From Penn Today and University of Chicago: “Researchers use a material’s ‘memory’ to encode unique physical properties”

From Penn Today

and

From University of Chicago

A new study shows that, as materials age, they “remember” prior stresses and external forces, which scientists and engineers can then use to create new materials with unique properties.

Examples of disordered systems trained in this study, including (from left) a jammed packing of discs, a network based on jamming, a disordered holey sheet, and a random network based on triangular lattice. A new study shows that disordered systems like these can “remember” prior stressors, which researchers can then use to imbue the material with unique properties. (Image: Daniel Hexner, Andrea Liu, Sidney Nagel, and Nidhi Pashine)

A new study published in Science Advances found that certain types of materials have a “memory” of how they were processed, stored, and manipulated. Researchers were then able to use this memory to control how a material ages and to encode specific properties that allow it to perform new functions. This creative approach for designing materials was the result of a collaboration between Penn’s Andrea Liu and Sidney R. Nagel, Nidhi Pashine, and Daniel Hexner from the University of Chicago.

Liu and Nagel have worked together for many years on the physics of disordered systems. In contrast to ordered systems, which have systematic and repeating patterns, disordered systems are arranged randomly. An illustrative example is a natural wall made of tightly packed dirt, where individual grains aren’t neatly stacked but instead clump together to form a rigid structure. Researchers are interested in these systems because their randomness allows them to be easily transformed into new mechanical metamaterials with unique mechanical properties.

An example of a disordered (left) versus and ordered system.

One important property that materials scientists would like to control is how a material responds when an external force is applied. When most materials are stretched in one direction, they shrink perpendicularly, and when compressed they expand perpendicularly, like a rubber band—when it is stretched it becomes thin, and when compressed becomes thicker.

Materials that do the opposite, ones that shrink perpendicularly when compressed and become thicker when stretched, are known as auxetics. These materials are rare but are suspected to be better at absorbing energy and be more fracture-resistant. Researchers are interested in creating auxetic materials to help improve the function of materials that, among other things, could absorb shock.

In this study, the researchers wanted to see if they could use a disordered material’s “memory” of the prior stresses it had encountered to transform the material into something new. First, they ran computer simulations of normal materials under pressure and selectively altered atomic bonds to see which changes could make the material auxetic. They discovered that, by cutting the bonds along the areas with the most external stress, they could digitally create an auxetic material.

A depiction of a sheet with a disordered pattern of holes. The sheet on the left is auxetic under compression along one of the major axes. With directed aging of the four holes (shown in red) while the sheet is under compression, the system gains non-auxetic properties. (Image: Daniel Hexner, Andrea Liu, Sidney Nagel, and Nidhi Pashine)

Using this insight, the team then took a Styrofoam-like material and added “memory” by allowing the material to age under specified stresses. To make the material auxetic they applied a constant pressure to the material and let it age naturally. “With the whole thing under pressure, it adjusted itself. It turned itself from a normal material into a mechanical metamaterial,” says Liu.

This incredibly simple and effective process is a step closer towards a materials science “holy grail” of being able to create materials with specific atomic-level structures without the need for high-resolution equipment or atomic-level modifications. The approach described in this paper instead only requires a bit of patience while the system gains “memory” and then ages naturally.

Liu says that it is a “totally different” way to think about making new materials. “You start with a disordered system, and if you apply the right stresses you can make it come out with the properties you want,” she says.

This work also has a strong connection to structures in biology. Organs, enzymes, and filament networks are natural examples of disordered systems that are difficult to emulate synthetically because of their complexity. Now, researchers could use this simpler approach as a starting point to create complex human-made structures that take inspiration from the wide range of properties seen in biology.

Nagel is optimistic about the future. “In addition to making auxetic materials,” he says, “we have also used a computer to design in precise mechanical control of distant parts of the material by applying local stresses. This too is inspired by biological activity. We now need to see if this, too, can be made to work by aging a real material in the laboratory.”

“The possibilities at this stage seem limitless,” says Nagel. “Only by further theoretical work and experimentation will we begin to understand what are the limits to this new concept of material design.”

This research was supported by National Science Foundation grants DMR-1420709 and DMR-1404841, U.S. Department of Energy grants FG02-03ER46088 and DE-FG02-05ER46199, and Simons Foundation awards 348125, 454945, and 327939.

See the full article here .

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An intellectual destination

One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

Academic life at Penn is unparalleled, with 100 countries and every U.S. state represented in one of the Ivy League’s most diverse student bodies. Consistently ranked among the top 10 universities in the country, Penn enrolls 10,000 undergraduate students and welcomes an additional 10,000 students to our world-renowned graduate and professional schools.

Penn’s award-winning educators and scholars encourage students to pursue inquiry and discovery, follow their passions, and address the world’s most challenging problems through an interdisciplinary approach.

From UC Riverside: “Simple experiment explains magnetic resonance”

From UC Riverside

December 5, 2019
Iqbal Pittalwala

Photo shows the experimental setup. Credit: Barsukov lab, UC Riverside.

Physicists at University of California, Riverside, have designed an experiment to explain the concept of magnetic resonance. The project was carried out by undergraduate students in collaboration with local high school teachers.

A versatile technique employed in chemistry, physics, and materials research, magnetic resonance describes a resonant excitation of electron or atomic nuclei spins residing in a magnetic field by means of electromagnetic waves. Magnetic resonance also provides the basis for magnetic resonance imaging, or MRI — the central noninvasive tool in diagnostic medicine and medical research.

“Two of my undergraduate students developed the demonstration experiment based on a compass, an object everybody can relate to,” said Igor Barsukov, an assistant professor in the UC Riverside Department of Physics and Astronomy, who supervised the project.

Barsukov explained the compass is placed in the middle of a wire coil that is fed with a small alternating voltage. A refrigerator magnet in the vicinity of the compass aligns its needle. When the fridge magnet is brought closer to the compass, the needle starts to oscillate at a “sweet spot.” When the magnet is moved away from the sweet spot, the oscillation stops. This oscillation corresponds to magnetic resonance of the compass needle in the magnetic field of the fridge magnet.

“During outreach events for the broader public, people often share with us their concerns about MRI procedures they need to undergo in a hospital,” Barsukov said. “They associate it with radiation. We wanted to design a hands-on, table-top experiment to alleviate their concerns and to provide a visual explanation for the underlying physics.”

Barsukov’s team initiated a collaboration with the Physics Teacher Academy, a UCR-based program providing training for local high school teachers, to ensure it is also suitable for a high-school classroom.

“Close interaction with the teachers changed our perspective on what a good demonstration experiment aimed at improving scientific literacy should be,” Barsukov said. “We decided to employ 3D-printing techniques for the experimental setup and smartphone-based voltage generators. It reduces the time burden for instructors and makes the presentation more accessible and appealing to students.”

Igor Barsukov (right) is seen here with coauthor David Nelson, an undergraduate student in Barsukov’s lab at UC Riverside. (UCR/Barsukov lab)

The project was recently published in The Physics Teacher and presented in early November 2019 in the educational section of Magnetism and Magnetic Materials, a major conference in magnetism research.

“The project turned out to be truly synergistic,” Barsukov said. “We learned a lot from the high school teachers we worked with and were able to design an exciting tool for outreach, which I can also use in my classes at UCR. Working on this project was a great lab experience for my students.”

Barsukov and his students were joined in the project by Daniel L. McKinney, a local high school teacher; and Michael Anderson, an associate professor of physics education at UC Riverside.

The work was funded by the National Science Foundation. The Physics Teacher Academy is supported by the California Science Project

See the full article here .

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The University of California, Riverside is one of 10 universities within the prestigious University of California system, and the only UC located in Inland Southern California.

Widely recognized as one of the most ethnically diverse research universities in the nation, UCR’s current enrollment is more than 21,000 students, with a goal of 25,000 students by 2020. The campus is in the midst of a tremendous growth spurt with new and remodeled facilities coming on-line on a regular basis.

We are located approximately 50 miles east of downtown Los Angeles. UCR is also within easy driving distance of dozens of major cultural and recreational sites, as well as desert, mountain and coastal destinations.

From Brookhaven National Lab: Women in STEM- “Meet Alessandra Colli: Engineering Improvements in 3-D-printed Metals”

From Brookhaven National Lab

December 3, 2019
Karen McNulty Walsh
kmcnulty@bnl.gov

Colli seeks to merge materials risk analysis with data collected at world-class science tools to improve safety, reliability, and opportunities in metal additive manufacturing.

Alessandra Colli with National Synchrotron Light Source II beamline scientist Larry Carr at a beamline used for far-infrared spectroscopy (MET). This beamline will help characterize filter samples made by Obsidian AM, a company partnering with Brookhaven Lab to explore 3-D printing as a strategy for producing high-precision radiation filters for next-generation cosmic microwave background studies.

With a background in electrical engineering and risk assessment, Alessandra Colli, a scientist at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, wants airplane engines to function flawlessly, rockets to be reliable, and a new telescope to be sensitive to signals that could solve secrets of the universe. Her focus, however, is not on the electronic circuitry that powers these complex devices, but rather on improving the structure and function of their many metallic components.

Colli is developing a strategy to leverage Brookhaven Lab’s materials-science capabilities and data analytics approaches to advance metal “additive manufacturing,” also known as 3-D printing. Compared with conventional metal manufacturing, 3-D printing offers great promise for building metal components with higher precision and greater reliability from the bottom up.

“When you are talking about reliability, most of the time you look at the system level—how the part performs in the field, in the real-world application,” Colli said. “We want to bring in the basic materials science—the kinds of studies we can do at the National Synchrotron Light Source II (NSLS-II) and the Center for Functional Nanomaterials (CFN) to look at material properties and defects at very small scales—along with analytical techniques being developed by our Computational Science Initiative to efficiently sift through that data.”

This approach could help scientists identify sources of material imperfections or weakness—and explore how different 3-D printing approaches or even new materials could improve a particular product.

“Industrial partners could come in and we can help them solve specific issues using the enormous capabilities of our DOE Office of Science user facilities,” Colli said.

3-D printed metals

Once used mainly for creating prototypes or models, additive manufacturing is moving into the mainstream for a range of industrial and defense applications, so much so that many industrial players address it as the next industrial revolution in manufacturing, Colli said. Using 3-D printing to manufacture precision metal engine components, high-tech filters, or even construction hinges and brackets offers ways to reduce waste of feedstock material and dramatically improve design to achieve better performance of the final product, she noted.

Instead of whittling down a larger block of metal, pouring molten material into a mold, or making separate components that must later be fastened together, 3-D printing uses a range of techniques to deposit the material layer by layer, printing only the desired object with little material wasted. The technology can create intricate objects and even allows construction from composite materials.

But to ensure durability, strength, resistance to corrosion, or other characteristics important for specific applications, it’s essential to understand not just what the manufactured part looks like and how it works in its application, but also what’s going on inside—the characteristics of the material itself.

Think about a piece that might be part of an airplane, or supporting parts for construction, part of a rocket engine or ship—these parts need extremely high reliability.

“With additive manufacturing, there can be different types of defects—residual stress that creates tension in an area where you may not want it; porosity formed by bubbles that create a weak spot where the part can break. We have a range of techniques that can see these structural characteristics and the materials’ chemical composition. And we can study them under different environmental conditions, like pressure or high heat, that when combined with certain material characteristics can cause a failure,” Colli said.

These tools can also help identify the best additive manufacturing processes for different applications, fine-tune manufacturing precision to take into account post-processing steps such as polishing or annealing, or explore new materials or combinations of materials that may improve functions.

Building collaborations

“There are lots of opportunities to grow collaborations with academic partners, industry, other departments at Brookhaven, and the user facilities here and at the other DOE Labs or research institutions around the world,” Colli said.

As an example, Colli notes one collaboration already underway among scientists in Brookhaven’s Sustainable Energy Technologies Department, Physics Department, Instrumentation Division, NSLS-II, and Obsidian AM (a small spin-off company from Yale University in Connecticut) that hopes to develop filters for cosmic microwave background radiation [CMB].

CMB per ESA/Planck

These filters, designed for use in next-generation telescopes, are typically fabricated from metal as meshes or grids that get laminated together. Their job is to screen out signals from other forms of radiation so scientists can collect echoes of the radiation leftover from the Big Bang. Filtering out the “noise” will help physicists decipher details about neutrinos, dark matter, and general relativity.

Scientific exploration of new materials, composites, and 3-D printing processes along with engineering studies of new applications will open many opportunities in metal additive manufacturing. This approach could guide the development of 3-D printed materials with reliability in harsh environments, reduced size and weight, or other characteristics optimized for specific applications.

“We are exploring plasma 3-D printing as a way to directly manufacture the full metamaterial for these filters. We’re starting by making sure we can print the metal part with optimal precision, but we are hoping to be able to print alternate layers of insulating material and metal grid directly using the same 3-D printing process,” Colli said.

This approach could be applied to making other layered metamaterials and composites, such as high-temperature superconductors (promising materials that carry electric current with no resistance) and magnets.

Colli is finalizing plans with professors at the North Carolina A&T State University and Rensselaer Polytechnic Institute to bring students in to learn about the various 3-D printing technologies, materials characterization tools such as x-ray diffraction, and approaches such as tensile stress testing. She is also collaborating with computational scientists to develop the tools and algorithms—many based on machine learning and other forms of “artificial intelligence”—to identify key indicators that will predict (and guide design to avoid) failure in additively manufactured metal components.

Varied background, open mind

“I’m not a materials scientist and I’m not a physicist, so to build this strategy and these collaborations, I had to learn everything too, including about the techniques; and I’m still learning,” Colli said. “My strength is to be able to understand both the small details and the big picture.”

Colli attributes her wide-scale vision to the diversity of topics she studied early in her career: electrical power engineering for her master thesis and risk analysis for her Ph.D., the former at the Polytechnic University of Milan in Italy and the latter at Delft University of Technology in The Netherlands. “Diversifying things gives perspective in terms of what you can learn and what you can see. It really opens up your mind,” she said.

She spent six years in The Netherlands developing methods to compare technological, environmental, and occupational risks of various energy technologies—fossil fuels, nuclear, and renewable energies such as solar. When she first came to Brookhaven Lab in 2011, she worked to integrate risk analysis into the economic side of evaluating energy systems.

Simulations of filters for cosmic microwave background radiation telescopes help identify the best configuration for optimal performance. This graphic shows one layer of the copper configuration simulated using CST Studio Suite, a 3-D electromagnetic analysis software program. The simulation determines what types of radiation get transmitted through or filtered out by the mesh.

The proximity of the Northeast Solar Energy Research Center to NSLS-II first sparked her idea that understanding material properties might help address an energy challenge: why photovoltaic solar cells sometimes crack.

“My idea was to apply my knowledge in risk analysis to reliability issues in photovoltaics. What is the impact of the different materials that make up these layered structures on the tendency of cracks to form and propagate, for example? We have the solar panels and the synchrotron right here to do the materials science testing,” she said.

In 2018, Jim Misewich, Associate Laboratory Director for Energy and Photon Sciences (EPS), asked her to develop the Lab’s strategy for metal additive manufacturing as part of the EPS Growth plan. This opportunity gave her a chance to bring her idea of correlating material properties with performance and reliability to a new challenge.

“I had to grow in my career, to go from being a scientist doing my job in the lab to develop a leadership mentality,” she said. With support from the Growth Office—including Elspeth McSweeney, Michael Cowell, and Jun Wang—she developed skills and sought professional training courses such as the Women in STEM Leadership program at Stony Brook University.

“It was a year of enormous growth,” she said. “When people believe in you and they give you a chance, you feel obligated to give something back and to be successful. Supporting other people at the Lab helps us push each other.”

Meaningful mentorship

Colli puts these philosophies into practice as she mentors students through Brookhaven Lab’s Office of Educational Programs.

“For me, research is always about teamwork. I am not the boss and you are not my slave; we work together, period. It’s a continuous exchange,” she said. “I let the students bring up ideas—have them tell me what we should do.”

Sometimes suspicious of this approach and a bit lost without a predetermined path, Colli’s students often end up with an appreciation of what it means to be part of the scientific process.

“I don’t care if they do perfect work or not. But when I see that they get engaged and they get passionate, that’s for me the best reward.”

From her own experience, she also tells them, “Don’t be afraid if you end up in a different field because that may only increase your knowledge and open up your mind in different directions.”

When she’s not developing new strategies at the Lab, Colli loves to connect with nature by hiking and especially riding her horse. “That is where I find my peace of mind,” she said.

“I really love to be on Long Island, and I love the U.S.,” she added, noting that she hopes to become a full U.S. citizen as soon as she is eligible. “I still have two years to wait for that and I’m counting the days.”

The metal additive manufacturing strategy is supported by Brookhaven Lab’s program development funds. NSLS-II and CFN are DOE Office of Science user facilities. The Computational Science Initiative is also supported by the DOE Office of Science.

See the full article here .

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One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

From École Polytechnique Fédérale de Lausanne: “Controlling the optical properties of solids with acoustic waves”

From École Polytechnique Fédérale de Lausanne

29.11.19
Majed Chergui
Nik Papageorgiou

Physicists from Switzerland, Germany, and France have found that large-amplitude acoustic waves, launched by ultrashort laser pulses, can dynamically manipulate the optical response of semiconductors.

One of the main challenges in materials science research is to achieve high tunability of the optical properties of semiconductors at room temperature. These properties are governed by “excitons”, which are bound pairs of negative electrons and positive holes in a semiconductor.

Excitons have become increasingly important in optoelectronics and the last years have witnessed a surge in the search for control parameters – temperature, pressure, electric and magnetic fields – that can tune excitonic properties. However, moderately large changes have only been achieved under equilibrium conditions and at low temperatures. Significant changes at ambient temperatures, which are important for applications, have so far been lacking.

This has now just been achieved in the lab of Majed Chergui at EPFL within the Lausanne Centre for Ultrafast Science, in collaboration with the theory groups of Angel Rubio (Max-Planck Institute, Hamburg) and Pascal Ruello (Université de Le Mans). Publishing in Science Advances, the international team shows, for the first time, control of excitonic properties using acoustic waves. To do this, the researchers launched a high-frequency (hundreds of gigahertz), large-amplitude acoustic wave in a material using ultrashort laser pulses. This strategy further allows for the dynamical manipulation of the exciton properties at high speed.

This remarkable result was reached on titanium dioxide at room temperature, a cheap and abundant semiconductor that is used in a wide variety of light-energy conversion technologies such as photovoltaics, photocatalysis, and transparent conductive substrates.

“Our findings and the complete description we offer open very exciting perspectives for applications such as cheap acousto-optic devices or in sensor technology for external mechanical strain,” says Majed Chergui. “The use of high-frequency acoustic waves, as those generated by ultrashort laser pulses, as control schemes of excitons pave a new era for acousto-excitonics and active-excitonics, analogous to active plasmonics, which exploits the plasmon excitations of metals.”

“These results are just the beginning of what can be explored by launching high-frequency acoustic waves in materials,” adds Edoardo Baldini, the lead author of the article who is currently at MIT. “We expect to use them in the future to control the fundamental interactions governing magnetism or trigger novel phase transitions in complex solids”.

Other contributors

University of the Basque Country
Max Planck Institute for the Structure and Dynamics of Matter
Simons Foundation (Flatiron Institute)
CNRS Joint Research Units

Funding

Swiss National Science Foundation (NCCR:MUST and R’EQUIP), European Research Council (Advanced Grant DYNAMOX), Horizon 2020

See the full article here .

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EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

From Brookhaven National Lab: “The Secret Behind Crystals that Shrink when Heated”

From Brookhaven National Lab

November 1, 2019

Karen McNulty Walsh
kmcnulty@bnl.gov
(631) 344-8350

Peter Genzer
genzer@bnl.gov
(631) 344-3174

Discovery yields new quantitative description of unusual behavior relevant to materials used in electronics, medicine, telecommunications, and more.

Igor Zaliznyak, a physicist in Brookhaven Lab’s Condensed Matter Physics and Materials Science Division (right), led a team of scientists including Alexei Tkachenko of the Lab’s Center for Functional Nanomaterials (left) to decipher the mechanism underlying scandium fluoride’s ability to shrink upon heating.

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have new experimental evidence and a predictive theory that solves a long-standing materials science mystery: why certain crystalline materials shrink when heated. Their work, just published in Science Advances, could have widespread application for matching material properties to specific applications in medicine, electronics, and other fields, and may even provide fresh insight into unconventional superconductors (materials that carry electric current with no energy loss).

The evidence comes from precision measurements of the distances between atoms in crystals of scandium fluoride (ScF3), a material known for its unusual contraction under elevated temperatures (also known as “negative thermal expansion”). What the scientists discovered is a new type of vibrational motion that causes the sides of these cube-shaped, seemingly solid crystals to buckle when heated, thus pulling the corners closer together.

“Normally as something heats up, it expands,” said Brookhaven physicist Igor Zaliznyak, who led the project. “When you heat something up, atomic vibrations increase in magnitude, and the overall material size increases to accommodate the larger vibrations.”

That relationship, however, doesn’t hold for certain flexible materials, including chainlike polymers such as plastics and rubber. In those materials, increasing heat increases vibrations only perpendicular to the length of the chains (picture the sideways vibrations of a plucked guitar string). Those transverse vibrations pull the ends of the chains closer together, resulting in overall shrinkage.

But what about scandium fluoride? With a solid, cubic crystalline structure, it looks nothing like a polymer—at least at first glance. In addition, a widespread assumption that the atoms in a solid crystal have to maintain their relative orientations, no matter what the crystal size, left physicists confounded to explain how this material shrinks when heated.

This animation shows how solid crystals of scandium fluoride shrink upon heating. While the bonds between scandium (green) and fluorine atoms (blue) remain relatively rigid, the fluorine atoms along the sides of the cubic crystals oscillate independently, resulting in a wide range of distances between neighboring fluorine atoms. The higher the temperature, the greater the buckling in the sides of the crystals leading to the overall contraction (negative thermal expansion) effect.

Neutrons and a dedicated student to the rescue

A group from the California Institute of Technology (Caltech) was using one method to explore this mystery at the Spallation Neutron Source (SNS), a DOE Office of Science user facility at Oak Ridge National Laboratory. Measuring how beams of neutrons, a type of subatomic particle, scatter off the atoms in a crystal can give valuable information about their atomic-scale arrangement. It’s particularly useful for lightweight materials like fluorine that are invisible to x-rays, Zaliznyak said.

Scientists used neutron scattering at the Spallation Neutron Source at Oak Ridge National Laboratory to investigate why certain crystalline materials shrink when heated. Credit: Oak Ridge National Laboratory

Hearing about this work, Zaliznyak noted that his colleague, Emil Bozin, an expert in a different neutron-scattering analysis technique, could probably advance understanding of the problem. Bozin’s method, known as “pair distribution function,” describes the probability of finding two atoms separated by a certain distance in a material. Computational algorithms then sort through the probabilities to find the structural model that best fits the data.

Zaliznyak and Bozin paired up with the Caltech team to collect data at SNS using Caltech’s ScF3 samples to track how the distances between neighboring atoms changed with increasing temperature.

David Wendt, a student who began a Brookhaven Lab High School Research Program internship in Zaliznyak’s lab following his sophomore year in high school (now a freshman at Stanford University), handled much of the data analysis. He continued working on the project throughout his high-school days, earning the position of first author on the paper.

“David basically reduced the data to the form that we could analyze using our algorithms, fitted the data, composed a model to model the positions of the fluorine atoms, and did the statistical analysis to compare our experimental results to the model. The amount of work he did is like what a good postdoc would do!” Zaliznyak said.

“I am very grateful for the opportunity Brookhaven Lab provided me to contribute to original research through their High School Research Program,” Wendt said.

Results: “soft” motion in a solid

The measurements showed that the bonds between scandium and fluorine don’t really change with heating. “In fact, they expand slightly,” Zaliznyak said, “which is consistent with why most solids expand.”

But the distances between adjacent fluorine atoms became highly variable with increasing temperature.

“We were looking for evidence that the fluorine atoms were staying in a fixed configuration, as had always been assumed, and we found quite the opposite!” Zaliznyak said.

Additional coauthors on the study included (from left) Kate Page, formerly of Oak Ridge National Laboratory, Brookhaven Lab physicist Emil Bozin, and ORNL instrument scientist Joerg Neuefeind. Credit: Genevieve Martin/Oak Ridge National Laboratory

Alexei Tkachenko, an expert in the theory of soft condensed matter at Brookhaven Lab’s Center for Functional Nanomaterials (another Office of Science user facility) made essential contributions to the explanation for this unexpected data.

Since the fluorine atoms appeared not to be confined to rigid positions, the explanation could draw on a much older theory originally developed by Albert Einstein to explain atomic motions by considering each individual atom separately. And surprisingly, the final explanation shows that heat-induced shrinkage in ScF3 bears a remarkable resemblance to the behavior of soft-matter polymers.

“Since every scandium atom has a rigid bond with fluorine, the ‘chains’ of scandium-fluoride that form the sides of the crystalline cubes (with scandium at the corners) act similar to the rigid parts of a polymer,” Zaliznyak explained. The fluorine atoms at the center of each side of the cube, however, are unrestrained by any other bonds. So, as temperature increases, the “underconstrained” fluorine atoms are free to oscillate independently in directions perpendicular to the rigid Sc-F bonds. Those transverse thermal oscillations pull the Sc atoms at the corners of the cubic lattice closer together, resulting in shrinkage similar to that observed in polymers.

Thermal matching for applications

This new understanding will improve scientists’ ability to predict or strategically design a material’s thermal response for applications where temperature changes are expected. For example, materials used in precision machining should ideally show little change in response to heating and cooling to maintain the same precision across all conditions. Materials used in medical applications, such as dental fillings or bone replacements, should have thermal expansion properties that closely match those of the biological structures in which they are embedded (think how painful it would be if your filling expanded while your tooth contracted when drinking hot coffee!). And in semiconductors or undersea fiberoptic transmission lines, the thermal expansion of insulating materials should match that of the functional materials to avoid impeding signal transmission.

Zaliznyak notes that an underconstrained open framework architecture like that in ScF3 is also present in copper-oxide and iron-based superconductors—where crystal lattice vibrations are thought to play a role in these materials’ ability to carry electric current with no resistance.

“The independent oscillation of atoms in these open-framework structures may contribute to these materials’ properties in ways we can now calculate and understand,” Zaliznyak said. “They might actually explain some of our own experimental observations that still remain a mystery in these superconductors,” he added.

“This work profoundly benefitted from the important advantages of the DOE national laboratories—including unique DOE facilities and our ability to have long-time-span projects where important contributions accumulate over time to culminate in a discovery,” Zaliznyak said. “It represents the unique confluence of different expertise among the coauthors, including a dedicated high-school student intern, which we were able to integrate synergistically for this project. It would not have been possible to successfully carry out this research without the expertise provided by all the team members.”

Brookhaven Lab’s role in this work was funded by the DOE Office of Science.

See the full article here .

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One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

From University of Washington – Mechanical Engineering: “Transforming titanium with 3D printing”

From University of Washington – Mechanical Engineering

October 28, 2019
Chelsea Yates
Photos by University of Washington

ME’s new titanium 3D printer is the only one of its kind at the UW and one of just a few at universities nationwide.

ME’s newest 3D printing lab explores additive manufacturing of complex structures with titanium.

3D printers can print objects from a variety of materials: plastics, ceramics, glass, nylon, resins, even chocolate. Thanks to recent advancements in additive manufacturing technology, engineers can add titanium to this list. An earth abundant metal, titanium is valued for its unique mechanical properties and high strength-to-weight ratio.

However, due to its strength and high melting point, titanium is difficult to convert from its raw form to a finished part. This makes manufacturing processes challenging and uneconomical, and it limits the applications of the metal. But engineers hope that advancements in 3D printing will change that.

“Titanium 3D printing has the potential to open new pathways in additive manufacturing for industries ranging from health to aerospace,” says ME professor Ramulu Mamidala, who leads the Metal 3D Printing Lab as part of the Washington state-funded JCDREAM (Joint Center for Deployment and Research in Earth Abundant Materials) initiative. “It’s really about discovering the art of the possible.”

In 2017, the lab acquired a 3D printer capable of printing titanium. It’s the only one of its kind at the UW and one of just a few at universities across the country.

The 3D printer uses titanium powder, which is dispensed in layers and consolidated to create a solid object. Leftover powder is collected and reused to reduce waste.

The print area is prepared for the printing process, which involves selective powder bed fusion technology using a high energy electron beam.

Titanium 3D printing: Why and how?

There are several benefits to printing titanium. In addition to being abundant and strong, it is corrosion resistant and melts at a much higher temperature than most common metals. It’s also lightweight and biocompatible, making it a very good material for surgical implants and medical devices.

ME lab engineer Bill Kuykendall checks the status of a print job. Printing takes place inside a vacuum chamber, where temperatures reach up to 1600 degrees Celsius and the titanium easily melts.

“3D printing titanium can result in excellent mechanical properties if ‘correct’ process parameters are used,” says Rishi Pahuja. He served as the lab’s primary research scientist last year while completing his mechanical engineering PhD.

“Our team is focused on studying the effect of these parameters on mechanical properties,” he adds. “We can attain precision and complexity in design that traditional 3D printing machines are not capable of achieving.”

ME’s titanium 3D printer uses selective powder bed fusion technology and a high energy electron beam in a process that generally takes place over two days. A 3D computer model is created by researchers, uploaded to the printer’s software and sliced into layers in preparation for the print. The printing takes place inside a vacuum chamber, where temperatures reach between 700 and 1600 degrees Celsius and titanium melts and flows easily. Titanium powder is dispensed in layers, and the electron beam fuses and consolidates each layer to the one before it, welding together hundreds of thousands of tiny particles of powder. Layer upon layer, a solid object is created and embedded within a block of powder.

Inside the chamber, an electron beam fuses layers of titanium powder together. Eventually, a solid object is created and embedded within a block of powder.

Once the print is finished and has cooled, the block is removed and the parts are extracted. Lab engineers collect and reuse the leftover powder to reduce waste and expenses. According to Mamidala, unlike conventional machining processes, where over 80% of the raw material is cut away and wasted, this process wastes less than 5%.

The researchers say this printing method is more versatile than traditional manufacturing methods, and because of how easily parts can be designed and printed, complex geometric forms can be easily created, allowing for more efficient prototyping and part testing.

Advancing possibilities

Once the print has finished and cooled, the powder block is removed and transferred to a separate station where the object is extracted from it.

From energy to transportation, many major industries currently depend on rare earth materials as well as materials mined using unsustainable practices. According to JCDREAM, heavy reliance on rare earth minerals and conflict resources has stifled U.S. industry growth. Through collaborative research, development, education and leadership the center hopes to make Washington state a leader in developing advanced, clean energy-focused manufacturing practices.

Mamidala sees titanium 3D printing technology development as a key way to do this.

“The more we can develop ways to use more earth-abundant materials like titanium in manufacturing, the more we can reduce our dependence on rare and unsustainable materials,” he explains.

He adds that it’s especially important for universities like the UW to be involved in this work.

“Titanium 3D printing is going to revolutionize industries where lightweight, complex geometries are essential to a design’s performance,” he says. “Additive manufacturing places us on the cusp of enabling the next major changes in aircraft and spacecraft capability; therefore, UW engineers with this experience will be in high demand worldwide as 3D printing continues to change how manufacturing occurs.”

As the powder is blasted away, the solid object — a wheel hub mount — begins to appear.

The finished wheel hub mount. Notice the intricate details. Titanium 3D printers are capable of creating complex geometric forms more so than traditional manufacturing methods.

Kuykendall, left, and research scientist Rishi Pahuja (ME PhD ’19), right, compare the finished product to their original computer model.

The Metal 3D Printing Lab is interested in exploring project ideas with the UW community. Lab engineers have already been working with the Boeing Advanced Research Center on several student capstone and test projects to replace multi-piece machine-made airplane parts with a single titanium part. They are also partnering with materials science and engineering researchers to determine how many times titanium powder can be recycled and with bioengineering researchers to develop the design of printed bone implants.

“3D printing titanium is going to revolutionize industries where lightweight, complex geometries are essential to a design’s performance,” says ME professor Ramulu Mamidala, center.

“Already, the printer is allowing us to realize and produce organic shapes inspired by natural structures that could only previously be imagined,” Mamidala says. “This technology further drives the creative side of engineering to solve problems in new ways and in this way it’s really bringing art, science and engineering together.”

See the full article here .

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The University of Washington is one of the world’s preeminent public universities. Our impact on individuals, on our region, and on the world is profound — whether we are launching young people into a boundless future or confronting the grand challenges of our time through undaunted research and scholarship. Ranked number 10 in the world in Shanghai Jiao Tong University rankings and educating more than 54,000 students annually, our students and faculty work together to turn ideas into impact and in the process transform lives and our world. For more about our impact on the world, every day.
So what defines us —the students, faculty and community members at the University of Washington? Above all, it’s our belief in possibility and our unshakable optimism. It’s a connection to others, both near and far. It’s a hunger that pushes us to tackle challenges and pursue progress. It’s the conviction that together we can create a world of good. Join us on the journey.

From JHU HUB: “Copper could help unlock the clean-energy potential of hydrogen fuel cells”

From JHU HUB

11.1.19
Lisa Ercolano
Matthew Chin

Hydrogen fuel cells may someday power automobiles and trucks, offering a source of energy that’s free of carbon emissions and pollutants. But their potential has been limited thus far by the high cost and instability of the platinum-nickel catalyst needed to spark the chemical reaction that produces clean electricity.

Using experiments and computer simulations, materials scientists from Johns Hopkins University and the University of California, Los Angeles have taken a major leap toward making that future possible. Their study, published in Matter, sheds new light on a method of stabilizing catalysts by adding copper and provides details on why the method works.

Copper in the Periodic Table

The UCLA team was led by Yu Huang, a professor of materials science and engineering. The Hopkins team was led by Tim Mueller, assistant professor of materials science and engineering.

“The problem is that platinum-nickel catalysts, which are very promising for use in fuel cells, degrade over time as the nickel dissolves,” explains Mueller, whose research focuses on developing and applying computational methods to allow researchers to understand the real-world behavior of materials and to develop new materials for advanced technologies. “Professor Huang’s group discovered that adding copper to the catalysts helped reduce the amount of nickel dissolution, and our group helped them figure out why, which is important for people who want to build on this research.”

In experiments, the UCLA researchers found that introducing copper atoms into specially shaped nanoparticles of platinum-nickel resulted in durability that proved to be 40% better, in terms of catalyst efficiency, than those without copper. These new catalysts were very stable—that is, more transition metals were retained in the platinum-nickel-copper particles, despite the corrosive condition that could leach them out. They were also more efficient in catalyzing the chemical reaction, compared to alloys of platinum-nickel and commercially used platinum-carbon.

To figure out why this was happening, Mueller’s team at Hopkins devised a model based on experimental data and performed computer simulations that revealed how individual atoms moved around the nanoparticles in the type of environment that the catalysts would encounter in a fuel cell.

“We ran simulations of the particles, both with and without copper, to see how the addition of copper affected the degradation of the particles,” said Liang Cao, a Johns Hopkins postdoctoral scholar of materials science and engineering, and a co-lead author of the study. “We were able to track the particles’ evolution on an atomic scale, and our simulations indicated that the particles that contained copper were more stable because they initially had more platinum on the surface, which protected the nickel and copper atoms from dissolving.”

According to Huang, the new study is a milestone in understanding the “atomistic structure-function relations in nanoscale materials and opens the door to new design strategies for high-performing nanoscale catalysts.”

See the full article here .

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About the Hub
We’ve been doing some thinking — quite a bit, actually — about all the things that go on at Johns Hopkins. Discovering the glue that holds the universe together, for example. Or unraveling the mysteries of Alzheimer’s disease. Or studying butterflies in flight to fine-tune the construction of aerial surveillance robots. Heady stuff, and a lot of it.

In fact, Johns Hopkins does so much, in so many places, that it’s hard to wrap your brain around it all. It’s too big, too disparate, too far-flung.

We created the Hub to be the news center for all this diverse, decentralized activity, a place where you can see what’s new, what’s important, what Johns Hopkins is up to that’s worth sharing. It’s where smart people (like you) can learn about all the smart stuff going on here.

At the Hub, you might read about cutting-edge cancer research or deep-trench diving vehicles or bionic arms. About the psychology of hoarders or the delicate work of restoring ancient manuscripts or the mad motor-skills brilliance of a guy who can solve a Rubik’s Cube in under eight seconds.

There’s no telling what you’ll find here because there’s no way of knowing what Johns Hopkins will do next. But when it happens, this is where you’ll find it.

The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”

The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”

What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.

From Lawrence Berkeley National Lab: “Living on the Edge: How a 2D Material Got Its Shape”

From Lawrence Berkeley National Lab

October 24, 2019
Theresa Duque
tnduque@lbl.gov
(510) 495-2418

Scientists at Berkeley Lab discover that nanoparticles’ ‘edge energy’ gets them in 2D shape for energy storage applications.

Illustration of a 3D cobalt-oxide nanoparticle growing into a 2D nanosheet. (Credit: Haimei Zheng/Berkeley Lab)

Ever since its discovery in 2004, graphene – an atomically thin material with amazing strength and electrical properties – has inspired scientists around the world to design new 2D materials to serve a broad range of applications, from renewable energy and catalysts to microelectronics.

While 2D structures form naturally in materials like graphene, some scientists have sought to make 2D materials from semiconductors called transition metal oxides: compounds composed of oxygen atoms bound to a transition metal such as cobalt. But while scientists have long known how to make nanoparticles of transition metal oxides, no one has found a controllable way to grow these 3D nanoparticles into nanosheets, which are thin 2D materials just a few atoms thick.

Now, a team of scientists led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has gained valuable insight into 3D transition metal oxide nanoparticles’ natural “edge” for 2D growth. Their findings were reported in Nature Materials.

Using a liquid-phase transmission electron microscope (TEM) at Berkeley Lab’s Molecular Foundry for the experiments, co-corresponding author Haimei Zheng and her team directly observed the dynamic growth of cobalt-oxide nanoparticles in a solution, and their subsequent transformation into a flat 2D nanosheet.

“Such a 3D to 2D transformation is much like the white of an egg spreading as it fries in a pan,” said Zheng, a senior staff scientist in Berkeley Lab’s Materials Sciences Division who led the study.

VIDEO: Cobalt-oxide nanoparticles in a solution transform into flat 2D nanosheets; video plays 15 times faster than real time. 3D to 2D growth observed using liquid-phase transmission electron microscopy at Berkeley Lab’s Molecular Foundry. (Credit: Haimei Zheng/Berkeley Lab)

In previous studies, scientists had assumed that only two major factors – bulk energy from the volume of the nanoparticles, and the nanoparticles’ surface energy – would drive the nanoparticles’ growth into a 3D shape, Zheng explained.

New energy comes to light

But calculations led by co-corresponding author Lin-Wang Wang revealed another energy that had been previously overlooked – edge energy. In a faceted, rectangular nanoparticle such as a transition metal oxide nanoparticle, the edge of a facet also contributes energy – in this case, positive energy – toward the nanoparticle’s growth and shape. But in order for a transition metal oxide nanoparticle to grow into a 2D nanosheet, the surface energy must be negative.

“And it’s the balance between these two energies, one negative and one positive, which determines the shape change,” Wang said. For smaller nanoparticles, positive edge energy wins, which leads to a compact 3D shape. But when the cobalt oxide nanoparticles grow larger, they ultimately reach a critical point where negative surface energy wins, resulting in a 2D nanosheet, he explained. Wang, a senior staff scientist in Berkeley Lab’s Materials Sciences Division, performed the calculations for the study on supercomputers at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC).

Uncovering these growth pathways, including the 3D-to-2D transition, Zheng added, provides new opportunities for the streamlined design of exotic new materials from compounds whose irregular atomic structures, such as transition metal oxides, are more challenging than graphene to synthesize into multilayered 2D devices.

Schematic illustrating the growth of 3D nanoparticles from a solution, and the 3D nanoparticles transformation into 2D nanosheets. (Credit: Haimei Zheng/Berkeley Lab)

Zheng and her team concluded that the study could not have been possible with a conventional electron microscope. By using liquid-phase TEM at the Molecular Foundry, the researchers were able to study the growth of atomically thin materials in solution by encapsulating the liquid sample in a specially designed liquid cell. The cell prevented the sample from collapsing in the high vacuum of the electron microscope.

“It would be impossible to know such a growth path without this in situ observation,” said first author Juan Yang, who was a visiting doctoral researcher at Berkeley Lab from Dalian University of Technology of China at the time of the study. “This discovery may transform our future design of materials with surface-enhanced properties for catalysis and sensing applications of the future.”

Next steps

The researchers next plan to focus on using liquid-cell TEM to grow more complex 2D materials such as heterostructures, which are like sandwiches of layered materials with different properties.

“Like an architect who is inspired by the way in which an ancient giant redwood has grown, materials scientists are inspired to design ever more complex structures for energy storage,” said Zheng, who pioneered liquid-cell TEM at Berkeley Lab in 2009. “But why do they grow that way? Our strength at Berkeley Lab is that we can study them at the atomic level and watch them grow in real time and figure out the mechanisms that would contribute to the design of better materials.”

This work was supported by the DOE Office of Science’s Basic Energy Sciences program and included research at the Molecular Foundry and National Energy Research Scientific Computing Center, which are DOE Office of Science User Facilities.

See the full article here .

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Bringing Science Solutions to the World
In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

A U.S. Department of Energy National Laboratory Operated by the University of California.

From Stanford University: “Stanford researchers create new catalyst that can turn carbon dioxide into fuels”

From Stanford University

October 17, 2019
Andrew Myers

Aisulu Aitbekova, left, and Matteo Cargnello in front of the reactor where Aitbekova performed much of the experiments for this project. (Image credit: Mark Golden)

Imagine grabbing carbon dioxide from car exhaust pipes and other sources and turning this main greenhouse gas into fuels like natural gas or propane: a sustainability dream come true.

Several recent studies have shown some success in this conversion, but a novel approach from Stanford University engineers yields four times more ethane, propane and butane than existing methods that use similar processes. While not a climate cure-all, the advance could significantly reduce the near-term impact on global warming.

“One can imagine a carbon-neutral cycle that produces fuel from carbon dioxide and then burns it, creating new carbon dioxide that then gets turned back into fuel,” said Matteo Cargnello, an assistant professor of chemical engineering at Stanford who led the research, published in Angewandte Chemie.

Although the process is still just a lab-based prototype, the researchers expect it could be expanded enough to produce useable amounts of fuel. Much work remains, however, before average consumer will be able to purchase products based on such technologies. Next steps include trying to reduce harmful byproducts from these reactions, such as the toxic pollutant carbon monoxide. The group is also developing ways to make other beneficial products, not just fuels. One such product is olefins, which can be used in a number of industrial applications and are the main ingredients for plastics.

Two steps in one

Previous efforts to convert CO2 to fuel involved a two-step process. The first step reduces CO2 to carbon monoxide, then the second combines the CO with hydrogen to make hydrocarbon fuels. The simplest of these fuels is methane, but other fuels that can be produced include ethane, propane and butane. Ethane is a close relative of natural gas and can be used industrially to make ethylene, a precursor of plastics. Propane is commonly used to heat homes and power gas grills. Butane is a common fuel in lighters and camp stoves.

Cargnello thought completing both steps in a single reaction would be much more efficient, and set about creating a new catalyst that could simultaneously strip an oxygen molecule off of CO2 and combine it with hydrogen. (Catalysts induce chemical reactions without being used up in the reaction themselves.) The team succeeded by combining ruthenium and iron oxide nanoparticles into a catalyst.

“This nugget of ruthenium sits at the core and is encapsulated in an outer sheath of iron,” said Aisulu Aitbekova, a doctoral candidate in Cargnello’s lab and lead author of the paper. “This structure activates hydrocarbon formation from CO2. It improves the process start to finish.”

The team did not set out to create this core-shell structure but discovered it through collaboration with Simon Bare, distinguished staff scientist, and others at the SLAC National Accelerator Laboratory. SLAC’s sophisticated X-ray characterization technologies helped the researchers visualize and examine the structure of their new catalyst. Without this collaboration, Cargnello said they would not have discovered the optimal structure.

“That’s when we began to engineer this material directly in a core-shell configuration. Then we showed that once we do that, hydrocarbon yields improve tremendously,” Cargnello said. “It is something about the structure specifically that helps the reactions along.”

Cargnello thinks the two catalysts act in tag-team fashion to improve the synthesis. He suspects the ruthenium makes hydrogen chemically ready to bond with the carbon from CO2. The hydrogen then spills onto the iron shell, which makes the carbon dioxide more reactive.

When the group tested their catalyst in the lab, they found that the yield for fuels such as ethane, propane and butane was much higher than their previous catalyst. However, the group still faces a few challenges. They’d like to reduce the use of noble metals such as ruthenium, and optimize the catalyst so that it can selectively make only specific fuels.

See the full article here .

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Stanford University campus. No image credit

Stanford University

Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

From MIT News: “A new way to corrosion-proof thin atomic sheets”

From MIT News

October 4, 2019
David L. Chandler

This diagram shows an edge-on view of the molecular structure of the new coating material. The thin layered material being coated is shown in violet at bottom, and the ambient air is shown as the scattered molecules of oxygen and water at the top. The dark layer in between is the protective material, which allows some oxygen (red) through, forming an oxide layer below that provides added protection. Illustration courtesy of the researchers.

Ultrathin coating could protect 2D materials from corrosion, enabling their use in optics and electronics.

A variety of two-dimensional materials that have promising properties for optical, electronic, or optoelectronic applications have been held back by the fact that they quickly degrade when exposed to oxygen and water vapor. The protective coatings developed thus far have proven to be expensive and toxic, and cannot be taken off.

Now, a team of researchers at MIT and elsewhere has developed an ultrathin coating that is inexpensive, simple to apply, and can be removed by applying certain acids.

The new coating could open up a wide variety of potential applications for these “fascinating” 2D materials, the researchers say. Their findings are reported this week in the journal PNAS, in a paper by MIT graduate student Cong Su; professors Ju Li, Jing Kong, Mircea Dinca, and Juejun Hu; and 13 others at MIT and in Australia, China, Denmark, Japan, and the U.K.

Research on 2D materials, which form thin sheets just one or a few atoms thick, is “a very active field,” Li says. Because of their unusual electronic and optical properties, these materials have promising applications, such as highly sensitive light detectors. But many of them, including black phosphorus and a whole category of materials known as transition metal dichalcogenides (TMDs), corrode when exposed to humid air or to various chemicals. Many of them degrade significantly in just hours, precluding their usefulness for real-world applications.

“It’s a key issue” for the development of such materials, Li says. “If you cannot stabilize them in air, their processability and usefulness is limited.” One reason silicon has become such a ubiquitous material for electronic devices, he says, is because it naturally forms a protective layer of silicon dioxide on its surface when exposed to air, preventing further degradation of the surface. But that’s more difficult with these atomically thin materials, whose total thickness could be even less than the silicon dioxide protective layer.

There have been attempts to coat various 2D materials with a protective barrier, but so far they have had serious limitations. Most coatings are much thicker than the 2D materials themselves. Most are also very brittle, easily forming cracks that let through the corroding liquid or vapor, and many are also quite toxic, creating problems with handling and disposal.

The new coating, based on a family of compounds known as linear alkylamines, improves on these drawbacks, the researchers say. The material can be applied in ultrathin layers, as little as 1 nanometer (a billionth of a meter) thick, and further heating of the material after application heals tiny cracks to form a contiguous barrier. The coating is not only impervious to a variety of liquids and solvents but also significantly blocks the penetration of oxygen. And, it can be removed later if needed by certain organic acids.

“This is a unique approach” to protecting thin atomic sheets, Li says, that produces an extra layer just a single molecule thick, known as a monolayer, that provides remarkably durable protection. “This gives the material a factor of 100 longer lifetime,” he says, extending the processability and usability of some of these materials from a few hours up to months. And the coating compound is “very cheap and easy to apply,” he adds.

In addition to theoretical modeling of the molecular behavior of these coatings, the team made a working photodetector from flakes of TMD material protected with the new coating, as a proof of concept. The coating material is hydrophobic, meaning that it strongly repels water, which otherwise would diffuse into the coating and dissolve away a naturally formed protective oxide layer within the coating, leading to rapid corrosion.

The application of the coating is a very simple process, Su explains. The 2D material is simply placed into bath of liquid hexylamine, a form of the linear alkylamine, which builds up the protective coating after about 20 minutes, at a temperature of 130 degrees Celsius at normal pressure. Then, to produce a smooth, crack-free surface, the material is immersed for another 20 minutes in vapor of the same hexylamine.

“You just put the wafer into this liquid chemical and let it be heated,” Su says. “Basically, that’s it.” The coating “is pretty stable, but it can be removed by certain very specific organic acids.”

The use of such coatings could open up new areas of research on promising 2D materials, including the TMDs and black phosphorous, but potentially also silicene, stanine, and other related materials. Since black phosphorous is the most vulnerable and easily degraded of all these materials, that’s what the team used for their initial proof of concept.

The new coating could provide a way of overcoming “the first hurdle to using these fascinating 2D materials,” Su says. “Practically speaking, you need to deal with the degradation during processing before you can use these for any applications,” and that step has now been accomplished, he says.

The team included researchers in MIT’s departments of Nuclear Science and Engineering, Chemistry, Materials Science and Engineering, Electrical Engineering and Computer Science, and the Research Laboratory of Electronics, as well as others at the Australian National University, the University of Chinese Academy of Sciences, Aarhus University in Denmark, Oxford University, and Shinshu University in Japan. The work was supported by the Center for Excitonics and the Energy Frontier Research Center funded by the U.S. Department of Energy, and by the National Science Foundation, the Chinese Academy of Sciences, the Royal Society, the U.S. Army Research Office through the MIT Institute for Soldier Nanotechnologies, and Tohoku University.

See the full article here .

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The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.