Materials science and engineering

Materials science and engineering

Date: February 1, 1997
Creator: Lesuer, D.R.
Description: During FY-96, work within the Materials Science and Engineering Thrust Area was focused on material modeling. Our motivation for this work is to develop the capability to study the structural response of materials as well as material processing. These capabilities have been applied to a broad range of problems, in support of many programs at Lawrence Livermore National Laboratory. These studies are described in (1) Strength and Fracture Toughness of Material Interfaces; (2) Damage Evolution in Fiber Composite Materials; (3) Flashlamp Envelope Optical Properties and Failure Analysis; (4) Synthesis and Processing of Nanocrystalline Hydroxyapatite; and (5) Room Temperature Creep Compliance of Bulk Kel-E.
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Reciprocal-Space Analysis of Compositional Modulation in Short-Period Superlattices Using Position-Sensitive X-Ray Detection

Reciprocal-Space Analysis of Compositional Modulation in Short-Period Superlattices Using Position-Sensitive X-Ray Detection

Date: November 10, 1998
Creator: Ahrenkiel, S.P.; Follstaedt, D.M.; Lee, S.R.; Millunchick, J.M.; Norman, A.G.; Reno, J.L. et al.
Description: Epitaxial growth of AlAs-InAs short-period superlattices on (001) InP can lead to heterostructures exhibiting strong, quasi-periodic, lateral modulation of the alloy composition; transverse satellites arise in reciprocal space as a signature of the compositional modulation. Using an x-ray diffractometer equipped with a position-sensitive x-ray detector, we demonstrate reciprocal-space mapping of these satellites as an efficient, nondestructive means for detecting and characterizing the occurrence of compositional modulation. Systematic variations in the compositional modulation due to the structural design and the growth conditions of the short-period superlattice are characterized by routine mapping of the lateral satellites. Spontaneous compositional modulation occurs along the growth front during molecular-beam epitaxy of (AlAs) (InAs)n short-period superlattices. The modulation is quasi-periodic and forms a lateral superlattice superimposed on the intended SPS structure. Corresponding transverse satellites arise about each reciprocal lattice point, and x-ray diffraction can be routinely used to map their local reciprocal-space structure. The integrated intensity, spacing, orientation, and shape of these satellites provide a reliable means for nondestructively detecting and characterizing the compositional modulation in short-period superlattices. The analytical efficiency afforded by the use of a PSD has enabled detailed study of systematic vacations in compositional modulation as a function of the average composition, the ...
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Melt-texturing of carbon containing YBa{sub 2}Cu{sub 3}O{sub 7-x}: Influence of processing parameters on microstructure and flux-pinning behavior

Melt-texturing of carbon containing YBa{sub 2}Cu{sub 3}O{sub 7-x}: Influence of processing parameters on microstructure and flux-pinning behavior

Date: January 1, 1994
Creator: Todt, V.R.; Sengupta, S.; Chen, Y.L.; Shi, Donglu; Poeppel, R.; McGinn, P.J. et al.
Description: A detailed study of the flux-pinning behavior of sintered and melt-textured YBa{sub 2}Cu{sub 3}O{sub 7-x} has been carried out by means of microstructural investigations (optical microscopy, SEM, TEM, EDS, DTA, and XRD) and magnetization measurements. It was found that both microstructure and magnetization behavior strongly depend on the starting material, the production method, and the maximum processing temperature. In our experiments, the critical current density, J{sub c}, increased with increasing processing temperature between 920{degrees}C and 1050{degrees}C (25 - 130 emu/cm{sup 3}), but those samples processed at temperatures just above the peritectic transformation point (1020 OC and 1030 OC) exhibited a decreased J{sub c}. The carbon content of the starting powder and the powder`s melting behavior seem to play an important role in the development of microstructure and flux-pinning behavior during melt-texturing. A comparison of our data with previously published results shows that an optimized melt-texturing process can result in materials with critical current densities comparable to those of samples produced by Quench-Melt Growth.
Contributing Partner: UNT Libraries Government Documents Department
Charge state defect engineering of silicon during ion implantation

Charge state defect engineering of silicon during ion implantation

Date: January 1997
Creator: Brown, R. A.; Ravi, J.; Erokhin, Y.; Rozgonyi, G. A. & White, C. W.
Description: Effects of in situ interventions which alter defect interactions during implantation, and thereby affect the final damage state, have been investigated. Specifically, we examined effects of internal electric fields and charge carrier injection on damage accumulation in Si. First, we implanted H or He ions into diode structures which were either reverse or forward biased during implantation. Second, we implanted B or Si ions into plain Si wafers while illuminating them with UV light. In each case, the overall effect is one of damage reduction. Both the electric field and charge carrier injection effects may be understood as resulting from changes in defect interactions caused in part by changes to the charge state of defects formed during implantation.
Contributing Partner: UNT Libraries Government Documents Department
Tensile behavior of nanocrystalline copper

Tensile behavior of nanocrystalline copper

Date: November 1995
Creator: Sanders, P. G.; Weertman, J. R. & Eastman, J. A.
Description: High density nanocrystalline copper produced by inert gas condensation was tested in tension. Displacements were measured using foil strain gauges, which greatly improved the accuracy of the strain data. The Young`s modulus of nanocrystalline copper was found to be consistent with that of coarse-grained copper. Total elongations of {approx} 1% were observed in samples with grain sizes less than 50 nm, while a sample with a grain size of 110 nm exhibited more than 10% elongation, perhaps signifying a change to a dislocation-based deformation mechanism in the larger-grained material. In addition, tensile tests were performed as a function of strain rate, with a possible trend of decreased strength and increased elongation as the strain rate was decreased.
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Microfabrication and characterization of high-density ferromagnetic arrays

Microfabrication and characterization of high-density ferromagnetic arrays

Date: February 24, 1999
Creator: Cerjan, C & Fernandez, A
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Process Hood Stand Support Steel

Process Hood Stand Support Steel

Date: October 2, 2000
Creator: SINGH, G.
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Impurity effects on pore formation at Al2O3/Alloy interfaces

Impurity effects on pore formation at Al2O3/Alloy interfaces

Date: November 30, 2001
Creator: Hou, Peggy Y.
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Can laterally overgrown GaN layers be free of structural defects?

Can laterally overgrown GaN layers be free of structural defects?

Date: July 31, 2002
Creator: Cherns, D. & Liliental-Weber, Z.
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Laboratory-directed research and development: FY 1996 progress report

Laboratory-directed research and development: FY 1996 progress report

Date: May 1, 1997
Creator: Vigil, J. & Prono, J.
Description: This report summarizes the FY 1996 goals and accomplishments of Laboratory-Directed Research and Development (LDRD) projects. It gives an overview of the LDRD program, summarizes work done on individual research projects, and provides an index to the projects` principal investigators. Projects are grouped by their LDRD component: Individual Projects, Competency Development, and Program Development. Within each component, they are further divided into nine technical disciplines: (1) materials science, (2) engineering and base technologies, (3) plasmas, fluids, and particle beams, (4) chemistry, (5) mathematics and computational sciences, (6) atomic and molecular physics, (7) geoscience, space science, and astrophysics, (8) nuclear and particle physics, and (9) biosciences.
Contributing Partner: UNT Libraries Government Documents Department
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