bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion Bonding of Superplastic 7075 Aluminum Alloy
Authors: Yan Huang , Jianzhong Cui , Longxiang Ma
Published: March 2011

Because of the presence of surface oxide films, aluminum alloys are very difficult to join by diffusion bonding processes when there are no interlayers between mating surfaces. In the present investigation, the diffusion bonding of superplastic 7075 aluminum alloy has been carried out using a special method for surface treatment in the temperature range 500∼520°C, at pressures of 2.07∼3.OMPa, times of 90∼150min and a vaccum of 1×10−5torr. The joint strength obtained is the same as the base metal strength of the alloy, and the joint microstructure is indistinguishable from that of the base metal. In this paper, the effect of the superplastic treatment of the alloy on the bonding process is discussed, and it is proposed that the bonding mechanism is the migration of the initial bond interface caused both by the diffusion of atoms and by the growth of grains during the diffusion bonding process.
Developement of SPF and SPF/DB Techniques for Ti and Al Alloys and their Applications
Authors: Wenhai Ji , Zhenguo Wang , Feiling Song
Published: March 2011

This paper deals with the new development of both SPF of an Al alloy and SPF/DB of an Ti alloy.

Based on a theoretical model, a pressure versus time curve was determined for optimizing the SPF parameters. The effects of applied back pressure and reverse billowing on the performance of 7475 and Al-Cu-Li-Mg-Zr alloys are discussed.

Some essential technological factors which affect the quality of the SPF/DB of the Ti-6A1–4V alloy have been studied, such as the effect of an o layer on the strength of the base metal, the gas filling method and the pre-forming of parts with curved surfaces etc. Examples of applications to the manufacturing of airplane spars and undercarriage doors are also shown in this paper.
Mechanical Properties of TiAl and (TiAl+Ti3 Al) Alloys Produced by Mechanical Alloying
Authors: Ochiai S. , Kobayashi M. , Michimura K.
Published: March 2011

Two representative titanium aluminides containing 48 and 52 at. pct Al were produced by a mechanical alloying (MA) process for the purpose of attaining fine microstructures. For the MA apparatus, an attritor mill and a conventional ball mill were both used and the results compared. Mechanically alloyed powders were consolidated by hot pressing. In addition to morphological changes in the powders during MA, microstructures and mechanical properties of the consolidated products were studied. In particular, the MA alloy with 48 at. pct Al comprised of both TiAl and Ti 33Al phases showed a high strain rate sensitivity exponent, above 0.3. This suggests a possibility of developing superplastic deformation.
Microstructure Change During High Strain Rate Superplastic Deformation in a PM 7475 AL-0. 7ZR Alloy
Authors: Matsuki K. , Tokizawa M. , Murakami Y.
Published: March 2011

Improvements of superplasticity in the high strain rate range have been achieved in a 7475 Al alloy with 0. 7 wt% Zr produced from rapidly solidified powder (PM7475-0.7Zr alloy), and the superplastic properties and microstructural changes with strain have been investigated.

The PM 7475-0.7 Zr alloy has a cold rolling structure, but on heating to the superplastic temperature of 520°C, the alloy developed a very fine subgrain structure of average subgrain size of less than 1 μm. The fine structure was stabilized with metastable cubic Al3Zr precipitate dispersions, and there exist a large number of less than 5° misorientation subboundaries together with a small number of highly misoriented ones.

After 117% strain at the high strain rate of 2. 5×10−1 S−1 the subboundaries with the misorientation of 5° – 15° Were observed to increase. During the initial stage of the deformation, m value and the contribution of boundary sliding to the deformation also increased with strain, and thus the alloy behaved superplastically during the following deformation.

The improvements of superplasticity with strain in the early stage of the high strain rate deformation of the alloy were interpreted to be closely related with the increase in misorientation of subboundaries stabilized with finely dispersed metastable Al3Zr precipitates.
The Effect of Cerium on Superplasticity of AL-6CU-0.35 MG-0.2ZR Alloy
Authors: Jingtao Wang , Qingling Wu , Jianzhong Cul , Haitao Zhou
Published: March 2011

The effect of Cerium addition on the superplasticity of Al-6Cu-0.35Mg-O.2Zr alloy is investigated. The superplastic elongation of the alloy is increased from 450% to 500–700% by the addition of 0.5wt% Cerium, with some decrease in superplastic tensile resistance, when the alloy is deformed at 789K(516°C) with a strain rate of 8.33×10−4S−1. Microstructure observation shows that the addition of Cerium decreases the grain growth rate both in static annealing and during superplastic deformation. This is considered to be the result of the enhanced pinning of fine Zirconium-rich precipitates and the additional pinning of Cerium-rich phase particles. TEM and X-ray diffraction analysis show that Cerium in the alloy forms Cerium-rich phases (AlgCu4Ce and Al4CuCe), and these phase particles join in the pinning of second phase particles on grain boundary, stablizing the microstructure. The addition of Cerium also affects the distribution of Zirconium and Zirconium Aluminide in the alloy.
Observations on Historical and Contemporary Developments in Superplasticity
Authors: Sherby Oleg D. , Wadsworth Jeffrey
Published: March 2011

The history of superplasticity is reviewed. The first scientific observation of superplasticity dates back to 1912. Sporadic reports of subsequent observations appear in the literature up to the review by Underwood in 1962. Since that time there have been a number of milestone achievements that have propelled the technology of superplasticity forward. These include commercial developments based on nickel, titanium, iron, and aluminum alloys. In more recent times the advent of superplasticity in ceramics and intermetallics has stimulated yet further interest in the field. At the present time there are major research efforts underway in the USA, USSR, Japan, China, and Europe to apply superplastic forming technology to the manufacture of complex components.
Microstructures, Grain Boundaries and Superplasticity in Fine Grained Ceramics
Authors: Carry C.
Published: March 2011

Deformation studies in compression and in tension have clearly shown evidence for superplasticity for a wide range of fine grained ceramics from both macroscopic and microscopic points of view. The main purpose of this paper is to focus attention on chemical effects in ceramic grain boundaries which can lead to a great variety of behavior. Grain boundary segregation or precipitation, residual impurities or doping elements, and glassy or liquid phases at grain boundaries can strongly affect the macroscopic flow properties of superplastic fine grained ceramics. Some microstructural and grain boundary features, mainly in two oxide materials (alumina and yttria doped zirconia), are analyzed, compared, and discussed in connection with their observed superplastic behavior. Special attention is devoted to the relation between the overall chemistry of the materials (impurities and doping elements) and to the grain boundary structure and chemistry (segregation, precipitation, intergranular phases). Some consequences and implications on the tailoring of ceramic microstructures for superplasticity are discussed. In addition, some recent hot forming and hot bonding experiments are also reported.
An Investigation of the Mechanical Behavior of a Superplastic Yttria-Stabilized Zirconia
Authors: Ma Yan , Langdon Terence G.
Published: March 2011

Experiments were conducted to determine the mechanical characteristics of an yttria-stabilized tetragonal zirconia containing 3 mol % Y2O3. Specimens were pulled in tension at elevated temperatures over a range of strain rates. It is demonstrated that this material exhibits good superplastic ductility, with tensile elongations >100% when the tests are conducted at low strain rates. Internal cavities are formed during deformation and it is shown that the cavitated area decreases with decreasing strain rate. At fast strain rates, of the order of 10−3 s−1, the cavities tend to link preferentially in a direction perpendicular to the tensile axis.
Superplastic Properties of Hipped and Extruded Iron Carbide
Authors: Kim W. J. , Ruano O. A. , Wolfenstine J. , Frommeyer G. , Sherby O. D.
Published: March 2011

Hipped and extruded materials were prepared from atomized-powders containing 5.25C, 1.5Cr and balance Fe. The materials consist of a matrix of 80 volume percent of iron carbide and 20 volume percent of a discontinous iron base phase. Both processed materials were reduced in thickness (6:1) at 720°C. The grain size was about 2 μm for the hipped-and-pressed material and about 4 μm for the extruded-and-pressed material. Compression tests were used to evaluate the strain-rate-sensitivity exponent, m, in the temperature range from 725°C to 950°C, over the strain rate range of 10−5 to 2 × 10−2 s−1. The as-hipped material does not exhibit superplastic behavior because the grain shape is not equiaxed. At low stresses, in the superplastic range (m≈0.5), the hipped-and-pressed material was weaker than the extruded-and-pressed material as a result of the fine grain size. At high stresses, when slip dominates the deformation process, m is about 0.2 and a reversal in the relative strength is obtained. Tensile tests were performed and elongations in excess of 600% were achieved. The hipped-and-pressed material was shown to be more ductile than the extruded-and pressed-material which is attributed to its fine grain size.
Superplastic Hobbing of Die Cavity and Its Numerical Simulation
Authors: Kaifeng Zhang , Wang Z. R. , Dianjian Guo , Yanwu Xu
Published: March 2011

In this paper, the superplastic and isothermal hobbing process for manufacturing die cavities is described. The technical parameters, the design method of the set-up and the lubrication are also mentioned. Recently, these technologies have been applied in hobbing automobile link rod dies and other parts. By means of finite element analysis and experiments, the deformation paramaters for superplastic hobbing are obtained. They can be used in determining the process and choosing the blank sizes.
A Re-Appraisal of Cavity Growth Processes in Superplasticity
Authors: Ma Yan , Langdon Terence G.
Published: March 2011

It is well known that cavities are nucleated and grow during the superplastic deformation of many materials. The various theories for cavity growth are examined with special emphasis on the role of growth by diffusion. It is demonstrated that the normal model for the diffusion growth of cavities is inadequate for superplastic materials when the grain boundary lengths are very small. By developing a new model for the growth of an isolated cavity to sizes exceeding the grain size, it is shown that the diffusion process may play a major role in cavity growth under a range of experimental conditions.
Lignins: Structure and Distribution in Wood and Pulp
Authors: Obst John R.
Published: March 2011

Lignin is the stuff that makes trees “woody.” Usually constituting from one-fifth to one-third of wood, lignin strongly influences its chemical and physical properties. A major use of wood is for the production of pulp for paper and paperboard products. The residual lignin in pulp fibers greatly affects paper properties and, therefore, the uses of these pulps.

Lignin is a rather unusual substance. Polymerized through radical coupling of propenylphenols, it forms several types of interunit bonds and a three-dimensional network may result. The lignin of gymnosperms (softwoods) is made up mostly of a single monomer type. As a result, the lignins of gymnosperms do not differ much from species to species. However, the lignins of angiosperms (hardwoods) do vary considerably among species because these lignins are derived from two monomer types which are often present in differing proportions. Furthermore, the ratio of monomer types may vary among different cell types and between cell regions within a species.

This review, intended mainly for those unfamiliar with the details of lignin chemistry, will provide an overview of the formation, structure and distribution of lignins in wood and of the distribution of lignin in pulp fibers.
Fibre Quality Factors in Papermaking — I The Importance of Fibre Length and Strength
Authors: Seth R.S.
Published: March 2011

Independent effects of fibre length and strength on the properties of pulp, and on the physical properties of the dry sheets have been demonstrated. Apart from improving formation, which indirectly influences many sheet properties, reducing fibre length has little direct effect on the sheet structural and optical properties, but does reduce mechanical properties. The loss in fibre strength also has little direct effect on the sheet structural and optical properties, but severely reduces those mechanical properties which are controlled by the breaking of fibres. Implications for market pulps are discussed.
The Differences Between Sonically and Mechanically Determined Elastic Moduli of Paper
Authors: Batten George L.
Published: March 2011

This paper examines the differences between sonically- and mechanically-determined paper elastic moduli. Four factors are examined for their contributions to observed differences. Two factors, thermodynamics and the low frequency approximation, relate to the sonic method; the other two factors, load cell stiffness and paper viscoelasticity, relate to the mechanical method. When all four factors are given proper consideration, the differences between the two methods are reduced to the order of experimental error. Quantitative relationships between the two moduli are given.
The Structure and Properties of Vicinal Water
Authors: Etzler Frank M. , Conners James J. , Ross Russell F.
Published: March 2011

The properties of water near surfaces are known to differ from those of the bulk. For instance, in 140 A diameter silica pores the density has been found to be 3% lower than that of the bulk while the heat capacity is 25% greater than that the bulk. Etzler [15] has proposed a statistical thermodynamic model for vicinal water. This model has been able to correlate a number of thermodynamic properties of water in silica pores. Furthermore, some of the microscopic implications of the model have been found to be consistent with molecular dynamics simulations. Here we discuss the results of a statistical geometric analysis of a molecular dynamics simulation which, as first suggested by Roentgen (1892), indicates that water indeed exists in “bulky” and “dense” states. Furthermore, recent results concerning the temperature dependence of the heat capacity of water in silica pores is discussed.
Effect of Synthetic Fiber and Binder Addition on the Strength Losses Associated with Corrugating Medium
Authors: Waterhouse John F.
Published: March 2011

The investigation is concerned with strategies to reduce losses in medium compressive strength during corrugating.

Medium handsheets with a non-random fiber orientation were made using a NSSC pulp and different levels of synthetic fiber addition, including glass and Kevlar pulp, at two levels of wet pressing. Corrugating was performed using a concora fluter, and compressive strength measurements were made in the tip and flank regions of the corrugated medium.

Forming losses are reduced by increased wet pressing with a greater improvement in the flank than the tip region of the flute. A small reduction in tip forming losses is found, for a given furnish when a film forming latex is used. However, a greater reduction is evident when a non-film forming latex is employed.

Forming loss measurements were also made on non-bonded and bonded laminates. The non-bonded laminates resulted in much lower forming losses, while the heat-activated laminates resulted in large forming losses similar to those found with conventional medium.

These experiments suggest that forming losses can be reduced if cost-effective systems are designed which do not activate until the fluting process is complete.
Chitosan-Coated Fibers for Use in Papermaking
Authors: Allan G. G. , Carroll J. P. , Hirabayashi Y. , Muvundamina M. , Winterowd J. G.
Published: March 2011

Chitosan was precipitated onto wood pulp, glass and polypropylene fibers suitable for papermaking. The coating which formed on the fibers was characterized by photomicrography after the formation of colored derivatives, and by scanning electron microscopy. The most uniform and adherent coatings were formed on the wood pulp fibers and the least were formed on the polypropylene fibers. Paper handsheets were readily formed from the chitosan-coated wood pulp and glass fibers, but not from the chitosan-coated polypropylene fibers.
A New Emphasis in Strategies for Developing Lignin-Based Plastics
Authors: Dutta Sunil , Sarkanen Simo
Published: March 2011

Lignins, a truly abundant group of biopolymers exhibiting some significant diversity, are usually thought to be constituted by a random proportionate distribution of ten different linkages between p-hydroxphenylpropane units. Over 20 million tons of kraft lignin derivatives are produced annually in the United States by the pulping industry, but 99.9% of these aromatic polymeric materials are consumed as fuel. Such industrial byproducts are generally viewed as being almost hopelessly complicated mixtures of partially degraded and condensed chemical species. However, a very different picture has begun to emerge from a more coherent understanding of the physicochemical behavior exhibited by kraft lignin preparations. Noncovalent interactions between the individual molecular components under a variety of solution conditions orchestrate pronounced associative processes that are characterized by a remarkable degree of specificity. Their consequences may be readily observed both size-exclusion chromatographically and electron microscopically, and are reflected in an anomalous variation of glass transition temperature, Tg, with molecular weight of paucidisperse kraft lignin fractions. How these effects may influence the mechanical properties of lignin-based polymeric materials is presently being scrutinized at the University of Minnesota.
Heteroepitaxy of Inp on Si for Optical Devices
Authors: Mori Hidefumi , Sugo Mitsuru , Tachikawa Masami , Itch Yoshio , Yamaguchi Masafumi
Published: March 2011

In situ measurements of dislocations at growth temperature have been made on the heteroepitaxial systems of GaAs/Si and GaP/Si. It was found that the etch pit densities of heteroepitaxial layers were as low as those of bulk wafers at the growth temperature and increase to 107 cm−2 when the layers cool down to room temperature. This means that the thermal stress determines the quality of heteroepitaxial layers.

The InP on Si system, in which the thermal expansion coefficient difference is smaller than other heteroepitaxial systems, has been studied. High quality InP has been obtained using a GaAs buffer layer, strained-layer superlattice insertion, and thermal cycle annealing and regrowth. Full width at half maximum of X-ray rocking curve was 110" at 13 µ thickness.

An InGaAsP laser diode emitting at 1.55 µm was successfully made on Si. The threshold current was 46 mA at room temperature for a ridge waveguide laser with a 4 µm width and a 200,µm cavity length.
In-Situ Patiterning and Regrowth of InP Based Heterostructures using a Native Oxide Mask
Authors: Wang Y. L. , Harriott L. R. , Temkin H.
Published: March 2011

We have successfully used an ultrathin (20-50 Å) native oxide layer on the surface of InP as an etch mask for transferring patterns onto the substrate. The oxide mask is grown in situ in O2 atmosphere, and the mask pattern is created by locally removing the oxide with a focused ion beam. Depending on the thickness of the mask, the required ion dose varies from 2×1014 to 2×1015 Ga/cm2. C12 etches the exposed areas selectively. Features as deep as 3 microns have been produced with such an ultrathin mask. High quality InGaAs and InP epitaxial layers have been overgrown on such patterned substrate. We have studied the formation and desorption of the oxide mask with Auger analysis. We also demonstrate that the secondary charged particle emission from a substrate during ion exposure provides a useful signal for the determination of the required dose.
Defects in Mbe-Grown GaAs/ScxEr1–xAs/GaAs Layers
Authors: Zhu Jane G. , Palmstrdøm Chris J. , Carter C. Barry
Published: March 2011

The microstructure and the structure of defects in GaAs/ScxEr1–xAs/GaAs (x=0 and 0.3) heterostructures grown on (100) GaAs substrates by molecular beam epitaxy have been characterized using transmission electron microscopy. The top GaAs layer forms islands on ScxEr1–xAs at the initial growth stage, and the area covered by GaAs varies with the growth temperature. In addition to regions of epitactic (100) GaAs, regions of {122}- and (111)-oriented GaAs are observed on (100)-oriented ScxEr1–xAs. A high density of stacking-fault pyramids is found in epilayers of GaAs grown on a thin epilayer of ErAs, where the ErAs layers are only one or two monolayers thick. The apex of each stacking-fault pyramid is located at the ScxEr1–xAs/GaAs interface.
InGaAs/AWAsSb Heterostructures Lattice-Matched to InP GRown by Molecular Beam Epitaxy
Authors: Nakata Y. , Sugiyama Y. , Inata T. , Ueda O. , Sasa S. , Muto S. , Fujii T.
Published: March 2011

We have successfully grown InGaAs/AIAsSb quantum-well (QW) structures lattice-matched to InP by molecular beam epitaxy for the first time. We studied the band-edge discontinuity and the interface abruptness of these heterostructures. A cross-sectional lattice image of InGaAs/AlAsSb QWs taken along the [100] axis showed atomically smooth heterointerfaces. The photoluminescence (PL) peak energy of the 20-nm-thick InGaAs well (0.758 eV) was lower than that of InGaAs bulk (0.799 eV), indicating that the InGaAs/AlAsSb system has a staggered lineup. The conduction band-edge discontinuity, ΔEc, was evaluated to be 1.74 ± 0.04 eV, which was derived from parameter fitting to the 4.2 K PL peak energy shifts of QWs as a function of InGaAs well width between 2.1 nm and 20 nm. The corresponding valence band-edge discontinuity, ΔEv, was 0.07 ± 0.02 eV. We also fabricated a resonant tunneling barrier structure of InGaAs (4.4 nm)/AlAsSb (2.9 nm), and obtained a very high peak-to-valley current ratio of 15 at 300 K.
Rapid Thermal Chemical Vapor Deposition: Selective Epitaxial Silicon Growth (SEG)
Authors: Osenbach J. W. , Ku Y. H. , Kermani A.
Published: March 2011

Rapid Thermal Chemical Vapor Deposition (RTCVD) offers great promise for deposition of high-quality, thin, abrupt interface epitaxial films. In addition, RTCVD systems operate under cold wall environment to minimize particles and cross contamination. SEG of silicon provides both isolation and active device wells with fine dimensional control. A combination of RTCVD and SEG holds great promise for future VLSI circuit technologies. In this paper, we present our results on selective growth of single crystal silicon using RTCVD.
Optical Approaches to Real-Time Analysis and Control of Crystal Growth
Authors: Aspnes D. E.
Published: March 2011

A variety of optical methods are now available for studying surface processes and for monitoring layer thicknesses and compositions during semiconductor crystal growth by molecular beam epitaxy (MBE), organometallic chemical vapor deposition (OMCVD), and related techniques. Spectroellipsometry (SE) and spectroreflectometry (SR), the older, primarily bulk-sensitive probes, are now augmented by new, primarily surface-sensitive probes such as reflectance-difference spectroscopy (RDS), second-harmonic generation (SHG), and laser light scattering (LLS). Examples of real-time growth studies now include SE determinations of thicknesses and compositions of AlxGa1–xAs layers on GaAs by organometallic molecular beam epitaxy (OMMBE) to 10 Å thickness scales, RDS determinations of surface dielectric anisotropy spectra of various (001) GaAs surfaces relevant to crystal growth by MBE, and LLS determinations of the evolution of surface roughness during chemical vapor deposition (CVD) growth on Si. Proven capabilities suggest new applications, particularly to growth-interrupted and metastable systems.
Heteroepitaxy of Ge on Vicinal Si(100)
Authors: Krishnamurthy Mohan , Drucker Jeff S. , Venables J.A.
Published: March 2011

The initial stages of germanium heteroepitaxy on vicinal Si(100) have been studied using in-situ deposition in a UHV STEM. Germanium was deposited using molecular beam techniques onto substrates misoriented 1° and 5* toward <110> held at room temperature, 375°C and 525°C. Film thicknesses were in the range 4-6 ML, just greater than the stable intermediate layer of 3-4ML (1ML = 0.14nm). The Ge clusters were observed using biassed secondary electron (b-SE) imaging with nanometer resolution. Comparisons were made between deposition at the elevated temperatures, and room temperature deposition followed by anneals at the same temperatures.

Annealing the low temperature deposits produces coarsening of the islands which is similar on the 1° and 5° samples. Island size distributions and other film growth parameters obtained from the 375°C and 525°C anneals indicate that the coarsening is different at these temperatures and is possibly affected by instabilities in the intermediate layer. Results of the high temperature depositions indicate that neither surface steps nor the edges of islands act as perfect sinks, and that diffusion distances are of the order of several microns. The nucleation density and size distributions are markedly different for deposition at 375°C and 525°C possibly due to competitive capture at strong sinks.

In a parallel set of experiments in a standard UHV chamber, macroscopic wafer samples were analyzed with RHEED, Auger and secondary electron spectroscopy. These correlate well with the intermediate layer thicknesses previously reported in the literature, and the large contrast observed in the b-SE images. Ex situ TEM studies of samples grown in this chamber show islands with various contrast features including those of coherent strain.
An Electron Microscopic Characterization of Mbe-Grown ZnSe/CaAs and ZnSe/Ge Heterointerfaces
Authors: Sant S.B. , Smith R.W. , Weatherly G.C.
Published: March 2011

Molecular beam epitaxy (MBE) grown ZnSe/GaAs and ZnSe/Ge heterointerfaces have been studied by transmission electron microscopy (TEM). Defect characterization of cross-sectional and planar specimens showed that ZnSe epitaxial films contain numerous twins that predominantly arise at the interface. Planar specimens of ZnSe/Ge were in-situ TEM annealed, for 5.5 hours at 873K. The twins are thermally very stable which would indicate that they arise during the growth process. The occurrence of these twins in the ZnSe film is explained by nucleation and growth of normal and twinned nuclei. Some of the ZnSe films grown on (10O)Ge substrates have low-angle boundaries indicating that the initial growth of the film is by the formation of islands.
Strain Relaxation Mechanisms in Lattice Mismatched Epitaxy
Authors: Hull R. , Bean J.C. , Bonar J.M. , Peticolas L.
Published: March 2011

The relaxation of strained epitaxial layers by the introduction of misfit dislocations is reviewed. Current theoretical and experimental understanding of the nucleation, propagation and interaction of misfit dislocations are summarized. The ramifications for applicability of strained layer epitaxy to practical device structures are discussed.
Rapid Thermal Oxidation of GeSi Strained Layers
Authors: Nayak D. K. , Kamjoo K. , Park J. S. , Woo J. C. S. , Wang K. L.
Published: March 2011

A cold-wall rapid thermal processor is used for the oxidation of commensurately grown GexSi1−x layers on Si substrates. It is shown for dry oxidation that the oxidation rate of GeSi is the same as that of Si. The dry oxidationrate of GeSi is independent of Ge concentration (up to 20 % considered in this study) in the GeSi layer. For wet oxidation, however, the rate of oxidation of the GexSi1−x layer is found to be significantly higher than that of pure Si, and the oxidation rate increases with the Ge concentration in GexSi1−x layer. Employing highfrequency and quasistatic Capacitance-Voltage measurements, it is found for a thin oxide that a fixed negative oxide charge density in the range of 1011 – 1012/cm2, and the interface trap level density (in the mid-gap region) of about 1012 /cm2.eV are present. Further, the density of this fixed oxide charge at the SiO2 /GeSi interface is found.to increase with the Ge concentration in the commensurately grown GeSi layers.
Properties of Interfaces between Superlattice Heterostructures and Uniform Alloy Materials as Realized by Impurity Induced Disordering
Authors: Thornton R. L. , Ponce F. A. , Anderson G. B. , Chung H. F.
Published: March 2011

In this paper present experimental results on the quality of AIGaAs material after high concentrations of impurities have been introduced for the purpose of impurity induced disordering. A comparison between Zn and Si diffusion is presented, and the nature of the transition region between uniform alloy and as-grown periodic structure has been characterized both experimentally and theoretically. Device implications of these observations is discussed.
Microtomy of Large Particle Zeolites for Tem
Authors: Ulan J. G. , Schooley C. , Gronsky R.
Published: March 2011

Uniformly thin specimens of powders, suitable for electron microscopy, can be prepared by ultramicrotomy. There is a size limit to the particles that can be studied since larger particles tend to be dislodged from the available resins when microtomed. A method is described to strengthen the binding of the organic resin to the inorganic zeolite, allowing large particles to be sectioned. The particle size limit increased from 3 μm to greater than 20 gim in diameter for FeZSM-5 aggregates. This method can be applied to a variety of oxide powder samples, extending the utility of microtomy as a materials science tool.
Preparation of Cross Sectional TEM Samples Using Lithographic Techniques and Reactive Ion Etching
Authors: Wetzel Jeffrey T. , Kavanagh K. L.
Published: March 2011

This paper summarizes methods used to create cross-sectional samples for transmission electron microscopy and introduces another variant of the technique all of which rely upon some combination of lithographic patterning and reactive ion etching. The basic idea pursued in using these techniques was to form, from a preselected location, samples that had a large transparent area without use of mechanical polishing or ion milling. Samples were successfully prepared in this manner, but room for improvement remains due to the limited range of diffraction conditions available for imaging or diffraction pattern formation.
Chemically Assisted Ion Beam Etching (CAIBE)- a New Technique for TEM Specimen Preparation of Materials
Authors: Alani Reza , Jones Joseph , Swann Peter
Published: March 2011

Chemically assisted ion beam etching (CAIBE) is widely practiced in the semiconductor industry. In the electron microscopy field, the CAIBE technique offers a new method for preparing specimens that are difficult to make by conventional inert gas milling techniques, e.g. indium containing type III-V compound semiconductors. CAIBE employs a collimated, molecular beam of a reactive species, e.g. iodine in combination with a conventional inert gas fast atom beam for thinning TEM specimens. CAIBE should not be confused with reactive ion beam etching (RIBE) which takes a chemically active species (e.g. iodine) and converts it into a beam of fast ions directed at the sample. CAIBE has three major advantages over (RIBE): i) corrosion of the ion gun components does not occur, ii) much smaller quantities of reactive gas are required and hence pump maintenance and pollution problems are minimized, iii) a wider range of chemicals may be used. Superior results are obtained if CAIBE is done on only one side of the specimen at a time. This is achieved using a new type of specimen holder post which enables very low angle milling and minimizes specimen contamination by sputtering from the holder. This new technique is described and results from iodine CAIBE milling, iodine RIBE milling and argon ion milling are compared for InP, InSb and GaAs as well as metals like tungsten. Also, the beneficial effects of very low angle (∼1°) argon ion milling in preparing specimens of silicide containing Si based IC wafers is reported.
Radiation Damage and its Annealing in Semiconductors
Authors: Narayan J. , Fletcher J.
Published: March 2011

Residual damage in the form of point defect clusters and amorphous regions has been investigated in ion and neutron irradiated silicon specimens. Annealing of this damage during conventional heating, flame annealing, and pulsed laser irradiation has been studied by plan-view and cross-section electron microscopy techniques. These results provide detailed information on annealing mechanisms, and emphasize the characterization of damage in the as-irradiated state.
Reduction of α-Particle Sensitivity in Dynamic Semiconductor Memories (16K d-RAMs) by Neutron Irradiation
Authors: Thompson Charles E. , Meese J. M.
Published: March 2011

Trace radioactive impurities found in all semiconductor devices induce soft errors in semiconductor memories by α-particle emission. Data taken on 16K d-RAMs which have been fast neutron irradiated to fluences from 1013 to 1016 n/cm2 show that soft errors in these devices can be significantly reduced while maintaining acceptable device operation. Reduction in soft error rate by factors as high as 80 are observed following irradiation and thermal annealing. The effect on device parameters is discussed as well as the defects responsible for this beneficial radiation processing. Estimates of the soft error rate improvement to be expected on higher density memory devices (64K and 256K d-RAMs) will also be presented.
Silicon-Sapphire Interface: A High Resolution Electron Microscopy Study
Authors: Ponce Fernando A.
Published: March 2011

The structure of the silicon-sapphire interface of CVD silicon on a (1102) sapphire substrate has been studied in crøss section by high resolution transmission electron microscopy. Multibeam images of the interface region have been obtained where both the silicon and sapphire lattices are directly resolved. The interface is observed to be planar and abrupt to the instrument resolution limit of 3 Å. No interfacial phase is evident. Defects are inhomogeneously distributed at the interface: relatively defect-free regions are observed in the silicon layer in addition to regions with high concentration of defects.
The Effect of Carbon on the Precipitation of Oxygen in Czochralski Silicon
Authors: Pinizzotto R. F. , SCHAAKE H. F.
Published: March 2011

Researchers in both the U. S. and Japan have reported that carbon impurities can significantly alter the precipitation of oxygen in CZ silicon. We have employed FTIR, x-ray topography and TEM to study this phenomenon in silicon containing < 2 × 1016 C cm−3 or 1.3 × 1017 C cm−3. A single step anneal of 16 hours at 1000°C will cause oxygen precipitation to occur in the high carbon material, while a 32 hour pre-anneal at 600°C is necessary for precipitation in the low carbon material. If a single anneal of 120 hours at 750°C is used, light precipitation occurs in both types of material. A pre-anneal of 15 minutes at 1000°C followed by 120 hours at 750°C reduces precipitation in the high carbon material only slightly, but completely eliminates precipitation in the low carbon material. It can be concluded that carbon causes heterogeneous nucleation of oxygen precipitation in CZ silicon and it is proposed that it does so by lowering the interfacial energy of the precipitates.
Investigation of Defect Concentration Distributions in Ion-Implanted and Annealed GaAs
Authors: Wang K.L. , Li G.P. , Asbeck P.M. , Kirkpatrick C.G.
Published: March 2011

Uncapped and Si3N4-capped annealing of GaAs grown with the horizontal Bridgman technique was investigated with deep-level transient spectroscopy. Electron trap concentration distributions were measured with a reduced noise DLTS system to ensure reliable data. Ion implantation using Se ions both prior to capping and through a Si3N4 cap was carried out. The evolution of defect energy levels and the changes in concentration distributions with anneal temperature were studied. It is concluded that the defects residing in the probed space-charge region can be annealed out with a Si3N4 cap at a temperature higher than 750 C.
Thermoelectric Power of Graphite Acceptor Compounds
Authors: Sugihara Ko
Published: March 2011

Temperature variations of the thermopower (TEP) of acceptor graphite intercalation compounds (GIC) are very different from that of pristine graphite. At low temperatures the TEP increases monotonically with T, then levels off above 150 K. This behavior is ascribed to the phonon drag effect. In the region where the TEP is nearly constant, phonon relaxation is mainly controlled by the Rayleigh scattering due to point defects or impurities. This process leads to T-independent phonon drag TEP. The importance of Rayleigh scattering is due to the large cross section diameter of the Fermi surface in GIC. At low temperatures where the boundary scattering becomes important, the TEP is proportional to T3 . Detailed calculations are carried out by solving the phonon-carrier coupled Boltzmann equation.
Low Field Galvanomagnetic Properties of Graphite Acceptor Compounds and their Relation to Trigonal Warping
Authors: Sugihara Ko
Published: March 2011

In first stage graphite intercalation compounds with cylindrical Fermi surfaces and isotropic relaxation times, no magnetoresistance occurs. Holzwarth pointed out that trigonal band warping provides a finite magnetoresistance in first stage compounds. A calculation of the galvanomagnetic coefficients of stage-2 acceptor compounds is performed including the effect of trigonal warping on the bands. In the present problem a perturbation calculation provides a good approximation. Without trigonal warping, the stage-2 compounds exhibit a finite magnetoresistance since they have two kinds of holes. Retaining terms up to order (γ3/γ0)2, the weak field magnetoresistance is calculated in limit H→0; Δρ/ρoH2 ≍ (e/h2c)2 (τ/EF)2 (3γ0b/2)4[1/4(γ1/EF)2+57/2(γ3/γ0)2] where b = 1.42 Å is the nearest C-C distance, EF the Fermi energy and τ the carrier relaxation time. The first term in curly brackets is due to the existence of the two kinds of holes. This formula indicates that the term due to trigonal warping is much larger than the other term.
The Chemistry and Characteristics of Nitric Acid-Graphite Intercalation
Authors: Su Sophia R. , Oblas Daniel W.
Published: March 2011

Gas-phase intercalation of graphite by nitric acid is a one-step process. The weight uptake of the sample is a function of nitric acid vapor pressure. A pure second stage compound was formed when the HNO3 reservoir was maintained at 17°C. Only a fourth stage compound was formed when the acid was kept at 0°C. The product gases due to intercalation and gas species evolved during deintercalation were analyzed by mass spectrometry. NO2 and H2O were the major components detected from the intercalation product gases. A small amount of oxygen was also present. The existence of O2 is probably due to the photo-chemical decomposition of nitric acid. As such, the photodecomposition of nitric acid is not a contributory factor in the intercalation chemistry.
Electrochemical Characteristics of Graphite Intercalation Compounds With Fluorine-Lithium Cells
Authors: Watanabe Nobuatsu , Touhara Hidekazu , Nakajima Tsuyoshi
Published: March 2011

The discharge reaction mechanism for two types of graphite fluorides, (CF)n and (C2F)n cathodes of lithium cells utilizing a 1 M LiClO4-propylene carbonate (PC) system were studied by means of x-ray diffraction, ESCA, NMR and transmission electron microscopy. It has been revealed that the discharge reaction proceeds through the formation of an intermediate solvated ternary compound of (C·F·Li)·PC or (C2· F·Li)·PC, and then they decompose to graphite with low crystallinity and LiF. The decomposition process is not involved in the electrochemical reaction and this discharge reaction infers the open-circuit voltage of cells. New graphite intercalation compounds, CxF(MFn)y(MFn=AIF3, MgF2) were prepared under a fluorine atmosphere of 1 atm in the temperature range between 20 and 400°C. These compounds are highly stable even in moist air and have high electrical conductivity. The discharge potentials of CxF(MFn)y-lithium cells are 2.5–2.8 V at current densities 40–400μA, which are higher than those of (CF)n or (C2F)n-lithium cells below 300μA.
Diffusive Motion of Alkali Atoms in Graphite: A Quasielastic Neutron Scattering Study
Authors: Zabel H. , Magerl A. , Rush J.J. , Dianoux A.J.
Published: March 2011

We have studied the diffusive motion of alkali atoms in thermodynamic equilibrium in RbC24 by quasielastic neutron scattering. The neutron spectra show Lorentzian line profiles. The widths increase with increasing temperature. In addition a ‘de Gennes’ narrowing is observed at Q=1.2 Å-1, which coincides with the first peak in the intercalant structure factor. The narrowing becomes more pronounced at higher temperatures in contrast to a normal liquid. The data can be interpreted by the motion of clusters of alkali atoms rather than by a liquid type motion. This adds a dynamical aspect to the “floating solid’ as described by Nelson and Halperin for the melting of a 2-dimensional solid.
Phase Transitions in Graphite – SbCl5Intercalates
Authors: Clarke Roy , Homma Hitoshi
Published: March 2011

Interlayer and intralayer ordering in SbCl5-GIC's are probed by X-ray diffuse scattering. A crossover from 3-d to quasi 2-d structure is observed at around stage 2. Surprisingly, different in-plane arrangements can be obtained under nominally the same preparation conditions at the same stage. A stripe-like incommensurate structure close to the √39 superperiod of graphite, and a 14×14 commensurate superlattice structure, have been observed in different samples. The formation of these groundstate structures, and their transitions to ‘disordered’ phases, are discussed in terms of the molecular degrees of freedom.
A Study of the Temperature-Dependence of Low-Frequency, Raman-Active Phonons in Stage-2 Graphite-K and Graphite-Rb Intercalation Compounds
Authors: Giergiel J. , Eklund P. C. , Al-Jishi R. , Dresselhaus G.
Published: March 2011

We report results from a Raman scattering study of stage 2 Graphite-Rb and Graphite-K in the low frequency region (ω < 150 cm-1) as a function of temperature (80K < T < 300K). Four features are seen in the 80K spectra and are interpreted in terms of a Born– von Kármán lattice dynamics model. The temperature-dependence of the Raman spectra is discussed in connection with reported phase transitions in stage 2 alkalimetal graphite compounds.
Phonon Spectrum of Second Stage Graphite-Bromine Intercalation Compounds
Authors: Simon Ch. , Batallan F. , Rosenman I. , Lauter H.
Published: March 2011

Coherent inelastic neutron scattering results on the second-stage graphite intercalation compound C8Br are presented. Phonons polarized along the c-axis and in the basal plane were observed. A phenomenological Born-von Kármán force constant model with non-axial symmetry is used with parameters adjusted in agreement with the results. Several specific points of the phonon spectrum which are outside of the limits of the model are discussed.
Ion-Implantation Studies of Graphite
Authors: Elman B.S. , Hom M. , Maby E.W. , Dresselhaus M.S.
Published: March 2011

Ion implantation of highly oriented pyrolytic graphite (HOPG) is studied using various characterization techniques, including Raman spectroscopy and Secondary Ion Mass Spectroscopy (SIMS). Particular attention is given to the annealing of the implantation-induced lattice damage using both hot substrate implantation (200 < T1< 1000°C) and postimplantation annealing. The Raman spectra provide detailed information on the implantation-induced structural disorder by analysis of the disorder-induced and Raman-allowed features in the first- and second-order spectra. SIMS measurements show that the implanted profile is essentially the same for hot substrate and room temperature implantation for the case of HOPG. It is shown that implantation at elevated temperatures prevents amorphization more effectively than implantation at room temperature and subsequent annealing at the same elevated temperature. The annealing results show that fundamentally different defects are created during room temperature and hot substrate implantation.
Specific Heat Anomaly of C24K Arising from Hydrogen Physisorption
Authors: Kondow Tauotsu , Mizutani Uichiro
Published: March 2011

Hydrogen/deuterium gas was absorbed in the potassium graphite intercalation compound, C24K, at 77K and then the low temperature specific heats were measured in situ as a function of the hydrogen concentration in the temperature range 1.5–6K. Enhancement of the electronic specific heats upon hydrogen sorption indicates formation of bound states in the vicinity of the Fermi level. Increase of the Debye temperatures by introduction of hydrogen shows the hardening of the lattice. An observed specific heat anomaly was ascribed to a dispersion-less optical phonon with characteristic temperatures of about 17K.
Intercalation of Acceptors and Donors in Highly Ordered Graphite Fibers
Authors: Chieu T.C. , Timp G. , Dresselhaus M.S.
Published: March 2011

The intercalation of various acceptors and donors into graphite fibers, prepared from benzene-derived precursor materials is investigated by Raman spectroscopy, x-ray diffraction, electron diffraction, lattice fringing, and electrical resistivity measurements. Evidence for formation of well-staged acceptor compounds is provided by Debye-Scherrer x-ray diffraction which probes the bulk fiber and by Raman spectroscopy which probes an optical skin depth (< 0.1 μm). Lattice fringing measurements provide direct observation of large regions (up to 50 Aring; × 400 Aring;) of defectfree single-staged regions. Values for the c-axis repeat distance Ic are obtained by indexing (00l) lines of the x-ray diffraction pattern. Raman results show characteristic upshifted modes for stage 1 acceptor compounds with a sharpening in linewidth as compared to the E2g2 mode of the pristine fiber. The room temperature electrical conductivity is increased about an order of magnitude upon intercalation and exhibits a metallic dependence on temperature. The highest air-stable room temperature conductivity 1.4 × 105 (Ω-cm)−l ever reported for an intercalated fiber has been achieved.
Electronic and Lattice Modes of Graphite-Cocl2
Authors: Lowe C.W. , Nicolini C. , Dresselhaus G.
Published: March 2011

Reflectivity measurements on graphite-CoCl2 intercalation compounds between 0.06 eV and 2.0 eV for stages 3 and 5 show sharp Drude edges and superimposed interband structure. Stage 5 shows structure near 0.4 eV and 0.55 eV while stage 5 shows structure between 0.12 eV and 0.55 eV. The observed number of interband transitions is equal to the stage index which is consistent with a recently proposed kz-axis zone-folding model of the electronic energy bands. In addition to the electronic optical transitions, features associated with lattice vibrations are observed in the spectra. In particular, the graphite-like IR mode near 1580 cm–1 is clearly resolved in the intercalation compounds. A reflectivity minimum and splitting of this vibrational mode is observed for both stages 3 and 5 of graphite-CoCl2.