We present the use of x-ray fluorescence spectroscopy (XFS) to a sensitive temperature diagnostic in shocked foams at temperatures of 30-75 eV. Cobalt-doped foams were shock compressed using a planar drive at the OMEGA laser facility and photo-pumped with a Zn Heα x-ray source. Analysis of the resulting cobalt Kβ x-ray fluorescence spectra using collisional radiative codes allows the temperature to be determined in the shocked foams. This method provides a sensitive and robust technique to determine temperatures in high-energy-density physics experiments in the tens of electronvolts temperature range. In these experiments, we find that radiation hydrodynamic simulations predict a lower temperature in the shocked foams compared to analysis of the XFS data using collisional radiative models. Although additional experiments with an independent temperature diagnostic to absolutely calibrate XFS spectra for these conditions will be required to resolve this discrepancy, these results demonstrate the excellent temperature sensitivity of XFS spectra for high-energy-density physics experiments.

The performance of metal and polymer foams used in inertial confinement fusion (ICF), inertial fusion energy (IFE), and high-energy-density (HED) experiments is currently limited by our understanding of their nanostructure and its variation in bulk material. We utilized an X-ray-free electron laser (XFEL) together with lensless X-ray imaging techniques to probe the 3D morphology of copper foams at nanoscale resolution (28 nm). The observed morphology of the thin shells is more varied than expected from previous characterizations, with a large number of them distorted, merged, or open, and a targeted mass density 14% less than calculated. This nanoscale information can be used to directly inform and improve foam modeling and fabrication methods to create a tailored material response for HED experiments.

Scale-up synthesis of calcium-based microporous metal-organic framework (SBMOF-1) up to similar to 400 g in a batch with a yield of > 90 % was achieved by a solvothermal reaction of sulfonyldibenzoic acid (SDB) with an excess of calcium chloride. Here, we observed that recrystallization of unreacted SDB at a solvothermal condition caused a moderate reaction yield (40-50 %) at the reference condition of C-CaCl2/ CSDB =1 and CSDB/ CSDB(ref)=1. Simply adding more reagents to the reactor did not increase the mass of product formed per unit volume due to a more pronounced loss of the yield at those conditions. By simultaneously changing the molar ratio of CaCl2 to SDB, CCaCl2/ CSDB, and the molar concentration of the SDB reagent, CSDB/ CSDB(ref), we explored %yield of the reaction. Interestingly, a linear improvement in the yield was observed from 21 % (at CCaCl2/ CSDB =0.5) up to 78 % (at CCaCl2/ CSDB =6) at a fixed ratio of CSDB/ CSDB(ref)=2 and the yield leveled off after further addition. Unlike those at CCaCl2/ CSDB =1, the yields at a high CaCl2 excess continued to improve with increasing the CSDB/ CSDB(ref). When a large pressure vessel (2500 mL EtOH, CCaCl2/ CSDB =6, CSDB/ CSDB(ref)=8) was used, about 415 g of SBMOF-1 with a yield of 92.3 % was produced, indicating 16 xthe space yield improvement. The ability to synthesize SBMOF-1 on a large scale allowed us to examine the long-term stability of SBMOF-1 for almost 200 days in the presence of varying levels of relative humidity

Over the past two decades, the diversity of metal and metalloid oxide materials prepared using sol–gel techniques has increased significantly. This transformation can be attributed in part to the development of the technique known as epoxide-assisted gelation. The process utilizes organic epoxides as co-reactants for the sol–gel polymerization of simple inorganic metal salts in aqueous or alcoholic media. In this approach, the epoxide acts as a proton scavenger, which drives hydrolysis and condensation of hydrated metal species in the sol–gel reaction. This process is generalizable and applicable to the synthesis of a wide range of metal and metalloid oxide aerogels, xerogels, and nanocomposites. In addition, modification of synthetic parameters allows for control over the structure and properties of the sol–gel product. The method is particularly amenable to the synthesis of multicomponent and nanocomposite sol–gel systems with intimately mixed nanostructures. This chapter describes both the reaction mechanisms associated with epoxide-assisted gelation and an overview of materials that have been prepared using this technique.

Carbon aerogels are a unique class of high surface area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility, and chemical inertness make them very promising materials for many applications, such as energy storage, catalysis, sorbents, and desalination. Since the first carbon aerogels were made via pyrolysis of resorcinol-formaldehyde-based organic aerogels, in the late 1980s, the field has really grown. Recently, in addition to RF-derived amorphous carbon aerogels, several other carbon allotropes have been realized in aerogel form: carbon nanotubes, graphene, graphite, and diamond. Finally, the development of 3D-printed aerogels provides the potential for carbon aerogels to have an even broader impact on energy-related technologies. Here, we will present recent work covering the novel synthesis of carbon nanotube, graphene, fullerene, graphite, and diamond aerogels.

Uniform, macroscopic monoliths (ranging from a few millimeters to a centimeter) of low-density gold foams with similar to 95% porosity and similar to 10-mu m-diameter pores were prepared by the casting of gold-coated polystyrene core-shell particles followed by the thermal removal of the polymer core. The Au foams were composed of unique hollow gold spheres and showed superior mechanical integrity and resilience compared to the foams we previously reported. Highly efficient seeding and electroless gold-plating methods in this study caused a significant morphological transition in the gold coatings from coarse particles to fine particles, and finally, to a continuous layer. A modified, scalable casting approach to form large uniform monoliths (up to similar to 1-cm diameter) and a gentle baking condition to minimize undesirable densification of the final foams enabled us to develop a simple, efficient synthetic route to nanostructured macroscopic low-density gold foams. To demonstrate the improved mechanical stability and machinability, a representative monolithic Au foam (similar to 0.9 g/cm(3)) was carefully cut into the hollow cylinder of gold foams by a series of machining and processing steps. Finally, we tried to understand the unique mechanical behaviors and properties of this gold foam by nanoindentation measurement.

The 3D chemical structure (4D spectromicroscopy) of nanoporous Al2O3 aerogels coated with ZnO by atomic layer deposition (ALD) was studied by multienergy scanning transmission X-ray microscopy. These materials are representative of a class of designer catalysts in which the nanoporous support is prepared separately from the active catalyst material, which is subsequently introduced by ALD, thereby allowing independent optimization of the morphology, chemistry, and spatial distribution of the support and catalyst. The samples studied were prepared by Ga ion and Xe plasma focused ion beam (FIB) milling as well as drop casting from water suspension. Zn L and Al K edge spectra of six samples with three different ZnO loadings were measured to investigate how loading and different sample preparation methods affect the 3D distribution of the ZnO and Al2O3. Scanning transmission X-ray microscopy (STXM) and ptychographic imaging at two energies each at the Zn L-3 and Al K edge were measured. The ptychography data were analyzed by using the SHARP reconstruction code to generate quantitative 2D chemical maps of the Al2O3 and the ZnO. The STXM and ptychography maps were then measured at a sequence of tilt angles, covering up to 160 degrees of rotation. The 3D structure of the ZnO and Al2O3 was derived from the tilt series data by tomographic reconstruction using a compressed sensing algorithm. A two-dimensional spatial resolution (half-period) of 6 nm, measured by Fourier ring correlation, and a 3D spatial resolution (half-period) of 9 nm, measured by Fourier shell correlation, were achieved when using the COSMIC beamline at the Advanced Light Source (ALS). The results show that for all of the ZnO loadings studied there is nonuniform coverage of the ZnO on the Al2O3 aerogel framework. In addition, we found that both FIB methods create sample artifacts, although the distortion was less with Xe plasma than Ga ion FIB.

Experiments using a single 527 nm wavelength beam interacting with sub- and supercritical density SiO2 and Ta2O5 foams examined laser propagation and backscatter from laser–plasma instabilities such as Stimulated Brillouin Scattering (SBS). Two densities of each material were examined, and multiple diagnostics were used to characterize the propagation and backscatter. For 5 mg/cc SiO2 (ne/nc = 0.375), the laser propagation distance was well approximated by treating the foam as a gas. However, for the 2 mg/cc SiO2 foam (ne/nc = 0.15), the same model over-predicts the propagation distance by ∼40%. Existing analytical theories on propagation through subcritical foams were able to account for this difference. The laser heat wave propagated ∼1/2 as far in Ta2O5 than SiO2 foams with similar electron density. We showed that this difference is due to the increased radiation losses in the higher Z foam. The fraction of backscattered light scales linearly with incident laser intensity for the range of intensities examined. Ta2O5 foams had significantly lower levels of backscatter (1–3%) than the SiO2 (4–8%), which is consistent with estimates of large Landau damping due to the presence of the oxygen atoms. The measured fraction of SBS backscattered laser energy for a 2 mg/cc SiO2 foam shot was ∼4 times lower than predicted by simulations assuming a gas-like foam. We found that we needed to assume increased ion heating such that Ti/Te ∼ 1.2–1.5 in the plasma to agree with the measured SBS reflectivity. Analytical models of laser-heated foams predict preferential heating of the ions as has been observed in previous experiments.

The ablative expansion of laser-heated materials is important for determining how hohlraum cavities can be utilized for inertial confinement fusion. The utility of a low-density foam layer to reduce the density of the expanding heated hohlraum wall is demonstrated in a series of experiments on the National Ignition Facility. X-ray radiography measurements of the expanding foam-lined Au wall in low aspect-ratio cylindrical geometry are used to compare the impact of Au-doped CH and Ta2O5 foams between 10 and 40 mg/cc on the wall expansion. HYDRA Simulations are used to estimate the x-ray transmission at the 1/4 nc surface, which is important in understanding the absorption of laser light by the plasma. These demonstrate for the first time that a foam layer reduces the expansion of a hohlraum-like target and illustrate that the interplay between the expanding foam plasma and the shock reflected by the hohlraum wall is critical in optimizing foam-liner parameters to achieve the maximum time for a symmetric drive on a capsule.

Experiments on the National Ignition Facility (NIF) to study hohlraums lined with a 20-mg/cc 400-μm-thick Ta_{2}O_{5} aerogel at full scale (hohlraum diameter = 6.72 mm) are reported. Driven with a 1.6-MJ, 450-TW laser pulse, the performance of the foam liner is diagnosed using implosion hot-spot symmetry measurements of the high-density carbon (HDC) capsule and measurement of inner beam propagation through a thin-wall 8-μm Au window in the hohlraum. Results show an improved capsule performance due to laser energy deposition further inside the hohlraum, leading to a modest increase in x-ray drive and reduced preheat due to changes in the x-ray spectrum when the foam liner is included. In addition, the outer cone bubble uniformity is improved, but the predicted improvement in inner beam propagation to improve symmetry control is not realized for this foam thickness and density.

We demonstrate the synthesis of high-surface-area, low-density refractory aerogels. The monolithic hafnium boride (HfB2) and zirconium boride (ZrB2) aerogels are prepared via borothermal reduction of precursor hafnia and zirconia aerogels, respectively, consisting of a fine mixture of boron nanoparticles and the metal oxide. This precursor boron-metal oxide (B-MO2) composite aerogel was synthesized by modifying the pure ethanol solvent typically used in the epoxide-initiated sol-gel synthesis of metal oxide aerogels with an ethanolic boron nanoparticle suspension. After reduction, precursor aerogels are converted to metal boride aerogels containing primary particles in the sub-100 nm regime. The relative densities of the HfB2 and ZrB2 aerogels are 3 and 7%, respectively, and could be tailored by simply changing the density of the precursor aerogels via modifying the reagent concentrations or the drying conditions. Thermal conductivities of the ZrB2 monoliths ranged from 0.18 to 0.33 W/(m K). The surface areas of the HfB2 and ZrB2 aerogels were 10 and 19 m(2)/g, respectively. Successful reduction of the aerogels to the diboride phase was confirmed by X-ray diffraction.

Herein we report the fabrication of ultralight gold aerogel monoliths with tunable densities and pore structures. Gold nanowires are prepared at the gram scale by substrate-assisted growth with uniform size, ultrathin diameters, high purity, and a high aspect ratio. Freeze-casting of suspensions of these nanowires produces free-standing, monolithic aerogels with tunable densities from 6 to 23 mg/cm3, which to the best of our knowledge represents the lowest density monolithic gold material. We also demonstrate that the pore geometries created during freeze-casting can be systematically tuned across multiple length scales by the selection of different solvents and excipients in the feedstock suspension. The mechanical behavior of porous materials depends on relative density and pore architectures.

The measurement of the density of materials, especially ultralow-density foams, is difficult in that the measurement must be precise and localizable. The density of the material is often governed by its cellular (i.e., porous) structure, and many techniques exist to create that structure. Often, the cellular structure can vary from one location within the material to another, and when at low densities (i.e., densities lower than similar to 500 mg/cm(3)), it can vary due to shrinkage during syneresis, collapse under the weight of gravity, or gas/water vapor uptake. Quantifying this variation is important for a variety of applications, especially when used in plasma physics targets. Knowing the density and its variation across the sample is critical for experimental results to be accurately predicted by physics calculations and for modeling the results of the physics targets. The use of quasi-monochromatic radiography provides a means to image the two-dimensional (2-D) distribution of density variation within silica aerogel materials and to quantitatively measure that variation from sample to sample and lot to lot. For this study, two batches of silica aerogels with targeted densities of similar to 20 mg/cm(3) were created, one batch at Lawrence Livermore National Laboratory, and the other batch at Los Alamos National Laboratory. Outlined here is a quasi-monochromatic radiography system using various X-ray sources coupled to a doubly curved crystal optic and X-ray charge-coupled device camera to image and characterize these materials. It was found that measuring the density both gravimetrically and using quasi-monochromatic radiography were statistically identical, although the two batches were found to be slightly higher than their targeted density due to shrinkage. The radiography system also provided 2-D information as to the aerogel quality, i.e., presence of voids, chipped material, or inclusions.

Compared to tedious, multi-step treatments for electroless gold plating of traditional thermoplastics, this communication describes a simpler three-step procedure for 3D printed crosslinked polyacrylate substrates. This allows for the synthesis of ultralight gold foam microlattice materials with great potential for architecture-sensitive applications in future energy, catalysis, and sensing.