Materials Day Poster Session presenters capped off the annual Materials Day Symposium with brief highlights of research ranging from solar energy and alternative fuels to spinal cord injury and neural networks for artificial intelligence.
Postdoc Grace Han, in Prof. Jeffrey Grossman’s group, Department of Materials Science and Engineering, described progress in creating materials which absorb photons from sunlight and convert them into heat energy through the charging and discharging cycle of organic photo switching molecules. “This is quite different from just heating water or concrete block by solar radiation in that we can actually store the energy and release energy by triggering,” Han said. These organic coatings can be integrated onto car windshields for deicing, fabrics for personal heating, or building materials for temperature control. Han’s poster also described a new process to harness waste heat from industrial furnaces, and store it for later release.
Janille Maragh, a graduate student in Professor Admir Masic’s lab, Department of Civil and Environmental Engineering, presented her work on sustainable construction materials. To study ancient Roman concrete from an archaeological site in Italy, she used Energy Dispersion Spectroscopy and Raman spectroscopy to map centimeter scale samples at microscopic resolution. “What we are trying to do is understand exactly what our sample is made of so can we understand this phenomenal material. … So we understand not only the bulk composition of our material but also their fracture surface.”
“Carbon monoxide is responsible for more than half of all fatal poisonings worldwide,” Vera Schroeder, a graduate student in Professor Timothy Swager’s lab, said. “Exposure to this odorless, colorless and tasteless gas is very difficult to detect for humans, which is compounded by the fact that the initial symptoms of poisoning – headache, dizziness, and confusion are non-specific.” Schroeder is developing bio-inspired carbon monoxide sensors that use a transistor-based design to activate a chemical change in iron atoms to detect carbon monoxide, even in air. “This new mode of sensor allows us to have a voltage activated, enhanced and highly specific response and we can detect carbon monoxide in air with much higher sensitivity than we detect CO2, oxygen or water,” she said.
Alfonso Juan Carrillo, a postdoc in the lab of Jennifer L. M. Rupp, the Thomas Lord Assistant Professor of Materials Science and Engineering, presented results of work on perovskite materials for solar-driven transformation of CO2 and water into fuels. Carillo selected the best candidate perovskite materials, synthesized these perovskites, analyzed their microstructure, and tested them in a fixed bed high-temperature reactor. “We use what are called thermochemical cycles,” Carillo said. As the perovskite absorbs oxygen, it can transform water and carbon dioxide into hydrogen and carbon monoxide.
Minghui Wang, a postdoc in Professor Karen Gleason’s lab, is creating thin-film microporous polymers for gas separation using chemical vapor deposition. Gas separation is important for industrial gas needs and carbon capture but heat-based methods are energy intensive,” he said. “One challenge is that you need to achieve both high flux and high gas selectivity for membrane materials. To do so, usually you need a rigid and microporous structure and also you need to fabricate very thin films, but to do both of them is kind of difficult. In our lab, we use chemical vapor deposition to deposit pinhole-free thin films by using this technique and using porphyrin as a monomer.” He achieved high selectivity for carbon dioxide and nitrogen separation using polymerized porphyrin on a flexible substrate.
Andrew Dane, a graduate student in Professor Karl Berggren’s group, discussed progress on improving speed and efficiency in superconducting nanowire single photon detectors. Two competing available materials tilt toward either speed or efficiency. “We changed the material deposition and made some devices and showed that we kind of combined the best of both worlds,” Dane said. “There is a quantum phase transition in the material that we’re working with and a lot of other interesting things.”
About a million Americans undergo hernia repair surgery each year and for one in four or them, hernia will re-occur. About half will experience some degree of chronic pain, said Sebastian Pattinson, a postdoc in the lab of Associate Professor of Mechanical Engineering A. John Hart. The surgical mesh used to mechanically reinforce the tissue as it heals causes many of these complications. Pattinson described a new 3D printing process that allows local customization of mechanical response in a surgical mesh and in particular allows for non-linear mechanical response in a way that mimics tissue. “We hope that these meshes will help alleviate the complications suffered by many patients all around the world,” Pattinson said.
Chemistry postdoc Zhou Lin, in Professor Troy A. Voorhis’ group, presented research on a process to double electric current in organic solar cells by splitting single excitons into pairs, a process that is called singlet fission. “We can generate two electric currents out of one high-energy photon so we can promote the efficiency of organic photovoltaics, that’s what we want,” Lin said. “Based on our electronic structure theory calculations, we are able to reproduce the experimental trend for the fission rate using three different isomers that can undergo this intramolecular singlet fission,” she said.
Yukio Cho, a graduate student in Prof. Harry L. Tuller’s lab, is working on mixed ionic and electronic conductor [MIEC] cathode materials for solid oxide fuel cells. Using electrochemical methods, Cho and colleagues synthesized n-type cathode material to improve the surface exchange. “We control the defects, control the electronic defects, and for the current result, we successfully synthesized n-type materials,” Cho said. “The expected good surface exchange capability is also confirmed through transfer diffusion measurements.”
Frank McGrogan, a graduate student in Professor Krystyn J. Van Vliet’s lab, presented his work with the Chemomechanics of Far-From-Equilibrium Interfaces [COFFEI] group on all-solid electrolytes in lithium ion battery systems. “One of the main sticking points is we have this problem of lithium metal unevenly plating the electrodes, crossing the electrolyte and shorting the cell. Our group has been treating this as a fracture issue. … We’ve demonstrated experimentally that fracture is indeed a mechanism for this lithium plating and shorting problem.”
“We’ve gone ahead and measured some mechanical properties including fracture properties of several important solid electrolytes and used these inputs in simulations to predict damage evolution,” McGrogan said. “I think that the way that our group has approached this problem and how we’re getting to the mechanism is going to change the way our field thinks about failure in all solid-state lithium ion batteries.”
Postdoc Dena Shahriari, who works with Professors Yoel Fink and Polina Anikeeva, shared an update on efforts to repair spinal cord damage by optically stimulating and guiding the growth of injured neurons. “We’re using a thermal drawing process, which is a high throughput technique which will allow us to create kilometer-long fibers in just one experiment,” Shahriari said. These highly flexible probes deliver light to the lesion of the spinal cord, and record at multiple sites of these neurons.
“For the tissue engineering part we needed to bridge the nerve gap, we needed to create porosity into these scaffolds, and for that we need to add a twist to this thermal drawing process that will allow us to not only create, but also control, porosity in that,” Shahriari said.
Gerald Wang, a graduate student in mechanical engineering under Prof. Nicolas Hadjiconstantinou, invited attendees to learn more about his poster by arranging it so that the first letters of each line spelled out “C-O-M-E.” He is exploring the fluid-solid interface atop a sheet of graphene. “It turns out when you put fluid in this environment under the right conditions, it will spontaneously arrange into a layered structure that mimics the solid below it. This layered fluid structure, practically indistinguishable from tiramisu or the layered cake of your preference, imparts upon the fluid remarkable fluid properties including enhanced heat transfer, remarkably long slip lengths and highly modified surface diffusivities very different from the bulk fluid.”
“It’s a very exciting story with some of the great actors and actresses of today including Van der Waals, high through-put simulation and molecular self-assembly. So there’s something for everybody whether you’re an experimentalist, a theorist, a computationalist, or you just like a good scaling relation, you should make like the letters and come on by,” Wang said.
Mary Elizabeth Wagner, a graduate student in the group of Associate Professor of Metallurgy Antoine Allanore, is working on a sustainable way to refine precious metals from nature and from recycled materials. “The problem is these expensive elements, silver, gold, platinum, are found in very, very tiny amounts, comparatively to copper, but they make up so much of the cost,” Wagner said.
“My idea in my research focuses on one system that can host electrochemistry for gold, for silver, and for platinum group metals,” Wagner said. Molten sulfide electrolytes are one promising system. “We should be able to treat all of these metals in one go, which should be able to provide an environmentally sustainable as well as a cost-effective way to treat these metals,” she said.
Vrindaa Somjit, a graduate student under Prof. Bilge Yildiz, is examining the effect of dopants on hydrogen solubility in alumina using a computational, first principles approach. Hydrogen may become a fuel of the future, but one of the main problems in making this a reality is the storage and transport of hydrogen. Hydrogen can penetrate steel and cause it to fail.
“One way to mitigate this problem of hydrogen embrittlement is by the use of permeation barrier coatings, and alpha-alumina is a promising candidate,” Somjit said. She set out to determine if dopants, extra chemical elements added to a compound, could improve the performance of alpha-alumina in resisting hydrogen penetration. “What we found is that actually dopants do not help in decreasing the hydrogen solubility because alpha-alumina itself lies at the bottom of the hydrogen solubility valley,” Somjit said.
Graduate student Chang Sub Kim, in Professor Harry Tuller’s group, conducts research to electrochemically pump oxygen in and out of a thin film of layered cuprate, which has potential as a cathode material. “An interesting fact is that it can accommodate both oxygen vacancies as well as interstitials. So in this study, I show you that I can control the region where I can access oxygen-access and also oxygen-deficient regions, and then show that I can simultaneously measure different materials properties such as oxygen surface reaction kinetics as well as in-plane conductivity, which agrees very well with the expected defect chemistry.”
Postdoc Yuming Chen in Professor Ju Li’s group, spoke about a project to develop a sodium-ion battery anode using nitrogen-doped carbon. Chen introduces nitrogen atoms into the structure of hollow carbon tubes to create larger spacing that allows sodium to penetrate the carbon tube and yield higher performance. These carbon tubes can be used as freestanding electrodes with long cycling life.
Ananya Balakrishna, a postdoc in Professor W. Craig Carter’s group, developed theoretical and computational models to investigate the link between material properties and microstructure. “In my research, I probe questions like what determines microstructural patterns, can we engineer microstructures to control macroscopic material properties,” she said. Her poster featured two projects describing microstructure in ferroelectric materials and in lithium battery electrodes.
“In lithium batteries, microstructures form during a typical charge/discharge cycle. In these microstructures, the underlying lattice symmetry has an effect on material properties, for example, certain lattice arrangements facilitate the faster propagation of diffusion of lithium ions and certain lattice arrangements cause non-uniform expansion of electrodes,” Balakrishna said. She is working on a phase field crystal model that couples lattice symmetry with the concentration field to describe electrode microstructure.
Menghsuan Sam Pan, a graduate student in Professor Yet-Ming Chiang’s group, focuses on using water-based sulfur batteries for low-cost energy storage. “It’s one of the lowest cost per stored charge in any electrochemically active materials, only behind water and oxygen,” Pan said. “When we work in soluble electrodes, we found that the sulfur can only be reversibly cycled between a di-sulfide and a tetra-sulfide regime, and with this we did some technical economic modeling to see the installed costs of the electrode. What surprised us is that the component that’s used to hold the electrode is more costly than the active material itself.”
Experiments showed these sulfide species cycle reversibly, precipitating into the electrode and then dissolving very well when they are cycled back, Pan said. “We cycled for more than 1,600 hours, more than two months,” he said, noting a 30 percent cost reduction in terms of cost per stored capacity.
Working under Professor Jeehwan Kim, graduate student Scott Tan is developing hardware for neural networks for artificial intelligence. He makes silicon-germanium cross-bar arrays with a reversible silver conductance channel to toggle the conductance state of these synaptic devices. “We’ve also used these devices in a simulation and showed that they can perform handwriting recognition with accuracy up to 95 percent,” Tan said.
Mechanical engineering graduate student Nicholas T. Dee presented work in Professor A. John Hart’s group on scalable roll-to-roll graphene production for membrane applications. “We’ve developed a roll-to-roll CVD reactor for this process that is unique in that it has two different zones, one specifically for annealing the substrate and catalyst and one zone for growth of the graphene,” Dee said. The researchers tuned the gas composition to achieve full coverage of monolayer graphene and explored the tradeoff between production rate and quality of the graphene. “We have demonstrated using our graphene produced in this high-throughput manner to produce nano-porous, atomically thin membranes for potential desalination applications,” he said.
Brad R. Nakanishi, a graduate student in Professor Antoine Allanore’s group, introduced his research on high-temperature materials chemistry in refractory metals. “What we’ve done, where experiment by conventional methods or prediction by first principles prove very complex and challenging, we’ve basically modified a floating zone furnace which has provided us with enhanced experimental throughput and also very unique ability to see and probe the properties of these refractory liquids,” Nakanishi said. His poster showed an image of the first direct electrolytic decomposition of aluminum oxide to oxygen gas and aluminum metal. “We’ve been using this approach to make fundamental thermodynamic property measurements like chemical potential,” he said. This work has implications for discovery of new materials for applications from aerospace to nuclear as well as discovery of new processes for materials extraction.
Chosen by guests who attended the Materials Day Poster Session, this year's Poster Session prize winners were Postdoc Dena Shahriari, electrical engineering and computer science; graduate student Vera Schroeder, chemistry; and Postdoc Sebastian Pattinson, mechanical engineering.
The annual MIT Materials Research Laboratory [MRL] Materials Day Symposium and Poster Session were held on Wednesday, Oct. 11, 2017.
Related: A magical dimension
|MIT MRL External Advisory Board Chair Julia Phillips [far left] moderated the Materials Day Symposium panel on “Frontiers in Materials Research.” She was joined by [from second left] Professors Karen Gleason, Caroline Ross, Timothy Swager, and Vladimir Bulović. The session was held Wednesday, Oct. 11, 2017.|
Newly discovered optical, electronic and magnetic behaviors at the nanoscale, multifunctional devices that integrate with living systems, and the predictive power of machine learning are driving innovations in materials science, a panel of MIT professors told the MIT Materials Research Laboratory [MRL] Materials Day Symposium.
“The development of new material sets is a key to the launch of new physical technologies,” Professor Vladimir Bulović, founding director of MIT.nano, said. “Once we get down to the nanoscale, we can start inducing quantum phenomena that were never quite accessible. So that scale between 1 nanometer, the typical size of a molecule, and on the order of, let’s say, 20 nanometers, that’s a magical dimension, where you can fine tune your optical, electronic and magnetic properties.”
Professor Caroline Ross, Associate Head of the Department of Materials Science and Engineering, cited a trend of harnessing nature to self assemble complex structures. “As we want to make things smaller and smaller, we need to have nature helping out,” she said. Ross noted progress on a range of new multi-functional materials that use, for example, extremely low voltage levels to control magnetism or that use strain to control electronic properties. “All of these can enable new kinds of devices from those materials, so you can imagine devices which are smart that can have memory or logic functions, that can have analog instead of just digital type of behavior, that can work together to make smart circuits. … The difficulties of integrating those types of materials will be well paid for by the new sorts of functionality we can get from the devices we make.”
MIT MRL External Advisory Board Chair Julia Phillips moderated the Materials Day Symposium panel on Wednesday, Oct. 11, 2017. Phillips is a former Sandia National Laboratories executive.
Professor Timothy Swager, Director of the Deshpande Center, said the expectation that new medical devices, for example, are compatible with our bodies demands different requirements than previous generations of electronics. “Thinking about how we interface complex dynamic chemically reactive systems with a material is really a very important area that, I think, will continue to be of importance and many good discoveries are going to come about as result of the interest in that area,” he said.
Associate Provost and Professor Karen Gleason spoke of the growing influence of machine learning on materials advances and the potential for one-dimensional and two-dimensional materials to provide better computers and memory storage. “It’s going be incredible for materials discovery as we learn how to use machine learning to predict what materials are optimal, but there’s also a credible place for materials in making this technology grow. Now computational power and memory and databases have gotten large enough that the predictive power is actually great.”
“The biggest component is you need the data so you need all of these sensors for accurate positioning, for detection of gases, for health. People want wearables,” Gleason said. “So I think this is an enormous field with tremendous impact in many different ways that materials can play.”
Bulović said while it takes a lot of perseverance to implement a new idea on the nanoscale, “It’s important to highlight that the invention of an idea happens in a moment, that eureka moment, but to actually scale that idea up so a million people can hold it in their hands, that takes a decade sometimes, especially if it’s in the materials space. Recognition of that is important in order to support the evolution of the new ideas.”
The annual Materials Day Symposium was hosted for the first time by the MIT Materials Research Laboratory, which formed from the merger of the Materials Processing Center and the Center for Materials Science and Engineering, effective Oct. 1, 2017. The MIT MRL will work hand-in-hand with MIT.nano, the central research facility being built in the heart of the MIT campus due to open in June 2018. MIT will receive a $2.5 million gift from the Arnold and Mabel Beckman Foundation to help develop a state-of-the-art cryo-electron microscopy (cryo-EM) center to be housed at the MIT.nano facility.
“I don’t think we can underestimate the value of the tool sets in providing us the direction to what we need to do to advance life as we know it,” Bulović said. “I get struck by the example of DNA … It took 80-plus years to obtain the first inkling that there was something twisted inside our cells. Then we debated for another decade, is this thing really a twisted molecule inside our cells. If you add it all up, 80, 90 years of debate. Today that’s reduced to a couple of hours of work by one graduate student who can take a cell, pull out a nucleus, put it under a scanning tunneling microscope or cryo electron microscope and see a twisted molecule we call DNA now.”
Swager noted that biologists also will use MIT.nano. “They are going to be using the cryo-EM in the basement, so nano is not only for engineers and molecule builders. … I think that’s going to be really exciting and where that fusion leads us, who knows.”
Moderator Phillips asked the panelists what tool sets that would like to see in MIT.nano. Gleason said she would like to see chemical vapor deposition for thin polymer films. Ross said that MIT needs to be at the forefront for materials characterization tools. “We need to have the best tools to do the best work,” Ross said. She would like to see MIT.nano get the best possible electron microscope and advanced deposition tools for oxide molecular beam epitaxy and building up complex materials layer by layer. Swager said it is important for the shared facility to house tools for rapid prototyping and fabrication of devices.
– Denis Paiste, Materials Research Laboratory
November 27, 2017
Related: Poster Highlights
Interdisciplinary materials research holds the key to solving the e2xistential challenges facing humanity, former Sandia National Laboratories executive Julia M. Phillips told the annual MIT Materials Research Laboratory [MRL] Materials Day Symposium on Wednesday, Oct. 11, 2017. “What is both very exciting for us as materials researchers, also a little frustrating, is that the real impact of materials occurs when they turn into something that you actually carry around in your pocket or whatever,” Phillips said.
During the second half of the 20th century, many of the technological advances that we take for granted today, such as laptop computers and smart phones, came from fundamental advances in materials research and the ability to control and make materials, she noted. Phillips, who retired from Sandia National Laboratories as Vice President and Chief Technology Officer, also serves as chair of the MRL External Advisory Board and is a member of the National Science Board.
MRL formed from the merger of the Materials Processing Center and the Center for Materials Science and Engineering, effective Oct. 1, 2017. MRL Director Carl V. Thompson noted in his introductory remarks, the appointment of Associate Professor of Materials Science and Engineering Geoffrey S.D. Beach as co-director of the MRL and principal investigator for the National Science Foundation Materials Research Science and Engineering Center.
Fueled by industrial needs and government-funded research in the post-World War II era, “Materials research was undeniably an early model for interdisciplinary research,” Phillips said. With new tools such as scanning probe microscopes to understand the structure and properties of materials, materials scientists in the last half of the 20th Century created whole new classes of materials and products, ranging from super alloys that enabled larger and more reliable jet engines to strained layer superlattices that underlie modern magnetic recording,7 lasers and infrared detectors.
Future gains will come from the ability to synthesize and control increasingly complex materials, Phillips says, noting progress in areas such as high-temperature superconductors, porous solids like metal organic frameworks, and metamaterials that generate new properties from combining biological materials, organics, ceramics and metals at near molecular scale precision in ways not found in nature. “Somewhere in the fuzzy space between molecules and materials,” Phillips notes, these newer materials have very interesting properties that are still in the process of being fully explored, and they will be exploited in the years to come. “It’s very clear to many people that these also will be transformational as we move forward,” she says.
The materials research approach, which brings together researchers from across different science and engineering fields to solve complex problems, provides a model for solving 21st Century challenges in energy, environment and sustainability; health care and medicine; vulnerability to human and natural threats; and expanding and enhancing human capability and joy. “These are exemplars, but you can see materials written all over this list, and I would posit that any comparable list you might come up with would have materials written all over it,” Phillips said. “In order to address those grand challenges, we really need to be able to treat realistically complex systems that bring together all of these disciplines from the sciences, from engineering, from the social and behavioral sciences, and arguably even from the arts.”
Progress in scientific understanding and computational modeling are accelerating researchers’ ability to predict the structure and properties of new materials before actually making them, Phillips said.
MIT faculty members Antoine Allanore, Polina Anikeeva, A. John Hart, Pablo Jarillo-Herrero, Juejun Hu, and Jennifer Rupp presented research updates on their recent work which spans a range from ultra-thin layered materials for new electronic devices and cellular level probes for the brain and spinal cord to larger scale methods for 3D printing and metals processing.
Merging 2D materials with CMOS
Associate Professor of Physics Pablo Jarillo-Herrero stacks atomically thin, two-dimensional [2D] layers of different materials to discover new properties. Jarillo-Herrero’s lab demonstrated photodetectors, solar cells and the world’s thinnest LED. With materials such as tungsten selenide [WSe2], changing the number of layers also changes their electronic properties. Although graphene itself has no bandgap, closely aligning the lattices of graphene and boron nitride opens a 30-millivolt bandgap in graphene, he said.
“You have full electronic control with gate voltages,” Jarillo-Herrero said. Using bilayer molybdenum ditelluride, which is 10,000 times thinner than a silicon solar cell, he showed in work published in Nature Nanotechnology, a photodetector just 10 nanometers thick can be integrated on a silicon photonic crystal waveguide.
“You can just stack this at the very end of your CMOS [complementary metal oxide semiconductor] processing, and you don’t have to do any extra fabrication, any extra growth, you can just slap it on top,” Jarillo-Herrero explained. “It can be made as thin as 4 nanometers, so it’s still ultra thin, and you have a high degree of control in an ultra thin platform. The whole thing is semitransparent so we can see the light go in and out.” These new devices can be operated at telecommunications wavelengths by tuning the bandgap of the material.
Phase change materials
Juejun (JJ) Hu, the Merton C. Flemings Associate Professor of Materials Science and Engineering, is reducing power consumption, shrinking device size and ramping up processing speed with innovative combinations of materials that alternate between two different solid states, or phases, such as an alloy of germanium, antimony, selenium and tellurium. These materials are the basis for nonvolatile storage, meaning their memory state is preserved even when the power is turned off. Hu collaborated with MIT Professor Jeffrey C. Grossman and former postdoc Huashan Li to identify desirable materials for these alloys from first principles calculations, and graduate materials science and engineering student Yifei Zhang did much of the experimental work.
An earlier generation of devices based on germanium, antimony and tellurium [GST] suffers from losses to light absorption by the material. To overcome this problem, Hu substituted some of the tellurium with a lighter element, selenium, creating a new four-element structure of germanium, antimony, selenium and tellurium [GSST]. “We increase the bandgap to suppress short wavelength absorption, and we actually minimize any carrier mobility to mitigate the free carrier absorption,” he explained. Switching between amorphous and crystalline states can be triggered with a laser pulse or an electrical signal.
Although the structural state switching happens on the order of 100 nanoseconds, figuring out the techniques to accomplish it took a year of work, Hu said. Specifically, he found that using materials that switch between amorphous and crystalline states allows light to be directed over two different paths and reduces power consumption. He coupled this GSST optical phase change material with silicon nitride microresonators and waveguides to show this behavior. These switches based on phase change materials can be connected in a matrix to enable variable light control on a chip. Ultimately, Hu hopes to use this technology to build re-programmable photonic integrated circuits.
New tools for brain exploration
Class of 1942 Associate Professor in Materials Science and Engineering Polina Anikeeva works at the border between synthetic devices and the nervous system. Traditional electronic devices, with hardness like a knife, can trigger a foreign-body response from brain tissue, which typically is as soft as pudding or yogurt. Working with Prof. Yoel Fink and other MIT colleagues, Anikeeva developed soft polymer-based devices to stimulate and record activity of brain and spinal cord tissue borrowing from optical fiber drawing techniques.
An early version of their multi-functional fibers included three key elements: conductive polyethylene carbon composite electrodes to record brain cell activity; a transparent polycarbonate waveguide with cyclic olefin copolymer cladding to deliver light; and microfluidic channels to deliver drugs.
“Using this structure, for the first time, we were able to record, stimulate and pharmacologically modulate neural activity,” Anikeeva said. But the device recorded activity from clusters of neurons, not individual neurons. Anikeeva and her team addressed this problem by integrating graphite into the polyethylene composite electrodes, which increased their conductivity enough to shrink them into a structure that is as thin as a human hair. The device has six electrodes, an optical waveguide and two microfluidic channels.
Yet adding graphite increased the size and hardness of the glassy polycarbonate device, so her group turned to a new process using rubbery, stretchy polymers that they then coated with a conductive metal nanowire mesh. “This mesh of conductive metal nanowires can maintain low impedance even at 100 percent strain, and it maintains its structural integrity without any changes up to 20 percent strain, which is sufficient for us to operate in the spinal cord,” Anikeeva said.
Her students implanted these nanowire-mesh coated fibers in mice, which allowed them to stimulate and record neural activity in the spinal cord. A video showed a mouse moving its hindlimb when an optical signal delivered to the lumbar spinal cord traveled down the sciatic nerve to the gastrocnemius muscle. In these experiments, the device implanted in mice showed no decline in performance a year after surgery, Anikeeva said.
More recently, Anikeeva developed iron oxide-based nanoparticles that heat up in an applied magnetic field, which can trigger a response from neurons in the brain that express ion channels that are sensitive to heat such as capsaicin receptor, the same mechanism that is triggered when we eat hot peppers. Experimenting with mice, Anikeeva injected these tiny particles deep in the brain in a section that is associated with reward. “In our lab, we have started by modeling hysteresis in magnetic nanoparticles, synthesizing a broad range of these nanomaterials by engineering iron oxide with dopants and looking at different sizes and shapes, developing power electronics and a biological tool kit to assess this process,” Anikeeva explained. “In this case, there is no external hardwire, no wires, no implants, nothing is sticking out of the brain… however, they can now perceive magnetic field.” she said. To quantify their results, the researchers measured calcium ion influx into neurons. Work is now focused on shortening the response time to a few thousandths of a second by improving the heat output of the magnetic nanoparticles.
Ceramics for Solid-State Batteries, CO2 Sensors and Memristive Computing
Jennifer L. M. Rupp, the Thomas Lord Assistant Professor of Materials Science and Engineering, presented research showing a solid lithium garnet electrolyte can lead to batteries miniaturized on an integrated circuit chip.
Safety concerns regarding lithium batteries stem from their liquid component, which serves as the electrolyte and presents a risk of catching fire in air. Replacing the liquid electrolyte with a solid one could make batteries safer, Rupp explained. Her research shows that a ceramic material made of garnet, a material that is perhaps more familiar as a gemstone, can effectively pass lithium through a battery cell, but because it is solid, can be very safe for batteries and also have the opportunity to be miniaturized to thin film architectures. This garnet is a four-element compound of lithium, lanthanum, zirconium and oxygen. “The lithium is completely encapsulated; there is no risk of inflammation,” Rupp said.
In published research, Rupp showed that pairing a lithium titanium oxide anode with a ceramic garnet electrolyte and blurring the interface between the two materials allowed much faster battery charging time for large-scale cells. Lessons learned from applying these garnet materials pointed also to a new use for carbon dioxide sensing. “We can reconfigure the electrodes to have one electrode which simply goes as a reference, and another which undergoes a chemical reaction with carbon dioxide, and we use a tracker potential to track the effective change of carbon dioxide concentration in the environment based on bulk processing,” she explained. Rupp is also developing strained multi-layer materials to improve storage for memristive memory and computing elements.
Frontier for metals at high temperature
Associate Professor of Metallurgy Antoine Allanore pointed out that from 1980 to 2010, the world almost doubled its consumption of materials, with the fastest growth in metals and minerals. Such demand is due to the formidable low cost and high productivity of materials processing. The majority of such processes involve at some stage a high temperature operation and often the molten state of matter. Developing the science and engineering of the molten state brings huge opportunities, for example heat management in high-temperature processes such as metals extraction and glass making.
Steelmaking, for example, is already a highly efficient manufacturing process, turning out rebar, coil or wires of steel at a cost less than 32 cents per kilogram [about 15 cents per pound]. “Productivity is actually the key criteria to make materials processing successful and matter at the scale of the challenge of adding 2 billion people in the next 20 years,” he said.
Allanore’s group demonstrated that tin sulfide at high temperature, about 1,130 degrees Celsius [2,066 Fahrenheit], is an effective thermoelectric generator. “We have indications that the theoretical figure of merit for some sulfides, can be up to 1 at 1,130 [degrees Celsius]. For molten copper sulfide for example, we have estimates of the thermal conductivity, the melting point, and we have a cost that is a little bit high in my opinion, but that’s the nature of the research,” Allanore said. When his group looked at existing data, they found that for many molten compounds of sulfur and a metal, such as tin, lead or nickel, the thermoelectric figure of merit, as well as the compositional phases, had never been quantified, opening a frontier for new materials science research at high temperature. “It’s actually very difficult to know what are the true properties of the liquid,” Allanore said. “I need to know if that material will have semiconductivity. I need to know if it’s going to be denser or lighter than another liquid. … We don’t actually have computational methods to predict such property for liquids at high temperature.”
To address the problem, Allanore studied the relation in high-temperature melts between transport properties, including electrical conductivity and Seebeck coefficients, and a thermodynamic property called entropy. “We’ve put together a theoretical model that connects the transport property, like thermal power, and the thermodynamic property like entropy. This is important because it works for semiconductors, it works for metallic materials and more importantly it allows to find out regions of immiscibility in liquids,” Allanore said. Immiscibility means a material in the given condition will separate into two phases that do not mix together and remain separate.
Allanore has also developed a new method for observing molten compounds such as alumina, using a floating zone furnace, which is a transparent quartz tube located at the focal distance of four lamps. “If we can do that with oxides, we would really like to do that with sulfides,” he explained, showing a picture of molten tin sulfide sitting on a graphite plate in the floating zone furnace. The wide range of temperatures and properties of molten materials, “the ultimate state of condensed matter”, allows for better heat management, higher processing temperatures and electricity harvesting or electrical control of heat flow, he said.
3D printing a new manufacturing model
Traditional manufacturing requires economies of scale, in particular, large production volumes because of the fixed costs necessary to set up the production process, but 3D printing and other additive manufacturing technologies offer an alternative of high-performance, customizable products and devices, Associate Professor of Mechanical Engineering A. John Hart said.
Additive manufacturing is already a $6 billion a year business with reach from Hollywood special effects to high-tech jet engine nozzles. “Additive manufacturing already enables a diverse collection of materials, applications, and related processes – including by extrusion of plastics, melting metals, using lasers, and by coordinated chemical reactions that essentially are done with point wise control,” Hart explained.
“We can think of accessing new spaces in terms of the value of the products we create using additive manufacturing, also generally known as 3D printing. 3D printing is reshaping the axes by which we judge the economic viability of a manufacturing process, and allowing us to access new value spaces. For instance, we can think not only about production volume, but think about advantages in complexity of geometries, and advantages by customization of products to specific markets or even individuals. In these ways, 3D printing is influencing the entire product life cycle,” Hart said.
For instance, Hart’s group studied existing 3D printers to discover how to speed up the process from about 60 minutes to just 5 to 10 minutes to print a handheld mechanical part such as a gear. Former graduate student Jamison Go [SM, 2015] led this work, Hart said, building a desktop 3D printer about the size of a small microwave oven. The system features a control system for the printhead that moves the motors to the corner; an extrusion mechanism that drives the feedstock polymer filament like a screw; and a laser that penetrates and melts the polymer.
“By combining the fast motion control, the high heat transfer, and the high force, we can overcome the limits of the existing system,” Hart explained. The new design is three to 10 times faster in build rate than existing machines. “These kinds of steps forward can also change how we think about producing objects. If you can make something fast, you can think about how you might, or how others might, work differently,” he said. He mentioned, for instance, physicians who may need to 3D print a part for an emergency medical operation, or a repair technician who could use a 3D printer rather than hold inventory of many spare parts.
Hart’s group is currently working in collaboration with Oak Ridge National Lab on algorithms for optimization of 3D printing toolpaths, and adapting his innovations to large-scale 3d printers. “We can think about upscaling these principles to high productivity systems that are not only printing small things but printing big things,” Hart said. Hart has also worked with 3D printing of cellulose, which can be used for customization of consumer products and antimicrobial devices, and is the world’s most abundant natural polymer. He co-founded the company Desktop Metal with three other MIT faculty members and Ric Fulop SL ’06, who serves as Desktop Metal’s CEO. “The company is only two years old and will soon ship its first product which enables an entirely new approach to metal 3D printing,” Hart said.
– Denis Paiste, MIT Materials Research Laboratory
October 30, 2017
Coming up in November Newsletter: Materials Day Panel Discussion and Poster Session coverage
Materials Day is the capstone event for MRL. The symposium and poster session are usually held in October. Speakers from industry as well as MIT professors present their latest research.
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Previous years topics include:
|2016||pdf Materials For Electrochemical Energy Storage (1.83 MB)|
|2015||pdf Quantum Materials (2.49 MB)|
|2014||New Frontiers in Metal Processing|
|2012||pdf Materials for Energy Harvesting (627 KB)|
|2011||pdf Computational Materials (3.48 MB)|
|2010||pdf Materials for Sensors (4.65 MB)|
|2009||pdf Materials for Energy (7.88 MB)|
|2008||pdf Nanostructure to Infrastructure to Sustainability (3.06 MB)|
|2007||pdf Thin Films and Coatings: Designed and Processed to Enhance Function and Performance (707 KB)|