Symposium X: Frontiers of Materials Research

SymposiumX2_800x533Bart Biebuyck, The Fuel Cells and Hydrogen Joint Undertaking

Development of Fuel Cells and Hydrogen Technologies in Europe Toward Commercialization from 2020 Onward

Written by Prachi Patel

Bart Biebuyck gave an excellent overview of the progress on fuel cell and hydrogen technologies in Europe. The Joint Undertaking is a public-private partnership of the European Commission, and the industry and research arms of the Hydrogen Europe group. With 1.7 billion Euros in funding, the partnership’s mission is to accelerate research and development (R&D) and bring these technologies to market readiness by 2020.

The goals of the Undertaking are to produce hydrogen in a green way by using less critical raw materials; low-cost fuel cells for transportation, heat, and electricity; and, the key driver for Europe, hydrogen storage for integrating renewables on the grid.

Several ongoing projects on electrolysis to produce hydrogen have already generated materials breakthroughs and slashed the cost of electrolysers since 2011, he said. This has boosted capacity. Megawatt scale electrolysers that produce green hydrogen fuel are now operating at various industrial plants around Europe. A large bakery in Völs, Austria, for instance, uses the hydrogen from its 3.4 MW hydro-electricity-powered electrolyser to heat bread ovens. This offsets the carbon emissions from baking bread, each gram of which produces a gram of carbon dioxide, Biebuyck said.

Research is also underway on using solar power to split water, but improvements in efficiency are needed, he said. The EU industry has launched an initiative to have a 40 GW electrolyser by 2040.

Next, he addressed progress in the area of fuel cells for transport. The focus of materials research here is to find catalysts that use little or, ideally, no platinum. Today’s platinum-based catalysts make up a third of fuel cell cost. Another avenue to reduce cost is to eliminate rare-earth materials found in some components.

The Joint Undertaking also supports fuel cell vehicles and infrastructure. Asian car manufacturers dominate the market today, but some European auto companies plan to have hydrogen car prototypes by 2025. As for refueling stations, there are 120 now in Europe, but 50 member states have committed to building more, reaching a target of about 850 by 2025. “We are also focusing on fuel cell buses to clean up cities,” Biebuyck said. Fuel-cell buses are expected to reach cost-parity with diesel and battery buses in the next 2–3 years. Meanwhile, the first fuel-cell garbage trucks are starting to appear on the market. 

Biebuyck went on to talk about the potential of fuel cells in railway transport, and promising demonstrations in hydrogen-powered aircraft and ships. For ships, there needs to be regulations, and there is a need for research on liquid-hydrogen storage and megawatt-scale fuel cells for ships.

Finally, in the area of heating and cooling, there is a need for research advances in solid-oxide fuel cells. Breakthrough concepts like 3D-printing are being funded by the Joint Undertaking. And installations of “washing machine-sized” micro combined heat and power systems are going up steadily in Europe.

Biebuyck ended by giving a glimpse into the future. Last year, 28 European countries signed an agreement to work on hydrogen research. In the 100 billion Euro Horizon Europe research program “you will find hydrogen and fuel cells many times in the text, even more than batteries,” he said.

But for solid progress to be made in this area, international cooperation is going to be critical, he stressed. And there is a dearth of talented materials scientists and engineers in the area. “We really need you,” he said to the audience, “because in hydrogen and fuel cells, materials research is very important. Look at hydrogen fuel cells, because I guarantee you it will be a successful future.”


Symposium X: Frontiers of Materials Research

Thursday_Symposium X_800x533Jonathan Arenberg, Northrop Grumman Aerospace Systems

NASA’s James Webb Space Telescope

Written by Prachi Patel

Many scientists and space enthusiasts eagerly await the launch of the James Webb Space Telescope, which NASA has now set to March 2021. In his talk, Jon Arenberg described the mission, design challenges, and development of “NASA’s next great leap in space science.”

He described the four fundamental science objectives of this powerful astronomical observatory. The JWST aims to detect light from the first glowing objects in the universe, the earliest stars and galaxies, to “see the beginning of time,” he said. It will also help scientists understand the assembly of galaxies; the birth of stars and planets; and investigate planetary systems to understand the origins of life.

Meeting these lofty goals poses many design challenges. Detecting very dim objects equates to being able to detect one or two photons. This requires large mirrors, an infrared telescope since the earliest stars and galaxies are red-shifted, and to keep equipment cold and stable. As an example of the strict materials property and behavior prediction needs for the telescope, Arenberg showed how, in 2006, Northrop Grumman demonstrated that the bonded composite backplane had a predictable distortion of just a few nm/K.

Then he detailed the telescope’s design: a 6.5 m telescope, a mirror that is more than 7 times Hubble’s area and weighs about half. The cooling requirement is especially tricky, with a sun-facing side that is 340–370 K, and a cold dark side that need cryogenic temperatures of 25–90 K. This temperature difference occurs over a 4.5-foot separation.

Materials science helps meet these challenges, Arenberg said. The five-layer sunshield is silicon-clad plastic, while the cold-facing side is vapor-deposited aluminum. These materials plus the four V shapes formed by the sunshield allow the drastic 300-K-drop in temperature. The large mirror is made of beryllium, which he said they chose because it is lightweight and has very low thermal expansion over the 45 K range of operational temperatures.

Arenberg then described other challenges that JWST engineers have addressed, such as the factors for determining the JWST’s circumsolar orbit, and the reliability needs to have such a large telescope that can be folded and unfolded.

Through a series of splendid photos, he illustrated the development and testing of the JWST’s parts of tests in NASA and Northrop Grumman’s immense test facilities. The entire telescope has also been tested end-to-end at NASA’s Johnson Space Center. Once all the tests are done, the telescope will be shipped to South America for launch.

Arenberg ended by looking into the future. “Science is very keen on answering questions such as how did the universe start, how does it work, and are we alone?” He said that answering such fundamental questions requires making nano- and pico-meter level measurements and predictions, which will need systems far beyond the level of Webb. “Uncertainty is expensive,” he said. “Uncertainty can be a mission-killer.” Removing this uncertainty will come down to clever system design and precisely understanding the fundamental properties and behavior of materials.


Symposium X: Frontiers of Materials Research

SymposiumX3_800x533Sunita Satyapal, US Department of Energy

Hydrogen and Fuel-Cell Technology Perspectives

Written by Prachi Patel

The energy landscape is changing in the United States. The country uses almost 100 Quadrillion BTUs of energy, an increasingly larger share of which is coming from natural gas and oil. Renewables form about 11% of the mix. And hydrogen fuel is one small part of that portfolio, Sunita Satyapal told her audience during Symposium X.

As a brief introduction to the first element, Satyapal outlined hydrogen’s good and bad. The gas has one of the highest energy content by weight of all conventional fuels. But tables turn when it comes to volumetric capacity, with hydrogen faring four times worse in energy content when compared to gasoline.

Satyapal focused on four main messages: the progress in and current status of hydrogen and fuel cell technologies; the US Department of Energy’s (DOE) H2@Scale initiative that aims to enable innovations that could make hydrogen a cost-competitive fuel; pressing research and development (R&D) needs and challenges; and how materials science and research collaborations could help address those.

Satyapal first highlighted the tremendous progress and commercial success in the area of fuel cells. Statistics include 12,000 fuel cell cars, more than a quarter million residential fuel cells in Japan, and more than 25,000 fuel-cell forklifts. She mentioned that steady market growth in the area is mostly in the transportation sector.

After showing the audience a sample of a fuel-cell membrane electrode assembly, Satyapal presented her main takeaway: that hydrogen fuel cells bring immense carbon emission benefits. In terms of life-cycle emissions, today’s gasoline vehicles give 450 grams of carbon dioxide equivalent emissions per mile. By comparison, due to the 60% efficiency of fuel cells, even if hydrogen is produced from natural gas, that carbon burden goes down to 252 grams of CO2e per mile.

Next Satyapal introduced DOE’s H2@Scale program, which aims to provide reliable and affordable hydrogen to all sectors. DOE has assessed hydrogen demand and supply across the U.S. and found that most regions have enough resources, she said.

Moving on to R&D needs, she said DOE’s main goal is to reduce cost. The costs of fuel cells, hydrogen fuel production and delivery infrastructure, and onboard storage systems are all still too high. The H2@Scale program plans to focus on R&D to cut costs in all three areas with an increased budget for DOE’s Fuel Cell Technologies Program in 2019.

To this end, DOE has created and is funding several different consortia. Satyapal talked about the promising work that has emerged from some of the materials-focused research consortia. The ElectroCat consortium, for example, aims to eliminate expensive platinum catalysts from fuel cells. In a recent article in the journal Science, members of the consortium reported an Iron-N complex that shows promise. “This is really exciting news,” she said. Another bit of exciting research comes from the HydroGEN consortium, with researchers at the University of Colorado Boulder showing successful use of machine learning to screen stable perovskites that can split water. The Hydrogen Materials­–Advanced Research consortium (HyMARC), meanwhile, is accelerating the development of breakthrough hydrogen storage materials.

SymposiumX4_800x533

Satyapal then addressed an area of research where the MRS audience might be able to help: hydrogen embrittlement, the phenomenon in which metals take up hydrogen, lose their ductility, and then crack. This is where DOE’s latest consortium, H-MAT, could help. Researchers in this consortium are trying to understand degradation mechanisms in storage materials, which include metal and polymers. Understanding hydrogen embrittlement could allow the innovation of better materials for hydrogen storage and delivery.

Finally, Satyapal highlighted the importance of collaborations. Over 20 countries are now members of an organization called the International Partnership for Hydrogen and Fuel Cells in the Economy (IPHE). She focused on Japan and Korea as countries with promising progress in the area. Japan has a goal to steeply increase the use of hydrogen in transportation, heating, and industrial processes by 2030 (the torch at the 2020 Olympics in Japan will be fueled by hydrogen), while Korea has announced USD $1.8 billion for hydrogen research.

To end, she pulled up a slide with a simple “Δt” on it, representing the concept of time. “The past always seems closer than the future,” she said. The last 20 years have gone by fast. And so will the next 20, even though 2040 looks far away right now. “We really need to accelerate progress.”


Symposium X Speaker and National Academy of Engineering Member Molly Stevens

Molly M. Stevens, Imperial College London, discusses her Symposium X talk, "Designing Bio-Responsive Hybrid Materials."

 

MRS TV presents new broadcasts each day during the Meeting.  View it on monitors throughout the convention center, online at mrs.org/spring2019, and in the following hotels:

  • Sheraton Phoenix – channel 89
  • Hyatt Regency – channel 58
  • Renaissance Phoenix – TV in lobby

Symposium X: Frontiers of Materials Research

Symposium-X_Tuesday_800x533Molly M. Stevens, Imperial College London

Designing Bio-Responsive Hybrid Materials

Written by Don Monroe

In her Symposium X presentation, Molly M. Stevens described a wide range of examples from her group employing materials in biomedical applications, as well as applying advanced materials characterization techniques to understand and improve the materials. She is also helping direct a project to bring advanced diagnostic capabilities enabled by cell phones to people in Africa.

Developing materials for regenerative medicine requires a balance between the complexity of the materials and the need to translate them into clinical use, Stevens stressed. A simple system that exploits the body’s natural regeneration can be effective, as illustrated by a calcium-contained gel that creates an in vivo bio-reactor to grow bone. “Sometimes you can get away with very simple materials systems,” she said, “but there are many other applications where that’s not going to work.”

Stem cells, for example, vary their differentiation in response to numerous mechanical and chemical cues, and different shapes of adhesion for stem cells were known to direct them toward bone-like or fat-like differentiation. Stevens and her research team used high-resolution microscopy, focused-ion-beam, and other tools to reveal how the adhesion geometry affects the cell-substrate interface, as well as the relevant developmental pathways.

They also studied the hierarchical organization of bone, and the relationship between its organic and mineral components, to inform scaffold design. In addition to providing a porous environment matched to the cells, the chemical influences can be profound, as Stevens showed with recent successful bone scaffolds incorporating strontium. She is also collaborating with chemists to create a versatile toolbox for functionalizing polymers in various ways, for example so they interact directly with cells in the body, she said, “because a lot of these conventional polymer systems are not necessarily inclined to do that.”

Stevens also collaborated with researchers from the Howard Hughes Medical Institute to explore arrays of very small needles made of porous silicon. The nanoscale porosity of the needles enables delivery of molecules, because the needles induce formation of vesicles that are taken into cells. Incorporation of a vascular growth factor in this way induced growth of new blood vessels.

The needles can further be used for monitoring tissue. Stevens showed on example where a needle-laden patch loaded with a biomarker identifies the margins of a tumor to assist surgeons. The needles were also effective for introducing quantum-dot biosensors the group had previously developed for lab drug screening, with the potential for real-time, in vivo, intracellular monitoring.

In her final topic, Stevens described the use of nanoparticle-based diagnostics in developing countries. The widespread availability of cell phones and their high-quality cameras, she said, creates an “opportunity to help democratize access to health care.” She is deputy director of a center that aims to implement these tools for early diagnosis.

For example, the center developed a tool based on nanoparticle-based “nanozymes” that are more temperature-stable than traditional enzymes and can directly detect one of the coat proteins of HIV at the point of care. “We were able to develop the most sensitive point-of-care test for HIV that had been developed to date.” She and her colleagues are working to distribute the test in South Africa, where workers have already performed 40,000 tests.


Symposium X—Frontiers of Materials Research

SymposiumX_800WidthErik Bakkers, Technische Universiteit Eindhoven

Bottom-Up Grown Nanowire Quantum Devices

Written by Don Monroe

Despite years of effort, scientists have yet to agree on a physical system for realizing the tremendous potential of quantum computing. Erik Bakkers described a relatively new strategy based on networks of epitaxial III-V nanowires that could exploit exotic collective electronic excitations to enable these applications.

In principle, quantum computing provides exponential increases in computational power from a relatively small number of quantum bits, or qubits. Such qubits can simultaneously represent two possible quantum states, but only until interaction with the environment destroys their coherent relationship. “Decoherence is the big problem of a quantum computer,” Bakkers said. “This is really the fundamental bottleneck.”

Bakkers and his collaborators have been exploring a strategy for overcoming this challenge using “Majorana fermions,” which are their own antiparticle and should be highly resistant to decoherence because they have “no charge, no spin, and no energy.” These entities were proposed decades ago as a model for neutrinos, but have recently been suggested to occur as quasiparticles in condensed-matter systems, in particular in one-dimensional superconductors. “If we can find this particle and control the quantum state, we could have very long decoherence time,” Bakkers said.

His group has been looking for this elusive particle in the proximity-induced superconductive state of InSb nanowires, whose electrons have very low effective mass, strong coupling to magnetic fields, and high spin-orbit coupling. Tunneling spectroscopy revealed the expected conductance peak in the center of the superconducting energy gap. “The data is all consistent with having Majoranas,” Bakkers concluded, although the first experiments were limited by a high density of states in the gap.

To make the wires, Bakkers’ team used an established method in which a ball of metal forms a eutectic with a semiconductor, and subsequent layer-by-layer growth on (111) facets produces long, highly uniform single-crystal nanowires. They developed ways to reduce As and P impurities, grow wires up to 60 µm long, and improve the interfaces, achieving low-temperature mobilities as high as 60,000 cm2/V·s. These nanowires produced extremely clean-induced superconducting gaps, and a magnetic field produces a clear mid-gap state with the predicted quantum conductance of 2e2/h. “We believe this is a very strong signature of having these Majorana states,” Bakkers said.

Exploiting these states for quantum computing will require fashioning these high-quality wires into loops and other circuits. Bakkers showed how to create such structures within the evacuated growth chamber. The gold balls that seed the nanowire growth were defined lithographically on (111) facets of a V-groove etched into a (100) substrate. Choosing the size and location of these seeds let the team create long wires that cross, merge, or shadow each other during later deposition.

In particular, Bakkers described “hashtag” structures (#) with pairs of InSb wires from opposing faces that merge to make “very high-quality wire-wire junctions,” although there can be twin boundaries at the interfaces. Painstakingly dislodging these structures in the electron microscope with a micromanipulator and transferring them to a separate substrate for electrical contacting allows their electrical characterization. The junctions showed the quantized conductance characteristic of ballistic transport, and the oscillating conductance as a function of magnetic field through the loop of the hashtag indicated a coherence length as large as 60 µm. Majorana-based qubits will require somewhat more complex structures, but these appear to be feasible.

Still, Bakkers noted that these techniques are “nice for academic studies, but not really scalable.” He and his collaborators are therefore exploring an alternative future path based on in-plane selective-area growth to create arbitrarily complex circuits in vacuum.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.


Symposium X—Frontiers of Materials Research

SymposiumX_800Width 230x230Mariana Bertoni, Arizona State University

What Is Next for Solar PV Technology?

Written by Arthur L. Robinson

Despite all the excitement now directed at perovskites as a candidate material for solar cells, Mariana Bertoni made it clear at the outset of her Symposium X presentation Wednesday that her vision of the future of solar photovoltaic technology is firmly grounded in silicon. Beginning with a look at progress in lowering the cost of solar technology, Bertoni then provided a tour through the many challenges and obstacles to its reaching the goal of becoming a mainline energy technology. The breadth of these challenges from basic materials performance to integration of the technology into daily life is evident from one many of us might not have thought of—aesthetics. For example, rooftop solar installations are, to be blunt, ugly, which can dampen consumer acceptance. As a result, solar shingles that address this issue are now coming online.

The world’s installed solar energy capacity is rapidly growing, up from 8 GW in 2007 to 402 GW in 2017 and is on track to add 120 GW/year after 2019, which will result in 1 TW installed capacity (residential, commercial, and utility) by 2023. Looking at the levelized (lifetime) cost of solar photovoltaic energy from 2009 to 2017 reveals that this cost has dropped so significantly that the cost per megawatt-hour for utility-scale installations is already comparable to that of natural gas and less expensive than coal and nuclear energy, while rooftop-installation costs remain in the nuclear range. A long-time US Department of Energy cost goal of $1 per Watt, initially greeted with incredulous dismay, was met in 2017, three years earlier than projected, and new reports from China suggest $0.30 per Watt or less will soon be achievable.

Bertoni likened today’s crystalline silicon technology to that of a Ford Model T: it is an established technology that has demonstrated its affordability and its potential but we are just getting started. For example, efficiency is a major performance factor for solar cells. Silicon (single crystalline and polycrystalline) dominates the market today with 90% of market share. In comparison to the theoretical efficiency limit of 29.1%, polycrystalline silicon solar cells were at 21.5% in 2017 and single-crystalline cells up to 26.6%, within 10% of the theoretical limit. Still, increased efficiency remains as a major opportunity area, joining increased yield and lower manufacturing and processing costs, for progress toward $0.03/kW-hr. Long-term performance, degradation, system-level and cell and module integration, and materials design provide further opportunities for cost lowering.

The solar photovoltaic production process begins with ingots or boules and proceeds in stages through wafers, photovoltaic cells, modules, and the installed system. The major cost elements are the silicon wafer (40%), the metallization (10-20%), and the module (comparable to the wafer cost). Among the examples she cited, Bertoni reviewed the use of a spalling technique to avoid the loss of material inherent in using a wire saw to cut wafers from a boule of crystalline silicon. In this technique, pulling a stressor layer attached to the end of the boule cleaves a silicon layer with thickness determined by the stressor layer and there is no material lost, although surface quality remains an issue. Then turning to the metallization process for the silver front contacts in the form of metal fingers that are narrow to expose the silicon to as much light as possible. A particle-filled paste is less expensive than pure silver but has a 10 times higher resistivity. A reactive ink process yields a resistivity comparable to pure silver, and solar cells made in this way have high performance.

When it comes to long-term performance, it turns out that changes in degradation rates are important in determining the power output over time; two different paths to the same power output in the far future can yield different integrated lifetime power production. Bertoni discussed imaging methods to investigate what causes degradation in modules due to module cracking. For example, stress levels concentrated near metal ribbons may depend on the encapsulation method used. Mapping water distribution and its effects in encapsulants is another example. And modeling how sodium from the front glass above the encapsulant diffuses through a module is a third. Interfaces also contribute to long-term performance degradation, with one example being an increase of series resistance with time due to surface recombination resulting from an increasing density of states at the interface.

Bertoni concluded her talk with a discussion of tandem solar cells with a good base cell and a wide-bandgap material with a high efficiency in the upper cell, which provide a way to increase the cell efficiency above 29%. A GaAs-Si tandem is the best current configuration. Even with high efficiency, the system cost can be a problem. Bertoni showed an analysis showing that tandem cells are never the best choice for utility-scale facilities, whereas for residential systems they are viable provided that the GaAs cost is low enough (less than $260/m2). Perovskites can play a role in the analysis if the top and bottom cells are both inexpensive relative to the overall cost of the system. From this, it appears that tandem cells will enter the market and compete with their silicon predecessors. In her final remark, Bertoni put in a plug for machine-learning in the search for new materials.

Symposium X—Frontiers of Materials Research features lectures aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.


Symposium X—Frontiers of Materials Research

Symp X-Kim-blogDae-Hyeong Kim, Seoul National University

Nanomaterials-Based Flexible and Stretchable Bioelectronics

Written by Don Monroe

Dae-Hyeong Kim of Seoul National University used three projects from his group to illustrate the potential for flexible and stretchable electronics for medical applications.

Kim’s first example concerned non-invasive monitoring of glucose levels for people with diabetes. Either high and low glucose is dangerous, and levels are currently controlled with frequent, painful blood measurements and insulin shots.

Kim’s research team developed devices to monitor glucose painlessly using sweat, rather than blood. The 100-fold lower glucose concentration is harder to measure, but Kim noted that the sweat and blood glucose concentration are highly correlated. Electronics incorporated in a patch or other device on sweating skin need to be stretchable, however.

The team improved the sensitivity by using nanostructures to increase the surface area. They exploited the same glucose oxidase enzyme used in current glucose strips, which generates electrically conductive species from glucose. This reaction is sensitive to temperature, humidity, and pH, however, so the team integrated sensors for these environmental variables to provide accurate measurements. Kim also noted that accuracy improved when participants followed a well-defined protocol, such as exercise or a foot bath to encourage sweating.

A later-generation device replaced the re-usable patch with a disposable strip, avoiding degradation of measurement accuracy over time. This device also included sensors for heart rate, blood oxygenation, and motion, and can be wirelessly connected to a cell phone or electronics. Kim illustrated monitoring of volunteers over 30 days, showing clear glucose concentration increases after meals, matching well with blood tests.

Ideally the glucose monitor will be coupled to integrated drug delivery. Kim described a transdermal delivery system using microneedles made of a biodegradable polymer containing a drug such as insulin. To control administration, his team has used a protective layer that can be melted away by applying heat to expose the polymer.

In his second example, Kim described an implantable retinal prosthesis. Previous external imagers are bulky and have low resolution, he noted, while fully implanted chips based on rigid silicon technology cover only a small fraction of the visual field and degrade over time due to their poor mechanical match with tissue.

Kim’s group developed a soft large-area image-sensor array based on MoS¬2 and graphene, extending the area using an icosahedral arrangement of patches. The overall thickness of the array was less than 1 µm, and it was connected to a flexible printed-circuit board using flexible cable. Animal experiments showed an evoked potential in the visual cortex reflecting transmission of the detected image. This “proves the system was working quite well,” Kim said.

Kim’s third example addressed heart failure, which reflects inefficient pumping due to erratic and poorly synchronized heart-tissue contraction. Current implanted-device strategies include electrical pacing by localized electrodes, which generally increases pumping by about 10%, or an external mesh that externally compresses the ventricles.

“Our approach combines these two approaches,” Kim said, by creating a flexible, conductive mesh for extended stimulation. Commercially available conductive rubbers are too resistive, so the team developed a material based on silver nanowires, which increased pumping by 50%.

“The effect is quite meaningful, but there are many issues for clinical translation,” Kim noted, mostly related to materials. In particular, the silver wires readily oxidize, increasing resistance, and dissolved silver is toxic to cells and tissues. The researchers solved these issues by passivating the wires with a gold sheath.

They also improved the tradeoff between flexibility and electrical conductivity by modifying the curing process to create phase segregation between nanowire-rich and polymer-rich regions. The resulting material showed up to 840% stretch with a conductivity up to 72,000 S/cm.

Symposium X—Frontiers of Materials Research features talks aimed at a broad materials audience to provide meeting attendees with an overview of leading-edge topics.


Symposium X—Frontiers of Materials Research

 

SymposiumX200x200Sergei V. Kalinin, Oak Ridge National Laboratory

The Lab on a Beam—Big Data and Artificial Intelligence in Scanning Transmission Electron Microscopy

Written by Arthur L. Robinson

In his Symposium X presentation Monday, Sergei Kalinin of the Oak Ridge National Laboratory presented his vision for a future in which there is a marriage joining materials data at the atomic level and big data, including machine learning and artificial intelligence. In his vision, this marriage can position scanning transmission electron microscopy (STEM) to transition from a purely imaging tool to an atomic-scale laboratory of electronic, phonon, and quantum phenomena in atomically engineered structures.

In what would become a theme running through his talk, Kalinin contrasted the traditional question of “how can we make our imaging tools better” to “what can we learn from these images?” For example, aberration-corrected STEM became commercially available about 10 years ago and opened the way for wide-spread atomic-resolution imaging in which atomic positions can be determined down to the picometer level in a variety of environments beyond the ultra-high vacuum previously required for this kind of resolution. A floodgate has opened for a huge flow of information, all available from STEM experiments. But what can we do with that information; how can we interpret it?” Kalinin asked.

As an example, Kalinin showed a video of an electron beam knocking out sulfur atoms one at a time while imaging MoS2, in effect watching a chemical reaction as it occurs. But what is really wanted is a way to convert the images to information about atomic coordinates and trajectories. It turns out that a neural network can be a useful way to address this task, once you are able to teach the network the physics it needs to identify features of interest, he said. For example, a downloadable deep learning network very accurately identified the mix of breeds in a dog from a photograph but also kept finding animals in an electron micrograph.

Kalinin’s Oak Ridge group has developed the tools to convert the image data into high-quality representations and they are publicly available. With these tools, the Oak Ridge group is constructing defect libraries cataloging defects that actually do occur in a given material. Kalinin pointed out the similarity that now arises to astrophysics and high-energy physics where the individual researcher model has largely disappeared and work is done via communities sharing resources, and asked whether materials researchers should adopt a similar approach.

Returning to his theme of what can materials researchers learn from the information, Kalinin illustrated the case of surfaces and interfaces, defects, and spatially inhomogeneous ferroelectric materials for which theories for bulk behavior are well in hand. Specifically, he showed that the value of the flexoelectric coupling of polarization and strain gradient in heterostructures of lead and strontium titanate can be determined from the shape of vortices in STEM images. Moreover, one can choose microscopic models from atomic-resolution image data, as Kalinin illustrated with the example of a superconductor comprising a tellurium-selenium solid solution in one plane and iron in the other. The segregation of the tellurium and selenium is controlled by a single parameter, the specific enthalpy for segregation. With neural networks, one can reliably determine the value of this parameter from the atomic positions and from this, determine the entire phase diagram.

These examples have been based on static images, but dynamic imaging is possible and brings us into the realm of chemistry. In one example, tungsten sulfide with molybdenum impurities and sulfur vacancies created by the electron beam, Kalinin described how to use neural networks to identify all the defects and then plot their trajectories in time. From this information, dominant point defects can be identified, diffusion parameters analyzed, and transformation pathways of composite defects studied.

For the next part of his presentation, Kalinin turned to the possibility of manipulation of matter and fabrication of structures atom by atom with the use of an electron beam. Parts of the puzzle to be solved include finding phenomena that are amenable to control by an electron beam, learning how to control the beam to follow different trajectories, expanding the dynamic range, incorporating feedback from other measurement tools, and ideally having an appropriate theory at hand. For example, the group incorporated feedback from the beam detector to tell the control system that crystallization had occurred and to move the beam.

An early example of automation was combining STEM with the control system that allows scanning probes to write pattern. In this case, the electron beam causes the crystallization of amorphous strontium titanate an atom at a time to write the ORNL pattern in the bulk surrounded by amorphous material. The process also works with silicon, where it was also demonstrated that controlled dopant profiles could be created by moving the impurities with the electron beam.

Looking further in the future, Kalinin turned to learning from Nature. Insects, for example, are in one sense ultimate machines but they are not controllable and cannot be miniaturized to the nanolevel. If one tries to build a nanomachine with similar capabilities a host of issues such as thinking, locomotion, and energy sources arise from trying to integrate too many functions in the nanomachine. Kalinin asked, “What if we use a single atom or small atom assembly as a functional element of a moving nanomachine and defer control and power functions to external entities?” As a first example, he discussed the use of an electron beam to move a cluster of silicon atoms on graphene.

In his summary, Kalinin pointed out the evolution of imaging from description to control. We are now at the stage where dynamic microscopies can tell us what atoms do. We still need to find out: what are local atomic functionalities; why do atoms do what they do; how can we direct them to do what we want.

Symposium X—Frontiers of Materials Research features talks aimed at a broad materials audience to provide meeting attendees with an overview of leading-edge topics.


Symposium X - David J. Mooney introduced fascinating founding in biomaterials

David J. Mooney,  a Professor of Bioengineering at the Harvard School of Engineering and Applied Sciences as well as a core faculty member at the Wyss Institute for Biologically Inspired Engineering at Harvard University, was invited as an honored speaker in the MRS Symposium X meeting. Mooney is a member of both the National Academy of Engineering and the National Academy of Medicine. The Mooney lab focuses on designing biomaterials that affect specific cells functions and making therapies more effective and practical through study of the mechanism of the chemical and mechanical signal that were sensed by cells. His research now focuses on therapeutic angiogenesis, regeneration of musculoskeletal tissues and cancer therapies. In the meeting, he introduced the influence of stress relaxation of hydrogel on cells and demonstrated that faster relaxation of gels promote cell spreading and enhance osteogenesis and new bone formation. Moreover, he put forward that ferrogel with magnetic stimulation can promote new tissue regeneration because active mechanical stimulation share a similar mechanism.