SLAC – Lightsources.org

Cutting-edge experiments reveal ‘hidden’ details in transforming material

2025/03/202025/03/21

Using SLAC’s LCLS for one of the first studies of its kind, researchers discover surprising behaviors of a complex material that could have important implications for designing faster microelectronic devices.

Phase changes are central to the world around us. Probably the most familiar example is when ice melts into water or water boils into steam, but phase changes also underlie heating systems and even digital memory, such as that used in smartphones.

Triggered by pulses of light or electricity, some materials can switch between two different phases that represent binary code 0s and 1s to store information. Understanding how a material transforms from one state or phase to another is key to tailoring materials with specific properties that could, for instance, increase switching speed or operate at lower energy costs.

Image: In X-ray photon correlation spectroscopy, X-rays interact with a sample and produce interference patterns, called speckle patterns, that encode information about the structure of the material at the atomic and nanoscale. As a material transforms from one phase to another, the speckle pattern will change. The research team used these patterns to follow the changes in real time as a material transformed from one crystalline phase to another, triggered by a single pulse of light.

Credit: Aaron Lindenberg/SLAC National Accelerator Laboratory

A Goldilocks promoter for a silver catalyst

2025/03/172025/03/20

Nickel dopants could improve sustainable production of ethylene oxide, a chemical widely used in industrial manufacturing.

Plastics, textiles, detergents, adhesives and antifreeze all have something in common: They were made using ethylene oxide. This colorless gas, a chemical building block in the industrial production of many materials, is itself produced by reacting oxygen with ethylene. However, maximizing the amount of ethylene oxide produced poses unique challenges.

Adding chlorine increases the efficiency of ethylene oxide production by 25 percent. But chlorine, which is corrosive to metal equipment, has its own drawbacks. Writing in Science, researchers at the University of California, Santa Barbara (UCSB), Tufts University, Brookhaven National Laboratory and Tulane University identified nickel as a promoter that can enhance the selectivity of the silver catalyst by about 25 percent, roughly the same amount as chlorine, but with fewer downsides. The team studied the interaction of nickel with the silver catalyst using X-rays from the Stanford Synchrotron Radiation Lightsource (SSRL) at the Department of Energy’s SLAC National Accelerator Laboratory.

“From an environmental standpoint, if you remove chlorine, that’s one less toxic and corrosive material out of the process stream,” said Adam Hoffman, a staff scientist at SLAC who contributed to this work. “And if you can improve a catalyst’s activity to a target chemical, it improves the sustainability of the process as a whole.”

Charles Sykes, a chemist at Tufts University who led the effort, said it also makes financial sense. “Every one percent increase in the efficiency of the process saves around $200 million annually,” he said.

A more selective catalyst doesn’t only maximize the amount of product, it is also more efficient overall. Post reaction, ethylene oxide must be separated from the side products and residual reactants, a process that requires additional energy inputs. If the reaction is more selective to ethylene oxide to begin with, it is easier to purify.

Image: A computer-generated image showing single nickel (Ni) atoms embedded in silver, used to enable efficient production of ethylene oxide.

Credit: Elizabeth Happel/Tufts University

Superfast collisions predict supercritical fluid properties

2024/12/182025/01/06

LCLS X-rays allowed researchers to connect the molecular dynamics of supercritical carbon dioxide, which is used in industrial and environmental applications, with its unique properties.

It’s a liquid! It’s a gas! No, it’s a supercritical fluid!

Neither gas nor liquid, supercritical fluids exhibit a unique mashup of the properties of both and arise when fluids are pushed to very high temperatures and pressures. Their properties make them ideal for a wide variety of chemical, pharmaceutical and environmental applications.

Supercritical carbon dioxide, for example, is often used to decaffeinate coffee – its liquid-like high density and gas-like rapid diffusion allows it to easily penetrate coffee beans and selectively extract the caffeine while preserving the beloved coffee taste. In carbon capture and sequestration, carbon dioxide emissions are stored underground in their supercritical fluid form to combat climate change. It’s also found in rocket propulsion systems, because it can efficiently store a lot of energy, and the atmospheres of some planets, such as Venus. It could also be used as a more environmentally-friendly fluid in future cooling systems.

Now, researchers at the Department of Energy’s SLAC National Accelerator Laboratory have uncovered new details of how supercritical fluids’ special properties arise from their molecular level dynamics. Their results are published in two studies in the journals Nature Communications and Physical Review Letters.

From static studies, researchers know that the molecular structure of supercritical fluids is made up of clusters of molecules of different sizes, but they haven’t been able to study the movement of these nanosized blobs until now.

“Probing these transient, fast-moving, nanoscale clusters is a challenge,” said Matthias Ihme, a professor of photon science at SLAC National Accelerator Laboratory, a professor of mechanical engineering at Stanford and a member of the Stanford PULSE Institute. The fact that supercritical fluids only form under high pressure and temperature further complicates their study, he said.

However, recent advances in X-ray free electron lasers allowed Ihme and his colleagues to use SLAC’s Linac Coherent Light Source (LCLS) to directly observe the ultrafast dynamics of molecular clusters in supercritical carbon dioxide. Those advances, said SLAC staff scientist Yanwen Sun, involved a decade-long effort to generate two bright, nearly identical LCLS X-ray flashes in rapid succession – making it possible to capture the kinds of dynamics Ihme and his team were interested in.

By measuring how the LCLS’s X-rays scattered off the samples over time, the authors found that the dynamics of these systems evolve within picoseconds, or trillionths of a second. Specifically, these results, published in Nature Communications, showed that the blobs transition from ballistic motion, which is relatively straight and predictable, to the more random and unpredictable Brownian motion.

Image: X-rays scatter off CO2 molecules, revealing the collision of unbound molecules with dense clusters shown in blue.

Credit: Matthias Ihme/SLAC National Accelerator Laboratory

Slow Atomic Movements Shed New Light on Unconventional Superconductivity

2024/12/042024/12/10

Materials known as unconventional superconductors can conduct electricity with no loss at higher temperatures than regular superconductors. But after 40 years of research, those temperatures are still quite cold – about 140 degrees Celsius below the freezing point of water. Engineering them to operate in much warmer conditions – a development that could spur revolutions in energy, microelectronics and other fields – requires a much better understanding of how these complex materials work.

Almost all the research so far has focused on very fast processes that may contribute to superconductivity – for instance, natural, high-frequency vibrations known as phonons that rattle a material’s atomic latticework trillions of times per second.

Now researchers at the Department of Energy’s SLAC National Accelerator Laboratory have taken a new look from the opposite direction: They observed how an exceedingly slow process known as atomic relaxation changes in the presence of two of the quantum states that intertwine in cuprate superconductors.

The results suggest that the relaxation process is a promising tool for exploring and understanding those two states – charge density waves (CDWs), which are stripes of higher and lower electron density in the material, and the superconducting state itself, which switches on when the material chills below its transition temperature.

The research team described the results today in the Proceedings of the National Academy of Sciences.

Image: A SLAC research team discovered how an exceedingly slow process known as atomic relaxation changes in the presence of two of the quantum states that intertwine in cuprate superconductors. The results suggest that the relaxation process is a promising tool for exploring and understanding those two states – charge density waves (depicted above), which are stripes of higher and lower electron density in the material, and the superconducting state itself, which switches on when the material chills below its transition temperature.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

A novel spray device helps researchers capture fast-moving cell processes

2024/06/062024/06/20

Cells are the basic units of life – but many of their fundamental processes happen so fast and at such small length scales that current scientific tools and methods can’t keep up, preventing us from developing a deeper understanding.

Now, researchers with SLAC National Accelerator Laboratory, Stanford University, Cornell University and other institutions have developed a new approach for watching basic biological processes unfold. The approach, which combines cryogenic electron microscopes with methods developed in X-ray crystallography, could lead to improved medicines and a deeper understanding of cell division, photosynthesis and host-pathogen interactions, among other subjects.

Reimagining a powerful spray tool

For many decades, scientists have relied on imaging techniques known as cryogenic electron microscopy (cryo-EM) and cryogenic electron tomography (cryo-ET) to see inside of cells, proteins, and other organisms and molecules. Both techniques use electron microscopes to capture snapshots of flash-frozen samples, which have revealed cellular structures in extraordinary detail. These approaches involve putting a sample on a thin small disk known as an electron microscopy grid and plunging it into a cryogenic liquid to freeze it very rapidly. This is great at preserving cellular samples in their native state, but the frozen snapshots don’t tell researchers much about dynamics. It is sort of like trying to learn dance moves by taking random images of someone dancing.

Currently in similar cryo-ET experiments, researchers hand-mix cell samples in order to take images of them in response to a stimuli. But hand-mixing takes time, kind of like mixing pancake batter by hand instead of with an electric mixer, meaning that experimenters can only observe changes in an organism at about ten second intervals – hundreds of times longer than many important processes take.

Researchers therefore turned to a spray nozzle device that is often used at X-ray free-electron laser (XFEL) and synchrotron facilities to mix samples for crystallography experiments. The device, known as a mixing injector coupled Gas Dynamic Virtual Nozzle (GDVN), is often used to study molecular movements that occur on extremely short timescales, like femtoseconds after activation with light or on millisecond to second timescales using chemical mixing, at XFELs like SLAC’s Linac Coherent Light Source (LCLS).

Image: A graphic representation of the spray nozzle device. The sample cells (green) mix with the simulant solution as the cells travel from left to right, out of the spray nozzle.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

New catalyst could cut pollution from millions of engines

2023/07/202023/07/26

Researchers demonstrate a way to remove the potent greenhouse gas from the exhaust of engines that burn natural gas.

Individual palladium atoms attached to the surface of a catalyst can remove 90% of unburned methane from natural-gas engine exhaust at low temperatures, scientists reported today in the journal Nature Catalysis.

While more research needs to be done, they said, the advance in single atom catalysis has the potential to lower exhaust emissions of methane, one of the worst greenhouse gases, which traps heat at about 25 times the rate of carbon dioxide.

Researchers from the Department of Energy’s SLAC National Accelerator Laboratory and Washington State University showed that the catalyst removed methane from engine exhaust at both the lower temperatures where engines start up and the higher temperatures where they operate most efficiently, but where catalysts often break down.

“It’s almost a self-modulating process which miraculously overcomes the challenges that people have been fighting – low temperature inactivity and high temperature instability,” said Yong Wang, Regents Professor in WSU’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering and one of four lead authors on the paper.

A growing source of methane pollution

Engines that run on natural gas power 30 million to 40 million vehicles worldwide and are popular in Europe and Asia. The natural gas industry also uses them to run compressors that pump gas to people’s homes. They are generally considered cleaner than gasoline or diesel engines, creating less carbon and particulate pollution.

However, when natural-gas engines start up, they emit unburnt, heat-trapping methane because their catalytic converters don’t work well at low temperatures. Today’s catalysts for methane removal are either inefficient at lower exhaust temperatures or they severely degrade at higher temperatures.

“There’s a big drive towards using natural gas, but when you use it for combustion engines, there will always be unburnt natural gas from the exhaust, and you have to find a way to remove that. If not, you cause more severe global warming,” said co-author Frank Abild-Pedersen, a SLAC staff scientist and co-director of the lab’s SUNCAT Center for Interface Science and Catalysis, which is run jointly with Stanford University. “If you can remove 90% of the methane from the exhaust and keep the reaction stable, that’s tremendous.”

A catalyst with single atoms of the chemically active metal dispersed on a support also uses every atom of the expensive and precious metal, Wang added.

“If you can make them more reactive,” he said, “that’s the icing on the cake.”

Unexpected help from a fellow pollutant

In their work, the researchers showed that their catalyst made from single palladium atoms on a cerium oxide support efficiently removed methane from engine exhaust, even when the engine was just starting.

They also found that trace amounts of carbon monoxide that are always present in engine exhaust played a key role in dynamically forming active sites for the reaction at room temperature. The carbon monoxide helped the single atoms of palladium migrate to form two- or three-atom clusters that efficiently break apart the methane molecules at low temperatures.

Then, as the exhaust temperatures rose, the clusters broke up into single atoms and redispersed, so that the catalyst was thermally stable. This reversible process enabled the catalyst to work effectively and used every palladium atom the entire time the engine was running – including when it started cold.

Researchers make a new type of quantum material with a dramatic distortion pattern

2023/02/222023/03/03

Created by an electronic tug-of-war between the material’s atomic layers, this ‘beautiful’ herringbone-like pattern could give rise to unique features that scientists are just starting to explore.

Researchers at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have created a new type of quantum material whose atomic scaffolding, or lattice, has been dramatically warped into a herringbone pattern.

The resulting distortions are “huge” compared to those achieved in other materials, said Woo Jin Kim, a postdoctoral researcher at the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC who led the study.

“This is a very fundamental result, so it’s hard to make predictions about what may or may not come out of it, but the possibilities are exciting,” said SLAC/Stanford Professor and SIMES Director Harold Hwang.

“Based on theoretical modeling from members of our team, it looks like the new material has intriguing magnetic, orbital and charge order properties that we plan to investigate further,” he said. Those are some of the very properties that scientists think give quantum materials their surprising characteristics.

The research team described their work in a paper published in Nature today.

Image: This illustration depicts a herringbone-like pattern in the atomic lattice of a quantum material created by researchers at SLAC and Stanford. An electronic tug-of-war between its layers has dramatically warped the lattice. Researchers are just staring to explore how this ‘huge’ distortion affects the material’s properties.

Credit: Greg Stewart/SLAC National Accelerator Laboratory