Lawrence Livermore National Laboratory

Getting to the Core of Plate Tectonics

Lawrence Livermore scientist Nathan Simmons and collaborators from the University of Chicago, Université du Québec à Montréal, the University of Florida, Kent State University, Syracuse University, and the University of Texas at Austin have found that heat from Earth’s core has a significant effect on tectonic plate movement. This research challenges the theory that movement of Earth’s tectonic plates is driven largely by negative buoyancy created as the tectonic plates cool. It also suggests that the underwater mountain ranges, known as mid-ocean ridges (MORs), are not passive boundaries between moving plates, as previously thought.

“Heat from the deep Earth likely plays a significant role in global plate tectonics,” says Simmons, a coauthor of the research published in the December 23, 2016, issue of Science Advances. “The cooling and sinking of plates is not the only significant plate-driving force.” Global-scale tomographic models of Earth’s mantle—the zone between Earth’s core and crust—were used to simulate mantle convection forward and backward in time. The simulations helped demonstrate the persistence of large-scale mantle upwelling beneath the East Pacific Rise region.

The East Pacific Rise has not significantly moved east–west for 50 to 80 million years, even as parts of it have spread asymmetrically. The researchers say these dynamics cannot be explained solely by subduction. “Through modeling and observations, we found that over the past 80 million years, plate separation along the East Pacific Rise is driven significantly by heat drawn from Earth’s core, which is uncharacteristic relative to other MORs,” adds Simmons.
Contact: Nathan Simmons (925) 422-2473 (

Probing Radiation Defect Dynamics

Researchers at Lawrence Livermore and Texas A&M University used a novel experimental method to study thermally activated defect interaction processes in silicon. Pulsed-ion beams were used to probe defect interaction dynamics. By measuring temperature dependencies of the dynamic annealing rate of defects, the researchers found two distinct regimes of defect interaction—at temperatures above and below 60ºC, respectively. Rate theory modeling, benchmarked against pulsed-beam data, pointed to a crucial role of both vacancy and interstitial diffusion, with the defect production rate limited by the migration and interaction of vacancies.

Understanding radiation defects in crystals has been a major materials challenge for decades. Stable defect formation often involves dynamic processes of migration and interaction of point defects generated by energetic particles. However, the exact pathways of defect formation have remained elusive, and most current predictions of radiation damage are essentially empirical fits to experimental data. This approach applies even to the best studied and arguably simplest material, crystalline silicon, which is the backbone of modern electronics. Until recently, scientists lacked experimental methods that could directly probe the dynamics of defect creation and annealing.

The research, appearing in the January 6, 2017, online edition of Scientific Reports, could lead to improvements in modern electronics performance. Sergei Kucheyev, Livermore project lead and coauthor for the paper, says, “This work provides a blueprint for future pulsed-beam studies of radiation defect dynamics in other technologically relevant materials.”
Contact: Sergei Kucheyev (925) 422-5866 (

Hydrogen from Photoelectrochemical Cells

Hydrogen production offers a promising approach for producing scalable and sustainable carbon-free energy. The key to a successful solar-to-fuel technology is the design of efficient, long-lasting, and low-cost photoelectrochemical cells (PECs), which are responsible for absorbing sunlight and driving water-splitting reactions (see image below). Lawrence Livermore scientist Tuan Anh Pham and collaborators from the University of California at Santa Cruz and the University of Chicago are fine-tuning the mechanisms to generate hydrogen from water and sunlight by investigating the interfaces between photoabsorbers, electrolytes, and catalysts in PECs.

Efficient PECs rely on the availability of abundant semiconducting photoelectrode materials that are responsible for absorbing sunlight and driving water-splitting reactions. “Despite steady efforts and some breakthroughs, no single material has yet been found that simultaneously satisfies the efficiency and stability required for the commercialization of PEC hydrogen-production technology,” says Pham, lead author of the research appearing in the January 9, 2017, online edition of Nature Materials.

With the growing complexity of PEC architectures, understanding the properties of the interfaces is crucial to predicting novel, better performing materials that can eventually lead to optimal device performance. The study addresses the challenges in describing PEC interfaces using first-principles techniques that focus on the interplay between their structural and electronic properties. The researchers also reviewed first-principles techniques relevant to solid and liquid interfaces.
Contact: Tuan Anh Pham (925) 423-6501 (