Newly observed optical state could enable quantum computing with photons.
|Scientists at MIT, Harvard University, and elsewhere have now demonstrated that photons can be made to interact — an accomplishment that could open a path toward using photons in quantum computing, if not in light sabers. Image, Christine Daniloff, MIT|
Try a quick experiment: Take two flashlights into a dark room and shine them so that their light beams cross. Notice anything peculiar? The rather anticlimactic answer is, probably not. That’s because the individual photons that make up light do not interact. Instead, they simply pass each other by, like indifferent spirits in the night.
But what if light particles could be made to interact, attracting and repelling each other like atoms in ordinary matter? One tantalizing, albeit sci-fi possibility: light sabers — beams of light that can pull and push on each other, making for dazzling, epic confrontations. Or, in a more likely scenario, two beams of light could meet and merge into one single, luminous stream.
It may seem like such optical behavior would require bending the rules of physics, but in fact, scientists at MIT, Harvard University, and elsewhere have now demonstrated that photons can indeed be made to interact — an accomplishment that could open a path toward using photons in quantum computing, if not in light sabers.
In a paper published Feb. 15, 2018, in the journal Science, the team, led by Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, and Professor Mikhail Lukin from Harvard University, reports that it has observed groups of three photons interacting and, in effect, sticking together to form a completely new kind of photonic matter.
In controlled experiments, the researchers found that when they shone a very weak laser beam through a dense cloud of ultracold rubidium atoms, rather than exiting the cloud as single, randomly spaced photons, the photons bound together in pairs or triplets, suggesting some kind of interaction — in this case, attraction — taking place among them.
While photons normally have no mass and travel at 300,000 kilometers per second (the speed of light), the researchers found that the bound photons actually acquired a fraction of an electron’s mass. These newly weighed-down light particles were also relatively sluggish, traveling about 100,000 times slower than normal noninteracting photons.
Vuletic says the results demonstrate that photons can indeed attract, or entangle each other. If they can be made to interact in other ways, photons may be harnessed to perform extremely fast, incredibly complex quantum computations.
“The interaction of individual photons has been a very long dream for decades,” Vuletic says.
Vuletic’s co-authors include Qi-Yung Liang, Sergio Cantu, and Travis Nicholson from MIT, Lukin and Aditya Venkatramani of Harvard, Michael Gullans and Alexey Gorshkov of the University of Maryland, Jeff Thompson from Princeton University, and Cheng Ching of the University of Chicago.
Biggering and biggering
Vuletic and Lukin lead the MIT-Harvard Center for Ultracold Atoms, and together they have been looking for ways, both theoretical and experimental, to encourage interactions between photons. In 2013, the effort paid off, as the team observed pairs of photons interacting and binding together for the first time, creating an entirely new state of matter.
In their new work, the researchers wondered whether interactions could take place between not only two photons, but more.
“For example, you can combine oxygen molecules to form O2 and O3 (ozone), but not O4, and for some molecules you can’t form even a three-particle molecule,” Vuletic says. “So it was an open question: Can you add more photons to a molecule to make bigger and bigger things?”
To find out, the team used the same experimental approach they used to observe two-photon interactions. The process begins with cooling a cloud of rubidium atoms to ultracold temperatures, just a millionth of a degree above absolute zero. Cooling the atoms slows them to a near standstill. Through this cloud of immobilized atoms, the researchers then shine a very weak laser beam — so weak, in fact, that only a handful of photons travel through the cloud at any one time.
The researchers then measure the photons as they come out the other side of the atom cloud. In the new experiment, they found that the photons streamed out as pairs and triplets, rather than exiting the cloud at random intervals, as single photons having nothing to do with each other.
In addition to tracking the number and rate of photons, the team measured the phase of photons, before and after traveling through the atom cloud. A photon’s phase indicates its frequency of oscillation.
“The phase tells you how strongly they’re interacting, and the larger the phase, the stronger they are bound together,” Venkatramani explains. The team observed that as three-photon particles exited the atom cloud simultaneously, their phase was shifted compared to what it was when the photons didn’t interact at all, and was three times larger than the phase shift of two-photon molecules. “This means these photons are not just each of them independently interacting, but they’re all together interacting strongly.”
The researchers then developed a hypothesis to explain what might have caused the photons to interact in the first place. Their model, based on physical principles, puts forth the following scenario: As a single photon moves through the cloud of rubidium atoms, it briefly lands on a nearby atom before skipping to another atom, like a bee flitting between flowers, until it reaches the other end.
If another photon is simultaneously traveling through the cloud, it can also spend some time on a rubidium atom, forming a polariton — a hybrid that is part photon, part atom. Then two polaritons can interact with each other via their atomic component. At the edge of the cloud, the atoms remain where they are, while the photons exit, still bound together. The researchers found that this same phenomenon can occur with three photons, forming an even stronger bond than the interactions between two photons.
“What was interesting was that these triplets formed at all,” Vuletic says. “It was also not known whether they would be equally, less, or more strongly bound compared with photon pairs.”
The entire interaction within the atom cloud occurs over a millionth of a second. And it is this interaction that triggers photons to remain bound together, even after they’ve left the cloud.
“What’s neat about this is, when photons go through the medium, anything that happens in the medium, they ‘remember’ when they get out,” Cantu says.
This means that photons that have interacted with each other, in this case through an attraction between them, can be thought of as strongly correlated, or entangled — a key property for any quantum computing bit.
“Photons can travel very fast over long distances, and people have been using light to transmit information, such as in optical fibers,” Vuletic says. “If photons can influence one another, then if you can entangle these photons, and we’ve done that, you can use them to distribute quantum information in an interesting and useful way.”
Going forward, the team will look for ways to coerce other interactions such as repulsion, where photons may scatter off each other like billiard balls.
“It’s completely novel in the sense that we don’t even know sometimes qualitatively what to expect,” Vuletic says. “With repulsion of photons, can they be such that they form a regular pattern, like a crystal of light? Or will something else happen? It’s very uncharted territory.”
– Jennifer Chu | MIT News Office
February 15, 2018
AIM Photonics participants to take long view at Roadmap Meeting at MIT March 26-27, 2018.
|Tom Marrapode, Director of Advanced Technology Development at Molex Optical Solutions Group, speaks about work on board-level optical interconnects at the AIM Photonics Academy fall 2017 meeting. Photo, Melissa Renzi, SUNY Polytechnic Institute.|
Industry and academic leaders from across the country and around the world will gather at MIT on Monday and Tuesday, March 26-27, 2018, for the spring AIM Photonics Technical Roadmap Meeting, titled “Photonic Integration 2035: Economics, Technology and Manufacturing.”
This marks the 20th year that the Photonics Roadmap meetings have been held. Begun under the Microphotonics Center at MIT as gatherings of 50 experts, the Roadmap meetings have grown to more than 200 people representing the technology supply chain, from materials to systems to end-users.
“This is the premier gathering of leaders implementing photonics technology,” says Professor Lionel Kimerling, executive of AIM Photonics Academy, which is the MIT-based education and workforce development arm of AIM Photonics. AIM Photonics is one of 14 public-private manufacturing innovation institutes created as part of a federal initiative to revitalize American manufacturing.
Participants will “gauge the system requirements and technology needs to maintain the ongoing exponential product ramp in the field,” Kimerling says. The March meeting includes time for breakout groups that focus on different technology areas covered in the Roadmap, where companies that normally compete against one another can participate in productive pre-competitive discussions.
“I have been very engaged in AIM Photonics Academy’s Roadmap meetings and technical working groups,” said Yi Qian, vice president of product management at MRSI. “I want to be part of the discussion with some of the world’s top experts of where integrated photonics is headed.”
At the spring meeting, AIM Photonics Academy and the International Electronics Manufacturing Initiative (iNEMI) plan to incubate Application Interest Groups (AIGs) in sensors, data centers, analog RF signal applications, LIDAR and phased array imaging. These industry-led initiatives have the potential to turn into AIM Photonics-funded technical projects.
The Integrated Photonic Systems Roadmap (IPSR), which can be downloaded from the iNEMI and AIM Photonics Academy websites, is more than 400 pages long, and continues to be updated to include new chapters and findings. Close to 1,000 people from more than 300 organizations in 17 countries have participated in the creation of the Roadmap.
AIM Photonics Academy and iNEMI are also collaborating on a Roadmap workshop at the Optical Fiber Communication Conference March 12, 2018, in San Diego. At that conference, Kimerling and Director of Roadmapping Robert Pfahl will discuss grand challenges and key needs for commercially viable, high-volume manufacturing of photonic-enabled functionality.
– Julie Diop, Materials Research Laboratory, AIM Photonics Academy
February 26, 2018
|Eindhoven University of Technology Professor Meint Smit speaks about “Photonic Integrated Circuits: How Foundries Transform Prototyping” during the spring 2017 AIM Photonics Roadmap meeting at MIT. Photo, Denis Paiste, MIT MRL|
Summer Scholar Ashley Del Valle Morales probes new silicon carbide system in MIT Microphotonics Center.
|Materials Science and Engineering graduate student Peter Su shows Summer Scholar Ashley Del Valle Morales how to operate a laser and detector system she will use during her summer project under Senior Research Scientist Dr. Anuradha Agarwal. The system combines an optical set up with a laser to drive light through an optical fiber into a sensor sample and collect light passed through resonators on the sample that help determine its quality as a sensor of target gas or liquid chemicals. Photo, Denis Paiste, Materials Processing Center|
Lasers operating at the infrared wavelength of 1550 nanometers power high-speed fiber-optic Internet communications. MIT Microphotonics Center Principal Research Scientist Dr. Anuradha Agarwal is developing chemical sensors based on the 1550 nanometer telecommunications wavelength using a new materials system built of silicon carbide on silicon dioxide on silicon.
MPC-CMSE Summer Scholar Ashley Del Valle Morales is working under Materials Science and Engineering graduate student Peter Su as part of a team in Agarwal’s lab to characterize this new system. Once the devices are fabricated, Del Valle Morales will use a laser system to determine how effectively the sensors detect the chemical N-methylaniline, a toxic industrial chemical.
Del Valle Morales, a rising junior at University of Puerto Rico, Mayaguez campus, also will test the silicon carbide based sensor before and after it is exposed to gamma rays. Tests will show whether detection capabilities or properties of the device change as a result of radiation exposure.
During the three-day selection process, in which this year’s group of 11 Summer Scholars heard presentations by faculty, postdocs and graduate students and also toured their labs, Del Valle says she was drawn to the Agarwal lab. “Because I have done research before, I know it’s really important to select a project you like and you’re interested in. Furthermore, a research in which you can expand your knowledge, so that was one point that helped me decide to join.
“I also liked the enthusiasm and the interest that the grad students and the principal research scientist showed. I think that’s very important. It makes me feel very welcome in the lab, and it makes me feel like I wouldn’t be alone in this whole process of learning something new,” Del Valle says.
“Having an MPC-CMSE Summer scholar working alongside a graduate student in our research program is an excellent opportunity for both the summer scholar and for our group,” Agarwal says. “Our graduate student learns how to be a good role model and mentor to the Summer Scholar who is typically just a few years younger, shares a passion for science and technology, and perhaps shares dreams and aspirations for a career in the field of engineering.”
“This year, the enthusiasm of our 2016 summer scholar, Ashley Del Valle Morales, is palpable and contagious. We are excited as she starts her research in microphotonic sensors,” Agarwal adds. “Research in our group progresses faster with the presence of a Summer Scholar, since we have a willing and able “scientist-in-training” in our midst. In fact, a 2009 MPC-CMSE Summer Scholar [Brian Albert], who came to us while still an undergrad at Columbia, graduated with a PhD in DMSE in 2016.”
Del Valle says she applied to the MPC-CMSE internship program in the spring knowing it was highly competitive because of the broad topics and choice of individual projects offered. “I started working on my essays and the whole application right away. I spent maybe three weeks writing and editing my essay with the help of my English professor,” she says.
MPC and CMSE sponsor the nine-week National Science Foundation Research Experience for Undergraduates (NSF REU) internships with support from NSF’s Materials Research Science and Engineering Centers program (grant number DMR-14-19807). The program runs from June 7 through Aug. 6, 2016.
– Denis Paiste, Materials Processing Center
June 29, 2016
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
|Mechanical engineering graduate student Caroline Wagner, right, explains lab equipment in the Ribbeck Lab for testing the microscopic mechanical properties of of biological gels such as mucus, to 2017 Summer Scholars, left, Luke P. Soule, Alexandra Oliveira, Stephanie E. Bauman, Amrita [Amy] Duggal and Gaetana H. Michelet. Ribbeck is exploring the basic science of self-healing polymer gels. Photo, Denis Paiste, MIT MRL|
The MIT Materials Research Laboratory is currently accepting applications from undergraduate students for the annual Summer Scholars program, which will run from June 17 to August 11, 2018. The 12 Research Experience for Undergraduates (REU) internships are supported, in part, through the National Science Foundation’s Materials Research Science and Engineering Centers program.
Interns will select their own projects from MIT faculty presentations given during the first few days of the program. Last year’s group, for example, participated in a diverse group of materials science, photonics, energy, and biomedical projects. The program, started in 1983, has brought hundreds of the best science and engineering undergraduates in the country to MIT for graduate-level materials research.
Past Summer Scholars have won prestigious graduate fellowships, been published as co-authors on MIT faculty-led research and achieved successful careers in industry and academia.
• After interning jointly under Professors Gareth McKinley and Katharina Ribbeck, Lucia Brunel (2017) was selected as a Marshall Scholar and plans to study materials science at Cambridge University after graduating from Northwestern University in June 2018. Brunel investigated the self-healing behavior of biological gels.
• Former Summer Scholars Ashley L. Kaiser (2016) and Alexander J. Constable (2015) were co-authors of a paper demonstrating a lower processing temperature for industrially important, glassy carbon led by Postdoc Itai Y. Stein and Professor of Aeronautics and Astronautics Brian L. Wardle. Kaiser is now a materials science and engineering graduate student at MIT.
• Michael Concepción Santana (2016) received a 2017 New Faces of Engineering College Edition award from DiscoverE. Interning under David H. Koch Professor of Engineering Michael J. Cima, Concepción Santana synthesized hydrogels that can indicate changes in pH near a patient’s tumor in an MRI scan.
• Sarah Goodman (2013) interned under Dr. Anu Agarwal and Professor Lionel Kimerling, using scanning electron microscopy to examine samples of a mid-IR waveguide with potential use for sensors. Goodman was honored by the MIT Office of Graduate Education as one of its 2017 Graduate Women of Excellence, and is currently Graduate Student Council (GSC) President. She is a graduate student in the group of Associate Professor of Materials Science and Engineering Silvija Gradecak.
• Jessica [Shipman] Morrison (2010) went on to earn a PhD at Boston University, where she pioneered a new kind of controllable solid-state lighting using a micro-electromechanical system. In April 2017, Morrison became a fellow at Lawrence Berkeley National Laboratory’s Cyclotron Road incubator, where she hopes to advance her company, Helux Technologies.
|Summer Scholar Michael Concepción Santana works under a hood in the Cima Lab, where Concepción worked on pH sensitive MRI contrast agents during summer 2016. Photo, Denis Paiste, MIT MRL.|
For more information about the Internship Program, please refer to the Summer Scholars portion of our website. The application deadline is February 16, 2018.
Researchers observe, for the first time, topological effects unique to an “open” system.
|A drawing illustrates the unusual topological landscape around a pair of features known as exceptional points (red dots), showing the emergence of a Fermi arc (pink line at center), and exotic polarization contours that form a Mobius-strip-like texture (top and bottom strips). Courtesy of the researchers|
Topological effects, such as those found in crystals whose surfaces conduct electricity while their bulk does not, have been an exciting topic of physics research in recent years and were the subject of the 2016 Nobel Prize in physics. Now, a team of researchers at MIT and elsewhere has found novel topological phenomena in a different class of systems — open systems, where energy or material can enter or be emitted, as opposed to closed systems with no such exchange with the outside.
This could open up some new realms of basic physics research, the team says, and might ultimately lead to new kinds of lasers and other technologies.
The results are being reported in the journal Science, in a paper by recent MIT graduate Hengyun “Harry” Zhou, MIT visiting scholar Chao Peng (a professor at Peking University), MIT graduate student Yoseob Yoon, recent MIT graduates Bo Zhen and Chia Wei Hsu, MIT Professor Marin Soljačić, the Francis Wright Davis Professor of Physics John Joannopoulos, the Haslam and Dewey Professor of Chemistry Keith Nelson, and the Lawrence C. and Sarah W. Biedenharn Career Development Assistant Professor Liang Fu.
In most research in the field of topological physical effects, Soljačić says, so-called “open” systems — in physics terms, these are known as non-Hermitian systems — were not studied much in experimental work. The complexities involved in measuring or analyzing phenomena in which energy or matter can be added or lost through radiation generally make these systems more difficult to study and analyze in a controlled fashion.
But in this work, the team used a method that made these open systems accessible, and “we found interesting topological properties in these non-Hermitian systems,” Zhou says. In particular, they found two specific kinds of effects that are distinctive topological signatures of non-Hermitian systems. One of these is a kind of band feature they refer to as a bulk Fermi arc, and the other is an unusual kind of changing polarization, or orientation of light waves, emitted by the photonic crystal used for the study.
Photonic crystals are materials in which billions of very precisely shaped and oriented tiny holes are made, causing light to interact in unusual ways with the material. Such crystals have been actively studied for the exotic interactions they induce between light and matter, which hold the potential for new kinds of light-based computing systems or light-emitting devices. But while much of this research has been done using closed, Hermitian systems, most of the potential real-world applications involve open systems, so the new observations made by this team could open up whole new areas of research, the researchers say.
Fermi arcs, one of the unique phenomena the team found, defy the common intuition that energy contours are necessarily closed curves. They have been observed before in closed systems, but in those systems they always form on the two-dimensional surfaces of a three-dimensional system. In the new work, for the first time, the researchers found a Fermi arc that resides in the bulk of a system. This bulk Fermi arc connects two points in the emission directions, which are known as exceptional points — another characteristic of open topological systems.
The other phenomenon they observed consists of a field of light in which the polarization changes according to the emission direction, gradually forming a half-twist as one follows the direction along a loop and returns back to the starting point. “As you go around this crystal, the polarization of the light actually flips,” Zhou says.
This half-twist is analogous to a Möbius strip, he explains, in which a strip of paper is twisted a half-turn before connecting it to its other end, creating a band that has only one side. This Möbius-like twist in light polarization, Zhen says, could in theory lead to new ways of increasing the amount of data that could be sent through fiber-optic links.
The new work is “mostly of scientific interest, rather than technological,” Soljačić says. Zhen adds that “now we have this very interesting technique to probe the properties of non-Hermitian systems.” But there is also a possibility that the work may ultimately lead to new devices, including new kinds of lasers or light-emitting devices, they say.
The new findings were made possible by earlier research by many of the same team members, in which they found a way to use light scattered from a photonic crystal to produce direct images that reveal the energy contours of the material, rather than having to calculate those contours indirectly.
“We had a hunch” that such half-twist behavior was possible and could be “quite interesting,” Soljačić says, but actually finding it required “quite a bit of searching to figure out, how do we make it happen?”
“Perhaps the most ingenious aspect of this work is that the authors use the fact that their system must necessarily lose photons, which is usually an obstacle and annoyance, to access new topological physics,” says Mikael Rechtsman, an assistant professor of physics at Pennsylvania State University who was not involved in this work. “Without the loss … this would have required highly complex 3-D fabrication methods that likely would not have been possible.” In other words, he says, the technique they developed “gave them access to 2-D physics that would have been conventionally thought impossible.”
The work was supported by the Army Research Office through the Institute for Soldier Nanotechnologies; S3TEC, an Energy Frontier Research Center funded by the U.S. Department of Energy; the U.S. Air Force; and the National Science Foundation.
Read more at the MIT News Office.
David L. Chandler | MIT News Office
January 11, 2018
Stonehill College meeting puts laser focus on enhancing regional integrated photonics training.
|MIT AIM Photonics Academy Executive Lionel Kimerling speaks during a meeting at Stonehill College in Easton, Mass., on Nov. 14, 2017. “With the help of the state, Massachusetts can be the Silicon Valley for the growth of ultra-high performance communications systems using integrated photonics,” Kimerling said. Photo, Rich Morgan|
MIT’s AIM Photonics Academy helped organize a gathering of more than 60 people at Stonehill College in Easton, Mass., on Nov. 14, 2017, to explore opportunities in integrated photonics, and discuss possibilities for a large investment to create a Lab for Education & Application Prototypes (LEAP) in integrated photonics at the college. Attendees came from companies, colleges and universities, the Massachusetts Manufacturing Extension Program, Massachusetts Technology Collaborative and aides to U.S. Rep. Joseph P. Kennedy III, D-Mass.
Integrated photonics uses complex optical circuits to process and transmit signals of light, similar to the routing of electrical signals in a computer microchip. In contrast to the electrical transmission in a microchip, a photonic integrated circuit can transmit multiple information channels simultaneously using different wavelengths of light with minimal interference and energy loss to enable high-bandwidth, low-power communications.
“Students need to be prepared for the jobs that are coming,” said Dr. Cheryl Schnitzer, associate professor of chemistry at Stonehill College. “It’s our obligation to teach them about the exploding field of photonics and integrated photonics.”
MIT’s AIM Photonics Academy is the education and workforce development arm of the AIM Photonics Institute, one of 14 Manufacturing USA institutes launched as part of a federal initiative to revitalize American manufacturing. The federal government has committed $110 million to the AIM Photonics Institute over five years. At the same time, the state of Massachusetts will spend $100 million on projects related to colleges and industry within the state, including $28 million to help launch AIM Photonics projects such as LEAP facilities.
|Anu Agarwal, MIT Principal Research Scientist, speaks during an AIM Photonics Academy meeting at Stonehill College in Easton, Mass., on Nov. 14, 2017. Stonehill is considering creation of a Lab for Education & Application Prototypes (LEAP) in integrated photonics at the college. Photo, Rich Morgan|
MIT received funding for the first LEAP facility, with a focus on packaging. The MIT Lab for Education & Application Prototypes is currently housed in Building 35, and will relocate to the fifth floor of MIT.nano in June 2018. A second LEAP site is in its final stages of planning at Worcester Polytechnic Institute, and it will also serve Quinsigamond Community College. AIM Photonics Academy and the Commonwealth of Massachusetts are in discussions to build four more LEAP Labs, including one at Stonehill College to serve the southeastern corner of the state. Once up and running, these labs will form a training network that helps Massachusetts become a major hub for photonics technology.
The meeting at Stonehill College, which also included the NextFlex Flexible Hybrid Electronics manufacturing innovation institute, generated many plans. The college has already connected with Bridgewater State and Bristol Community Colleges about creating photonic tracks in their programs. A team from AIM Photonics Academy, Stonehill College and MassTech will begin visiting companies to follow up on how they might get engaged in a LEAP Lab at Stonehill.
Companies were enthusiastic about the opportunity to expand in these areas, as well. “Any time you add high-tech education to an area, you are going to incubate high-tech companies,” noted John Lescinskas of Brockton Electro-Optics. “You’re planting a seed. It can lead to a tree, or even a forest.”
Massachusetts is an optimal location for this initiative to take place. Integrated photonics “is a technology that originated in Massachusetts, at MIT,” said AIM Photonics Academy Executive Lionel Kimerling. “With the help of the state, Massachusetts can be the Silicon Valley for the growth of ultra-high performance communications systems using integrated photonics,” Kimerling said.
– Julie Diop, Program Manager, AIM Photonics Academy
November 27, 2017
Ultrathin films of a semiconductor that emits and detects light can be stacked on top of silicon wafers.
|Researchers have designed a light-emitter and detector that can be integrated into silicon CMOS chips. This illustration shows a molybdenum ditelluride light source for silicon photonics. Illustration, Sampson Wilcox|
The huge increase in computing performance in recent decades has been achieved by squeezing ever more transistors into a tighter space on microchips.
However, this downsizing has also meant packing the wiring within microprocessors ever more tightly together, leading to effects such as signal leakage between components, which can slow down communication between different parts of the chip. This delay, known as the “interconnect bottleneck,” is becoming an increasing problem in high-speed computing systems.
One way to tackle the interconnect bottleneck is to use light rather than wires to communicate between different parts of a microchip. This is no easy task, however, as silicon, the material used to build chips, does not emit light easily, according to Pablo Jarillo-Herrero, an associate professor of physics at MIT.
Now, in a paper published in the journal Nature Nanotechnology, researchers describe a light emitter and detector that can be integrated into silicon CMOS chips. The paper’s first author is MIT postdoc Ya-Qing Bie, who is joined by Jarillo-Herrero and an interdisciplinary team including Dirk Englund, an associate professor of electrical engineering and computer science at MIT.
Read more at the MIT News Office.
Helen Knight | MIT News Office
October 23, 2017
Materials Day 2017
Bringing together researchers from different science and engineering fields promises solutions to global needs in energy, health and quality of life.
Interdisciplinary materials research holds the key to solving the existential 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.
- Frontier for metals at high temperature Frontier for metals at high temperature
- MIT Materials Research Lab Director MIT Materials Research Lab Director
- Merging 2D materials with CMOS Merging 2D materials with CMOS
- Safer lithium batteries Safer lithium batteries
- 3D printing a new manufacturing model 3D printing a new manufacturing model
- Interdisciplinary model key to progress Interdisciplinary model key to progress
- New tools for brain exploration New tools for brain exploration
- Phase change materials Phase change materials
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