bluuebunny/crossref_metadata_2025 huggingface dataset:
Superplasticity in Ll2 Intermetallic Alloys
Authors: Nieh T. G.
Published: March 2011

Recent advances in superplasticity of L12 intermetallic alloys are reviewed. Results show that superplastic elongations of over 500% can be obtained in this group of materials. These intermetallic alloys include nickel silicide, Ni3 Si, and nickel aluminide, Ni3Al. In this review, the superplastic properties of these alloys are presented. The microstructural characteristics, e.g., grain size, phases, and texture, are described and correlated to the superplastic properties. The effects of alloying additions, temperature, and strain rate on the superplastic properties of these materials are discussed. In addition, the superplastic deformation mechanisms are proposed. Comparison of the superplastic characteristics of the intermetallic alloys are made with metal alloys and ceramic materials.
Superplasticity of Ultra-High Carbon Steels Containing 3-5%Aluminum
Authors: Kum Dong-Wha , Kang Hyung , Kim Tong-Hoon
Published: March 2011

To study the effect of Al on superplasticity of ultra-high carbon steel (UHCS), 3–5%Al was added to the UHCS, and superplastic behavior was measured at 700–800°C. To produce the fine and superplastic microstructure, an isothermal rolling at 700°C was used, and the grain size of ferrite was less than about 2μm in diameter after the process.

Significant improvement in superplasticity was observed; the strain-rate sensitivity was high upto a strain-rate of 10−2 s−1, and 402% elongation was measured at 750°C and at an engineering strain-rate of 5000%/min(i.e., 8.3×10−2s−1). It has been determined that the Al-addition leads to a finer grain size, which, in turn, improved the superplastic properties of the ultra-high carbon steels.
Significance of High Rate Superplasticity in Metallic Materials
Authors: Furushiro Norio , Hori Shigenori
Published: March 2011

It has been expected that “High rate superplastic materials” will be developed for industrial applications. The Dorntype equation for high temperature deformation suggests that strain rate can be increased if the grain size is decreased. This means that grain refinement can effectively establish high strain rate superplastic materials.

It is well known that a high degree of grain size refinement will result from the addition of zirconium to Al-base alloys. Powder-metallurgical processing with rapidly solidified powders is also available for the improvement of superplasticity by both the refinement of the solidified structure and the maintenance of the stable fine structure of a 7475 Al alloy during recrystallization and deformation. Therefore. P/M 7475 Al alloys containing Zr up to 0.9 wt% were selected as candidate specimens. The objective of the present paper includes the clarification of the role and the effective amount of Zr to obtain high strain rate superplastic materials. As a result, the addition of 0.3%Zr or more is effective in grain refinement of the P/M 7475 Al alloy. However, alloys containing 0.7 and 0.9 wt%Zr only show superplasticity at 793K. The optimum strain rate is shifted to a higher range with increasing Zr. The alloy of 7475 Al-0.9%Zr shows the maximum elongation of 900% at the remarkably high strain rate of 3.3×10−1 s−1.

The deformation mechanism of such high stain rate superplasticity will be discussed briefly, by considering the effect of the fine particles of Zr on superplastic behavior.
A Mechanism of Superplastic Deformation and Deformation Induced Grain Growth Based on Grain Switching
Authors: Sato Eiichi , Kuribayashi Kazuhiko , Horiuchi Ryo
Published: March 2011

Grain growth depending on strain is generally observed during structural superplasticity. A new deformation model is proposed in order to explain this grain growth.

This model is based on grain switching by Ashby and Verrall. The modification is to introduce grain size irregularity. The grain structure with minimum irregularity consists of one 5–7 pair in hexagonal array, which corresponds to edge dislocation. While the tensile stress oblique to the pair results the grain switching described by dislocation glide, the stress parallel to it results the grain switching which transforms the pentagon into the quadrilateral and then removes it. The latter can be described by dislocation climb and results the enhancement of grain growth. The expansion into three dimensions is discussed.
Superplasticity in Geological Materials
Authors: Paterson M. S.
Published: March 2011

The term “superplasticity” is taken as meaning high-strain-rate-sensitivity flow when it is used in geological contexts involving predominantly compressive stress states. Such flow has been observed in calcite and olivine polycrystalline aggregates in laboratory tests and the mechanism deduced to be diffusion-controlled granular flow. From microstructural observations, similar deformation processes are inferred to have occurred in a number of geological situations. On the basis of extrapolation from experiment to geology, superplastic flow might be expected under some geological conditions in calcite and olivine rocks at grain sizes approaching the order of one millimetre, while there are indications that the grain size limit for quartzites may be rather smaller. However, the knowledge of superplasticity in most rocks is still very fragmentary, especially in regard to mechanisms where a fluid phase may be involved, as in porous rocks.
Low Temperature Sintering and Deformation of Nanocrystalline TiO2
Authors: Hahn H. , Logas J. , Höfler H. J. , Kurath P. , Averback R. S.
Published: March 2011

The sintering and deformation kinetics of nanocrystalline (n-) TiO2 were studied. It was found that pressureless sintering yields densities above 95 % with modest increase in grain size whereas pressure assisted sintering (1GPa) results in high density samples without grain growth. In addition compression tests were performed. Large true strains up to 0.6 and strain rates as high as 8 × 10−5 s−1 were observed at 810 °C without fracturing. The sintering and creep results are discussed in terms of the microstructure and diffusion coefficients in n-TiO2.
Effects of Azidosilane Treatments of Wood and Cellulose Fiber Surfaces on Adhesion to Polypropylene
Authors: Kolosick Paul C. , Scott C.T. , Koutsky J.A. , Myers G.E.
Published: March 2011

Wood strip surfaces (Aspen and Birch) and cellulose fibers (Birch, pulped paper fibers) were treated with azidosilane coupling agent, via immersion in methylene chloride and methanol solutions respectively, and then subsequently dried. Polypropylene films were compression molded to the wood surfaces and peel forces were measured. The treated cellulose fibers were suspended and mixed with polypropylene fibers in water, formed into thin sheets by wet forming, dried, and compression molded to melt the polypropylene.

Treated wood surfaces gave two to six times the dry peel force versus untreated wood surfaces. However, the wet peel force of treated wood degraded to that of untreated wood. The elongation, fail stress, and tensile energy absorption of treated molded sheets were all increased over the untreated fibers for both dry and wet testing; the wet-tested properties were especially enhanced by the silane treatment.
Tensile Creep of Paperboard—Effect of Humidity Change Rates
Authors: Gunderson Dennis E. , Tobey Wayland E.
Published: March 2011

Experimental results now available are not adequate to define the mechanism of cyclic creep response of paperboard or to test plausible hypotheses. The present study examines the effect of rate-of-change of humidity on tensile creep response while monitoring the quantities of water adsorbed and desorbed by the specimen. Relative humidity is cycled between 30 and 90 percent relative humidity. Rate of humidity change in each cycle is held constant at values from 0.01 to 6 percent relative humidity per minute. Moisture sorbed by the web in each cycle is resolved to an accuracy better than ±0.05 percent moisture content. Results suggest that cyclic creep response is independent of the rate at which humidity changes. The results appear to reject the hypothesis that cyclic creep behavior is the result of a progressive increase in equilibrium moisture content.
Paper Coatings: High Performance Composites?
Authors: Lepoutre Pierre
Published: March 2011

A pigmented paper coating is a composite material made of pigment, polymeric binder and microvoids. Its structure is designed to meet a difficult balance of optical, mechanical and fluid transport properties. The coating must be opaque and bright. It should withstand in-plane and out-of-plane stresses during calendering, printing, and converting operations. It should allow controlled movement of liquids and fluids during high speed printing and glueing.

The structure of paper coatings is examined and relationships between surface and bulk structural parameters and end-use properties are discussed. Namely, it is shown how pigment size and size distribution, its shape and orientation, the colloidal interactions between pigment and binder in the suspension all affect the final structure and properties. Finally, the profound influence of the porous network on the optical, mechanical and printing properties is emphasized.
The Performance of Precipitated Calcium Carbonate Fillers in Fine Quality Printing and Writing Papers
Authors: Gill Robert A.
Published: March 2011

The trend toward alkaline papermaking has accelerated over the past four years due to the availability of inexpensive, high quality precipitated calcium carbonate. This movement has been largely brought about through on-site production of precipitated calcium carbonate (PCC). Over ten facilities exist in North America providing the host mills with custom-made PCC products to provide specific properties for the paper grades being manufactured.

Laboratory studies were recently conducted to investigate the performance of paper-grade PCC fillers in fine quality printing papers. This investigation focused on the effect of changes in PCC particle size, size distribution, surface area, and morphology on paper properties. The PCC fillers were also compared to other filler materials such as ground limestone and kaolin.

In general, the results show that sheet properties are greatly influenced by the size and shape of the PCC product used. The data reveal strong correlations between average particle size and/or surface area, and sheet properties such as opacity, porosity, tensile strength, bulk, and sizing within certain filler morphologies.
UV-Visible Response of Kraft Lignin in Soft Wood Black Liquor
Authors: Dong Daojie , Fricke Arthur L.
Published: March 2011

UV-visible light absorption is an analytical method that is commonly used to determine the concentration of lignin in solution; however, there are uncertainties with this method, particularly for use in determining lignin concentration in black liquors. To try to resolve these uncertainties, a detailed study of UV-visible absorption by lignin in solution has been made.

A dual beam UV-visible instrument capable of repetitive scan was used. The effects of lignin concentration, lignin molecular weight, molecular weight dispersion, and solvent were examined as well as the effect of the reference solvent. Measurements were made for lignin dissolved in dilute caustic, DMF, THF, and DMSO. Measurements for soft wood black liquors were also made. A refined method for determining lignin concentration in soft wood black liquors resulted that is now being used in our research to evaluate lignin concentration in soft wood black liquor.

The results of the current work have led to improvements in this analytical method so that it appears to be less affected by lignin characteristics and by solution complexities.
Micromechanics Models for Predicting the Elastic and Strength Behavior of Paper Materials
Authors: Perkins Richard W.
Published: March 2011

This paper presents a review of micromechanics models that have been used to predict the elastic and strength behavior of paper materials. The models discussed are based on a fiber network model that takes into account the properties of the fibers and the properties of the fiber-to-fiber bond.

Elastic models are described for a range of paper density and basis weight ranging from tissue papers to paperboard materials. The effects of fiber curl for low density systems is discussed. Models for predicting both the initial modulus of the paper and the nonlinear elastic behavior for small finite strains is presented. Differences between tensile and compressive straining regimes are addressed.

Limit load theory is discussed for predicting the strength of the network. Damage mechanics theory is employed to take into account hypothesized processes of fiber fracture and bond delaminations, and to relate the inelastic network micromechanics to the prediction of the strength of the material.
Improvement of Inp-GaAs-Si Quality by Thermal-Cycle Growth
Authors: Vernon S.M. , Keavney C.J. , Gagnon E.D. , Karam N.H. , Haegel N.M. , Mazzi V.P.
Published: March 2011

Single-crystal films of InP have been deposited on GaAs, GaAs-coated Si, and InP substrates by metalorganic chemical vapor deposition (MOCVD). Defect-reduction schemes involving various thermal annealing recipes have been developed and characterized. Material quality has been assessed by a variety of methods including transmission electron microscopy, X-ray rocking curve analysis, low-temperature photoluminescence, lifetime measurements, Hall-effect measurements, electrochemical profiling, and Nomarski microscopy. The use of either a thermal-cycle-growth or a thermal-cycle-annealing process leads to heteroepitaxial InP film quality which is significantly improved over that of its as-grown state, with the thermal-cycle growth appearing to be the more effective technique.
Misfit Dislocations at Mismatched Epitactic Heterojunctions
Authors: Zhu Jane G. , Carter C. Barry , Palmstrom Chris J.
Published: March 2011

The formation and structures of misfit dislocations are significant factors in understanding heteroepitaxy of lattice-mismatched materials. In this study, GaAs/Si, CoGa/GaAs and ErAs/GaAs heterojunctions in materials grown by molecular-beam epitaxy have been characterized using transmission electron microscopy. Different types of misfit dislocations have been generated at these interfaces. The different dislocation configurations are discussed, along with interactions between 60° and 90° dislocations in GaAs/Si heterojunctions; the 60° dislocations might be associated with surface steps or edges of islands. The growth of antiphase boundary structures in the CoGa and ErAs grown on GaAs are proposed.
The Heteroepitaxy and Characterization of Inp and GaInP on Silicon for Solar Cell Applications
Authors: Al-Jassim M.M. , Ahrenkiel R.K. , Wanlass M.W. , Olson J.M. , Vernon S.M.
Published: March 2011

InP and GaInP layers were heteroepitaxially grown on (100) Si substrates by atmospheric pressure MOCVD. TEM and photoluminescence (PL) were used to measure the defect density and the minority carrier lifetime in these structures. The direct growth of InP on Si resulted in either polycrystalline or heavily faulted single-crystal layers. The use of GaAs buffer layers in InP/Si structures gave rise to significantly improved morphology and reduced the threading dislocation density. The best InP/Si layers in this study were obtained by using GaAs-GaInAs graded buffers. Additionally, the growth of high quality GaInP on Si was demonstrated. The minority carrier lifetime of 7 ns in these layers is the highest of any III-V/Si semiconductor measured in our laboratory.
Optimisation Of The Heteroepitaxy Of Ge On GaAs For Minority-Carrier Lifetime
Authors: Venkatasubramanian R. , Timmons M.L. , Bothra S. , Borrego J.M.
Published: March 2011

Growth of Ge on GaAs at reasonably high temperatures, which produce better crystallinity in the Ge, presents serious difficulties due to the dissociation of the GaAs substrate. In this paper, we describe the growth of a lowtemperature buffer layer of Ge on GaAs that prevents decomposition of the GaAs during high-temperature growth of Ge. Using this approach, we present the first report of highly specular, mass-transport-limited high-temperature growth of Ge on GaAs that is comparable to the homoepitaxy of Ge. The factors affecting the minority-carrier lifetime of Ge on GaAs, using such an epitaxial growth technique, were studied with a non-invasive microwave technique. Lifetime variations, from very low values to about 0.45 μsec, were obtained as a function of the growth conditions. Significantly, the removal of the surface oxide on the GaAs substrate prior to low-temperature buffer-layer growth, terminating the flow of germane(GeH4) during the ramp to high growth temperatures, thinner buffer layers, and high-temperature growth of Ge were found to be important for obtaining long lifetimes.
Alternative Chemistries for Mocvd Growth of III/V Materials
Authors: Lum R.M. , Klingert J.K.
Published: March 2011

Alkyl substituted arsine compounds, RnAsH3–α are attractive alternatives to arsine, AsH3. for metalorganic chemical vapor deposition (MOCVD) of GaAs-based compounds because they are typically low vapor pressure liquids which can be stored and handled more safely than the high-pressure gas cylinders used for AsH3. Despite their increased safety, the alkylarsines have not been widely used due to carbon incorporation problems and high background doping levels in the deposited films. To determine the impact of alternative growth chemistries on MOCVD processes we have investigated the thermochemistry controlling the decomposition of AsH3 and its alkyl substitutes. Data are presented on the thermal stability of the Ascompounds, their resulting growth properties, and the composition and formation kinetics of the volatile products formed during thermal decomposition in an H2 ambient. The gas phase reactions controlling decomposition are identified. The implications of our results for CVD growth models and the potential of alkylarsine compounds for different CVD processes are discussed.
Mbe Growth of Strained-Layer InSb/InAlSb Structures
Authors: Whitehouse C.R. , Mcconville C.F. , Williams G.M. , Cullis A.G. , Barnett S.J. , Saker M.K. , Skolnick M.S. , Pitt A.D.
Published: March 2011

The MBE growth and related materials characterisation of InSb/InAlSb strained-layer structures is described. Band-gap considerations and critical thickness calculations are presented and indicate that this material system should offer considerable device potential. Detailed structural studies, performed using both transmission electron microscopy and X-ray diffraction, confirm the growth of high quality multiple quantum-wells, and 2K photoluminescence has shown corresponding energy upshifted transitions.
Einstein Rzlation in Quantum Wires of Tetragonal Sediconduc Tors
Authors: Ghatak Kamakhya P. , De B. , Mondal M. , Biswas S. N.
Published: March 2011

We have studied the Einstein relation for the diffusivity. mobility ratio (7PT) on the basis of a newly derived electron energy spectrum in QW f tetragonal semiconductors, within the framework of K. P method by considering all types of anisotropies of the energy band parameters. It is found, taking n-Cd3 As2 as an example that the DUTZ increases with electron concentration and decreases with film thickness in an oscillatory manner respectively. The theoretical results are in good aoreement with the suggested experimental method of determining the DMR in degenerate semiconductors having arbitrary dispersion law.
Characterization of Mbe GaAs Layers Grown at 200°C–300°C
Authors: Wie C.R. , Xie K. , Bardin T.T. , Pronko J.G. , Look D.C. , Evans K.R. , Stutz C.E.
Published: March 2011

Lattice parameter, RBS channeling, and T-dependent Hall effect and resistivity are measured in 5 μm GaAs layers MBE-grown at 200°C, 250°C and 305°C, and subsequently annealed. Perpendicular lattice parameter was increased by 0.15% for 200 °C, 0.10% for 250°C, and 0.05% for 305°C sample. No parallel mismatch was observed. In annealing up to 800°C, most recovery of lattice parameter occured at 350°C-450°C. For samples annealed at 500° C − 600°C, the conductivity activation energy was higher in the furnace annealed sample than in the RTA-annealed sample, indicating possible depth nonuniformity in furnace annealed sample. The 600°C RTA annealed sample indicated a donor activation energy of 0.61 eV. A 600°C furnace annealed sample indicated the deep donor concentration of 1.5×1018 cm−3. Maximum mobility in the 500–600°C annealed sample was 3000–3500 cm2/Vs, limited by the neutral impurity scattering and polar optical phonon scattering.
A Novel Approach to the Assessment of Semiconductor Hetero-Interfaces in Multilayer Structures
Authors: Rimmer J.S. , Missous M , Peaker A.R. , Hamilton B.
Published: March 2011

We demonstrate the novel use of CV simulation to determine the level of charge at each interface in multilayer GaAs/AlGaAs heterostructures. The gettering of charged centres at the earliest grown interfaces is quantitatively appraised and the parallel application of PL decay lifetime measurements determines their effectiveness as recombination centres. A direct relationship is found between the magnitude of the charged states and the recombination velocity. Estimates of a 1eV activation energy and a hole capture cross section of 10−15 cm2 were also obtained. This suggests that the dominant recombination centre could be observed as a hole trap.
The Influence of Substrate Patterning on Threading Dislocation Density and Residual Stress in GaAs/Si Heteroepitaxial Layers.
Authors: Sohn Hyunchul , Weber Eicke R. , Tu Jay , Lee Henry P. , Wang Shy
Published: March 2011

The growth of GaAs films by MBE on mesa-type patterned Si substrates has been investigated. Mesa widths were varied from 10 µm to 200 µm and were prepared using chemical etching with Si3N4 masks and reactive ion etching. The residual stress in the epitaxial layer was estimated using low temperature (7K) photoluminescence and the defect distribution was studied by cross sectional TEM, dislocation densities were in addition determined by etch pits. The residual stress and the dislocation density decreased monotonically with the reduction of growth area. By the incorporation of strained layers with the reduction of growth area, the etch pit density in GaAs layers on mesas was reduced further.
Luminescence of Mbe SimGen Strained Monolayer Superlattices
Authors: Kallel M. A. , Arbet-Engels V. , Karunasiri R. P. G. , Wang K. L.
Published: March 2011

SimGen strained monolayer superlattices (SMS) have been fabricated by molecular beam epitaxy (MBE) and characterized using photoluminescence (PL). Symmetrically strained structures with different periodicities have been grown on top of a Si1−xGex alloy buffer layer. Luminescence features below (above) the Si (Ge) energy bandgap have been observed and attributed to either dislocations in the buffer layer or to energy band transitions in the SMS.
Confinement of Threading Dislocations in Simox with a GeSi Strained Layer
Authors: Namavar F. , Cortesi E. , Perry D.L. , Johnson E.A. , Kalkhoran N.M. , Manke J.M. , Karam N.H. , Pinizzotto R.F. , Yang H.
Published: March 2011

We have investigated improving the crystalline quality of epitaxial silicon grown on SIMOX by confining threading dislocations in the original Si top layer using a GeSi strained layer. Epitaxial Si/GeSi/Si structures were grown by CVD on SIMOX and Si substrates with a GeSi alloy layer about 1000 − 1500 angstroms thick with Ge concentrations of about 0−20%. A Ge concentration in the alloy layer of about 5.5% or higher appears to be necessary in order to bend any of the threading dislocations from the original SIMOX top layer. For a higher Ge concentration of about 16%, most of the threading dislocations appear to be bent and confined by the GeSi layer. In addition, the GeSi strained layers grown by CVD (at about 1000°C) appear to be high quality and no misfit dislocations were observed in the regions studied by XTEM and plane view TEM.
Rapid Thermal Processing of Buried Sil−xGex Strained Layers; Photoluminescence Decay and Misfit Dislocation Generation.
Authors: Houghton D.C. , Rowell N.L.
Published: March 2011

The thermal constraints for device processing imposed by strain relaxation have been determined for a wide range of Si-Ge strained heterostructures. Misfit dislocation densities and glide velocities in uncapped Sil-xGex alloy layers, Sil-xGex single and multiple quantum wells have been measured using defect etching and TEM for a range of anneal temperatures (450°C-1000°C) and anneal times (5s-2000s). The decay of an intense photoluminescence peak (∼ 10% internal quantum efficiency ) from buried Si1-xGex strained layers has been correlated with the generation of misfit dislocations in adjacent Sil-xGex /Si interfaces. The misfit dislocation nucleation rate and glide velocity for all geometries and alloy compositions (0<x<0.25) were found to be thermally activated processes with activation energies of (2.5±0.2)eV and (2.3-0.65x)eV, respectively. The time-temperature regime available for thermal processing is mapped out as a function of dislocation density using a new kinetic model.
Island Formation in Ge on Si Heteroepitaxy
Authors: Eaglesham D.J. , Gossmann H.-J. , Cerullo M.
Published: March 2011

We present a study of island formation (the transition from 2D to 3D growth) during the Stranski-Krastanow (S-K) growth of Ge on Si. The energetic driving force for S-K island formation should be the ability to relax the islands by dislocation introduction. Here, we show that Ge islands formed on Si (100) are initiallydislocation-free, in the presence of a 2D “sea” that is far in excess of the equilibrium 3 monolayers (ML). We call this phase of growth “dislocation-free S-K”. The 2-D sea does not collapse until dislocated islands are produced at an average coverage of = 7 ML. We call the dislocation-free island phase “coherent S-K” growth. The corresponding 2D-3D transition on Si (111) appears to reach equilibrium far faster, and we have not observed dislocation-free island formation: dislocated islands are seen at = 5 ML. As expected, the kinetics allow us to suppress island formation on (100) by reducing the growth temperature. These thick 2D films are analogous to those grown on As-covered surfaces, but have a microstructure dominated by edge dislocations.
Photoluminescence from Coherently Strained Si1−xGex Alloys
Authors: Rowell N.L. , Noël J.-P. , Houghton D.C. , Perovic D.D.
Published: March 2011

An intense, broad photoluminescence PL peak, with an internal quantum efficiency as high as 31%, has been observed from a variety of structures containing Si1−xGex strained layers on Si(100) substrates; i.e. Si1−xGex thick random alloy layers, single quantum wells (SQW) and multiple quantum wells (MQW) with layers thick enough so that zone folding effects were not relevant. This peak, which shifted consistently and predictably with Ge concentration( 0.06 < × < 0.53), had its high energy edge near the established band gap for strained SiGe. PL excitation spectroscopy indicated that no phonons were involved in the process causing the SiGe PL peak. Samples deposited at ~ 400 °C exhibited low PL intensity, whereas annealing at ~ 600 °C enhanced the intensity by as much as two orders of magnitude. This anneal treatment was found to remove grown-in defect complexes without creating a significant density of misfit dislocations. The PL peak energy at 4.2 K varied from 620 to 990 meV for Ge fractions x from 0.53 to 0.06. When the samples were forced to relax, e.g. by higher temperature annealing, the luminescence of this peak either shifted to near the relaxed bandgap or was quenched by deep, dislocation related states. Prior to such relaxation, the efficient PL was due to exciton accumulation in the strained Si1−xGex layers of single and multiple quantum wells, where the bandgap was locally reduced. It is suggested that the recombination of electrons and holes occuring within a high-density electron hole condensate (EHC) can cause the observed spectrum.
Gas Source Si-Mbe
Authors: Hirayama Hiroyuki , Hiroi Masayuki , Koyama Kazuhisa , Tatsumi Toru
Published: March 2011

Gas source Si molecular beam epitaxy (Si-MBE) apparatus has been devised. The growth mechanism was studied using reflection high energy electron diffraction (RHEED) intensity oscillation. Si epitaxial layers grew through a dissociative adsorption of Si2H6 molecules on Si surfaces. This dissociative adsorption enables a selective epitaxial growth on SiO2 patterned Si wafers. At low temperatures, the growth rate was limited by a desorption of hydrogen which terminates surface dangling bonds. Doping with B, Sb and P were also studied. B doping was achieved using HBO2 Knudsen cell or B2H6 gas dopant. Sb doping used an ionized doping cell. P doping was achieved using PH3 gas dopant. The effect of B doping on the growth was studied using RHEED oscillation. A doped layer's selective epiataxial growth was possible by selective epitaxial growth under doping. This technique was applied to bipolar transistor fabrication. Moreover, using GeH4, Si1−xGex compound growth and its selective epitaxial growth was achieved. Using this Si1−xGex selectively grown layer, a Si1−xGex base heterobipolar transistor (HBT) was also fabricated. An electron cyclotron resonance (ECR) gas source Si-MBE cell was used for a low temperature surface cleaning and a surface termination by atomic hydrogen.
Carbon Doped Silicon Emitters Fabricated Using Limited Reaction Processing
Authors: Ruddell F.H. , Armstrong B.M. , Gamble H.S. , Affolter K.B. , Moynagh P.B. , Rosser P.J.
Published: March 2011

This paper describes the deposition of in-situ doped N-type silicon carbide layers in a Limited Reaction Processing (LRP) reactor. Silane/propane/ phosphine gas chemistry was used at temperatures less than 1000°C and SIMS, XPS and TEM analysis techniques aided layer characterisation. A low thermal budget deposition process (1 min at 970°C) was employed to form the emitters of Sic/Si heterojunction NPN bipolar transistors. These devices yielded a factor of two increase in emitter Gummel number compared to diffused emitters.
Characterization and Griwth of Oicanic Multiple Qanm Well Structures
Authors: So F.F. , Forrest S.R. , Shi Y.Q. , Steier W.H.
Published: March 2011

Multiple quantum well structures consisting of alternating layers of two crystalline organic semiconductors, namely, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) and 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA), have been grown by organic molecular beam deposition. The layer thickness was varied from 10 to 200 Å. Birefringence measurements indicate that there is a strong structural ordering in all PrCDA layers, although the PrCDA and NTCDA crystal structures are incommensurate. From optical absorption measurements, it is found there is a blue shift in the lowest energy PICDA singlet exciton line with decreasing layer thickness. A model based on exciton quantum confinement is proposed to explain the energy shift. We have measured the low temperature photoluminescence spectra of organic quantum well structures, and found a slight red shift in the spectra with decreasing well width. These results are also discussed.
Nucleation and Growth Mechanisms in Hetero-Epitaxial Films
Authors: Venables J.A. , Drucker J.S. , Krishnamurthy M. , Raynerd G. , Doust T.
Published: March 2011

Nucleation and growth mechanisms in the formation of heteroepitaxial films are reviewed. The various processes can be incorporated into rate equations to model the number density and size distribution of clusters.Recent work on extensions of this approach to include the effect of surface steps and other surface imperfections is highlighted.

The most important processes are being studied experimentally using a combination of surface-analytic and -microscopic techniques, based on SEM and STEM instrumentation. Recent examples are given in which nucleation densities, surface diffusion lengths and the effects of steps have been studied in the systems Ag/Si(lll) and Ge/Si(100).
Preparation of Cross-Sectional TEM Samples of PbTe and CdxPb1−x Te on BaF2
Authors: McCaffrey John P. , Das Suhit R. , Cook John G.
Published: March 2011

Epitaxial PbTe and CdxPb1−xTe films have been grown on single crystal (111) BaF2 by low energy bias sputtering, and have been analyzed by transmission electron microscopy (TEM) and transmission electron diffraction (TED). Preparation of suitable cross-sectional TEM samples was made difficult by the tendency of the substrate to cleave apart during dimpling, and by the epoxy forming bridges across the sample during atom milling. Suitable preparation techniques were developed employing back-polishing the BaF2 substrates to <0.2 mm thickness, using a suitable epoxy, and shielding the argon atom beam during milling to prevent milling parallel to the surface. In cases where an epoxy bridge did form across the sample, the bridge was broken manually or by atom milling, depending upon the area of sample which was being investigated. These techniques are applicable to other materials which produce similar problems during TEM sample preparation.
The Role of Ultramicrotomy in the Microstructural Studies of Rapidly Solidified Aluminium Alloy Powders
Authors: Chowdhury A. J. S. , Freundlich A. , Sheppard T.
Published: March 2011

The as-produced high hardness of rapidly solidified aluminium powder alloys make TEM specimen preparation difficult. Conventional methods, i.e. electrothinning or ion-beam thinning of electroplated foils or compacts, although adequate for some powders, are not suitable for many other new and novel alloy powders. In this paper we discuss ultramicrotomy of such powders and the prospects and limitations of the method.
Fabrication of Planar and Cross-Sectional TEM Specimens Using a Focused Ion Beam
Authors: Young R. J. , Kirk E. C. G. , Williams D. A. , Ahmed H.
Published: March 2011

A new technique using a focused ion beam has been developed for the fabrication of transmission electron microscopy specimens in pre-selected regions. The method has been proven in the fabrication of both cross-sectional and planar specimens, with no induced artefacts. The lateral accuracy achievable in the selection of an area for cross-sectional analysis is better than one micrometre. The technique has been applied to a number of silicon and III-V based integrated circuits, and is expected to be suitable for many other materials and structures.
A Technique for Preparing “Two in One” Cross-Sectional TEM Specimens
Authors: Ma Guang-Hwa M. , Chevacharoenkul Sopa
Published: March 2011

A modified “two-in-one” cross-sectional TEM sample preparation technique is described. By coating a thin layer of “marker” to distinguish one sample from the other, two samples could be simultaneously prepared in one TEM cross-sectional specimen. Therefore, the specimen preparation time is reduced by nearly one half. The coating can be done in an existing ion-mill. Criteria for choosing a suitable marker as well as tips on getting good quality specimens are described. An example of applying this technique to a processing-microstructure study of an ultra-shallow junction formation in silicon is demonstrated.
Experimental Measurement of Transmission Electron Microscope Specimen Temperature during Ion Milling
Authors: Bahnck D. , Hull R.
Published: March 2011

Semiconductor materials and devices are commonly investigated by transmission electron microscopy to obtain microstructural information. The results are useful only when a thinned sample is representative of the parent material. The technique of ion milling can introduce artifacts arising from beam heating during specimen preparation. A survey of specimen temperatures during argon and iodine ion milling of silicon, indium phosphide and gallium arsenide was made by encasing a thermocouple in a specimen and varying ion beam energy and beam angle of incidence. The results indicate, for example, that the typical temperature of silicon specimen preparation is less than 140°C. By decreasing the beam energy and incident angle, the milling temperature can be reduced. Design improvements on the ion mill can also sink heat away from the specimen.
Wedge Cleaving and Ultramicrotomy as Alternative TEM Sample Preparation Methods in Materials Science
Authors: Ruterana P. , Laub D. , Buffat P-A.
Published: March 2011

The use of two methods for preparation of TEM samples has been investigated. It has been possible to show the practical details of the wedge cleaving method and illustrate it with original results on III-V semiconductors and on metallic thin layers on Silicon. Chemical etching of AlGaAs in heterostructures was clearly observed and can further be quantified. Preferred oxidation of AlAs was shown to be important this can be a problem to a faithful interpretation of images from cross section samples prepared in more conventional ways. Efficient microtomy for use in materials science is still in the development stage, however we think to have found the best conditions for sectioning very soft metals like copper. We hope to decrease the compression in these materials by using lower angle diamond knives
Rapid Preparation of Cross-Sectional TEM Samples from Electroplated Copper
Authors: Dinan T. E. , Landolt D. , Ruterana P , Buffat P.-A.
Published: March 2011

Methods were investigated for the rapid preparation of cross-sectional TEM samples from electroplated copper. Electropolishing and ultramicrotomy were used. The electropolished samples were sandwiched in a copper/nickel alloy and electropolished using a nitric acid/methanol mixture. Large transparent areas were obtained and it was possible to position the area of interest at the point where the hole would appear. Ultramicrotomed samples cut with 45° diamond knives were electron transparent but the crystalline structure of the sample was severely damaged. However, it was possible to identify the conditions by which good ultramicrotomed samples might be produced in the future.
Delineation of p-n Junctions on Cross Sectional TEM Device Samples
Authors: Knoesen Dirk , Zhang Fang , Rozgonyi George A.
Published: March 2011

The delineation of n-p junctions is one of the techniques routinely required in the analysis of electronic devices. The delineation of the junction profile is typically done either in a scanning electron microscope (SEM) or by angle lapping / staining/ optical microscopy. Recently TEM foils have been selectively etched to simultaneously provide an interface demarcation and an image of processed induced dislocations. A case study is presented in this report on concentration dependent delineation techniques with emphasis on the special problems associated with cross sectional transmission electron microscopy (XTEM) samples. The etchants used in delineating junctions for the SEM or with angle lapping / optical microscopy of transistors are too aggressive for the extremely thin TEM foils. This paper discusses etchants which deliver reproducible, high contrast delineations in XTEM samples with known concentration profiles.
Ultramicrotomy for Materials Science
Authors: Malis T. F. , Steele D.
Published: March 2011

Diamond knife sectioning, or ultramicrotomy, is being used increasingly as an attractive alternative or complimentary means of producing quality TEM specimens. This paper represents a first attempt to provide a basic methodology for this technique for materials scientists, point out its drawbacks, provide a comprehensive listing of more than three decades of widely-scattered and ingeneous applications, and illustrate the diversity of these applications with clear examples. Suggestions will be made for further improvements in ultramicrotomy so that it can be applied in a more routine fashion to modern advanced materials or TEM applications involving demanding chemical microanalysis.
Improved Methods and Novel Techniques for Jet Electropolishing of TEM Foils
Authors: Kestel Bernard J.
Published: March 2011

Experience has shown that the difficulties encountered in jet polishing of TEM foils can be minimized by the selection of equipment and an electrolyte appropriate for each material. The use of a jet polishing instrument for more than one type of specimen preparation after minor modification will be presented. Some insights on the relationship and manipulation of the parameters involved in achieving well polished TEM foils having appropriate surface quality, thin area, and perforation size will be included. Methods used to develop new electrolytes for specific purposes and the results of their use on both conventional and superconducting materials will be shown. A technique to calibrate equipment for more reproducible specimen hole size, use of new electrolytes on various materials, the salvage of unsatisfactory foils, and thinning of undersized specimens will be reviewed.
Mechanical Polishing to Submicron Thickness for Extensive Thin Area in Heterogeneous Samples
Authors: Dawson-Elli David F. , Turowski Marek A. , Kelly Thomas F. , Kim Yeon-Wook , Zreiba Nuri A. , Chen-Ming Tens , Mei Zhou
Published: March 2011

Ion-milling-based sample preparation has the advantage that thin area can be obtained from almost any material. It has the disadvantage, however, that the amount of thin area can often be quite limited. This poses a problem when a large sampling area is needed from materials which must be thinned by ion milling. Cross-sectioned samples and grossly heterogeneous materials are two examples where this problem may be encountered. The group at IBM in East Fishkill have developed methods for mechanical grinding and polishing of TEM samples down to about I micron thickness. They use this as a starting point for final thinning by ion milling. This approach produces a large uniform thin area in a short time in the ion mill. We have built jigs that allow us to make these mechanically-thinned samples. We have also made flat-bottomed dimples using ultra-precision dimple grinders to achieve similar results. Both of these approaches are described. Examples are taken from cross-section samples of thin films on silicon, from steels with large carbides, and from rapidly solidified metal spheres embedded in electroplated copper.
Application of Channeling to Defect Studies in Crystals
Authors: Chu W. K.
Published: March 2011

Channeling of fast, light ions in crystals has been widely used as a tool for studying crystal defects. Backscattering yield measurement on ions incident along major axial or planar crystalline directions provides information on the depth distribution of the structural defects in the first few microns. The channeling technique in defect detection is not as sensitive as Transmission Electron Spectroscopy, nor is it accurate in measuring the absolute numbers of defect density. Channeling measurements can give only an indication of the degree of lattice disorder. It is possible to distinguish one type of defect from another by carefully studying the energy dependence of the dechanneling. The dechanneling interpretation is not always unique, and in practice it is difficult to obtain structure information through that method. Despite these negative qualities, channeling is an attractive and unique method in certain defect studies. For example, it is sensitive for studying the lattice location of impurity atoms at substitutional or interstitial sites. Clustering of substitutional impurity atoms will show a displacement of the impurity atoms from lattice sites due to the change of bond distance. Channeling is sensitive for measuring impurity displacement as small as 0.1A°. This has been demonstrated in the study of arsenic clustering formation in Si. Interfacial relaxation and contraction in a multi-layered structure made by molecular beam epitaxy has been detected by dechanneling along various axial directions. Channeling study on surface and interface structures has developed over the past few years. In this paper, I will use examples to illustrate the unique features of the channeling technique and its application to defect studies in single crystals.
Detection of Point Defect Chains in Ion Irradiated Silicon by High Resolution Electron Microscopy
Authors: Krakow W. , Tan T.Y. , Foell H.
Published: March 2011

In a lattice imaging study of As+ ion damaged Si, we have detected =110> chain type defects which are not associated with any significant strain or configurational changes. By image matching of the experimental and calculated micrographs of vacancies and interstitials, it is established that about 100% more interstitial atoms may incorporate into a defective chain. A structure model of this defect is proposed wherein a di-interstitial, occupying the =100> split position, is incorporated into every available site along a =110> chain.
Transient Capacitance Studies of a Low-Lying Electron Trap in n-type Silicon
Authors: Jellison G. E. , Cleland J. W. , Young R. T.
Published: March 2011

A new electron trap has been observed in electronirradiated n-type silicon at Ec − ET = 0.105 eV using transient capacitance techniques. It is found that the maximum transient capacitance response is observed only when the majority carrier pulse width is much smaller than some characteristic time constant, and when the time between pulses is much larger than another characteristic time constant. It is shown that this defect is related to an electron trap at Ec−ET = 0.172 eV (probably the oxygenvacancy or A-center); it is believed that this trap is induced by the electric field found in the depletion region of a p-n junction.
Ebic Investigation of Hydrogen Passivated Structural Defects in Efg Silicon Ribbon
Authors: Sullivan T. D. , AST D. G.
Published: March 2011

EBIC contrast of structural defects in as-received and hydrogen passivated polysilicon ribbon is studied using aluminum Schottky barrier diodes. Enhanced charge collection after passivation is demonstrated by comparing the EBIC signal from two sections of a split ribbon, one half of which was passivated. Electrical activity of specific linear defects before and after passivation is examined by recording charge collection profiles across these defects under standardized conditions of beam voltage and current. Such measurements show that passivation does reduce the electrical activity of selected defects. Possible reasons for this behavior will be discussed.
Real-Time X-Ray Topographic Observation of Melting and Growth of Silicon Crystals
Authors: Chikawa Jun-Ichi , Sato Fumio
Published: March 2011

A technique for the direct viewing of topographic images was developed based on a television system using an x-ray sensing PbO-vidicon camera tube (resolution 25 μm). Melting and growth processes of plate-shaped crystals were observed in an argon flow by this technique. The observation showed that dislocations have very high mobilities by superheating and the equilibrium dislocation density of zero is achieved just before melting. In melting of dislocation-free crystals, liquid drops (locally molten regions) were observed inside the crystals. While, crystallites appeared in the supercooled melt near the growth interface. It was found that both the drops and crystallites are not formed in 5% hydrogen/95% argon environment. Melting behavior of crystals covered with oxide films indicates that the solid-liquid interfacial free energy is greatly lowered by oxygen impurity. This oxygen effect may be responsible for both the drop and crystallite formation. Origin of swirl defects in dislocation-free crystals is discussed in the basis of these observations. Both composite and common a/2<110> dislocations were observed near the growth interface: The former are composed of three a/2<110> dislocations and are present at the interface so that, as the crystal grows, they propagate into the new crystal. They influence the interface morphology, when their Burgers vectors have the component perpendicular to the interface. The common dislocations cannot exist stably at the interface and are driven into the newly grown dislocation-free region by thermal stresses.