Scientists speculate that lonsdaleite, a hexagonal form of diamond found in meteorite fragments around the world, is created when graphite-bearing meteors strike Earth. The violent impact generates incredible heat and pressure, transforming the graphite into diamond while retaining the graphite’s original hexagonal structure. Recent Livermore dynamic high-pressure experiments, which mimic meteor-impact conditions, created a lonsdaleite structure for the first time in a laboratory. The research appears in the March 14, 2016, edition of Nature Communications.
The research team, which includes scientists from Livermore, the University of California (UC) at Berkeley, SLAC National Accelerator Laboratory, and international institutions, conducted the experiments at SLAC’s Linac Coherent Light Source. Graphite samples were shock-compressed to pressures of up to nearly 203 gigapascals (2 million atmospheres) to trigger the structural transitions from graphite to diamond and lonsdaleite. The results indicate that the lonsdaleite found in nature could serve as evidence of violent meteor impacts.
“Our experiments show that above the pressure range studied in our experiments, the lonsdaleite structure can be generated in a very pure form. Since pure lonsdaleite is supposedly even harder than diamond, our results already have important industry applications,” says Dominik Kraus, who conducted this research while working as a postdoc within Livermore’s National Ignition Facility and Photon Science Principal Directorate. Kraus now serves as the Helmholtz Young Investigator group leader at Helmholtz-Zentrum Dresden-Rossendorf in Germany.
Contact: Tilo Doeppner (925) 422-2147 (doeppner1@llnl.gov).
Graphene metal oxide (GMO) nanocomposites are renowned for their potential energy storage and conversion applications. For lithium-ion batteries, nanosize metal oxide particles and highly conductive graphene are considered beneficial for shortening lithium diffusion pathways and reducing polarization in the electrode, leading to enhanced performance. In research featured on the cover of the March 21, 2016, edition of the Journal of Materials Chemistry A, Livermore materials scientists synthesized and compared the electrochemical performance of three GMO nanocomposite structures and found that two of them greatly improved reversible lithium storage capacity.
As part of the experiments, the team dipped prefabricated graphene aerogel electrodes in solutions of metal oxide nanoparticles, which became anchored on the surface of the graphene pores, making them fully accessible to the electrolyte. The method can deposit most types of metal oxides onto the same prefabricated three-dimensional graphene structure, allowing for direct comparison of electrochemical performance of a wide range of GMOs.
“Surprisingly, we saw that the graphene’s capacity is mainly determined by active materials and the type of metal oxide bound onto the graphene surface,” says Morris Wang, a Livermore materials scientist and author of the paper. The work was funded through Livermore’s Laboratory Directed Research and Development Program.
Contact: Morris Wang (925) 422-6083 (wang35@llnl.gov).
In March 2016, Lawrence Livermore received a first-of-its-kind, brain-inspired supercomputing platform for deep learning developed by IBM Research. Based on a breakthrough neurosynaptic computer chip called IBM TrueNorth, the scalable platform processes the equivalent of 16 million neurons and 4 billion synapses yet consumes the energy equivalent of a hearing-aid battery—a mere 2.5 watts.
The brain-like, neural network design of the IBM Neuromorphic System can infer complex cognitive tasks such as pattern recognition and integrated sensory processing far more efficiently than conventional chips. The system will be used to explore new computing capabilities important to the National Nuclear Security Administration’s (NNSA’s) missions in cybersecurity, stockpile stewardship, and nonproliferation. NNSA’s Advanced Simulation and Computing (ASC) Program will evaluate machine-learning applications as well as deep-learning algorithms and architectures and conduct general computing feasibility studies.
The Laboratory also acquired an end-to-end ecosystem to create and program energy-efficient machines that mimic the brain’s perception, action, and cognition abilities. Jim Brase, Livermore’s leader for the Data Science Initiative, says, “Neuromorphic computing represents the potential that machine intelligence will change how we conduct science.”
Contact: Jim Brase (925) 422-6992 (brase1@llnl.gov).
For the first time, Lawrence Livermore researchers have shown that carbon nanotubes as small as 0.8 nanometers in diameter are 10 times faster than bulk water at transporting protons. The transport rates in these nanotube pores, which form one-dimensional (1D) water wires, also exceed those of biological channels and human-made proton conductors, making carbon nanotubes the fastest known proton conductor. The research appears in the April 4, 2016, online edition of the journal Nature Nanotechnology.
The Livermore team, along with colleagues from Lawrence Berkeley National Laboratory and the University of California at Berkeley, created a simple and versatile experimental system for studying transport in ultra-narrow carbon nanotube (CNT) pores. The researchers used CNT porins, a technology developed earlier at Livermore that uses CNTs embedded in a lipid membrane to mimic biological ion-channel functionality. The team’s key breakthrough was creating nanotube porins with a diameter of less than 1 nanometer, which allowed the researchers for the first time to achieve true 1D water confinement.
“Our results show that when you squeeze water into the nanotube, protons move through that water even faster than through normal water,” says Aleksandr Noy, a Livermore biophysicist and a lead author of the paper. Practical applications include proton exchange membranes, proton-based signaling in biological systems, and the emerging field of proton bioelectronics, called protonics.
Contact: Aleksandr Noy (925) 423-3396 (noy1@llnl.gov).
Lawrence Livermore and Yale University researchers found that climate models aggressively make clouds “brighter” as the planet warms, causing the models to underestimate how much global warming will occur from increasing atmospheric carbon dioxide. The research appears in the April 8, 2016, edition of Science.
As the atmosphere warms, clouds become brighter as ice within them turns to liquid. This “cloud-phase feedback” acts as a brake on global warming as liquid clouds reflect more sunlight back into space than ice clouds. Clouds in most climate models contain too much ice, causing the stabilizing cloud-phase feedback to be unrealistically strong.
The researchers used a state-of-the-art climate model to modify parameters that brought relative amounts of liquid and ice in the model’s clouds into agreement with those observed in nature. Correcting the bias led to a weaker cloud-phase feedback, and thus an increase in global warming.
In nature, clouds containing both ice crystals and liquid droplets are common at temperatures well below freezing. The relative amount of liquid in these “mixed-phase” clouds increases as the atmosphere warms. Lawrence Livermore coauthor Mark Zelinka says, “Most climate models are a little too eager to glaciate below freezing, so they are likely exaggerating the increase in cloud reflectivity as the atmosphere warms.”
Recent studies indicate that other cloud-feedback mechanisms involving changes in cloud altitude and coverage may also exacerbate global warming. Zelinka says, “Clouds do not seem to want to do us any favors when it comes to limiting global warming.”
Contact: Mark Zelinka (925) 423-5146 (zelinka1@llnl.gov).
In research appearing in the April 7, 2016, edition of Journal of Applied Physics, Livermore physicists describe a new experimental method to determine the equation of state (EOS) of low-symmetry anisotropic crystalline materials. A material’s EOS describes how material properties such as volume and internal energy are affected by intense pressure and temperature. For most materials, a prescribed set of experiments, including high-pressure x-ray diffraction (XRD), are conducted to determine sample volume under various pressure–temperature conditions.
While experimenting with an unusual insensitive explosive compound, the research team discovered the material’s complicated crystal structure limited their ability to determine its volume with high-pressure XRD. “To accurately predict performance characteristics of the material, we needed another method for determining its equation of state,” says Sorin Bastea, a Livermore computational physicist and the project leader. Based on pioneering research at Cornell University demonstrating direct volume measurements with large crystals, Livermore physical chemist Joe Zaug theorized a similar method could work with smaller structures. He conducted microscopy and interferometry measurements on a 10-micrometer-size triaminotrinitrobenzene (TATB) crystal pressurized in a diamond anvil cell. The results matched remarkably well with published x-ray results and helped the team extend the pressure range of TATB’s EOS.
Team member and Livermore physicist Elissaios Stavrou later applied the method to measure the EOS of a sample up to 30 gigapascals (300,000 times normal atmospheric pressure), which enabled the researchers to calculate performance characteristics for the insensitive explosive they were studying. This new experimental approach provides researchers with a simple and direct method for measuring the high-pressure EOS of complex crystalline materials.
Contact: Sorin Bastea (925) 422-2178 (bastea2@llnl.gov).