Assistant professor in EECS and DMSE is developing materials with novel structures and useful applications, including renewable energy and information storage.
|Jennifer Rupp's current ceramics research applications range from battery-based storage for renewable energy, to energy-harvesting systems, to devices used to store data during computation. Photo courtesy of Jennifer Rupp.|
Ensuring that her research contributes to society’s well-being is a major driving force for Jennifer Rupp.
“Even if my work is fundamental, I want to think about how it can be useful for society,” says Rupp, the Thomas Lord Assistant Professor of Materials Science and Engineering and an assistant professor in the Department of Electrical Engineering and Computer Science (EECS) at MIT.
Since joining the Department of Materials Science and Engineering in February 2017, she has been focusing not only on the basics of ceramics processing techniques but also on how to further develop those techniques to design new practical devices as well as materials with novel structures. Her current research applications range from battery-based storage for renewable energy, to energy-harvesting systems, to devices used to store data during computation.
Rupp first became intrigued with ceramics during her doctoral studies at ETH Zurich.
“I got particularly interested in how they can influence structures to gain certain functionalities and properties,” she says. During this time, she also became fascinated with how ceramics can contribute to the conversion and storage of energy. The need to transition to a low-carbon energy future motivates much of her work at MIT. “Climate change is happening,” she says. “Even though not everybody may agree on that, it’s a fact.”
One way to tackle the climate change problem is by capitalizing on solar energy. Sunshine falling on the Earth delivers roughly 170,000 terawatts per year — about 10,000 times the energy consumed annually worldwide. “So we have a lot of solar energy,” says Rupp. “The question is, how do we profit the most from it?”
To help convert that solar energy into a renewable fuel, her team is designing a ceramic material that can be used in a solar reactor in which incoming sunlight is controlled to create a heat cycle. During the temperature shifts, the ceramic material incorporates and releases oxygen. At the higher temperature, it loses oxygen; at the lower temperature, it regains the oxygen. When carbon dioxide and water are flushed into the solar reactor during this oxidation process, a split reaction occurs, yielding a combination of carbon monoxide and hydrogen known as syngas, which can be converted catalytically into ethanol, methanol, or other liquid fuels.
While the challenges are many, Rupp says she feels bolstered by the humanitarian ethos at MIT. “At MIT, there are scientists and engineers who care about social issues and try to contribute with science and their problem-solving skills to do more,” she says. “I think this is quite important. MIT gives you strong support to try out even very risky things.”
In addition to continuing her work on new materials, Rupp looks forward to exploring new concepts with her students. During the fall of 2017, she taught two recitation sections of 3.091 (Introduction to Solid State Chemistry), a class that has given thousands of MIT undergraduates a foundation in chemistry from an engineering perspective. This spring, she will begin teaching a new elective for graduate students on ceramics processing and engineering that will delve into making ceramic materials not only on the conventional large-scale level but also as nanofabricated structures and small-system structures for devices that can store and convert energy, compute information, or sense carbon dioxide or various environmental pollutants.
To further engage with students, Rupp has proposed an extracurricular club for them to develop materials science comic strips. The first iteration is available on Instagram (@materialcomics) and it depicts three heroes who jump into various structures to investigate their composition and, naturally, to have adventures. Rupp sees the comics as an exciting avenue to engage the nonscientific community as a whole and to illustrate the structures and compositions of various everyday materials.
“I think it is important to create interest in the topic of materials science across various ages and simply to enjoy the fun in it,” she says.
Rupp says MIT is proving to be a stimulating environment. “Everybody is really committed and open to being creative,” she says. “I think a scientist is not only a teacher or a student; a scientist is someone of any age, of any rank, someone who simply enjoys unlocking creativity to design new materials and devices.”
This article appears in the Autumn 2017 issue of Energy Futures, the magazine of the MIT Energy Initiative.
Kelley Travers | MIT Energy Initiative
MIT News Office, February 9, 2018
MIT researchers create predictable patterns from unpredictable carbon nanotubes.
Integrating nanoscale fibers such as carbon nanotubes (CNTs) into commercial applications, from coatings for aircraft wings to heat sinks for mobile computing, requires them to be produced in large scale and at low cost. Chemical vapor deposition is a promising approach to manufacture CNTs in the needed scales, but it produces CNTs that are too sparse and compliant for most applications. Applying and evaporating a few drops of a liquid such as acetone to the CNTs is an easy, cost-effective method to more tightly pack them together and increase their stiffness, but until now, there was no way to forecast the geometry of these CNT cells.
MIT researchers have now developed a systematic method to predict the two-dimensional patterns CNT arrays form after they are packed together, or densified, by evaporating drops of either acetone or ethanol. CNT cell size and wall stiffness grow proportionally with cell height, they report in a Communication in the Feb. 14, 2018, issue of Physical Chemistry Chemical Physics [PCCP].
One way to think of this CNT behavior is to imagine how entangled fibers such as wet hair or spaghetti collectively reinforce each other. The larger this entangled region is, the higher its resistance to bending will be. Similarly, longer CNTs can better reinforce one another in a cell wall. The researchers also find that CNT binding strength to the base on which they are produced, in this case, silicon, makes an important contribution to predicting the cellular patterns that these CNTs will form.
“These findings are directly applicable to industry because when you use CVD, you get nanotubes that have curvature, randomness and are wavy, and there is a great need for a method that can easily mitigate these defects without breaking the bank,” AeroAstro Postdoc Itai Y. Stein [SM '13, PhD '16] says. Co-authors include materials science and engineering graduate student Ashley L. Kaiser, MechE Postdoc Kehang Cui, and senior author Brian L. Wardle, Professor of Aeronautics and Astronautics.
“From our previous work on aligned carbon nanotubes (CNTs) and their composites, we learned that more tightly packing the CNTs is a highly effective way to engineer their properties,” Wardle says. “The challenging part is to develop a facile way of doing this at scales that are relevant to commercial aircraft (100’s of meters), and the predictive capabilities that we developed here are a large step in that direction."
Carbon nanotubes are highly desirable because of their thermal, electrical, and mechanical properties, which are directionally dependent. Earlier work in Wardle’s lab demonstrated that waviness reduces the stiffness of CNT arrays by as little as 100 times, and up to 100,000 times. The technical term for this stiffness, or ability to bend without breaking, is elastic modulus. Carbon nanotubes are from 1,000 to 10,000 times longer than they are thick, so they deform principally along their length.
For an earlier Applied Physics Letters paper, Stein and colleagues used nanoindentation techniques to measure stiffness of aligned carbon nanotube arrays and found them to be 1,000 to 10,000 times less stiff than the theoretical stiffness of individual carbon nanotubes. Stein, Wardle and former visiting MIT graduate student Hülya Cebeci also developed a theoretical model explaining changes at different packing densities of the nanofibers. [Cebeci is now a professor of aerospace engineering at Istanbul Technical University.]
The new work shows that CNTs compacted by the capillary forces from first wetting them with acetone or ethanol and then evaporating the liquid also produces CNTs that are 100s to 1000s of times less stiff than expected by theoretical values. This capillary effect, known as elastocapillarity, is similar to a how a sponge often dries into a more compact shape after being wetted and then dried.
“Our findings all point to the fact that the CNT wall modulus is much lower than the normally assumed value for perfect CNTs because the underlying CNTs are not straight. Our calculations show that the CNT wall is at least two orders of magnitude less stiff than we expect for straight CNTs, so we can conclude that the CNTs must be wavy,” Stein says.
Heat adds strength
The researchers used a heating technique to increase the adhesion of their original, undensified CNT arrays to their silicon wafer substrate. CNTs densified after heat treatment were about four times harder to separate from the silicon base than untreated CNTs. Kaiser and Stein, who share first authorship of the paper, are currently developing an analytical model to describe this phenomenon and tune the adhesion force, which would further enable prediction and control of such structures.
“Many applications of vertically aligned carbon nanotubes (VACNTs), such as electrical interconnects, require much denser arrays of nanotubes than what is typically obtained for as-grown VACNTs synthesized by chemical vapor deposition (CVD),” says Mostafa Bedewy, assistant professor at the University of Pittsburgh, who was not involved in this work. “Hence, methods for post-growth densification, such as those based on leveraging elastocapillarity have previously been shown to create interesting densified CNT structures. However, there is still a need for a better quantitative understanding of the factors that govern cell formation in densified large-area arrays of VACNTs. The new study by the authors contributes to addressing this need by providing experimental results, coupled with modeling insights, correlating parameters such as VACNT height and VACNT-substrate adhesion to the resulting cellular morphology after densification.”
“There are still remaining questions about how the spatial variation of CNT density, tortuosity [twist], and diameter distribution across the VACNT height affects the capillary densification process, especially that vertical gradients of these features can be different when comparing two VACNT arrays having different heights,” Bedewy notes. “Further work incorporating spatial mapping of internal VACNT morphology would be illuminating, although it will be challenging as it requires combining a suite of characterization techniques.”
The variety of length scales and physical and chemical mechanisms present in carbon nanotubes and other nanoscale materials makes it easy to either oversimplify or to focus on the wrong mechanism, Stein cautions. “Our current predictive capabilities from this paper are very useful, because we give other researchers in the field a pragmatic solution for how they could at least get some predictability, so that they can accelerate their materials design process, and have a working prototype sooner,” Stein says. “In the meantime, while other groups can utilize this new information, which is the best we can do given our current data, we are going to work on collecting a richer dataset that will allow us to investigate the underlying mechanisms and thereby enable even better prediction in the future,” he adds.
Graduate student Kaiser, who was a 2016 MIT Summer Scholar, analyzed the densified CNT arrays with scanning electron microscopy [SEM] in the MIT Materials Research Laboratory’s NSF-MRSEC supported Shared Experimental Facilities. While gently applying liquid to the CNT arrays in this study caused them to densify into predictable cells, vigorously immersing the CNTs in liquid imparts much stronger forces to them, forming randomly shaped CNT networks. “When we first started exploring densification methods, I found that this forceful technique densified our CNT arrays into highly unpredictable and interesting patterns. As seen optically and via SEM, these patterns often resembled animals, faces, and even a heart – it was a bit like searching for shapes in the clouds,” Kaiser says. A colorized version of her optical image showing a CNT heart is featured on the cover of the Feb. 14, 2018, print edition of Physical Chemistry Chemical Physics, which coincides with Valentine’s Day.
“I think there is an underlying beauty in this nanofiber self-assembly and densification process, in addition to its practical applications,” Kaiser adds. “The CNTs densify so easily and quickly into patterns after simply being wet by a liquid. Being able to accurately quantify this behavior is exciting, as it may enable the design and manufacture of scalable nanomaterials.”
The ultimate goal of this research is to be able to precisely predict the post-processing nanofiber pattern beforehand, Kaiser says. “When we have a specific end-goal structure in mind, such as this cellular pattern, we’d like to be able to accurately design its geometry based on our process,” Kaiser says. “With that capability, this liquid-based densification technique could be used to create large-scale nanofiber systems for a wide range of applications.”
This work made use of the MIT Materials Research Laboratory Shared Experimental Facilities, which are supported in part by the MRSEC Program of the National Science Foundation, and MIT Microsystems Technology Laboratories. This research was supported in part by Airbus, ANSYS, Embraer, Lockheed Martin, Saab AB, Saertex, and TohoTenax through MIT's Nano-Engineered Composite Aerospace Structures Consortium and by NASA through the Space Technology Research Institute for Ultra-Strong Composites by Computational Design.
– Denis Paiste, Materials Research Laboratory
February 14, 2018
MIT engineers have just introduced an element of fun into microfluidics.
Video, Melanie Gonick/MIT
The field of microfluidics involves minute devices that precisely manipulate fluids at submillimeter scales. Such devices typically take the form of flat, two-dimensional chips, etched with tiny channels and ports that are arranged to perform various operations, such as mixing, sorting, pumping, and storing fluids as they flow.
Now the MIT team, looking beyond such lab-on-a-chip designs, has found an alternative microfluidics platform in “interlocking, injection-molded blocks” — or, as most of us know them, LEGO bricks.
“LEGOs are fascinating examples of precision and modularity in everyday manufactured objects,” says Anastasios John Hart, associate professor of mechanical engineering at MIT.
Indeed, LEGO bricks are manufactured so consistently that no matter where in the world they are found, any two bricks are guaranteed to line up and snap securely in place. Given this high degree of precision and consistency, the MIT researchers chose LEGO bricks as the basis for a new modular microfluidic design.
In a paper published in the journal Lab on a Chip, the team describes micromilling small channels into LEGOs and positioning the outlet of each “fluidic brick” to line up precisely with the inlet of another brick. The researchers then sealed the walls of each modified brick with an adhesive, enabling modular devices to be easily assembled and reconfigured.
Each brick can be designed with a particular pattern of channels to perform a specific task. The researchers have so far engineered bricks as fluid resistors and mixers, as well as droplet generators. Their fluidic bricks can be snapped together or taken apart, to form modular microfluidic devices that perform various biological operations, such as sorting cells, mixing fluids, and filtering out molecules of interest.
“You could then build a microfluidic system similarly to how you would build a LEGO castle — brick by brick,” says lead author Crystal Owens, a graduate student in MIT’s Department of Mechanical Engineering. “We hope in the future, others might use LEGO bricks to make a kit of microfluidic tools.”
Hart, who is also director of MIT’s Laboratory for Manufacturing and Productivity and the Mechanosynthesis Group, primarily focuses his research on new manufacturing processes, with applications ranging from nanomaterials to large-scale 3-D printing.
“Over the years, I’ve had peripheral exposure to the field of microfluidics and the fact that prototyping microfluidic devices is often a difficult, time-consuming, resource-intensive process,” Hart says.
Owens, who worked in a microfluidics lab as an undergraduate, had seen firsthand the painstaking efforts that went into engineering a lab on a chip. After joining Hart’s group, she was eager to find a way to simplify the design process.
Most microfluidic devices contain all the necessary channels and ports to perform multiple operations on one chip. Owens and Hart looked for ways to, in essence, explode this one-chip platform and make microfluidics modular, assigning a single operation to a single module or unit. A researcher could then mix and match microfluidic modules to perform various combinations and sequences of operations.
In casting around for ways to physically realize their modular design, Owens and Hart found the perfect template in LEGO bricks, which are about as long as a typical microfluidic chip.
“Because LEGOs are so inexpensive, widely accessible, and consistent in their size and repeatability of mounting, disassembly, and assembly, we asked whether LEGO bricks could be a way to create a toolkit of microfluidic or fluidic bricks,” Hart says.
Building from an idea
To answer this question, the team purchased a set of standard, off-the-shelf LEGO bricks and tried various ways to introduce microfluidic channels into each brick. The most successful method turned out to be micromilling, a well-established technique commonly used to drill extremely fine, submillimeter features into metals and other materials.
Owens used a desktop micromill to first mill a simple, 500-micron-wide channel into the side wall of a standard LEGO brick. She then taped a clear film over the wall to seal it and pumped fluid through the brick’s newly milled channel. She observed that the fluid successfully flowed through the channel, demonstrating the brick functioned as a flow resistor — a device that allows very small amounts of fluid to flow through.
Using this same technique, she fabricated a fluid mixer by milling a horizontal, Y-shaped channel, and sending a different fluid through each arm of the Y. Where the two arms met, the fluids successfully mixed. Owens also turned a LEGO brick into a drop generator by milling a T-shaped pattern into its wall. As she pumped fluid through one end of the T, she found that some of the liquid dropped down through the middle, forming a droplet as it exited the brick.
To demonstrate modularity, Owens built a prototype onto a standard LEGO baseplate consisting of several bricks, each designed to perform a different operation as fluid is pumped through. In addition to making the fluid mixer and droplet generator, she also outfitted a LEGO brick with a light sensor, precisely positioning the sensor to measure light as fluid passed through a channel at the same location.
Owens says the hardest part of the project was figuring out how to connect the bricks together, without fluid leaking out. While LEGO bricks are designed to snap securely in place, there is nevertheless a small gap between bricks, measuring between 100 and 500 microns. To seal this gap, Owens fabricated a small O-ring around each inlet and outlet in a brick.
“The O-ring fits into a small circle milled into the brick surface. It’s designed to stick out a certain amount, so when another brick is placed beside it, it compresses and creates a reliable fluid seal between the bricks. This works simply by placing one brick next to another,” Owens says. “My goal was to make it straightforward to use.”
View the embedded image gallery online at:
“An easy way to build”
The researchers note just a couple drawbacks to their method. At the moment, they are able to fabricate channels that are tens of microns wide. However, some microfluidic operations require much smaller channels, which cannot be made using micromilling techniques. Also, as LEGO bricks are made from thermoplastics, they likely cannot withstand exposure to certain chemicals that are sometimes used in microfluidic systems.
“We’ve been experimenting with different coatings we could put on the surface to make LEGO bricks, as they are, compatible with different fluids,” Owens says. “LEGO-like bricks could also be made out of other materials, such as polymers with high temperature stability and chemical resistance.”
For now, a LEGO-based microfluidic device could be used to manipulate biological fluids and perform tasks such as sorting cells, filtering fluids, and encapsulating molecules in individual droplets. The team is currently designing a website that will contain information on how others can design their own fluidic bricks using standard LEGO pieces.
“Our method provides an accessible platform for prototyping microfluidic devices,” Hart says. “If the kind of device you want to make, and the materials you work with, are suitable for this kind of modular design, this is an easy way to build a microfluidic device for lab research.”
This research was supported in part by a National Science Foundation Graduate Research Fellowship, the MIT Mechanical Engineering Department Ascher H. Shapiro Fellowship, the MIT Lincoln Laboratory Advanced Concepts Committee, a 3M Faculty Award, and the National Science Foundation EAGER/Cybermanufacturing Program.
Jennifer Chu | MIT News Office
January 30, 2018
Merger of the Materials Processing Center and the Center for Materials Science and Engineering melds a rich history of materials science and engineering breakthroughs.
|MIT MRL Director Carl V. Thompson. Photo, Denis Paiste, MIT MRL.|
The Materials Research Laboratory at MIT starts from a foundation of fundamental scientific research, practical engineering applications, educational outreach and shared experimental facilities laid by its merger partners, the Materials Processing Center and the Center for Materials Science and Engineering.
“We’re bringing them together and that will make communication both inside and outside MIT easier and will make it clearer especially to people outside MIT that for interdisciplinary research on materials, this is the place to learn about it,” says MRL Director Carl V. Thompson.
The Materials Research Laboratory serves interdisciplinary groups of faculty researchers, spanning the spectrum of basic scientific discovery through engineering applications and entrepreneurship to ensure that research breakthroughs have impact on society. The center engages with approximately 150 faculty members and scientists from across the Schools of Science and Engineering who are conducting materials science research. MRL will work with MIT.nano to enhance the toolset available for groundbreaking research as well as collaborate with the MIT Innovation Initiative and The Engine.
MRL will benefit from the long history of research breakthroughs under MPC and CMSE such as “perfect mirror” technology developed through CMSE in 1998 that led to a new kind of fiber optic surgery and a spinout company, OmniGuide Surgical, and the first germanium laser operating at room temperature, which is used for optical communications, in 2012 through MPC’s affiliated Microphotonics Center.
The Materials Processing Center brings to the partnership its wide diversity of materials research, funded by industry, foundations and government agencies, while the Center for Materials Science and Engineering brings its seed projects in basic science and Interdisciplinary Research Groups, educational outreach and shared experimental facilities, funded under the National Science Foundation Materials Research Science and Engineering Center program [NSF-MRSEC]. Combined research funding was $21.5 million for the fiscal year ended June 30, 2017.
MPC’s research volume more than doubled during the past nine years under Thompson’s leadership. “We do have a higher profile in the community both internal as well as external. We developed over the years a close collaboration with CMSE, including outreach. That will be greatly amplified through the merger,” he says. Thompson is the Stavros Salapatas Professor of Materials Science and Engineering at MIT.
Tackling energy problems
With industrial support, MPC and CMSE launched the Substrate Engineering Lab in 2004. MPC affiliates include the AIM Photonics Academy, the Center for Integrated Quantum Materials and the MIT Skoltech Center for Electrochemical Energy Storage. Other research includes Professor Harry L. Tuller’s Chemomechanics of Far-From-Equilibrium Interfaces (COFFEI) project, which aims to produce better oxide-based semiconductor materials for fuel cells, and Senior Research Scientist Jurgen Michel’s Micro-Scale Optimized Solar-Cell Arrays with Integrated Concentration (MOSAIC) project, which aims to achieve overall efficiency of greater than 30 percent.
The MPC kicked off the Singapore-MIT Alliance for Research and Technology Center’s program in Low Energy Electronic Systems [SMART-LEES] in January 2012, managing the MIT part of the budget. SMART-LEES, led by Eugene A. Fitzgerald, the Merton C. Flemings-SMA Professor of Materials Science and Engineering at MIT, was renewed for another five years in January 2017.
Shared experimental facilities, including X-Ray diffraction, scanning and transmission electron microscopy, probe microscopy, and surface analytical capabilities, are used by more than 1,100 individuals each year. “The amount of investment that needs to be made to keep state-of-the-art shared facilities at a university like MIT is on the order of 1 to 2 million dollars per year in new investment and new tools. That kind of funding is very difficult to get. It certainly doesn’t come to us through just NSF funding,” says TDK Professor of Polymer Materials Science and Engineering Michael F. Rubner, who is retiring after 16 years as CMSE director. “MIT.nano, in concert with MRL, will be able to work together to look at new strategies for trying to maintain state-of-the-art equipment and to find funding sources and to figure out ways to not only get the equipment in, but to have highly trained professionals running that equipment.”
Associate Professor of Materials Science and Engineering Geoffrey S.D. Beach succeeds Rubner as co-director of the MIT MRL and principal investigator for the NSF-MRSEC.
Spinning out jobs
|Merton C. Flemings, founding director [1980-82] of MIT Materials Processing Center and retired Toyota Professor of Materials Processing. Photo, Denis Paiste, MIT MRL.|
NSF-MRSEC-funded research through CMSE has led to approximately 1,100 new jobs through spinouts such as American Superconductor [superconductivity], OmniGuide Surgical [optical fibers] and QD Vision [quantum dots], which Samsung acquired in 2016. Many of these innovations began with seed funding, CMSE’s earliest stage of support, and evolved through joint efforts with MPC, such as microphotonics research that began with a seed grant in 1993, followed by Interdisciplinary Research Group funding a year later. In 1997, MIT researchers published two key papers in Nature and Physical Review Letters, won a two-year, multi-university award through DARPA for Photonic Crystal Engineering, and formed the Microphotonics Center. Further research led to the spinout in 2002 of Luminus Devices, which specializes in solid-state lighting based on light emitting diodes [LEDs].
“Our greatest legacy is bringing people together to produce fundamental new science, and then allowing those researchers to explore that new science in ways that may be beneficial to society, as well as to develop new technologies and launch companies,” Rubner says. He recalls that research in complex photonic crystal structures began with Francis Wright Davis Professor of Physics John D. Joannopoulos as leader. “They got funding through us, at first as seed funding and then IRG [interdisciplinary research group] funding, and over the years, they have continued to get funding from us because they evolved. They would seek a new direction, and one of the new directions they evolved into was this idea of making photonic fibers, so they went from photonic crystals to photonic fibers and that led to, for example, the launching of OmniGuide.” An outgrowth of basic CMSE research, the company’s founders included Professors Joannopolous, Yoel Fink, and Edwin L. [“Ned”] Thomas, who served as William and Stephanie Sick Dean of the George R. Brown School of Engineering at Rice University from 2011 to 2017.
Under Fink’s leadership, that work evolved into Advanced Functional Fabrics of America [AFFOA], a public-private Manufacturing Innovation Institute devoted to creating and bringing to market revolutionary fibers and textiles. The institute, which is a separate nonprofit organization, is led by Fink, while MIT on-campus research is led by Lammot du Pont Professor of Chemical Engineering Gregory C. Rutledge.
Susan D. Dalton, NSF-MRSEC Assistant Director, recalls the evolution of perfect mirror technology into life-saving new fiber optic surgery. “From an administrator’s point of view,” Dalton says, “it’s really exciting because day to day, things happen that you don’t know are going to happen. When you think about saving people’s lives, that’s amazing, and that’s just one example,” she says.
Government, industry partners
Through its Collegium and close partnership with the MIT Industrial Liaison Program (ILP), MPC has a long history of government and industrial partnerships as well as individual faculty research projects. Merton C. Flemings, who is MPC’s founding director [1980-82], and a retired Toyota Professor of Materials Processing, recalls that the early focus was primarily on metallurgy, but ceramics work also was important. “It’s gone way beyond that, and it’s a delight to see what’s going on,” he notes.
“From the time of initiation of the MPC, we had interdepartmental participation, and quite soon after its formation, we initiated an industrial collegium to share in research formulation and participate in research partnerships. I believe our collegium was the first to work collaboratively with the Industrial Liaison Program. It was also at a period in MIT history when working directly with the commercial sector was rare,” Flemings says.
Founded in February 1980, the Materials Processing Center won early support from NASA, which was interested in processing materials in space. A question being asked then was: “What would it be like when you’re in zero gravity and you try and purify a metal or make anything out there? Dr. John R. Carruthers headed this zero gravity materials processing activity in NASA, and as he considered the problem, he realized we didn’t really have much of a science base of materials processing on earth, let alone in space. With that in mind, at Carruthers’ instigation, NASA provided a very generous continuing grant to MIT that was essential to us starting in those early years,” Flemings explains.
Carruthers went on to become director of research with Intel and is now Distinguished Professor of Physics, at Portland [Oregon] State University. The two men – Flemings at MIT and Carruthers at the University of Toronto – had been familiar with each other’s work in the study of how metals solidify, before Carruthers joined NASA as director of its materials processing in space program in 1977. Both Flemings and Carruthers wanted to understand how the effects of gravitationally driven convection influenced the segregation processes during metals solidification.
|Dr. John R. Carruthers headed zero gravity materials processing activity in NASA, and provided critical early funding for MIT Materials Processing Center. Courtesy photo.|
“In molten metal baths, as the metal solidifies into ingots, the solidification process is never uniform. And so the distribution of the components being solidified is very much affected by fluid flow or convection in the molten metal,” Carruthers explains. “We were both interested in what would happen if you could actually turn gravity down because most of the convective effects were influenced by density gradients in the metal due to thermal and compositional effects. So, we were quite interested in what would happen given that those density gradients existed, if you could actually turn the effects of gravity down.”
“When the NASA program came around, they wanted to try to use the low gravity environment of space to actually fabricate materials,” Carruthers recalls. “After a couple of years at NASA, I was able to secure some block grant funding for the center. It subsequently, of course, has developed its own legs and outgrown any of the initial funding that we provided, which is really great to see, and it’s a tribute to the MIT way of doing research, of course, as well. I was really quite proud to be part of the early development of the center,” Carruthers says. “Many of the things we learned in those days are relevant to other areas. I’m finding a lot of knowledge and way of doing things is transferrable to the biomedical sciences, for example, so I’ve become quiet interested in helping to develop things like nanomonitors, you know, more materials science-oriented approaches for the biomedical sciences.”
Expanding research portfolio
From its beginnings in metals processing with NASA support, MPC evolved into a multi-faceted center with diverse sponsors of research in energy harvesting, conversion and storage; fuel cells; quantum materials and spintronics; materials integration for microsystems; photonic devices and systems; materials systems and sustainability; solid-state ionics; as well as metals processing, an old topic that is hot again.
MRL-affiliated MIT condensed matter physicists include experimentalists Raymond C. Ashoori, Joseph G. Checkelsky, Nuh Gedik, and Pablo Jarillo-Herrero, who are exploring quantum materials for next-generation electronics, such as spintronics and valleytronics, new forms of nanoscale magnetism, and graphene-based optoelectronic devices. Riccardo Comin explores electronic phases in quantum materials. Theorists Liang Fu and Senthil Todadri envision new forms of random access memory, Majorana fermions for quantum computing, and unusual magnetic materials such as quantum spin liquids.
In the realm of biophysics, Associate Professor Jeff Gore tests fundamental ideas of theoretical ecology and evolutionary dynamics through experimental studies of microbial communities. Class of 1922 Career Development Assistant Professor Ibrahim Cissé uses physical techniques that visualize weak and transient biological interactions to study emergent phenomena in live cells with single molecule sensitivity. On the theoretical front, Professor Thomas D. & Virginia W. Cabot Career Development Associate Professor of Physics Jeremy England focuses on structure, function, and evolution in the sub-cellular biophysical realm.
Alan Taub, Professor of Materials Science and Engineering at the University of Michigan, has become a member of the new Materials Research Laboratory External Advisory Board. Taub previously served in senior materials science management roles with General Motors, Ford Motor Co. and General Electric and served as chairman of the Materials Processing Center Advisory Board from 2001-2006. He notes that under Director Lionel Kimerling [1993-2008], MPC embraced the new area of photonics. “That transition was really well done,” Taub says. The MRL-affiliated Microphotonics Center has produced collaborative roadmapping reports since 2007 to guide manufacturing research and address systems requirements for networks that fully exploit the power of photonics. Taub also is chief technical officer of LIFT Manufacturing Innovation Institute, in which MIT Assistant Professor of Materials Science and Engineering Elsa Olivetti and senior research scientist Randolph E. [Randy] Kirchain are engaged in cost modeling.
From its founding, Taub notes, MPC engaged the faculty with industry. Advisory board members often sponsored research as well as offering advice. “So it was really the way to guide the general direction, you know, teach them that there are things industry needs. And remember, this was the era well before entrepreneurism. It really was the interface to the Fortune 500’s and guiding and transitioning the technology out of MIT. That’s why I think it survived changes in technology focus, because at its core, it was interfacing industry needs with the research capabilities at the Institute,” Taub says.
|Alan Taub, Professor of Materials Science and Engineering at the University of Michigan, has become a member of the new Materials Research Laboratory External Advisory Board. Courtesy photo.|
Susan Rosevear, who is the Education Officer for the NSF-MRSEC, is responsible for an extensive array of programs, including the Summer Scholars program, which is primarily funded through NSF’s Research Experience for Undergraduates (REU) program. Each summer a dozen or so top undergraduates from across the country spend about two months at MIT as lab interns working with professors, postdocs and graduate students on cutting edge research.
CMSE also conducts summer programs for community college students and teachers, middle and high school teachers, and participates in the Women’s Technology Program and Boston Area Girls' STEM Collaborative. “Because diversity is also part of our mission, part of what our mission from NSF is, in all we do, we try to broaden participation in science and engineering,” Rosevear says.
Teachers who participate in these programs often note how collaborative the research enterprise is at MIT, Rosevear notes. Several have replaced cookbook-style labs with open-ended projects that let students experience original research.
Confidence to test ideas
Merrimack [N.H.] High School chemistry teacher Sean Müller first participated in the Research Experience for Teachers program in 2000. “Through my experiences with the RET program, I have learned how to ‘run a research group’ consisting of my students. Without this experience, I would not have had the confidence to allow my students to research, develop, and test their original ideas. This has also allowed me to coach our school’s Science Olympiad team to six consecutive state titles, to mentor a set of students that developed a mini bio-diesel processor that they sold to Turner Biodiesel, and to mentor another set of students that took second place in Embedded Systems at I.S.E.F. [Intel International Science and Engineering Fair] last year for their ChemiCube chemical dispensing system,” Müller says.
Müller says he is always looking for new ideas and researching older ideas to develop lab activities in his classroom. “One year my students made light emitting thin films. We have grown beautiful bismuth crystals in our test furnace, and currently I am working out how to make glow-in-the-dark zinc sulfide electroluminescent by doping it with copper so that we can make our own electroluminescent panels,” he says. “Next year we are going to try to make the clear see-through wood that was in the news earlier this year. I am also bringing in new materials that they have not seen before such as gallium-indium eutectic. These novel materials and activities generate a very high level of enthusiasm and interest in my students, and students that are excited, interested, and motivated learn more efficiently and more effectively.”
Müller developed a relationship with Prof. Steve Leeb that has brought Müller back to MIT during past summers to present a brief background in polymer chemistry, supplemented by hands-on demonstrations and activities, for the Science Teacher Enrichment Program (STEP) and Women’s Technology program. “Last year I showed them how they could use their cell phone and a polarized film to see the different areas of crystallization in polymers when they are stressed,” Müller says. “I enjoy the presentation because it is more of a conversation with all of the teachers, myself included, asking questions about different activities and methods and discussing what has worked and what has not worked in the past.”
Looking back on his nine years as MPC director, Thompson says, “The MPC served a broad community, but many people at MIT didn’t know about it because it was in the basement of Building 12. So one of the things that I wanted to do was raise the profile of MPC so people better understood what the MPC did in order to better serve the community.” MPC rolled out a new logo and developed a higher profile Web page, for example. “I think that was successful. I think many more people understand who we are and what we do and that enables us to do more,” Thompson says. In 2014 MPC moved to Building 24 as the old Building 12 was razed to make way for MIT.nano. The new MRL is consolidating its offices in Building 13.
“Research breakthroughs by their very nature are hard to predict, but what we can do is we can create an environment that leads to research breakthroughs,” Thompson says. “The successful model in both MPC and CMSE is to bring together people interested in materials, but with different disciplinary backgrounds. We’ve done that separately, we’ll do it together, and the expectation is that we’ll do it even more effectively.”
– Denis Paiste, Materials Research Laboratory
October 10, 2017
Updated January 25, 2018
Study finds topological materials could boost the efficiency of thermoelectric devices.
|MIT researchers, looking for ways to turn heat into electricity, find efficient possibilities in certain topological materials.|
What if you could run your air conditioner not on conventional electricity, but on the sun’s heat during a warm summer’s day? With advancements in thermoelectric technology, this sustainable solution might one day become a reality.
Thermoelectric devices are made from materials that can convert a temperature difference into electricity, without requiring any moving parts — a quality that makes thermoelectrics a potentially appealing source of electricity. The phenomenon is reversible: If electricity is applied to a thermoelectric device, it can produce a temperature difference. Today, thermoelectric devices are used for relatively low-power applications, such as powering small sensors along oil pipelines, backing up batteries on space probes, and cooling minifridges.
But scientists are hoping to design more powerful thermoelectric devices that will harvest heat — produced as a byproduct of industrial processes and combustion engines — and turn that otherwise wasted heat into electricity. However, the efficiency of thermoelectric devices, or the amount of energy they are able to produce, is currently limited.
Now researchers at MIT have discovered a way to increase that efficiency threefold, using “topological” materials, which have unique electronic properties. While past work has suggested that topological materials may serve as efficient thermoelectric systems, there has been little understanding as to how electrons in such topological materials would travel in response to temperature differences in order to produce a thermoelectric effect.
In a paper published in the Proceedings of the National Academy of Sciences, the MIT researchers identify the underlying property that makes certain topological materials a potentially more efficient thermoelectric material, compared to existing devices.
“We’ve found we can push the boundaries of this nanostructured material in a way that makes topological materials a good thermoelectric material, more so than conventional semiconductors like silicon,” says Te-Huan Liu, a postdoc in MIT’s Department of Mechanical Engineering. “In the end, this could be a clean-energy way to help us use a heat source to generate electricity, which will lessen our release of carbon dioxide.”
Liu is first author of the PNAS paper, which includes graduate students Jiawei Zhou, Zhiwei Ding, and Qichen Song; Mingda Li, assistant professor in the Department of Nuclear Science and Engineering; former graduate student Bolin Liao, now an assistant professor at the University of California at Santa Barbara; Liang Fu, the Biedenharn Associate Professor of Physics; and Gang Chen, the Soderberg Professor and head of the Department of Mechanical Engineering.
A path freely traveled
When a thermoelectric material is exposed to a temperature gradient — for example, one end is heated, while the other is cooled — electrons in that material start to flow from the hot end to the cold end, generating an electric current. The larger the temperature difference, the more electric current is produced, and the more power is generated. The amount of energy that can be generated depends on the particular transport properties of the electrons in a given material.
Scientists have observed that some topological materials can be made into efficient thermoelectric devices through nanostructuring, a technique scientists use to synthesize a material by patterning its features at the scale of nanometers. Scientists have thought that topological materials’ thermoelectric advantage comes from a reduced thermal conductivity in their nanostructures. But it is unclear how this enhancement in efficiency connects with the material’s inherent, topological properties.
To try and answer this question, Liu and his colleagues studied the thermoelectric performance of tin telluride, a topological material that is known to be a good thermoelectric material. The electrons in tin telluride also exhibit peculiar properties that mimic a class of topological materials known as Dirac materials.
The team aimed to understand the effect of nanostructuring on tin telluride’s thermoelectric performance, by simulating the way electrons travel through the material. To characterize electron transport, scientists often use a measurement called the “mean free path,” or the average distance an electron with a given energy would freely travel within a material before being scattered by various objects or defects in that material.
Nanostructured materials resemble a patchwork of tiny crystals, each with borders, known as grain boundaries, that separate one crystal from another. When electrons encounter these boundaries, they tend to scatter in various ways. Electrons with long mean free paths will scatter strongly, like bullets ricocheting off a wall, while electrons with shorter mean free paths are much less affected.
In their simulations, the researchers found that tin telluride’s electron characteristics have a significant impact on their mean free paths. They plotted tin telluride’s range of electron energies against the associated mean free paths, and found the resulting graph looked very different than those for most conventional semiconductors. Specifically, for tin telluride and possibly other topological materials, the results suggest that electrons with higher energy have a shorter mean free path, while lower-energy electrons usually possess a longer mean free path.
The team then looked at how these electron properties affect tin telluride’s thermoelectric performance, by essentially summing up the thermoelectric contributions from electrons with different energies and mean free paths. It turns out that the material’s ability to conduct electricity, or generate a flow of electrons, under a temperature gradient, is largely dependent on the electron energy.
Specifically, they found that lower-energy electrons tend to have a negative impact on the generation of a voltage difference, and therefore electric current. These low-energy electrons also have longer mean free paths, meaning they can be scattered by grain boundaries more intensively than higher-energy electrons.
Going one step further in their simulations, the team played with the size of tin telluride’s individual grains to see whether this had any effect on the flow of electrons under a temperature gradient. They found that when they decreased the diameter of an average grain to about 10 nanometers, bringing its boundaries closer together, they observed an increased contribution from higher-energy electrons.
That is, with smaller grain sizes, higher-energy electrons contribute much more to the material’s electrical conduction than lower-energy electrons, as they have shorter mean free paths and are less likely to scatter against grain boundaries. This results in a larger voltage difference that can be generated.
What’s more, the researchers found that decreasing tin telluride’s average grain size to about 10 nanometers produced three times the amount of electricity that the material would have produced with larger grains.
Liu says that while the results are based on simulations, researchers can achieve similar performance by synthesizing tin telluride and other topological materials, and adjusting their grain size using a nanostructuring technique. Other researchers have suggested that shrinking a material’s grain size might increase its thermoelectric performance, but Liu says they have mostly assumed that the ideal size would be much larger than 10 nanometers.
“In our simulations, we found we can shrink a topological material’s grain size much more than previously thought, and based on this concept, we can increase its efficiency,” Liu says.
Tin telluride is just one example of many topological materials that have yet to be explored. If researchers can determine the ideal grain size for each of these materials, Liu says topological materials may soon be a viable, more efficient alternative to producing clean energy.
“I think topological materials are very good for thermoelectric materials, and our results show this is a very promising material for future applications,” Liu says.
This research was supported in part by the Solid-State Solar Thermal Energy Conversion Center, an Energy Frontier Research Center of U.S. Department of Energy; and the Defense Advanced Research Projects Agency (DARPA).
Jennifer Chu | MIT News Office
January 16, 2018
Design is major stepping stone toward portable artificial-intelligence devices.
|From left: MIT researchers Scott H. Tan, Jeehwan Kim, and Shinhyun Choi. Image: Kuan Qiao|
When it comes to processing power, the human brain just can’t be beat.
Packed within the squishy, football-sized organ are somewhere around 100 billion neurons. At any given moment, a single neuron can relay instructions to thousands of other neurons via synapses — the spaces between neurons, across which neurotransmitters are exchanged. There are more than 100 trillion synapses that mediate neuron signaling in the brain, strengthening some connections while pruning others, in a process that enables the brain to recognize patterns, remember facts, and carry out other learning tasks, at lightning speeds.
Researchers in the emerging field of “neuromorphic computing” have attempted to design computer chips that work like the human brain. Instead of carrying out computations based on binary, on/off signaling, like digital chips do today, the elements of a “brain on a chip” would work in an analog fashion, exchanging a gradient of signals, or “weights,” much like neurons that activate in various ways depending on the type and number of ions that flow across a synapse.
In this way, small neuromorphic chips could, like the brain, efficiently process millions of streams of parallel computations that are currently only possible with large banks of supercomputers. But one significant hangup on the way to such portable artificial intelligence has been the neural synapse, which has been particularly tricky to reproduce in hardware.
Now engineers at MIT have designed an artificial synapse in such a way that they can precisely control the strength of an electric current flowing across it, similar to the way ions flow between neurons. The team has built a small chip with artificial synapses, made from silicon germanium. In simulations, the researchers found that the chip and its synapses could be used to recognize samples of handwriting, with 95 percent accuracy.
The design, published in the journal Nature Materials, is a major step toward building portable, low-power neuromorphic chips for use in pattern recognition and other learning tasks.
The research was led by Jeehwan Kim, the Class of 1947 Career Development Assistant Professor in the departments of Mechanical Engineering and Materials Science and Engineering, and a principal investigator in MIT’s Research Laboratory of Electronics and Microsystems Technology Laboratories. His co-authors are Shinhyun Choi (first author), Scott Tan (co-first author), Zefan Li, Yunjo Kim, Chanyeol Choi, and Hanwool Yeon of MIT, along with Pai-Yu Chen and Shimeng Yu of Arizona State University.
Too many paths
Most neuromorphic chip designs attempt to emulate the synaptic connection between neurons using two conductive layers separated by a “switching medium,” or synapse-like space. When a voltage is applied, ions should move in the switching medium to create conductive filaments, similarly to how the “weight” of a synapse changes.
But it’s been difficult to control the flow of ions in existing designs. Kim says that’s because most switching mediums, made of amorphous materials, have unlimited possible paths through which ions can travel — a bit like Pachinko, a mechanical arcade game that funnels small steel balls down through a series of pins and levers, which act to either divert or direct the balls out of the machine.
Like Pachinko, existing switching mediums contain multiple paths that make it difficult to predict where ions will make it through. Kim says that can create unwanted nonuniformity in a synapse’s performance.
“Once you apply some voltage to represent some data with your artificial neuron, you have to erase and be able to write it again in the exact same way,” Kim says. “But in an amorphous solid, when you write again, the ions go in different directions because there are lots of defects. This stream is changing, and it’s hard to control. That’s the biggest problem — nonuniformity of the artificial synapse.”
|Researchers in the emerging field of "neuromorphic computing" have attempted to design computer chips that work like the human brain. Instead of carrying out computations based on binary, on/off signaling, like digital chips do today, the elements of a "brain on a chip" would work in an analog fashion, exchanging a gradient of signals, or "weights," much like neurons that activate in various ways depending on the type and number of ions that flow across a synapse.|
A perfect mismatch
Instead of using amorphous materials as an artificial synapse, Kim and his colleagues looked to single-crystalline silicon, a defect-free conducting material made from atoms arranged in a continuously ordered alignment. The team sought to create a precise, one-dimensional line defect, or dislocation, through the silicon, through which ions could predictably flow.
To do so, the researchers started with a wafer of silicon, resembling, at microscopic resolution, a chicken-wire pattern. They then grew a similar pattern of silicon germanium — a material also used commonly in transistors — on top of the silicon wafer. Silicon germanium’s lattice is slightly larger than that of silicon, and Kim found that together, the two perfectly mismatched materials can form a funnel-like dislocation, creating a single path through which ions can flow.
The researchers fabricated a neuromorphic chip consisting of artificial synapses made from silicon germanium, each synapse measuring about 25 nanometers across. They applied voltage to each synapse and found that all synapses exhibited more or less the same current, or flow of ions, with about a 4 percent variation between synapses — a much more uniform performance compared with synapses made from amorphous material.
They also tested a single synapse over multiple trials, applying the same voltage over 700 cycles, and found the synapse exhibited the same current, with just 1 percent variation from cycle to cycle.
“This is the most uniform device we could achieve, which is the key to demonstrating artificial neural networks,” Kim says.
As a final test, Kim’s team explored how its device would perform if it were to carry out actual learning tasks — specifically, recognizing samples of handwriting, which researchers consider to be a first practical test for neuromorphic chips. Such chips would consist of “input/hidden/output neurons,” each connected to other “neurons” via filament-based artificial synapses.
Scientists believe such stacks of neural nets can be made to “learn.” For instance, when fed an input that is a handwritten ‘1,’ with an output that labels it as ‘1,’ certain output neurons will be activated by input neurons and weights from an artificial synapse. When more examples of handwritten ‘1s’ are fed into the same chip, the same output neurons may be activated when they sense similar features between different samples of the same letter, thus “learning” in a fashion similar to what the brain does.
Kim and his colleagues ran a computer simulation of an artificial neural network consisting of three sheets of neural layers connected via two layers of artificial synapses, the properties of which they based on measurements from their actual neuromorphic chip. They fed into their simulation tens of thousands of samples from a handwritten recognition dataset commonly used by neuromorphic designers, and found that their neural network hardware recognized handwritten samples 95 percent of the time, compared to the 97 percent accuracy of existing software algorithms.
The team is in the process of fabricating a working neuromorphic chip that can carry out handwriting-recognition tasks, not in simulation but in reality. Looking beyond handwriting, Kim says the team’s artificial synapse design will enable much smaller, portable neural network devices that can perform complex computations that currently are only possible with large supercomputers.
“Ultimately we want a chip as big as a fingernail to replace one big supercomputer,” Kim says. “This opens a stepping stone to produce real artificial hardware.”
This research was supported in part by the National Science Foundation.
Jennifer Chu | MIT News Office
January 22, 2018
|First row (l-r): Stephen Bell, Timothy Cronin, Nikta Fakhri, Robert Griffin. Second row (l-r): Jacqueline Hewitt, William Minicozzi, Aaron Pixton, Gabriela Schlau-Cohen. Third row (l-r): Alexander Shalek, Scott Sheffield, Susan Solomon, Stefani Spranger.|
The School of Science has appointed 12 faculty members to named professorships.
The new appointments are:
Stephen Bell, the Uncas (1923) and Helen Whitaker Professor in the Department of Biology: Bell is a leader in the field of DNA replication, specifically in the mechanisms controlling initiation of chromosome duplication in eukaryotic cells. Combining genetics, genomics, biochemistry, and single-molecule approaches, Bell has provided a mechanistic picture of the assembly of the bidirectional DNA replication machine at replication origins.
Timothy Cronin, the Kerr-McGee Career Development Professor in the Department of Earth, Atmospheric and Planetary Sciences: Cronin is a climate physicist interested in problems relating to radiative‐convective equilibrium, atmospheric moist convection and clouds, and the physics of the coupled land‐atmosphere system.
Nikta Fakhri, the Thomas D. and Virginia W. Cabot Professor in the Department of Physics: Combining approaches from physics, biology, and engineering, Fakhri seeks to understand the principles of active matter and aims to develop novel probes, such as single-walled carbon nanotubes, to map the organization and dynamics of nonequilibrium heterogeneous materials.
Robert Griffin, the Arthur Amos Noyes Professor in the Department of Chemistry: Griffin develops new magnetic resonance techniques to study molecular structure and dynamics and applies them to interesting chemical, biophysical, and physical problems such as the structure of large enzyme/inhibitor complexes, membrane proteins, and amyloid peptides and proteins.
Jacqueline Hewitt, the Julius A. Stratton Professor in Electrical Engineering and Physics in the Department of Physics: Hewitt applies the techniques of radio astronomy, interferometry, and image processing to basic research in astrophysics and cosmology. Current topics of interest are observational signatures of the epoch of reionization and the detection of transient astronomical radio sources, as well as the development of new instrumentation and techniques for radio astronomy.
William Minicozzi, the Singer Professor of Mathematics in the Department of Mathematics: Minicozzi is a geometric analyst who, with colleague Tobias Colding, has resolved a number of major results in the field, among them: proof of a longstanding S.T. Yau conjecture on the function theory on Riemannian manifolds, a finite-time extinction condition of the Ricci flow, and recent work on the mean curvature flow.
Aaron Pixton, the Class of 1957 Career Development Professor in the Department of Mathematics: Pixton works on various topics in enumerative algebraic geometry, including the tautological ring of the moduli space of algebraic curves, moduli spaces of sheaves on 3-folds, and Gromov-Witten theory.
Gabriela Schlau-Cohen, the Thomas D. and Virginia W. Cabot Professor in the Department of Chemistry: Schlau-Cohen’s research employs single-molecule and ultrafast spectroscopies to explore the energetic and structural dynamics of biological systems. She develops new methodology to measure ultrafast dynamics on single proteins to study systems with both sub-nanosecond and second dynamics. In other research, she merges optical spectroscopy with model membrane systems to provide a novel probe of how biological processes extend beyond the nanometer scale of individual proteins.
Alexander Shalek, the Pfizer Inc.-Gerald Laubach Career Development Professor in the Department of Chemistry: Shalek studies how our individual cells work together to perform systems-level functions in both health and disease. Using the immune system as his primary model, Shalek leverages advances in nanotechnology and chemical biology to develop broadly applicable platforms for manipulating and profiling many interacting single cells in order to examine ensemble cellular behaviors from the bottom up.
Scott Sheffield, the Leighton Family Professor in the Department of Mathematics: Sheffield is a probability theorist, working on geometrical questions that arise in such areas as statistical physics, game theory and metric spaces, as well as long-standing problems in percolation theory.
Susan Solomon, the Lee and Geraldine Martin Professor in Environmental Studies in the Department of Earth, Atmospheric and Planetary Sciences: Solomon focuses on issues relating to both atmospheric climate chemistry and climate change, and is well-recognized for her insights in explaining the cause of the Antarctic ozone “hole” as well as her research on the irreversibility of global warming linked to anthropogenic carbon dioxide emissions and on the influence of the ozone hole on the climate of the southern hemisphere.
Stefani Spranger, the Howard S. (1953) and Linda B. Stern Career Development Professor in the Department of Biology: Spranger studies the interactions between cancer and the immune system with the goal of improving existing immunotherapies or developing novel therapeutic approaches. Spranger seeks to understand how CD8 T cells, otherwise known as killer T cells, are excluded from the tumor microenvironment, with a focus on lung and pancreatic cancers.
– School of Science
MIT News Office
January 19, 2018
New metal-mesh membrane could solve longstanding problems and lead to inexpensive power storage.
|A type of battery first invented nearly five decades ago could catapult to the forefront of energy storage technologies, thanks to a new finding by researchers at MIT and other institutions. Illustration modified from an original image by Felice Frankel|
A type of battery first invented nearly five decades ago could catapult to the forefront of energy storage technologies, thanks to a new finding by researchers at MIT. The battery, based on electrodes made of sodium and nickel chloride and using a new type of metal mesh membrane, could be used for grid-scale installations to make intermittent power sources such as wind and solar capable of delivering reliable baseload electricity.
The findings are being reported in the journal Nature Energy, by a team led by MIT professor Donald Sadoway, postdocs Huayi Yin and Brice Chung, and four others.
Although the basic battery chemistry the team used, based on a liquid sodium electrode material, was first described in 1968, the concept never caught on as a practical approach because of one significant drawback: It required the use of a thin membrane to separate its molten components, and the only known material with the needed properties for that membrane was a brittle and fragile ceramic. These paper-thin membranes made the batteries too easily damaged in real-world operating conditions, so apart from a few specialized industrial applications, the system has never been widely implemented.
But Sadoway and his team took a different approach, realizing that the functions of that membrane could instead be performed by a specially coated metal mesh, a much stronger and more flexible material that could stand up to the rigors of use in industrial-scale storage systems.
“I consider this a breakthrough,” Sadoway says, because for the first time in five decades, this type of battery — whose advantages include cheap, abundant raw materials, very safe operational characteristics, and an ability to go through many charge-discharge cycles without degradation — could finally become practical.
While some companies have continued to make liquid-sodium batteries for specialized uses, “the cost was kept high because of the fragility of the ceramic membranes,” says Sadoway, the John F. Elliott Professor of Materials Chemistry. “Nobody’s really been able to make that process work,” including GE, which spent nearly 10 years working on the technology before abandoning the project.
As Sadoway and his team explored various options for the different components in a molten-metal-based battery, they were surprised by the results of one of their tests using lead compounds. “We opened the cell and found droplets” inside the test chamber, which “would have to have been droplets of molten lead,” he says. But instead of acting as a membrane, as expected, the compound material “was acting as an electrode,” actively taking part in the battery’s electrochemical reaction.
“That really opened our eyes to a completely different technology,” he says. The membrane had performed its role — selectively allowing certain molecules to pass through while blocking others — in an entirely different way, using its electrical properties rather than the typical mechanical sorting based on the sizes of pores in the material.
In the end, after experimenting with various compounds, the team found that an ordinary steel mesh coated with a solution of titanium nitride could perform all the functions of the previously used ceramic membranes, but without the brittleness and fragility. The results could make possible a whole family of inexpensive and durable materials practical for large-scale rechargeable batteries.
The use of the new type of membrane can be applied to a wide variety of molten-electrode battery chemistries, he says, and opens up new avenues for battery design. “The fact that you can build a sodium-sulfur type of battery, or a sodium/nickel-chloride type of battery, without resorting to the use of fragile, brittle ceramic — that changes everything,” he says.
The work could lead to inexpensive batteries large enough to make intermittent, renewable power sources practical for grid-scale storage, and the same underlying technology could have other applications as well, such as for some kinds of metal production, Sadoway says.
Sadoway cautions that such batteries would not be suitable for some major uses, such as cars or phones. Their strong point is in large, fixed installations where cost is paramount, but size and weight are not, such as utility-scale load leveling. In those applications, inexpensive battery technology could potentially enable a much greater percentage of intermittent renewable energy sources to take the place of baseload, always-available power sources, which are now dominated by fossil fuels.
The research team included Fei Chen, a visiting scientist from Wuhan University of Technology; Nobuyuki Tanaka, a visiting scientist from the Japan Atomic Energy Agency; MIT research scientist Takanari Ouchi; and postdocs Huayi Yin, Brice Chung, and Ji Zhao. The work was supported by the French oil company Total S.A.
David L. Chandler | MIT News Office
January 22, 2018
Boston Globe-affiliated health and science report STAT featured Associate Professor Katharina Ribbeck’s work on mucus with an article and video on its website on January 17, 2018.
While many of us think of mucus as mere tissue fillers, Katharina Ribbeck views it differently. “Mucus really is the unsung hero that has been taming problematic pathogens for millions of years,” Ribbeck tells STAT multimedia producer Hyacinth Empinado. “It really is the battleground location of our microbial interactions.”
Read more at STAT.
Video, Hyacinth Empinado/STAT
60 from industry and academia gather for three-day immersion into designing complex optical circuits during AIM Photonics Academy winter session.
|AIM Photonics Winter Academy drew more than 60 people together at MIT Jan. 16-18,2018, for lectures and design labs on integrated photonics. Photo, Denis Paiste, MIT MRL.|
How can driverless cars detect obstructions when it’s foggy outside? What new forms of light communications can supercharge the internal housekeeping of data centers to enable ever faster cloud computing? Can we detect a gas leak along a 1,000-mile pipeline remotely, at ultralow cost? These were some of the questions students investigated at an AIM Photonics Academy training session.
More than 60 people gathered at MIT on Jan. 16, 2018, for three days of lectures and design labs on integrated photonics. The program was organized by AIM Photonics Academy, which is part of AIM Photonics Institute, one of 14 institutes jointly funded with federal government to accelerate advanced manufacturing in the United States. Attendees, mostly from industry, came from the U.S. and abroad.
Integrated photonics uses complex optical circuits to process and transmit signals of light, similar to the routing of electrical signals in a computer microchip. Students learned how to design device components and lay out photonic integrated circuits (PICs), for submission to AIM’s multi-project wafer facility in Albany. They also learned about different applications for PICs, including datacom, sensors and LIDAR for driverless cars.
The technology is still emerging, and companies are looking for outside training to fill in the gaps they are unable to fill by themselves. Lockheed Martin’s AIM Program Manager Nick Rhenwrick described why he has been sending employees to AIM Academy trainings: “This partnership is critical for accelerating the adoption of Photonic Integrated Chip technology across our enterprise.”
The three-day AIM Winter Academy is part of a suite of AIM Academy education and training offerings. AIM Photonics Academy will post teaching packages and roll out online self-paced courses in integrated photonics that will be available for free on its website, and in the spring will begin rolling out edX courses to give students critical hands-on experience designing photonic integrated circuits.
These initiatives are geared for higher-skilled learners. Concurrently, AIM Photonics Academy is committed to introducing younger students to integrated photonics, and is working with TED-Ed to create three videos for students in K-12.
Sharing know-how widely
Education director Sajan Saini spoke about the feedback he received from students in the Winter Academy, “They’re excited about the new technology, want to figure out how to deploy it, and are committed to the time and effort needed to master fabless photonics tools. The time is ripe to disseminate our online and onsite teaching content as broadly as possible.”
Photonic integrated circuits have the potential to offer blockbuster solutions for driverless cars, data centers, gas sensors and microwave communications in the coming years. The emergence of an expert manufacturing platform and multiple applications-driven demands are the hallmarks of an extended period of industrial innovation, and integrated photonics is primed to offer high-performance, efficient solutions.