A next-generation X-ray beamline now operating at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) brings together a unique set of capabilities to measure the properties of materials at the nanoscale.
Called COSMIC, for Coherent Scattering and Microscopy, this X-ray beamline at Berkeley Lab's Advanced Light Source (ALS) allows scientists to probe working batteries and other active chemical reactions, and to reveal new details about magnetism and correlated electronic materials. COSMIC has two branches that focus on different types of X-ray experiments: one for X-ray imaging experiments and one for scattering experiments. In both cases, X-rays interact with a sample and are measured in a way that provides, structural, chemical, electronic, or magnetic information about samples.
The beamline is also intended as an important technological bridge toward the planned ALS upgrade, dubbed ALS-U, that would maximize its capabilities. Now, after a first-year ramp-up during which staff tested and tuned its components, the scientific results from its earliest experiments are expected to get published in journals later this year.
A study published earlier this month in the journal Nature Communications, based primarily on work at a related ALS beamline, successfully demonstrated a technique known as ptychographic computed tomography, which mapped the location of reactions inside lithium ion batteries in 3-D. That experiment tested the instrumentation that is now permanently installed at the COSMIC imaging facility.
The researchers aim to provide an entirely new class of tools for the materials sciences, as well as for environmental and life sciences. Ptychography achieves spatial resolution finer than the X-ray spot size by phase retrieval from coherent diffraction data. The ptychographic tomography technique that researchers used in this latest study allowed them to view the chemical states within individual nanoparticles. They looked at a piece of a battery cathode in 3-D with a resolution that was unprecedented for X-rays. This provides new insight into battery performance both at the single-particle level and across statistically significant portions of a battery cathode.
COSMIC is focused on a range of “soft” or low-energy X-rays that are particularly well-suited for analysis of chemical composition within materials. Ptychographic tomography can be particularly useful for looking at cellular components. The X-ray beam at COSMIC is focused to a spot about 50 nanometers in diameter; however, ptychography can routinely enhance the spatial resolution by a factor of 10 or more. The current work was performed with a 120-nanometer beam that achieved a 3-D resolution of about 11 nanometers.
COSMIC's X-ray beam is also brighter than the ALS beamline that was used to test its instrumentation, and it will become even brighter once ALS-U is complete. This brightness can translate to an even higher nanoscale resolution and can also enable far more precision in time-dependent experiments. Making efficient use of this brightness requires fast detectors, which are developed by the ALS detector group. The current detector can operate at a data rate of up to 400 megabytes per second and can now generate a few terabytes of data per day. Next-generation detectors, to be tested shortly, will produce data 100 times faster.
An important component of COSMIC is the development of advanced mathematics and computation able to quickly reconstruct information from the data as it is collected. To develop these tools COSMIC coupled with CAMERA, which was created to bring state-of-the-art mathematics and computing to DOE scientific facilities. Building real-time advanced algorithms and the high-performance ptychographic reconstruction code for COSMIC was a multiyear effort between mathematicians, computer scientists, software engineers, software experts, and beamline scientists.
The code the team developed to improve ptychographic imaging at COSMIC, dubbed SHARP, is now available to all light sources across the DOE complex. For COSMIC, the SHARP code runs on a dedicated graphics processing unit (GPU) cluster managed by Berkeley Lab's High Performance Computing Services. Besides ptychography, COSMIC is also equipped for experiments that use X-ray photon correlation spectroscopy, or XPCS, a technique that is useful for studying fluctuations in materials associated with exotic magnetic and electronic properties.
COSMIC enables scientists to see such fluctuations occurring in milliseconds, compared to time increments of multiple seconds or longer, at predecessor beamlines. A new COSMIC end-station with applied magnetic field and cryogenic capabilities is now being built, with early testing set to begin this summer. Scientists have already used COSMIC's imaging capabilities to explore a range of nanomaterials, battery anode and cathode materials, cements, glasses, and magnetic thin films.