From Stanford University: “Stanford researchers shine light on the defects responsible for messy behavior in quantum materials”

From Stanford University

February 24, 2020
Taylor Kubota

Researchers are investigating light-emitting defects in materials that may someday enable quantum-based technologies, such as quantum computers, quantum networks or engines that run on light. Once understood, these defects can become controllable features.

Researchers studied a material capable of emitting bright quantum light. Materials like this could someday enable the creation of quantum computers, which would be much faster and more efficient than current computers. (Image credit: Getty Images)

In a future built on quantum technologies, planes and spaceships could be fueled by the momentum of light. Quantum computers will crunch through complex problems spanning chemistry to cryptography with greater speed and energy efficiency than existing processors. But before this future can come to pass, we need bright, on-demand, predictable sources of quantum light.

Toward this end, a team of Stanford University material scientists, physicists and engineers, in collaboration with labs at Harvard University and the University of Technology Sydney, have been investigating hexagonal boron nitride, a material that can emit bright light as a single photon – a quantum unit of light – at a time. And it can do this at room temperature, making it easier to use compared to alternative quantum sources.

Unfortunately, hexagonal boron nitride has a significant downside: It emits light in a rainbow of different hues. “While this emission is beautiful, the color currently can’t be controlled,” said Fariah Hayee, the lead author and a graduate student in the lab of Jennifer Dionne, associate professor of materials science and engineering at Stanford. “We wanted to know the source of the multi-color emission, with the ultimate goal of gaining control over emission.”

By employing a combination of microscopic methods, the scientists were able to trace the material’s colorful emission to specific atomic defects. A group led by co-author Prineha Narang, assistant professor of computational materials science at Harvard University, also developed a new theory to predict the color of defects by accounting for how light, electrons and heat interact in the material.

“We needed to know how these defects couple to the environment and if that could be used as a fingerprint to identify and control them,” said Christopher Ciccarino, a graduate student in the NarangLab at Harvard University and co-author of the paper.

The researchers describe their technique and different categories of defects in a paper published in the Feb. 24 issue of the journal Nature Materials.

Multiscale microscopy

Identifying the defects that give rise to quantum emission is a bit like searching for a friend in a crowded city without a cellphone. You know they are there, but you have the scan the full city to find their precise location.

By stretching the capabilities of a one-of-a-kind, modified electron microscope developed by the Dionne lab, the scientists were able to match the local, atomic-scale structure of hexagonal boron nitride with its unique color emission. Over the course of hundreds of experiments, they bombarded the material with electrons and visible light and recorded the pattern of light emission. They also studied how the periodic arrangement of atoms in hexagonal boron nitride influenced the emission color.

“The challenge was to tease out the results from what can seem to be a very messy quantum system. Just one measurement doesn’t tell the whole picture,” said Hayee. “But taken together, and combined with theory, the data is very rich and provides a clear classification of quantum defects in this material.”

In addition to their specific findings about types of defect emissions in hexagonal boron nitride, the process the team developed to collect and classify these quantum spectra could, on its own, be transformative for a range of quantum materials.

“Materials can be made with near atomic-scale precision, but we still don’t fully understand how different atomic arrangements influence their opto-electronic properties,” said Dionne, who is also director of the Photonics at Thermodynamic Limits Energy Frontier Research Center (PTL-EFRC). “Our team’s approach reveals light emission at the atomic-scale, en route to a host of exciting quantum optical technologies.”

A superposition of disciplines

Although the focus now is on understanding which defects give rise to certain colors of quantum emission, the eventual aim is to control their properties. For example, the team envisions strategic placement of quantum emitters, as well as turning their emission on and off for future quantum computers.

Research in this field requires a cross-disciplinary approach. This work brought together materials scientists, physicists and electrical engineers, both experimentalists and theorists, including Tony Heinz, professor of applied physics at Stanford’s School of Humanities and Sciences and of photon science at the SLAC National Accelerator Laboratory, and Jelena Vučković, the Jensen Huang Professor in Global Leadership in the School of Engineering.

“We were able to lay the groundwork for creating quantum sources with controllable properties, such as color, intensity and position,” said Dionne. “Our ability to study this problem from several different angles demonstrates the advantages of an interdisciplinary approach.”

Additional Stanford co-authors of this paper include Leo Yu, a postdoctoral scholar in the Heinz lab, and Jingyuan Linda Zhang, who was a graduate student in the Ginzton Laboratory during this research. Other co-authors include researchers from the University of Technology Sydney in Australia. Dionne is also a member of Stanford Bio-X, an affiliate of the Precourt Institute for Energy and a member of the Wu Tsai Neurosciences Institute at Stanford. Vučković is also a professor of electrical engineering and a member of Stanford Bio-X and of the Wu Tsai Neurosciences Institute.

This research was funded by the Department of Energy, Stanford’s Diversifying Academia, Recruiting Excellence Doctoral Fellowship Program, the National Science Foundation and the Betty and Gordon Moore Foundation.

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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 ETH Zürich: “Time-resolved measurement in a memory device”

From ETH Zürich

19.02.2020
Oliver Morsch

Researchers at ETH have measured the timing of single writing events in a novel magnetic memory device with a resolution of less than 100 picoseconds. Their results are relevant for the next generation of main memories based on magnetism.

The chip produced by IMEC for the experiments at ETH. The tunnel junctions used to measure the timing of the magnetisation reversal are located at the centre (Image courtesy of IMEC).

At the Department for Materials of the ETH in Zürich, Pietro Gambardella and his collaborators investigate tomorrow’s memory devices. They should be fast, retain data reliably for a long time and also be cheap. So-​called magnetic “random access memories” (MRAM) achieve this quadrature of the circle by combining fast switching via electric currents with durable data storage in magnetic materials. A few years ago researchers could already show that a certain physical effect – the spin-​orbit torque – makes particularly fast data storage possible. Now Gambardella’s group, together with the R&D-​centre IMEC in Belgium, managed to temporally resolve the exact dynamics of a single such storage event – and to use a few tricks to make it even faster.

Magnetising with single spins

To store data magnetically, one has to invert the direction of magnetisation of a ferromagnetic (that is, permanently magnetic) material in order to represent the information as a logic value, 0 or 1. In older technologies, such as magnetic tapes or hard drives, this is achieved through magnetic fields produced inside current-​carrying coils. Modern MRAM-​memories, by contrast, directly use the spins of electrons, which are magnetic, much like small compass needles, and flow directly through a magnetic layer as an electric current. In Gambardella’s experiments, electrons with opposite spin directions are spatially separated by the spin-​orbit interaction. This, in turn, creates an effective magnetic field, which can be used to invert the direction of magnetisation of a tiny metal dot.

“We know from earlier experiments, in which we stroboscopically scanned a single magnetic metal dot with X-​rays, that the magnetisation reversal happens very fast, in about a nanosecond”, says Eva Grimaldi, a post-​doc in Gambardella’s group. “However, those were mean values averaged over many reversal events. Now we wanted to know how exactly a single such event takes place and to show that it can work on an industry-​compatible magnetic memory device.”

Time resolution through a tunnel junction

Electron microscope image of the magnetic tunnel junction (MTJ, at the centre) and of the electrodes for controlling and measuring the reversal process. (Image: P. Gambardella / ETH Zürich)

To do so, the researchers replaced the isolated metal dot by a magnetic tunnel junction. Such a tunnel junction contains two magnetic layers separated by an insulation layer that is only one nanometre thick. Depending on the spin direction – along the magnetisation of the magnetic layers, or opposite to it – the electrons can tunnel through that insulating layer more or less easily. This results in an electrical resistance that depends on the alignment of the magnetization in one layer with respect to the other and thus represents “0” and “1”. From the time dependence of that resistance during a reversal event, the researchers could reconstruct the exact dynamics of the process. In particular, they found that the magnetisation reversal happens in two stages: an incubation stage, during which the magnetisation stays constant, and the actual reversal stage, which lasts less than a nanosecond.

The magnetic tunnel junction (yellow and red disks) in which the magnetisation of the red disk is inverted by electron spins (blue and yellow arrows). The reversal process is measured through the tunnel resistance (vertical blue arrows).

Small fluctuations

“For a fast and reliable memory device it is essential that the time fluctuations between the individual reversal events are minimized”, explains Gambardella’s PhD student Viola Krizakova. So, based on their data the scientists developed a strategy to make those fluctuations as small as possible. To that end, they changed the current pulses used to control the magnetisation reversal in such a way as to introduce two additional physical phenomena. The so-​called spin-​transfer torque as well as a short voltage pulse during the reversal stage now resulted in a reduction of the total time for the reversal event to less than 0,3 nanoseconds, with temporal fluctuations of less than 0,2 nanoseconds.

Application-​ready technology

“Putting all of this together, we have found a method whereby data can be stored in magnetic tunnel junctions virtually without any error and in less than a nanosecond”, says Gambardella. Moreover, the collaboration with the research centre IMEC made it possible to test the new technology directly on an industry-​compatible wafer. Kevin Garello, a former post-​doc from Gambardella’s lab, produced the chips containing the tunnel contacts for the experiments at ETH and optimized the materials for them. In principle, the technology would, therefore, be immediately ready for use in a new generation of MRAM.

Gambardella stresses that MRAM memories are particularly interesting because, differently from conventional main memories such as SRAM or DRAM, they don’t lose their information when the computer is switched off, but are still equally fast. He concedes, though, that the market for MRAM memories currently does not demand such high writing speeds since other technical bottlenecks such as power losses caused by large switching currents limit the access times. In the meantime, he and his co-​workers are already planning further improvements: they want to shrink the tunnel junctions and use different materials that use current more efficiently.

Science paper:
“Grimaldi E, et al. Single-​shot dynamics of spin–orbit torque and spin transfer torque switching in three-​terminal magnetic tunnel junctions.”
Nature Nanotechnology

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ETH Zürich is one of the leading international universities for technology and the natural sciences. It is well known for its excellent education, ground-breaking fundamental research and for implementing its results directly into practice.

Founded in 1855, ETH Zürich today has more than 18,500 students from over 110 countries, including 4,000 doctoral students. To researchers, it offers an inspiring working environment, to students, a comprehensive education.

Twenty-one Nobel Laureates have studied, taught or conducted research at ETH Zürich, underlining the excellent reputation of the university.

From SLAC National Accelerator Lab: “Researchers show how electric fields affect a molecular twist within light-sensitive proteins”

From SLAC National Accelerator Lab

February 12, 2020
By Ali Sundermier

A better understanding of this phenomenon, which is crucial to many processes that occur in biological systems and materials, could enable researchers to develop light-sensitive proteins for areas such as biological imaging and optogenetics.

A team of scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University has gained insight into how electric fields affect the way energy from light drives molecular motion and transformation in a protein commonly used in biological imaging. A better understanding of this phenomenon, which is crucial to many processes that occur in biological systems and materials, could enable researchers to finely tune a system’s properties to harness these effects, for instance using light to control neurons in the brain. Their findings were published in Science in January.

Twist and shout

Human vision, photosynthesis and other natural processes harvest light with proteins that contain molecules known as chromophores, many of which twist when light hits them. The hallmark of this twisting motion, called photoisomerization, is that part of the molecule rotates around a particular chemical bond.

When light hits certain chromophores in proteins, it causes them to twist and change shape. This atomic reconfiguration, known as photoisomerization, changes the molecule’s chemical and physical properties. The hallmark of this process is a rotation that occurs around a chemical bond in the molecule. New research shows that the electric fields within a protein play a large role in determining which bond this rotation occurs around. (Chi-Yun Lin/Stanford University)

“Something about the protein environment is steering this very specific and important process,” says Steven Boxer, a biophysical chemist and Stanford professor who oversaw the research. “One possibility is that the distribution of atoms in the molecular space blocks or allows rotation about each chemical bond, known as the steric effect. An alternative has to do with the idea that when molecules with double bonds are excited, there is a separation of charge, and so the surrounding electric fields might favor the rotation of one bond over another. This is called the electrostatic effect.”

A different tune

To find out more about this process, the researchers looked at green fluorescent protein, a protein frequently used in biological imaging whose chromophore can respond to light in a number of ways that are sensitive to its local environment within the protein, producing fluorescent light of various colors and intensities.

Stanford graduate students Matt Romei and Chi-Yun Lin, who led the study, tuned the electronic properties of the chromophore within the protein by introducing chemical groups that systematically added or subtracted electrons from the chromophore to engineer an electric field effect. Then they measured how this affected the chromophore’s twisting motion.

With the help of coauthor Irimpan Mathews, a scientist at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), the researchers used an X-ray technique called macromolecular crystallography at SSRL beamlines 7-1, 12-2 and 14-1 to map the structures of these tuned proteins to show that these changes had little effect on the atomic structure of the chromophore and surrounding protein.

SLAC/SSRL

Then, using a combination of techniques, they were able to measure how changes to the chromophore’s electron distribution affected where rotation occurred when it was hit by light.

“Until now, most of the research on photoisomerization in this particular protein has been either theoretical or focused on the steric effect,” Romei says. “This research is one of the first to investigate the phenomenon experimentally and show the importance of the electrostatic effect. Once we plotted the data, we saw these really nice trends that suggest that tuning the chromophore’s electronic properties has a huge impact on its bond isomerization properties.”

Honing tools

These results also suggest ways to design light-sensitive proteins by manipulating the environment around the chromophore. Lin adds that this same experimental approach could be used to study and control the electrostatic effect in many other systems.

“We’re trying to figure out the principle that controls this process,” Lin says. “Using what we learn, we hope to apply these concepts to develop better tools in fields such as optogenetics, where you can selectively manipulate nerves to lead to certain functions in the brain.”

Boxer adds that the idea that the organized electric fields within proteins are important for many biological functions is an emerging concept that could be of interest to a broad audience.

“Much of the work in our lab focuses on developing methods to measure these fields and connect them with function such as enzymatic catalysis,” he says, “and we now see that photoisomerization fits into this framework.”

This work was funded in part by the National Institutes of Health (NIH). SSRL is a DOE Office of Science user facility. The SSRL Structural Molecular Biology Program is supported by the NIH and the DOE Office of Biological and Environmental Research. Part of this work was performed at the Stanford Nano Shared Facilities and supported by the National Science Foundation.

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SLAC/LCLS II projected view

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

SSRL and LCLS are DOE Office of Science user facilities.

From Brookhaven National Lab: “Making High-Temperature Superconductivity Disappear to Understand Its Origin”

From Brookhaven National Lab

February 3, 2020
Ariana Manglaviti
amanglaviti@bnl.gov
(631) 344-2347

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

Scientists have collected evidence suggesting that a purely electronic mechanism causes copper-oxygen compounds to conduct electricity without resistance at temperatures well above absolute zero.

Brookhaven Lab physicists (from left to right) Genda Gu, Tonica Valla, and Ilya Drozdov at OASIS, a new on-site experimental machine for growing and characterizing oxide thin films, such as those of a class of high-temperature superconductors (HTS) known as the cuprates. Compared to conventional superconductors, HTS become able to conduct electricity without resistance at much warmer temperatures. The team used the unique capabilities at OASIS to make superconductivity in a cuprate sample disappear and then reappear in order to understand the origin of the phenomenon.

When there are several processes going on at once, establishing cause-and-effect relationships is difficult. This scenario holds true for a class of high-temperature superconductors known as the cuprates. Discovered nearly 35 years ago, these copper-oxygen compounds can conduct electricity without resistance under certain conditions. They must be chemically modified (“doped”) with additional atoms that introduce electrons or holes (electron vacancies) into the copper-oxide layers and cooled to temperatures below 100 Kelvin (−280 degrees Fahrenheit)—significantly warmer temperatures than those needed for conventional superconductors. But exactly how electrons overcome their mutual repulsion and pair up to flow freely in these materials remains one of the biggest questions in condensed matter physics. High-temperature superconductivity (HTS) is among many phenomena occurring due to strong interactions between electrons, making it difficult to determine where it comes from.

That’s why physicists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory studying a well-known cuprate containing layers made of bismuth oxide, strontium oxide, calcium, and copper oxide (BSCCO) decided to focus on the less complicated “overdoped” side, doping the material so much so that superconductivity eventually disappears. As they reported in a paper published on Jan. 29 in Nature Communications, this approach enabled them to identify that purely electronic interactions likely lead to HTS.

“Superconductivity in cuprates usually coexists with periodic arrangements of electric charge or spin and many other phenomena that can either compete with or aid superconductivity, complicating the picture,” explained first author Tonica Valla, a physicist in the Electron Spectroscopy Group of Brookhaven Lab’s Condensed Matter Physics and Materials Science Division. “But these phenomena weaken or completely vanish with overdoping, leaving nothing but superconductivity. Thus, this is the perfect region to study the origin of superconductivity. Our experiments have uncovered an interaction between electrons in BSCCO that correlates one to one with superconductivity. Superconductivity emerges exactly when this interaction first appears and becomes stronger as the interaction strengthens.”

Only very recently has it become possible to overdope cuprate samples beyond the point where superconductivity vanishes. Previously, a bulk crystal of the material would be annealed (heated) in high-pressure oxygen gas to increase the concentration of oxygen (the dopant material). The new method—which Valla and other Brookhaven scientists first demonstrated about a year ago at OASIS, a new on-site instrument for sample preparation and characterization—uses ozone instead of oxygen to anneal cleaved samples. Cleaving refers to breaking the crystal in vacuum to create perfectly flat and clean surfaces.

“The oxidation power of ozone, or its ability to accept electrons, is much stronger than that of molecular oxygen,” explained coauthor Ilya Drozdov, a physicist in the division’s Oxide Molecular Beam Epitaxy (OMBE) Group. “This means we can bring more oxygen into the crystal to create more holes in the copper-oxide planes, where superconductivity occurs. At OASIS, we can overdope surface layers of the material all the way to the nonsuperconducting region and study the resulting electronic excitations.”

OASIS combines an OMBE system for growing oxide thin films with angle-resolved photoemission spectroscopy (ARPES) and spectroscopic imaging–scanning tunneling microscopy (SI-STM) instruments for studying the electronic structure of these films. Here, materials can be grown and studied using the same connected ultrahigh vacuum system to avoid oxidation and contamination by carbon dioxide, water, and other molecules in the atmosphere. Because ARPES and SI-STM are extremely surface-sensitive techniques, pristine surfaces are critical to obtaining accurate measurements.

For this study, coauthor Genda Gu, a physicist in the division’s Neutron Scattering Group, grew bulk BSCCO crystals. Drozdov annealed the cleaved crystals in ozone in the OMBE chamber at OASIS to increase the doping until superconductivity was completely lost. The same sample was then annealed in vacuum in order to gradually reduce the doping and increase the transition temperature at which superconductivity emerges. Valla analyzed the electronic structure of BSCCO across this doping-temperature phase diagram through ARPES.

“ARPES gives you the most direct picture of the electronic structure of any material,” said Valla. “Light excites electrons from a sample, and by measuring their energy and the angle at which they escape, you can recreate the energy and momentum of the electrons while they were still in the crystal.”

In measuring this energy-versus-momentum relationship, Valla detected a kink (anomaly) in the electronic structure that follows the superconducting transition temperature. The kink becomes more pronounced and shifts to higher energies as this temperature increases and superconductivity gets stronger, but disappears outside of the superconducting state. On the basis of this information, he knew that the interaction creating the electron pairs required for superconductivity could not be electron-phonon coupling, as theorized for conventional superconductors. Under this theory, phonons, or vibrations of atoms in the crystal lattice, serve as an attractive force for otherwise repulsive electrons through the exchange of momentum and energy.

“Our result allowed us to rule out electron-phonon coupling because atoms in the lattice can vibrate and electrons can interact with those vibrations, regardless of whether the material is superconducting or not,” said Valla. “If phonons were involved, we would expect to see the kink in both the superconducting and normal state, and the kink would not be changing with doping.”

The team believes that something similar to electron-phonon coupling is going on in this case, but instead of phonons, another excitation gets exchanged between electrons. It appears that electrons are interacting through spin fluctuations, which are related to electrons themselves. Spin fluctuations are changes in electron spin, or the way that electrons point either up or down as tiny magnets.

Moreover, the scientists found that the energy of the kink is less than that of a characteristic energy at which a sharp peak (resonance) in the spin fluctuation spectrum appears. Their finding suggests that the onset of spin fluctuations (instead of the resonance peak) is responsible for the observed kink and may be the “glue” that binds electrons into the pairs required for HTS.

Next, the team plans to collect additional evidence showing that spin fluctuations are related to superconductivity by obtaining SI-STM measurements. They will also perform similar experiments on another well-known cuprate, lanthanum strontium copper oxide (LSCO).

“For the first time, we are seeing something that strongly correlates with superconductivity,” said Valla. “After all these years, we now have a better grasp of what may be causing superconductivity in not only BSCCO but also other cuprates.”

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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 Penn Today: “Looking to mud to study how particles become sticky”

From Penn Today

February 5, 2020
Katherine Unger Baillie

A collaboration of geophysicists and fluids mechanics experts led to a fundamental new insight into how tiny ‘bridges’ help particles of all kinds form aggregates.

Using a model system of glass particles, researchers from Penn found “solid bridges” formed by smaller-size particles between larger ones. The same bridges were present in suspensions of clay, a common component of natural soils. These structures provided stability, the team found, even when a moving channel of water threatened to wash the particle clumps away. (Video: Jerolmack laboratory)

Tiny ‘bridges’ help particles stick together. Credit: CC0 Public Domain

It happens outside every time it rains: The soil gets wet and may form sticky mud. Then it dries. Later it might rain again. Each wetting and rewetting affects the structure and stability of the soil. These changes are taken into account when, for example, architects and engineers design, site, and construct buildings. But more broadly, the science of how particles stick together and then pull apart touches fields as diverse as natural hazards, crop fertilization, cement production, and pharmaceutical design.

Uniting these disparate fields, a team at the University of Pennsylvania has found that when particles are wet and then allowed to dry, the size of those particles has a lot to do with how strongly they stick together and whether they stay together or fall apart the next time they are wetted.

What lends these sticky aggregates strength, the team found, are thin bridges formed when particles of the material are suspended in a liquid and then left to dry, leaving thin strands of particles that connect larger clumps. The strands, which the researchers call solid bridges, increase the aggregates’ stability 10- to 100-fold.

The researchers reported their findings in the journal Proceedings of the National Academy of Sciences.

“This solid bridging phenomenon may be ubiquitous and important in understanding the strength and erodibility of natural soils,” says Paulo Arratia, a fluid mechanics engineer in Penn’s School of Engineering and Applied Science and a coauthor on the study.

“We found that a particle’s size can outweigh the contribution of its chemical properties when it comes to determining how strongly it sticks to other particles,” says Douglas Jerolmack, a geophysicist in the School of Arts and Sciences and the paper’s corresponding author.

The research team was led by Ali Seiphoori, formerly a postdoc in Jerolmack’s lab and now at the Massachusetts Institute of Technology, and included physics postdoc Xiao-guang Ma. The current work developed from investigations they had been pursuing in conjunction with Penn’s Perelman School of Medicine on asbestos, specifically how its needle-like fibers stick to one other and to other materials to form aggregates. That got them thinking more generally about what determines the strength and stability of an aggregate.

The group took an experimental approach to answering this question by creating a simple model of particle aggregation. They suspended glass spheres of two sizes, 3 microns and 20 microns, in a droplet of water. (For reference, a human hair is roughly 50 to 100 microns in width.) As the water evaporated, the edges of the droplet retreated, dragging the particles inward. Eventually the shrinking water droplet transformed into multiple smaller droplets connected by a thin water bridge, known as a capillary bridge, before that, too, evaporated.

The team found that the extreme suction pressures caused by evaporation pulled the small particles so tightly together that they fused together in the capillary bridges, leaving behind solid bridges between the larger particles, to which they also bound, once the water evaporated completely.

When the team rewet the particles, applying water in a controlled flow, they found that aggregates composed solely of the 20-micron particles were much easier to disrupt and resuspend than those composed of either the smaller particles, or mixtures of small and larger particles.

“We found that if aggregates composed of only particles larger than 5 microns were rewet, they collapsed,” Jerolmack says. “But under 5 microns, nothing happens, the aggregates were stable.”

In further tests with mixtures of particles of five different sizes—more closely mimicking natural soil composition—the researchers found the same bridging effect at different scales. The largest particles were bridged by the second largest, which were in turn bridged by the third largest, and so on. Even mixtures that contained only a small fraction of smaller particles became more stable thanks to solid bridging.

How much more stable? To find out, Seiphoori painstakingly glued the probe of an atomic-force microscope to a single particle, let it set, and then quantified the “pull-off force” required to remove that particle from the aggregate. Repeating this for particles in aggregates of both big and small particles, they found that particles were 10 to 100 times harder to pull off when they had formed a solid bridge structure than in other configurations.

To convince themselves that the same would be true with materials besides their experimental glass beads, they performed similar experiments using two types of clay that are both common components of natural soils. The principals held; the smaller clay particles and the presence of solid bridges made aggregates stable. And the reverse was also true. When clay particles smaller than 5 microns were removed from the suspensions, their resulting aggregates lost cohesion.

“Clay soils are thought to be fundamentally cohesive,” says Jerolmack, “and that cohesiveness has usually been attributed to their charge or some other mineralogic property. But we found this very surprising thing that it doesn’t seem to be the fundamental properties of clay that make it sticky but rather the fact that clay particles tend to be very small. It’s a brand-new explanation for cohesion.”

These new insights about the contribution of particle size to aggregate stability open up new possibilities for considering how to enhance stability of materials like soil or cement when desired. “You could envision stabilizing soils before a construction project by adding smaller particles that help bind the soil together,” Jerolmack says.

In addition, the production of a variety of materials, from medical devices to LED screen coatings, relies on thin film deposition, which the researchers say might benefit from the controlled production of aggregates that they observed in their experiments.

See the full article here .

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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 MIT News: “Engineers mix and match materials to make new stretchy electronics”

From MIT News

February 5, 2020
Jennifer Chu

With a new technique, MIT researchers can peel and stack thin films of metal oxides — chemical compounds that can be designed to have unique magnetic and electronic properties. The films can be mixed and matched to create multi-functional, flexible electronic devices, such as solar-powered skins and electronic fabrics. Image: Felice Frankel

MIT researchers, from left to right: Kuan Qiao, Jeehwan Kim, Hyun S. Kum, Wei Kong, Sang-Hoon Bae, Jaewoo Shim, Sangho Lee, Chanyeol Choi. Image: Kuan Qiao

Next-generation devices made with new “peel and stack” method may include electronic chips worn on the skin.

At the heart of any electronic device is a cold, hard computer chip, covered in a miniature city of transistors and other semiconducting elements. Because computer chips are rigid, the electronic devices that they power, such as our smartphones, laptops, watches, and televisions, are similarly inflexible.

Now a process developed by MIT engineers may be the key to manufacturing flexible electronics with multiple functionalities in a cost-effective way.

The process is called “remote epitaxy” and involves growing thin films of semiconducting material on a large, thick wafer of the same material, which is covered in an intermediate layer of graphene. Once the researchers grow a semiconducting film, they can peel it away from the graphene-covered wafer and then reuse the wafer, which itself can be expensive depending on the type of material it’s made from. In this way, the team can copy and peel away any number of thin, flexible semiconducting films, using the same underlying wafer.

In a paper published today in the journal Nature, the researchers demonstrate that they can use remote epitaxy to produce freestanding films of any functional material. More importantly, they can stack films made from these different materials, to produce flexible, multifunctional electronic devices.

The researchers expect that the process could be used to produce stretchy electronic films for a wide variety of uses, including virtual reality-enabled contact lenses, solar-powered skins that mold to the contours of your car, electronic fabrics that respond to the weather, and other flexible electronics that seemed until now to be the stuff of Marvel movies.

“You can use this technique to mix and match any semiconducting material to have new device functionality, in one flexible chip,” says Jeehwan Kim, an associate professor of mechanical engineering at MIT. “You can make electronics in any shape.”

Kim’s co-authors include Hyun S. Kum, Sungkyu Kim, Wei Kong, Kuan Qiao, Peng Chen, Jaewoo Shim, Sang-Hoon Bae, Chanyeol Choi, Luigi Ranno, Seungju Seo, Sangho Lee, Jackson Bauer, and Caroline Ross from MIT, along with collaborators from the University of Wisconsin at Madison, Cornell University, the University of Virginia, Penn State University, Sun Yat-Sen University, and the Korea Atomic Energy Research Institute.

Buying time

Kim and his colleagues reported their first results using remote epitaxy in 2017. Then, they were able to produce thin, flexible films of semiconducting material by first placing a layer of graphene on a thick, expensive wafer made from a combination of exotic metals. They flowed atoms of each metal over the graphene-covered wafer and found the atoms formed a film on top of the graphene, in the same crystal pattern as the underlying wafer. The graphene provided a nonstick surface from which the researchers could peel away the new film, leaving the graphene-covered wafer, which they could reuse.

In 2018, the team showed that they could use remote epitaxy to make semiconducting materials from metals in groups 3 and 5 of the periodic table, but not from group 4. The reason, they found, boiled down to polarity, or the respective charges between the atoms flowing over graphene and the atoms in the underlying wafer.

Since this realization, Kim and his colleagues have tried a number of increasingly exotic semiconducting combinations. As reported in this new paper, the team used remote epitaxy to make flexible semiconducting films from complex oxides — chemical compounds made from oxygen and at least two other elements. Complex oxides are known to have a wide range of electrical and magnetic properties, and some combinations can generate a current when physically stretched or exposed to a magnetic field.

Kim says the ability to manufacture flexible films of complex oxides could open the door to new energy-havesting devices, such as sheets or coverings that stretch in response to vibrations and produce electricity as a result. Until now, complex oxide materials have only been manufactured on rigid, millimeter-thick wafers, with limited flexibility and therefore limited energy-generating potential.

The researchers did have to tweak their process to make complex oxide films. They initially found that when they tried to make a complex oxide such as strontium titanate (a compound of strontium, titanium, and three oxygen atoms), the oxygen atoms that they flowed over the graphene tended to bind with the graphene’s carbon atoms, etching away bits of graphene instead of following the underlying wafer’s pattern and binding with strontium and titanium. As a surprisingly simple fix, the researchers added a second layer of graphene.

“We saw that by the time the first layer of graphene is etched off, oxide compounds have already formed, so elemental oxygen, once it forms these desired compounds, does not interact as heavily with graphene,” Kim explains. “So two layers of graphene buys some time for this compound to form.”

Peel and stack

The team used their newly tweaked process to make films from multiple complex oxide materials, peeling off each 100-nanometer-thin layer as it was made. They were also able to stack together layers of different complex oxide materials and effectively glue them together by heating them slightly, producing a flexible, multifunctional device.

“This is the first demonstration of stacking multiple nanometers-thin membranes like LEGO blocks, which has been impossible because all functional electronic materials exist in a thick wafer form,” Kim says.

In one experiment, the team stacked together films of two different complex oxides: cobalt ferrite, known to expand in the presence of a magnetic field, and PMN-PT, a material that generates voltage when stretched. When the researchers exposed the multilayer film to a magnetic field, the two layers worked together to both expand and produce a small electric current.

The results demonstrate that remote epitaxy can be used to make flexible electronics from a combination of materials with different functionalities, which previously were difficult to combine into one device. In the case of cobalt ferrite and PMN-PT, each material has a different crystalline pattern. Kim says that traditional epitaxy techniques, which grow materials at high temperatures on one wafer, can only combine materials if their crystalline patterns match. He says that with remote epitaxy, researchers can make any number of different films, using different, reusable wafers, and then stack them together, regardless of their crystalline pattern.

“The big picture of this work is, you can combine totally different materials in one place together,” Kim says. “Now you can imagine a thin, flexible device made from layers that include a sensor, computing system, a battery, a solar cell, so you could have a flexible, self-powering, internet-of-things stacked chip.”

The team is exploring various combinations of semiconducting films and is working on developing prototype devices, such as something Kim is calling an “electronic tattoo” — a flexible, transparent chip that can attach and conform to a person’s body to sense and wirelessly relay vital signs such as temperature and pulse.

“We can now make thin, flexible, wearable electronics with the highest functionality,” Kim says. “Just peel off and stack up.”

This research was supported, in part, by the U.S. Defense Advanced Research Projects Agency.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

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 Arizona State University: “Science at the interface: Bioinspired materials reveal useful properties”

From Arizona State University

January 27, 2020

The design of sophisticated new materials is undergoing brisk technological advancement. Innovations in material science promise transformative improvements in industries ranging from energy to manufacturing.

In a new study, researchers at ASU’s Biodesign Institute and their colleagues explore new materials with physical properties that can be custom-tailored to suit particular needs. The work is inspired by mechanisms in nature, where the complex three-dimensional structure of surrounding proteins influences the electrochemical properties of metals at their core.

The advances could have broad implications for the design of many new innovations useful for semiconductor technology, sustainable energy and industrial production.

Material world

Lead author Brian Wadsworth and his collaborators describe techniques for immobilizing metal complexes onto physical supports that are both transparent and conductive. The resulting hybrid materials permit synthetic control over the configuration, allowing researchers to regulate the shuttling of electrons within the composite material.

Precise control over material performance may be accomplished through modification of material interfaces. According to corresponding author Gary Moore, “any time two things touch each other, they form an interface. Material interfaces are central to our work.” It is in these regions that modifications designed to adjust a material’s physical properties take place.

The current study extends the group’s earlier efforts with semiconductor materials, which involved the capture and conversion of solar energy to produce fuels. Accomplishing this requires the ability to control reactions and chemical entities that increase their rate, known as catalysts. “Our use of molecules on surfaces can have a wide range of applications, including solar energy conversion, catalysis, and chemical manufacturing via green chemistry,” Moore says.

In addition to Wadsworth and Moore, both researchers in the Biodesign Center for Applied Structural Discovery, the team includes Diana Khusnutdinova and Jennifer M. Urbine, (formerly with the Biodesign Institute and currently at Intel and the doctoral program at UC Irvine, respectively). Ahlea S. Reyes, who began working in the Moore lab as a high school student and is currently an undergraduate at ASU, also contributed to the new study.

The research graces the cover of the latest issue of the journal ACS Applied Materials & Interfaces.

Control center

Catalysts play a vital role in processes involving the conversion of energy and are important in both biology and technology. The current study provides valuable information that could lead to advances in efficiency, reliability and scalability of sustainable energy solutions. The mounting energy crisis puts efforts to better understand the electrochemistry of new materials on the fast track and opens far-reaching possibilities for new technologies.

Conventional catalysts like those used in industry are usually based on two-dimensional surfaces. Here, reactants are brought together in order to produce a desired product. Catalysts speed up the rate of such reactions. One of the most basic transformations is hydrogen production, where electrons and protons are brought together to form molecular hydrogen. In this case, platinum is commonly used as a catalyst.

Nature, however, has found a cheaper and more efficient means of hydrogen production. “Biology doesn’t use two dimensional sheets of platinum,” Moore explains. Instead, life forms carry out this transformation with the aid of specialized enzymes. “Enzymes often contain metal centers where the reactivity is occurring, but their specificity comes from their unique three-dimensional structures.”

Their unique approach results in materials inspired by such three-dimensional architectures in order to guide reactions that bring together multiple substrates— substances on which catalysts act. Creating three-dimensional soft matter environments, similar to those found in proteins, permits researchers to apply fine-grained control of these reactions in both space and time.

“Brian has worked out an approach to attach relatively thin molecular coatings, including polymers, onto an electrode surface,” Moore says. “Now these electrode surfaces have three-dimensional molecular environments, where we can purposefully deposit a metal center.” These metal centers are the sites of so-called reduction-oxidation or redox reactions, where electrons are gained or lost.

Overcoming metal fatigue

The method helps overcome one of the primary limiting factors in designing effective catalysts. Conventional catalysts typically use rare earth metals like platinum, which, as their name implies, are scarce and very costly. Instead, by creating a three-dimensional hybrid material consisting of structurally well-defined homogeneous components that are bonded to a heterogeneous support structure, the synthetic material can be made with far cheaper and more earth-abundant metals like cobalt (used in the current study). The authors stress that these innovations can not only reduce the cost of new materials but improve their efficiency and stability as well. “Again, that’s the bio-inspired part of our vision for developing these molecular coatings,” Moore says.

In order to design the new material, Wadsworth uses some of the sophisticated attachment chemistries developed in earlier work on light-gathering semiconductors. Experiments described in the new paper investigate the effects of applying these chemistries to the surfaces of conducting materials. This enables the researchers to directly probe the electrochemical properties of the embedded metal centers. “We’re getting mechanistic information on how the soft material or protein-like environments control the chemistry occurring at the metal center,” Wadsworth says.

Once the metal-containing complexes are bound to the electrode surface, the surrounding molecular environment can be subtly modified to alter the redox responses. “Every chemical transformation involves changes in structure and energy that are associated with a chemical potential,” Moore says. “The coatings reported in this work enable the surface-immobilized metal centers to operate across a relatively large span of potentials for applications in a range of chemical processes and emerging technologies.”

Catalyzing research

Some of these new ideas were recently discussed at the Winter Inter-American Photochemical Society (I-APS) Conference, which took place in Sarasota, Florida, January 2-5, 2020. The lively conference was co-organized by Moore and his colleague Elizabeth Young of Lehigh University and brought together leading scientists in all areas of the photochemical sciences, from North and South America.

At the meeting, Wadsworth presented a poster titled “Bridging Concepts between Heterogeneous-, Homogeneous-, and Bio-Catalysis to Model Photoelectrosynthetic Reactions” and received an award supported by the journal ACS Applied Materials & Interfaces, (the same journal featuring the current research cover story).

The researchers believe one of the strengths of bio-inspired and molecular-based strategies is the diversity in structure and function this approach enables. “Diversity brings increased creativity and promotes innovation. This notion is leveraged not only in the materials we construct, but also in the team of researchers that guide the ongoing evolution of our science,” Moore says. “The current work features contributions from high school, undergraduate, graduate, and postgraduate students from across the globe.”

In addition to his research position at the Biodesign Institute, Moore is assistant professor in the School of Molecular Sciences at ASU, a Julie Ann Wrigley Global Institute for Sustainability scholar and guest faculty at Berkeley Lab. Moore’s research efforts and role as an exceptional scientific mentor were honored with a 2016 NSF CAREER Award.

See the full article here .

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Please help promote STEM in your local schools.

Stem Education Coalition

ASU is the largest public university by enrollment in the United States. Founded in 1885 as the Territorial Normal School at Tempe, the school underwent a series of changes in name and curriculum. In 1945 it was placed under control of the Arizona Board of Regents and was renamed Arizona State College. A 1958 statewide ballot measure gave the university its present name.
ASU is classified as a research university with very high research activity (RU/VH) by the Carnegie Classification of Institutions of Higher Education, one of 78 U.S. public universities with that designation. Since 2005 ASU has been ranked among the Top 50 research universities, public and private, in the U.S. based on research output, innovation, development, research expenditures, number of awarded patents and awarded research grant proposals. The Center for Measuring University Performance currently ranks ASU 31st among top U.S. public research universities.

ASU awards bachelor’s, master’s and doctoral degrees in 16 colleges and schools on five locations: the original Tempe campus, the West campus in northwest Phoenix, the Polytechnic campus in eastern Mesa, the Downtown Phoenix campus and the Colleges at Lake Havasu City. ASU’s “Online campus” offers 41 undergraduate degrees, 37 graduate degrees and 14 graduate or undergraduate certificates, earning ASU a Top 10 rating for Best Online Programs. ASU also offers international academic program partnerships in Mexico, Europe and China. ASU is accredited as a single institution by The Higher Learning Commission.

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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Please help promote STEM in your local schools.

Stem Education Coalition

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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Please help promote STEM in your local schools.

Stem Education Coalition

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.

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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.