From Caltech: “New Metamaterial Morphs Into New Shapes, Taking on New Properties”

From Caltech

September 11, 2019

Robert Perkins
(626) 395‑1862
rperkins@caltech.edu

A newly developed type of architected metamaterial has the ability to change shape in a tunable fashion.

While most reconfigurable materials can toggle between two distinct states, the way a switch toggles on or off, the new material’s shape can be finely tuned, adjusting its physical properties as desired. The material, which has potential applications in next-generation energy storage and bio-implantable micro-devices, was developed by a joint Caltech-Georgia Tech-ETH Zürich team in the lab of Julia R. Greer.

Greer, the Ruben F. and Donna Mettler Professor of Materials Science, Mechanics and Medical Engineering in Caltech’s Division of Engineering and Applied Science, creates materials out of micro- and nanoscale building blocks that are arranged into sophisticated architectures that can be periodic, like a lattice, or non-periodic in a tailor-made fashion, giving them unusual physical properties.

Most materials that are designed to change shape require a persistent external stimulus to change from one shape to another and stay that way: for example, they may be one shape when wet and a different shape when dry—like a sponge that swells as it absorbs water.

By contrast, the new nanomaterial deforms through an electrochemically driven silicon-lithium alloying reaction, meaning that it can be finely controlled to attain any “in-between” states, remain in these configurations even upon the removal of the stimulus, and be easily reversed. Apply a little current, and a resulting chemical reaction changes the shape by a controlled, small degree. Apply a lot of current, and the shape changes substantially. Remove the electrical control, and the configuration is retained—just like tying off a balloon. A description of the new type of material was published online by the journal Nature on September 11.

Defects and imperfections exist in all materials, and can often determine a material’s properties. In this case, the team chose to take advantage of that fact and build in defects to imbue the material with the properties they wanted.

“The most intriguing part of this work to me is the critical role of defects in such dynamically responsive architected materials,” says Xiaoxing Xia, a graduate student at Caltech and lead author of the Nature paper.

For the Nature paper, the team designed a silicon-coated lattice with microscale straight beams that bend into curves under electrochemical stimulation, taking on unique mechanical and vibrational properties. Greer’s team created these materials using an ultra-high-resolution 3D printing process called two-photon lithography. Using this novel fabrication method, they were able to build in defects in the architected material system, based on a pre-arranged design. In a test of the system, the team fabricated a sheet of the material that, under electrical control, reveals a Caltech icon.

“This just further shows that materials are just like people, it’s the imperfections that make them interesting. I have always had a particular liking for defects, and this time Xiaoxing managed to first uncover the effect of different types of defects on these metamaterials and then use them to program a particular pattern that would emerge in response to electrochemical stimulus,” says Greer.

A material with such a finely controllable ability to change shape has potential in future energy storage systems because it provides a pathway to create adaptive energy storage systems that would enable batteries, for example, to be significantly lighter, safer, and to have substantially longer lives, Greer says. Some battery materials expand when storing energy, creating a mechanical degradation due to stress from the repeated expanding and contracting. Architected materials like this one can be designed to handle such structural transformations.

“Electrochemically active metamaterials provide a novel pathway for development of next generation smart batteries with both increased capacity and novel functionalities. At Georgia Tech, we are developing the computational tools to predict this complex coupled electro-chemo-mechanical behavior,” says Claudio V. Di Leo, assistant professor of aerospace engineering at the Georgia Institute of Technology.

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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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From MIT News: “Creating new opportunities from nanoscale materials”

From MIT News

September 5, 2019
Denis Paiste | Materials Research Laboratory

Left to right: Postdoc Shu Fen Tan, graduate student Kate Reidy, and Professor Frances Ross, all of the Department of Materials Science and Engineering, sit in front of a high vacuum evaporator system. The equipment was housed temporarily in MIT.nano while Ross’s lab was built out in Building 13. Photo: Denis Paiste/Materials Research Laboratory.

MIT Professor Frances Ross has designed several custom sample holders for examining nanoscale materials in gases and liquid media in the electron microscope. For liquid environments, thin windows of silicon nitride surround the liquid but allow the electron beam to pass through. For gas environments, the sample holder (shown here) must heat and tilt the sample without compromising its cleanliness. Photo: Denis Paiste/Materials Research Laboratory.

When gold is deposited on “dirty” graphene (left), blobs of gold collect around impurities. But when gold grows on graphene that has been heated and cleansed of impurities (right), it forms perfect triangles of gold. Images: Kate Reidy/MIT.

Professor Frances Ross (left), graduate student Kate Reidy (center), and postdoc Shu Fen Tan work together at the high vacuum evaporator chamber that is part of an electron microscopy suite donated to MIT by IBM. Photo: Denis Paiste/Materials Research Laboratory.

Niobium deposited on top of graphene produces structures that look like the frost patterns formed on the inside of windows in winter, or the feathery patterns of some ferns. They are called dendritic structures. Image: Kate Reidy/MIT.

An electron diffraction image of niobium deposited on top of graphene shows that certain crystal planes of niobium align with the crystal planes of the graphene, which is known as epitaxial growth. When a 3-D material is grown on top of a 2-D layer, this perfectly aligned atomic arrangement is often important for device makers. Image: Kate Reidy/MIT.

Clean deposition of gold nanoislands on molybdenum disulfide MoS2 with visible moiré patterns. Image: Kate Reidy/MIT.

A hundred years ago, “2d” meant a two-penny, or 1-inch, nail. Today, “2-D” encompasses a broad range of atomically thin flat materials, many with exotic properties not found in the bulk equivalents of the same materials, with graphene — the single-atom-thick form of carbon — perhaps the most prominent. While many researchers at MIT and elsewhere are exploring two-dimensional materials and their special properties, Frances M. Ross, the Ellen Swallow Richards Professor in Materials Science and Engineering, is interested in what happens when these 2-D materials and ordinary 3-D materials come together.

“We’re interested in the interface between a 2-D material and a 3-D material because every 2-D material that you want to use in an application, such as an electronic device, still has to talk to the outside world, which is three-dimensional,” Ross says.

“We’re at an interesting time because there are immense developments in instrumentation for electron microscopy, and there is great interest in materials with very precisely controlled structures and properties, and these two things cross in a fascinating way,” says Ross.

“The opportunities are very exciting,” Ross says. “We’re going to be really improving the characterization capabilities here at MIT.” Ross specializes in examining how nanoscale materials grow and react in both gases and liquid media, by recording movies using electron microscopy. Microscopy of reactions in liquids is particularly useful for understanding the mechanisms of electrochemical reactions that govern the performance of catalysts, batteries, fuel cells, and other important technologies. “In the case of liquid phase microscopy, you can also look at corrosion where things dissolve away, while in gases you can look at how individual crystals grow or how materials react with, say, oxygen,” she says.

Ross joined the Department of Materials Science and Engineering (DMSE) faculty last year, moving from the nanoscale materials analysis department at the IBM Thomas J. Watson Research Center. “I learned a tremendous amount from my IBM colleagues and hope to extend our research in material design and growth in new directions,” she says.

Recording movies

During a recent visit to her lab, Ross explained an experimental setup donated to MIT by IBM. An ultra-high vacuum evaporator system arrived first, to be attached later directly onto a specially designed transmission electron microscope. “This gives powerful possibilities,” Ross explains. “We can put a sample in the vacuum, clean it, do all sorts of things to it such as heating and adding other materials, then transfer it under vacuum into the microscope, where we can do more experiments while we record images. So we can, for example, deposit silicon or germanium, or evaporate metals, while the sample is in the microscope and the electron beam is shining through it, and we are recording a movie of the process.”

While waiting this spring for the transmission electron microscope to be set up, members of Ross’ seven-member research group, including materials science and engineering postdoc Shu Fen Tan and graduate student Kate Reidy, made and studied a variety of self-assembled structures. The evaporator system was housed temporarily on the fifth-level prototyping space of MIT.nano while Ross’s lab was being readied in Building 13. “MIT.nano had the resources and space; we were happy to be able to help,” says Anna Osherov, MIT.nano assistant director of user services.

“All of us are interested in this grand challenge of materials science, which is: ‘How do you make a material with the properties you want and, in particular, how do you use nanoscale dimensions to tweak the properties, and create new properties, that you can’t get from bulk materials?’” Ross says.

Using the ultra-high vacuum system, graduate student Kate Reidy formed structures of gold and niobium on several 2-D materials. “Gold loves to grow into little triangles,” Ross notes. “We’ve been talking to people in physics and materials science about which combinations of materials are the most important to them in terms of controlling the structures and the interfaces between the components in order to give some improvement in the properties of the material,” she notes.

Shu Fen Tan synthesized nickel-platinum nanoparticles and examined them using another technique, liquid cell electron microscopy. She could arrange for only the nickel to dissolve, leaving behind spiky skeletons of platinum. “Inside the liquid cell, we are able to see this whole process at high spatial and temporal resolutions,” Tan says. She explains that platinum is a noble metal and less reactive than nickel, so under the right conditions the nickel participates in an electrochemical dissolution reaction and the platinum is left behind.

Platinum is a well-known catalyst in organic chemistry and fuel cell materials, Tan notes, but it is also expensive, so finding combinations with less-expensive materials such as nickel is desirable.

“This is an example of the range of materials reactions you can image in the electron microscope using the liquid cell technique,” Ross says. “You can grow materials; you can etch them away; you can look at, for example, bubble formation and fluid motion.”

A particularly important application of this technique is to study cycling of battery materials. “Obviously, I can’t put an AA battery in here, but you could set up the important materials inside this very small liquid cell and then you can cycle it back and forth and ask, if I charge and discharge it 10 times, what happens? It does not work just as well as before — how does it fail?” Ross asks. “Some kind of failure analysis and all the intermediate stages of charging and discharging can be observed in the liquid cell.”

“Microscopy experiments where you see every step of a reaction give you a much better chance of understanding what’s going on,” Ross says.

Moiré patterns

Graduate student Reidy is interested in how to control the growth of gold on 2-D materials such as graphene, tungsten diselenide, and molybdenum disulfide. When she deposited gold on “dirty” graphene, blobs of gold collected around the impurities. But when Reidy grew gold on graphene that had been heated and cleaned of impurities, she found perfect triangles of gold. Depositing gold on both the top and bottom sides of clean graphene, Reidy saw in the microscope features known as moiré patterns, which are caused when the overlapping crystal structures are out of alignment.

Physicists at MIT and Harvard University have found that graphene, a lacy, honeycomb-like sheet of carbon atoms, can behave at two electrical extremes: as an insulator, in which electrons are completely blocked from flowing; and as a superconductor, in which electrical current can stream through without resistance. Courtesy of the researchers.

The gold triangles may be useful as photonic and plasmonic structures. “We think this could be important for a lot of applications, and it is always interesting for us to see what happens,” Reidy says. She is planning to extend her clean growth method to form 3-D metal crystals on stacked 2-D materials with various rotation angles and other mixed-layer structures. Reidy is interested in the properties of graphene and hexagonal boron nitride (hBN), as well as two materials that are semiconducting in their 2-D single-layer form, molybdenum disulfide (MoS2) and tungsten diselenide (WSe2). “One aspect that’s very interesting in the 2-D materials community is the contacts between 2-D materials and 3-D metals,” Reidy says. “If they want to make a semiconducting device or a device with graphene, the contact could be ohmic for the graphene case or a Schottky contact for the semiconducting case, and the interface between these materials is really, really important.”

“You can also imagine devices using the graphene just as a spacer layer between two other materials,” Ross adds.

For device makers, Reidy says it is sometimes important to have a 3-D material grow with its atomic arrangement aligned perfectly with the atomic arrangement in the 2-D layer beneath. This is called epitaxial growth. Describing an image of gold grown together with silver on graphene, Reidy explains, “We found that silver doesn’t grow epitaxially, it doesn’t make those perfect single crystals on graphene that we wanted to make, but by first depositing the gold and then depositing silver around it, we can almost force silver to go into an epitaxial shape because it wants to conform to what its gold neighbors are doing.”

Electron microscope images can also show imperfections in a crystal such as rippling or bending, Reidy notes. “One of the great things about electron microscopy is that it is very sensitive to changes in the arrangement of the atoms,” Ross says. “You could have a perfect crystal and it would all look the same shade of gray, but if you have a local change in the structure, even a subtle change, electron microscopy can pick it up. Even if the change is just within the top few layers of atoms without affecting the rest of the material beneath, the image will show distinctive features that allow us to work out what’s going on.”

Reidy also is exploring the possibilities of combining niobium — a metal that is superconducting at low temperatures — with a 2-D topological insulator, bismuth telluride. Topological insulators have fascinating properties whose discovery resulted in the Nobel Prize in Physics in 2016. “If you deposit niobium on top of bismuth telluride, with a very good interface, you can make superconducting junctions. We’ve been looking into niobium deposition, and rather than triangles we see structures that are more dendritic looking,” Reidy says. Dendritic structures look like the frost patterns formed on the inside of windows in winter, or the feathery patterns of some ferns. Changing the temperature and other conditions during the deposition of niobium can change the patterns that the material takes.

All the researchers are eager for new electron microscopes to arrive at MIT.nano to give further insights into the behavior of these materials. “Many things will happen within the next year, things are ramping up already, and I have great people to work with. One new microscope is being installed now in MIT.nano and another will arrive next year. The whole community will see the benefits of improved microscopy characterization capabilities here,” Ross says.

MIT.nano’s Osherov notes that two cryogenic transmission electron microscopes (cryo-TEM) are installed and running. “Our goal is to establish a unique microscopy-centered community. We encourage and hope to facilitate a cross-pollination between the cryo-EM researchers, primarily focused on biological applications and ‘soft’ material, as well as other research communities across campus,” she says. The latest addition of a scanning transmission electron microscope with enhanced analytical capabilities (ultrahigh energy resolution monochromator, 4-D STEM detector, Super-X EDS detector, tomography, and several in situ holders) brought in by John Chipman Associate Professor of Materials Science and Engineering James M. LeBeau, once installed, will substantially enhance the microscopy capabilities of the MIT campus. “We consider Professor Ross to be an immense resource for advising us in how to shape the in situ approach to measurements using the advanced instrumentation that will be shared and available to all the researchers within the MIT community and beyond,” Osherov says.

Little drinking straws

“Sometimes you know more or less what you are going to see during a growth experiment, but very often there’s something that you don’t expect,” Ross says. She shows an example of zinc oxide nanowires that were grown using a germanium catalyst. Some of the long crystals have a hole through their centers, creating structures which are like little drinking straws, circular outside but with a hexagonally shaped interior. “This is a single crystal of zinc oxide, and the interesting question for us is why do the experimental conditions create these facets inside, while the outside is smooth?” Ross asks. “Metal oxide nanostructures have so many different applications, and each new structure can show different properties. In particular, by going to the nanoscale you get access to a diverse set of properties.”

“Ultimately, we’d like to develop techniques for growing well-defined structures out of metal oxides, especially if we can control the composition at each location on the structure,” Ross says. A key to this approach is self-assembly, where the material builds itself into the structure you want without having to individually tweak each component. “Self-assembly works very well for certain materials but the problem is that there’s always some uncertainty, some randomness or fluctuations. There’s poor control over the exact structures that you get. So the idea is to try to understand self-assembly well enough to be able to control it and get the properties that you want,” Ross says.

“We have to understand how the atoms end up where they are, then use that self-assembly ability of atoms to make a structure we want. The way to understand how things self-assemble is to watch them do it, and that requires movies with high spatial resolution and good time resolution,” Ross explains. Electron microscopy can be used to acquire structural and compositional information and can even measure strain fields or electric and magnetic fields. “Imagine recording all of these things, but in a movie where you are also controlling how materials grow within the microscope. Once you have made a movie of something happening, you analyze all the steps of the growth process and use that to understand which physical principles were the key ones that determined how the structure nucleated and evolved and ended up the way it does.”

Future directions

Ross hopes to bring in a unique high-resolution, high vacuum TEM with capabilities to image materials growth and other dynamic processes. She intends to develop new capabilities for both water-based and gas-based environments. This custom microscope is still in the planning stages but will be situated in one of the rooms in the Imaging Suite in MIT.nano.

“Professor Ross is a pioneer in this field,” Osherov says. “The majority of TEM studies to-date have been static, rather than dynamic. With static measurements you are observing a sample at one particular snapshot in time, so you don’t gain any information about how it was formed. Using dynamic measurements, you can look at the atoms hopping from state to state until they find the final position. The ability to observe self-assembling processes and growth in real time provides valuable mechanistic insights. We’re looking forward to bringing these advanced capabilities to MIT.nano.” she says.

“Once a certain technique is disseminated to the public, it brings attention,” Osherov says. “When results are published, researchers expand their vision of experimental design based on available state-of-the-art capabilities, leading to many new experiments that will be focused on dynamic applications.”

Rooms in MIT.nano feature the quietest space on the MIT campus, designed to reduce vibrations and electromagnetic interference to as low a level as possible. “There is space available for Professor Ross to continue her research and to develop it further,” Osherov says. “The ability of in situ monitoring the formation of matter and interfaces will find applications in multiple fields across campus, and lead to a further push of the conventional electron microscopy limits.”

See the full article here .

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From Brookhaven National Lab: “Smarter Experiments for Faster Materials Discovery”

From Brookhaven National Lab

August 28, 2019
Cara Laasch,
laasch@bnl.gov
(631) 344-8458,

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

Scientists created a new AI algorithm for making measurement decisions; autonomous approach could revolutionize scientific experiments.

(From left to right) Kevin Yager, Masafumi Fukuto, and Ruipeng Li prepared the Complex Materials Scattering (CMS) beamline at NSLS-II for a measurement using the new decision-making algorithm, which was developed by Marcus Noack (not pictured).

A team of scientists from the U.S. Department of Energy’s Brookhaven National Laboratory and Lawrence Berkeley National Laboratory designed, created, and successfully tested a new algorithm to make smarter scientific measurement decisions.

The algorithm, a form of artificial intelligence (AI), can make autonomous decisions to define and perform the next step of an experiment. The team described the capabilities and flexibility of their new measurement tool in a paper published on August 14, 2019 in Nature Scientific Reports.

From Galileo and Newton to the recent discovery of gravitational waves, performing scientific experiments to understand the world around us has been the driving force of our technological advancement for hundreds of years. Improving the way researchers do their experiments can have tremendous impact on how quickly those experiments yield applicable results for new technologies.

Over the last decades, researchers have sped up their experiments through automation and an ever-growing assortment of fast measurement tools. However, some of the most interesting and important scientific challenges—such as creating improved battery materials for energy storage or new quantum materials for new types of computers—still require very demanding and time-consuming experiments.

By creating a new decision-making algorithm as part of a fully automated experimental setup, the interdisciplinary team from two of Brookhaven’s DOE Office of Science user facilities—the Center for Functional Nanomaterials (CFN) [below] and the National Synchrotron Light Source II (NSLS-II) [below]—and Berkeley Lab’s Center for Advanced Mathematics for Energy Research Applications (CAMERA) offers the possibility to study these challenges in a more efficient fashion.

The challenge of complexity

The goal of many experiments is to gain knowledge about the material that is studied, and scientists have a well-tested way to do this: They take a sample of the material and measure how it reacts to changes in its environment.

A standard approach for scientists at user facilities like NSLS-II and CFN is to manually scan through the measurements from a given experiment to determine the next area where they might want to run an experiment. But access to these facilities’ high-end materials-characterization tools is limited, so measurement time is precious. A research team might only have a few days to measure their materials, so they need to make the most out of each measurement.

“The key to achieving a minimum number of measurements and maximum quality of the resulting model is to go where uncertainties are large,” said Marcus Noack, a postdoctoral scholar at CAMERA and lead author of the study. “Performing measurements there will most effectively reduce the overall model uncertainty.”

As Kevin Yager, a co-author and CFN scientist, pointed out, “The final goal is not only to take data faster but also to improve the quality of the data we collect. I think of it as experimentalists switching from micromanaging their experiment to managing at a higher level. Instead of having to decide where to measure next on the sample, the scientists can instead think about the big picture, which is ultimately what we as scientists are trying to do.”

“This new approach is an applied example of artificial intelligence,” said co-author Masafumi Fukuto, a scientist at NSLS-II. “The decision-making algorithm is replacing the intuition of the human experimenter and can scan through the data and make smart decisions about how the experiment should proceed.”

This animation shows a comparison between a traditional grid measurement (left) of a sample with a measurement steered by the newly-developed decision-making algorithm (right). This comparison shows that the algorithm can identify the edges and inner part of the sample and focuses the measurement in these regions to gain more knowledge about the sample.

More information for less?

In practice, before starting an experiment, the scientists define a set of goals they want to get out of the measurement. With these goals set, the algorithm looks at the previously measured data while the experiment is ongoing to determine the next measurement. On its search for the best next measurement, the algorithm creates a surrogate model of the data, which is an educated guess as to how the material will behave in the next possible steps, and calculates the uncertainty—basically how confident it is in its guess—for each possible next step. Based on this, it then selects the most uncertain option to measure next. The trick here is by picking the most uncertain step to measure next, the algorithm maximizes the amount of knowledge it gains by making that measurement. The algorithm not only maximizes the information gain during the measurement, it also defines when to end the experiment by figuring out the moment when any additional measurements would not result in more knowledge.

“The basic idea is, given a bunch of experiments, how can you automatically pick the next best one?” said James Sethian, director of CAMERA and a co-author of the study. “Marcus has built a world which builds an approximate surrogate model on the basis of your previous experiments and suggests the best or most appropriate experiment to try next.”

To use the decision-making algorithm for their measurements, the team needed to automate the measurement and also the data analysis. This image shows how all pieces are integrated with each other to form a closed looped. The algorithm receives analyzed data from the last measurement step, adds this data to its model, calculates the best next step, and sends its decision to the beamline to execute the next measurement.

How we got here

To make autonomous experiments a reality, the team had to tackle three important pieces: the automation of the data collection, real-time analysis, and, of course, the decision-making algorithm.

“This is an exciting part of this collaboration,” said Fukuto. “We all provided an essential piece for it: The CAMERA team worked on the decision-making algorithm, Kevin from CFN developed the real-time data analysis, and we at NSLS-II provided the automation for the measurements.”

The team first implemented their decision-making algorithm at the Complex Materials Scattering (CMS) beamline at NSLS-II, which the CFN and NSLS-II operate in partnership. This instrument offers ultrabright x-rays to study the nanostructure of various materials. As the lead beamline scientist of this instrument, Fukuto had already designed the beamline with automation in mind. The beamline offers a sample-exchanging robot, automatic sample movement in various directions, and many other helpful tools to ensure fast measurements. Together with Yager’s real-time data analysis, the beamline was—by design—the perfect fit for the first “smart” experiment.

The first “smart” experiment

The first fully autonomous experiment the team performed was to map the perimeter of a droplet where nanoparticles segregate using a technique called small-angle x-ray scattering at the CMS beamline. During small-angle x-ray scattering, the scientists shine bright x-rays at the sample and, depending on the atomic to nanoscale structure of the sample, the x-rays bounce off in different directions. The scientists then use a large detector to capture the scattered x-rays and calculate the properties of the sample at the illuminated spot. In this first experiment, the scientists compared the standard approach of measuring the sample with measurements taken when the new decision-making algorithm was calling the shots. The algorithm was able to identify the area of the droplet and focused on its edges and inner parts instead of the background.

“After our own initial success, we wanted to apply the algorithm more, so we reached out to a few users and proposed to test our new algorithm on their scientific problems,” said Yager. “They said yes, and since then we have measured various samples. One of the most interesting ones was a study on a sample that was fabricated to contain a spectrum of different material types. So instead of making and measuring an enormous number of samples and maybe missing an interesting combination, the user made one single sample that included all possible combinations. Our algorithm was then able to explore this enormous diversity of combinations efficiently,” he said.

What’s next?

After the first successful experiments, the scientists plan to further improve the algorithm and therefore its value to the scientific community. One of their ideas is to make the algorithm “physics-aware”—taking advantage of anything already known about material under study—so the method can be even more effective. Another development in progress is to use the algorithm during synthesis and processing of new materials, for example to understand and optimize processes relevant to advanced manufacturing as these materials are incorporated into real-world devices. The team is also thinking about the larger picture and wants to transfer the autonomous method to other experimental setups.

“I think users view the beamlines of NSLS-II or microscopes of CFN just as powerful characterization tools. We are trying to change these capabilities into a powerful material discovery facility,” Fukuto said.

This work was funded by the DOE Office of Science (ASCR and BES).

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BNL Center for Functional Nanomaterials

BNL NSLS-II

BNL NSLS II

BNL RHIC Campus

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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 SLAC National Accelerator Lab: “First report of superconductivity in a nickel oxide material”

August 28, 2019
Glennda Chui
glennda@slac.stanford.edu
(650) 926-4897

Made with ‘Jenga chemistry,’ the discovery could help crack the mystery of how high-temperature superconductors work.

An illustration depicts a key step in creating a new type of superconducting material: Much like pulling blocks from a tower in a Jenga game, scientists used chemistry to neatly remove a layer of oxygen atoms. This flipped the material into a new atomic structure – a nickelate – that can conduct electricity with 100 percent efficiency. (Greg Stewart/SLAC National Accelerator Laboratory)

Scientists at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have made the first nickel oxide material that shows clear signs of superconductivity – the ability to transmit electrical current with no loss.

Also known as a nickelate, it’s the first in a potential new family of unconventional superconductors that’s very similar to the copper oxides, or cuprates, whose discovery in 1986 raised hopes that superconductors could someday operate at close to room temperature and revolutionize electronic devices, power transmission and other technologies. Those similarities have scientists wondering if nickelates could also superconduct at relatively high temperatures.

At the same time, the new material seems different from the cuprates in fundamental ways – for instance, it may not contain a type of magnetism that all the superconducting cuprates have – and this could overturn leading theories of how these unconventional superconductors work. After more than three decades of research, no one has pinned that down.

The experiments were led by Danfeng Li, a postdoctoral researcher with the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC, and described today in Nature.

“This is a very important discovery that requires us to rethink the details of the electronic structure and possible mechanisms of superconductivity in these materials,” said George Sawatzky, a professor of physics and chemistry at the University of British Columbia who was not involved in the study but wrote a commentary that accompanied the paper in Nature. “This is going to cause an awful lot of people to jump into investigating this new class of materials, and all sorts of experimental and theoretical work will be done.”

To create a new type of superconducting material, scientists at SLAC and Stanford first made a thin film of a common material known as perovskite, left; “doped” it with strontium; and then exposed it to a chemical that yanked out a layer of oxygen atoms, much like removing a stick from a tower of Jenga blocks. This made the film flip into a different atomic structure known as a nickelate, right. Tests showed that this nickelate can conduct electricity with no resistance. (Danfeng Li/SLAC National Accelerator Laboratory and Stanford University)

A difficult path

Ever since the cuprate superconductors were discovered, scientists have dreamed of making similar oxide materials based on nickel, which is right next to copper on the periodic table of the elements.

But making nickelates with an atomic structure that’s conducive to superconductivity turned out to be unexpectedly hard.

“As far as we know, the nickelate we were trying to make is not stable at the very high temperatures – about 600 degrees Celsius – where these materials are normally grown,” Li said. “So we needed to start out with something we can stably grow at high temperatures and then transform it at lower temperatures into the form we wanted.”

He started with a perovskite – a material defined by its unique, double-pyramid atomic structure – that contained neodymium, nickel and oxygen. Then he doped the perovskite by adding strontium; this is a common process that adds chemicals to a material to make more of its electrons flow freely.

This stole electrons away from nickel atoms, leaving vacant “holes,” and the nickel atoms were not happy about it, Li said. The material was now unstable, making the next step – growing a thin film of it on a surface – really challenging; it took him half a year to get it to work.

‘Jenga chemistry’

Once that was done, Li cut the film into tiny pieces, loosely wrapped it in aluminum foil and sealed it in a test tube with a chemical that neatly snatched away a layer of its oxygen atoms – much like removing a stick from a wobbly tower of Jenga blocks. This flipped the film into an entirely new atomic structure – a strontium-doped nickelate.

SIMES researcher Danfeng Li explains the delicate ‘Jenga chemistry’ behind making a new nickel oxide material, the first in a potential new family of unconventional superconductors. (Linda McCulloch, SLAC National Accelerator Laboratory)

“Each of these steps had been demonstrated before,” Li said, “but not in this combination.”

He remembers the exact moment in the laboratory, around 2 a.m., when tests indicated that the doped nickelate might be superconducting. Li was so excited that he stayed up all night, and in the morning co-opted the regular meeting of his research group to show them what he’d found. Soon, many of the group members joined him in a round-the-clock effort to improve and study this material.

Further testing would reveal that the nickelate was indeed superconducting in a temperature range from 9-15 kelvins – incredibly cold, but a first start, with possibilities of higher temperatures ahead.

More work ahead

Research on the new material is in a “very, very early stage, and there’s a lot of work ahead,” cautioned Harold Hwang, a SIMES investigator, professor at SLAC and Stanford and senior author of the report. “We have just seen the first basic experiments, and now we need to do the whole battery of investigations that are still going on with cuprates.”

Among other things, he said, scientists will want to dope the nickelate material in various ways to see how this affects its superconductivity across a range of temperatures, and determine whether other nickelates can become superconducting. Other studies will explore the material’s magnetic structure and its relationship to superconductivity.

SIMES researchers from the Stanford departments of Physics, Applied Physics and Materials Science and Engineering also contributed to the study, which was funded by the DOE Office of Science and the Gordon and Betty Moore Foundation’s Emergent Phenomena in Quantum Systems Initiative.

See the full article here .

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SLAC/LCLS

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.

From UCLA Newsroom: “Technique could make better membranes for next-generation filtration”

From UCLA Newsroom

August 20, 2019
Writer
Wayne Lewis

Media Contact
Nikki Lin
310-206-8278
nlin@cnsi.ucla.edu

UCLA scientists’ method will allow more advanced materials to be used for desalination and other processes.

UCLA postdoctoral scholar Brian McVerry and doctoral student Mackenzie Anderson examine an ultra-thin membrane film on a glass plate used in the T-FLO process. Marc Roseboro/UCLA

Deriving drinkable water from seawater, treating wastewater and conducting kidney dialysis are just a few important processes that use a technology called membrane filtration.

The key to the process is the membrane filter — a thin, semi-porous film that allows certain substances such as water to pass through while separating out other, unwanted substances. But in the past 30 years, there have been no significant improvements in the materials that make up the key layers of commercially produced membrane filters.

Now, UCLA researchers have developed a new technique called thin-film liftoff, or T-FLO, for creating membrane filters. The approach could offer a way for manufacturers to produce more effective and energy-efficient membranes using high-performance plastics, metal-organic frameworks and carbon materials. To date, limitations in how filters are fabricated have prevented those materials from being viable in industrial production.

A study describing the work is published in the journal Nano Letters.

“There are a lot of materials out there that in the lab can do nice separations, but they’re not scalable,” said Richard Kaner, UCLA’s Dr. Myung Ki Hong Professor of Materials Innovation and the study’s senior author. “With this technique, we can take these materials, make thin films that are scalable, and make them useful.”

In addition to their potential for improving types of filtration that are performed using current technology, membranes produced using T-FLO could make possible an array of new forms of filtration, said Kaner, who also is a distinguished professor of chemistry and biochemistry, and of materials science and engineering, and a member of the California NanoSystems Institute at UCLA. For example, the technique might one day make it feasible to pull carbon dioxide out of industrial emissions — which would enable the carbon to be converted to fuel or other applications while also reducing pollution.

Filters like the ones used for desalination are called asymmetric membranes because of their two layers: a thin but dense “active” layer that rejects particles larger than a specific size, and a porous “support” layer that gives the membrane structure and allows it to resist the high pressures used in reverse osmosis and other filtering processes. The first asymmetric membrane for desalination was devised by UCLA engineers in the 1960s.

Today’s asymmetric membranes are made by casting the active layer onto the support layer, or casting both concurrently. But to manufacture an active layer using more advanced materials, engineers have to use solvents or high heat — both of which damage the support layer or prevent the active layer from adhering.

In the T-FLO technique, the active layer is cast as a liquid on a sheet of glass or metal and cured to make the active layer solid. Next, a support layer made of epoxy reinforced with fabric is added and the membrane is heated to solidify the epoxy.

The use of epoxy in the support layer is the innovation that distinguishes the T-FLO technique — it enables the active layer to be created first so that it can be treated with chemicals or high heat without damaging the support layer.

The membrane then is submerged in water to wash out the chemicals that induce pores in the epoxy and to loosen the membrane from the glass or metal sheet.

Finally, the membrane is peeled off of the plate with a blade — the “liftoff” that gives the method its name.

“Researchers around the world have demonstrated many new exciting materials that can separate salts, gases and organic materials more effectively than is done industrially,” said Brian McVerry, a UCLA postdoctoral scholar who invented the T-FLO process and is the study’s co-first author. “However, these materials are often made in relatively thick films that perform the separations too slowly or in small samples that are difficult to scale industrially.

“We have demonstrated a platform that we believe will enable researchers to use their new materials in a large, thin, asymmetric membrane configuration, testable in real-world applications.”

The researchers tested a membrane produced using T-FLO for removing salt from water, and it showed promise for solving one of the common problems in desalination, which is that microbes and other organic material can clog the membranes. Although adding chlorine to the water can kill the microbes, the chemical also causes most membranes to break down. In the study, the T-FLO membrane both rejected the salt and resisted the chlorine.

In other experiments, the new membrane was also able to remove organic materials from solvent waste and to separate greenhouse gases.

Mackenzie Anderson, a UCLA doctoral student, is co-first author of the study.

The research was supported by the U.S./China Clean Energy Research Center for Water-Energy Technologies and the National Science Foundation. The project is aligned with UCLA’s Sustainable LA Grand Challenge.

See the full article here .

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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 SLAC National Accelerator Lab: “Scientists report two advances in understanding the role of ‘charge stripes’ in superconducting materials”

From SLAC National Accelerator Lab

Ali Sundermier
Glennda Chui

The studies could lead to a new understanding of how high-temperature superconductors operate.

High-temperature superconductors, which carry electricity with zero resistance at much higher temperatures than conventional superconducting materials, have generated a lot of excitement since their discovery more than 30 years ago because of their potential for revolutionizing technologies such as maglev trains and long-distance power lines. But scientists still don’t understand how they work.

One piece of the puzzle is the fact that charge density waves – static stripes of higher and lower electron density running through a material – have been found in one of the major families of high-temperature superconductors, the copper-based cuprates. But do these charge stripes enhance superconductivity, suppress it or play some other role?

In independent studies, two research teams report important advances in understanding how charge stripes might interact with superconductivity. Both studies were carried out with X-rays at the Department of Energy’s SLAC National Accelerator Laboratory.

Exquisite detail

In a paper published today in Science Advances, researchers from the University of Illinois at Urbana-Champaign (UIUC) used SLAC’s Linac Coherent Light Source (LCLS) X-ray free-electron laser [below] to observe fluctuations in charge density waves in a cuprate superconductor.

This cutaway view shows stripes of higher and lower electron density – “charge stripes” – within a copper-based superconducting material. Experiments with SLAC’s X-ray laser directly observed how those stripes fluctuate when hit with a pulse of light, a step toward understanding how they interact with high-temperature superconductivity. (Greg Stewart/SLAC National Accelerator Laboratory)

They disturbed the charge density waves with pulses from a conventional laser and then used RIXS, or resonant inelastic X-ray scattering, to watch the waves recover over a period of a few trillionths of a second. This recovery process behaved according to a universal dynamical scaling law: It was the same at all scales, much as a fractal pattern looks the same whether you zoom in or zoom out.

With LCLS, the scientists were able to measure, for the first time and in exquisite detail, exactly how far and how fast the charge density waves fluctuated. To their surprise, the team discovered that the fluctuations were not like the ringing of a bell or the bouncing of a trampoline; instead, they were more like the slow diffusion of a syrup – a quantum analog of liquid crystal behavior, which had never been seen before in a solid.

“Our experiments at LCLS establish a new way to study fluctuations in charge density waves, which could lead to a new understanding of how high-temperature superconductors operate,” says Matteo Mitrano, a postdoctoral researcher in professor Peter Abbamonte’s group at UIUC.

This team also included researchers from Stanford University, the National Institute of Standards and Technology and Brookhaven National Laboratory.

Hidden arrangements

Another study, reported last month in Nature Communications, used X-rays from SLAC’S Stanford Synchrotron Radiation Lightsource (SSRL) to discover two types of charge density wave arrangements, making a new link between these waves and high-temperature superconductivity.

SLAC/SSRL

Led by SLAC scientist Jun-Sik Lee, the research team used RSXS, or resonant soft X-ray scattering, to watch how temperature affected the charge density waves in a cuprate superconductor.

“This resolves a mismatch in data from previous experiments and charts a new course for fully mapping the behaviors of electrons in these exotic superconducting materials,” Lee says.

“I believe that exploring new or hidden arrangements, as well as their intertwining phenomena, will contribute to our understanding of high-temperature superconductivity in cuprates, which will inform researchers in their quest to design and develop new superconductors that work at warmer temperatures.”

The team also included researchers from Stanford, Pohang Accelerator Laboratory in South Korea and Tohoku University in Japan.

SSRL and LCLS are DOE Office of Science user facilities. Both studies were supported by the Office of Science.

See the full article here .

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SLAC/LCLS

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.

From University of Washington: “Scientists can now control thermal profiles at the nanoscale”

From University of Washington

August 9, 2019
James Urton

Handwritten notes from David J. Masiello, associate professor of chemistry at the University of WashingtonDavid J. Masiello / U. of Washington

At human scale, controlling temperature is a straightforward concept. Turtles sun themselves to keep warm. To cool a pie fresh from the oven, place it on a room-temperature countertop.

At the nanoscale — at distances less than 1/100th the width of the thinnest human hair — controlling temperature is much more difficult. Nanoscale distances are so small that objects easily become thermally coupled: If one object heats up to a certain temperature, so does its neighbor.

When scientists use a beam of light as that heat source, there is an additional challenge: Thanks to heat diffusion, materials in the beam path heat up to approximately the same temperature, making it difficult to manipulate the thermal profiles of objects within the beam. Scientists have never been able to use light alone to actively shape and control thermal landscapes at the nanoscale.

At least, not until now.

In a paper published online July 30 by the journal ACS Nano, a team of researchers reports that they have designed and tested an experimental system that uses a near-infrared laser to actively heat two gold nanorod antennae — metal rods designed and built at the nanoscale — to different temperatures. The nanorods are so close together that they are both electromagnetically and thermally coupled. Yet the team, led by researchers at the University of Washington, Rice University and Temple University, measured temperature differences between the rods as high as 20 degrees Celsius. By simply changing the wavelength of the laser, they could also change which nanorod was cooler and which was warmer, even though the rods were made of the same material.

“If you put two similar objects next to each other on a table, ordinarily you would expect them to be at the same temperature. The same is true at the nanoscale,” said lead corresponding author David Masiello, a UW professor of chemistry and faculty member in both the Molecular & Engineering Sciences Institute and the Institute for Nano-Engineered Systems. “Here, we can expose two coupled objects of the same material composition to the same beam, and one of those objects will be warmer than the other.”

Masiello’s team performed the theoretical modeling to design this system. He partnered with co-corresponding authors Stephan Link, a professor of both chemistry and electrical and computer engineering at Rice University, and Katherine Willets, an associate professor of chemistry at Temple University, to build and test it.

Their system consisted of two nanorods made of gold — one 150 nanometers long and the other 250 nanometers long, or about 100 times thinner than the thinnest human hair. The researchers placed the nanorods close together, end to end on a glass slide surrounded by glycerol.

This figure shows evidence that the two nanorods were heated to different temperatures. The researchers collected data on how the heated nanorods and surrounding glycerol scattered photons from a beam of green light. The five graphs show the intensity of that scattered light at five different wavelengths, and insets show images of the scattered light. Arrows indicate that peak intensity shifts at different wavelengths, an indirect sign that the nanorods were heated to different temperatures.Bhattacharjee et al., ACS Nano, 2019.

They chose gold for a specific reason. In response to sources of energy like a near-infrared laser, electrons within gold can “oscillate” easily. These electronic oscillations, or surface plasmon resonances, efficiently convert light to heat. Though both nanorods were made of gold, their differing size-dependent plasmonic polarizations meant that they had different patterns of electron oscillations. Masiello’s team calculated that, if the nanorod plasmons oscillated with either the same or opposite phases, they could reach different temperatures — countering the effects of thermal diffusion.

Link’s and Willets’ groups designed the experimental system and tested it by shining a near-infrared laser on the nanorods. They studied the beam’s effect at two wavelengths — one for oscillating the nanorod plasmons with the same phase, another for the opposite phase.

The team could not directly measure the temperature of each nanorod at the nanoscale. Instead, they collected data on how the heated nanorods and surrounding glycerol scattered photons from a separate beam of green light. Masiello’s team analyzed those data and discovered that the nanorods refracted photons from the green beam differently due to nanoscale differences in temperature between the nanorods.

“This indirect measurement indicated that the nanorods had been heated to different temperatures, even though they were exposed to the same near-infrared beam and were close enough to be thermally coupled,” said co-lead author Claire West, a UW doctoral candidate in the Department of Chemistry.

The team also found that, by changing the wavelength of near-infrared light, they could change which nanorod — short or long — heated up more. The laser could essentially act as a tunable “switch,” changing the wavelength to alter which nanorod was hotter. The temperature differences between the nanorods also varied based on their distance apart, but reached as high as 20 degrees Celsius above room temperature.

The team’s findings have a range of applications based on controlling temperature at the nanoscale. For example, scientists could design materials that photo-thermally control chemical reactions with nanoscale precision, or temperature-triggered microfluidic channels for filtering tiny biological molecules.

The researchers are working to design and test more complex systems, such as clusters and arrays of nanorods. These require more intricate modeling and calculations. But given the progress to date, Masiello is optimistic that this unique partnership between theoretical and experimental research groups will continue to make progress.

“It was a team effort, and the results were years in the making, but it worked,” said Masiello.

West’s co-lead authors on the paper are Ujjal Bhattacharjee, a former researcher at Rice University now at the Indian Institute of Engineering Science and Technology, Shibpur, and Seyyed Ali Hosseini Jebeli, a researcher at Rich University. Co-authors are Harrison Goldwyn and Elliot Beutler, both doctoral students in the UW Department of Chemistry; Xiang-Tian Kong and Zhongwei Hu, both research associates in the UW Department of Chemistry; and Wei-Shun Chang, a former research scientist at Rice, now an assistant professor of chemistry and biochemistry at the University of Massachusetts Dartmouth. The research was funded by the National Science Foundation, the Robert A. Welch Foundation, and the University of Washington.

For more information, contact Masiello at 206-543-5579 or masiello@uw.edu.

See the full article here .

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

From Penn Today: “Materials for a more sustainable future”

From Penn Today

August 12, 2019
Erica K. Brockmeier Writer
Eric Sucar Photographer

Using a collaborative approach and their expertise in fundamental chemical research, new Chemistry Department faculty member Thomas Mallouk and his group address challenges faced by engineers and materials scientists.

Thomas Mallouk is the new Vagelos Professor in Energy Research who brought his lab to Penn in May. His group conducts fundamental chemistry research that helps solve problems faced by engineers and materials scientists.

On the second floor of the Chemistry 1958 building, just above the general chemistry labs, the Mallouk research group is busy at work. Between long lines of lab benches, computer desks, and even a small glassblowing workshop, their work spans a wide range of applications, from motors smaller than the width of a human hair to biologically-inspired solar batteries.

Thomas Mallouk, who came to Penn’s Department of Chemistry in May, and his team work in the area of materials chemistry and have several ongoing projects on renewable energy and sustainability. Mallouk is also the Vagelos Professor in Energy Research at the Vagelos Institute for Energy Science and Technology (VIEST), where he will support ongoing and burgeoning collaborations between the School of Arts and Sciences and the School of Engineering and Applied Science.

Mallouk and the students in his lab bring a unique approach to fundamental chemistry research. “Our most effective work has been taking somebody else’s problem, often an engineering or physics problem, fields populated by very smart people who have one thing in common: They’re not going to synthesize something new,” explains Mallouk. “Then we try to apply what we know about chemistry to their problem.”

Graduate student Jeremy Hitt, who also works on fuel cells alongside Yan, enjoys the open culture of the Mallouk lab, where everyone is willing to lend a hand and eager to collaborate with other researchers.

One problem that Mallouk is excited to pursue further is energy conversion and energy storage in solar cells. Because solar energy is costly to store, the energy has to be used or converted at the same time it’s collected. A viable long-term storage solution would allow solar energy to be used during seasons or days when there is less light available, and Mallouk’s group is focused on gaining fundamental insights using electrochemistry research to get there.

Several researchers in his group, including graduate student Zhifei Yan, use inspiration from biology to build dye-sensitized solar cells that convert solar energy into electricity, hydrogen, or other energy-rich fuels such as methanol. “It’s an inorganic mimic of a biological system, like a plant,” explains Yan. “The ‘leaf’ absorbs the energy, and then it oxidizes water into oxygen and reduces carbon dioxide into compounds that store energy in chemical bonds.”

Post-doc Luis De Jesus Baez works on 2D materials, atomically-thin synthetic materials that exhibit new properties because their atoms are confined to two dimensions. He was recently awarded the IUPAC-SOLVAY International Award for Young Chemists for Best Ph.D. Thesis.

The Mallouk lab also works on 2D materials, atomically-thin synthetic materials that exhibit new properties due to their atoms being confined to two dimensions. Postdoc Luis de Jesús Baez is studying the different aspects of these unique materials, and how their properties can be tuned. “We can synthesize, stabilize, and make the materia] better. We can functionalize their structures and make them do specific work, like CO2 reduction or for energy storage in batteries and supercapacitors,” de Jesús Baez says.

But it’s not all about energy. The Mallouk lab has also been working with autonomously powered nanoscale and microscale swimmers, about the size of a bacterial cell, that are propelled by either electrochemical reactions or ultrasound. Graduate student Jeff McNeill is looking for ways to control their movements using magnetism and is also exploring ways to power the microrobots with different fuels, like urea or glucose, so they could be used inside of the human body.

And while these microscopic swimmers have a number of possible applications, from cleaning wastewater to delivering drugs, Mallouk says he enjoys working on this project in part for the fun of it. “The problem of anthropogenic climate change has become increasingly urgent, and this motivates our focus on energy-related projects. But we also want to explore pure science questions, and that is what our nanomotor project is about,” he says.

Along with the nanomotors project, McNeil is also working with a type of nanowire that moves in unexpected patterns in response to acoustic waves. They are working with physicists in France to try to understand the theoretical underpinnings of this phenomenon.

Whether the group is focused on sustainability, energy, or miniaturized motors, the approach is always the same: Focusing on problems and using their expertise in materials chemistry to find a solution. “We want to solve problems by understanding the fundamental processes that are happening and then solving it little by little,” says de Jesús Baez. “There is beauty in tackling problems by considering different perspectives.”

By actively collaborating with other groups, including several engineering labs, the members of Mallouk’s group are able to diversify their skillsets and focus on problems without limiting themselves to one method or area of study. “It’s easier to do interdisciplinary work,” says Yan about their group’s approach. “We borrow from other areas, so we won’t limit ourselves to just electrochemistry. We just solve the problem.”

But because of the broader nature of their work, de Jesús Baez says, collaborations are instrumental for delving deeply when a problem requires a closer look. “Sometimes you want to get into that specific detail that will really hit the nail on the head. If you look from too high you may forget to look at the small things, and collaborations help you maintain this view in focus,” he says.

Because of the importance of collaboration in his group’s progress, Mallouk says that coming to Penn at this stage of his 34-year career was the perfect move. “More and more, chemistry is becoming very interdisciplinary and integrated with other sciences, and that happens here at Penn a lot. There’s an opportunity for a tremendous number of new collaborations here,” he says.

Mallouk’s students and postdocs, all of whom were responsible for physically packing up the lab and shipping the numerous boxes of equipment and supplies to Philadelphia earlier this summer, are also looking forward to the new types of research that they can do here. “It will be really nice having the med school right there,” says McNeill. “I could envision myself sitting down with a physician and saying, ‘What can we do with these nanomotors and materials that would be beneficial to you?’”

Mallouk is also looking forward to working with VIEST, where he will serve on the executive committee and manage resource allocations for internal grant proposals. He also hopes to gain some externally-funded projects on energy in the future. VIEST “is a lively place that brings people together with all different kinds of expertise and gets us talking and thinking of energy-relevant ideas,” says Mallouk.

VIEST director Karen Goldberg says that bringing Mallouk to Penn is a huge win for the Institute. “We are looking forward to Mallouk playing a leading role in our solar energy conversion efforts. His expertise in electrochemistry and materials is unparalleled, and his team brings unique vision, tremendous knowledge, diverse instrumentation, and wonderful scientific curiosity and enthusiasm,” she says.

Mallouk will be teaching general chemistry in the fall and is looking forward to “assembling an army” of undergrads for his lab. They will join the 10 graduate students and two postdocs who moved with him from Pennsylvania State University, as well as two new Ph.D. students who have joined the group at Penn. But looking beyond his first year of teaching and getting his lab established, Mallouk says that he’s excited for what the future has in store for his research group.

“I want to continue to work on good fundamental science,” he says. “We often diffuse into areas just from a chance conversation, but we’ve had a very long focus on energy, an increasingly urgent problem, so I want to continue to work in that area.”

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 Stanford University: “Stanford researchers design a light-trapping, color-converting crystal”

From Stanford University

August 7, 2019

Taylor Kubota
Stanford News Service
(650) 724-7707
tkubota@stanford.edu

Researchers propose a microscopic structure that changes laser light from infrared to green and traps both wavelengths of light to improve efficiency of that transformation. This type of structure could help advance telecommunication and computing technologies. (Image credit: Getty Images)

Five years ago, Stanford postdoctoral scholar Momchil Minkov encountered a puzzle that he was impatient to solve. At the heart of his field of nonlinear optics are devices that change light from one color to another – a process important for many technologies within telecommunications, computing and laser-based equipment and science. But Minkov wanted a device that also traps both colors of light, a complex feat that could vastly improve the efficiency of this light-changing process – and he wanted it to be microscopic.

“I was first exposed to this problem by Dario Gerace from the University of Pavia in Italy, while I was doing my PhD in Switzerland. I tried to work on it then but it’s very hard,” Minkov said. “It has been in the back of my mind ever since. Occasionally, I would mention it to someone in my field and they would say it was near-impossible.”

In order to prove the near-impossible was still possible, Minkov and Shanhui Fan, professor of electrical engineering at Stanford, developed guidelines for creating a crystal structure with an unconventional two-part form. The details of their solution were published Aug. 6 in Optica, with Gerace as co-author. Now, the team is beginning to build its theorized structure for experimental testing.

An illustration of the researchers’ design. The holes in this microscopic slab structure are arranged and resized in order to control and hold two wavelengths of light. The scale bar on this image is 2 micrometers, or two millionths of a meter. (Image credit: Momchil Minkov)

A recipe for confining light

Anyone who’s encountered a green laser pointer has seen nonlinear optics in action. Inside that laser pointer, a crystal structure converts laser light from infrared to green. (Green laser light is easier for people to see but components to make green-only lasers are less common.) This research aims to enact a similar wavelength-halving conversion but in a much smaller space, which could lead to a large improvement in energy efficiency due to complex interactions between the light beams.

The team’s goal was to force the coexistence of the two laser beams using a photonic crystal cavity, which can focus light in a microscopic volume. However, existing photonic crystal cavities usually only confine one wavelength of light and their structures are highly customized to accommodate that one wavelength.

So instead of making one uniform structure to do it all, these researchers devised a structure that combines two different ways to confine light, one to hold onto the infrared light and another to hold the green, all still contained within one tiny crystal.

“Having different methods for containing each light turned out to be easier than using one mechanism for both frequencies and, in some sense, it’s completely different from what people thought they needed to do in order to accomplish this feat,” Fan said.

After ironing out the details of their two-part structure, the researchers produced a list of four conditions, which should guide colleagues in building a photonic crystal cavity capable of holding two very different wavelengths of light. Their result reads more like a recipe than a schematic because light-manipulating structures are useful for so many tasks and technologies that designs for them have to be flexible.

“We have a general recipe that says, ‘Tell me what your material is and I’ll tell you the rules you need to follow to get a photonic crystal cavity that’s pretty small and confines light at both frequencies,’” Minkov said.

Computers and curiosity

If telecommunications channels were a highway, flipping between different wavelengths of light would equal a quick lane change to avoid a slowdown – and one structure that holds multiple channels means a faster flip. Nonlinear optics is also important for quantum computers because calculations in these computers rely on the creation of entangled particles, which can be formed through the opposite process that occurs in the Fan lab crystal – creating twinned red particles of light from one green particle of light.

Envisioning possible applications of their work helps these researchers choose what they’ll study. But they are also motivated by their desire for a good challenge and the intricate strangeness of their science.

“Basically, we work with a slab structure with holes and by arranging these holes, we can control and hold light,” Fan said. “We move and resize these little holes by billionths of a meter and that marks the difference between success and failure. It’s very strange and endlessly fascinating.”

These researchers will soon be facing off with these intricacies in the lab, as they are beginning to build their photonic crystal cavity for experimental testing.

See the full article here .

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Stanford University

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

From École Polytechnique Fédérale de Lausanne: “Digitizing and replicating the world of materials”

From École Polytechnique Fédérale de Lausanne

7.29.19

Sandy Evangelista EPFL Press Service
sandy.evangelista@epfl.ch
+41 79 502 81 06

Wenzel Jakob Professor of EPFL’s Realistic Graphics Lab
Wenzel.Jakob@epfl.ch
+41 21 693 13 29
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A team of EPFL researchers has set itself the lofty goal of building the biggest-ever database that digitizes the visual appearance of all natural and synthetic materials in the world.

Is it possible to digitally replicate the way light shines off silk, the kaleidoscope of colors on butterfly wings, or the structure of fabrics, plastics, and stones? A team of researchers at EPFL’s Realistic Graphics Lab, headed by Wenzel Jakob, is developing computer models to do just that. Their process begins by meticulously digitizing any material they can lay their hands on, using a sophisticated machine called a gonio-photometer.

Imagine taking a photo of a car on a sunny day: the picture will only capture its appearance for that specific viewpoint and illumination, but it cannot tell us how the same car would look from another viewpoint later in the evening. In contrast to a camera, a gonio-photometer measures the light reflected by a material at different angles, capturing the essence of what gives the car’s painted surface its particular look: shiny, pearlescent, metallic, faded, etc. The resulting data is much richer than a single photograph and can be used to generate photorealistic computer images of objects made from those same materials within arbitrary virtual scenes.

Digitize a butterfly wing © 2019 EPFL Alain Herzog

The team at EPFL, led by Prof. Wenzel Jakob, studies the way in which light interacts with various materials so that this process can be reproduced in a software simulation. “Our goal is to put together a very comprehensive library of materials—not just to recreate them, but also to understand mathematically what makes them look the way that they do,” says Jakob. The researchers intend to digitize samples ranging from a sheet of paper and a piece of plastic from a pen to a butterfly wing and even a piece of fabric from a Darth Vader costume. “This kind of material data is invaluable in areas like architecture, computer vision, or the entertainment industry. We’ve recently started working with Weta Digital and Industrial Light & Magic, who make movies like Avatar and Star Wars,” he adds.

Wenzel Jakob uses a photo-goniometer © 2019 EPFL Alain Herzog

The gonio-photometer is an impressive machine some five meters long. It is operated in a room, whose walls have been covered with black cloth to absorb the light reflected by the sample being analyzed. The sample is placed in the center of the device, where it is observed from the tip of a robotic arm that spins with a speed of up to 3 meters per second so that measurements can be taken rapidly for many configurations. “A conventional camera only records red, green and blue color information that is visible to the human eye. We instead use a spectrometer that records hundreds of wavelengths throughout the entire visual spectrum, extending even to UV and infrared. That wealth of data provides us with much more information about a material that enables us to simulate its appearance extremely precisely,” says Jakob.

The team has developed a new algorithm that takes full control of the gonio-photometer to only capture a small subset of an inconceivably large four-dimensional space, enabling materials to be digitized much more rapidly than was previously possible. Jakob’s group also develops the Mitsuba Renderer, a widely used open source software platform that simulates light computationally to create photorealistic images of virtual worlds. With the acquired data, these simulations can now achieve an unprecedented level of accuracy.

On July 29, Jakob received ACM SIGGRAPH’s Significant New Researcher Award. ACM, the Association For Computing Machinery, announced that Jakob was selected for the prestigious prize in recognition of his theoretical and algorithmic contributions to the field, as well as for his work in developing open source software for research.

See the full article here .

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