Magnetic Domain Observation on Melt-Spun Nd-Fe-B Ribbons Using Magnetic Force Microscopy
Authors: Gavrin A. , Sellers C. , Liouw S.H.
Published: April 2011

We have used Magnetic Force Microscopy (MFM) to study the magnetic domain structures of melt-spun Nd-Fe-B ribbons. The ribbons are commercial products (Magnequench International, Inc. MQP-B and MQP-B+) with a thickness of approximately 20 microns. These materials have identical composition, Nd12.18B5.36Fe76.99Co5.46, but differ in quenching conditions. In order to study the distribution of domain sizes through the ribbon thickness, we have prepared cross-sectional samples in epoxy mounts. In order to avoid artifacts due to tip-sample interactions, we have used high coercivity CoPt coated MFM tips. Our studies show domain sizes typically ranging from 50-200 nm in diameter. This is in agreement with studies of similar materials in which domains were investigated in the plane of the ribbon. We also find that these products differ substantially in mean domain size and in the uniformity of the domain sizes as measured across the ribbon. While the B+ material shows nearly uniform domain sizes throughout the cross section, the B material shows considerably larger domains on one surface, followed by a region in which the domains are smaller than average. This structure is presumably due to the differing quench conditions. The region of coarse domains varies in thickness, disappearing in some areas, and reaching a maximum thickness of 2.75 µm in others. We also describe bulk magnetic measurements, and suggest that.
Applications of Rare-Earth Permanent Magnet Structures to Electrical Machinery
Authors: Leupold H.A. , Tilak A.S. , Marchand R.J. , Lagraffe D.A.
Published: April 2011

A variety of promising permanent magnet structures based upon the magic cylinder and magic mangle concepts are investigated with regard to their suitability for application to electrical generators and motors. Such structures feature high magnetic flux densities in large volumes relative to their masses and bulks as well as minimal stray fields and net magnetic moments. Magic mangles also afford small moments of inertia of their rotating elements thereby resulting in improved rotational responsiveness. One computer calculation showed that a small conventional electric generator can be replaced by a magic mangle with 70% more flux amplitude but with only one half the mass and bulk.
Small Brushless Dc-Motor With Sensorless Control - A Hollow Shaft Prototype
Authors: Hanitsch R. , Frenzel B.
Published: April 2011

The features of the prototype with NdFeB-magnets will be presented and also the sensorless control strategy will be outlined. Measured and calculated data show good agreement. Focus will be on the magnetic circuit and the thermal behaviour and not on the control aspects of the motor. Specific parameters demonstrate the good quality of the drive system. A thermal analysis was also done in order to meet the requirements given by the medical specialists.
New series of Sm2TM17magnet materials for applications at temperatures up to 550°C
Authors: Chen Christina H. , Walmer Marlin S. , Walmer Michael H. , Liu Sam , Kuhl G. Edward , Simon Gerard K.
Published: April 2011

A new series of Sm(CowFevCuxZry)zmagnet products with1Hcup to 13 kOe at 400°C has been developed. These magnets have low temperature coefficients ofiHcand a straight line B vs. H (extrinsic) demagnetization curve up to 550°C. A straight line extrinsic curve provides greater design flexibility and facilitates reduced size and weight of magnetic circuits. The straight line extrinsic demagnetization B curves are required for magnets used in dynamic applications. The maximum use temperature, defined here as TM, can be determined by finding the maximum temperature at which the B curve is a straight line. The results of this work show that increasing the Co content in the magnet enhances high temperature performance. A higher Co content provides a lower temperature coefficient β ofiHe. Magnets with Co content w = 0.65 have β = 0.26%C from 25°C to 300°C. Magnets with w = 0.82 have β = 0.116%C from 25°C to 300°C. The lower β results in a higher (BH)maxat high temperature, and a higher TM. The TMis 240°C for w = 0.65,330°C for w = 0.68, 400°C for w = 0.76, 490°C for w = 0.78, and 550°C for w = 0.82. By increasing the Co content and adjusting the content of other elements, along with appropriate changes of processing parameters, a new series of magnets has been developed for use at temperatures from 400°C to 550°C. Magnetic properties vs. temperature for the new series of magnets, in comparison to those of the best commercial magnets, are shown in this paper to illustrate the improvements which have been made. Magnetic properties at different temperatures vs. Co content for the series are also reported in this paper.
Hydrogenation Disproportionation Desorption Recombination Processes Applied to NdFeB-, SmFe- and SmCo-Type Alloys
Authors: Gutfleisch O. , Kubis M. , Handstein A. , Müller K.-H. , Schultz L.
Published: April 2011

Recent aspects of hydrogenation disproportionation desorption and recombination (HDDR) phenomena in NdFeB-, SmFe- and SmCo-type alloys are reviewed in this paper. The effects of additives on hydrogen sorption and magnetic properties are discussed. The possibilities of producing magnetically anisotropic NdFeB HDDR magnets by hot deformation or alternatively pre-aligning and compacting anisotropic powders are described. Current models for the inducement of magnetic anisotropy in NdFeB HDDR powder are summarized and it is shown that anisotropic powder can be produced from a ternary compound when using a modified processing route. The application of ‘extreme’ hydrogenation conditions, namely high hydrogen pressure or reactive milling in a hydrogen atmosphere at enhanced temperatures, allows the disproportionation of thermodynamically very stable compounds such as Sm2Fe17−xGax(x≥l), SmCo5or Sm2Co17. Reactive milling and subsequent recombination in vacuum lead to structures, of both the disproportionated and the recombined type, which are on a remarkably finer scale than those commonly observed for standard HDDR procedures. Exchange coupling between the nano-scaled grains can result in magnetically single phase behavior despite a multiphase microstructure and in particular for the Sm2Co17alloy, a remanence enhancement was observed after recombination at temperatures ≤700°C.
Magnetization Reversal In Melt-Ouenched NdFeB
Authors: Crew D.C. , Lewis L.H. , Mccormick P.G. , Street R. , Panchanathan V.
Published: April 2011

Melt-quenched NdFeB is an important modem permanent magnet material. However there still remains doubt as to the magnetization reversal mechanism which controls coercivity in material prepared by this processing route. To investigate this problem a new technique based on measurements of reversible magnetization along recoil curves has been used. The technique identifies the presence of free domain walls during magnetic reversal. For this study samples of isotropic (MQI), hot pressed (MQII) and die upset (MQIII) melt-quenched NdFeB were examined. The results indicate that in MQI free domain walls are not present during reversal and the reversal mechanism is most likely incoherent rotation of some form. Free domain walls are also not present during reversal in the majority of grains of MQII, even though initial magnetization measurements indicate that the grain size is large enough to support them. In MQIII free domain walls are present during reversal. These results are attributed to the reduced domain wall nucleation field in MQII compared with MQII and the increased dipolar interactions in MQIII.
Interferometry of Optical Second Harmonic Generation from Gd-Containing Langmuir-Blodgett Superstructures: Magneto-Induced Effects
Authors: Vishnevskaya E.I. , Didenko N.V. , Fedyanin A.A. , Khomutov G.B. , Murzina T V. , Nikulin A.A. , Aktsipetrov O.A.
Published: April 2011

Nonlinear magneto-optical Kerr effect in Gd-containing Langmuir-Blodgett superstructures is studied by second harmonic generation (SHG) interferometry. The intensity of the regular magneto-induced second harmonic (SH) is found to be by a factor of about 2 larger than the intensity of the regular SH component of a non-magnetic origin. The phase shift between the magneto-induced and non-magnetic contributions to the nonlinear polarization is about 46° The intensity of the magnetization-independent hyper-Rayleigh scattering (HRS) is by two orders larger than that of mnagneto-induced HRS.
Nanocrystalline Soft Magnetic Fe-M-B (M = Zr, Hf, Nb) “NANOPERM,” Fe-M-O (M = Zr, Hf, Rare Earth) Alloys and Their Applications
Authors: Makino A. , Inoue A. , Masumoto T.
Published: April 2011

New soft magnetic nanocrystalline materials in Fe-M-B (M = Zr, Hf, Nb) and Fe-M-O (M = Zr, Hf, rare earth) systems have been fabricated by use of partial crystallization of melt-spun amorphous phase and sputtering-induced partial crystallization, respectively. These alloys have a mixed structure of nanoscale a-Fe grains and an amorphous phase containing large amount of M, B and M, O, respectively. This structural property should be a dominant factor for achieving good soft magnetic properties in both alloys. The Fe85.5Zr2Nb4B8.5 ribbon exhibits a high mag- netic flux density (Bs) of 1.64 T and a high permeability of 60,000 at 1 kHz as well as a very low core loss of 0.09 W/kg at B = 1.4 T and 50 Hz. The soft magnetic Fe-M-O films with high O content of 10-35 at.% maintain high permeability up to the high frequency above 100 MHz be- cause of higher electrical resistively of 6 to 23 µΩm than those of other conventional soft mag- netic alloy films. The Fe-M-B ribbons "NANOPERM" should be more suitable for low frequen- cy transformers. The Fe-M-O films are useful for high frequency applications such as thin-film inductors and transformers for micro switching converters for portable electric equipment.
Soft Magnetic Properties and Structure of Nanocrystalline Alloys Based on Finemet
Authors: Todd I. , Davies H.A. , Gibbs M.R.J. , Kendall D. , Major R.V.
Published: April 2011

The effects of partial substitution of Al for Fe in Fe73.5-xAlxSi13B9Nb3Cu1, nano composite alloys both on the a.c. magnetic properties such as permeability and core loss, saturation magnetostriction and core loss are presented. The observed improvements in material properties are discussed in relation to the nanocrystallite and residual glass component chemistry.
Effect of Cu On Microstructural Evolution of Nanocrystalline Soft and Hard Magnetic Materials
Authors: Hono K. , Ping D. H. , Hirosawa S.
Published: April 2011

The nanocrystallization processes in Fe-Si-B-Nb-Cu and Fe-Nd-B(-Cu-Nb) amorphous alloys have been studied by transmission electron microscopy (TEM) and a three dimensional atom probe (3DAP). Cu additions are effective in refining the nanocrystalline microstructures of both alloys, because Cu atom clusters formed prior to the crystallization reaction serve as heterogeneous nucleation sites for the primary crystals. However, the clustering behaviors of Cu atoms in these two alloy systems are different, i.e., Cu completely dissolves in the Nd2Fe1 4B phase in the final microstructure of the Nd4.5Fe75.8B18.5Cu0.2Nb1 alloy, whereas CL' clusters grow to fcc-Cu particles in the Fe73.5Si13.5B9Nb3Cu1 alloy. The nanocrystallization processes in these two alloys clarified by the 3DAP results are compared.
Lorentz Microscopy and Electron Holography of Nanocrystalline Magnetic Materials
Authors: Graef Marc De
Published: April 2011

This paper employs an analytical model for the phase shifts imparted on a beam electron by a spherical particle with a uniform magnetization. Model image simulations of Fresnel and Foucault type Lorentz microscopy contrast are presented. Estimates of a lower particle size limit for which no magnetic information can be extracted from the images are given and compared to similar estimates for the electron holography observation method. It is concluded that conventional Lorentz methods have a lower particle size limit of around 30 nm (for cobalt particles), while electron holography can be used to even smaller sizes.
Pvd Growth of Fcc Metal Films on Single Crystal Si and Ge Substrates
Authors: Westmacott K.H. , Hinderberger S. , Radetic and U. Dahmen T.
Published: April 2011

Epitaxial films of the fcc metals Al, Au, Ag and Ni were grown by physical vapor deposition on Si and Ge (111), (110) and (100) substrates at different deposition temperatures. The epitaxial relationships and morphological features of these films were characterized by transmission electron microscopy and diffraction in plan view and cross section. Ag formed single crystal films on all substrates at all temperatures. Au and Al could be grown as bicrystals, and under some conditions, Al and Ni grew as tricrystal films. The morphological effects of diffusion at the metal/substrate interface are ascribed to diffusion induced grain boundary migration.
Investigations On In Situ Nanocrystallization And Magnetic Properties For Amorphous Fe78Si9B13 Ribbons
Authors: Sun Xiangeheng , Cabral-Prieto A. , Yacaman M. Jose , Sun Wensheng
Published: April 2011

The amorphous state of ferromagnetic Fe78Si9B13 (Metglas 2605S-2) and its nanocrystallization were investigated by in situ transmission electron microscope (TEM), Xray diffraction (XRD), Mossbauer spectroscopy (MS), differential scanning calorimeters (DSC) and magnetic moment measurements. The Mössbauer spectrum exhibited an essentially symmetric hyperfine field pattern of 259KOe in as-quenched amorphous state at room temperature. The Curie and crystallization temperature were determined to be Tc=708K and Tx= 803K, respectively. The Tx value was in good agreement with DSC measurement results. The occupied fraction of the nanocrystalline phases of α-Fe(Si) and Fe2B at in situ optimum annealing temperature was about 57% and 43%, respectively. It is notable that the magnetization of the amorphous phase decreases more rapidly with increasing temperature than those of nanocrystalline ferromagnetism, suggesting the presence of the distribution of exchange interaction in the amorphous phase or high metalloid contents.