A5068573530- Energetic Materials and Combustion
- Diamond and Carbon-based Materials Research
- High-pressure geophysics and materials
- Quantum Dots Synthesis And Properties
- Molecular Junctions and Nanostructures
- Nuclear Physics and Applications
- Combustion and Detonation Processes
- Thermal and Kinetic Analysis
- High-Velocity Impact and Material Behavior
- Ion-surface interactions and analysis
- Silicon Nanostructures and Photoluminescence
- Semiconductor materials and devices
- Graphene research and applications
- Semiconductor materials and interfaces
- Force Microscopy Techniques and Applications
- Supercapacitor Materials and Fabrication
- Nanowire Synthesis and Applications
- Chalcogenide Semiconductor Thin Films
- X-ray Spectroscopy and Fluorescence Analysis
- Carbon Nanotubes in Composites
- Boron and Carbon Nanomaterials Research
- Graphite, nuclear technology, radiation studies
- Metal and Thin Film Mechanics
- Magnetism in coordination complexes
- Additive Manufacturing Materials and Processes
Lawrence Livermore National Laboratory
2015-2024
Justus-Liebig-Universität Gießen
2007-2021
SLAC National Accelerator Laboratory
2010-2021
Stanford Synchrotron Radiation Lightsource
2010-2017
Universität Ulm
2017
Lawrence Livermore National Security
2017
National Security Technologies (United States)
2016
Los Alamos National Laboratory
2016
Kansas State University
2010
University of Maine
2010
Circumventing spatter Laser powder bed fusion is an additive manufacturing technique that laser-melts layer by to build a three-dimensional (3D) part. Khairallah et al. used experiments and multiphysics model determine the origin of melt defect formation degrade properties built parts (see Perspective Polonsky Pollock). Informed modulation laser power important avoid disturbing creating shadowing. This reduces pore formations leads more uniform 3D-printed parts. Science , this issue p. 660 ;...
A new class of castable cerium strengthened aluminum alloys has phenomenal high temperature properties without the need for heat treatment.
Advanced in situ characterization is essential for determining the underlying dynamics of laser-material interactions central to both laser welding and rapidly expanding field additive manufacturing. Traditional techniques leave a critical experimental gap understanding complex subsurface fluid flow metal evaporation inherent laser-induced heating metal. Herein, ultra-high-speed transmission X-ray imaging revealed be bridging this information gap, particularly via comparison with validation...
We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra the diamondoid exhibited peak at low-kinetic energy threshold; up to 68% all emitted electrons were within this single peak. The intensity emission is indicative diamondoids being negative affinity materials. With an distribution width less than 0.5 volts, source may find application in technologies such as microscopy, beam...
Developing three-dimensional (3D) graphene assemblies with properties similar to those individual sheets is a promising strategy for graphene-based electrodes. Typically, the synthesis of 3D relies on van der Waals forces holding together, resulting in bulk that do not reflect reported sheets. Here, we report use sol−gel chemistry introduce chemical bonding between and control aerogels. Adjusting synthetic parameters allows wide range over surface area, pore volume, size, as well nature...
The electronic structure of ${\mathrm{TiO}}_{2}$ aerogels is studied by soft x-ray absorption near-edge (XANES) spectroscopy. High-resolution O K-edge and Ti ${L}_{2,3}$-edge XANES spectra are compared with those rutile, anatase, unrelaxed amorphous phases full-density ${\mathrm{TiO}}_{2}.$ Results show that all the main spectroscopic features aerogels, reflecting element-specific partial density empty states correlation effects, can be attributed to absence long-range order in...
Polymer-derived, monolithic three-dimensional nanographene (3D-NG) bulk material with tunable properties is produced by a simple and inexpensive approach. The mass-producible, combines chemical inertness mechanical strength hierarchical porous architecture graphene-like surface area. This provides an opportunity to control its electron transport dynamically means of electrochemical-induced interfacial electric fields.
The local structure and composition of Cu ions dispersed in CdSe nanocrystals is examined using soft X-ray absorption near edge spectroscopy (XANES). Using L-edge XANES photoelectron measurements (XPS), we find that the exist Cu(I) oxidation state. We also observed signal directly proportional to molar percent present our final material. Se indicates changes density states with doping, due a chemical bonding effect, supports statistical doping mechanism. Photoluminescence (PL) indicate may...
Quantum-confinement effects in the conduction band of deposited germanium nanocrystals are measured to be greater than similar-sized silicon nanocrystals. The particles condensed out gas phase and their electronic properties determined with x-ray absorption spectroscopy. edge shifts range from 0.2 eV for 2.7 nm up 1.1 1.2 particles.
Ultralow density polymers, metals, and ceramic nanofoams are valued for their high strength-to-weight ratio, surface area, insulating properties ascribed to structural geometry. We obtain the labrynthine internal structure of a tantalum oxide nanofoam by x-ray diffractive imaging. Finite-element analysis from reveals mechanical consistent with bulk samples diffusion-limited cluster aggregation model, while excess mass on nodes discounts dangling fragments hypothesis percolation theory.
The dynamics of carbon condensation in detonating high explosives remains controversial. Detonation model validation requires data for processes occurring at nanometer length scales on time ranging from nanoseconds to microseconds. A new detonation endstation has been commissioned acquire and provide time-resolved small-angle x-ray scattering (SAXS) explosives. Hexanitrostilbene (HNS) was selected as the first investigate due its ease initiation using exploding foils flyers, vacuum...
Abstract Transit through the carbon liquid phase has significant consequences for subsequent formation of solid nanocarbon detonation products. We report dynamic measurements condensation and solidification into nano-onions over ∽200 ns by analysis time-resolved, small-angle X-ray scattering data acquired during a hydrogen-free explosive, DNTF (3,4-bis(3-nitrofurazan-4-yl)furoxan). Further, thermochemical modeling predicts direct to graphite transition products ~200 post-detonation. Solid...
HMX-based explosives LX-10 and PBX-9501 were heated through the β-δ phase transition. Ultra-small angle x-ray scattering (USAXS) molecular diffraction simultaneously recorded as HMX was heated. Mesoscale voids structure dramatically change promptly with transition, rather than other thermal effects. Also, induced damage, observed in USAXS, occurs more readily at elevated temperatures; such, dose reduced to mitigate this effect. Optical microscopy performed during a similar heating cycle...
The electronic structure of three-dimensional nanostructures (aerogels) is studied by soft x-ray absorption near-edge (XANES) spectroscopy. High-resolution O -edge and Sn - XANES spectra monolithic nanocrystalline rutile aerogels with different surface areas (i.e., surface-to-volume atom fractions) are compared full-density tetragonal SnO. Spectra interpreted based on the densities states in calculated both cluster (self-consistent real-space multiple scattering) band-structure (linear...
The electronic structure of monodispersed, hydrogen-passivated diamond clusters (diamondoids) in the gas phase has been studied with x-ray absorption spectroscopy. data show that bulk-related unoccupied states do not exhibit any quantum confinement. Additionally, density below bulk edge appears, consisting features correlated to CH and CH2 hydrogen surface termination, resulting an effective redshift lowest states. results contradict commonly used very successful confinement model for...
Formation of biomineral structures is increasingly attributed to directed growth a mineral phase from an amorphous precursor on organic matrix. While many in vitro studies have used calcite formation organothiol self-assembled monolayers (SAMs) as model system investigate this process, they generally focused the stability calcium carbonate (ACC) or maximizing control over order final phase. Little known about early stages formation, particularly structural evolution SAM and mineral. Here we...
Aerogel materials have myriad scientific and technological applications due to their large intrinsic surface areas ultralow densities. However, creating a nanodiamond aerogel matrix has remained an outstanding intriguing challenge. Here we report the high-pressure, high-temperature synthesis of diamond from amorphous carbon precursor using laser-heated anvil cell. Neon is used as chemically inert, near-hydrostatic pressure medium that prevents collapse under by conformally filling aerogel's...
The detonation of carbon-rich high explosives yields solid carbon as a major constituent the product mixture, and depending on thermodynamic conditions behind shock front, variety allotropes morphologies may form evolve. We applied time-resolved small-angle X-ray scattering (TR-SAXS) to investigate dynamics clustering during PBX 9502, an explosive composed 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) 5 wt % fluoropolymer binder. Solid formation was probed from 0.1 2.0 μs front revealed rapid...
Abstract Monolithic porous bulk materials have many promising applications ranging from energy storage and catalysis to high density physics. High resolution additive manufacturing techniques, such as direct laser writing via two photon polymerization (DLW‐TPP), now enable the fabrication of highly microlattices with deterministic morphology control. In this work, DLW‐TPP is used print millimeter‐sized foam reservoirs (down 0.06 g cm −3 ) tailored density‐gradient profiles, where varied by...
Laser powder bed fusion (LPBF) additive manufacturing and laser welding are powerful metal processing techniques with broad applications in advanced sectors such as the biomedical aerospace industries. One common process variable that can tune laser-material interaction dynamics these two is adjustment of composition pressure atmosphere which conducted. While some physical mechanisms governed by ambient well known from literature, it remains unclear how extend to distinct conditions LPBF. In...
Detonation nanodiamond (DND) is known to form aggregates that significantly reduce their unique nanoscale properties and require postprocessing separate. How when DND an important question has not been answered experimentally could provide the foundation for approaches limit aggregation. To answer this question, time-resolved small-angle X-ray scattering was performed during detonation of high-explosives are expected condense particulates in diamond, graphite, liquid regions carbon phase...
Condensed-phase hydrogen-terminated diamond clusters (diamondoids) have been studied with soft-x-ray emission and x-ray-absorption spectroscopy. The occupied unoccupied electronic states measured these methods imply an increasing highest molecular orbital--lowest orbital gap decreasing diamondoid size, the shifting entirely in states, contrast to other semiconductor nanocrystals. These experimental results are compared theoretical calculations on structure of diamondoids.
Abstract Hot‐spot models of initiation and detonation show that voids or porosity ranging from nanometer to micrometer in size within highly insensitive energetic materials affect initiability properties. Thus, the knowledge void distribution, how it changes with volume expansion seen temperature cycling, are important understanding properties explosive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB). In this paper, distributions 2 nm μm regime, obtained small‐angle X‐ray scattering...