bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Dynamical Spin Susceptibility of Paramagnetic La2CuO4
Authors: Winter H. , Szotek Z. , Temmerman W. M.
Published: March 2011

The self-consistent one-electron wave functions and energy bands obtained by the LMTO-ASA method within the local density approximation (LDA) are used to calculate the wave vector and frequency dependent non-interacting spin susceptibility of paramagnetic La2CuO4 in the body-centred tetragonal (bct) structure. We show that the tendency towards the antiferromagnetic instability is strongly dependent on the effects of the matrix elements which lead to a substantial depression of the susceptibility, especially near the X-point. The Fermi surface nesting properties, although important for the susceptibility, are by far not sufficient for the instability and the interband transitions turn out to be of great significance. Our results indicate that the susceptibility is at least 3 times too small to drive this system through a transition to the antiferromagnetic state, and we discuss possible reasons for this failure.
Molecular Dynamics Simulations of Grain-Boundary Diffusion for Varying TILT Angle Geometries
Authors: Plimpton Steven J.
Published: March 2011

The effect of structure and geometry on grain boundary self-diffusion is investigated. Using static structures found by relaxation techniques (conjugate gradients) as starting points for a molecular dynamic simulation of a bicrystal model, diffusion coefficients and activation energies are calculated for (100) fcc Al and bcc α-Fe tilt boundaries. These quantities are derived by monitoring the mean-squared displacement of atoms in the grain boundary region as the simulation progresses and as the temperature of the simulated solid is changed. The angular, directional, and structural dependence of the simulated diffusion are discussed and compared to experimental measures and theoretical predictions. The implementation of the molecular dynamics algorithm on a parallel supercomputer is also briefly discussed to illustrate the performance benefits these computers make possible.
Electronic Structure of Epitaxial Silicon Interfaces
Authors: Fujitani Hideaki , Asano Setsuro
Published: March 2011

Using the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA), we studied the electronic structure of the Si(111) interface for four different materials: CaF2, NiSi2, CoSi2, and YSi2. We examined how the interface states and Schottky barrier height depend on the interface atomic structure.
Theory of Structural and Electronic Properties of Silicon Nitride and Carbon Nitride
Authors: Liu Amy Y. , Cohen Marvin L.
Published: March 2011

Using a first principles pseudopotential total energy approach with a localized basis for the electronic wave functions, we have investigated the structural and bonding properties of β-Si3N4 and β-C3N4, which is a proposed structure for carbon nitride. The latter system is used as a prototype for studying the properties of possible covalent C-N solids. For β-Si3N4, calculated structural properties such as lattice constant and bulk modulus are in excellent agreement with experimental values. This gives support for the predicted properties of β-C3N4.β/C3N4 is found to be a good candidate for a new low-compressibility solid, with compressibility comparable to diamond. Despite similarities between β-Si3N4 and β-C3N4 in terms of crystal structure and valency of constituent elements, differences are found in their electronic bonding properties. A comparison of the bonding in β-Si3N4 and β-C3N4 with other first and second row semiconductors is useful for understanding trends in the structural properties of these materials.
Diffusion of Light in Antarctic Sea Ice
Authors: Buckley R G , Trodahl H J
Published: March 2011

It is important to understand the diffusion sun light in sea ice as this interaction exerts a strong influence over the weather in polar regions and over the growth of microbial communities in the sub-ice water column. Sea ice is a granular composite of ice, brine, air and at low temperatures precipitated salts, in which the proportion and disposition of these components vary with depth, with temperature and thermal history. It is demonstrated that by using a simple in situ technique, supported by Monto Carlo simulations, the diffusive transport of light through a weakly absorbing composite such as sea ice can be characterised. The radiation field both within and emergent from the ice is found to reflect the anisotropic structure of the ice, in particular, the scattering is found to be highly anisotropic so that the light is channelled predominantly vertically. The technique will be illustrated with experimental results collected in McMurdo Sound, Antarctica.
A Quantum Percolation Model for Magnetoconductance of Granular Metal Films
Authors: Zhang Zhao-Qing , Sheng Ping
Published: March 2011

A quantum percolation model is introduced to study the magnetoconductance of granular metal films. This model incorporates the granular property of the films and enables us to study the magnetoconductance in the strong scattering regime. Our calculations show a sign change in magnetoconductance as the temperature varies. There also exist oscillations in the magnetoconductance as the magnetic field is increased. Both observations are consistent with some recent experimental data.
Percolative Properties of Al-Ge Composite thin Films
Authors: Kapitulnik A. , Hsu J.W.P. , Hahn M.R.
Published: March 2011

Part of the work described below was delivered as an invited talk by one of us (A.K.) at the special symposium to honour Dr. Ben Abeles for his 65th birthday. During the questions part of my talk, I was asked by Ben Abeles: ‘what about magnetoresistance…’. I answered that this is a complicated issue and I don't have time to discuss this matter. After my talk Ben explained that he always asks this question because his thesis was on magnetoresistance measurements. I remembered this question and decided that this paper would be an excellent place give to the answer. Hence section IV.2 is specialy dedicated to Dr. Ben Abeles.
Conduction Mechanisms in Discontinuous Copper Films
Authors: BiegaŃski P. , Mozrzymas-Dobierzewska E.
Published: March 2011

Copper films of coverage coefficients ranging between 0.2 and 1 were evaporated onto glass substrates under vacuum conditions (p ≃ 10−8 Torr). For these films, the temperature dependences of resistance were measured in vacuo in situ. Making use of the obtained data TCR values, as a function of coverage coefficient and the activation energy for the films with different coverage coefficients were established. The resistance of films was found to change, and TCR values approaching zero for coverage coefficients between 0.63 and 0.75. This interval (∆qc) can be regarded as the percolation interval for discontinuous Cu films.
Experimental Study and Percolation Model of Compactified Metallic Mixtures Sintering by Electrical Discharge
Authors: Pakhomov A.B. , Peregood B.P. , Sarychev A.K. , Vinogradov A.P.
Published: March 2011

Different ways of pulsed current use for compaction of conducting materials have been studied during recent years, mainly in connection with technological problems of powder metallurgy. As a rule, the current is driven through a blank placed in a mould under external pressure [1-6]. Pulsed current action on a blank may lead to either partial or complete melting of granules [1,2], to the heating of granules and their plasticity increase [3], to the destruction of oxide films and granules surface activation [4,5] and to the break-down and sintering of chains forming channels in the direction of current [6].
Infrared Optical Guided Modes in Plasma Deposited Gold Clusters Embedded in a Polymer Matrix
Authors: Parmigiani F. , Jurichi M. , Kay E. , Swalen J.D.
Published: March 2011

Measurements of the refractive index of discontinuous metallic films, consisting of gold clusters embedded in a dielectric matrix prepared in a capacitively coupled coplanar diode radio frequency discharged system, are reported.

These composite films were analyzed to determine the metal volume fraction, the thickness and the cluster size.

Optical characterizations in the visible and near infrared regions of the electromagnetic spectrum, particularly, in the near-IR region (Nd/YAG laser wavelength 1.0642 μm), where the absorption coefficient of these materials is very low (k < 0.001) were performed. Optical guided modes analysis allowed careful measurement of the effective medium refractive index.
Study on Thermal Hysteresis of Elastic Modulus in Granular Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O
Authors: Wang Yening , Sun Linhai , Wu Jin , Gu Min
Published: March 2011

A large thermal hysteresis ( > 100 K) of elastic modulus was measured for coarse grained Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O. Whereas, only a small thermal hysteresis (2∼3 K) near the velocity minima at 240 K, and 150 K was observed in Bi2 Sr2 CaCu2 O8 single crystal, which were found to be associated with phaselike transitions (PLT). The investigations of isothermal recovery of modulus for coarse grained YBCO and BSCCO disclose that the large thermal hysteresis may be attributed to the defects of pore size generated in the interconnecting region between grains as a result of PLT of weak first order but covering a wide temperature range. The mechanism of a large thermal hysteresis for coarse grained samples has been discussed in detail.
Magnetic Penetration Depth Measurements and Inhomogeneity in YBa2Cu3O7−δ Superconducting Thin Films
Authors: Anlage Steven M. , Langley Brian W. , Halbritter Jurgen , Eom Chang-Beom , Switz Neil , Geballe T. H. , Beasley M. R.
Published: March 2011

The microstrip resonator technique has been applied to study the temperature dependence of the magnetic penetration depth in high quality YBa2Cu3O7−δ thin films. The temperature dependence at low temperatures comes out directly from measured data, with no assumptions about transmission line geometry, dielectric properties, or a model for the temperature dependence of the penetration depth. One can interpret the data in terms of either an exponential decay of λ(T) at low temperatures or as a power law decay. The energy gaps obtained from the exponential decay at low temperature are found to be significantly smaller than weak coupled BCS theory and power-law exponents are in the range of 1.3 to 3.2. These results will be discussed in terms of microscopic theories and the possibility that materials properties dominate the measurement.
Superconductivity in Granular Snx (SiO2)100−x Thin Films
Authors: Beamish John R. , Patterson B.M. , Unruh K.M.
Published: March 2011

The resistivity of sputter deposited Snx (SiO2)100−x films has been measured for Sn concentration x between 50 and 90 atomic percent. Films with more than 53 percent Sn are superconducting at low temperatures with transition temperatures slightly above that of bulk Sn. The enhancement is 0.11 K for the 90 percent film, increasing to 0.24 K in the 55 percent film. As the metal concentration decreases, the transition region broadens, with the resistance beginning to decrease about 1 K above the transition in the highest resistance films. The films remain superconducting in substantial magnetic fields. In the 55 percent film, a magnetic field of 1 T reduces the transition temperature by 1 K and a field greater than 2 T is needed to eliminate superconductivity. At the largest field of 6 T, there is no sign of superconductivity in any sample, and the resistances increase down to the lowest temperatures measured (100 mK).
Synthesis and Magnetic Characteristics of Granular Co Dispersions in a Polymer Matrix
Authors: Kay Eric , Laurent C. , Parkin S.S.P. , Mauri D.
Published: March 2011

We have produced thin film composite matrices containing granular transition metals in the zero valent state and have found onset of percolation at a much lower volume fraction than was the case for Au, albeit for significantly smaller transition metal particles. At volume fractions below percolation these granular composites are superparamagnetic down to 6°K. Remanent magnetization and hysteretic ferromagnetic behavior was not observed until we were slightly above the onset of electrical percolation. We interpret this result as indicative of ferromagnetic ordering among the transition metal grains. No significant reduction in magnetic moment due to size effects or to chemical interaction with the matrix was observed. A very small size dispersion of the metal clusters was indicated both from magnetic a well as electron microscopy measurements.
Structural and Magnetic Properties of Fe/Al2O3, Granular Systems
Authors: Dormann J.L. , Fiorani D.
Published: March 2011

Several samples of granular material consisting of Fe small particles dispersed in an alumina matrix were studied by means of various techniques. Structural results show that the particle surface is partially oxidized with occurrence of bonds with the matrix. Depending on the particle size, one observes b.c.c. a-Fe or amorphous structure. Magnetic properties are relevant of superparamagnetism phenomena, but the strong magnetic interactions between particles (due to the close compact arrangement) lead to a phase transition at zero temperature. It is also briefly discussed the magnetic volume determination and the influence on the properties of the magnetic disorder arising at the particle surface.
Elements of the Diagenesis of Sedimentary Rocks
Authors: Cohen Morrel H.
Published: March 2011

Three of the most important elements of the diagenesis of sedimentary rocks are consolidation, porosity reduction, and pressure dissolution or cementation. These are discussed qualitatively with special emphasis on the central role of contact formation in controlling both the driving forces and the kinetics of morphological change. It is shown, in particular, that the equilibrium forces would drive the rocks towards collapse of their porosity earlier in diagenesis were they not prevented by kinetic barriers. At greater depths these barriers are effectively removed by pressure concentration at the small contacts. We propose an explicit, qualitative mechanism leading to the observed morphologies and identify specific problems for quantitative analysis.
Self—Regulating Behavior of Ferromagnetic Granules in Inductive Sintering Process
Authors: Bulatova L.S. , Dmitriev A.V.
Published: March 2011

A physical model is presented to describe solid—phase sintering of pressed ferromagnetic powders under conditions of self—organization.
Influence of Microgeometry on Membrane Potential of Shaly Sands
Authors: Sen Pabitra N.
Published: March 2011

The microgeometry of the pore space influences the membrane potential Em. and theDC electrical conductivity σ of a shaly sand in a similar manner, independent of the details of the geometry: Em and σ being related via the conductivities of cations and σanions;σ=σcation + σ onion, and Em α σ cation/(σcation + σanion). This explicit relationship is used to investigate the role of the geometrical factors which influence both Em and σ in a related manner. The dependence of σ on the water conductivity σw can be well approximated with four geometrical parameters which can be obtained from the slopes and the interceptsof σ vs. σw curve at high and low salinities. We show that these geometrical factors appear in the expression for Em a well. These geometrical parameters (one of them is the formation factor) vary from rock to rock, and any trend in these parameters depend on the local geology.
Structure and Reactivity of Granular Noble Metal Catalysts
Authors: Deckman H. W. , Fung S. C. , Matturro M. G. , McHenry J. A.
Published: March 2011

The deactivation / reactivation behavior of fresh granular Pt metal catalysts supported on alumina is used to obtain information about the nature of catalytically activesites. It is found that relatively fresh catalysts can in some cases be reactivated by evolving only ∼1/100 of a monolayer of molecules off the Pt metal. This implies that either less than ∼1/100 of the surface is catalytically active with a site turnover frequency of greater than ∼100 reactions/(site-sec) orthat the reactivation process does not evolve small cracked molecules from the catalyticsites and involves some other physical or chemical change of the catalyst surface.
Noncrystalline Solids Prepared by Compacting Nanometer — Sized Particles
Authors: Weissmüller J. , Jing J. , Krämer A. , Birringer R. , Gonser U. , Gleiter H.
Published: March 2011

A new method of preparing amorphous solids is presented. X-ray diffraction, thermal stability and Mgssbauer spectroscopy give evidence for an atomic structure with reduced short–range order in Si75Auz5 and Pd72FeloSil8 alloys prepared by this method.
Fabricaton Of Granular Materials by High-Pressure Sputitering
Authors: Chow G.M. , Holtz R.L. , Chien C.L. , Edelstein A.S.
Published: March 2011

A brief study of the fabrication of granular materials by high-pressure sputtering is presented. This method utilizes sputtering at high pressures (p > 100 mTorr) in a thermal gradient to produce nanoscale particles, which are then embedded in a matrix by normal sputtering (p ∼ a few mTorr). The shape, size and the degree of aggregationof these nanoscale crystals can be changed by varying such processing parameters as the sputtering gas pressure and the target voltage. Examples are presented of nanocomposite films containing Mo nanocrystals (grain size ranging from 3 to 20 nm ) in an Al matrix.
Kinetics of Grain Growth Across Bond Interface During Diffusion Bonding
Authors: Yan Huang , Jianzhong Cui , Longxiang Ma
Published: March 2011

Generally, the elimination of the voids in bond interface is considered to be the rate-controlling mechanism for diffusion bonding. In an earlier paper, the author proposed a new theoretical model for solid-state diffusion bonding of similar matals, in which the grain growth across the bond interface was considered to be the governing mechanism for diffusion bonding. The aim of the model is to understand how the joint strength is affected both by process variables (temperature, pressure, time) and by the microstructures of the materials being joined. In this paper, the mechanism of grain growth and recrystallization is discussed, and the calculation of an appropriate kinetic equation is made based on a diffusion bonding experiment on a hot-rolled 7075 aluminum alloy. The calculated results basically agree with those of the experiment.
The Strength and Fracture Behaviour of Diffusion Bonded Joints in Al-Li(8090) Alloy Sheet
Authors: Partridge P. G. , Dunford D. V.
Published: March 2011

Solid state and transient liquid phase diffusion bonded joints have been made between Al-Li 8090 alloy and 8090 alloy/SiC particulate metal matrix composite. In this paper some shear and peel strengths are reported and the factors that affect the strength and fracture behaviour are discussed. Comparisons are made with other published data for bonded joints in Al-Li alloys.
Commercial Production, Superplastic Performance and Property Determination of 8090 SPF Alloy
Authors: Grimes Roger , Dunwoody Barry J. , Jones John A.
Published: March 2011

8090SPF alloy sheet has been in commercial production for about three years. This paper describes some of the property statistics of the commercially produced material, including tensile and superplastic results.

Properties have been determined for test components formed with back pressure with different levels of superplastic strain. Results from tensile and corrosion tests are presented.
m-δ Relationship and Structural Evolution during a Constant Strain-Rate Superplastic Deformation of an Aluminum Alloy
Authors: Zhou Shanyou , Zhang Dongming , Lin Dongliang , Lin T. L.
Published: March 2011

At 515° C with a constant strain-rate of 6.7× 10−3 min−1,tensile specimen of LC4 aluminum alloy with an initial average grain size of 8.7μm exhibited good superplasticity. A fracture elongation of 4649% was obtained. Under such deformation conditions, the m-δrelationship belongs to the mL=mmax type , with a maximum m value of 0.78 at 94% strain. The m-δ relationship can be expressed as δI(%)= (CI ×0.0067(mI−0.5) −1) × 100. During superplastic deformation, three kinds of structural evolution take place, namely the formation of precipitate-free zones adjacent to grain boundaries due to diffusional creep, grain coarsening and cavity generation. The m-δ relationship of superplasticity of the alloy mentioned above can be explained on the basis of the structural evolution during superplastic deformation.
High Rate Superplastic Deformation Mechanisms in IN90211 Mechanically Alloyed Aluminum
Authors: Bieler Thomas R. , Mukherjee Amiya K.
Published: March 2011

IN90211 has exhibited superplastic elongations above 500% at high homologous temperatures (0.76–0.82 Tm). A high strain rate and flow stress for optimum elongation was measured (1–5/sec, 20–60 MPa, 425–485 °C). The apparent strain rate sensitivity of m≈0.25 differs from the usual m≈0.5 observations of superplastic deformation. An analysis of the data at several strains indicates a highly temperature dependent threshold stress is present, with either a n=2 or n=3 assumption for the stress exponent. The magnitude of the threshold stresses in IN90211 are smaller than usually observed in a dispersion strengthened matrix (1–20% instead of ≈50% of the Orowan stress). Experimental evidence from creep experiments supports the n=3 deformation mechanism as the rate limiting step of deformation.
Behavio of Supeaplastically Extruded Cu-26wt%Zn–3.5wt%Al Shape Memory Alloy
Authors: Zhengyt Zheng , Weijian Zhcng , Fuzeng Lin , Yingsheng Chew
Published: March 2011

The influence of superplastic extrusion on the microstructures and the shape memory effect of the Cu-Zn-Al shape memory alloys has been investigated. The shape memory alloy Cu-26%wt%Zn-3.5wt%Al is superplastio with an index of strain rate sensitivity n = 0.48 at 600°C, at a strain of . After extrusion under the superplastio condition the miorostruotures are improved and no cavities are observed. The superplastically extruded specimens of this alloy were heat-treated to obtain the shape memory effect. These specimens indicate that no deterioration of shape memory effect of the alloy is induced by the superplastio extrusion and the shape memory effect of the alloy is somewhat improved.
Dissipative Structures and Superplasticity
Authors: Chen Hechun , Smith Reginald W. , Shi Jiwei , Zhengheng Yang
Published: March 2011

The characteristics of superplasticity are discussed from the viewpoint of irreversible thermodynamics, in particular, system evolution and the formation of dissipative structures. A mathematical model combining determinism with indeterminism is used to analyze plastic deformation and superplasticity in metals. Since the plastic deformation of a metal is in essence a dissipative process occurring in a system far away from thermodynamic equilibrium, the instability of the system resulting from structure fluctuations (defects) and thermodynamic bifurcations (possible thermodynamic states) will result in many deformation mechanisms being available to provide the deformation observed in the system. Thus it is virtually impossible to describe all the possible models in conventional terms i.e. by the application of the method of determinism. A new model is proposed, and is shown to account for much of the experimental data reported.
Dynamic Grain Growth in Superplastic Y-TZP and Al2O3/YTZ
Authors: Nieh T. G. , Tomasello C. M. , Wadsworth J.
Published: March 2011

Both static and dynamic grain growth have been studied during superplastic deformation of fine-grained yttria-stabilized tetragonal zirconia (Y-TZP) and alumina reinforced yttria-stabilized tetragonal zirconia (Al2O3/YTZ). Grain growth was observed in both materials at temperatures above 1350° C. In the case of Y-TZP, both static and dynamic grain growth were found to obey a similar equation of the form: where D is the instantaneous grain size, Do is the initial grain size, t is the time, and k is a kinetic constant which depends primarily on temperature and grain boundary energy. The activation energies for Y-TZP were approximately 580 and 520 kJ/mol, for static and dynamic grain growth, respectively. In the case of Al2O3/YTZ, it was found that the grain growth rate for the Al2O3 phase was slower than that for the ZrO2 phase. The growth rate of the ZrO2 phase in Al2O3/YTZ is, however, similar to that in monolithic ZrO2, i.e., Y-TZP.
Mechanical Behavior and Cavitation in Commercial and High Purity Zn-22% Al
Authors: Park Kyung-Tae , Earthman James C. , Mohamed Farghalli A.
Published: March 2011

An investigation was conducted on the superplastic Zn-22% Al alloy to examine the effect of impurity level on mechanical behavior and cavitation in the alloy. In conducting the investigation, three grades of Zn-22% Al containing different levels of impurities (6 ppm, 100 ppm, and 180 ppm) were used. The results show that the deformation behavior of Zn- 22% Al at low stresses is influenced by the impurity level of the alloy, and that the extent of cavitation increases with increasing impurity content. These two findings lend support to the concept of attributing low-stress superplastic deformation to strong impurity segregation at boundaries.
Is Superplasticity in the Future of Nanophase Materials?
Authors: Siegel R. W.
Published: March 2011

The ultrafine grain sizes and high diffusivities in nanophase materials assembled from atomic clusters suggest that these materials may have a strong tendency toward superplastic mechanical behavior. Both small grain size and enhanced diffusivity can be expected to lead to increased diffusional creep rates as well as to a significantly greater propensity for grain boundary sliding. Recent mechanical properties measurements at room temperature on nanophase Cu, Pd, and TiO2, however, give no indications of superplasticity. Nonetheless, significant ductility has been clearly demonstrated in these studies of both nanophase ceramics and metals. The synthesis of cluster-assembled nanophase materials is described and the salient features of what is known of their structure and mechanical properties is reviewed. Finally, the answer to the question posed in the title is addressed.
Processing of Nanocrystalline Ceramics
Authors: Ciftcioglu Muhsin , Mayo Merrilea J.
Published: March 2011

Methods of preparing non-agglomerated powders for three systems -- yttria, titania, and yttria-stabilized zirconia -- are reviewed. The non-agglomerated nature of these powders should make it possible to sinter them into dense ceramic bodies with nanocrystalline grain sizes. Experiments with yttria-stabilized zirconia have shown that this is indeed the case, with mean linear intercept grain sizes of 60 nm resulting from original powder particle diameters of 13 nm. This ultrafine-grained zirconia is shown, in turn, to have superplastic forming rates 34 times faster than a 0.3 μm-grained commercial zirconia of the same composition.
Grain Growth During Sintering of Nanocrystalline Y and/or CE-Doped Tetragonal Zirconia
Authors: Boutz Michel M. R. , Theunissen G. S. A. M. , Winnubst A. J. A. , Burggraaf A. J.
Published: March 2011

A non-isothermal analysis of grain growth in tetragonal zirconia ceramics doped with various amounts of yttria and/or ceria in the temperature range 700–1150°C is presented. In these nanocrystalline ceramics, prepared by the gel precipitation technique, two grain growth regimes are recognized. At temperatures up to 900–1000°C grain growth proceeds slowly at high values of porosity (55%→35%); probably by means of a surface diffusion mechanism. At higher temperatures grain growth is much faster and occurs in locally dense regions by a normal grain growth or an impurity drag mechanism. Apparent activation energies are given for five compositions in both regimes.

The isothermal sintering behavior of 3 mol% Y2O3-containing TZP at 1050°C is analysed. A dense ceramic with a crystallite size in the nanometer regime (< 100nm) is obtained.
The Role of Dislocations in the Superplastic Deformation of a Duplex Stainless Steel
Authors: Parayil T. R. , Dunlop G. L. , Howell P. R.
Published: March 2011

Transmission electron microscopy (TEM) has been employed to examine the role of dislocations in the superplastic deformation of a duplex stainless steel. In particular, matrix, grain boundary and interphase interface dislocation distributions have been documented after testing in region II. It is concluded that dislocation activity is of importance during superplastic flow and both loop sources and dislocation pile-ups have been observed. The presence of highly distorted dislocation arrays also suggests that grain and interphase boundary sliding is intimately linked to the motion of grain and interphase boundary dislocations. Finally, it is argued that dislocation multiplication in interphase interfaces can involve the operation of loop sources.
Application of a Continuous Annealing Process to the Production of Superplastic High-Carbon Steels
Authors: Seto K. , Kato T. , Abe H.
Published: March 2011

High-carbon steels with carbon content of more than 0.8wt% have been known to be superplastic by refining their microstructure. Many methods such as warm rolling have been proposed to refine the microstructure. But most of them are considered to be difficult to use as an actual production method. To make high-carbon steels superplastic and economical, application of a cold rolling and continuous annealing process has been examined.

Changes in microstructure of high-carbon hot rolled steels during the cold rolling and continuous annealing was investigated. By cold rolling with a reduction of more than 50%, a lamellar pearlite structure is deformed and heavily sheared, and a large strain energy is stored. Rapid annealing at temperatures just below the A1 temperature(1000K) is shown to spheroidize the sheared pearlite and to recrystallize the ferrite grains. After processing, the final structure consists of very fine cementite particles with 0.05–0.2μm diameter in a very fine equiaxed ferrite matrix with 0.1–0.5μm diameter. The processed steel shows total elongations of more than 700% and a strain rate sensitivity index of about 0.5 when deformed at 973K.
On the Interaction Between Moisture and Wood Fibre Materials
Authors: Salmén Lennart
Published: March 2011

The effect of water on wood fibre materials is described from the standpoint of how the water is absorbed by the individual wood polymers. The main influence on physical properties are thus associated with water acting as a plasticizing agent for lignin and carbohydrates. Effects of drying restraints on paper are discussed in relation to a molecular orientation of the constituent polymers, made possible in the vicinity of the water-induced softening points.
An Investigation of Factors Effecting Coating Structure
Authors: Kline James E.
Published: March 2011

The properties of coatings have been studied on a theoretical level using model systems of spherical polymeric pigments applied to a mylar substrate. Using binderless coatings, the expected void filling, gloss and light scattering relationships to particle size and polydispersity were observed. The addition of binders to the coatings yields results which depart from those expected and observed without binders. These results have led to two seemingly opposed views that the binder either coats the pigment and causes expansion of the structure or fills the voids without greatly effecting the pigment structure. Pigment blends were selected which were expected to show a difference between the two conflicting theories, and starch and latex binders added. The data obtained failed to favor one theory over the other, indicating that both are probably operative. Greater decreases in gloss were observed with the polymeric pigments, probably due to an undesirable interaction between the pigments and binders causing agglomeration of the coating materials and severe disruption of the coated surface. The data obtained is reviewed in light of the “real world” behavior of paper coatings to examine reasons why the theoretical contributions of pigments and binders are not often observed.
Materials Science of Lignocellulosics
Authors: Rowell Roger M.
Published: March 2011

Wood and other lignocellulosics have been used as “engineering materials” because they are economical, low in processing energy, renewable, and strong. In some schools of thought, however, lignocellulosics are not considered “materials” in that they do not have consistent, predictable, reproducible, continuous, and uniform properties. This is true for solid lignocellulosics such as wood, but not necessarily true for composites made from lignocellulosics. The chemistry of the components of lignocellulosics can be modified to produce a material with consistent, predictable, and uniform properties. Properties such as dimensional instability, biodegradability, flammability, and degradation due to ultraviolet light, acids, and bases can be altered to produce property-enhanced composites.
Preparation of In Situ Magnetically Loaded Cellulose Fibers
Authors: Ricard Serge , Marchessault Robert H.
Published: March 2011

Magnetic paper handsheets with pigment loadings in the order of 10–30%, depending on the experimental conditions, have been made using the established “lumen-loading” technology. These sheets have bulk magnetic properties comparable with the computer floppy-disk products. In order to minimize the particle size of pigments and thereby explore a new level of optical and magnetic properties, in situ synthesis of pigment particles is a second approach. This chemistry starts with a carboxymethylcellulose substrate with ion-exchange properties for Fe(ll). The substrates, before and after oxidation reactions to produce ferrite particles, are characterized by: conductimetric titration, x-ray diffraction, thermogravimetric analysis, and magnetization determination. Electron microscopy and diffraction provide insight on the ferrite morphologicals. These specialty fibers allow exploration of new concepts in papermaking, information storage, security printing and paper handling.
The Structures of Cellulose
Authors: Atalla Rajai H.
Published: March 2011

This report presents an overview of studies on the structures of cellulose. After presenting a brief historical perspective, the report reviews diffractometrically based structural models and then describes recent developments based on models that are consistent with both diffractometric and spectroscopic observations. The primary impetus for development of these models was provided by Raman and 13C NMR (CP-MAS) spectral results that could not be rationalized on the basis of classical structural models, which are constrained by diffractometric data alone. The structures derived from integrating the spectral information into the data base, which constrain the models, represent relatively small but very significant departures from those structures derived on the basis of diffractometry alone. In addition to rationalizing all the structurally sensitive information, the new models provide a basis for complementary use of spectroscopic and diffractometric methods to monitor variations of the states of aggregation of celluloses with source and history. Thus, it is now possible to investigate the effects of different processing variables, which are important in industrial practice, on both secondary and tertiary levels of structure in celluloses. These levels of structure have a major influence on the material properties of commercial celluloses, yet adequate characterization of these levels has been quite elusive.
Heteroepitaxy Between Lattice Mismatched Materials with Van Der Waals Interactions
Authors: Koma Atsushi
Published: March 2011

The lattice matching condition encountered usually in the heteroepitaxial growth has been proved to be relaxed drastically, if one uses the interface having van der Waals nature. Such interface can be realized on a cleaved face of a layered material or a quasi-one dimensional material and on a surface of a dangling-bond-terminated three dimensional material. Various kinds of heterostructures, which cannot be made by conventional growth methods, can be fabricated by using a variety of layered transition metal dichalcogenides, in which there exist superconducting, metallic, semiconducting or insulating layered materials. Moreover those heterostructures have been found to be grown on such an ordinary three-dimensional material as GaAs, if the dangling bonds on its surface are terminated by suitable atoms.
Dislocation Arrays in Epitaxial Interfaces.
Authors: Beanland R. , Pond R. C.
Published: March 2011

A method for analysing the form of dislocation arrays which accommodate misfit at epitaxial interfaces based on the Frank-Bilby expression of the dislocation content of an interface is presented. Emphasis is placed on the deformation of a crystal in the presence of a dislocation array, and ease of formulation through use of an orthogonal reference frame. Several aspects of epitaxial growth are subsequently addressed, including the uniqueness of a dislocation array accommodating a given misfit. In the case of growth on vicinal cubic surfaces, it is shown that dislocations generated to relieve misfit may also lead to misorientation of the overlayer. From experimental measurements of dislocation densities using transmission electron microscopy, it is possible to calculate the state of strain in a metastable misfitting epitaxial layer. When misfit is not isotropic in the interface (such as for silicon or niobium grown on sapphire) it is shown that dislocation line directions may not lie along low index directions in either crystal, a point which is particularly important with regard to studies of interfacial structure by high resolution electron microscopy.
Characteristics of Mocvd-Grown AlGaAs/GaAs Sqw Lasers and GaAs Mesfetsfabrication on Si Substrate with SiO2-Back Coating
Authors: Egawa Takashi , Tada Hitoshi , Kobayashi Yasufumi , Nozaki Shinji , Soga Tetsuo , Jimbo Takashi , Umeno Masayoshi
Published: March 2011

We discuss room temperature CW operation of AlGaAs/GaAs SQW lasers and GaAs MESFETs with good pinch-off characteristic on SiO2 -back coated Si. The all-MOCVD-grown,SQW laser on Si with thermal-cycle annealing, which has the EPD of 1.5 × 107 cm−2, has the threshold current as low as 55 mA (1.41 kA/cm2) under CW operation at room temperature. The pinch-off and the sidegating effect characteristics of GaAs MESFETs on Si have been improved by using SiO2-back coating of Si and higher growth temperature. The maximum transconductance of 160 mS/mm has been obtained for the MESFET with a 2.5 × 15 µm gate. The main origin of sidegating effect associates with the channel layer-undoped GaAs layer beneath it interface. The SiO2 -back coating is found effective to obtain a lower background electron concentration in undoped GaAs layer and to control doping of the active layer in GaAs/Si.
Study of the Tnfluence of Structural Properties on Si and Be Doping of Heteroepitaxial InAsSb on GaAs-Coated Si Substrates for Infrared Photodiodes
Authors: Boeck J. De , Dobbelaere W. , Hove M. Van , Vanhellemont J. , Raedt W. De , Vandervorst W. , Mertens R. , Borghs G.
Published: March 2011

The behavior of Si and Be impurities in InAsx Sb1−x (0.05<x<0.45) heteroepitaxial layers grown on GaAs-coated Si by MBE is characterised. Siis found to act as an n-type dopant for the growth conditions used. The calibration of the Si n-type doping as a function of the Sisource temperature is obtained by infrared absorption spectrometry, stripping Hall and SIMS depth profiling. At high doping levels the amphoterical characterof the Si impurities becomes evident. SIMS is used to investigate the dopant incorporation and the formation of diode structures. The influence of the mismatched epitaxy on the transport properties is investigated by stripping Hall measurements. In order to establish the correlation between crystalline properties of the epilayers and the ability to fabricate diodes, we compare the defect structure of InAs and In(As)Sb p-'i'-n diodes.
Buried Metal/III-V Semiconductor Heteroepitaxy: Approaches to Lattice Matching
Authors: PalmstrØM C.J. , Harbison J. P. , Sands T. , Ramesh R. , Finstad T. G. , Mounier S. , Zhu J.G. , Carter C.B. , Florez L.T. , Keramidas V.G.
Published: March 2011

Metallic transition metal aluminides and gallides with the CsCI structure and semi-metallic rare earth monopnictides with the NaCi structure have been grown as buried conducting layers in III-V compound semiconductor heterostructures. The criteria for achieving (100) oriented epitaxial growth on (100)111-V semiconductor surfaces is different for each class of materials. The methods used to achieve III-V/metal/llI-V heteroepitaxial structures are discussed here with emphasis on the different approaches needed for the aluminides or gallides and the monopnictides. Work producing exact lattice matching between the buried metal and surrounding semiconductor layers makes possible the separation of lattice mismatch effects from those due to other interface parameters. Results to date indicate that defect structures in the overgrown semiconductor layers arise more because of differences in crystal symmetry, interface chemistry and bonding across the interface than lattice mismatch.
The Influence of Initial Growth on Defect Generation in Mocvd Grown GaAs/Si Heteroepitaxial Layers
Authors: George T. , Weber E.R. , Nozaki S. , Wu A.T. , Umeno M.
Published: March 2011

The structural quality of GaAs/Si layers deposited directly at the normal growth temperatures (650°C,750°C) is compared with that of layers grown by the standard two-step growth process using Metalorganic Chemical Vapor Deposition (MOCVD). The directly grown layers are highly twinned and polycrystalline in nature whereas the two step growth process produces single crystal layers even at growth temperatures as high as 800°C. The origin of these effects is related to the initial growth of the GaAs, which is in the form of highly defective separate islands, for the case of direct growth, and connected single crystal islands for the case of two-step growth. The directly grown islands exhibit a “ripening” type behavior, with a strong dependence of the Si substrate surface coverage by the GaAs layer, on the growth temperature. The generation of structural defects such as stacking faults and microtwins, which destroy the epitaxial relationship could be triggered by the presence of surface imperfections on the Si substrate.
GaAs Heteroepitaxy on Substrate-Engineered Silicon Using SixGe1–x Multilayer Structures
Authors: Posthill J.B. , Venkatasubramanian R. , Malta D.P. , Hattangady S.V. , Fountain G.G. , Timmons M.L. , Markunas R.J.
Published: March 2011

The novel concept of using a SixGe1–x multilayer structure as a buffer layer between a silicon substrate and a GaAs epitaxial layer to accommodate the GaAs/Si 4.1% lattice mismatch is introduced. Initial results using a 340 nm trilayer SixGe1–x multilayer structure are presented and are critically assessed. Significant potential is demonstrated, and the work to date indicates that certain guidelines and procedures must be adhered to for this method of threading dislocation reduction to be effective.
Nucleation and Defect Structures of GaAs Films Grown on Reactive Ion Etched Si Substrates
Authors: Lee Henry P. , George Thomas , Sohn Hyunchul , Tu Jay , Weber Eicke R. , Wang Shyh
Published: March 2011

The nucleation and interfacial defect structure of thin GaAs films grown on reactive ion etched Si substrates by normal molecular beam epitaxy (MBE) and modulated molecular beam epitaxy (MMBE) at 300°C were studied by plan view and high resolution cross-sectional electron microscopy (TEM). Plan view TEM micrographs show a pronounced three-dimensional (3-d) island type nucleation for the MBE grown sample. A high density of microtwins is also found in these nucleated islands from high resolution cross-sectional TEM micrographs. The 3-d nucleation and the interfacial twinning is suppressed however in the MMBE grown samples. The FWHM of the (400) Bragg peak for 3 μm thick GaAs on Si films shows a reduction of 60 arcseconds when the initial buffer layer is grown by MMBE as compared to normal MBE.
Semiconductor Resonant Tunneling Device Physics and Applications
Authors: Reed Mark A. , Seabaugh Alan C. , Kao Yung-Chung , Randall John N. , Frensley William R. , Luscombe James H.
Published: March 2011

A discussion of resonant tunneling physics in both diode and transistor heterojunction structures is presented. It is evident the In(GaAI)As/InP system is significantly superior for this application. We also present results on resonant tunneling in lower dimensional systems.
On the Thermoelectric Power in Quantum Dots of Non-Parabolic Semiconductors in Thr Presence of a Classically Large Field
Authors: Ghatak Ktamkahya P. , De B. , Mondal M. , Biswas S.N.
Published: March 2011

We have studied the thermoelectric power in quantum dots (QDs) of non-parabolic semiconductors in the presence of a classically large magnetic field and we have taken A3N B2V, ternary chalcopyrite, II-VI and III-V semiconductors. It is found that the thermopower increases with increasing film thickness and decreasing electron concentration respectively in all the cases. The numerical values are greatest for Cd3As2 and least for InAs and the theoretical results are in ageement with the experimental observation as reported elsewhere.
X-ray Study of Interdiffusion and Strain Relaxation in Annealed (SimGen)p Atomic Layer Superlattices
Authors: Baribeau J.-M. , Pascual R. , Saimoto S.
Published: March 2011

We have studied interdiffusion and strain relaxation induced by annealing in (SimGen)p atomic layer superlattices grown by MBE using x-ray diffraction techniques. In these expertments, an interdiffusion coefficient Dλ. was determined by monitoring as a function of time, for annealing temperatures between 550° C and 700° C, the decay of the low angle first order 000 diffraction peak arising from the composition modulation wavelength ° of the superlattice. Strain relaxation was studied by measuring the angular shift of the superlattice 400 reflection on annealing. The strain was found to decrease exponentially and although most of the relaxation occurred within the first few minutes of annealing, residual strain was detected after several hours of heat treatment. During relaxation the low angle reflection peak intensity exhibited a rapid decay corresponding to an interdiffusion coefficient Dλ of the order of 5 × 10−23 m2s−1 at 700° C on structures grown on (100) Si with λ ≅ 1.5 nm. After most of the strain has been relieved, a slower linear decay rate was observed indicating a significant decrease of Dλ. The variation of Dλ with periodicity was explored and interdiffusion for structures grown on (100) Si and on Sil-xGex (0<x<l) buffers was compared.
Si/Ge Strained-Layer Epitaxy: Sil−xGex Alloy Buffer Layers and Ultra-Short Period SimGen Superlattices.
Authors: Ospelt M. , Henz J. , MÜller E. , KÄnel H. Von
Published: March 2011

Sil−xGex alloy layers and ultra-short period SimGen superlattices on alloy buffer layers of the same concentration have been grown by MBE. The superlattices as a whole have been shown to have the lattice constant of the underlying alloy buffer layer, the individual Si and Ge layers being fully strained. Samples with a graded Ge content have been used to study the relaxation as a function of Ge content by means of X-ray diffraction and RBS and channeling.

Transmission electron spectroscopy reveals that interface roughness is not simply statistical in these superlattices. Rather, electron diffraction shows additional features from a period doubling in the (111) directions, indicating that a corresponding interfacial ordering occurs. These features show 2- or 3-dimensional behavior depending on the thickness of the Si and Ge layers in the superlattices. Annealing studies show these features to persist even for annealing temperatures where the superlattices disintegrate into alloys.