bluuebunny/crossref_metadata_2025 huggingface dataset:
High Voltage P-N Junction Diodes in Silicon Carbide Using Field Plate Edge Termination
Authors: Chilukuri R. K. , Ananthanarayanan P. , Nagapudi V. , Baliga B. J.
Published: April 2011

In this paper, we report the successful use of field plates as planar edge terminations for P+-N as well as N+-P planar ion implanted junction diodes on 6H- and 4H-SiC. Process splits were done to vary the dielectric material (SiO2 vs. Si3N4), the N-type implant (nitrogen vs. phosphorous), the P-type implant (aluminum vs. boron), and the post-implantation anneal temperature. The nitrogen implanted diodes on 4H-SiC with field plates using SiO2 as the dielectric, exhibited a breakdown voltage of 1100 V, which is the highest ever reported measured breakdown voltage for any planar ion implanted junction diode and is nearly 70% of the ideal breakdown voltage. The reverse leakage current of this diode was less than 1×10−5 A/cm2 even at breakdown. The unterminated nitrogen implanted diodes blocked lower voltages (∼840V). In contrast, the unterminated aluminum implanted diodes exhibited higher breakdown voltages (∼80OV) than the terminated diodes (∼275V). This is attributed to formation of a high resistivity layer at the surface near the edges of the diode by the P-type ion implant, acting as a junction termination extension. Diodes on 4H-SiC showed higher breakdown than those on 6H-SiC. Breakdown voltages were independent of temperature in the range of 25 °C to 150 °C, while the leakage currents increased slowly with temperature, indicating surface dominated components.
Electrical and Optical Study of Charge Traps at Passivated GaAs Surfaces
Authors: Mochizuki Yasunori
Published: April 2011

Performance of GaAs-based FETs is strongly affected by the electrical properties of passivated surfaces via the surface charges induced at interface states and at the traps within the passivation films. In order to study these two kinds of sources, a set of new characterization techniques are respectively developed for the GaAs interface system, which is in a largely different situation from that for the SiO2/Si interfaces. Our optical technique based on electroreflectance allows accurate evaluation of interface states and is especially useful for the material systems with strong surface pinning. For the study of trapping centers in CVD dielectrics, use of thermally oxidized Si interfaces is found to be quite convenient. The experimental findings are further discussed in conjunction with FET characteristics and an importance of time-domain control of the surface charges is emphasized in the power FET operation. This concept turns out to be the main motivation of a new MESFET structure with a filed-modulating plate (FPFET) which has achieved a state-of-the-art RF performance based on GaAs.
DX Center Energy Level in InxAl1−xAs Compounds
Authors: Sari Hüseyin , wieder Harry H.
Published: April 2011

The presence of DX centers in InxAl1−xAs, primarily in the indirect portion of the InxAl1−xAs bandgap, has been determined using modulation doped InxAl1−xAs/InyGa1−yAs heterostructures by means of persistent photoconductivity (PPC) and galvanomagnetic measurements. From the cooling bias experiment, the PPC, and self consistent Poisson and Schrddinger simulations the ratio of the ionized shallow donors to the DX centers is obtained. Using this ratio in the grand canonical ensemble (GCE) the energy level of DX centers is determined. It is found that the DX energy level merges with the conduction band at x ≅ 0.42 and is resonant with the conduction band in higher indium concentration.
Si1−xGexOxidation by Plasma Assisted Processing: Oxide Uniformity and Electrical Properties
Authors: Busani T. , Plantier H. , Devine R. A. B. , Hernandez C. , Campidelli Y.
Published: April 2011

Anodic oxides of SixGe1−x(0 ≤ x ≤ 1 ) alloys have been made by plasma assisted oxidation in a microwave frequency (2.45 GHz) reactor working in the constant current bias mode. Oxide films ∼15 – 40 nm (depending upon the Ge concentration) were obtained in 10 minutes without a temperature rise of the substrate of more than 100 °C. Detailed infrared absorption studies of the oxides enabled the Si-O-Si, Ge-O-Ge and Si-O-Ge vibrational modes to be identified, the strongest being at 1056, 858 and 1000 cm−1respectively. These modes are associated with the O asymmetric stretch, their values are at lower wavenumbers than in bulk oxides due partly to ultraviolet radiation induced structural modification and partly to thin film optic effects. A statistical model for the different bonds present in SixGe1−xO2, when used to simulate the infrared spectrum does not predict the experimentally observed form, the Ge-O-Ge peak is in general too intense in the experimental spectrum. Auger electron spectroscopy profiling of the SixGe1−xoxides suggests that there is a build-up of Ge close to the surface/oxide interface so that when combined with the infrared data, we conclude that there is a GeO2rich region at the surface/oxide interface. The oxide is, however, globally stoichiometric. Electrical measurements (C(V) and interface state density) were begun on metal-oxide-semiconductor (MOS) capacitors for Si1−xGex. oxides over the range of concentrations 0 ≤ x ≤ 1. Only Si1−xGexoxides with x≤0.15 appear to yield satisfactory MOS capacitor curves.
Modeling of Surface Manipulation by Femtosecond Laser Pulses
Authors: Gruzdeva A. S. , Gruzdev V. E.
Published: April 2011

There are discussed some fundamental physical aspects of surface manipulation by femtosecond laser pulses. Among touched on problems are formation processes of shock electromagnetic waves and surface ripple structures. Proposed theoretical model of femtosecond laser-pulse interaction with matter is illustrated by results of FDTD modeling of linear and nonlinear light scattering by rough surface. Possibility of surface roughness modification and required for that optimal laser-pulse parameters are discussed on the bases of obtained results.
Novel in-situ Ion Bombardment Process for A Thermally Stable (> 800 °C) Plasma Deposited Dielectric
Authors: Ren F. , Lothian J. R. , Pearton S. J. , Wilson R. G. , LaRoche J. R. , Lee J. W. , Johnson D. , Zavada J. M.
Published: April 2011

We demonstrated an in-situ dielectric film passivation technique by dividing a thick film deposition into many thin film (<40Å) depositions and incorporating the ion bombardment between the depositions. N2 was used for the plasma treatment to passivate the SiNx film and a well passivated and thermally stable SiNx was achieved with this process. The refractive index of N2 treated SiNx film only changed 0.3% when the SiNx film was heated up to 1000 °C and the film with a continuous deposition showed a 2.5% change. From the results of SIMS analysis, the N2 treated SiNx film showed a excellent thermal stability after heat up to 1000 °C. The etch rates of passivated SiNx film in BOE and diluted HF are ≤40 Å/min which is much slower than that of un-treated SiNx (135 Å/min).
Studies of Surface State Densities of Semiconductors by Room-Temperature Photoreflectance
Authors: Hwan J. S. , Chang G. S.
Published: April 2011

In this study, we develop a novel approach to determine the surface Fermi level and the surface state densities of semiconductors. The built-in electric field and thus the surface barrier height are evaluated from the Franz-Keldysh oscillations in the PR spectra. Based on the thermionic-emission theory and current-transport theory, the surface state density as well as the pinning position of the surface Fermi level can be determined from the dependence of the surface barrier height on the pump beam intensity. Even though this method is significantly simpler, easier to perform, and time efficient compared with other approaches, the results obtained agree with the literature.
Passivation of InGaAs/InP heterostructures
Authors: Driad R. , Lu Z. H. , McKinnon W. R. , Laframboise S. , McAlister S. P. , Poole P. J. , Raymond S. , Charbonneau S.
Published: April 2011

In this study we report different surface treatments and device designs that can be used to improve the performance of InGaAs/InP heterostructure devices. The surface properties of InGaAs (100) after sulfur or UV-ozone passivation were investigated by photoluminescence and high energy-resolution X-ray photoelectron spectroscopy. The base leakage current and the dc current gain of InGaAs/InP heterostructure bipolar transistors (HBTs) have been used to evaluate the efficiency of the passivation treatments. Although these treatments successfully passivated large area HBTs, the improved device characteristics degraded after a dielectric was deposited by plasma enhanced chemical vapor deposition (PECVD) or even just with time. Nevertheless, we found a combined surface treatment that is successful even under PECVD deposition – a UV-ozone treatment that produces a sacrificial oxide that is then removed by HF. This approach will be contrasted with a different method based on an optimized HBT layer structure with a thin InP emitter. In this case, the thin layer of depleted InP from the emitter left on the extrinsic base passivates the surface, and no treatment is required.
Surface-modified manganese dioxide for alkaline-manganese battery
Authors: Nunome Jun , Nakashima Takuya , Yoshizawa Hiroshi , Nitta Yoshiaki
Published: April 2011

The surface-modification of manganese dioxide has been carried out for the purpose of increasing the discharge capacity of alkaline manganese battery. The characteristics of the obtained material has been investigated by using XAFS (X-ray absorption fine structure), Raman spectroscopy and ESR. It seems that composite oxide of Ti and Mn is formed on the surface of the surface-modified manganese dioxide (SMMD) particles. XRD measurement data on the discharged product demonstrates that SMMD suppresses the byproduct, and discharge characteristics of SMMD is improved compared to the conventional manganese dioxide.
A new family of salts for lithium Secondary batteries
Authors: Baril D. , Brranger S. , Ravet N. , Michot C. , Armand M.
Published: April 2011

A novel family of salts suitable for lithium battery application was synthesized and characterized. These salts have a large delocalized anion whose charge is spread over a single SO2and a phenyl ring. Remarkable properties were obtained for the lithium N-(3-trifluoromethyl phenyl) trifluoromethanesulfonamide salt or LiTFPTS. The electrochemical stability window is around 4.0 V and its conductivity in solid poly(ethylene oxide) or PEO is close to the one of the lithium perchlorate salt. Calorimetric analysis also showed that LiTFPTS behaves as a plasticizer since it hinders, to a certain extent, the PEO crystallization when it is used in a solid polymer matrix. Above all, its synthesis is quite straightforward and leads to potentially inexpensive salts as the starting amines are made commercially on a large scale.
Enhanced Ion mobility in Aluminosilicate/Polysiloxane Network Polyelectrolytes
Authors: Siska David P. , Shriver Duward F.
Published: April 2011

A new series of polysiloxane-based single-ion conductors was prepared. These contain solvating oligoether sidechains and covalently linked aluminosilicate or alkoxy/siloxy-aluminate anions attached to the polysiloxane backbone. Of these two systems, the polymers containing aluminosilicate [(SiO)4Al]− anions show higher room temperature conductivities (10−6 S/cm) than those with alkoxy/siloxyaluminate [(SiO)2(CH2O)2A1]− anions (10−7 S/cm). The incorporation of longer covalent tethers between the alkoxy/siloxyaluminate anion and the polymer backbone results in enhanced room temperature conductivities at high ion loadings. Differential scanning calorimetry data provide a rationale for the high conductivity.
Nanocomposite Based Electrolytes for Lithium-Ion Batteries
Authors: Riley M.W. , Fedkiw P.S. , Khan S.A.
Published: April 2011

Nanocomposite electrolytes based on lithium hectorite (LiHect) clay dispersed in highdielectric organic solvents such as ethylene carbonate (EC) and propylene carbonate (PC) are shown to exhibit room-temperature conductivities exceeding 10−4 S/cm. The LiHect-based composites reveal lithium ion transference numbers of ∼0.8, as measured by the steady-state current method. In addition, dynamic rheological techniques show this system to be mechanically stable with elastic modulus G' exceeding 107 dynes/cm 2 and yield stress exceeding 104 dynes/cm2.
Surface Structure and Electrochemical Characteristics of Ti-V-Cr BCC-Type Solid Solution Alloys Sintered with NI
Authors: Tsuji Yoichiro , Yamamoto Osamu , Matsuda Hiromu , Toyoguchi Yoshinori
Published: April 2011

Ti-V-Cr bcc-type solid solution alloys can absorb a large amount of hydrogen and be applied to active materials of the negative electrode in Ni-MH batteries. However, because of the insolubility of Ni into these alloys, the electrochemical characteristics like discharge capacity and cycle life were poor. In order to increase the discharge capacity of hydrogen absorbing alloy electrodes, Ti-V-Cr bcc-type alloy powders were sintered with Ni in order to form Ni contained surface layer on the alloy surface. As sintering temperature rose up, the surface composition changed from TiNi to Ti2Ni. TiNi surface layer showed better electrochemical characteristics. For the Ni adding method, Ni electroless plating was preferred because of good adhesion. As a result of optimized conditions, a discharge capacity of 570 mAh/g and an improvement of cycle life were achieved.
Transition Metal D$ LaGaO3 Perovskite Fast Oxide Ion Conductor and Intermediate Temperature Solid Oxide Fuel Cell
Authors: Ishihara Tatsumi , Shibayama Takaaki , Honda Miho , Nishiguchi Hiroyasu , Takita Yusaku
Published: April 2011

Doping transition metal cation is known to enhance the electric conduction of solid electrolytes, however, the ionic conduction can be improved by doping the small amount of transition metal, in particular, doping Co is effective for improving the oxide ion conductivity. In this investigation, oxide ion conductivity of LaGaO3 based oxide doped with Co were investigated in detail. It was found that LaGaO3 doped with Co for Ga site (LSGMC) show a notable oxide ion conductivity over a wide range of oxygen partial pressures, although a hole conduction was appeared by addition of excess amount of Co. Considering the electrical conductivity and transport number of oxide ion, the optimized composition of LSGMC seems to be existed at La0.8.Sr0.2, Ga0.8,.Mg0.115 CO0.085O3. Power generation characteristics of fuel cells was greatly improved by using LSGMC for electrolyte and extremely large power density can be obtained on both H2- O2 and H2-air cells. In particular, the maximum power density was attained to a value of 1.53 and 0.50 W/cm2 at 1073 and 873 K, respectively, on H2–O2 cell when the thickness of electrolyte was 0.18 mm. Furthermore, almost similar large power density was attained when air was used as oxidant. The high power density of cell demonstrated in this study suggests that the operating temperature of SOFC can be decreased by using LSGMC for electrolyte.
Effects of Microstructure on the Electrical Conductivity of SrCo0.8Fe0. 2O3_δ
Authors: Zhang K. , Miranova M. , Yang Y. L. , Jacobson A. J. , Salama K.
Published: April 2011

The effect of microstructure on the electrical conductivity of SrCO0.8Fe0.2O3_δ (SCFO) was investigated in air using a four-point dc method. In the test temperature range of 200 to 900 °C, the electrical conductivity of this material was observed to increase with the increase of the average grain size in the lower temperature region where the conductivity increases with the increase of the temperature. The activation energy is decreased with the increase of the grain size in this region, 0.04 ± 0.004 ev for 4.1μm sample and 0.01 ± 0.001 ev for 14.8 μm sample. When temperature is further increased, the conductivity of this material decreases with the increase of the temperature, and the grain size effect becomes less noticeable.
Recent DOE Sponsored Electrochemical Capacitor Test Results
Authors: Wright R. B. , Murphy T. C. , Jamison D. K. , Rogers S. A.
Published: April 2011

Electrochemical capacitors (ultracapacitors) are being developed for hybrid vehicles as candidate power assist devices for the fast response engine and for other energy storage systems that can utilize the high power densities available from these devices. Ultracapacitors show promise toward being able to accept high regenerative pulses and high power delivery capabilities while exhibiting very high cycle life. This paper will present recent test data from two U.S. Department of Energy (DOE) supported ultracapacitor projects designed to meet the fast response engine requirements. Constant-current and constant-power test results will be presented that have been acquired from recent prototype capacitors supplied by SAFT America, Inc. (ten devices), and Maxwell Energy Products, Inc. (two devices). The SAFT capacitors are rated at 0.5 V to 3 V with capacitance ratings ranging from 135 F to 138 F. Capacitor cells rated at 2.3 V and 101.4 F were also evaluated that were produced by Maxwell Energy Products, Inc. Both sets of devices used proprietary carbon electrodes with non-aqueous electrolytes in their design. From the constant-current discharge tests, the discharge current dependence of the capacitance, equivalent series resistance, and RC-time constant were determined as well as the capacitors’ voltage dependence of the capacitance. Constant-power discharge tests permitted the specific energy as a function of the specific power to be determined, and also the discharge/charge round trip efficiency as a function of the magnitude of the constant-power discharge.
The stabilization of layered Manganese Oxides for use in Rechargeable Lithium Batteries
Authors: Whittingham M. Stanley , Zavalij Peter , Zhang Fan , Sharma Pramod , Moore Gregory
Published: April 2011

The layered structure LixTiS2 and LixCoO2 are excellent reversible cathodes for lithium batteries. However, layered lithium manganese oxides are metastable relative to the spinel form on cycling in lithium batteries. They may be stabilized in the layer form by insertion of larger ions such as potassium in the interlayer region, which minimizes the diffusion of the manganese ions from the MnO2 blocks. Their low conductivity is an impediment to their use in high rate batteries. Cobalt can be doped into the layered alkali manganese dioxides, MxMn1-yCoyO2 for M = K or Na, during the hydrothermal synthesis from the alkali permanganates. A single phase is obtained up to about 5% mole cobalt. The cobalt doping is found to enhance the conductivity by two orders of magnitude relative to pure KxMnO2.
Phosphazene Backbones for Siloxanes and Organic Polymers
Authors: Kickelbick Guido , Miller Peter J. , Matyjaszewski Krzysztof
Published: April 2011

2,2,4,4,6,6-Hexachlorocyclotriphosphazene was modified by nucleophilic substitution to obtain building blocks for organic polymers and siloxane networks. 2,2,4,4,6,6-Hexachlorocyclotriphosphazene was substituted with functional groups to enable atom transfer radical polymerization (ATRP) as well as silicon alkoxide as precursors for the sol-gel process. ATRP was carried out with methyl acrylate followed by a chain extension with iso-bornyl acrylate to obtain new thermoplastic elastomers. The sol-gel process was carried out with acid, base and fluoride catalysts and the resulting materials were compared by TGA and DSC measurements.
Synthesis of Hybrid Organic-Inorganic Sol-Gel Coatings for Corrosion Resistance
Authors: Metroke T. L. , Parkhill R. L. , Knobbe E. T.
Published: April 2011

1H-13C and 1H- 29Si CP/MAS NMR spectroscopy has been used to characterize the structure of sol-gel derived hybrid materials prepared from 3-glycidoxypropyltrimethoxysilane (GLYMO) and tetraethylorthosilicate (TEOS) as a function of hydrolysis water ratio and organic content. 1H-13C CP/MAS NMR data indicate that the concentration of hydrolysis water (R value) has a fundamental effect on the nature of the acid-catalyzed hydrolysis and ring opening products. 1H-29Si CP/MAS NMR data suggest that for low R values, the ormosils are composed of a silica network with epoxide groups randomly dispersed throughout. At high R values, epoxide functionalities were found to coat the surfaces of dense silica particles. Salt spray analysis indicates that the corrosion resistance behavior of thin films derived from GLYMOTEOS ormosils decreases as the concentration of hydrolysis water increases and improves as the organic content in the film increases. These observations can be related to the underlying thin film structure.
Mechanical Properties of Low Dielectric-Constant Organic-Inorganic Hybrids
Authors: Cook Robert F.
Published: April 2011

Spin-on glasses, generated by the condensation of an organic-inorganic hybrid silsesquioxane (SSQ), have great potential as low dielectric-constant semiconductor interconnection materials. After curing and condensation SSQ materials consist of an amorphous, inorganic, –Si–O-Sibridging network with organic, non-bridging –Si–R side groups. Relative dielectric constants in the range 2.5–3.3 are obtained for SSQ materials, depending on the curing conditions, and compare with 4.0 for conventionally-used fused silica. The non-bridging side groups significantly disrupt the SSQ network—occupying more than 25% of the Si bonds—and lead to materials that are considerably less stiff, hard and tough than fused silica. Perhaps more importantly, SSQ materials have thermal expansion coefficients greater than that of the intended Si substrate and therefore finish curing in a state of residual tension, leading to a susceptibility to stress-corrosion cracking. In this paper the development of thermomechanical properties during curing of SSQ spin-on glasses is considered and related to the driving force for film cracking deriving from the residual tension. Various crack suppression schemes involving mechanisms both intrinsic and extrinsic to the base SSQ are discussed.
Effect of Curing Strategies on Porosity in Silanemodified Silica Colloidal Coatings
Authors: Daniels M. W. , Francis L. F.
Published: April 2011

Suspensions of silica (20 nim) in propoxyethanol were used to make porous silica coatings. A silane coupling agent, glycidoxypropyltrimethoxysilane (GPS), was added as a binder to increase coating durability and prevent cracking. GPS addition prevented crack formation but only when added in large amounts (GPS to silica weight ratio 0.5 to 1) such that porosity was filled by a GPS-based siloxane polymer. Attempts to enhance the fracture toughness of porous coatings through UV curing and glycol additions failed to lead to improvements in the critical cracking thickness (CCT). However, addition of triethylenetetramine resulted in a 3-fold increase in the CCT. Wear resistance increased for both the UV-cured and amine-cured coatings.
Organic/Inorganic Hybrid Sol-Gel Derived Hard Coatings on Plastics
Authors: Chan C. M. , Cao G. Z. , Fong H. , Sarikaya M. , Robinson T. , Nelson L.
Published: April 2011

We investigated sol-gel derived silica based hard coatings on modified polyester substrates. The silica network was modified by incorporating an organic component and adding transition metal oxides. These modifications resulted in tailored thermal, optical and mechanical properties of the coatings. Various low temperature densification techniques were studied including appropriate sol-preparation procedure, enhanced solvent evaporation, ultraviolet (UV) irradiation, and low-temperature (below 150°C) heating. Oxygen plasma etching was applied to improve the adhesion of the sol-gel coatings on the plastic surface. Nanoindentation analysis revealed that the sol-gel coatings have a surface hardness up to 2.5±0.27 GPa, approximately an order of magnitude higher than that of the plastic surface.
Preparation and Properties of Inorganic-Organic Hybrids From Vinyland 3-Methacryloxypropyltrimethoxysilane
Authors: Takamura N. , Gunji T. , Abe Y.
Published: April 2011

The organic-inorganic polymer hybrids consisting of carbon-carbon and siloxane chains were prepared by radical polymerization of vinyltrimethoxysilane (VTS) and 3-methacryloxypropyltrimethoxysilane (MAS) followed by hydrolytic polycondensation. Polyvinyltrimethoxysilane (PVTS) and poly(3-methacryloxypropyltrimethoxysilane) (S-PMA) with various molecular weights Mw=3900–64800 were prepared by polyaddition of VTS and MAS, respectively. PVTS and S-PMA provided transparent and flexible free-standing films and coating films. With increasing carbon-carbon chain length, the elasticity of the films increased, while the tensile strength and Young's modulus decreased. The adhesive strength of the coating films on organic substrates was particularly dependent on the solubility parameter, polarity and crystallinity of each substrate. The pencil-hardness of coating films was clearly increased with increasing degree of condensation of sila-functional group in PVTS and S-PMA.
Tear Strengths of Poly(Dimethylsiloxane) Networks Reinforced with in-Situ Precipitated Silica
Authors: Kumudinie Chandima , Mark James E.
Published: April 2011

The tear strengths of in-situ filled poly(dimethylsiloxane) (PDMS) networks were investigated using “trouser-tear” tests. The filled PDMS networks were prepared by the simultaneous curing and in-situ precipitation technique, the silica reinforcing phase being obtained by the hydrolysis and condensation of tetraethoxysilane present in excess of that required for the chain end-linking process. Transmission electron micrographs showed well-dispersed and unagglomerated silica particles, and thermogravimetric analysis indicated that the silica particles gave some improvements in thermal stability. In the tearing tests, “stick-slip” tearing was observed at higher rates, especially for the filled networks. The tear strengths were found to increase with increase in the amount of silica incorporated, with the largest increases occurring at the low silica contents.
Mechanical Properties of Soluble Polymer/Silica Gel Hybrids
Authors: Klein L. C. , Wert J. Van , Beaudry C. L.
Published: April 2011

Strengths have been measured for silica gels prepared with poly(ethylene oxide) (PEO) and poly(vinyl acetate) (PVAc). The modulus of rupture was determined using standard three-point bending in a mechanical tester. The samples were prepared by mixing tetraethylorthosilicate with the polymers dissolved in water (PEO) or water/ethanol(PVAc). Molecular weights between 200 and 3400 were used for PEO. Substitutions of the polymer for silica represented between 5 and 25% on a weight basis. In these systems, the interactions between the polymer and the silica network are largely through hydrogen bonding, between ether oxygens in PEO and silanols and between hydroxyls in PVAc and silanols. The extent of the bonding increases with increasing aging time, as indicated by an almost linear increase in the modulus of rupture. The increase for PEO was greater than for PVAc. Among PEO samples, the strengths were higher for higher molecular weights at the same weight fraction.
Viscoelastic Responses of Inorganic-Oranic Hybrids Polymers
Authors: Lee Andre
Published: April 2011

The properties of nano-structured plastics are determined by complex relationships between the type and size of the nano-reinforcement, the interface and chemical interaction between the nano-reinforcement and the polymeric chain, along with macroscopic processing and microstructural effects. In this paper we investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of nano-reinforcement, namely organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers. Glass transitions of these nano-composites were studied using differential scanning calorimetry. Small strain stress relaxation under uniaxial deformation was examined to provide insights into the timedependent viscoelastic behavior of these nano-composites. Since the size of POSS macromer is comparable to the distance between molecular junctions, hence as we increase the amount of POSS macromers, the glass transition temperature, Tg, as observed by DSC increase. However for epoxy network reinforced with clay, we did not observe any effect on the Tg due to the presence of clay reinforcements. In small strain stress relaxation experiments, both types of reinforcement provided some enhancement in creep resistance, namely the characteristic relaxation time as determined using a stretched exponential relaxation function increased with the addition of reinforcements. However, due to different reinforcement mechanisms, enhancement in the instantaneous modulus was observed for clay-reinforced epoxies, while the instantaneous modulus was not effected in POSS-epoxy nano-composites.
Synthesis-Morphology-Mechanical Properties Relationships Of Polymer-Silica Nanocomposite Hybrid Materials
Authors: Hajji P. , David L. , Gerard J. F. , Kaddami H. , Pascault J. P. , Vigier G.
Published: April 2011

Two types of polymer-silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO2 nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol-gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis, morphology and mechanical properties are discussed mainly on the basis of solid state 29Si nuclear magnetic resonance spectroscopy (NMR), transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA).
Synthesis & Characterization of Optically-Active Lanthanide-Doped Hybrid Inorganic-Organic Systems
Authors: Taylor-Smith R.E. , Choi K. M.
Published: April 2011

The materials chemistry of sol-gel-derived inorganic-organic molecular composites offers significant potential for molecular-level systems design. One focus in this arena is the chemical design and microstructural engineering of optically-active systems. We report the generation of rare-earth-doped inorganic-organic hybrids, based on a bridged polysilsesquioxane architecture. Derived from lanthanide precursors such as Erbium isopropoxide, which we co-condense with the requisite silsesquioxane monomer, these systems exhibit significant optical activity. In experiments on hybrids doped with Erbium, we conclusively demonstrate strong fluorescence at wavelengths in the vicinity of 1540 nm, from stimulation with 488 nm radiation. We discuss materials-driven impacts of the bridged-silsesquioxane architecture on system complexities arising from the solution sol-gel route which would affect fluorescence efficiencies and luminescence levels, such as hydroxyl impurities and clustering-effects.
Materials Properties and Utilization of Fe3B/Nd2Fe14B-Type Nanocomposite Permanent Magnets Based on Nd-Fe-Cr-Co-B
Authors: Hirosawa S. , Kanekiyo H. , Shigemoto Y.
Published: April 2011

Recent progresses of materials development and their utilization of Cr-and-Co-doped Fe3B/Nd2Fe14B-type nanocomposite permanent magnets are reported. A practical balance between enhanced intrinsic coercivity and temperature stability of magnetic properties has been realized by simultaneous additions of Cr and Co. This type of magnets are less susceptible to oxidation because of the less rare-earth content. Consequently, even fine powders (e. g., under 38 micrometer sieve) are physically and chemically stable in contrast to the conventional Nd2Fe14B-type melt-spun materials. The stability in terms of the structural losses is also superior to that of the Nd2Fe14B-type melt-spun materials. Utilization of the Cr-and-Co-doped Fe3B/Nd2Fe14B nanocomposite permanent magnets as a hard magnetic component of injection-molded resin-bonded magnets seems promising because of the excellent stability of the magnetic properties of fine powders. Direct quenching of a melt into the nanocomposite structure has become possible recently in addition to the conventional processing route of crystallization of an amorphous precursor, opening up the possibility of less-expensive production of the material.
Magnetic Properties of Polymer Bonded Exchange-Spring NdFeB Magnets
Authors: Mokal B. , Smith N.A. , Williams A.J. , Harris I.R.
Published: April 2011

The production of remanence enhanced powders, using a method of mechanical alloying of free iron to melt spun ribbon, has been studied. The final composition is Nd8. 1Fe77.1Co10.9B3.9 and both hard and soft materials possess an initial fine grain size; approximately 30nm for the Nd2Fe14B phase in the melt spun ribbon and 1µm for the α-Fe. The magnetic properties of resin bonded magnets fabricated using such material have been measured and found to exhibit exchangespring behaviour. The experiments performed in this work are described with respect to the volume fraction of the soft phase and subsequent annealing temperature of the as-milled material. Remanence enhancement has been observed and this can be attributed to the exchange interactions between the ferromagnetic soft and hard phases. For a 30% by volume addition of α-Fe, typical values of remanence were found to be ∼880mT with a coercivity of ∼250 kA/m. The reversible and irreversible components of the magnetisation have been determined, to demonstrate the exchange coupling and coercivity behaviours respectively.
Magnetic Properties of α Fe/NdFeB Nanocomposite Alloys Prepared by Two-Step Rapid Solidification
Authors: Yamasaki M. , Mizuguchi H. , Morioka H , Hamano M. , Inoue A.
Published: April 2011

In order to obtain directly powders of nanocomposite a Fe/NdFeB alloys with the composition of NdxFebaICO8NbyB, where x: 8.0-8.5, y: 1.5-2.5, z: 6.0-6.5 in at%, have been prepared using the two-step rapid solidification apparatus, which is composed of a gas atomizing system at the upper side and a collision-and-solidificating rotor system at the lower side. It is found that the coercivity (HcJ) of flat-shaped powders obtained depends on powder sizes. The best HcJ in each sieved powder is 525 kA/m (6.60 kOe) for a size more than 500 p m, 449 kA/m (5.64 kOe) for 150-500 pm, and 391 kA/m (4.91 kOe) for 50-150 p m. These values are not so high compared to those of powders of ribbons prepared using a single-roller melt spinning apparatus. This should be attributed to the powder size distribution that causes fluctuation of the quenching rate. Thickness of the flat powder is found to be controllable up to 70/g m, which is useful to get compression molded bonded magnets with a high density and thus a high remanence (Br). An epoxy-bonded magnet with (BH)max: 61.8 kJ/m 3 (7.76 MGOe), Br: 0.732 T (7.32 kG), HcJ: 427 kA/m (5.36 kOe), and density of 6.20 Mg/m 3 is obtained.
Nd Rich Nd-Fe-B Tailored for Maximum Coercivity
Authors: Girt Er. , Krishnan Kannan M. , Thomas G. , Echer C. J. , Altounian Z.
Published: April 2011

The coercive field, He, in rapidly quenched Nd-Fe-B was found to increase for samples with excess of Nd. In addition, Hc, strongly depends on the Fe/B ratio, increasing from 1.67 T for Fe/B = 1.07 to 2.05 T for Fe/B = 14.6 in Nd30(Fe,B)70. The increase in Hc seems to correlate with an increase of the γ-Nd phase in the sample. The initial magnetization curves of Nd30(Fe,B)70 show that the domain wall pinning plays a more important role as the Fe/B ratio increases. Thus, γ-Nd may play an important role in promoting a pinning mechanism. The excess of Nd in rapidly quenched Nd-Fe-B samples was also found to promote growth of Nd2Fe14B grains elongated in shape.
Hysteresis Loops and Coercivity Mechanisms in Sintered and Nanocrystalline Permanent Magnets
Authors: Kronmüller H. , Goll D. , Kleinschroth I. , Zern A.
Published: April 2011

The hysteresis loops of nanocrystalline (nc) permanent magnets (pms) produced by the melt-spin technique have been investigated for compositions based on the intermetallic compounds R2Fe14B (R = Nd, Pr) and the carbides Sm2Fe17−xGaxCy. The following three types of pms have been studied: 1) High-coercivity pins with exchange decoupled grains. 2) High-remanence exchange-spring pms. 3) High-coercive-high-remanence composite pins with exchange coupled soft and hard magnetic grains. The temperature dependence of the coercive field μ0Hc for all three types ofpms obeys a relation for a modified nucleation field, Hc = (2K1/Js)α - Neff Ms (K1 = first anisotropy constant, Ms = spontaneous magnetization). For an analysis of the characteristic differences between the microstructural parameters a and Neff as obtained for the three types of pms, computational micromagnetism on the basis of the Finite Element Technique is applied. This powerful method allows a quantitative analysis of the role of grain size, grain boundaries (gbs), texture of easy directions and of soft magnetic phases in composite materials. In order to obtain satisfactory results, a self-adapting algorithm has been developed where the mesh size is adapted to the gradients of the direction cosines of the spontaneous magnetization. It turns out that excellent magnetic properties of composite pms can only be obtained if the gbs are as ideal as possible. Remanence and coercive field are found to decrease linearly with a corresponding reduction of both, the crystal anisotropy and the exchange constant within the gbs. In composite pins the diameters of the soft magnetic grains should be smaller than twice the domain wall width, of the hard magnetic phase in order to obtain a remarkable remanence enhancement. From these model calculations general rules for the development of optimized nc pms with large remanences and large coercivities are derived.
Thermal Plasma Synthesis of γ-FeN, Nanoparticles as Precursors for the Fe16N2 Synthesis by Annealing
Authors: Turgut Z. , Ferguson D. E. , Huang M. Q. , Wallace W. E. , Mchenry M. E.
Published: April 2011

An ordered Fe16N2 phase has been reported with iron moments as high as 3.2 μB. It is precipitated from nitrogen martensite structures ideally containing 10.5 at.% nitrogen. Due to the highly distorted crystal structure and metastability of this phase non-equilibrium processing routes are sought to synthesize this phase. Here we report on radio frequency (RF) plasma torch synthesis which is used to produce FeN. nanoparticles quenched into a body centered tetragonal bct) structure as precursors for further annealing studies to form α“- Fe16N2 phase. We have employed a Tekna PL-50 type 50 kW, RF plasma torch. A plasma gas mixture containing 40 standard liters per minute (slpm) Ar and 8 slpm Hydrogen - 70 slpm Ar gas was used as a sheath gas. Iron powder ( < 10 μm) was injected into the plasma stream using Ar flowing 15 slpm as a carrier gas. Nitrogen and Ammonia were used as a nitrogenization sources. Relatively low injection rates were used in order to achieve smaller particle sizes and thus faster quenching rates. We were able to produce particles containing up to 45 % of the quenched γ-phase. Observations based on x-ray diffraction (XRD) determination of lattice expansion and phase transition temperatures observed by differential thermal analysis (DTA) indicated that the quenched phase contains 6.5 atomic % nitrogen. Scherrer analysis of the fine particle broadening indicated that the average particle size for γ- phase is 27 nm, whereas this value is found to be 55 nm. for α-Fe. Nitrogen is well known for its grain size refinement in Fe thin films. Saturation magnetizations were found to be as low as 123 emu/g due to the presence of the nonmagnetic γ-FeNx phase.
Polymer Coated Nanoparticulate Ferrite Powders: Properties and Application
Authors: Vollath D. , Szabó D. V. , Fuchs J.
Published: April 2011

Superparamagnetic behavior is characterized by a thermally fluctuating vector of magnetization, leading to magnetization curves free of hysteresis: it is a property of isolated ferrite particles with sizes below ca. 10 nm. These particles fulfil the condition Kv < kT with K … energy of unisotropy, v … volume of the particle, kT has the usual meaning. To produce a superparamagnetic macroscopic part it is necessary to avoid the interaction of the particles. This can be achieved by coating the particles with a second non-magnetic phase. This special material can be synthesized using the microwave plasma process. Because of the specific interaction of charged particles with an oscillating electrical field, microwave plasmas excel in relatively low reaction temperatures. The low reaction temperature and the electrical charging of the particles in the plasma reduce the probability of agglomeration. Therefore, it is possible to pass the gas stream with the as produced particles through a second reaction zone, where the particles will be coated with a polymer. The thickness of the coating can be adjusted in the range from 1 to 5 nm. The composition of the ferrite kernel is selected either for maximum susceptibility or maximum frequency of application. They may consist either of maghemite, manganese-, manganese-zinc-, or magnesium iron spinell for maximum susceptibility or cobalt-iron spinelle type material for maximum frequency. Polymer coated ferrite nanoparticles can be consolidated by hot pressing with temperatures around 100 °C. Superparamagnetism is shown by static magnetic measurements and Moessbauer spectrometry. Dynamic measurements of the complex susceptibility show interesting properties up to frequencies in the gigahertz range.
Magnetic Properties of Hitperm (Fe,Co)88Zr7B4Cu1 Nanocrystalline Magnets (Invited)
Authors: Willard M. A. , Gingras M. , Lee M. J. , Harris V. G. , Laughlin D. E. , Mchenry M. E.
Published: April 2011

Alloys consisting of Fe-Co-M-B-Cu (with M = Zr, Hf, Nb), called HITPERM alloys, have been developed. Synchrotron X-radiation studies have been used to show that the ferromagnetic phase in an equiatomic FeCo-based alloy is the α'-FeCo phase. Since both the α'-FeCo phase and the FeCo-based amorphous phase of the nanocrystalline alloy have high Curie temperatures, a high magnetization persists up to the α -> γ structural phase transformation temperature of 980°C. Room temperature AC permeability measurements have shown that the alloys maintain a high permeability of ∼2000 up to a frequency of 20 kHz. The room temperature core loss has also been shown to be competitive with commercial high temperature magnetic alloys with a value of 1 W/g at Bs = 10 kG andf= 10 kHz. Analysis of extended X-ray absorption fine structure (EXAFS) data is consistent with a two-phase mixture of nanocrystalline body centered cubic derivative FeCo structure and an amorphous Zr-rich phase. A differential scanning calorimetry study of the primary crystallization reaction shows an activation energy of 323.3 kJ/mol. As a preliminary study of phase and grain stability, broadening of X-ray diffraction peaks indicates little grain growth after annealing at 600 °C for 3072 hours.
Surface Analysis Of The Nanocrystalline Fe-Based Alloys By Conversion Electron Mossbauer Spectroscopy
Authors: Grabias A. , Kopcewicz M. , Idzikowski B.
Published: April 2011

A combined conversion electron and γ-transmission Mössbauer spectroscopy is applied to investigate the differences in the surface and bulk crystallization of the amorphous Fe-M-B-Cu (M: Zr, Ti, Nb, Ta) alloys. It is shown that the surface crystallization occurs at an annealing temperature lower than in the bulk. The nanocrystalline bcc Fe phase is significantly more abundant at the surface than in the bulk in the entire annealing temperature range.
Crystallization and Nanocrystallization Kinetics of Fe-Based Amorphous Alloys
Authors: Hsiao A. , Turgut Z. , Willard M.A. , Selinger E. , Laughlin D.E. , Mchenry M.E. , Hasegawa R.
Published: April 2011

In this work we describe crystallization kinetics as inferred from time-dependent magnetization studies and thermal analysis for an Allied Signal amorphous Fe-based METGLAS® 2605SA-1 alloy and a NANOPERM (Fe88Zr7B4Cu1) alloy. We illustrate and contrast several phenomena important to understanding crystallization kinetics in particular to the NANOPERM alloy system. In METGLAS® 2605SA-1 primary and secondary crystallization events are observed in differential scanning calorimetry data (DSC) at temperatures of 504 °C and 549 °C, respectively for data taken at a 10 °C/min scan rate. Both temperatures are greater than the Curie temperature of the amorphous alloy. For the NANOPERM alloy primary crystallization (as determined from differential thermal analysis (DTA)) occurs at 500 °C and secondary crystallization at 730 °C and M(t) at temperatures near the primary crystallization temperature is dominated (at short times < 1 hour) by the primary crystallization event. Using the Johnson-Mehl-Avrami equation for isothermal transformations and the Kissinger equation for constant heating transformations, we find corresponding models for the crystallization kinetics of the NANOPERM alloy.
Element-Specific Magnetization Reversal in Fe/Ce Multilayers
Authors: Munzenberg M. , Arend M. , Felsch W. , Pizzini S. , Fontaine A. , Neisius T. , Pascarelli S.
Published: April 2011

Fe/Ce multilayers are magnetically soft with coercive fields of a few Oersteds. In these structures the Ce-5d states are magnetically polarized by hybridization with the 3d states of Fe. The element selectivity of X-ray magnetic circular dichroism (XMCD) is used to measure the magnetization reversal of the Ce-5d states at room temperature. Comparison with the macroscopic magnetization curves studied by the magnetooptical Kerr effect (MOKE) reveal that the ordered Ce-5d moment is not directly coupled to the overall Fe-layer magnetization: the coercitivity of the Ce hysteresis is reduced a factor of two. In view of previous 57Fe Mössbauer spectra this is attributed to an effect of the interface where nominally 1 atomic layer of Fe and Ce are intermixed. Magnetization reversal is initiated in this region due to a reduced magnetocrystalline anisotropy and then propagates into the Fe layers. This interpretation is supported by an experiment on a hydrided multilayer Fe/CeH2.6_6: In this case, there is no intermixing at the interfaces and the magnetization of the Ce-5d electrons follows the Fe-layer magnetization directly.
High Performance, Light weight Thermoplastic/Rare Earth Alloy Magnets
Authors: Xiao Jun , Otaigbe Joshua U.
Published: April 2011

We report progress on our exploratory research on surface modification of magnetic NdFeB fillers, characterization of suitable magnetic rare earth alloy powders and high-performance polymer matrices, processability, and properties of novel thermoplastic/NdFeB magnets. The results suggest that blending liquid crystal polymer (LCP) with a high-thermoplastic polymer such as polyphenylene sulfide (PPS) provides the required balance of properties. These properties include superior magneto-mechanical performance, minimal melt viscosity at optimal NdFeB volume loading, enhanced thermal stability, high stiffness, high strength, improved dimensional stability, and excellent chemical resistance; making the thermoplastics magnets suitable for use in high temperature and aggressive environments where commercial polymer-bonded magnets are not useable.