bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Exchange-Coupling in CoPt/Co Bilayer thin Films
Authors: Kim J. , Barmak K. , Lewis L. H. , Crewt D. C. , Welcht D. O.
Published: April 2011

Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700°C and fully transformed from the FCC phase to the magnetically hard, ordered L1 0 phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8-225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.
Controlled Assembly of Monodisperse ε-Cobalt-Based Nanocrystals
Authors: Sun S. , Murray C. B. , Doyle H.
Published: April 2011

General synthetic routes to monodisperse c-cobalt (β-Mn type phase) nanocrystals (ε-Co) and controlled assembly of these nanocrystals are presented in this paper. The ε-Co particles are obtained by superhydride reduction of cobalt chloride (anhydrous or hexahydrate) in a high temperature solution phase (200°C) in the presence of a combination of long chain diol, oleic acid and trialkylphosphine. Monodisperse nanocrystals are isolated by size selective precipitation. As synthesized cobalt particles are each a single crystal with a complex cubic structure related to the beta phase of elemental manganese (β-Mn). Self-assembly of these uniform cobalt particles on solid substrates is induced by evaporation of the carrier solvent producing 2-D and 3-D magnetic superlattices. Annealing of assembled ε-Co nanocrystal arrays converts them to the hcp cobalt crystal arrays. The inter-particle distance can be adjusted by selected thermal treatments or by chemical ligand exchange. This control over particle dimensions, crystallinity and assembly offers a model system for the study of ultra-high density recording media.
A Novel Apparatus for the Synthesis of Graphite Encapsulated Metallic Nanocrystals
Authors: Klug K.L. , Johnson D.L. , Dravid V.P.
Published: April 2011

Graphite encapsulated metal nanocrystals (GEM nanocrystals) are a promising new class of materials with both scientific and industrial significance. Several encapsulating graphite layers protect the nanoscale metallic core without compromising the inherent magnetic properties of the metal, thereby enhancing studies of small particle magnetism. The size and single domain nature of these particles immediately suggest a wide variety of potential applications ranging from increased density magnetic data storage to immunoassays. Encapsulated nanoparticles have traditionally been synthesized by evaporating a composite metal/graphite anode via an electric arc. While effective, that method also results in a great deal of unwanted amorphous carbon debris in the product. Based on past synthesis runs and observations, an improved apparatus for GEM production has been designed with the goals of increasing GEM yield and reducing soot production. The four segment system consists of I ) a chamber capable of arc or resistive evaporation of raw material(s), 2) a tube furnace for the chemical vapor deposition of carbon on raw material(s) via hydrocarbon dissociation, 3) an increased-efficiency powder collection unit, and 4) a final powder reservoir. Details of the new apparatus are presented here.
Gmr Effect and Properties of CoAg Granular Films Formed by Implantation with a Metal Vapor Vacuum Arc Ion Source
Authors: Wong S.P. , Chiah M.F. , Cheung W.Y. , Ke N. , Xu J.B. , Zhang X.X.
Published: April 2011

Cobalt-silver granular thin films were formed by Co implantation into Ag using a metal vapor vacuum arc (MEVVA) ion source. The magnetic field dependence and the temperature variation of the giant magnetoresistance (GMR) effect and their relation with the processing conditions were studied and discussed in conjunction with results of Rutherford backscattering spectrometry, atomic force microscopy, magnetic force microscopy (MFM), and SQUID measurements. Anomalous temperature dependence of the coercive field Hc in the perpendicular-to-film direction determined from GMR measurements was observed for some samples. For one sample, Hc shows a maximum value at around 240K and decreases with decreasing temperature from 240K to 20K. The temperature variation of the magnetization M of this sample exhibits a minimum. The maximum in the Hc-T curve corresponds well with the minimum in the M-T curve. The M-T curve suggests that there is more than one magnetic phase present in this sample. The domain structures of the implanted granular films as revealed by MFM images exhibit very different features compared with those of sputter deposited CoAg granular films.
Crystalline Texture Of Cocrpt Films On Crmn//ial And Cr/Nial Underlayer Structures
Authors: Zou J. , Lu B. , Bayer A.E. , Laughlin D.E. , Lambeth D.N.
Published: April 2011

In this study, we examine the effects of CrMn/NiAI and Cr/NiAl underlayer structures on the crystalline texture and microstructure of CoCrPt magnetic films using x-ray and electron diffraction. The former underlayer structure was found to induce better CoCrPt (1010) texture. The stress in the CoCrPt layer was measured. The effective in-plane anisotropy energy densities of the CoCrPt films on the above two underlayers were also measured by using out-of-plane torque and Miyajima methods and the result was consistent with the texture analysis.
C-Axis Perpendicularly Oriented Barium Ferrite Thin Film Media On Silicon Substrate
Authors: Zhuang Zailong , Kryder Mark H. , White Robert M. , Laughlin David E.
Published: April 2011

Barium ferrite thin films with excellent perpendicular c-axis orientation were successfully fabricated on Si substrate without any buffer layer. To compensate for possible barium deficiency due to the inter-diffusion between films and substrate, a barium-rich target was used. For a 900 Å-thick film, the perpendicular remanent squareness is about 0.9, while the in-plane remanent squareness is about 0.3. The saturation magnetization (Ms) is about 220 emu/cc, while the coercivity is around 3500 Oe. X-ray diffraction (XRD) results show the (001) perpendicular c-axis texture in the films. It was also found that the rapid thermal annealing conditions greatly affect the magnetic properties of barium ferrite films. With a certain flow rate of oxygen gas in the rapid thermal annealer (RTA), barium ferrite films generally crystallize with good perpendicular c-axis texture. Without oxygen gas, the hexagonal barium ferrite phase fails to develop; instead spinel Fe 30 4 phase forms. The reason for the collapsing of hexagonal barium ferrite texture is thought to be an oxygen deficiency in the barium ferrite films due to the reduction of oxygen in the films during the high temperature annealing.
Microstructural and Magnetic Improvements in Tube-Cast Pr-Fe-B-Cu Alloys Via Heat Treatments and Rapid Upset Forging
Authors: Hatch G P , Williams A J , Harris I R
Published: April 2011

Alloys of Pr-Fe-B-Cu were cast into Cu and stainless steel tubes. It could be seen that a preferred crystallographic orientation was obtained after cooling. Fine platelets of Pr2Fe1 4B matrix phase were formed, surrounded by various grain boundary phases, and there was a significant reduction in the amount of free Fe present, in comparison to conventional slab cast alloys. In order to improve the magnetic properties in the as-cast state, two alternative routes were used. The first involved a series of two step heat treatments to develop an improved microstructure. After an optimum heat treatment of 1000 'C for 24 hours + 500°C for 3 hours, significantly improved magnetic properties were obtained for a 17.5 % Pr alloy; Br = 752 mT, Hci = 613 kAm−1 and BHmax = 96 kJm−3. The second route involved a rapid upset forging [RUF] process, with a strain rate of 11.5 s−1, to hot deform the alloys. Following post-forging heat treatments, properties of Br = 966 mT, Hci = 780 kAm−3 and BHmax = 160 kJm−3 were obtained for a 15% Pr alloy. That nature of the improvements in properties as a result of heat treatments and RUF were investigated and are discussed in the present work.
Dislocation Forest Interactions: Simulation and Prediction
Authors: Wickham L. K. , Schwarz K. W. , Stölken J. S.
Published: April 2011

Using linear elastic dislocation dynamics simulations, we show that junction formation between dislocations from various interacting slip systems can be predicted by a simple self-energy calculation. We find that this prediction is robust: dislocation curvature and external stress produce little change in the simulation results for junction formation. One key to this success appears to be a separation of timescales, where movement of the far away dislocation arms (under, for example, external stress) is typically slow compared to the process of making a junction. The self-energy calculation we describe gives a rule for dislocation encounters which should allow a considerable saving in computational effort, allowing one to impose correct interaction outcomes without calculating the interactions in detail. We also find that dislocations often come together under attraction without forming a junction. The resulting “cross-linked” state provides an additional type of connection between dislocations. We include preliminary results on the persistence of junctions and cross-linked states under stress.
Simulation of Dislocation Dynamics in Ni3Al: A Study of Velocity Autocorrelations
Authors: Erdonmez C. K. , Chrzan D. C.
Published: April 2011

The yield strength anomaly in some L12 compounds has been linked to the thermally assisted cross slip of screw superdislocations. This work continues earlier efforts to understand the yield strength anomaly in L12 alloys using computer simulations of dislocation motion. Dislocations are modelled within isotropic elasticity theory, and simple rules are used to model the cross-slip process in the two dimensional geometry of the simulation. The velocity of a single dislocation in Ni3Al is studied as a function of the applied stress. The observed velocities vary nonlinearly with the applied stress. Further, dislocations are observed to become immobile for small applied loads. At high stresses, the dislocations are observed to advance relatively unhindered by the thermally activated cross slip process. Fluctuations in the velocity of the dislocations are studied, and their autocorrelation function shows an increased correlation time near a threshold stress. This threshold stress is identified with the critical stress proposed in earlier works.
Transition Temperatures in Plastic Yielding and Fracture of Semiconductors
Authors: Pirouz P. , Kubin L. P. , Demenet J. L. , Hong M. H. , Samant A. V.
Published: April 2011

Recent experiments on deformation of semiconductors show an abrupt change in the variation of the critical resolved shear stress, τy, with temperature, T. This implies a change in the deformation mechanism at a critical temperature Tc. In the cases examined so far in our laboratory and elsewhere, this critical temperature appears to coincide approximately with the brittle-ductile transition temperature, TBDT. In this paper, the deformation experiments performed on the wide bandgap semiconductor, 4H-SiC, over a range of temperatures and strain rates are described together with the characterization of induced dislocations below and above Tc by transmission electron microscopy. Based on these results, and those of Suzuki and coworkers on other compound semiconductors, some understanding of the different mechanisms operating at low and high temperatures in tetrahedrally coordinated materials has been gained, and a new model for their brittle-ductile transition has been proposed.
Dislocation Mobility in Two-Dimensional Lennard-Jones Material
Authors: Bailey Nicholas P. , Sethna James P. , Myers Christopher R.
Published: April 2011

In seeking to understand at a microscopic level the response of dislocations to stress we have undertaken to study as completely as possible the simplest case: a single dislocation in a two dimensional crystal. The intention is that results from this study will be used as input parameters in larger length scale simulations involving many defects. We present atomistic simulations of defect motion in a two-dimensional material consisting of atoms interacting through a modified Lennard-Jones potential. We focus on the regime where the shear stress is smaller than its critical value, where there is a finite energy barrier for the dislocation to hop one lattice spacing. In this regime motion of the dislocation will occur as single hops through thermal activation over the barrier. Accurate knowledge of the barrier height is crucial for obtaining the rates of such processes. We have calculated the energy barrier as a function of two components of the stress tensor in a small system, and have obtained good fits to a functional form with only a few adjustable parameters.
Modeling of the Dislocation Formation at Pores and Inclusions under Thermo-Mechanical Shear Loads
Authors: Rentsch R. , Vitek V.
Published: April 2011

Materials used in many technical applications contain a broad variety of defects. In both metals and ceramics, pores and inclusions influence significantly the elastic and plastic response. They can limit or broaden the range of applicability of the materials for high performance components and play, therefore, a very significant role in engineering applications.

This study focuses on the onset of dislocation formation and its intensity at pores and hard inclusions during the deformation process. For this purpose a molecular dynamics model of an fcc metal containing pores and/or inclusions was developed. This model material was then sheared at different strains and related development of the dislocation substructures investigated.
Symmetry Investigation of Textured Polycrystal Properties (Invited)
Authors: Maudlin P. J. , Bingert J. F. , Gray G. T. , Garrett R. K.
Published: April 2011

Tantalum plate and rod materials that demonstrate mild-to-strong anisotropic plastic flow during large deformation are analyzed in terms of tensorial property symmetry. Texture interrogations of these materials reveal duplex orientation components that have implications with regard to the symmetry realized during plastic deformation; specifically these materials show less symmetry than one would expect from a cursory examination of the texture. Mesoscale polycrystal simulations are performed to probe a general shape for the yield surface function based on a discrete orientation distribution representation of the material texture and previously established single-crystal deformation modes. The yield surface shape is mathematically represented in terms of second and higher-order tensors. A plastic compliance analysis is presented and applied to graphically map the deformation symmetry contained in these tensors for both ideal and real materials. Compliance results are shown to be consistent with finite element simulations of r-value specimens loaded in uniaxial tension.
Identification of 2D Boundaries from 3D Atom Probe Data, and Spatial Correlation of Atomic Distributions with Interfaces
Authors: Hellman O.C. , Vandenbroucke J.A. , Rüsing J. , Isheim D. , Seidman D.N.
Published: April 2011

The Three Dimensional Atom Probe produces a real space map of the elemental identities and positions of atoms field-evaporated from a sharply pointed specimen. The analyzed volume is on the order of 20 nm × 20 nm × 100 nm. This is large enough to enclose microstructural features such as grain- or heterophase boundaries. Correlation of the measured atomic positions with such features results in an atom-by-atom description of the chemical environment of these crystallographic defects. We describe here a method for identifying these interfaces and profiling the composition in the vicinity of the interfaces without any assumptions about the interface geometry. This approach is applied to quantitative determination of interfacial segregation of Ag at a MgO/Cu(Ag) heterophase interface. We discuss the implications of our technique with respect to classical treatments of segregation at interfaces.
Modelling of Grain Refinement in Aluminium Alloys
Authors: Greer A. L. , Tronche A. , Vandyoussefi M.
Published: April 2011

Commercial grain refiners for aluminium solidification are so potent that the barrier forgrain initiation is that for free growth rather than for nucleation itself. In this case quantitative prediction of grain size is possible. For small melt volumes a successful isothermal-melt model is presented. This is extended to directional solidification in a temperature gradient using cellular-automaton modelling of grain growth with finite-element heat-flow calculations.
Characterization and Modeling of Precipitation Kinetics in Aluminium 7000 Alloys
Authors: Werenskiold J.C. , Deschamps A.
Published: April 2011

The precipitation kinetics of 7108.70 aluminum alloy has been investigated in a wide range of temperatures by in situ Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM), and computer modeled by use of an internal-state variable model which predicts the evolution of microstructural parameters. The modeling and experiments were done for isothermal heat treatment at 120, 140, 150, 160 and 170°C. The industrial T6 and T7 treatments have also been investigated.
The Strain Gradient Effects in Micro-Indentation Hardness Experiments
Authors: Xue Z. , Huang Y. , Gao H. , Nix W.D.
Published: April 2011

Micro-indentation experiments have shown very strong size dependence of the indentation hardness, a phenomenon that cannot be explained by classical plasticity theories. A theory of mechanism-based strain gradient (MSG) plasticity has been developed based on the Taylor model in dislocation theories, and is intended for materials and structures whose dimension controlling plastic deformation falls roughly between 0.1 to 10 microns. The MSG plasticity theory is used in the present study to investigate the size effects observed in micro-indentation experiments. It is shown that the theory can indeed reproduce micro-indentation experimental data, thus providing an important self-consistent check of the MSG plasticity theory.
The Role of Boron in the Mechanical Milling of Titanium-6 %Aluminium-4% Vanadium Powders
Authors: Brown A.P. , Brydson R. , Hammond C. , Godfrey T.M.T. , Wisbey A.
Published: April 2011

The reduction in grain size of a metal can lead to significant improvement in mechanical properties. Mechanical alloying (MA) with a second phase is a possible route to producing fine-grained, particulate reinforced material. This study describes the microstructural development of Ti-6%Al-4%V milled with increasing concentrations of boron. Mechanical milling of Ti-6%Al-4%V powder produces a nanocrystalline material. MA of Ti-6%Al-4%V with boron results in the alloying of the two to form either a boride or an amorphous phase when the local concentration of boron is ∼ 50 at.%. During milling, the boron tends to remain near to its original particle form and in these boron-rich regions TiB is formed. Beyond these regions small amounts of boron (a few at.%) mix with the titanium matrix and reduce further the grain size of the titanium. An increase in the global concentration of boron increases the volume fraction of boride produced.
Formation of bulk magnetic nanostructured Fe40Ni40P14B6 alloys by metastable liquid state phase separation
Authors: Li Q. , Kui H.W.
Published: April 2011

METGLAS alloy #2826 (Fe40Ni40P14B6) is a eutectic alloy. Its melt can undergo metastable liquid state spinodal decomposition deep in the undercooling regime ΔT defined as ΔT = T1 - T where T1 is the liquidus of the alloy and T is the temperature at which the decomposition reaction takes place. Micrographs of undercooled Fe40Ni40P14B6 of ΔT = 209, 260 and 307 K were displayed. All of them exhibit refined microstructures, esp. the one with the largest ΔT.
Residual Stress Determination and Subsurface Microstructure in Ground and Polished Alumina/Silicon Carbide Nanocomposites and Monolithic Alumina Ceramics
Authors: Wu H.Z. , Roberts S.G. , Winn A.J. , Derby B.
Published: April 2011

The surface residual stress state induced by grinding and polishing an alumina/silicon carbide nanocomposite and monolithic alumina has been investigated using Hertzian indentation and fluorescence spectroscopy. Specimens were ground and then polished with diamond slurry with grit sizes ranging between 8 μm and 1 μm. The results show that the surface residual stress state in the nanocomposites is more sensitive to surface treatment than that in the monolithic alumina. Surfaces of both ceramics were examined in cross-section by TEM and direct observations were made of the plastic deformation induced by different surface treatments. There is a change in the predominant deformation micromechanism from twinning in the alumina to dislocation generation in the nanocomposites.
The Microstructure and Properties of Framework Zirconium Phosphates Based Nanocomposites -Catalysts of Alkane Isomerization
Authors: Sadykov Vladislav A. , Pavlova S. N. , Zabolotnaya G. V. , Maximovskaya R. I. , Kochubei D. I. , Kriventsov V. V. , Odegova G. V. , Ostrovskii N. M. , Bel'skaya O. B. , Duplyakin V. K. , Zaikovskii V. I. , Paukshtis E. A. , Burgina E. B. , Tsybulya S. V. , Chaikina M. V. , Kuznetsova N. N. , Lunin V. V. , Roy R. , Agrawal D. K.
Published: April 2011

The structure and surface properties of composites based upon high-surface-area framework zirconium phosphates with supported WO3, MoO3 and Pt nanoparticles were studied by using combination of structural and spectral methods. The effect of these promoters on performance of zirconium phosphates in the reaction of pentane and hexane isomerization is considered.
XPS Study of Pt/CexZr1−xO2/Si Composite Systems
Authors: Norman A. , Sporken R. , Galtayries A. , Mirabella F. , Keveney K. , Pijolat M. , Baker R. , Bernal S.
Published: April 2011

This work describes the study of the surface reduction of ceria zirconia mixed oxides (CeZrO) as either thin films or powders, both with and without Pt present. XPS was used to measure the composition of the surface and the oxidation states of all metals contained within the material. The thin films of CeZrO showed little reactivity towards the reducing conditions used. Grazing incidence angle XRD showed the presence of Ce0.75Zr0.25O2. The thin films prepared with Pt showed that surface reduction of Ce4+ occurred under reducing conditions. The size of the Pt clusters was also determined from the data. The Pt was found to always exist in the metallic state. The Zr4+ was not seen to change during all treatments. For the powder samples the Ce4+ was readily reduced to approximately 60%. Pt was found to be initially oxidised with the % of metallic Pt increasing with reduction temperature. Again no change in the Zr was observed.
Atomic Scale Characterisation of Electrodeposited Nanocrystalline Ni-P Alloys
Authors: Abraham Matthias , Thuvandert Mattias , Lane Helen M. , Cerezo Alfred , Smith George D.W.
Published: April 2011

Nanocrystalline Ni-P alloys produced by electrodeposition have been characterised by three-dimensional atom probe (3DAP) analysis. In the as-deposited materials, there are indications of some variation in P concentration between grains and segregation to grain boundaries. After heat treatment however, strong grain boundary segregation and the formation of Ni3P precipitates have been observed.
Insulator-Metal Transition in Nanostructured Ni-Al Thin Films
Authors: Ng H.P. , Ngan A.H.W.
Published: April 2011

The electrical resistance of Ni-Al alloy thin films prepared by dc magnetron sputtering process was found to be abnormally high at room temperature. However, when heated at elevated temperatures, the resistance dropped significantly, exhibiting a remarkable negative temperature coefficient of resistance (TCR). The phenomenon was found to be substrate-independent. Cross-sectional transmission electron microscopy revealed that the films were essentially nanocrystalline and porous in nature. Analysis of the current density-electric field characteristics yielded a satisfactory agreement with either the space charge limited or the Poole-Frenkel models for electrical conduction. The negative TCR effect diminishes and the usual metallic resistance is restored in thicker films, probably due to reduction in particle separation and further coalescence of neighbouring crystallites.
Raman Shift and Broadening in Stress-Minimized Ge Nanocrystals in Silicon Oxide Matrix
Authors: Jie YX , Huan CHA , Wee ATS , Shen ZX
Published: April 2011

Ge nanocrystals (nc-Ge) embedded in silicon oxide films were synthesized using RF magnetron sputtering and post-annealing procedure. To minimize the stress effect and inhomogeneity, we intentionally lower the cooling rates and reduce the temperature gradient during annealing. Significant Raman shifts ranging from 2.0 to 5.8 cm−1have been observed from samples annealed at different temperatures. The size-dependent shift and broadening is found to be in good agreement with the phonon confinement mode together with the Gaussian weighting function, and the isotropic T02 phonon dispersion relation introduced by Sasaki et al. The Raman spectra can also be well-fitted using peaks calculated from the phonon confinement model. The inhomogeneous Raman peak broadening from our samples annealed at lower temperatures are attributed to the non-Gaussian size distribution of Ge nanocrystals.
Protein Supported Metallic Nanostructures as Catalysts
Authors: Behrens S. , Habicht W. , Boukis N. , Dinjus E. , Baum M. , Unger E.
Published: April 2011

Highly oriented proteins with characteristic nanometer dimensions are used as a template for the synthesis and support of metallic nanoparticles. Following a bottom-up approach, noble metal particles in the nanometer size range were obtained by the reduction of the corresponding metal salts in the presence of the protein assemblies. The catalytic activity of the protein-supported particles was determined by hydrogenation reactions.
Carboxylate-Alumoxanes: Precursors for Heterogeneous Catalysts
Authors: Jones Christopher D. , Brown David S. , Marshall Larry L , Barrona Andrew R.
Published: April 2011

Carboxylate-alumoxanes are organic substituted alumina nano-particles synthesized from boehmite in aqueous solution which are an inexpensive and environmentally benign precursor for the fabrication of nano-, meso-, and macro-scale aluminum based ceramics. The use of carboxylate-alumoxanes as a novel high surface area alumina support for heterogeneous catalysis will be discussed. The ability to perform further chemistry on the organic ligands of the carboxylate-alumoxanes allows for attachment of catalysts. During calcination, the organic ligands are burned out, leaving behind the catalyst in a well-dispersed manner. To demonstrate this concept, the metathesis of C16 olefins using a molybdenum oxide catalyst supported on alumina will be discussed using the carboxylate-alumoxane method.
The Formation of High-Coercivity, Oriented, Nanophase Cobalt Precipitates in Al2O3 Single Crystals by Ion Implantation
Authors: Honda S. , Modine F. A. , Haynes T. E. , Meldrum A. , Budai J. D. , Song K. J. , Thompson J. R. , Boatner L. A.
Published: April 2011

Ion-implantation and thermal-processing methods have been used to form nanophase magnetic precipitates of metallic cobalt that are embedded in the near-surface region of single crystals of Al2O3. The Co precipitates are isolated, single-crystal particles that are crystallographically oriented with respect to the host Al2O3 lattice. Embedded nanophase Co precipitates were formed by the implantation of Co+ at an energy of 140 keV and a dose of 8 × 1016 ions/cm2 followed by annealing in a reducing atmosphere. The implanted/annealed Co depth profile, particle size distributions and shapes, and the orientational relationship between the nanophase precipitates and the host crystal lattice were determined using RBS/channeling, transmission electron microscopy, and x-ray diffraction. Magneto-optical effects arising from Co precipitates formed in the near-surface region of Al2O3 were observed and characterized using magnetic circular dichroism. Magnetic properties of the Co-particle/host nanocomposites were investigated in the temperature range of 77 to 295 K in applied fields of up to 10 kG using a superconducting quantum interference device (SQUID) magnetometer. Implantation of the Co particles by Pt or Xe ions produced a large anisotropic increase in their coercivity. Accordingly, these magnetic nanoparticle systems may be of interest for magnetic data storage applications. Details of the magnetic properties of the Co/Al2O3 nanocomposites including their retentivity, coercivity, saturation field, and magnetic anisotropy are presented.
Triple-Period (TP)-A and CuPt-A Type Ordering in Al0.5In0.5As Grown by Metalorganic-Vapor-Phase-Epitaxy
Authors: Suzuki Tohru , Ichihasfh Toshinari , Tsuji Masayoshi
Published: April 2011

The triple-period (TP)-A and CuPt-A type ordering, which have been so far reported only for MBE grown alloys, were observed, in addition to CuPt-B type ordering, in Al0.5In0.5As alloys grown by MOVPE at 500°C. This indicates that (2×3) and (1×2) surface reconstructions occur on the surface even during MOVPE growth, although the (2×1) surface reconstruction and CuPt-B type ordering are dominant for the growth conditions examined.
Kinetic Instability of Semiconductor Alloy Growth
Authors: Ipatova I. P. , Malyshkin V. G. , Shchukin V. A. , Maradudin A. A. , Wallis R. F.
Published: April 2011

A kinetic theory of the instability of homogeneous alloy growth with respect to fluctuations of alloy composition is developed. The growth mechanism studied is the step-flow growth of an alloy from the vapor on a surface vicinal to the (001) surface of a cubic substrate. The epitaxial growth implies that the adsorbed atoms migrate on the surface during growth of each monolayer, and that their motion is “frozen” after the completion of the monolayer. Frozen fluctuations in all completed monolayers create, via the composition-dependent lattice parameter, an effective potential which influences the surface migration of adatoms. The migration consists of diffusion and strain-induced drift in the effective potential. For temperatures lower than a certain critical temperature Tc, strain-induced drift dominates diffusion and results in the kinetic instability of the homogeneous alloy growth. In the linear approximation in the fluctuation amplitude, the instability means the exponential increase of the fluctuation amplitude with the thickness of the epitaxial film. It is shown that the critical temperature of kinetic instability Tc, increases with the increase of elastic effects. The wave vector kc of the most unstable mode of composition fluctuations is determined by the interplay of anisotropic elastic interaction and anisotropic diffusion on a stepped vicinal surface. The direction of the wave vector kc differs from the lowest-stiffness direction of the crystal, and any direction of kc is possible.
Steady-State Structures in Composition-Modulated Alloys: Kinetic Phase Transition Between 1D and 2D Patterns
Authors: Shchukin V. A. , Starodubtsev A. N.
Published: April 2011

A non-linear continuum theory of self-organized growth of composition-modulated structures in alloys is developed. It is shown that, for a lattice-matched alloy, where compositional and morphological instabilities are uncoupled in the linear regime, the two instabilities are coupled due to non-linear effects. Due to non-linear coupling, composition-induced stresses may lead to an instability of the advancing surface against undulations. A non-planar surface profile favors kinetic phase transition from the growth of a 1D modulated structure to the growth of a 2D one. A steady-state phase diagram in variables “temperature — growth velocity” is constructed which contains regions of homogeneous alloy growth, of 1D steady-state structures, of 2D steady-state structures, and the region where both 1D and 2D structures are possible. For zinc-blend semiconductors, the interplay between the anisotropic elasticity and anisotropic surface diffusion may lead to the kinetic phase transition between the growth of a 2D structure modulated in the elastically soft directions [100] and [010] to the growth of a 1D structure modulated in the direction of the fast diffusion [110]. Our theory explains this type of transition observed in the growth of InAlAs/InP.
Fullerene-Incorporated Nanocomposite Resist System for Nanolithograpy
Authors: Ishii T. , Nozawa H. , Kuramochi E. , Tamamura T.
Published: April 2011

A nanocomposite resist system that incorporates sub-nm fullerene molecules ( C60 and/or C70) into a conventional resist material is proposed for nanolithograpy. Fullerene has physically and chemically resistant characteristics, and its incorporation reinforces the original resist film, leading to substantial improvements in resist performance: etching resistance, pattern contrast, mechanical strength and thermal resistance. We have prepared a system composed of a positive-type electron beam resist, ZEP520, and C60 or a C60/C70 mixture and through the fabrication of high electron mobility transistors (HEMTs), X-ray masks, and groove-grating mirrors for lasers with nanometer dimensions confirmed improved resist performance, particularly resolution improvements due to enhanced etching resistance. By making use of a characteristic unique to the nanocomposite, which is that sensitivity readily changes with the fullerene content due to a dissolution inhibiting effect of fullerene, we have constructed a fullerene-incorporated bilayer resist system for a lift-off process and have successfully fabricated a highly-ordered array of self-organized boxlike nanostructures and a mold for nanoprinting. Further, solubility enhancement by fullerene derivatives has been examined for a higher degree of fullerene incorporation and better sensitivity characteristics in future nanocomposite resist systems.
New High Resolution Liquid Crystal Electron Beam Resists
Authors: Robinson A. P. G. , Palmer R. E. , Tada T. , Kanayamat T. , Allen M. T. , Preecel J. A. , Harris K. D. M.
Published: April 2011

We report the development of a new family of electron beam resists based on liquid crystalline polysubstituted derivatives of triphenylene. These new resists show excellent performance in terms of both high resolution and high durability to plasma etching. Films of the derivatives have been produced in a controlled manner via room temperature spin coating on hydrogen terminated silicon substrates. The dissolution behaviour of the derivatives in various organic solvents was altered by exposure to a 20 keV electron beam. The solubility of the derivative hexapentyloxytriphenylene, in polar solvents, was substantially increased by electron doses greater than ∼ 3 × 10-4 C/cm2 (positive tone behaviour). Doses greater than ∼ 2.5 × 10-3 C/cm2 led to negative tone behaviour in both polar and non-polar solvents. Other derivatives also demonstrated a reduction in their dissolution rate for doses between ∼ 1 × 10-3 and ∼ 7 × 10-3 C/cm2. The derivative sensitivity was found to be roughly proportional to the molecular mass. Negative tone patterns were found to have an etch durability ∼ 70 % greater than that of a conventional novolac based negative tone resist (SAL601). The performance of these new resists has been demonstrated by the definition of line and space patterns with a resolution of ∼ 14 nm, whilst structures with an aspect ratio of.∼ 50 to 1 were etched into the silicon substrate.
Carbon Dioxide – Dilated Block Copolymer Templates for Nanostructured Materials
Authors: Brown Garth D. , Watkins James J.
Published: April 2011

Periodic polymer/metal (Pt or Ag) and polymer/semiconductor (PbS) nanocomposites are prepared using block copolymers dilated with carbon dioxide (CO2) as templates. Specifically, organometallic compounds (metal precursors) are dissolved into supercritical CO2 and infused into polystyrene-block-poly(acrylic acid) or polystyrene-block-poly(vinylpyridine) copolymers. Upon infusion, the acid or pyridine block selectively binds the metal precursor. The excess is removed from the polystyrene phase by subsequent CO2 extraction. Reduction of the bound organometallic with hydrogen or hydrogen sulfide yields the desired metal or semiconductor clusters, which are confined to the precursor-binding domain and remain positioned on the copolymer lattice. The composites are characterized by transmission electron microscopy, x-ray scattering and electron diffraction.
A New Purged UV Spectroscopic Ellipsometer to characterize 157nm nanolithographic materials
Authors: Boher Pierre , Piel Jean Philippe , Evrard Patrick , Stehle Jean Louis
Published: April 2011

Spectroscopic ellipsometry has long been recognized as the technique of choice to characterize thin films and multilayers. It is now intensively used in microelectronics and especially for the microlithographic applications. Instrumentation for the next generation of UV lithography at 157nm requires special optical setup since oxygen and water are extremely absorbing below 190nm. The ellipsometer discussed in this paper works into a purged glove box to reduce the oxygen and water contamination in the part per million ranges. The optical setup has been especially studied for microlithographic applications. It includes for example a premonochromator in the polariser arm to avoid resist photobleaching. Technical details of the system and some first measurement results on substrates and thin films are reported hereafter.
Localized Charge Storage in CeO2/Si(111) By Electrostatic Force Microscopy
Authors: Jones J. T. , Bridger P. M. , Marsh O. J. , McGill T. C.
Published: April 2011

In this report, the local patterning of charge into CeO2/Si structures by scanning probe microscopy is examined. An electrostatic force microscope (EFM) has been used to write and image localized dots of charge on to double barrier CeO2/Si/CeO2/Si(lll) structures. By applying a large tip bias Vtip = 6 – 10 V and reducing the tip to sample separation to z = 3 – 5 nm for write times of t = 30 – 60 s, arrays of charge dots 60 – 250 nm FWHM have been written. The dependence of dot size and total stored charge on various writing parameters such as tip writing bias, tip to sample separation, and write time is examined. The total stored charge is found to be Q = 5 – 200 e per charge dot. These dots of charge are shown to be stable over periods of time greater than 24 hrs, with an initial charge decay time constant of τ ∼ 9.5 hrs followed by a period of much slower decay with τ > 24 hrs. Charge decay time constants are found to be dependent on the thickness of the lower CeO2 tunneling barrier.
Tailoring Grain-Boundary Segregation to Control Mechanical Properties
Authors: Williams D. B. , Keast V. J.
Published: April 2011

Recent advances in our understanding of the role of the chemistry of grain boundaries in controlling the mechanical properties of materials (in particular intergranular brittle fracture) are reviewed. It is now possible in a modem field-emission gun (FEG) analytical transmission electron microscope (AEM) to measure the chemistry of sub-nanometer films of GB segregants while at the same time observing the effect (if any) on the bonding of the atoms within a nanometer of the boundary plane. This has been accomplished by the development of X-ray mapping (XRM) a powerful new tool for the study of segregation. For the first time, in the same instrument, on the same grain boundary, any changes in the boundary chemistry can be correlated with the occurrence or absence of brittle failure, which is often associated with boundary segregation. There is strong evidence that boundary segregation is extremely nonuniform, even in some strongly embrittling systems (e.g. Cu-Bi) and in these same systems, embrittling segregants introduce subtle but consistent changes in the bonding. Non-embrittling segregants (e.g. Ag in Cu) do not introduce detectable bonding changes.
Impact of Grain Boundary Character on Electrical Property in Polycrystalline Silicon
Authors: Hamada Shu , Kawahara Koichi , Tsurekawa Sadahiro , Watanabe Tadao , Sekiguchi Takashi
Published: April 2011

Grain boundaries in polycrystalline silicon are most likely to generate localized states in band gap. The localized states play a dominant role in determining the performance of solar cells by acting as traps or recombination center of carriers. In the present investigation, the scanning electron microscope - electron channeling pattern(SEM/ECP) method and SEM - electron back scattered diffraction pattern(SEM/EBSD) technique were applied to characterize the grain boundaries in p-type polycrystalline silicon with 99.999%(5N) in purity. Thereafter, temperature dependence of electrical activity of individual grain boundaries was measured by an electron beam induced current(EBIC) technique.

It has been found that temperature dependence of EBIC contrast at grain boundaries can change, depending on the misorientation angle the orientation of the boundary plane. The results can be explained by the difference in the position of the localized state within the band gap on the basis of the Shockley-Read-Hall statistics. The {111} ∑3 symmetrical tilt boundary has shallow states, while high ∑ boundaries have deep states. Low angle boundaries reveal high electrical activities. The EBIC contrast at low angle boundaries was found to increase with increasing misorientation angle up to 2° followed by an almost constant value. High electrical activity at low angle boundaries is probably attributed to a stress field of primary dislocations forming low angle boundaries.
Structure and Properties of Polycrystalline Materials From Simulation: An Interfacial Perspective
Authors: Phillpot S. R. , Keblinski P. , Wolf D. , Cleri F.
Published: April 2011

We have recently developed a novel molecular-dynamics simulation method to grow polycrystals from a melt containing randomly oriented crystalline seeds. The resulting microstructures contain only randomly oriented (i.e., high-energy) grain boundaries. We find that these grain boundaries, which are highly constrained by their close proximity to grain junctions, are highly disordered in fcc metals and amorphous in silicon. From simulations of infinitely extended high-energy grain boundaries in bicrystals, we find that such highly disordered and amorphous grain boundaries are actually the thermodynamic ground state; by contrast, low-energy grain boundaries are crystalline. High-energy grain boundaries in diamond, however, are structurally ordered at the expense of a significant amount of graphite-like bonding. We show that these complex grain boundary structures have important effects on properties including grain boundary diffusion (fcc metals and silicon), grain boundary diffusion creep (silicon) and grain boundary electrical activity and strength (diamond). The implications for engineering materials with prescribed properties are discussed.
Oxidation Resistant Ceramic Composites: How Weak Interfaces Became Designed Failure Processes
Authors: Kerans Ronald J.
Published: April 2011

Interest in ceramic composites arises from their potential for dramatically improved damage tolerance, as compared to monolithic ceramics, while delivering similar high-temperature properties. The remarkable toughening effect resulting from the proper combination of brittle phases is dependent upon the failure process developing in a particular way; matrix cracks must deflect into fiber debonding cracks that run in or near the fiber/matrix interface and permit some relative displacement. In early composites the requirements for crack deflection and good composite behavior seem to have been almost fortuitously satisfied by native C layers; however, the most productive uses of ceramic composites are dependent upon the development of fiber coatings that not only promote the desired interfacial failure, but also satisfy the additional requirement of being oxidation resistant. Though conceptually simple, the management of a failure process—specifically, predetermining the progress of cracks on a very local level—places a very demanding and unprecedented requirement on the materials designer. Historically, the details of fracture events were of interest principally for insight into means of avoiding them. The composite problem imposes the new requirement that we design to promote a special kind of fracture, and control post-fracture fiction within a certain range. This truly is a higher level of sophistication than heretofore attained, and its complexities have deterred many investigators from seriously addressing the problem. Nevertheless, there has been progress both in depth of understanding and in actual achievement of viable systems. Moreover, very interesting properties of several families of materials have been uncovered. These issues will be outlined and discussed in more detail with the objective of developing a broad view of the lessons learned and opportunities revealed.
Interface Characterization Using the Automated-EBSP Technique
Authors: Sutliff John A.
Published: April 2011

The use of the electron back scattering pattern (EBSP) technique of electron diffraction (also referred to as EBSD and BKD) to study microstructure continues to gain popularity in the materials characterization community. The technique's ability to rapidly measure lattice orientation with good relative accuracy provides a statistically powerful tool for investigating the misorientation character of interfaces. It is certainly possible to gather basic misorientation data on thousands of interfaces in only a couple of hours. This invited talk will discuss the detection and characterization of interfaces in polycrystalline materials using the automated-EBSP technique with specific discussion of sub-grain and twin boundaries in deformed and/or annealed materials. This paper will also attempt to demonstrate with data from γγ' Ni-base superalloys that the process of acquiring, with high accuracy, all the spatial, orientation, and chemical information associated with boundaries during an extended data acquisition is a substantial experimental challenge. Combining quantitative image analysis of traditional high-resolution scanning electron micrographs with the EBSP data can help correct some of the distortions commonly encountered in EBSP data.
Control of Grain Boundary Microstructures in Liquid-Phase Sintered Alumina
Authors: Ravishankar N. , Carter C. Barry
Published: April 2011

The elimination of the grain boundary liquid in liquid-phase sintered materials is examined for the case of anorthite liquid in alumina grain boundaries. It is shown that under suitable conditions the liquid can exude from the grain boundary to the free surface. The proposed driving force is provided by the difference in energies and wetting behavior of the grain boundary and the free surface at high temperatures. The results emphasize the importance of the crystallography of the boundary and the nature of free surfaces (i.e., the surface energies) on the exudation behavior.