Surface engineering of glazing materials and structures using plasma processes (open access)

Surface engineering of glazing materials and structures using plasma processes

A variety of coatings is commercially produced on a very large scale, including transparent conducting oxides and multi-layer silver-based low-emissivity and solar control coatings. A very brief review of materials and manufacturing process is presented and illustrated by ultrathin silver films and chevron copper films. Understanding the close relation between manufacturing processes and bulk and surface properties of materials is crucial for film growth and self-assembly processes.
Date: April 10, 2003
Creator: Anders, Andre & Monteiro, Othon R.
System: The UNT Digital Library
Dislocation Density-Based Constitutive Model for the Mechanical Behavior of Irradiated Cu (open access)

Dislocation Density-Based Constitutive Model for the Mechanical Behavior of Irradiated Cu

Performance degradation of structural steels in nuclear environments results from the development of a high number density of nanometer scale defects. The defects observed in copper-based alloys are composed of vacancy clusters in the form of stacking fault tetrahedra and/or prismatic dislocation loops, which impede dislocation glide and are evidenced in macroscopic uniaxial stress-strain curves as increased yield strengths, decreased total strain to failure, decreased work hardening and the appearance of a distinct upper yield point above a critical defect concentration (neutron dose). In this paper, we describe the development of an internal state variable model for the mechanical behavior of materials subject to these environments. This model has been developed within an information-passing multiscale materials modeling framework, in which molecular dynamics simulations of dislocation--radiation defect interactions, inform the final coarse-grained continuum model. The plasticity model includes mechanisms for dislocation density growth and multiplication and for radiation defect density evolution with dislocation interaction. The general behavior of the constitutive (single material point) model shows that as the defect density increases, the initial yield point increases and the initial strain hardening decreases. The final coarse-grained model is implemented into a finite element framework and used to simulate the behavior of tensile …
Date: April 10, 2003
Creator: Arsenlis, A.; Wirth, B. D. & Rhee, M.
System: The UNT Digital Library
Optimization of Beam Injection into the First Accelerating Module at TTF With Cavity Dipole Mode Signals (open access)

Optimization of Beam Injection into the First Accelerating Module at TTF With Cavity Dipole Mode Signals

The TESLA Test Facility (TTF) is a user facility for intense VUV-FEL light. The facility is densely equipped with diagnostics, essential in obtaining the necessary beam parameters, in particular the low emittance. However there is no dedicated component for alignment of the beam in the accelerating modules, each containing eight superconducting cavities. Large beam offsets can lead to an increase of the beam emittance. The centering of the beam in these modules is therefore important, mostly at the low energy end. A misalignment of the first TTF module with respect to the gun axis has already been observed using cavity dipole modes. This paper presents the experimental results of the optimization of the beam injection into the first module, based on the monitoring of dipole modes through the couplers installed for wakefield damping. For this we use a spectrum analyzer together with a multiplexer. By scanning the beam position and tilt with two pairs of steerers, we can find the trajectory which minimizes the dipole modes amplitude. The impact of the beam steering in the module on the beam is discussed. A time domain setup is also being presented.
Date: April 10, 2006
Creator: Baboi, N.; Kreps, G.; Schlarb, H.; Wendt, M.; Frisch, J.; McCormick, D. et al.
System: The UNT Digital Library
Size-Resolved Particle Number and Volume Emission Factors for On-Road Gasoline and Diesel Motor Vehicles (open access)

Size-Resolved Particle Number and Volume Emission Factors for On-Road Gasoline and Diesel Motor Vehicles

Average particle number concentrations and size distributions from {approx}61,000 light-duty (LD) vehicles and {approx}2500 medium-duty (MD) and heavy-duty (HD) trucks were measured during the summer of 2006 in a San Francisco Bay area traffic tunnel. One of the traffic bores contained only LD vehicles, and the other contained mixed traffic, allowing pollutants to be apportioned between LD vehicles and diesel trucks. Particle number emission factors (particle diameter D{sub p} > 3 nm) were found to be (3.9 {+-} 1.4) x 10{sup 14} and (3.3 {+-} 1.3) x 10{sup 15} kg{sup -1} fuel burned for LD vehicles and diesel trucks, respectively. Size distribution measurements showed that diesel trucks emitted at least an order of magnitude more particles for all measured sizes (10 < D{sub p} < 290 nm) per unit mass of fuel burned. The relative importance of LD vehicles as a source of particles increased as D{sub p} decreased. Comparing the results from this study to previous measurements at the same site showed that particle number emission factors have decreased for both LD vehicles and diesel trucks since 1997. Integrating size distributions with a volume weighting showed that diesel trucks emitted 28 {+-} 11 times more particles by volume than …
Date: April 10, 2009
Creator: Ban-Weiss, George A.; Lunden, Melissa M.; Kirchstetter, Thomas W. & Harley, Robert A.
System: The UNT Digital Library
Chemical Effect of Dry and Wet Cleaning of the Ru Protective Layer of the Extreme ultraviolet (EUV) Lithography Reflector (open access)

Chemical Effect of Dry and Wet Cleaning of the Ru Protective Layer of the Extreme ultraviolet (EUV) Lithography Reflector

The authors report the chemical influence of cleaning of the Ru capping layer on the extreme ultraviolet (EUV) reflector surface. The cleaning of EUV reflector to remove the contamination particles has two requirements: to prevent corrosion and etching of the reflector surface and to maintain the reflectivity functionality of the reflector after the corrosive cleaning processes. Two main approaches for EUV reflector cleaning, wet chemical treatments [sulfuric acid and hydrogen peroxide mixture (SPM), ozonated water, and ozonated hydrogen peroxide] and dry cleaning (oxygen plasma and UV/ozone treatment), were tested. The changes in surface morphology and roughness were characterized using scanning electron microscopy and atomic force microscopy, while the surface etching and change of oxidation states were probed with x-ray photoelectron spectroscopy. Significant surface oxidation of the Ru capping layer was observed after oxygen plasma and UV/ozone treatment, while the oxidation is unnoticeable after SPM treatment. Based on these surface studies, the authors found that SPM treatment exhibits the minimal corrosive interactions with Ru capping layer. They address the molecular mechanism of corrosive gas and liquid-phase chemical interaction with the surface of Ru capping layer on the EUV reflector.
Date: April 10, 2009
Creator: Belau, Leonid; Park, Jeong Y.; Liang, Ted; Seo, Hyungtak & Somorjai, Gabor A.
System: The UNT Digital Library
The NLO Multileg Working Group: Summary Report (open access)

The NLO Multileg Working Group: Summary Report

None
Date: April 10, 2008
Creator: Bern, Z.; Bernicot, C.; Binoth, T.; Boudjema, F.; Britto, R.; Campbell, J. et al.
System: The UNT Digital Library
Novel High Transverse Momentum Phenomena in Hadronic and Nuclear Collisions (open access)

Novel High Transverse Momentum Phenomena in Hadronic and Nuclear Collisions

I discuss a number of novel phenomenological features of QCD in high transverse momentum reactions. The presence of direct higher-twist processes, where a proton is produced directly in the hard subprocess, can explain the 'baryon anomaly' - the large proton-to-pion ratio seen at RHIC in high centrality heavy ion collisions. Direct hadronic processes can also account for the deviation from leading-twist PQCD scaling at fixed x{sub T} = 2 p{sub T}/{radical}s. I suggest that the 'ridge' --the same-side long-range rapidity correlation observed at RHIC in high centrality heavy ion collisions is due to the imprint of semihard DGLAP gluon radiation from initial-state partons which have transverse momenta biased toward the trigger. A model for early thermalization of the quark-gluon medium is also outlined. Rescattering interactions from gluon-exchange, normally neglected in the parton model, have a profound effect in QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, the breakdown of the Lam-Tung relation in Drell-Yan reactions, nuclear shadowing--all leading-twist dynamics not incorporated in the light-front wavefunctions of the target computed in isolation. Anti shadowing is shown to be quark flavor specific and thus different in charged and neutral deep inelastic lepton-nucleus scattering. I …
Date: April 10, 2009
Creator: Brodsky, Stanley J.
System: The UNT Digital Library
Dynamic Estimation of the Sound-Speed Profile from Broadband Acoustic Measurements (open access)

Dynamic Estimation of the Sound-Speed Profile from Broadband Acoustic Measurements

None
Date: April 10, 2007
Creator: Carriere, O; Hermand, J; Meyer, M & Candy, J V
System: The UNT Digital Library
Field evidence for strong chemical separation of contaminants in the Hanford Vadose Zone (open access)

Field evidence for strong chemical separation of contaminants in the Hanford Vadose Zone

Water and chemical transport from a point source withinvadose zone sediments at Hanford were examined with a leak testconsisting of five 3800-liter aliquots of water released at 4.5 m depthevery week over a 4-week period. The third aliquot contained bromide, D2Oand 87Sr. Movement of the tracers was monitored for 9 months by measuringpore water compositions of samples from boreholes drilled 2-8 m from theinjection point. Graded sedimentary layers acting as natural capillarybarriers caused significant lateral spreading of the leak water. D2Oconcentrations>50 percent of the concentration in the tracer aliquotwere detected at 9-11 m depth. However, increased water contents, lowerd18O values, and geophysical monitoring of moisture changes at otherdepths signified high concentrations of leak fluids were added where D2Oconcentrations were<3 percent above background, suggesting limitedmixing between different aliquots of the leak fluids. Initially highbromide concentrations decreased more rapidly over time than D2O,suggesting enhanced transport of bromide due to anion exclusion. Nosignificant increase in 87Sr was detected in the sampled pore water,indicating strong retardation of Sr by the sediments. These resultshighlight some of the processes strongly affecting chemical transport inthe vadose zone and demonstrate the significant separation of contaminantplumes that can occur.
Date: April 10, 2007
Creator: Conrad, Mark E.; DePaolo, Donald J.; Maher, Katharine; Gee,Glendon W. & Ward, Anderson L.
System: The UNT Digital Library
Barium in Twilight Zone suspended matter as a potential proxy for particulate organic carbon remineralization: Results for the North Pacific (open access)

Barium in Twilight Zone suspended matter as a potential proxy for particulate organic carbon remineralization: Results for the North Pacific

This study focuses on the fate of exported organic carbon in the twilight zone at two contrasting environments in the North Pacific: the oligotrophic ALOHA site (22 degrees 45 minutes N 158 degrees W; Hawaii; studied during June-July 2004) and the mesotrophic Subarctic Pacific K2 site (47 degrees N, 161 degrees W; studied during July-August 2005). Earlier work has shown that non-lithogenic, excess particulate Ba (Ba{sub xs}) in the mesopelagic water column is a potential proxy of organic carbon remineralization. In general Ba{sub xs} contents were significantly larger at K2 than at ALOHA. At ALOHA the Ba{sub xs} profiles from repeated sampling (5 casts) showed remarkable consistency over a period of three weeks, suggesting that the system was close to being at steady state. In contrast, more variability was observed at K2 (6 casts sampled) reflecting the more dynamic physical and biological conditions prevailing in this environment. While for both sites Ba{sub xs} concentrations increased with depth, at K2 a clear maximum was present between the base of the mixed layer at around 50m and 500m, reflecting production and release of Ba{sub xs}. Larger mesopelagic Ba{sub xs} contents and larger bacterial production in the twilight zone at the K2 site …
Date: April 10, 2008
Creator: Dehairs, F.; Jacquet, S.; Savoye, N.; Van Mooy, B. A. S.; Buesseler, K.; Bishop, J. K. B. et al.
System: The UNT Digital Library
Cosmic microwave background: Past, future, and present (open access)

Cosmic microwave background: Past, future, and present

Anisotropies in the Cosmic Microwave Background (CMB) carry an enormous amount of information about the early universe. The anisotropy spectrum depends sensitively on close to a dozen cosmological parameters, some of which have never been measured before. Experiments over the next decade will help us extract these parameters, teaching us not only about the early universe, but also about physics at unprecedented energies. One of the dangers now is that scientist are tempted to ignore the present data and rely too much on the future. This would be a shame, for hundreds of individuals have put in a great amount of time building state-of-the-art instruments, making painstaking observations at remote places on and off the globe. It seems unfair to ignore all the data that has been taken to date simply because there will be more and better data in the future. The author then makes the following claims: (1) the theory of CMB anisotropies is understood; (2) using this understanding, he is able to extract from future observations extremely accurate measurements of about ten cosmological parameters; (3) taken at face value, present data determines one of these parameters, the curvature of the universe; and (4) the present data is …
Date: April 10, 2000
Creator: Dodelson, S.
System: The UNT Digital Library
Modeling Supercritical Carbon Dioxide Injection in Heterogeneous Porous Media (open access)

Modeling Supercritical Carbon Dioxide Injection in Heterogeneous Porous Media

We investigate the physical processes that occur during the sequestration of carbon dioxide (CO2) in liquid-saturated, brine-bearing geologic formations using the numerical simulator TOUGH2. CO2 is injected in a supercritical state that has a much lower density and viscosity than the liquid brine it displaces. In situ, the supercritical CO2 forms a gas-like phase, and also partially dissolves in the aqueous phase, creating a multi-phase, multi-component environment that shares many important features with the vadose zone. The flow and transport simulations employ an equation of state package that treats a two-phase (liquid, gas), three-component (water, salt, CO2) system. Chemical reactions between CO2 and rock minerals that could potentially contribute to mineral trapping of CO2 are not included. The geological setting considered is a fluvial/deltaic formation that is strongly heterogeneous, making preferential flow a significant effect, especially when coupled with the strong buoyancy forces acting on the gas-like CO2 plume. Key model development issues include vertical and lateral grid resolution, grid orientation effects, and the choice of characteristic curves.
Date: April 10, 2003
Creator: Doughty, Christine & Pruess, Karsten
System: The UNT Digital Library
Modeling supercritical CO2 injection in heterogeneous porous media (open access)

Modeling supercritical CO2 injection in heterogeneous porous media

We investigate the physical processes that occur during the sequestration of CO{sub 2} in brine-bearing geologic formations using TOUGH2. An equation of state package that treats a two-phase (liquid, gas), three-component (water, salt, and CO{sub 2}) system is employed. CO{sub 2} is injected in a supercritical state that has a much lower density and viscosity than the liquid brine it displaces. In situ, the supercritical CO{sub 2} forms a gas-like phase, and also partially dissolves in the aqueous phase. Chemical reactions between CO{sub 2} and rock minerals that could potentially contribute to mineral trapping of CO{sub 2} are not included. The geological setting considered is a fluvial/deltaic formation that is strongly heterogeneous, making preferential flow a significant effect, especially when coupled with the strong buoyancy forces acting on the gas-like CO{sub 2} plume. Key model development concerns include vertical and lateral grid resolution, grid orientation effects, and the choice of characteristic curves.
Date: April 10, 2003
Creator: Doughty, Christine & Pruess, Karsten
System: The UNT Digital Library
Cross-flow Ultrafiltration Scaling Considerations (open access)

Cross-flow Ultrafiltration Scaling Considerations

One legacy of the nuclear age is radioactive waste and it must be stabilized to be stored in a safe manner. An important part of the stabilization process is the separation of radioactive solids from the liquid wastes by cross-flow ultrafiltration. The performance of this technology with the wastes to be treated was unknown and, therefore, had to be obtained. However, before beginning a filter study the question of experimental scale had to be addressed. Of course, carrying out experiments using full-size equipment is always ideal, but rarely practical when dealing with plant size processes. Flow loops that will handle millions of liters of slurries, which are either highly caustic or acidic, with flow rates of 10,000 lpm make full-scale tests prohibitively expensive. Moreover, when the slurries happen to be radioactive such work is also very dangerous. All of these considerations lend themselves to investigations at smaller scales and in many situations can be treated with computational analyses. Unfortunately, as scale is reduced it becomes harder to provide prototypic results and the two and three phase multi-component mixtures challenge accurate computational results. To obtain accurate and representative filter results the use of two scales were chosen: (1) Small-scale--would allow the …
Date: April 10, 2006
Creator: Duignan, M
System: The UNT Digital Library
Metrics and Benchmarks for Energy Efficiency in Laboratories (open access)

Metrics and Benchmarks for Energy Efficiency in Laboratories

A wide spectrum of laboratory owners, ranging from universities to federal agencies, have explicit goals for energy efficiency in their facilities. For example, the Energy Policy Act of 2005 (EPACT 2005) requires all new federal buildings to exceed ASHRAE 90.1-2004 [1] by at least 30%. A new laboratory is much more likely to meet energy efficiency goals if quantitative metrics and targets are specified in programming documents and tracked during the course of the delivery process. If not, any additional capital costs or design time associated with attaining higher efficiencies can be difficult to justify. This article describes key energy efficiency metrics and benchmarks for laboratories, which have been developed and applied to several laboratory buildings--both for design and operation. In addition to traditional whole building energy use metrics (e.g. BTU/ft{sup 2}.yr, kWh/m{sup 2}.yr), the article describes HVAC system metrics (e.g. ventilation W/cfm, W/L.s{sup -1}), which can be used to identify the presence or absence of energy features and opportunities during design and operation.
Date: April 10, 2008
Creator: Engineers, Rumsey; Mathew, Paul; Mathew, Paul; Greenberg, Steve; Sartor, Dale; Rumsey, Peter et al.
System: The UNT Digital Library
Beam-beam simulations for separated beams (open access)

Beam-beam simulations for separated beams

We present beam-beam simulation results from a strong-strong gaussian code for separated beams for the LHC and RHIC. The frequency spectrum produced by the beam-beam collisions is readily obtained and offers a good opportunity for experimental comparisons. Although our results for the emittance blowup are preliminary, we conclude that, for nominal parameter values, there is no significant difference between separated beams and center-on-center collisions.
Date: April 10, 2000
Creator: Furman, Miguel A.
System: The UNT Digital Library
Criteria for the Certification of Non-Radioactive Hazardous Waste (open access)

Criteria for the Certification of Non-Radioactive Hazardous Waste

In 1991, in response to the Department of Energy (DOE) Moratorium on the shipment of hazardous waste from Radioactive Materials Management Areas (RMMAs), Lawrence Livermore National Laboratory (LLNL) developed a process to use a combination of generator knowledge and/or sampling and analyses to certify waste as non-radioactive. The analytical process used the minimum detectable activity (MDA) as the de minimus value. In the past twelve years, a great deal of operating experience has shown the LLNL certification process has serious limitations including: (1) Procedure-specified analytical methodologies have resulted in the inability to adopt new techniques and methods that are more rapid, safer, and produce less waste. (2) The characterization of materials as radioactive or non-radioactive is dependent on method-specific detection limits, not on an objective risk-based standard. (3) There are substantial differences in the limits for surface contamination, sewer discharges, and hazardous waste moratorium determinations, even though all of these methods are used to free-release materials from radiological controls. LLNL, in conjunction with the Chamberlain Group and Dade Moeller & Associates, Inc., is pursuing a risk-based approach to determine whether waste is non-radioactive, consistent with DOE guidance. This paper discusses the approach, which includes defining the radionuclides considered, establishing the …
Date: April 10, 2003
Creator: Gagner, S D; Gaylord, R; Govers, R; Kennedy, W E; Hunnacek, M M & Kennedy, A M
System: The UNT Digital Library
Making nanostructured pyrotechnics in a beaker (open access)

Making nanostructured pyrotechnics in a beaker

Controlling composition at the nanometer scale is well known to alter material properties in sometimes highly desirable and dramatic ways. In the field of energetic materials component distributions, particle size, and morphology, effect both sensitivity and reactivity performance. To date nanostructured energetic materials are largely unknowns with the exception of nanometer-sized reactive powders now being produced at a number of laboratories. We have invented a new method of making nanostructured energetic materials, specifically explosives, propellants, and pyrotechnics, using sol-gel chemistry. The ease of this synthetic approach along with the inexpensive, stable, and benign nature of the metal precursors and solvents permit large-scale syntheses to be carried out. This approach can be accomplished using low cost processing methods. We will describe here, for the first time, this new synthetic route for producing metal-oxide-based pyrotechnics. The procedure employs the use of stable and inexpensive hydrated-metal inorganic salts and environmentally friendly solvents such as water and ethanol. The synthesis is straightforward and involves the dissolution the metal salt in a solvent followed by the addition of an epoxide, which induces gel formation in a timely manner. Experimental evidence suggests that the epoxide acts as an irreversible proton scavenger that induces the hydrated-metal species …
Date: April 10, 2000
Creator: Gash, A. E.; Simpson, R. L.; Tillotson, T. M.; Satcher, J. H. & Hrubesh, L. W.
System: The UNT Digital Library
DNA-PKcs is critical for telomere capping (open access)

DNA-PKcs is critical for telomere capping

The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is critical for DNA repair via the non-homologous end joining (NHEJ) pathway. Previously, it was reported that bone marrow cells and spontaneously transformed fibroblasts from SCID (severe combined immunodeficiency) mice have defects in telomere maintenance. The genetically defective SCID mouse arose spontaneously from its parental strain CB17. One known genomic alteration in SCID mice is a truncation of the extreme carboxyl-terminus of DNA-PKcs, but other as yet unidentified alterations may also exist. We have used a defined system, the DNA-PKcs knockout mouse, to investigate specifically the role DNA-PKcs specifically plays in telomere maintenance. We report that primary mouse embryonic fibroblasts (MEFs) and primary cultured kidney cells from 6-8 month old DNA-PKcs deficient mice accumulate a large number of telomere fusions, yet still retain wildtype telomere length. Thus, the phenotype of this defect separates the two-telomere related phenotypes, capping and length maintenance. DNA-PKcs deficient MEFs also exhibit elevated levels of chromosome fragments and breaks, which correlate with increased telomere fusions. Based on the high levels of telomere fusions observed in DNA-PKcs deficient cells, we conclude that DNA-PKcs plays an important capping role at the mammalian telomere.
Date: April 10, 2001
Creator: Gilley, David; Tanaka, Hiromi; Hande, M. Prakash; Kurimasa,Akihiro; Li, Gloria C. & Chen, David J.
System: The UNT Digital Library
First principles simulation of a superionic phase of hydrogen fluoride (HF) at high pressures and temperatures (open access)

First principles simulation of a superionic phase of hydrogen fluoride (HF) at high pressures and temperatures

The authors have conducted Ab initio molecular dynamics simulations of hydrogen fluoride (HF) at pressures of 5-66 GPa along the 900 K isotherm. They predict a superionic phase at 33 GPa, where the fluorine atoms are fixed in a bcc lattice while the hydrogen atoms diffuse rapidly with a diffusion constant of between 2 x 10{sup -5} and 5 x 10{sup -5} cm{sup 2}/s. They find that a transformation from asymmetric to symmetric hydrogen bonding occurs in HF at 66 GPa and 900 K. With superionic HF they have discovered a model system where symmetric hydrogen bonding occurs at experimentally achievable conditions. Given previous results on superionic H{sub 2}O[1,2,3] and NH{sub 3}[1], they conclude that high P,T superionic phases of electronegative element hydrides could be common.
Date: April 10, 2006
Creator: Goldman, N & Fried, L E
System: The UNT Digital Library
2006 Reversible Associations in Structural and Molecular Biology Conference-January 15-20, 2006 (open access)

2006 Reversible Associations in Structural and Molecular Biology Conference-January 15-20, 2006

Many biological processes are carried out through the formation of macromolecular complexes, ranging from the simplest conformational organization to the most sophisticated interactions among complexes themselves. Reversible associations generate specific local conformations, active site configurations, and subunit--subunit interfaces, and encompass larger scale quaternary rearrangements and dissociation events. Assembled complexes exhibit properties different from those of component parts, such that 'the whole is greater than the sum of the parts', resulting in biological functioning of the assembly. This Gordon Research Conference brings together researchers from what may appear to be disparate fields with the common focus of applying quantitative kinetic and thermodynamic analysis to reversible macromolecular interactions. This conference will include the following session topics: (1) Protein design in evolution and recognition; (2) Emerging technologies; (3) Single molecule mechanics; (4) Nucleic acid/protein recognition; (5) Lipid/protein recognition; (6) Protein switches and networks; (7) Advances in classic technologies; (8) Ligand/macromolecule complexes and drug design; and (9) Selected student oral presentations; all from the perspective of reversibly associating systems. A wide array of techniques are typically covered, from single molecule to computational methods, chromatography and analytical ultracentrifugation, spectroscopic dynamics and titration calorimetry. The quantitative analysis of assembled complexes demonstrates that these biologically important functions …
Date: April 10, 2007
Creator: Gray, Gary Ackers Nancy Ryan
System: The UNT Digital Library
An Analysis of the X-Ray Diffraction Signal for the (alpha) - (epsilon) Transition in Shock-Compressed Iron: Simulation and Experiment (open access)

An Analysis of the X-Ray Diffraction Signal for the (alpha) - (epsilon) Transition in Shock-Compressed Iron: Simulation and Experiment

Recent published work has shown that the phase change of shock compressed iron along the [001] direction does transform to the {epsilon} (HCP) phase similar to the case for static measurements. This article provides an indepth analysis of the experiment and NEMD simulations, using x-ray diffraction in both cases to study the crystal structure upon transition. Both simulation and experiment are consistent with a compression and shuffle mechanism responsible for the phase change from BCC to HCP. Also both show a polycrystalline structure upon the phase transition, due to the four degenerate directions the phase change can occur on, with grain sizes measured of 4nm in the NEMD simulations and {approx} 2nm in the experiment. And looking at the time scale of the transition the NEMD shows the transition from the compressed BCC to HCP is less then 1.2 ps where the experimental data places an upper limit on the transition of 80 ps.
Date: April 10, 2006
Creator: Hawreliak, J; Colvin, J D; Kalantar, D H; Lorenzana, H E; Stolken, J S; Davies, H M et al.
System: The UNT Digital Library
Characterization of chemical bonding in low-k dielectric materialsfor interconnect isolation: a xas and eels study (open access)

Characterization of chemical bonding in low-k dielectric materialsfor interconnect isolation: a xas and eels study

The use of low dielectric constant materials in the on-chipinterconnect process reduces interconnect delay, power dissipation andcrosstalk noise. To achieve the requirements of the ITRS for 2007-2009minimal sidewall damage from etch, ash or cleans is required. In chemicalvapor deposited (CVD) organo-silicate glass (OSG) which are used asintermetal dielectric (IMD) materials the substitution of oxygen in SiO2by methyl groups (-CH3) reduces the permittivity significantly (from 4.0in SiO2 to 2.6-3.3 in the OSG), since the electronic polarizability islower for Si-C bonds than for Si-O bonds. However, plasma processing forresist stripping, trench etching and post-etch cleaning removes C and Hcontaining molecular groups from the near-surface layer of OSG.Therefore, compositional analysis and chemical bonding characterizationof structured IMD films with nanometer resolution is necessary forprocess optimization. OSG thin films as-deposited and after plasmatreatment are studied using X-ray absorption spectroscopy (XAS) andelectron energy loss spectroscopy (EELS). In both techniques, the finestructure near the C1s absorption or energy loss edge, respectively,allows to identify C-H, C-C, and C-O bonds. This gives the opportunity todifferentiate between individual low-k materials and their modifications.The O1s signal is less selective to individual bonds. XAS spectra havebeen recorded for non-patterned films and EELS spectra for patternedstructures. The chemical bonding is compared for as-deposited …
Date: April 10, 2006
Creator: Hoffmann, P.; Schmeisser, D.; Engelmann, H. J.; Zschech, E.; Stegmann, H.; Himpsel, F. et al.
System: The UNT Digital Library
Methods and Results of Reducing Following Error in the LLNL Large Optics Diamond Turning Machine (open access)

Methods and Results of Reducing Following Error in the LLNL Large Optics Diamond Turning Machine

The USAF Integrated Flight Experiment (IFX) Project is part of the development of the Space Based Laser (SBL) Program. The LLNL Large Optics Diamond Turning Machine (LODTM) is responsible for diamond turning the aspheric laser cavity mirrors. These large optics must be manufactured to micro-inch tolerances. The optics are made of silicon to minimize cooling requirements and weight in the SBL. Diamond turning silicon presents many challenges to the LODTM; one of which is silicon's anisotropic property. When cutting these cones shaped optics, the machine sees many different crystallographic planes of the silicon. These planes present different degrees of material hardness. The tool is held in position but it experiences a force variation as it cuts across the different crystallographic planes. This force variation is reflected back into the machine control system and presents a dynamic disturbance that increases the servo system following error. The affect of this error is to cut a part that is not round but 'squareish', i.e. at the micro-inch level. Two methods were used to reduce the following error or increase the machine dynamic stiffness. Each method relies on the fact that the cutting process is cyclic. The two methods are described below. Method one …
Date: April 10, 2001
Creator: Hopkins, D J
System: The UNT Digital Library