bluuebunny/crossref_metadata_2025 huggingface dataset:
Superlattices of Semiconductor Quantum Size Particles in Layered Organic Acids
Authors: Popovitz-Biro Ronit , Guo Shouwu , Hensel Volker , Shavit Edna , Lahav Meir
Published: April 2011

The preparation of lead sulfide and cadmium sulfide quantum size particles arranged in periodic layers within organic matrices is described. Superlattices of the particles have been generated in crystals or thin films of long chain amphiphilic acids by topotactic gas-solid reactions of the lead or cadmium salts, that pack in layer structures, with H2S gas. X-ray powder diffraction and transmission electron microscopy reveal that the crystalline order of the reactant has been partially retained in the organic-inorganic composite. This approach is demonstrated by examples of organic acids bearing an aromatic ring along the hydrocarbon chain, such as derivatives of phenyl propionic and benzoic acids.
Selective Depositions of Fe-Containing Oxide Films on Mixed Selfassembled Organic Monolayers using Microcontact Printing
Authors: Shin Hyunjung , Im Hyejin , Hong Seungbum , Lee Kyongmi , Lim Geunbae , Jeon Jong Up , Kim Eung Soo , Pak Y. Eugene
Published: April 2011

In situ patterning of crystalline iron oxide thin layers has been achieved via microcontact printing (μCP) and selective deposition. μCP was used to pattern two different surface moieties of selfassembled organic monolayers (SAMs) on Au/Cr/Si substrates. An elastomeric stamp (poly(dimethylsiloxane); PDMS) having a submicron-size patterned relief structure was used to transfer either hexadecanethiol (HDT) SAMs, which are to sustain deposition of iron oxide precipitates, or hydrophilic SAMs (e.g. dithiothreitol (DTT)). Selective deposition is realized through precipitation of iron oxide phases from aqueous solutions at ambient temperature (<100°C). Aqueous solutions of 0.05 M of iron nitrate (Fe(NO3)2•9H20) containing urea under nitric acid (pH < 2) were prepared for selective depositions. X-ray photoelectron spectroscopic (XPS) results showed that iron oxide precipitates were deposited onto hydrophilic SAMs, but not onto HDT surfaces. As-deposited films onto DTT-SAM surfaces at 80°C were crystalline α-Fe2O3 (hematite). Fe3O4 and γ-Fe2O3 films were synthesized via annealing of as-deposited α-Fe2O3. Scanning electron microscopy, x-ray diffractometry, vibrating sample magnetometry, and optical microscopy were used to characterize the films' microstructures and properties.
Synthesis and Characterization of Titania and Vanadia Thin Films at Organic Self-Assembled Monolayers
Authors: Niesen T. P. , Wolff J. , Bill J. , Guire M. R. De , Aldinger F.
Published: April 2011

Functionalized self-assembled monolayers (SAMs) on single-crystal Si wafers have been used as substrates for the deposition of titania and vanadia thin films. The formation of a titanium chelate was used to stabilize an otherwise spontaneously precipitating aqueous titanium solution. Uniform titania films have been synthesized from Ti(O2)2+ in aqueous HCl solutions at 80°C on sulfonated SAMs. Vanadium oxide hydrate films, V2O5·0.7 H2O, have been directly formed from aqueous vanadate solutions on NH2-terminated SAMs at 45°C. In the as-deposited films, water molecules were intercalated between the vanadium oxide layers. Subsequent annealing at 350°C in air led to nanocrystalline V2O5.
Synthesis of Tio2 Meso-Structured Thin Films
Authors: Zhou H. S. , Honma I.
Published: April 2011

Highly ordered self-assembly organized silica meso-structured architecture have attracted increasing attention because these materials provide a rich source for scientific research and technological applications. This approach to meso-structured materials has been extended to non-silica oxides, especially transition-metal-oxides which might promise applications involving electron transfer and photocatalysts. We report the syntheses of TiO2 transition-metal-oxides meso-structured thin films (MSTF) using a surfactant templating processing with spin coating method. X-ray diffraction patterns of the films showed that the films generally oriented in a lamellar structure. The phase transferring in TiO2 MSTF was also investigated.
Characterization of Organically Modified Silicates by 17O Solid State MAS and MQ-MAS NMR
Authors: Gualandris V. , Maquet J. , Babonneau F. , Florian P. , Massiot D.
Published: April 2011

Organically modified silicates have been prepared, using methyltriethoxysilane and tetraethoxysilane in various molar ratios. The final network is thus composed of trifunctionnal T units and tetrafunctionnal Q units. Three types of oxo bridges can be formed through the competitive self-condensation or co-condensation reactions : (T)-O-(T), (Q)-O-(Q) and (T)-O-(Q). 17O-enriched water was used as reactant in order to selectively enrich the various oxo bridges, and to perform 17O solid state MAS-NMR. The combination of MAS experiments recorded at two different magnetic fields, and of the recently discovered MQ-MAS experiments allowed us to identify clearly the three types of oxo bridges. Quantitative analysis was extracted from the MAS-NMR spectra, and compared with calculations based on randomly distributed Si units.
Thermal Stability of Structurally Controlled Lamellae and Hexagonal Mesoporous Silicate Thin Films
Authors: Honma I. , Endo A. , Kundu D. , Zhou H. S.
Published: April 2011

Thin films of mesoporous materials have been synthesized recently as lamellar, one dimensional hexagonal and cubic structures at substrate surfaces as well as at air/liquid interfaces. The present work investigates thermally induced structural changes of lamellar and one-dimensional hexagonal(1-dH) mesostructured silicate thin films, which is less known at the moment. The 1-dH films proved to be much more thermally stable than the lamellar ones; Open-pore one dimensionalhexagonalmesoporous thin films are obtained by the calcination of the films, where as the lamellarphase has collapsed after the surfactants removal.
Organic/Inorganic Molecular Hybrid Materials From Cubic Silsesquioxanes
Authors: Laine R. M. , Asuncion M. , Baliat S. , Filho N. L. Dias , Harcup J. , Sutorik A. C. , Viculis L. , Yee A. F. , Zhang C. , Zhu Q.
Published: April 2011

Octafunctionalized silsesquioxanes [(RsiO1.5)8, cubes] offer potential as rigid, hard nanoplatforms to which a variety of organofunctional groups can be appended. Crosslinking these groups leads to novel organic/inorganic nanocomposites that consist primarily of interfacial interactions. These materials can be 100% interphase. We present efforts to develop nanocomposite materials that consist of both continuous and discontinuous organic/inorganic phases. We then discuss methods of probing the properties of these materials.
Preparation and Properties of PVC-Silica Composites using Different Catalysts Via Sol-Gel Process
Authors: Asif Khan M. , Sarwar M.I. , Ahmad Z.
Published: April 2011

Novel micro-composites from Polyvinyl chloride (PVC) and silica were prepared using sol-gel technique. Different catalysts were used for the in-situ generation of silica network from tetraethylorthosilicate (TEOS) in the PVC matrix. Thin transparent films containing various proportions of silica in PVC were cast by the solvent elution technique. Mechanical properties of these films were studied. The results showed an increase in the value of Young's modulus and strain at rupture by the addition of small amount of silica in PVC. However, the stress at yields point and stress at rupture decreased with the addition of silica contents. Scanning electron microscopy (SEM-EDAX) studies were also performed on these samples.
X-Ray And Neutron Small Angle Scattering Investigations On Precursor Derived B-C-N Ceramics
Authors: Sauter D. , Schempp S. , Weinmann M. , Müller A. , Bill J. , Lamparter P. , Aldinger F.
Published: April 2011

Amorphous11B31,9C36,8N31,3ceramic samples were produced by thermolysis of poly(borosesquicarbodiimide) of idealized formula [B2(NCN)3]nat 1100°C in inert gas atmosphere. Small angle scattering (SAS) experiments reveal, that the as-obtained ceramics are chemically inhomogeneous. Using small angle neutron and X-ray scattering measurements, the temperature dependency of the medium range order was investigated. The SAS curves show a strong temperature dependence of the Guinier-radius (RG) of the scattering regions. Contrast variation by X-ray and neutron diffraction shows that the observed SAS signal is caused by amorphous BC2N enclosing amorphous boron-nitride segregations. The fact, that the measured invariant remains constant over the whole temperature range supports the view of complete phase separation.
Organic-Inorganic Hybrid Materials Processing And Applications
Authors: Schmidt H. K. , Mennig M. , Nonninger R. , Oliveira P. W. , Schirra H.
Published: April 2011

Hybrid materials as inorganic-organic nanostructured composites require tailored surface chemistry in order to obtain a homogeneous distribution of the nanoparticles in the matrix. For this reason, nanoparticles with organic functions have been synthesized, first, to provide the desired ζ-potential at a given pH value, second, to avoid irreversible agglomeration due to the spacing effect, and third, to provide the appropriate surface chemistry. I could be shown that using this approach, it is possible to switch the ζ-potential of SiO2 nanoparticles from a negative to a positive potential at neutral and to bind DNA fragments to the particles for an effective transfection into cells. Other examples show that nanoparticles (TiO2, SiC2) coated with epoxy and methacryloxy groupings can be used as coating sol for the fabrication of thin films with green densities up to 67 % by volume only by photochemical crosslinking of the polymerizable groupings. Using this approach, interference layers have been fabricated on transparent plastics. In soft matrices, these particles permit to establish appropriate ζ-potentials and in electric fields by electrophoresis, it was possible to up-concentrate them to form gradient index optics. The investigations show that surface chemistry-tailored nanoparticles are a useful tool for the fabrication of nanocomposite hybrids.
Fabrication Of Grin-Lenses By Contactless Electrophoretic-Gradient Formation In Transparent Nanocomposites
Authors: Oliveira P. W. , Mennig M. , Schmidt H.
Published: April 2011

A new approach to effective radial gradient refractive index (GRIN) lenses has been developed. It is based on the electrophoresis of ZrO2 nanoparticles with surface charges (ζ-potential) in a solvent free organic-inorganic hybrid matrix, synthesized from dodecandioldimethacrylate (DDDMA), methacryl silane (MPTS) and a complex of zirconium n-propylate (ZR) with methacrylic acid (MA). A DC-electric field of 2000 V/cm is applied by a set of ring electrodes on top and bottom of a cylindrical mould containing the matrix sol. The refractive index profile is measured in situ as a function of time by interferometry. The refractive index profile can be conserved by photopolymerisation of the matrix. The resulting refractive index profiles are calculated by computer simulation based on electrophoretical diffusion theory and they are measured by real time Mach-Zehnder Interferometry. The parabolic refractive index gradient of the lenses obtained by variation of concentration of ZrO2 is in very good agreement with the result of computer simulation. By this method, it is possible to obtain 1 cm radial GRIN lenses with a Δn=0.07 within 5 h.
Sol-Gel Chemistry by Ring-Opening Polymerization
Authors: Rahimian Kamyar , Loy Douglas A.
Published: April 2011

Sol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. We have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits us to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through a chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solvent is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which we have successfully demonstrated.
Isotropic and Anisotropic Nd-Fe-B Magnet Developments
Authors: Panchanathan V.
Published: April 2011

This paper deals with the magnetic and technological properties of isotropic Nd-Fe-B magnets over a wide range of Nd and B contents. They can be used to determine the optimum composition based on requirements. In anisotropic magnets, Nd and B ranges for production of high energy product rings was determined in Nd-Fe-Co-Ga-B system. This is also used in production.
Micromagnetics of Nanocrystalline Permanent Magnets
Authors: Schrefl T. , Fidler J.
Published: April 2011

Micromagnetic finite element calculations provide the theoretical limits for the remanence, the coercive field, and the coercive squareness of nanocomposite Nd2Fe14B/α-Fe,Fe3B,Fe23B6magnets. The influence of the intrinsic magnetic properties and the microstructure were investigated using an energy minimization technique. The coercive field reaches a maximum as a function of the average grain size at about 15 nm - 20 nm. The replacement of α-Fe with Fe3B improves the coercive field but deteriorates the loop shape. The reduction of the magnetization and the exchange constant in the soft magnetic Fe3B phase by 20% improves the coercive field without a significant loss in the remanence. An increase of the hard phase anisotropy by 8% enhances the coercive field by more the 100 kA/m in two-phase α-Fe/Nd2Fe14B and by 60 kA/m in two-phase Fe3B/Nd2Fe14B magnets. Dynamic simulations for magnetostatically interacting particles of a bonded magnet show a slight influence of the particle arrangement on magnetization reversal. The interaction field in the range of 100 kA/m to 200 kA/m rapidly decreases the distance from the particle.
Analysis of Magnetization Processes in Nanocomposite Hard Magnetic Materials from Macroscopic Magnetic Measurements and X-RAY Magnetic Circular Dichroism
Authors: David Stéphane , Mackay Kenneth , Bonfim Marlio , Pizzii Stefania , Fontaine Alain , Givord Dominique
Published: April 2011

A series of RExTMbalBy (3≤x≤5.5, 15≤y≤25 at%) nanocomposite magnets were prepared using the classical method of alloy rapid quenching and subsequent devitrification. Appropriate elemental additions and substitutions allowed the technical magnetic properties to be optimized. The analysis of the both hysteresis cycles and static susceptibility measurements in the range 20K-300K reveals that magnetization reversal in these materials can be interpreted schematically as a two-step process : the initial magnetization reversal is dominated by reversible processes while irreversible processes, which characterize the coercivity mechanism, occur at larger field values. To complement this study, X-Ray Magnetic Circular Dichroism (XMCD) spectroscopy was applied as an element-selective probe of magnetization reversal in nanocomposite samples. This allowed the hysteresis cycles of both hard and soft phases to be separated from the total cycle. Magnetization processes in these bulk heterogeneous systems are discussed in the light of information brought by the complementary applied experimental techniques.
Residual Amorphous Phase in a Fe/NdFeB Nanoconipositie Hard Magnets
Authors: Hamano M. , Yamasaki M. , Mizuguchi H. , Kobayashi T. , Yamamoto H. , Inoue A.
Published: April 2011

A residual amorphous phase can be observed when Nd content is less than 8 at% in a a Fe/NdFeB nanocomposite with various additional elements which was prepared by melt-spinning and heat treatment. The surface velocity of the single-roller melt-spinner for optimal coercive force (Hcj) was 10-15 m/s. By adding Nb, Hcj increases monotonically. Nearly homogeneous crystal size of around 5 nm is observed in a sample composition of NdxFex Cox Nb2,B2 With Nd=8 at%, the maximum Hcj is as large as 575kA/m (7.22kOe) at Nb=2.5 at%, and the best (BH)max is 154kJ/m3 (19.4MGOe) at Nb=0.5 at% in optimally heat-treated and pulse-current magnetized samples. By high-resolution transmission electron microscopy, a residual amorphous phase is observed in all alloy ribbons with Nd=8 at%, which shows soft magnetic properties and is thought to act as a crystal growth inhibitor. To estimate the existing ratio of the amorphous phase and crystallized phases, the Mössbauer effect has been studied. It was found that the ratio of the crystallized Nd2Fe14B1 phase increases with increasing Nb content and that several wt% of the residual amorphous phase is certified. Epoxy-resin bonded magnets were prepared by compression molding, and revealed that, comparing to the MQP bonded magnet using conventional MQP-B powder, their (BH)max are in the same order of 72kJ/m3 (9MGOe), and magnetization at lower magnetic field than 800kA/m (10kOe) is superior. Initial flux loss at 100°C for 1.8ks, however, is in the range of 3-8% depending on Nb contents.
Magnetization and Interactions of Single Domain Sm2Co17 Particles Embedded in CaO Matrix
Authors: Liu Wenge , Mccormick Paul G.
Published: April 2011

Investigation of the interactions in two magnetic composite systems composed of ∼8 vol% isolated Sm2Co17 nanoparticles of different size ranges in a CaO matrix has been made by comparing the isothermal remanent magnetization curves (IRM) with the dc demagnetization curves (DCD) using Wohlfarth remanence relation. The presence of a weak demagnetizing field was evidenced in the sample with smaller magnetic particles (7-90nm), indicating the magnetostatic interaction between the magnetic particles was dominant in this sample. The large positive deviation from Wolhfarth relation in the sample with larger particles (10-250nm) suggests the presence of multigrain particles in which neighboring grains interact strongly with each other. The hysteresis curves of the two composite systems were measured at temperatures between 5 and 350K. A nearly linear temperature dependence of the coercivity was observed in both samples up to 350 K. From these results it is shown that although the sizes of the Sm2Co17 particles are well below the critical size for single domain particle, there is no evidence that the magnetization reversals in these particles are coherent rotation.
Microstructural Investigation of RE3(Fe.V) 29 (RE = Nd, Tb) Magnetic Materials
Authors: Bernardi J. , Noner M. , Fidler J. , Han X.F. , Yang F.M.
Published: April 2011

The microstructure of V stabilized RE3(Fe,V)29 (RE=Nd,Tb) has been investigated by transmission electron microscopy (TEM). The investigated samples were prepared by arc melting and subsequent annealing above 910°C. X-ray diffraction confirms that the samples can be indexed based on a monoclinic Nd3(Fe,Ti)29-type structure (3:29) with A2/m space group. Our TEM investigation confirms that Nd3(Fe,V)29 contains usually grains with 3:29 structure and A 2/m space group. In addition grains with rhombohedral Th2Zn17 structure are observed regularly. The Tb3(FeV)29 alloy consists also of grains with monoclinic Nd3(Fe,Ti)29-type structure and contains a high density of planer defects like crystallographic twins or antiphase boundaries. Twinning occurs preferably on (402) of the monoclinic 3:29 structure. No tetragonal RE(Fe,V)12 phase or Fe is found.
Chemical Ordering and Microstructural Affects on Magnetic Properties of Sm2Fe17 and Sm2Fe17Nx
Authors: Meacham B.E. , Dennis K.W. , Mccallum R.W. , Shield J.E.
Published: April 2011

The effect of chemical order and defect structure on the magnetization process in Sm2Fe17 and Sm2Fe17Nx has been investigated. In Sm2Fe17, chemical disorder results in the development of random anisotropy and a small degree of magnetic hardness. The anisotropy is reduced as long-range order increases. The motion of domain walls in Sm2Fe17Nx is more dependent on the antiphase domain structure than on the amount of long-range order.
Permanent Magnetism in Exchange-Coupled Nanocomposites
Authors: Skomski R. , Liu J. P. , Sellmyer D.J.
Published: April 2011

The magnetic properties of permanent magnetic nanocomposites are investigated both experimentally and by model calculations. Rare-earth transition-metal films and nanocomposite thin films containing a L10hard phase (PtFe) have been prepared by plasma sputtering and heat treatment. By choosing suitable heat-treatment processes a nearly ideal nanostructure and high energy products of up to about 50 MGOe have been achieved for the Fe-Pt system. The behavior of the nanocomposites is discussed in terms of a model applicable to nearly ideal magnets, where there are no pronounced shoulders in the hysteresis loops. Analytic expressions for M(H) are obtained for a number of cases, and it is discussed how the loops depend on the micromagnetic parameters of the involved phases. A novel aspect of magnetic nanostructures is that very small magnetic grains exhibit very large energy products, even if they are intrinsically soft-magnetic.
The Influence of Microstructure on the Magnetic Properties in Nanostructured Copt L10Thin Films
Authors: Jeong S. , Mchenry M.E. , Laughlin D.E.
Published: April 2011

We have applied the Neel's spin pair potential model to model the dependence of magnetocrystalline anisotropy on the long range order parameter. We have produced CoPt nanoscale thin films, with and without an immiscible second phase, by RF and DC magnetron sputtering. These thin films showed a shoulder in their magnetic hysteresis, indicative of a disordered soft magnetic phase for samples annealed above 600 °C while it was barely detectable in 500-600 °C annealed samples. A (111) texture is observed in as-deposited and annealed films is identified as one of the possible contributions to the lower coercivity squareness S* and perpendicular magnetic properties. Micromagnetic calculations confirmed a poor exchange interaction, identified rotational energy barriers and inferred that the ordered region was not fully ordered. The initial stage of ordering clearly showed a discontinuous type transformation.
Chemical Characterization of Magnetic Materials at High Spatial Resolution
Authors: Scott John Henry J.
Published: April 2011

The fabrication of nanoscale magnetic materials and novel heterostructures has placed great demands on the analytical tools used to characterize the chemical and structural variations in these samples. Attempts to determine the composition, phase, crystallinity, and interface structure of nanoscale materials often involve tradeoffs between accuracy, sensitivity, and spatial resolution. Traditional techniques such as electron energy-loss spectroscopy (EELS), energy dispersive x-ray spectrometry (EDS), secondary ion mass spectrometry (SIMS), and scanning Auger microscopy (SAM) will be surveyed in this context. Powerful new tools for probing the chemical heterogeneity of materials at ultrafine length scales will also be discussed, including energy-filtered transmission electron microscopy (EFTEM) and spectrum imaging, as well as recent advances in new methods such as backscattered electron Kikuchi patterns (BEKP) and microcalorimetry.
Giant Magnetoresistance of Electrostatic Self-Assembled Fe3O4Nanocluster and Polymer Thin-Films
Authors: Liu Yanjing , Claus Richard O. , Zhang Fajian
Published: April 2011

Giant magnetoresistance (GMR) as large as 25% at 25°C has been observed for multilayer ultrathin films of iron oxide (Fe3O4) nanoclusters and polyimide molecules alternately adsorbed onto single crystal silicon and quartz substrates using a novel self-assembly technique. This process involves the alternate dipping of a substrate into an aqueous solution of anionic polyimide precursor (polyamic salt, PAA) followed by dipping it into an aqueous solution of cationic polydiallyldimethylammonium chloride (PDDA)-coated Fe3O4, nanoparticles. The regular formation of alternating monolayers is verified by UV-vis spectroscopy and contact angle measurements. Vibrating sample magnetometry indicates the formation of ultrasoft films.
Air Force Application of Advanced Magnetic Materials
Authors: Fingers R.T. , Rubertus C. S.
Published: April 2011

A national initiative is underway to develop and test a more electric aircraft (MEA) and is being led by the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio. The MEA concept is based on utilizing electric power to drive aircraft subsystems which are currently driven by a combination of hydraulic, pneumatic, electric and mechanical power transfer systems. A major objective of this effort is to increase military aircraft reliability, maintainability and supportability and to drastically reduce the need for ground support equipment. These improvements will be realized through the further advancement of key MEA technologies, including magnetic bearings, aircraft integrated power units (IPU), and starter/generators (IS/G) internal to an aircraft main propulsion engine. These advanced developments, as well as weapon and space power applications, are the driving force for the new emphasis on high temperature and high strength magnetic materials for power applications. In determining the best magnetic material for an application it is typically necessary to conduct an engineering trade-off analysis which takes into consideration mechanical behavior, electrical loss, and magnetic properties under the conditions of actual usage. New materials solutions are required to meet these challenges, as designers often find the magnetic material performance to be the technological limitation.
Properties of Giant Magneto-Impedance Material for A Novel Integrating Magnetic Sensor
Authors: Gore J.G. , Tomka G.J. , Milne J. , Maylin M.G. , Squire P.T. , Atkinson D.
Published: April 2011

A novel magnetic field sensor, based on the giant magneto-impedance effect is described and analysed. The sensor utilises an amorphous wire, annealed under optimised conditions. The conditions required for the optimisation of the magnetic properties of the wire are shown. The wire can be up to 2m long, and integrates the field over the length of the wire. It operates in open-loop mode. With a bias field of ∼500 A/m it achieves a sensitivity of 0.02 A/m and linearity of better than 5% for external fields between ±300 A/m.
Magnetic Force Microscopy Study of New Nanocrystalline Soft Magnetic Ribbons.
Authors: Hawley M. E. , Brown G. W. , Thoma D. J. , Willard M. A. , Laughlin D. E. , McHenry M. E.
Published: April 2011

New nanocrystalline, multicomponent extremely soft magnetic materials with superior high temperature magnetic properties hold great promise in power applications. Fabricated in ribbon form by rapid solidification methods, the initial material is amorphous. By controlled annealing procedures, the amorphous material was transformed into a nanocrystalline form with the degree of crystallinity determined by the annealing temperature and time. The magnetic structures of ribbons, as-fabricated and annealed at temperatures from 550 to 750 °C were examined by magnetic force microscopy to determine the impact of residual stress and nanocrystallinity on the observed structure. A correlation was seen between the magnetic structures and surface microstructure. The wheel side of the as-processed ribbon was rougher than the top side of the ribbon and a complicated magnetic domain structure was present in the amorphous material. After annealing, nanocrystals formed, increasing in size with increasing temperature. The lowest temperature annealed sample had a bimodal grain size distribution and a combination of stripe and localized domains. After annealing little difference was seen between the two sides of the ribbons. Stripe domains were absent in the ribbons annealed at the highest temperatures.
Processing Sm-Fe(Ta)-N hard magnetic materials
Authors: Žužek K , Mcguiness PJ , Kobe S
Published: April 2011

SmFe based alloys interstitially modified with nitrogen are potential candidates for high energy permanent magnets. In order to obtain the optimum properties a thorough understanding of the starting material and processing parameters is required. The microstructures of two cast alloys of composition Sm13.8Fe82.2 Ta4.0 and Sm13.7 Fe86.3 were carefully examined with a SEM equipped with EDX and the exact stoichiometries of the phases were determined. The SmFeTa material was found to contain significant amounts of TaFe2as well as the Sm2Fe17, SmFe2, SmFe3 phases observed in the SmFe material but without the a-iron dendrites which are characteristic of the latter material. The optimum conditions necessary to provide the highest coercivities using the conventional HDDR process, and for the HDDR process combined with pre-milling were investigated. The coercivities obtained after using the HDDR process and subsequent nitriding were 680 kA/m for the SmFeTaN and 360 kA/m for the SmFeN samples. Significantly higher coercivites of 1000 kA/m for SmFeN and 1275 kA/m for SmFeTaN were achieved by reducing the particle size with milling prior to the HDDR process.The better coercivities obtained with the Ta containing sample were found to be due to the presence of a much smaller amount of a. The milling prior to the HDDR treatment improves the magnetic properties because of the small particle size which prevents the grains growing too large, with their consequent very negative effect on the coercivity.
Neutron Diffraction Characterization of Permanent Magnet Phases
Authors: Yelon William B.
Published: April 2011

Neutron diffraction has been invaluable in the characterization of intermetallic magnetic phases due to the unique properties of the neutron and the availability of high performance powder diffractometers that allow large numbers of samples to be investigated. The structural data derived from these studies serves as fundamental input for theory, and constraints on analyses of data from other methods, such as Mossbauer spectroscopy. The empirical structure-property relations derived from these studies serves to guide synthesis of new compounds and may help to define the next generation of high performance permanent magnets.
Forest Hardening and Boundary Conditions in 2-D Simulations of Dislocations Dynamics
Authors: Gómez-García D. , Devincre B. , Kubin L.P.
Published: April 2011

Dislocations are the elementary carriers of plastic flow and are ideally at the base of any physical model for plastic deformation. In the last few years, several 3-D simulations of Dislocation Dynamics (DD) have been devoted to the analysis of single crystal plasticity at small strains [1–5]. However, such DD simulations have some limitations which restrict their domain of application: (i) In many materials, there is a lack of accurate input regarding the mechanisms governed by the core properties of dislocations. (ii) The plastic strain amplitude that can be simulated is usually small (e.g. smaller than 1% in f.c.c. crystals). (iii) The boundary conditions of the simulations are generally rather crude and may introduce spurious size effects and various other artefacts. Most of the time, the questions of stress equilibrium and dislocations flux at the external surfaces are not addressed.
Dislocation Structure and Deformation Behavior of Intermetallic Compounds
Authors: Mills M. J. , Viswanathan G. B. , Srinivasan R. , Savage M.F. , Noebe R.D. , Daw M. S.
Published: April 2011

The fine structure of dislocations in intermetallic compounds can have a profound influence on their macroscopic mechanical properties. The development of appropriate models of deformation requires consideration of dislocation core structure, possible dissociation or decomposition reactions, overall dislocation morphology and relevant dislocation interactions based on detailed transmission electron microscopy study. This empirical information may be rationalized based on both atomistic and continuum-level dislocation modeling. The specific cases of jogged 1/2<110] ordinary dislocations in γ-TiAl and a<101> superdislocations in NiAl are discussed.
Study of the Mechanical Behavior of BCC Transition Metals Using Bond-Order Potentials
Authors: Mrovec M. , Vitek V. , Nguyen-Manh D. , Pettifor D. G. , Wang L. G. , Sob M.
Published: April 2011

Deformation properties of body-centered-cubic transition metals are controlled by the core structure of screw dislocations and their studies involve extensive computer simulations. In this paper we present the recently constructed bond-order potentials (BOP) that are based on the realspace parametrized tight-binding method. In order to examine the applicability of the potentials we have evaluated the energy differences of alternative structures, investigated several transformation paths leading to large distortions and calculated phonon dispersions. Using these potentials we have calculated γ-surfaces that relate to the dislocation core structures and discuss then the importance of directional bonding in studies of dislocations in transition metals.
Computer Simulation of the Effect of Copper on Defect Production and Damage Evolution in Ferritic Steels
Authors: Perlado J. M. , Marian J. , Lodi D. , De La Rubia T. Díaz
Published: April 2011

It has long been noticed that the effect of Cu solute atoms is important for the microstructural evolution of ferritic pressure vessel steels under neutron irradiation conditions. Despite the low concentration of Cu in steel, Cu precipitates form inside the α-Fe surrounding matrix and by impeding free dislocation motion considerably contribute to the hardening of the material. It has been suggested that Cu-rich clusters and combined Cu solute atoms-defect clusters that may act as initiating structures of further precipitates nucleate during annealing of displacement cascades. In order to assess the importance of the different mechanisms taking place during collision events in the formation and later evolution of these structures, a detailed Molecular Dynamics (MD) analysis of displacement cascades in a Fe-1.3% at. Cu binary alloy has been carried out. Cascade energies ranging from 1 to 20 keV have been simulated at temperatures of 100 and 600 K using the MDCASK code, in which the Ackland-Finnis-Sinclair many-body interatomic potential has been implemented. The behaviour of metastable Cu selfinterstitial atoms (SIAs) in the form of mixed Fe-Cu features is studied as well as their impact on the resulting defect structures. It is observed that above 300 K generated Cu SIAs undergo recombination with no substantial effect on the after-cascade microstructure while at 100 K Cu SIAs remain sessile and exhibit a considerable binding to interstitial and vacancy clusters. Finally, the effect that the production of vacancies via collision cascades may have on the self diffusion of Cu solute atoms is quantitatively addressed by means of determining diffusion coefficients for Cu atoms under different microstructural conditions.
Study of Electrical Properties of Dislocations in ZNS Using Electric Force Microscopy
Authors: Bai G. F. , Petrenko V. F. , Baker I.
Published: April 2011

A combination of electric force microscopy (EFM) and non-contact scanning force microscopy (SFM) was used to study micro-indentation-induced dislocation bands in sphaleritic ZnS single crystals. Large local distortions in electrical potential from the dislocation bands were observed in the EFM images. For the first time, the electric charges of resting partial Zn(g) and S(g) dislocations were determined quantitatively. The results compare well with theoretical models.
Surface Relaxations of Aluminum Simulated by Bond Order Potentials
Authors: Nishitani S. R. , Ohgushi S. , Adachi H. , Aoki M.
Published: April 2011

An interatomic potential for aluminum was developed, which is based on empirical tight binding approximations. The model successfully reproduced the shear constants, structure energy differences, and phonon dispersion curves. This transferable potential was applied on static surface relaxations, and shows good agreements with experimental results on the oscillatory damped behavior of the multilayer relaxations and the expansion of the (111) surface.
A Discrete Dislocation Analysis of Crack Growth under Cyclic Loading
Authors: Cleveringa H.H.M. , Van Der Giessen E. , Needleman A.
Published: April 2011

Cyclic loading of a plane strain mode I crack under small scale yielding is analyzed using discrete dislocation dynamics. The dislocations are all of edge character, and are modeled as line singularities in an elastic solid. At each stage of loading, superposition is used to represent the solution in terms of solutions for edge dislocations in a half-space and a nonsingular complementary solution that enforces the boundary conditions, which is obtained from a linear elastic, finite element solution. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated into the formulation through a set of constitutive rules. An elastic relation between the opening traction and the displacement jump across a cohesive surface ahead of the initial crack tip is also specified, which permits crack initiation and crack growth to emerge naturally. It is found that crack growth can occur under cyclic loading conditions even when the peak stress intensity factor is smaller than the stress intensity required for crack growth under monotonic loading conditions.
A Multiple Slip Plane Model for Crack-Tip Plasticity
Authors: Noronha S. J. , Roberts S. G. , Wilkinson A. J.
Published: April 2011

A single slip plane dislocation dynamics based model for the brittle to ductile transition has been extended to have multiple slip planes around the crack-tip. The crack-tip plastic behaviour is studied for a variety of dislocation source configurations. The results are presented for the case of iron. The effect of modelling the plastic-zone as a single slip plane and as an array of parallel slip planes are compared.
The Effect of Material Inhomogeneity on Serrated Plastic Flows
Authors: Li X. , Tong W.
Published: April 2011

Serrated plastic flows or propagating Portevin-Le Chatelier (PLC) bands in uniaxial tensile aluminum alloy sheet samples were analyzed by a 3D finite element model. A local dynamic strain aging viscoplasticity model motivated by dislocation dynamics was implemented in an ABAQUS user material subroutine. When the sheet metal was assumed to be spatially homogeneous, individual plastic deformation bands inclined about 50° with regard to the axial tensile loading were predicted by the model to propagate along the thin sheet sample, similar to the experimentally observed behavior of the solid solution strengthened alloy AA5182-0. When the sheet metal was assumed to be inhomogeneous by making a few material elements slightly harder or softer, the model predicted a propagating single neck formed by double shear bands, similar to the behavior of the precipitation strengthened alloy AA6111-T4.
Self-Affine Fractal Characterization of a TNT Fracture Surface
Authors: Meisel L. V. , Scanlon R. D. , Johnson M. A. , Lanzerotti Y. D.
Published: April 2011

A trinitrotoluene (TNT) fracture surface image is characterized in terms of a self-affine fractal structure. The fracture surface was produced by high acceleration in an ultracentrifuge when the TNT strength was exceeded. An atomic force microscope (AFM) captured the topography of a 4 micron square region on the fracture surface. The present analysis supports a self-affine description of the TNT fracture surface (wavelengths of 0.016 micron to 4.0 micron) and provides a new prespective on fracture processes in TNT. An essential step in self-affine fractal characterization of surfaces is the determination of reference surfaces. A self-affine fracture surface can be described in terms of a single-valued height function. In the TNT fracture surface, single-valued height functions, which describe surface texture can only be defined with respect to curved reference surfaces. By employing curved reference surfaces, we have demonstrated that self-affine fractal scaling can be used to characterize the TNT fracture surface. This provides important information that is not evident in the analysis of individual surface scans.
Dislocation Interactions with Lamellar Grain Boundaries in Titanium Aluminum Intermetallics
Authors: Wiezorek Jörg M. K. , Zhang Xiao-Dong , Fraser Hamish L.
Published: April 2011

The interactions of dislocations asscociated with deformation modes active in hard orientation compressed polysynthetically-twinned (PST) TiAl with lamellar boundaries have been studied by transmission electron microscopy (TEM). The deformation modes observed in the γ-phase involved soft superdislocation and hard ordinary dislocation slip, and hard twin systems. The transfer of these latter hard twin shears occurred across all types of lamellar (γ/γ)- and frequently across (γ/α2)-boundaries. Slip of superdislocations in the minority U2-phase lamellae has been shown to be associated with both direct transfer of piled-up twinning dislocation shears across the lamellar boundaries and the activation of interfacial sources due to pile-up stresses. The active deformation modes were consistent with macroscopic shape changes of the PST-TiAI when the various defect interactions with the lamellar boundaries and the proposed shear trasnfer processes were considered.
Atomistic Modeling of Interfacial Diffusion in the Lamellar Li0 TiAl
Authors: Nomura M. , Luzzi D. E. , Vitek V.
Published: April 2011

Atomistic simulation employing many-body central-force potentials was performed to elucidate the diffusion mechanisms in the bulk and at lamellar interfaces assuming a vacancy mechanism. First the self- diffusion of Ti and Al in stoichiometric structures was studied. It was found that the diffusion was faster along lamellar interfaces than in the bulk; the effective activation energy for the diffusion coefficient is about ∼15% lower. The simulations were then extended to investigate diffusion along lamellar boundaries with segregated Ti which is likely in Ti rich alloys. The surprising result is that diffusion remains practically unchanged when compared with the stoichiometric case. The reason is that while the path controlling the diffusion is different, the corresponding effective formation and migration energies are practically the same as in the stoichiometric case.
A Model for Predicting Weld Metal Grain Refinement in G-V Space
Authors: Grong Ø. , Cross C.E.
Published: April 2011

A model has been developed which allows for the graphical representation of undercooling and nucleation site density in G-V space (i.e. temperature gradient G versus growth rate V). This model is used to explain a unique grain structure in weldments where equiaxed grains may be found both at the fusion boundary and along the center of the weld metal. Details of this model will be given and discussed in relation to grain refinement predictions in G- V space.
Modeling the Effect of Noise on Multiscale Dislocation Cell Structures
Authors: Miodownik M. A. , Holm E. A. , Browne D.J.
Published: April 2011

Plastic flow in metals occurs by a dislocation mechanism in which strain is accommodated by a dislocation flux. This results in tangled networks of dislocations which self-organize into stable cell structures with two characteristic length scales. These structures have a number of remarkable properties not least of which is that they exhibit scaling. We examine the idea that the evolution of geometrically necessary boundaries is dominated byrandom fluctuations, construct a simple model of cell orientations and show that scaling of misorientation distributions emerges a direct result of Gaussian white noise. We investigate whether hierachical microstructures containing both incidental dislocation boundaries and geometrically necessary boundaries can be studied using the same model. The results are compared with the experimental measurements and show good agreement.
Synchroshear Versus Conventional Shear Mechanisms in Transitionmetal Disilicides with the C40 Structure
Authors: Inui H. , Yamaguchi M.
Published: April 2011

The deformation behavior of (0001) <1210> basal slip in single crystals of five different transitionmetal disilicides with the C40 structure has been investigated in the temperature range from room temperature to 1500°C in compression. These disilicides are found to be classified into two groups depending on the onset temperature for plastic flow. The low-temperature group, which consists of VSi2, NbSi2 and TaSi2, exhibits the onset temperature for plastic flow around 0.3 T/Tm (melting temperature) and deforms by a conventional shear mechanism. In contrast, the high temperature group, which consists of CrSi2 and Mo(Si,Al)2, exhibits the onset temperature around 0.6T/Tm and deforms by a synchroshear mechanism. Factors affecting the deformation mechanism in these C40 disilicides are discussed in terms of directionality of atomic bonding and the relative stability of the C40 phase with respect to the C11b phase.
Solution-Processed Inorganic Transistors and Sub-Micron Non-Lithographic Patterning using Nanoparticle Inks
Authors: Ridley Brent A. , Nivi Babak , Hubert Brian N. , Bulthaup Colin A. , Wilhelm Eric J. , Jacobson Joseph M.
Published: April 2011

Pyridine solutions of CdSe nanocrystals were solution-deposited in the fabrication of thin film transistors (TFTs). A peak mobility of 1 cm2V−1s−1 and an ON/OFF ratio of 3×104 were observed for TFTs processed at 350 °C. The nanocrystals acted as a precursor to the bulk material, coalescing to form a semiconductor thin film when heated at plastic-compatible temperatures. Single crystalline regions several hundred times the size of the original semiconductor nanocrystals were observed for films processed at 350 °C. We also report a process for direct liquid phase deposition and patterning of nanoparticle inks at sub-micron resolutions by elastomeric embossing and AFM nanospotting. These results suggest that microelectronic devices produced from nanoparticle-based inks can enjoy the processing advantages usually associated with organic materials while retaining the performance advantages typically associated with inorganic materials.
Synthesis of Self-Capped Metal Sulfide Nanoparticles
Authors: Lazell Mike , O'Brien Paul
Published: April 2011

In this paper we report the synthesis of metal sulfide nanocrystals, (CdS and ZnS), from the thermolysis, between 150 – 300 °C, in a dynamic vacuum, of the novel long chain asymmetric metal dithiocarbamates, bis(N-methyloctadecyldithiocarbamato) cadmium(II) or zinc(lI), [M {S2CN(C18H37)(CH3)}2].

These nanoparticles ‘self-cap’ during preparation. Different size nanocrystals were synthesised, at different temperatures and there was a change in phase from cubic to hexagonal CdS at a decomposition temperature greater than 300 °C.
Controlled Growth of Amorphous Silicon Nanowires Via a Solid-Liquid-Solid (SLS) Mechanism
Authors: Yan H. F. , Xing Y. J. , Hang Q. L. , Yu D. P. , Xu J. , Zhang H. Z. , Xi Z. H. , Feng S. Q.
Published: April 2011

Amorphous silicon nanowires (a-SiNW's) with average diameter around 20 nm were synthesized at about 950° C under an Ar/H2 atmosphere on large area of a (11) Si substrate without supplying any gaseous or liquid Si sources. The Si substrate, deposited with a layer of Ni of about 40 nm thick, served itself as a silicon source for the growth of the a-SiNWs. Different from the well-known vapor-liquid-solid (VLS) for conventional whisker growth, it was found that growth of the a-SiNWs was controlled by a solid-liquid-solid mechanism, which is analogous to the VLS model.