From Penn Today: “Using stress to shape microlevel structures”

From Penn Today

May 20, 2020
Erica K. Brockmeier

A new study describes how external forces drive the rearrangement of individual particles in disordered solids, enabling new ways to imbue materials with unique mechanical properties.

Disordered materials, such as the glass used in smartphone screens, have many useful properties but are fragile if dropped or crushed. New research describes how external forces drive the rearrangement of individual particles in this class of materials. This fundamental finding could enable new ways to imbue materials with unique mechanical properties—like a phone screen that won’t shatter, for example.

New research published in the Proceedings of the National Academy of Sciences describes how external forces drive the rearrangement of individual particles and shape microlevel structures in disordered materials. The study, conducted by graduate student Larry Galloway, postdoc Xiaoguang Ma, and faculty members Paulo Arratia, Douglas Jerolmack, and Arjun Yodh, provides new insights into how the microscopic structure of disordered, glass-like solids is related to external stressors and the resulting shifts in the motions of individual particles. These findings provide potential new approaches for creating customizable materials that have unique mechanical properties.

Throughout history, people have looked for ways to make materials more resilient, flexible, and durable, whether it be Damascus steel swords or vulcanized rubber. Nowadays, state-of-the-art imaging technologies allow scientists to study materials at the atomic level, but even with this enhanced resolution it remains a challenge to study materials when they are under external forces. This makes it difficult to develop “bottom-up” design approaches that can imbue materials with specified mechanical properties.

One class of materials that are particularly challenging, both to study and to manipulate, is disordered materials. Unlike ordered materials, which have crystalline structures with atoms in well-defined predictable locations, like on a honeycomb lattice, the atoms in disordered materials are arranged randomly, like grains in a pile of sand. Disordered materials, such as the glass used in smartphone screens, have many useful properties but are fragile if dropped or crushed.

To better understand how disordered materials could be modified in a way that gives them new properties, the researchers studied them during plastic deformation. This process, where the material is driven to flow and the atoms, molecules, or particles that make up the material can easily slip past one another, causes permanent rearrangements in the material’s overall structure. The researchers’ goal was to look for quantifiable relationships connecting a material’s ability to change under the influence of external stress to how the individual particles rearrange.

The team conducted experiments using a “model” disordered material made of 50,000 colloidal particles designed to mimic atoms. The individual “atoms” were spread thinly across a water interface, and the researchers used a small magnetic needle to push the layer of atoms with a shearing force, causing them to flow along specific paths. Using video collected during the shearing process, they were able to track the movements of all 50,000 particles.

Using this dataset, the researchers calculated two quantities that turned out to be crucial for understanding the disordered solid’s response: excess entropy and relaxation time. Excess entropy is a measure of the overall sample structure that characterizes how disordered the material is. Particle relaxation is a measure of a material’s response dynamics and characterizes how quickly individual particles move past one another.

“We noticed that these two quantities relate really nicely to each other,” Galloway says about the analysis of this dataset, which the researchers used to quantify how quickly the colloidal “atoms” move past one another when a stress is applied and to compare that rate to how disordered the final material became.

The concept of excess entropy had previously been used to study liquids and systems that are in equilibrium, meaning that all of the forces acting on a system are in balance. The present work is the first experiment to apply these ideas to systems that are out of equilibrium, such as the plastically deforming disordered material studied here. “We found that the same concept, excess entropy, often utilized in the standard theory of liquids, could help us understand how solids deform plastically,” says Ma.

By quantifying the relationship between structure, or excess entropy, and dynamics, or relaxation time, during plastic deformation, the team identified a connection between the shifts in the location of individual particles and the material’s overall structure. “First, we applied an external stress to push the material,” Yodh says. “Then, the particles in the material material rearranged and ultimately relaxed into a new internal structure. We discovered that the faster this external force is applied, the faster the particles rearrange and the more disordered the final material structure becomes, as reflected by its excess entropy.”

A diagram of the experimental design and results. A shearing force was applied to particles (shown in gray). The researchers found that the speed of the external force being applied was related to how ordered the final material became. (Image: Larry Galloway)

This improved understanding of how a material’s dynamics relates to its microstructure at the single-particle level can now help materials scientists understand the “history” of a given material. “If I know the rate of plastic deformation, then I can predict the amount of order of the material in its final state. Alternatively, if you look at a material and measure its microstructural order, then I can tell you something about the plastic deformation process that drove it there,” says Ma.

The researchers are now planning additional experiments to calculate excess entropy more locally and to look at systems that are even more disordered than that used in this experiment. If they find that the physical principles established in the present work can be generalized to other types of materials, it could pave the way for new approaches relating atomic-level measurements to desirable mechanical properties. “Then, you could learn how to prepare a material in a certain way, by shearing faster or slower, such that you have a screen that doesn’t shatter,” says Arratia.

See the full article here .

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From Brookhaven National Lab: “Electrons Break Rotational Symmetry in Exotic Low-Temp Superconductor”

From Brookhaven National Lab

May 19, 2020

Ariana Manglaviti
amanglaviti@bnl.gov
(631) 344-2347

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

Scientists previously observed this peculiar behavior—characterized by electrons preferentially traveling along one direction, decoupled from the host crystal structure—in other materials whose ability to conduct electricity without energy loss cannot be explained by standard theoretical frameworks.

Scientists patterned thin films of strontium ruthenate—a metallic superconductor containing strontium, ruthenium, and oxygen—into the “sunbeam” configuration seen above. They arranged a total of 36 lines radially in 10-degree increments to cover the entire range from 0 to 360 degrees. On each bar, electrical current flows from I+ to I-. They measured the voltages vertically along the lines (between gold contacts 1-3, 2-4, 3-5, and 4-6) and horizontally across them (1-2, 3-4, 5-6). Their measurements revealed that electrons in strontium ruthenate flow in a preferred direction unexpected from the crystal lattice structure.

Scientists have discovered that the transport of electronic charge in a metallic superconductor containing strontium, ruthenium, and oxygen breaks the rotational symmetry of the underlying crystal lattice. The strontium ruthenate crystal has fourfold rotational symmetry like a square, meaning that it looks identical when turned by 90 degrees (four times to equal a complete 360-degree rotation). However, the electrical resistivity has twofold (180-degree) rotational symmetry like a rectangle.

This “electronic nematicity”—the discovery of which is reported in a paper published on May 4 in the Proceedings of the National Academy of Sciences—may promote the material’s “unconventional” superconductivity. For unconventional superconductors, standard theories of metallic conduction are inadequate to explain how upon cooling they can conduct electricity without resistance (i.e., losing energy to heat). If scientists can come up with an appropriate theory, they may be able to design superconductors that don’t require expensive cooling to achieve their near-perfect energy efficiency.

“We imagine a metal as a solid framework of atoms, through which electrons flow like a gas or liquid,” said corresponding author Ivan Bozovic, a senior scientist and the leader of the Oxide Molecular Beam Epitaxy Group in the Condensed Matter Physics and Materials Science (CMPMS) Division at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and an adjunct professor in the Department of Chemistry at Yale. “Gases and liquids are isotropic, meaning their properties are uniform in all directions. The same is true for electron gases or liquids in ordinary metals like copper or aluminum. But in the last decade, we have learned that this isotropy doesn’t seem to hold in some more exotic metals.”

Scientists have previously observed symmetry-breaking electronic nematicity in other unconventional superconductors. In 2017, Bozovic and his team detected the phenomenon in a metallic compound containing lanthanum, strontium, copper, and oxygen (LSCO), which becomes superconducting at relatively higher (but still ultracold) temperatures compared to low-temperature counterparts like strontium ruthenate. The LSCO crystal lattice also has square symmetry, with two equal periodicities, or arrangements of atoms, in the vertical and horizontal directions. But the electrons do not obey this symmetry; the electrical resistivity is higher in one direction unaligned with the crystal axes.

We see this kind of behavior in liquid crystals, which polarize light in TVs and other displays,” said Bozovic. “Liquid crystals flow like liquids but orient in a preferred direction like solids because the molecules have an elongated rod-like shape. This shape constrains rotation by the molecules when packed close together. Liquids are typically symmetric with respect to any rotation, but liquid crystals break such rotational symmetry, with their properties different in the parallel and perpendicular directions. This is what we saw in LSCO—the electrons behave like an electronic liquid crystal.”

With this surprising discovery, the scientists wondered whether electronic nematicity existed in other unconventional superconductors. To begin addressing this question, they decided to focus on strontium ruthenate, which has the same crystal structure as LSCO and strongly interacting electrons.

Brookhaven Lab scientists (left to right) Anthony Bollinger, Ivan Bozovic, Xi He, Ian Robinson, and Jie Wu of the Condensed Matter Physics and Materials Science Division and collaborators at Cornell found evidence of an electronic “liquid crystal” state in a superconductor called strontium ruthenate. In this exotic state, electrons flow in a preferred direction that is unexpected from the arrangement of atoms in the host material’s crystal lattice.

At the Kavli Institute at Cornell for Nanoscale Science, Darrell Schlom, Kyle Shen, and their collaborators grew single-crystal thin films of strontium ruthenate one atomic layer at a time on square substrates and rectangular ones, which elongated the films in one direction. These films have to be extremely uniform in thickness and composition—having on the order of one impurity per trillion atoms—to become superconducting.

To verify that the crystal periodicity of the films was the same as that of the underlying substrates, the Brookhaven Lab scientists performed high-resolution x-ray diffraction experiments.

“X-ray diffraction allows us to precisely measure the lattice periodicity of both the films and the substrates in different directions,” said coauthor and CMPMS Division X-ray Scattering Group Leader Ian Robinson, who made the measurements. “In order to determine whether the lattice distortion plays a role in nematicity, we first needed to know if there is any distortion and how much.”

Bozovic’s group then patterned the millimeter-sized films into a “sunbeam” configuration with 36 lines arranged radially in 10-degree increments. They passed electrical current through these lines—each of which contained three pairs of voltage contacts—and measured the voltages vertically along the lines (longitudinal direction) and horizontally across them (transverse direction). These measurements were collected over a range of temperatures, generating thousands of data files per thin film.

The crystal structure of strontium ruthenate, which is made up of ruthenium (red), strontium (blue), and oxygen (green).

Compared to the longitudinal voltage, the transverse voltage is 100 times more sensitive to nematicity. If the current flows with no preferred direction, the transverse voltage should be zero at every angle. That wasn’t the case, indicating that strontium ruthenate is electronically nematic—10 times more so than LSCO. Even more surprising was that the films grown on both square and rectangular substrates had the same magnitude of nematicity—the relative difference in resistivity between two directions—despite the lattice distortion caused by the rectangular substrate. Stretching the lattice only affected the nematicity orientation, with the direction of highest conductivity running along the shorter side of the rectangle. Nematicity is already present in both films at room temperature and significantly increases as the films are cooled down to the superconducting state.

“Our observations point to a purely electronic origin of nematicity,” said Bozovic. “Here, interactions between electrons bumping into each other appear to have a much stronger contribution to electrical resistivity than electrons interacting with the crystal lattice, as they do in conventional metals.”

Going forward, the team will continue to test their hypothesis that electronic nematicity exists in all nonconventional superconductors.

“The synergy between the two CMPMS Division groups at Brookhaven was critical to this research,” said Bozovic. “We will apply our complementary expertise, techniques, and equipment in future studies looking for signatures of electronic nematicity in other materials with strongly interacting electrons.”

This work was funded by the DOE Office of Science, the Gordon and Betty Moore Foundation, and the National Science Foundation.

See the full article here .

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Brookhaven campus

BNL Center for Functional Nanomaterials

BNL NSLS-II

BNL NSLS II

BNL RHIC Campus

BNL/RHIC Star Detector

BNL Phenix Detector

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 Georgia Institute of Technology: “Surfaces That Grip Like Gecko Feet Could Be Easily Mass-Produced”

From Georgia Institute of Technology

May 7, 2020
Ben Brumfield
(404-272-2780)
ben.brumfield@comm.gatech.edu

The slightest bit of shear tension makes gecko adhesion surfaces grip, and the release of that same tension makes them let go. The same gripping surfaces can pick up objects of all shapes, sizes, and materials with the exception of Teflon and other non-stick surfaces. Credit: Georgia Tech / Varenberg lab

The inset on the upper right illustrates how the gecko adhesion surface is made by pushing lab razor blades into a setting polymer. The razor blades are pulled out, leaving indentations and stretching some of the polymer up, resulting in flexible walls that produce the gecko adhesion effect. Credit: Georgia Tech / Varenberg lab

Why did the gecko climb the skyscraper? Because it could; its toes stick to about anything. Engineers can already emulate the secrets of gecko stickiness to make strips of rubbery materials that can pick up and release objects, but simple mass production for everyday use has been out of reach until now.

Researchers at the Georgia Institute of Technology have developed, in a new study [below], a method of making gecko-inspired adhesive materials that is much more cost-effective than current methods. It could enable mass production and the spread of the versatile gripping strips to manufacturing and homes.

Polymers with “gecko adhesion” surfaces could be used to make extremely versatile grippers to pick up very different objects even on the same assembly line. They could make picture hanging easy by adhering to both the picture and the wall at the same time. Vacuum cleaner robots with gecko adhesion could someday scoot up tall buildings to clean facades.

“With the exception of things like Teflon, it will adhere to anything. This is a clear advantage in manufacturing because we don’t have to prepare the gripper for specific surfaces we want to lift. Gecko-inspired adhesives can lift flat objects like boxes then turn around and lift curved objects like eggs and vegetables,” said Michael Varenberg, the study’s principal investigator and an assistant professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering.

Current grippers on assembly lines, such as clamps, magnets, and suction cups, can each lift limited ranges of objects. Grippers based on gecko-inspired surfaces, which are dry and contain no glue or goo, could replace many grippers or just fill in capability gaps left by other gripping mechanisms.

Drawing out razors

The adhesion comes from protrusions a few hundred microns in size that often look like sections of short, floppy walls running parallel to each other across the material’s surface. How they work by mimicking geckos’ feet is explained below.

Up to now, molding has produced these mesoscale walls by pouring ingredients onto a template, letting the mixture react and set to a flexible polymer then removing it from the mold. But the method is inconvenient.

“Molding techniques are expensive and time-consuming processes. And there are issues with getting the gecko-like material to release from the template, which can disturb the quality of the attachment surface,” Varenberg said.

The researchers’ new method formed those walls by pouring ingredients onto a smooth surface instead of a mold, letting the polymer partially set then dipping rows of laboratory razor blades into it. The material set a little more around the blades, which were then drawn out, leaving behind micron-scale indentations surrounded by the desired walls.

Varenberg and first author Jae-Kang Kim published details of their new method in the journal ACS Applied Materials & Interfaces on April 6, 2020.

Forget about perfection

Though the new method is easier than molding, developing it took a year of dipping, drawing, and readjusting while surveying finicky details under an electron microscope.

“There are many parameters to control: Viscosity and temperature of the liquid; timing, speed, and distance of withdrawing the blades. We needed enough plasticity of the setting polymer to the blades to stretch the walls up, and not so much rigidity that would lead the walls to rip up,” Varenberg said.

Gecko-inspired surfaces have a fine topography on a micron-scale and sometimes even on a nanoscale, and surfaces made via molding are usually the most precise. But such perfection is unnecessary; the materials made with the new method did the job well and were also markedly robust.

“Many researchers demonstrating gecko adhesion have to do it in a cleanroom in clean gear. Our system just plain works in normal settings. It is robust and simple, and I think it has good potential for use in industry and homes,” said Varenberg, who studies surfaces in nature to mimic their advantageous qualities in human-made materials.

Gecko foot fluff

Behold the gecko’s foot. It has ridges on its toes, and this has led some in the past to think their feet stick by suction or some kind of clutching by the skin.

But electron microscopes reveal a deeper structure – spatula-shaped bristly fibrils protrude a few dozen microns long off those ridges. The fibrils make such thorough contact with surfaces down to the nanoscale that weak attractions between atoms on both sides appear to add up enormously to create overall strong adhesion.

In place of fluff, engineers have developed rows of shapes covering materials that produce the effect. A common shape makes a material’s surface look like a field of mushrooms that are a few hundred microns in size; another is rows of short walls like those in this study.

“The mushroom patterns touch a surface, and they are attached straightaway, but detaching requires applying forces that can be disadvantageous. The wall-shaped projections require minor shear force like a tug or a gentle grab to generate adherence, but that is easy, and letting go of the object is uncomplicated, too,” Varenberg said.

Varenberg’s research team used the drawing method to make walls with U-shaped spaces in between them and walls with V-shaped spaces in between. They worked with polyvinylsiloxane (PVS) and polyurethane (PU). The V-shape made in PVS worked best, but polyurethane is the better material for industry, so Vanenberg’s group will now work toward achieving the V-shape gecko gripping pattern in PU for the best possible combination.

See the full article here .

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Please help promote STEM in your local schools.

The Georgia Institute of Technology, commonly referred to as Georgia Tech, is a public research university and institute of technology located in the Midtown neighborhood of Atlanta, Georgia. It is a part of the University System of Georgia and has satellite campuses in Savannah, Georgia; Metz, France; Athlone, Ireland; Shenzhen, China; and Singapore.

The school was founded in 1885 as the Georgia School of Technology as part of Reconstruction plans to build an industrial economy in the post-Civil War Southern United States. Initially, it offered only a degree in mechanical engineering. By 1901, its curriculum had expanded to include electrical, civil, and chemical engineering. In 1948, the school changed its name to reflect its evolution from a trade school to a larger and more capable technical institute and research university.

Today, Georgia Tech is organized into six colleges and contains about 31 departments/units, with emphasis on science and technology. It is well recognized for its degree programs in engineering, computing, industrial administration, the sciences and design. Georgia Tech is ranked 8th among all public national universities in the United States, 35th among all colleges and universities in the United States by U.S. News & World Report rankings, and 34th among global universities in the world by Times Higher Education rankings. Georgia Tech has been ranked as the “smartest” public college in America (based on average standardized test scores).

Student athletics, both organized and intramural, are a part of student and alumni life. The school’s intercollegiate competitive sports teams, the four-time football national champion Yellow Jackets, and the nationally recognized fight song “Ramblin’ Wreck from Georgia Tech”, have helped keep Georgia Tech in the national spotlight. Georgia Tech fields eight men’s and seven women’s teams that compete in the NCAA Division I athletics and the Football Bowl Subdivision. Georgia Tech is a member of the Coastal Division in the Atlantic Coast Conference.

From Lawrence Berkeley National Lab: “Making a Material World Better, Faster Now: Q&A With Materials Project Director Kristin Persson”

From Lawrence Berkeley National Lab

May 8, 2020
Theresa Duque
(510) 424-2866
tnduque@lbl.gov

World-renowned computational materials scientist from Berkeley Lab and UC Berkeley looks back on a career founded in quantum mechanics, and looks ahead to faster clean-energy solutions with machine learning.

Materials Project Director Kristin Persson (Credit: Roy Kaltschmidt/Berkeley Lab)

Kristin Persson is at the helm of a materials revolution.

Since 2011, she has led the Materials Project, an open-access online database that virtually delivers the largest collection of materials properties to scientists from every corner of the globe who are searching for the next big thing in batteries, solar cells, and computer chips.

Harnessing the power of supercomputers at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), and customized machine-learning algorithms based on state-of-the art quantum mechanical theory, Persson developed the Materials Project with open-access service, accuracy, speed, and user-friendliness in mind.

NERSC at LBNL

NERSC Cray Cori II supercomputer, named after Gerty Cori, the first American woman to win a Nobel Prize in science

NERSC Hopper Cray XE6 supercomputer, named after Grace Hopper, One of the first programmers of the Harvard Mark I computer

NERSC Cray XC30 Edison supercomputer

NERSC GPFS for Life Sciences

The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

NERSC PDSF computer cluster in 2003.

PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

Future:

Cray Shasta Perlmutter SC18 AMD Epyc Nvidia pre-exascale supeercomputer

NERSC is a DOE Office of Science User Facility.

Scientists seeking to design a better battery electrode, for example, only need to log into their free Materials Project user account. A few keystrokes here, a mouse click there, and users enter the online database’s vast, virtual catalog of most known inorganic materials and thousands more that may exist. The Materials Project narrows the 124,000 inorganic compounds, and some 35,000 molecules, down to the best candidate – without the Materials Project, that search would take months to do.

“The Materials Project is unique in its ability to calculate a multitude of properties using high-quality first-principles calculations for materials research. With our data we can serve everyone – industry, academia, the whole world – without having to compete for profit in the private sector,” said Persson, a computational materials scientist who holds titles of senior faculty scientist in the Energy Storage & Distributed Resources Division in Berkeley Lab’s Energy Technologies Area and professor of materials science and engineering at UC Berkeley.

“And as somebody who passionately cares about the environment, I just want to come up with the next clean-energy solution as fast as possible,” she said.

In the Q&A below, Persson shares what inspired her to launch the Materials Project, her thoughts on the future of materials research and machine learning, and how she found her own way into a STEM (science, technology, engineering, and math) career.

Q: What inspired you to launch the Materials Project database?

Persson: When I was a postdoc at MIT, I was working on what’s known as density functional theory, a technique for modeling the electronic structure of materials in their ground state, or the material’s lowest energy state. At the time, DFT was still fairly new and the group I was in had just started to explore how the technique could be used in high-throughput computing, a technique that automatically runs the same analytical process simultaneously on multiple computer systems.

Word had gotten around about our work. And in 2004, a U.S.-based battery manufacturer asked us if we could use our high-throughput computing technique – which uses multiple computers to automatically run the same process over thousands of compounds – to search for a better material for its battery’s electrode chemistry.

In addition to funding the project, our industry partner gave us free time on their supercomputer. Having access to that much computing power really opened up a new world for me. I was comfortable with using computational DFT techniques to understand how individual materials work, but the idea of turning it around and using it on a supercomputer as an automated screening vehicle was game-changing. Suddenly you can screen hundreds of materials per day for a specific property, learn about chemistry and structural trends, and become smarter about where to look. Without a supercomputer, screening those same materials would take a team of researchers months to complete.

The data from that project laid the foundation for the Materials Project. And when I was hired by Berkeley Lab in 2008, I brought that vision with me. During my second year here, I got funding from the Laboratory Directed Research and Development program to develop the nascent Materials Project’s capabilities and make it open access so it could serve a diverse community of materials scientists – like battery researchers, photovoltaics researchers, and researchers who specialize in data storage materials. In 2011, we launched the Project to the public and we have since continuously improved it with more materials, better search capabilities, and even more importantly, more diverse coverage of properties and analyses algorithms. Recently, and thanks to our broad and comprehensive datasets, we are adding state-of-the-art machine-learning algorithms to help researchers understand and identify functional materials.

Today, the Materials Project is the largest materials data provider in the world, serving data more than a million times a day to more than 120,000 users all over the world, and it’s been cited by thousands of papers.

Nobody has ever had this kind of data at their fingertips before. It’s a complete paradigm change in that sense. It’s exciting to know that researchers all over the world are publishing papers that used data from the Materials Project.

Many of them are energy-related researchers, spanning batteries, catalysis, photovoltaics, thermoelectrics, et cetera, but I’ve been pleasantly surprised to see it used in other fields, like alloy design, scintillators, high-pressure and magnetic materials, and even astrophysics. It is extremely rewarding when people call you up and say, “Hey, a paper published in this journal said they used the Materials Project to understand the formation of concrete in space!”

The Materials Project wouldn’t have been able to generate all that data without the support of the Basic Energy Sciences program within the Department of Energy’s Office of Science and Berkeley Lab’s supercomputers at NERSC. Similarly, many of the crucial, early software and architecture choices were made together with experts in the Computational Research Division. The interdisciplinary nature of the Project – combining domain knowledge, high-performance computing, and modern data infrastructure and dissemination, is really perfectly suited for a national lab, where you can build collaborative, long-term teams with permanent staff.

Q: How can the Materials Project help to accelerate technological advancements for clean energy?

Persson: The loop of materials design, synthesis, and characterization is traditionally intensely time-consuming. We hope that data-driven approaches fueled by computations can accelerate each aspect of that loop, enabling new materials for powerful rechargeable batteries for electric cars, or semiconductors that could make artificial photosynthesis a reality. With the Materials Project, clean-energy researchers can virtually test hundreds to thousands of components and then focus on the most promising candidates, use simulations and associated machine learning to accelerate the identification of new materials, and use computational insights and guidelines for optimal synthesis conditions.

As our data grows, we are building machine-learning tools and curated datasets into the database, which saves researchers time and money so they can focus on their important work to help the world. And because we cast it in a way that any materials scientist can understand, such as phase diagrams, bandgaps, and electronic conductivity, I can see the Materials Project becoming a cornerstone in all materials scientists’ portfolio because they don’t have to become a computational expert to use this data – however, as with all data, they do need to understand its limitations and level of accuracy.

Q: What’s your dream machine-learning materials app?

Persson: Harnessing both experimental and computed data with on-the-fly machine learning for rapid iterations and insights. With machine learning, the fuel is the data. And researchers from both industry and academia agree that if we want to take advantage of what machine learning has to offer, we still need high-quality, diverse, curated data.

As someone whose role is to provide that data, I’m very interested in what robotics can do for the experimental side of materials science. Robotically automated materials synthesis could help us gather high-quality, robust data by making sure that an experiment is done exactly the same way every time it’s performed. And that’s very hard to do with humans, because people are different and will perform the same task in slightly different ways.

I am often asked if robots will replace scientists. Robots, just like the supercomputers at NERSC, are extremely powerful tools to produce data faster and more robustly. However, robots will not replace humans. They will just broaden our experience; enable us to make better, informed decisions; and help us focus on what we do best – use our amazing and creative human brain to solve the scientific and engineering problems of the day.

Q: What’s next for the Materials Project?

Persson: I’d like to do more industry outreach and make the Materials Project an integrated part of both the academic as well as the industrial science process. When I was a graduate student, density functional theory was a fairly young technique, so if you’re a manager at a semiconducting company and you haven’t hired anybody who completed their Ph.D. in the last 15 years, you probably don’t even know that materials databases like the Materials Project even exist.

I’d also like to collaborate with our partners across the national laboratory system. I see the Materials Project growing into a data institute, harnessing both computed as well as standardized experimental datasets, where we not only provide large sets of machine-learning data to other labs and industry researchers but we also work directly with them so they know how to use all of the machine-learning features and simulations that the Materials Project has to offer.

Q: When you were a child, did you dream of becoming a scientist?

Persson: No, not really. Actually, when I was very young, I wanted to be an opera singer. I loved singing – I still do, and when I was little, opera seemed like the perfect environment for that. Then I considered becoming an archaeologist. I was drawn to archaeology because I love history and enjoy discovering how people lived – I was always fascinated by the idea of unearthing stories of people from ancient eras: what they thought, what they believed in, and how they lived day to day.

Q: Were you always good at math?

Persson: It depends on how far back you are asking. Between the ages of 7 and 11, I had pretty mediocre grades across the board.

I remember a particular, standardized math test, at the age of 10, that I didn’t do well on. Feeling very disappointed and honestly nervous about my future, I started doing an hour of math a day by myself, without a tutor. I did basic math – I learned by redoing all sorts of problems wherever I could find them in textbooks just to make sure I understood what was going on.

It wasn’t easy because no one was directing me. Instead, it was my own growing ambition and determination that drove me. By the time I was 12, I was at the head of my class in every single subject.

Q: What led you to computational materials science?

Persson: When I was in college I initially wanted to study medicine, but I ended up studying engineering physics, which is very broad and fast-paced. And it was during that time when I fell in love with quantum mechanics. I thought it was the most beautiful thing ever – physics suddenly made sense together with the math, and it was gorgeous.

When I completed my master’s degree – my thesis was on neutrino oscillations, which is essentially theoretical particle physics – I was awarded a doctoral fellowship that would allow me to go wherever I wanted to go.

After interviewing four different professors in four very different fields, I ended up choosing the computational materials group in the Theoretical Physics Department at the Royal Institute of Technology in Stockholm, Sweden, because I liked their methodology. They used simulations together with theoretical frameworks to figure out how materials work on the fundamental level of electrons and atoms.

And that’s why I tell my graduate students, “Don’t expect that by the age of 25 you will know exactly what you want to do in life. There are so many interesting topics when you dig deeper.” And for me, it was important that I was happy with the methodology, the every-day tasks, and getting along with the people you work with.

The Materials Project is supported by the DOE Office of Science.

NERSC is a DOE Office of Science User Facility located at Berkeley Lab.

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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 Duke University via phys.org: “New handle for controlling electromagnetic properties could enable spintronic computing”

From Duke University

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From phys.org

April 13, 2020
Ken Kingery

A large, perfect crystal of iron sulfide that was painstakingly grown for the research experiments probing the change of atomic vibrations across magnetic transition. Credit: Haidong Zhou, University of Tennessee.

Materials scientists at Duke University have shown the first clear example that a material’s transition into a magnet can control instabilities in its crystalline structure that cause it to change from a conductor to an insulator.

If researchers can learn to control this unique connection between physical properties identified in hexagonal iron sulfide, it could enable new technologies such as spintronic computing. The results appear April 13 in the journal Nature Physics.

Commonly known as troilite, hexagonal iron sulfide can be found natively on Earth but is more abundant in meteorites, particularly those originating from the Moon and Mars. Rarely encountered in the Earth’s crust, most troilite on Earth is believed to have originated from space.

Despite its relative rarity, troilite has been studied since 1862 without much fanfare. A recent theoretical paper, however, suggested that there might be novel physics at play between the temperatures of 289 and 602 degrees Fahrenheit—the temperature range at which troilite becomes both magnetic and an insulator.

“The paper theorized that the way the atoms shift in their crystalline structure is impacting the mineral’s properties through a pretty complicated effect that hasn’t been seen before,” said Olivier Delaire, associate professor of mechanical engineering and materials science, physics and chemistry at Duke. “The most important aspect is this interaction between magnetic properties and atomic dynamics, which is a subject that has not been investigated a lot before but is opening up new possibilities in computing technologies.”

To get to the heart of the material’s odd behavior, Delaire and his colleagues turned to Haidong Zhou, assistant professor of experimental condensed matter physics at the University of Tennessee, for the difficult task of growing perfect crystals of troilite. The researchers then took samples to Oak Ridge National Laboratory and Argonne National Laboratory to blast them with neutrons and x-rays, respectively.

When particles such as neutrons or x-rays bounce off the atoms inside a material, researchers can take this scattering information to reconstruct its atomic structure and dynamics. Because neutrons have their own internal magnetic moment, they can also reveal the direction of each atom’s magnetic spin. But because neutrons interact weakly with atoms, x-rays are also very handy for resolving a material’s atomic structure and atomic vibrations in tiny crystals. The researchers compared results from the two different scans using quantum mechanical models created on a supercomputer at Lawrence Berkeley National Laboratory to make sure they understood what was happening.

After watching the changes that occur through troilite’s phase transformations, the researchers discovered previously unseen mechanisms at work. At high temperatures, the magnetic spins of troilite atoms point in random directions, making the material non-magnetic. But once the temperature drops below 602 degrees Fahrenheit, the magnetic moments naturally align and a magnet is born.

The alignment of those magnetic spins shifts the vibration dynamics of the atoms. That shift causes the entire crystalline atomic structure to deform slightly, which in turn creates a band gap that electrons cannot jump across. This causes the troilite to lose its ability to conduct electricity.

“This is the first clear example that the alignment of magnetic spins can control the instabilities of a material’s crystal structure,” said Delaire. “And because these instabilities lead to a connection between the crystal’s magnetic and conductivity properties, this is the type of material that’s exciting in terms of enabling new types of devices.”

The ability to tune a material’s magnetic state by applying electrical currents, and vice versa, would be essential for the realization of technologies such as spin electronics, Delaire said. Known as spintronics for short, this emerging field seeks to use an electron’s intrinsic spin and associated magnetic moment to store and manipulate data. Combined with an electron’s traditional role in computing, this would allow computer processors to become denser and more efficient.

Through this paper, Delaire and his colleagues have identified the magnetic controls of the distortion mechanisms of the crystal structure, giving researchers a handle to manipulate one with the other. While that handle is currently based in temperature changes, the next step for researchers is to look at applying external magnetic fields to see how they might affect the material’s atomic dynamics.

Whether or not troilite becomes the new silicon for the next generation of computing technology, Delaire says finding this unique mechanism in such a well-known material is a good lesson for the entire field.

“It’s surprising that, even though you have a compound that is relatively simple, you can have this fancy mechanism that could end up enabling new technologies,” said Delaire. “In a sense, it’s a wakeup call that we need to reconsider some of the simpler materials to look for similar effects elsewhere.”

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Younger than most other prestigious U.S. research universities, Duke University consistently ranks among the very best. Duke’s graduate and professional schools — in business, divinity, engineering, the environment, law, medicine, nursing and public policy — are among the leaders in their fields. Duke’s home campus is situated on nearly 9,000 acres in Durham, N.C, a city of more than 200,000 people. Duke also is active internationally through the Duke-NUS Graduate Medical School in Singapore, Duke Kunshan University in China and numerous research and education programs across the globe. More than 75 percent of Duke students pursue service-learning opportunities in Durham and around the world through DukeEngage and other programs that advance the university’s mission of “knowledge in service to society.”

From UC Irvine via phys.org: “Team designs carbon nanostructure stronger than diamonds”

From UC Irvine

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phys.org

April 13, 2020
Brian Bell

With wall thicknesses of about 160 nanometers, a closed-cell, plate-based nanolattice structure designed by researchers at UCI and other institutions is the first experimental verification that such arrangements reach the theorized limits of strength and stiffness in porous materials. Credit: Cameron Crook and Jens Bauer / UCI

Researchers at the University of California, Irvine and other institutions have architecturally designed plate-nanolattices—nanometer-sized carbon structures—that are stronger than diamonds as a ratio of strength to density.

In a recent study in Nature Communications, the scientists report success in conceptualizing and fabricating the material, which consists of closely connected, closed-cell plates instead of the cylindrical trusses common in such structures over the past few decades.

“Previous beam-based designs, while of great interest, had not been so efficient in terms of mechanical properties,” said corresponding author Jens Bauer, a UCI researcher in mechanical & aerospace engineering. “This new class of plate-nanolattices that we’ve created is dramatically stronger and stiffer than the best beam-nanolattices.”

According to the paper, the team’s design has been shown to improve on the average performance of cylindrical beam-based architectures by up to 639 percent in strength and 522 percent in rigidity.

Members of the architected materials laboratory of Lorenzo Valdevit, UCI professor of materials science & engineering as well as mechanical & aerospace engineering, verified their findings using a scanning electron microscope and other technologies provided by the Irvine Materials Research Institute.

“Scientists have predicted that nanolattices arranged in a plate-based design would be incredibly strong,” said lead author Cameron Crook, a UCI graduate student in materials science & engineering. “But the difficulty in manufacturing structures this way meant that the theory was never proven, until we succeeded in doing it.”

Bauer said the team’s achievement rests on a complex 3-D laser printing process called two-photon lithography direct laser writing. As an ultraviolet-light-sensitive resin is added layer by layer, the material becomes a solid polymer at points where two photons meet. The technique is able to render repeating cells that become plates with faces as thin as 160 nanometers.

Bauer said the team’s achievement rests on a complex 3-D laser printing process called two-photon polymerization direct laser writing. As a laser is focused inside a droplet of an ultraviolet-light-sensitive liquid resin, the material becomes a solid polymer where molecules are simultaneously hit by two photons. By scanning the laser or moving the stage in three dimensions, the technique is able to render periodic arrangements of cells, each consisting of assemblies of plates as thin as 160 nanometers.

One of the group’s innovations was to include tiny holes in the plates that could be used to remove excess resin from the finished material. As a final step, the lattices go through pyrolysis, in which they’re heated to 900 degrees Celsius in a vacuum for one hour. According to Bauer, the end result is a cube-shaped lattice of glassy carbon that has the highest strength scientists ever thought possible for such a porous material.

Bauer said that another goal and accomplishment of the study was to exploit the innate mechanical effects of the base substances. “As you take any piece of material and dramatically decrease its size down to 100 nanometers, it approaches a theoretical crystal with no pores or cracks. Reducing these flaws increases the system’s overall strength,” he said.

“Nobody has ever made these structures independent from scale before,” added Valdevit, who directs UCI’s Institute for Design and Manufacturing Innovation. “We were the first group to experimentally validate that they could perform as well as predicted while also demonstrating an architected material of unprecedented mechanical strength.”

Nanolattices hold great promise for structural engineers, particularly in aerospace, because it’s hoped that their combination of strength and low mass density will greatly enhance aircraft and spacecraft performance.

Other co-authors on the study were Anna Guell Izard, a UCI graduate student in mechanical & aerospace engineering, and researchers from UC Santa Barbara and Germany’s Martin Luther University of Halle-Wittenberg. The project was funded by the Office of Naval Research and the German Research Foundation.

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Since 1965, the University of California, Irvine has combined the strengths of a major research university with the bounty of an incomparable Southern California location. UCI’s unyielding commitment to rigorous academics, cutting-edge research, and leadership and character development makes the campus a driving force for innovation and discovery that serves our local, national and global communities in many ways.

With more than 29,000 undergraduate and graduate students, 1,100 faculty and 9,400 staff, UCI is among the most dynamic campuses in the University of California system. Increasingly a first-choice campus for students, UCI ranks among the top 10 U.S. universities in the number of undergraduate applications and continues to admit freshmen with highly competitive academic profiles.

UCI fosters the rigorous expansion and creation of knowledge through quality education. Graduates are equipped with the tools of analysis, expression and cultural understanding necessary for leadership in today’s world.

Consistently ranked among the nation’s best universities – public and private – UCI excels in a broad range of fields, garnering national recognition for many schools, departments and programs. Times Higher Education ranked UCI No. 1 among universities in the U.S. under 50 years old. Three UCI researchers have won Nobel Prizes – two in chemistry and one in physics.

The university is noted for its top-rated research and graduate programs, extensive commitment to undergraduate education, and growing number of professional schools and programs of academic and social significance. Recent additions include highly successful programs in public health, pharmaceutical sciences and nursing science; an expanding education school; and a law school already ranked among the nation’s top 10 for its scholarly impact.

From MIT News: “Novel method for easier scaling of quantum devices”

From MIT News

March 5, 2020
Rob Matheson

An MIT team found a way to “recruit” normally disruptive quantum bits (qubits) in diamond to, instead, help carry out quantum operations. This approach could be used to help scale up quantum computing systems. Image: Christine Daniloff, MIT.

System “recruits” defects that usually cause disruptions, using them to instead carry out quantum operations.

In an advance that may help researchers scale up quantum devices, an MIT team has developed a method to “recruit” neighboring quantum bits made of nanoscale defects in diamond, so that instead of causing disruptions they help carry out quantum operations.

Quantum devices perform operations using quantum bits, called “qubits,” that can represent the two states corresponding to classic binary bits — a 0 or 1 — or a “quantum superposition” of both states simultaneously. The unique superposition state can enable quantum computers to solve problems that are practically impossible for classical computers, potentially spurring breakthroughs in biosensing, neuroimaging, machine learning, and other applications.

One promising qubit candidate is a defect in diamond, called a nitrogen-vacancy (NV) center, which holds electrons that can be manipulated by light and microwaves. In response, the defect emits photons that can carry quantum information. Because of their solid-state environments, however, NV centers are always surrounded by many other unknown defects with different spin properties, called “spin defects.” When the measurable NV-center qubit interacts with those spin defects, the qubit loses its coherent quantum state — “decoheres”— and operations fall apart. Traditional solutions try to identify these disrupting defects to protect the qubit from them.

In a paper published Feb. 25 in Physical Review Letters, the researchers describe a method that uses an NV center to probe its environment and uncover the existence of several nearby spin defects. Then, the researchers can pinpoint the defects’ locations and control them to achieve a coherent quantum state — essentially leveraging them as additional qubits.

In experiments, the team generated and detected quantum coherence among three electronic spins — scaling up the size of the quantum system from a single qubit (the NV center) to three qubits (adding two nearby spin defects). The findings demonstrate a step forward in scaling up quantum devices using NV centers, the researchers say.

“You always have unknown spin defects in the environment that interact with an NV center. We say, ‘Let’s not ignore these spin defects, which [if left alone] could cause faster decoherence. Let’s learn about them, characterize their spins, learn to control them, and ‘recruit’ them to be part of the quantum system,’” says the lead co-author Won Kyu Calvin Sun, a graduate student in the Department of Nuclear Science and Engineering and a member of the Quantum Engineering group. “Then, instead of using a single NV center [or just] one qubit, we can then use two, three, or four qubits.”

Joining Sun on the paper are lead author Alexandre Cooper ’16 of Caltech; Jean-Christophe Jaskula, a research scientist in the MIT Research Laboratory of Electronics (RLE) and member of the Quantum Engineering group at MIT; and Paola Cappellaro, a professor in the Department of Nuclear Science and Engineering, a member of RLE, and head of the Quantum Engineering group at MIT.

Characterizing defects

NV centers occur where carbon atoms in two adjacent places in a diamond’s lattice structure are missing — one atom is replaced by a nitrogen atom, and the other space is an empty “vacancy.” The NV center essentially functions as an atom, with a nucleus and surrounding electrons that are extremely sensitive to tiny variations in surrounding electrical, magnetic, and optical fields. Sweeping microwaves across the center, for instance, makes it change, and thus control, the spin states of the nucleus and electrons.

Spins are measured using a type of magnetic resonance spectroscopy. This method plots the frequencies of electron and nucleus spins in megahertz as a “resonance spectrum” that can dip and spike, like a heart monitor. Spins of an NV center under certain conditions are well-known. But the surrounding spin defects are unknown and difficult to characterize.

In their work, the researchers identified, located, and controlled two electron-nuclear spin defects near an NV center. They first sent microwave pulses at specific frequencies to control the NV center. Simultaneously, they pulse another microwave that probes the surrounding environment for other spins. They then observed the resonance spectrum of the spin defects interacting with the NV center.

The spectrum dipped in several spots when the probing pulse interacted with nearby electron-nuclear spins, indicating their presence. The researchers then swept a magnetic field across the area at different orientations. For each orientation, the defect would “spin” at different energies, causing different dips in the spectrum. Basically, this allowed them to measure each defect’s spin in relation to each magnetic orientation. They then plugged the energy measurements into a model equation with unknown parameters. This equation is used to describe the quantum interactions of an electron-nuclear spin defect under a magnetic field. Then, they could solve the equation to successfully characterize each defect.

Locating and controlling

After characterizing the defects, the next step was to characterize the interaction between the defects and the NV, which would simultaneously pinpoint their locations. To do so, they again swept the magnetic field at different orientations, but this time looked for changes in energies describing the interactions between the two defects and the NV center. The stronger the interaction, the closer they were to one another. They then used those interaction strengths to determine where the defects were located, in relation to the NV center and to each other. That generated a good map of the locations of all three defects in the diamond.

Characterizing the defects and their interaction with the NV center allow for full control, which involves a few more steps to demonstrate. First, they pump the NV center and surrounding environment with a sequence of pulses of green light and microwaves that help put the three qubits in a well-known quantum state. Then, they use another sequence of pulses that ideally entangles the three qubits briefly, and then disentangles them, which enables them to detect the three-spin coherence of the qubits.

The researchers verified the three-spin coherence by measuring a major spike in the resonance spectrum. The measurement of the spike recorded was essentially the sum of the frequencies of the three qubits. If the three qubits for instance had little or no entanglement, there would have been four separate spikes of smaller height.

“We come into a black box [environment with each NV center]. But when we probe the NV environment, we start seeing dips and wonder which types of spins give us those dips. Once we [figure out] the spin of the unknown defects, and their interactions with the NV center, we can start controlling their coherence,” Sun says. “Then, we have full universal control of our quantum system.”

Next, the researchers hope to better understand other environmental noise surrounding qubits. That will help them develop more robust error-correcting codes for quantum circuits. Furthermore, because on average the process of NV center creation in diamond creates numerous other spin defects, the researchers say they could potentially scale up the system to control even more qubits. “It gets more complex with scale. But if we can start finding NV centers with more resonance spikes, you can imagine starting to control larger and larger quantum systems,” Sun says.

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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.

From Pennsylvania State University: “Two-dimensional metals open pathways to new science”

From Pennsylvania State University

March 09, 2020
Walt Mills

A single atomic layer of metal is capped by a layer of graphene, allowing for new layered materials with unique properties. Image: Yihuang Xiong/Penn State.

An atomically thin materials platform developed by Penn State researchers in conjunction with Lawrence Berkeley National Lab and Oak Ridge National Lab will open a wide range of new applications in biomolecular sensing, quantum phenomena, catalysis and nonlinear optics.

“We have leveraged our understanding of a special type of graphene, dubbed epitaxial graphene, to stabilize unique forms of atomically thin metals,” said Natalie Briggs, a doctoral candidate and co-lead author on a paper in the journal Nature Materials. “Interestingly, these atomically thin metals stabilize in structures that are completely different from their bulk versions, and thus have very interesting properties compared to what is expected in bulk metals.”

Traditionally, when metals are exposed to air they rapidly begin to oxidize — rust. In as short as one second, metal surfaces can form a rust layer that would destroy the metallic properties. In the case of a 2D metal, this would be the entire layer. If you were to combine a metal with other 2D materials via traditional synthesis processes, the chemical reactions during synthesis would ruin the properties of both the metal and layered material. To avoid these reactions, the team exploited a method that automatically caps the 2D metal with a single layer of graphene while creating the 2D metal.

The researchers start with silicon carbide that they heat to a high temperature. The silicon leaves the surface, and the remaining carbon reconstructs into epitaxial graphene. Importantly, the graphene/silicon carbide interface is only partially stable and is readily passivated by nearly any element, if the element has access to this interface.

The team provides this access by poking holes in the graphene with an oxygen plasma, and then they evaporate pure metal powders onto the surface at high temperatures. The metal atoms migrate through the holes in the graphene to the graphene/silicon carbide interface, creating a sandwich structure of silicon carbide, metal and graphene. The process to create the 2D metals is called confinement heteroepitaxy, or CHet.

“We call it CHet because of the confined nature of the metal, and the fact that it is epitaxial — the atoms all line up — to the silicon carbide, an important aspect to the unique properties we see in these systems,” noted Joshua Robinson, senior author and associate professor of materials science and engineering, Penn State.

“In this paper, the focus is on the fundamental properties of the metals that are going to enable a new set of research topics,” said Robinson. “It shows that we are able to develop novel 2D materials systems that are applicable in a variety of hot topics such as quantum, where graphene is a key link that allows us to think about combining very different materials that normally could not be combined to form the basis for superconducting or photonic qubits.”

Next steps in their studies will involve proving out the superconducting, sensing, optical and catalytical properties of these layered materials. Beyond creating unique 2D metals, the team is continuing to explore new 2D semiconducting materials with CHet that would be of interest to the electronics industry in future electronics beyond silicon.

Additional authors from Penn State include former doctoral student in the Robinson group and co-lead author Brian Bersch, doctoral student Yuanxi Wang, and professors Cui-Zu Chang, Jun Zhu, Adri van Duin and Vincent Crespi.

The Northrop Grumman Corp. primarily funded this work with additional funding from the Semiconductor Research Corporation, the National Science Foundation and the Alfred P. Sloan Research Fellowship.

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About Penn State

WHAT WE DO BEST

We teach students that the real measure of success is what you do to improve the lives of others, and they learn to be hard-working leaders with a global perspective. We conduct research to improve lives. We add millions to the economy through projects in our state and beyond. We help communities by sharing our faculty expertise and research.

Penn State lives close by no matter where you are. Our campuses are located from one side of Pennsylvania to the other. Through Penn State World Campus, students can take courses and work toward degrees online from anywhere on the globe that has Internet service.

We support students in many ways, including advising and counseling services for school and life; diversity and inclusion services; social media sites; safety services; and emergency assistance.

Our network of more than a half-million alumni is accessible to students when they want advice and to learn about job networking and mentor opportunities as well as what to expect in the future. Through our alumni, Penn State lives all over the world.

The best part of Penn State is our people. Our students, faculty, staff, alumni, and friends in communities near our campuses and across the globe are dedicated to education and fostering a diverse and inclusive environment.

From UCLA Newsroom: “UCLA-led research team produces most accurate 3D images of ‘2D materials’”

From UCLA Newsroom

March 9, 2020
Wayne Lewis

Image showing the 3D atomic coordinates of molybdenum (blue), sulfur (yellow) and added rhenium (orange). A 2D image is shown beneath the 3D model.

Scientists develop innovative technique to pinpoint coordinates of single atoms.

A UCLA-led research team has produced in unprecedented detail experimental three-dimensional maps of the atoms in a so-called 2D material — matter that isn’t truly two-dimensional but is nearly flat because it’s arranged in extremely thin layers, no more than a few atoms thick.

Although 2D-materials–based technologies have not yet been widely used in commercial applications, the materials have been the subject of considerable research interest. In the future, they could be the basis for semiconductors in ever smaller electronics, quantum computer components, more-efficient batteries, or filters capable of extracting freshwater from saltwater.

The promise of 2D materials comes from certain properties that differ from how the same elements or compounds behave when they appear in greater quantities. Those unique characteristics are influenced by quantum effects — phenomena occurring at extremely small scales that are fundamentally different from the classical physics seen at larger scales. For instance, when carbon is arranged in an atomically thin layer to form 2D graphene, it is stronger than steel, conducts heat better than any other known material, and has almost zero electrical resistance.

But using 2D materials in real-world applications would require a greater understanding of their properties, and the ability to control those properties. The new study, which was published in Nature Materials, could be a step forward in that effort.

The researchers showed that their 3D maps of the material’s atomic structure are precise to the picometer scale — measured in one-trillionths of a meter. They used their measurements to quantify defects in the 2D material, which can affect their electronic properties, as well as to accurately assess those electronic properties.

“What’s unique about this research is that we determine the coordinates of individual atoms in three dimensions without using any pre-existing models,” said corresponding author Jianwei “John” Miao, a UCLA professor of physics and astronomy. “And our method can be used for all kinds of 2D materials.”

Miao is the deputy director of the STROBE National Science Foundation Science and Technology Center and a member of the California NanoSystems Institute at UCLA. His UCLA lab collaborated on the study with researchers from Harvard University, Oak Ridge National Laboratory and Rice University.

The researchers examined a single layer of molybdenum disulfide, a frequently studied 2D material. In bulk, this compound is used as a lubricant. As a 2D material, it has electronic properties that suggest it could be employed in next-generation semiconductor electronics. The samples being studied were “doped” with traces of rhenium, a metal that adds spare electrons when replacing molybdenum. That kind of doping is often used to produce components for computers and electronics because it helps facilitate the flow of electrons in semiconductor devices.

To analyze the 2D material, the researchers used a new technology they developed based on scanning transmission electron microscopy, which produces images by measuring scattered electrons beamed through thin samples. Miao’s team devised a technique called scanning atomic electron tomography, which produces 3D images by capturing a sample at multiple angles as it rotates.

The scientists had to avoid one major challenge to produce the images: 2D materials can be damaged by too much exposure to electrons. So for each sample, the researchers reconstructed images section by section and then stitched them together to form a single 3D image — allowing them to use fewer scans and thus a lower dose of electrons than if they had imaged the entire sample at once.

The two samples each measured 6 nanometers by 6 nanometers, and each of the smaller sections measured about 1 nanometer by 1 nanometer. (A nanometer is one-billionth of a meter.)

The resulting images enabled the researchers to inspect the samples’ 3D structure to a precision of 4 picometers in the case of molybdenum atoms — 26 times smaller than the diameter of a hydrogen atom. That level of precision enabled them to measure ripples, strain distorting the shape of the material, and variations in the size of chemical bonds, all changes caused by the added rhenium — marking the most accurate measurement ever of those characteristics in a 2D material.

“If we just assume that introducing the dopant is a simple substitution, we wouldn’t expect large strains,” said Xuezeng Tian, the paper’s co-first author and a UCLA postdoctoral scholar. “But what we have observed is more complicated than previous experiments have shown.”

The scientists found that the largest changes occurred in the smallest dimension of the 2D material, its three-atom-tall height. It took as little as a single rhenium atom to introduce such local distortion.

Armed with information about the material’s 3D coordinates, scientists at Harvard led by Professor Prineha Narang performed quantum mechanical calculations of the material’s electronic properties.

“These atomic-scale experiments have given us a new lens into how 2D materials behave and how they should be treated in calculations, and they could be a game changer for new quantum technologies,” Narang said.

Without access to the sort of measurements generated in the study, such quantum mechanical calculations conventionally have been based on a theoretical model system that is expected at a temperature of absolute zero.

The study indicated that the measured 3D coordinates led to more accurate calculations of the 2D material’s electronic properties.

“Our work could transform quantum mechanical calculations by using experimental 3D atomic coordinates as direct input,” said UCLA postdoctoral scholar Dennis Kim, a co-first author of the study. “This approach should enable material engineers to better predict and discover new physical, chemical and electronic properties of 2D materials at the single-atom level.”

Other authors were Yongsoo Yang, Yao Yang and Yakun Yuan of UCLA; Shize Yang and Juan-Carlos Idrobo of Oak Ridge National Laboratory; Christopher Ciccarino and Blake Duschatko of Harvard; and Yongji Gong and Pulickel Ajayan of Rice.

The research was supported by the U.S. Department of Energy, the U.S. Army Research Office, and STROBE National Science Foundation Science and Technology Center. The scanning transmission electron microscopy experiments were conducted at the Center for Nanophase Materials Sciences, a DOE user facility at Oak Ridge National Laboratory.

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For nearly 100 years, UCLA has been a pioneer, persevering through impossibility, turning the futile into the attainable.

We doubt the critics, reject the status quo and see opportunity in dissatisfaction. Our campus, faculty and students are driven by optimism. It is not naïve; it is essential. And it has fueled every accomplishment, allowing us to redefine what’s possible, time after time.

This can-do perspective has brought us 12 Nobel Prizes, 12 Rhodes Scholarships, more NCAA titles than any university and more Olympic medals than most nations. Our faculty and alumni helped create the Internet and pioneered reverse osmosis. And more than 100 companies have been created based on technology developed at UCLA.

From Caltech: “Microstructures Self-Assemble into New Materials”

From Caltech

March 02, 2020
Robert Perkins
(626) 395‑1862
rperkins@caltech.edu

Caltech

A new process developed at Caltech makes it possible for the first time to manufacture large quantities of materials whose structure is designed at a nanometer scale—the size of DNA’s double helix.

Pioneered by Caltech materials scientist Julia R. Greer, “nanoarchitected materials” exhibit unusual, often surprising properties—for example, exceptionally lightweight ceramics that spring back to their original shape, like a sponge, after being compressed. These properties could be desirable for applications ranging from ultrasensitive tactile sensors to advanced batteries, but so far, engineers have only been able to create them in very limited amounts. To create a material whose structure is designed at such a small scale, they often have to be assembled nano-layer by nano-layer in a 3-D printing process that uses a high-precision laser and custom-synthesized chemicals. That painstaking process limits the overall amount of material that can be built.

Now, a team of engineers at Caltech and ETH Zürich have developed a material that is designed at the nanoscale but assembles itself—with no need for the precision laser assembly. For the first time, they were able to create a sample of nanoarchitected material at the cubic-centimeter scale.

“We couldn’t 3-D print this much nanoarchitected material even in a month; instead we’re able to grow it in a matter of hours,” says Carlos Portela, postdoctoral scholar at Caltech and lead author of a study on the new process that was published by the journal Proceedings of the National Academy of Sciences (PNAS) on March 2.

At the nanoscale, the material looks like a sponge but is actually an assembly of interconnected curved shells. That’s the key to the material’s high stiffness- and strength-to-weight ratios: the smoothly curved thin shells, like those of an egg, are free of corners or junctions, which are usually weak points leading to failure in other similar materials. This provides unique mechanical benefits with a minimum of material actually used. In testing, a sample of the material was able to achieve strength-to-density ratios comparable to some forms of steel, while thinner-walled configurations exhibit negligible damage and recovery after repeated compression.

“This new fabrication route, supported by the experimental and numerical analysis that we’ve conducted, gets us one step closer to being able to produce nanoarchitected materials at a useful scale, with a marked ease of fabrication,” says Greer, the Ruben F. and Donna Mettler Professor of Materials Science, Mechanics, and Medical Engineering and coauthor of the PNAS paper.

Though it is measurably more resilient than virtually all nanoarchitected materials with similar densities synthesized by the Greer group, what makes these so-called nano-labyrinthine materials particularly special is that they assemble themselves. This achievement, led by Caltech graduate student Daryl Yee, works like this: two materials that don’t dissolve into each other are mixed together, blending them to create a disordered state. Heating up the mixture polymerizes the materials so that the current geometry gets locked in place. One of the two materials is then removed, leaving nanoscale shells. The resulting porous template is subsequently coated, and then the second polymer is removed. What’s left is lightweight nano-shell network.

The process requires extreme precision; if incorrectly heated, the microstructure will either melt together or collapse and will not lead to interconnected shells. But for the first time, the team sees the potential to scale up nanoarchitecture.

“It is exciting to see our computationally designed optimal nanoscale architectures being realized experimentally in the lab,” says Dennis M. Kochmann, corresponding author of the PNAS paper and professor of mechanics and materials at ETH Zürich and a visiting associate in aerospace at Caltech. His team, including former Caltech graduate student A. Vidyasagar and Sebastian Krödel and Tamara Weissenbach of ETH Zürich, predicted the versatile properties of the nano-labyrinthine materials through theory and simulations.

Next, the team plans to expand the tunability and versatility of the process by exploring pathways to carefully control the microstructure, expand on the material options for the nano-shells, and push for the production of larger volumes of the material.

See the full article here .

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The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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