A Livermore team has manufactured a new type of graphene aerogel microlattice with an engineered architecture via a three-dimensional (3D) printing technique known as direct-ink writing. The graphene aerogels are mechanically stiff, lightweight, highly conductive, and extremely compressible (exhibiting up to 90 percent compressive strain) with a large surface area. The research appeared in the April 22, 2015, edition of Nature Communications.
For this process, an aqueous graphene oxide suspension and silica filler are combined to form a homogenous, highly viscous ink that is then loaded into a syringe barrel and extruded through a micronozzle to pattern 3D structures. Previous attempts at creating bulk graphene aerogels produced a largely random pore structure, which prevented researchers’ ability to tailor the transport and other mechanical properties of the material for specific applications such as batteries and pressure sensors.
“Making graphene aerogels with tailored macroarchitectures using a controllable and scalable assembly method was a significant challenge,” says Livermore scientist Marcus Worsley, who co-authored the paper. “Three-dimensional printing allows one to intelligently design the pore structure of the aerogel, permitting control over mass transport and optimization of physical properties, such as stiffness.” The new 3D printing technique will enable fabrication of complex aerogel architectures for energy storage applications, sensors, nanoelectronics, and catalysis, among others.
Contact: Marcus Worsley (925) 424-4831 (worsley1@llnl.gov).
Researchers at the National Ignition Facility (NIF) together with collaborators from the Laboratory for Laser Energetics at the University of Rochester, the Massachusetts Institute of Technology Plasma Science and Fusion Center, Los Alamos National Laboratory, and General Atomics have been testing target capsules that are 10 to 15 percent thinner than those used in previous experiments. In a paper published in the April 6, 2015, online edition of Physical Review Letters, the team detailed the results of several thin-capsule shots representing different ablator thicknesses.
In inertial confinement fusion experiments, the fusion fuel implodes at a high speed in reaction to the rapid ablation, or blow-off, of the outer layers of the target capsule. However, to reach the conditions needed for ignition, the fuel must implode symmetrically at a peak velocity of about 350 kilometers per second without producing hydrodynamic instabilities that can dampen the fusion reactions. The team’s thin-capsule implosions have demonstrated higher velocity and better symmetry control at lower laser powers and energies than their nominal-thickness counterparts. “Little to no hydrodynamic mix of ablator material into the capsule hot spot was observed,” says Tammy Ma, a physicist in the NIF and Photon Science Principal Directorate who co-authored the research paper. The team also achieved higher neutron yield and inferred hot-spot pressure with each of the progressively thinner capsules. Ma says, “This result can be attributed to the gain in velocity due to the thinner ablator.”
Contact: Tammy Ma (925) 423-8902 (ma8@llnl.gov).
Galaxies are often found in clusters, which contain many “red and dead” members that stopped forming stars in the distant past. An international team of astronomers, including Lawrence Livermore’s William Dawson, has discovered that these comatose galaxies can sometimes come back to life. If clusters of galaxies merge, a huge shock wave can drive the birth of a new generation of stars. The research appeared in the April 24, 2015, edition of Monthly Notices of the Royal Astronomical Society.
Over billions of years, galaxy clusters build up structure in the universe by merging with adjacent clusters. When this collision happens, a huge release of energy produces a shock wave that travels through the cluster like a tsunami. Until recently, no evidence existed that this process greatly affected the galaxies. However, the team observed the merging galaxy cluster CIZA J2242.8+5301, nicknamed the “Sausage,” located 2.3 billion light years away and found that the galaxies in the cluster were revived, forming stars at a tremendous rate. Their research implies that the merger of galaxy clusters has a major affect on star formation, in particular, massive, short-lived stars that explode as supernovae a few million years later.
Every cluster of galaxies in the nearby universe has experienced a series of mergers during its lifetime and thus should have undergone a period of extremely vigorous star production. The challenge is observing these clusters during the brief period when the galaxies are still being affected by the shock. The next step in the team’s research is to study if the Sausage cluster is unique and whether these bursts of star formation require very particular conditions. By studying a much bigger sample of galaxies, the team aims to reveal exactly how this process occurs.
Contact: William Dawson (925) 424-3732 (dawson29@llnl.gov).
On April 1, 1995, the Hubble Space Telescope captured the famous images of the “Pillars of Creation” in the Eagle Nebula. Twenty years later to the day, a team at Livermore’s National Ignition Facility (NIF) conducted the first experiment in a new campaign aimed at understanding how stars are born in these cosmic formations. The experimental series investigates the origin and dynamics of pillar formation at the boundaries of HII regions (star-forming molecular hydrogen clouds) in the presence of ablative stabilization. This process prevents the growth of traditional Rayleigh–Taylor hydrodynamic instability pillars that are well known in the context of inertial confinement fusion.
The experiment’s first shot was designed to study target debris and the performance of a three-hohlraum array. The NIF laser fired a 10-nanosecond pulse of ultraviolet light into each of the three hohlraums in sequence, and the hohlraums re-radiated the energy as a 30-nanosecond x-ray pulse. The x rays drove a shock into a layered foam and successfully created a miniature version of a pillar. The next four scheduled NIF shots focus on the “cometary model,” one of several different theories scientists have advanced to explain the physics of pillar formation. The team will study whether pillars could form from a dense cloud core, resembling the head of a comet with vaporized and shocked matter stretched out like a comet’s tail, and also whether more exotic, theorized nonlinear hydrodynamic instabilities could play a role.
NIF is the only facility that can generate an x-ray source that is sufficiently intense, long-lasting, and collimated to drive cometary flows and directional instabilities in scaled laboratory experiments and to permit assessment of models for producing flows that generate pillars. The results of the team’s research could guide new ground-based observations of molecular clouds. In addition, the team will investigate deeply nonlinear hydrodynamic instabilities in the presence of sustained, highly directional illumination. Furthermore, the NIF experiments could generate exotic instabilities that have only been theorized or seen in astrophysical simulations.
Contact: Jave Kane (925) 424-5805 (kane7@llnl.gov).
Researchers from Lawrence Livermore and the University of California at Davis have found that covering an implantable neural electrode with nanoporous gold could eliminate the risk of scar tissue forming over the electrode’s surface. The team, which included Laboratory scientists Monika and Juergen Biener, demonstrated that the nanostructure of nanoporous gold achieves close physical coupling of neurons by maintaining a high neuron-to-astrocyte surface coverage ratio. Close physical coupling between neurons and the electrode plays a crucial role in recording fidelity of neural electrical activity. The findings were featured on the cover of the April 8, 2015, issue of Applied Materials and Interfaces.
Neural interfaces (e.g., implantable electrodes or multiple-electrode arrays) have emerged as transformative tools to monitor and modify neural electrophysiology, both for fundamental studies of the nervous system, and to diagnose and treat neurological disorders. These interfaces require low electrical impedance to reduce background noise and close electrode–neuron coupling for enhanced recording fidelity. One main obstacle in maintaining robust electrode–neuron coupling is that scar tissue can potentially encapsulate the electrode.
Typically, low-impedance nanostructured electrode coatings rely on chemical cues from pharmaceuticals or surface-immobilized peptides to suppress scar tissue formation over the electrode surface. However, the team found that nanoporous gold, produced by an alloy corrosion process, is a promising candidate to reduce scar tissue formation. Their results show that nanoporous gold topography, not surface chemistry, reduces astrocyte surface coverage. Nanoporous gold has attracted significant interest for use in electrochemical sensors, catalytic platforms, fundamental structure–property studies at the nanoscale, and tunable drug release.
Contact: Monika Biener (925) 424-6157 (biener3@llnl.gov) or Juergen Biener (925) 422-9081 (biener2@llnl.gov).
National Ignition Facility (NIF) scientists and engineers are endeavoring to fit a three-meter-long x-ray microscope into the space between the back of the diagnostic insertion manipulator and the inner wall of the facility’s target bay. Livermore physicist Louisa Pickworth, the project’s lead scientist, explains that the new Kirkpatrick-Baez optic (KBO) diagnostic is needed to obtain high-resolution images of the “hot spots” at the center of target capsules during NIF inertial confinement fusion implosions.
The specially designed diagnostic will provide improved spatial resolution, higher imaging throughput (signal strength), and the ability to select wavelength, which is currently unavailable using standard pinhole framing camera technology. To achieve those goals, four pairs of mirrors that make up four x-ray imaging channels must be precisely aligned. In addition, the overlapping image axis of the four pairs needs to be aligned to within a 50-micrometer radius of the center of the NIF target, and the positioning must be highly repeatable between experiments.
Development of the KBO diagnostic was a collaboration between Livermore’s NIF and Photon Science Principal Directorate and the Physical and Life Sciences Directorate. To provide wavelength filtering to accommodate different experimental needs, the team developed special multilayer coatings for the KBO system’s mirrors. Extensive simulations and off-line testing of the system’s optics and other components have produced good results, showing substantial improvements in throughput and resolution over pinhole imaging systems. The first phase of the project, labeled KBO 1, is scheduled for this fall, with subsequent phases scheduled for next fiscal year.
Contact: Louisa Pickworth (925) 423-1309 (pickworth1@llnl.gov).