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Inertial Confinement Fusion Materials Science

Description: Demonstration of thermonuclear ignition and gain on a laboratory scale is one of science's grand challenges. The National Ignition Facility (NIF) is committed to achieving inertial confinement fusion (ICF) by 2010. Success in this endeavor depends on four elements: the laser driver performance, target design, experimental diagnostics performance, and target fabrication and target materials performance. This article discusses the current state of target fabrication and target materials performance. The first three elements will only be discussed insofar as they relate to target fabrication specifications and target materials performance. Excellent reviews of the physics of ICF are given by Lindl [Lindl 1998] and Lindl et al. [Lindl 2004]. To achieve conditions under which inertial confinement is sufficient to achieve thermonuclear burn, an imploded fuel capsule is compressed to conditions of high density and temperature. In the laboratory a driver is required to impart energy to the capsule to effect an implosion. There are three drivers currently being considered for ICF in the laboratory: high-powered lasers, accelerated heavy ions, and x rays resulting from pulsed power machines. Of these, high-powered lasers are the most developed, provide the most symmetric drive, and provide the most energy. Laser drive operates in two configurations. The first is direct drive where the laser energy impinges directly on the ICF capsule and drives the implosion. The second is indirect drive, where the energy from the laser is first absorbed in a high-Z enclosure or hohlraum surrounding the capsule, and the resulting x-rays emitted by the hohlraum material drives the implosion. Using direct drive the laser beam energy is absorbed by the electrons in the outer corona of the target. The electrons transport the energy to the denser shell region to provide the ablation and the resulting implosion. Laser direct drive is generally less efficient and more hydrodynamically ...
Date: June 1, 2004
Creator: Hamza, A V
Partner: UNT Libraries Government Documents Department

Nanoscale Synthesis and Characterization Laboratory Annual Report 2007

Description: The Nanoscale Synthesis and Characterization Laboratory's (NSCL) primary mission is to create and advance interdisciplinary research and development opportunities in nanoscience and technology. The NSCL is delivering on its mission providing Laboratory programs with scientific solutions through the use of nanoscale synthesis and characterization. While this annual report summarizes 2007 activities, we have focused on nanoporous materials, advanced high strength, nanostructured metals, novel 3-dimensional lithography and characterization at the nanoscale for the past 3 years. In these three years we have synthesized the first monolithic nanoporous metal foams with less than 10% relative density; we have produced ultrasmooth nanocrystalline diamond inertial confinement fusion capsules; we have synthesized 3-dimensional graded density structures from full density to 5% relative density using nanolithography; and we have established ultrasmall angle x-ray scattering as a non-destructive tool to determine the structure on the sub 300nm scale. The NSCL also has a mission to recruit and to train personnel for Lab programs. The NSCL continues to attract talented scientists to the Laboratory. Andrew Detor from Massachusetts Institute of Technology, Sutapa Ghosal from the University of California, Irvine, Xiang Ying Wang from Shanghai Institute of Technology, and Arne Wittstock from University of Bremen joined the NSCL this year. The NSCL is pursuing four science and technology themes: nanoporous materials, advanced nanocrystalline materials, novel three-dimensional nanofabrication technologies, and nondestructive characterization at the mesoscale. The NSCL is also pursuing building new facilities for science and technology such as nanorobotics and atomic layer deposition.
Date: April 7, 2008
Creator: Hamza, A V
Partner: UNT Libraries Government Documents Department

Growth of silicon carbide on silicon via reaction of sublimed fullerenes and silicon

Description: Epitaxial silicon carbide films are grown on Si(100) substrates at a surface temperature of 1,200 K via fullerene precursors. Films have been grown up to a thickness of 2,500 {angstrom}. The growth rate of the SiC film is not limited by the surface reaction rate of fullerene with silicon at these temperatures, rather by the arrival rate of the reactants Si (by diffusion from substrate or from gas phase) or fullerene. This results in rapid film growth. Films have been characterized by low energy electron diffraction, ultraviolet photoelectron spectroscopy and Auger electron spectroscopy. Stoichiometric, epitaxial SiC films are grown. Supply of silicon to the growing SiC surface via sublimation greatly reduces the tendency for silicon diffusion to form voids at the Si/SiC interface.
Date: February 1, 1996
Creator: Hamza, A.V. & Balooch, M.
Partner: UNT Libraries Government Documents Department

Microscopic failure behavior of nanoporous Gold

Description: Nanoporous metals have recently attracted considerable interest fueled by potential sensor and actuator applications. One of the key issues in this context is the synthesis of high yield strength materials. Nanoporous Au (np-Au) has been suggested as a candidate due to its monolithic character. The material can be synthesized by dealloying Ag-Au alloys, and exhibits an open sponge-like morphology of interconnecting Au ligaments with a typical pore size distribution on the nanometer length scale. Unfortunately, very little is known about the mechanical properties of np-Au besides a length-scale dependent ductile-brittle transition. A key question in this context is: what causes the macroscopic brittleness of np-Au? Is the normal dislocation-mediated plastic deformation suppressed in nanoscale Au ligaments, or is the brittleness a consequence of the macroscopic morphology? Here, we report on the fracture behavior of nanoporous Au studied by scanning electron microscopy. Specifically, we demonstrate the microscopic ductility of nanometer-sized Au ligaments. The observed fracture behavior seems to be general for nanoporous metals, and can be understood in terms of simple fuse networks.
Date: January 10, 2005
Creator: Biener, J.; Hodge, A. & Hamza, A.
Partner: UNT Libraries Government Documents Department

Nanoscale Synthesis and Characterization Laboratory Annual Report 2005

Description: The Nanoscale Synthesis and Characterization Laboratory's (NSCL) primary mission is to create and advance interdisciplinary research and development opportunities in nanoscience and technology. The initial emphasis of the NSCL has been on development of scientific solutions in support of target fabrication for the NIF laser and other stockpile stewardship experimental platforms. Particular emphasis has been placed on the design and development of innovative new materials and structures for use in these targets. Projects range from the development of new high strength nanocrystalline alloys to graded density materials to high Z nanoporous structures. The NSCL also has a mission to recruit and train personnel for Lab programs such as the National Ignition Facility (NIF), Defense and Nuclear Technologies (DNT), and Nonproliferation, Arms control and International security (NAI). The NSCL continues to attract talented scientists to the Laboratory.
Date: January 3, 2006
Creator: Hamza, A V & Lesuer, D R
Partner: UNT Libraries Government Documents Department

Simulation of three-phase fluidized bioreactors for denitrification

Description: Fluidized-bed bioreactors were developed and operated at three scales (diameters of 0.1, 0.2, and 0.5 m) by the Chemical Technology Division. The performance of these reactors in denitrification was simulated using the following modified form of Monod kinetics to describe the reaction kinetics: rate = V/sub max/ (NO/sub 3//sup -//K/sub s/ + NO/sub 3//sup -/) (% biomass). In the fluids-movement portion of the simulation the tanks-in-series approximation to backmixing was used. This approach yielded a V/sub max/ of 3.5 g/m/sup 3/-min (% biomass) and a K/sub s/ of 163 g/m/sup 3/ for the 0.5-m bioreactor. Values of V/sub max/ and K/sub s/ were also determined for data derived from the 0.1-m bioreactor, but inadequate RTD data reduced the confidence level in these results. A complication in denitrification is the multi-step nature of the reduction from nitrate to nitrite to hyponitrite and finally to nitrogen. An experimental study of the effect of biomass loading upon denitrification was begun. It is recommended that the experimental work be continued.
Date: March 1, 1981
Creator: Hamza, A.V.; Dolan, J.F. & Wong, E.W.
Partner: UNT Libraries Government Documents Department

Deformation Behavior of Nanoporous Metals

Description: Nanoporous open-cell foams are a rapidly growing class of high-porosity materials (porosity {ge} 70%). The research in this field is driven by the desire to create functional materials with unique physical, chemical and mechanical properties where the material properties emerge from both morphology and the material itself. An example is the development of nanoporous metallic materials for photonic and plasmonic applications which has recently attracted much interest. The general strategy is to take advantage of various size effects to introduce novel properties. These size effects arise from confinement of the material by pores and ligaments, and can range from electromagnetic resonances to length scale effects in plasticity. In this chapter we will focus on the mechanical properties of low density nanoporous metals and how these properties are affected by length scale effects and bonding characteristics. A thorough understanding of the mechanical behavior will open the door to further improve and fine-tune the mechanical properties of these sometimes very delicate materials, and thus will be crucial for integrating nanoporous metals into products. Cellular solids with pore sizes above 1 micron have been the subject of intense research for many years, and various scaling relations describing the mechanical properties have been developed.[4] In general, it has been found that the most important parameter in controlling their mechanical properties is the relative density, that is, the density of the foam divided by that of solid from which the foam is made. Other factors include the mechanical properties of the solid material and the foam morphology such as ligament shape and connectivity. The characteristic internal length scale of the structure as determined by pores and ligaments, on the other hand, usually has only little effect on the mechanical properties. This changes at the submicron length scale where the surface-to-volume ratio becomes large and the ...
Date: November 28, 2007
Creator: Biener, J.; Hodge, A. M. & Hamza, A. V.
Partner: UNT Libraries Government Documents Department

Bonding Low-density Nanoporous Metal Foams Using Sputtered Solder

Description: A method has been developed for bonding low-density nanoporous metal foam components to a substrate using solder that is sputtered onto the surfaces. Metal foams have unusual properties that make them excellent choices for many applications, and as technologies for processing these materials are evolving, their use in industry is increasing dramatically. Metal foams are lightweight and have advantageous dynamic properties, which make them excellent choices for many structural applications. They also provide good acoustic damping, low thermal conductivity, and excellent energy absorption characteristics. Therefore, these materials are commonly used in the automotive, aerospace, construction, and biomedical industries. The synthesis of nanoporous metal foams with a cell size of less then 1 {micro}m is an emerging technology that is expected to lead to widespread application of metal foams in microdevices, such as sensors and actuators. One of the challenges to manufacturing components from metal foams is that they can be difficult to attach to other structures without degrading their properties. For example, traditional liquid adhesives cannot be used because they are absorbed into foams. The problem of bonding or joining can be particularly difficult for small-scale devices made from nanoporous foam, due to the requirement for a thin bond layer. The current study addresses this problem and develops a method of soldering a nanoporous metal foam to a substrate with a bond thickness of less than 2 {micro}m. There are many applications that require micro-scale metal foams precisely bonded to substrates. This study was motivated by a physics experiment that used a laser to drive a shock wave through an aluminum foil and into a copper foam, in order to determine the speed of the shock in the copper foam. To avoid disturbing the shock, the interface between the copper foam and the aluminum substrate had to be as thin ...
Date: August 21, 2007
Creator: Bono, M; Cervantes, O; Akaba, C; Hamza, A; Foreman, R & Teslich, N
Partner: UNT Libraries Government Documents Department

Highly-resolved 2D HYDRA simulations of Double-Shell Ignition Designs

Description: Double-shell (DS) targets (Amendt, P. A. et al., 2002) offer a complementary approach to the cryogenic baseline design (Lindl, J. et al., 2004) for achieving ignition on the National Ignition Facility (NIF). Among the expected benefits are the ease of room temperature preparation and fielding, the potential for lower laser backscatter and the reduced need for careful shock timing. These benefits are offset, however, by demanding fabrication tolerances, e.g., shell concentricity and shell surface smoothness. In particular, the latter is of paramount importance since DS targets are susceptible to the growth of interface perturbations from impulsive and time-dependent accelerations. Previous work (Milovich, J. L. et al., 2004) has indicated that the growth of perturbations on the outer surface of the inner shell is potentially disruptive. To control this instability new designs have been proposed requiring bimetallic inner shells and material-matching mid-Z nanoporous foam. The challenges in manufacturing such exotic foams have led to a further evaluation of the densities and pore sizes needed to reduce the seeding of perturbations on the outer surface of the inner shell, thereby guiding the ongoing material science research efforts. Highly-resolved 2D simulations of porous foams have been performed to establish an upper limit on the allowable pore sizes for instability growth. Simulations indicate that foams with higher densities than previously thought are now possible. Moreover, while at the present time we are only able to simulate foams with average pore sizes larger than 1 micron (due to computational limitations), we can conclude that these pore sizes are potentially problematic. Furthermore, the effect of low-order hohlraum radiation asymmetries on the growth of intrinsic surface perturbations is also addressed. Highly-resolved 2D simulations indicate that the transverse flows that are set up by these low-order mode features (which can excite Kelvin-Helmholtz instabilities) are not large enough to ...
Date: June 30, 2006
Creator: Milovich, J L; Amendt, P; Hamza, A; Marinak, M & Robey, H
Partner: UNT Libraries Government Documents Department

Synthesis and Characterization of Bimodal Nanoporous Cu Foams: Working Towards Inertial Fusion Energy

Description: For the National Ignition Facility, at the Lawrence Livermore National Laboratory, nanoporous structures play a crucial role in the development of targets for high energy density experiments. Here we present a new bottom-up synthesis technique termed filter-casting for the creation of bimodal macro/nanoporous Cu structures. Homogeneous nanoporous monoliths can be synthesized using Cu nanoparticles and bimodal porosities can be achieved using sacrificial polystyrene spheres as a template. Control over the structure and composition is critical for target manufacturing. The measured densities of the Cu foam range between 1070-3390 mg/cm{sup 3}. Filter-casting is a powerful new method for directly synthesizing large nanoporous monoliths with predetermined composition, pore size, and pore structure.
Date: September 28, 2007
Creator: Cervantes, O; Hayes, J R & Hamza, A
Partner: UNT Libraries Government Documents Department

Nanoporous gold as a highly active substrate for surface-enhanced Raman scattering spectroscopy

Description: Colloidal solutions of metal nanoparticles are currently among most studied substrates for sensors based on surface-enhanced Raman scattering (SERS). However, such substrates often suffer from not being cost-effective, reusable, or stable. Here, we develop nanoporous Au as a highly active, tunable, a.ordable, stable, bio-compatible, and reusable SERS substrate. Nanoporous Au is prepared by a facile process of free corrosion of AgAu alloys followed by annealing. Results show that nanofoams with average pore sizes of {approx} 250 nm exhibit the largest SERS signal for 632.8 nm excitation. This is attributed to the electromagnetic SERS enhancement mechanism with additional field localization within pores.
Date: March 28, 2006
Creator: Kucheyev, S O; Hayes, J R; Biener, J & Hamza, A V
Partner: UNT Libraries Government Documents Department

FY04 LDRD Final Report:Properties of Actinide Nanostructures

Description: Two papers completely describe the objectives and work performed in this laboratory directed research and development (LDRD) project. The first paper published in Review of Scientific Instruments (UCRL-JC-152913) describes the purpose, construction, and operation of a novel instrument to produce and characterize actinide nanostructures by pulsed laser deposition. The second paper submitted to Physical Review B (UCRL-JRNL-209427) describes our work quantifying the oxidation of pulsed laser deposited depleted uranium nanostructures by following the evolution of the electronic structure.
Date: February 22, 2005
Creator: Hamza, A. V.; Trelenberg, T. W. & Tobin, J. G.
Partner: UNT Libraries Government Documents Department

Dislocation nucleation in bcc Ta single crystals studied by nanoindentation

Description: The study of dislocation nucleation in closed-packed metals by nanoindentation has recently attracted much interest. Here, we address the peculiarities of the incipient plasticity in body centered cubic (bcc) metals using low index Ta single-crystals as a model system. The combination of nanoindentation with high-resolution atomic force microscopy provides us with experimental atomic-scale information on the process of dislocation nucleation and multiplication. Our results reveal a unique deformation behavior of bcc Ta at the onset of plasticity which is distinctly different from that of closed-packed metals. Most noticeable, we observe only one rather than a sequence of discontinuities in the load-displacement curves. This and other differences are discussed in context of the characteristic plastic deformation behavior of bcc metals.
Date: August 8, 2007
Creator: Biener, M M; Biener, J; Hodge, A M & Hamza, A V
Partner: UNT Libraries Government Documents Department

Oxidation of uranium nanoparticles produced via pulsed laser ablation

Description: An experimental apparatus designed for the synthesis, via pulsed laser deposition, and analysis of metallic nanoparticles and thin films of plutonium and other actinides was tested on depleted uranium samples. Five nanosecond pulses from a Nd:YAG laser produced films of {approx}1600 {angstrom} thickness that were deposited showing an angular distribution typical thermal ablation. The films remained contiguous for many months in vacuum but blistered due to induced tensile stresses several days after exposure to air. The films were allowed to oxidize from the residual water vapor within the chamber (2 x 10{sup -10} Torr base pressure). The oxidation was monitored by in-situ analysis techniques including x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and scanning tunneling microscopy (STM) and followed Langmuir kinetics.
Date: December 7, 2005
Creator: Trelenberg, T W; Glade, S C; Tobin, J G; Felter, T E & Hamza, A V
Partner: UNT Libraries Government Documents Department

Characterization of Uranium Particles Produced via Pulsed Laser Deposition

Description: We have constructed an experimental apparatus for the synthesis (via pulsed laser deposition) and analysis of nanoparticles and thin films of plutonium and other actinides. In-situ analysis techniques include x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS). Also, the oxidation kinetics and the reaction kinetics of actinides with other gaseous species can be studied with this experimental apparatus. Preliminary results on depleted uranium are presented.
Date: November 11, 2003
Creator: Glade, S C; Trelenberg, T W; Tobin, J & Hamza, A
Partner: UNT Libraries Government Documents Department

Novel Approaches to Surface Analysis and Materials Engineering Using Highly Charged Ions

Description: Complex problems in materials science require very sensitive, high spatial resolution (< 100 nm) determination of chemical (molecular) structures in near-surface volumes. Slow, highly charged ions (HCIs) provide a new, unique tool for probing chemical structure on a nanometer scale. The authors have explored the potential of these new highly charged ion based techniques in studies of materials with programmatic significance such as high explosives and actinide surfaces. Specifically the are studying HCI based surface analysis techniques (such as secondary ion mass spectrometry, SIMS) that are capable of achieving sensitivity of less than 10{sup 9} atoms/cm{sup 2}. In addition, this technique can determine chemical structure and hydrogen concentration. These attributes make this technique especially important to Laboratory missions in enhanced surveillance and nonproliferation. The unique advantage of HCIs over singly charged ions is the extreme energy density that is deposited into a nanometer-sized near-surface volume at the impact of a single HCI. For example, a Au{sup 69+} ion deposits about 0.5 MJ/cm{sup 3}. This high energy density causes the emission of a large number of secondary particles (electrons, ions, neutral atoms, and clusters) from surfaces. The emitted particles act as probes of the energy dissipation mechanism, and their yields are of technological significance. The HCI-emission microscope concept they developed uniquely combines all three aspects, high spatial resolution with highly sensitive compositional analysis and chemical structure determination. The experiments have shown that individual HCI impacts lead to copious electron emission, over 200 electrons per incident highly charged ion. In addition, highly charged ion induced secondary ion mass spectrometry (HCI-SIMS) provides considerably more information per ion impact than conventional SIMS. Combining these two phenomena provides a unique tool to study important materials issues necessary for the laboratory to accomplish its missions.
Date: February 2, 2000
Creator: Hamza, A.; Schenkel, T.; Barnes, A. & Schneider, D.
Partner: UNT Libraries Government Documents Department

Monolithic Nanocrystalline Au Fabricated by the Compaction of Nanoscale Foam

Description: We describe a two-step dealloying/compaction process to produce nanocrystalline Au. First, nanocrystalline/nanoporous Au foam is synthesized by electrochemically-driven dealloying. The resulting Au foams exhibit porosities of 60 and 70% with pore sizes of {approx} 40 and 100 nm, respectively, and a typical grain size of <50 nm. Second, the nanoporous foams are fully compacted to produce nanocrystalline monolithic Au. The compacted Au was characterized by TEM and X-ray diffraction and tested by depth-sensing nanoindentation. The compacted nanocrystalline Au exhibits an average grain size of <50 nm and hardness values ranging from 1.4 to 2.0 GPa, which are up to 4.5 times higher than the hardness values obtained from polycrystalline Au.
Date: July 28, 2004
Creator: Hodge, A M; Biener, J; Hsiung, L M; Hamza, A V & Satcher Jr., J H
Partner: UNT Libraries Government Documents Department

Hydrogen--deuterium exchange in KD2PO4

Description: Depth profiles of {sup 1}H and {sup 2}D in rapidly-grown KD{sub 2x}H{sub 2(1-x)}PO{sub 4} (DKDP) single crystals are studied by elastic recoil detection analysis. Results show that, at ambient conditions, deuteration in the first {approx} 500 nm from the sample surface significantly decreases within the first several days after D{sub 2}O surface polishing. This effect is attributed to the deuterium-hydrogen exchange. The effective diffusion coefficient of this process is strongly dependent on both the degree of deuteration and sample growth conditions. Physical mechanisms of the D/H exchange are discussed.
Date: November 4, 2003
Creator: Kucheyev, S O; Felter, T E; Siekhaus, W J; Nelson, A J & Hamza, A V
Partner: UNT Libraries Government Documents Department

Surface charge compensation for a highly charged Ion emissionmicroscope

Description: A surface charge compensation electron flood gun has been added to the Lawrence Livermore National Laboratory (LLNL) highly charged ion (HCI) emission microscope. HCI surface interaction results in a significant charge residue being left on the surface of insulators and semiconductors. This residual charge causes undesirable aberrations in the microscope images and a reduction of the Time-Of-Flight (TOF) mass resolution when studying the surfaces of insulators and semiconductors. The benefits and problems associated with HCI microscopy and recent results of the electron flood gun enhanced HCI microscope are discussed.
Date: April 1, 2003
Creator: McDonald, J.W.; Hamza, A.V.; Newman, M.W.; Holder, J.P.; Schneider, D.H.G. & Schenkel, T.
Partner: UNT Libraries Government Documents Department

ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

Description: Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications.
Date: March 24, 2011
Creator: Biener, M M; Biener, J; Wichmann, A; Wittstock, A; Baumann, T F; Baeumer, M et al.
Partner: UNT Libraries Government Documents Department