Friday, 22 March 2019 17:22

10 interns chosen for 2019

MIT Materials Research Laboratory announces 10 recipients of Research Experience for Undergraduates (REU) internships.
Summer Scholar Fernando Nieves Bench Work 3379 DPaiste

2018 Summer Scholar Fernando Nieves Muñoz works at a bench in the lab of Professor of Materials Science and Engineering Krystyn Van Vliet. Photo, Denis Paiste, Materials Research Laboratory.

The MIT Materials Research Laboratory [MRL] has selected 10 top-ranking undergraduates to conduct graduate-level research on the MIT campus in Cambridge, Mass., from June 16 to Aug. 10, 2019. They were chosen from among 286 applicants.

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, explored a wide range of research from working with materials as soft as silk to as hard as iron and from temperatures as low as -452.47 degrees Fahrenheit to as high as 1,984 F.

This year’s Summer Scholars and their home institutions are:

- Isabel Albelo, University of California - Los Angeles

- Leah Borgsmiller, Northwestern University

- Jared Bowden, University of Massachusetts Amherst

- Clement Ekaputra, University of Pittsburgh

- Nathan Ewell, Case Western Reserve University

- Marcos Logrono, University of Puerto Rico - Mayaguez Campus

- Chris Moore, University of Washington

- Ariane Marchese, Hunter College of the City University of New York

- Melvin Nunez Santiago, University Ana G. Mendez at Gurabo, Puerto Rico

- Carly Tymm, Dartmouth College 

Summer Scholars are supported in part by the National Science Foundation’s Research Experience for Undergraduates (REU) program, which is administered by the MIT Materials Research Science and Engineering Center.

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.

back to newsletterMarch 25, 2019 

Monday, 26 March 2018 13:42

2018 Summer Scholars selected

MIT Materials Research Laboratory announces 12 recipients of Research Experience for Undergraduates (REU) internships.
Summer Scholar Intro Syringe 3546 Web
Twelve recipients of Research Experience for Undergraduates (REU) internships will select their own projects from MIT faculty presentations given during the first few days of the Summer Scholars program. Image, Denis Paiste, MRL.

The MIT Materials Research Laboratory [MRL] has selected 12 top-ranking undergraduates to conduct graduate-level research on the MIT campus in Cambridge, Mass., from June 17 to August 11, 2018.

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, conducted supervised research on projects in materials science, photonics, energy, and biomedical fields.

This year’s Summer Scholars and their major fields of study are:

- Danielle Beatty, University of Utah, Materials Science and Engineering

- Alvin Chang, Oregon State University, Chemical Engineering, Biological Engineering, with minor in Entrepreneurship

- Simon Egner, University of Illinois at Urbana-Champaign, Materials Science and Engineering

- Elizabeth Hallett, University of Arkansas-Fayetteville, Chemical Engineering

- Julianna LaLane, University of Puerto Rico at Mayaguez, Mechanical Engineering

- Michael Molinski, University of Rhode Island, Chemical Engineering

- Abigail Nason, University of Florida, Materials Science and Engineering,

- Fernando Nieves Munoz, University of Puerto Rico, Mayaguez, Mechanical Engineering

- Sarai Patterson, University of Utah, Materials Science and Engineering

- Sabrina Shen, Johns Hopkins University, Materials Science and Engineering

- Ryan Tollefsen, Oregon State University, Physics

- Ekaterina Tsotsos, Brown University, Materials Engineering

Summer Scholars serve as interns through the MIT MRL and are supported in part by the National Science Foundation’s Research Experience for Undergraduates (REU) program, which is administered by the MIT Materials Research Science and Engineering Center, and the AIM Photonics Academy.

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.

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Thursday, 27 September 2018 10:53

2018 Summer Scholars videos

Summer Scholars Video Promo Combo Web

Watch MIT MRL Summer Scholars videos.


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Friday, 11 October 2019 16:53

2019 Materials Day Poster Session winners

MIT Materials Research Laboratory 2019 Poster Session winners are Mechanical Engineering graduate student Erin Looney, Media Arts and Sciences graduate student Bianca Datta, and Materials Science and Engineering Postdoctoral Associate Michael Chon. 

The Poster Session was held immediately after the Materials Day Symposium on Oct. 9, 2019. Winners, who were selected by non-MIT affiliated attendees, each receive a $500 award.

Bianca Datta
Media Arts and Sciences graduate student

POSTER: “Simulation-based optimization towards fabrication of bio-inspired nanostructures exhibiting structural coloration.”

Datta is using simulation techniques and rapid prototyping to design surfaces that display color like butterfly wings.

Advisor: Christine Ortiz, Morris Cohen Professor of Materials Science and Engineering

Michael Chon
Postdoctoral Associate

POSTER: “High capacity CMOS-compatible thin film batteries on flexible substrates”

Chon is developing all solid-state flexible microbatteries that combine a germanium anode, a ruthenium dioxide cathode and lithium phosphorous oxynitride (LiPON) solid electrolyte. The thin film batteries can be stacked and folded or incorporated directly into integrated circuits.

Advisor: Carl V. Thompson, Stavros Salapatas Professor of Materials Science and Engineering, and Director, Materials Research Laboratory

Erin E. Looney
Mechanical Engineering graduate student

POSTER: “Machine learning-based classification of environmental conditions for PV module testing and design”

Looney simulates solar cell material operation under real world conditions by combining temperature, solar spectra and humidity data to estimate performance with 95 percent accuracy. She showed that a statistical method called a k-means algorithm can produce these results with 1,000 times fewer data inputs.

Advisor: Tonio Buonassisi, Professor of Mechanical Engineering

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 – Materials Research Laboratory
Updated October 28, 2019

Fabric samples are headed to the International Space Station for resiliency testing; possible applications include cosmic dust detectors or spacesuit smart skins.

Earlier this month a team of MIT researchers sent samples of various high-tech fabrics, some with embedded sensors or electronics, to the International Space Station. The samples (unpowered for now) will be exposed to the space environment for a year in order to determine a baseline for how well these materials survive the harsh environment of low Earth orbit.

MIT Fabrics Space 01 press 0

A team of MIT researchers has sent a panel of passive smart fabric samples to the International Space Station for a year to help determine how well these fabrics survive low Earth orbit.

Image credit: Courtesy of Space BD/JAXA and edited by MIT News

The hope is that this work could lead to thermal blankets for spacecraft, that could act as sensitive detectors for impacting micrometeoroids and space debris. Ultimately, another goal is new smart fabrics that allow astronauts to feel touch right through their pressurized suits.

Three members of MIT’s multidisciplinary team, graduate students Juliana Cherston of the Media Lab, and Yuchen Sun of the Department of Chemistry, and postdoc Wei Yan of the Research Laboratory of Electronics and the Department of Materials Science and Engineering, discussed the experiment’s ambitious aims with MIT News.

Q:​ Can you describe the fabric samples that you sent to the International Space Station, and what kinds of information you are hoping to get from them after their exposure in space?

Cherston: The white color of the International Space Station is actually a protective fabric material called Beta cloth, which is a Teflon-impregnated fiberglass designed to shield spacecraft and spacesuits from the harsh elements of low Earth orbit. For decades, these fabrics have remained electrically passive, despite offering large-area real estate on the exterior of space assets.

We imagine turning this spacecraft skin into an enormous space debris and micrometeoroid impact sensor. The samples that we worked with JAXA, the Japanese space agency, and Space BD to send to the International Space Station incorporate materials like charge-sensitive synthetic fur — an early concept — and vibration-sensitive fiber sensors — our project’s focus — into space-resilient fabrics. The resulting fabric may be useful for detecting cosmic dust of scientific interest, and for damage detection on spacecraft. 

It’s easy to assume that since we’re already sending these materials to space, the technology must be very mature. In reality, we are leveraging the space environment  to complement our important ground-testing efforts. All of these fabric sensors will remain unpowered for this first in-space test, and the quilt of samples occupies a total area of 10 by 10 centimeters on the exterior walls of the station.

Our focus is on baselining their resiliency to the space environment. In one year, these samples will return to Earth for postflight analysis. We’ll be able to measure any erosion from atomic oxygen, discoloration from UV radiation, and any changes to fiber sensor performance after one year of thermal cycling. There is some chance that we will also find hints of micron-scale micrometeoroids. We’re also already preparing for an electrically powered deployment currently scheduled for late 2021 or early 2022 (recently awarded to the project by the ISS National Lab). At that point we’ll apply an additional protective coating to the fibers and actually operate them in space.

Yan: The fabric samples contain thermally drawn “acoustic” fibers developed with ISN funding that are capable of converting mechanical vibration energy into electric energy (via the piezoelectric effect). When micrometeoroids or space debris hit the fabric, the fabric vibrates, and the “acoustic” fiber generates an electrical signal. Thermally drawn multimaterial fibers have been developed by our research group at MIT for more than 20 years; what makes these acoustic fibers special is their exquisite sensitivity to mechanical vibrations. The fabric has been shown in ground facilities to detect and measure impact regardless of where the space dust impacted the surface of the fabric.

Q: What is the ultimate goal of the project? What kinds of uses do you foresee for advanced fabrics in the space environment?

Cherston: I am particularly keen to demonstrate that instrumentation useful for fundamental scientific inquiry can be incorporated directly into the fabric skin of persistent spacecraft, which to date is unused and very precious real estate. In particular, I am beginning to evaluate whether these skins are sensitive enough to detect cosmic dust produced in million-year-old supernova explosions tens or hundreds of light-years away from Earth. Just last year, an isotopic signature for this type of interstellar dust was discovered in fresh Antarctic snow, so we believe that some of this dust is still whizzing around the solar system, holding clues about the dynamics of supernova explosions. In-situ characterization of their distribution and kinematics is currently my most ambitious scientific goal.

More generally, I’d love to see advanced fibers and fabrics tackle other questions of fundamental physical interest in space, maybe by leveraging optical fibers or radiation sensitive materials to create large aperture sensors.

Some students in my group have also developed a conceptual prototype in which sensory data on the exterior skin of a pressurized spacesuit armband is mapped to haptic actuators on the wearer’s biological skin. Using this system, astronauts will be able to feel texture and touch right through their spacesuits! This direct experience of a new environment is very central to humanity’s drive to explore.

An impact-sensitive skin can also be used for damage detection on persistent space craft. In practice, the fabric’s ability to localize damage from space debris and micrometeoroids is how we will really sell the concept to aerospace engineers.

Yan: Although the space age began 63 years ago when Soviet Union’s Sputnik 1 was launched into an elliptical low Earth orbit, many unanswered questions remain regarding the effect of the space environment on humans, as well as the safety of astronauts as they operate in the space environment. While our project’s main focus has been on augmenting fabrics used on the exterior of spacecraft, I also envision that future spacesuits will be electrically active and highly multifunctional.

Textiles buried within the suit will be able monitor the health condition of astronauts in real time by interrogating physiological signals over large areas. Fabrics may also serve as  localized heating and cooling systems, radiation dosimeters, and efficient communications infrastructure (via fabric optics and acoustics). They may harvest solar energy as well as small amounts of energy from vibration, and store this energy in fiber batteries or supercapacitors, which would allow the system to be self-powered. Fabrics might even serve as part of an exoskeleton that assists astronauts in maneuvering on planetary bodies and in microgravity. One broad vision at play is to pack an enormous amount of function into space resilient textiles, creating an analogue of “Moore’s law” for space fabrics.

​​​Q: What got you interested in this subject, and what has this experience been like for you in getting the materials ready to be sent into space?

Yan: Space is definitely a new frontier for our research, while lots of terrestrial applications have been envisioned in ambient conditions and even under water. From low Earth orbit to planetary bodies, space is a unique environment with atomic oxygen, radiation, high speed impactors, and extreme temperature cycling. How will the fibers and fabrics perform there and what changes will be induced in the fiber materials? How should electronic fabrics be designed in order to meet demands of aerospace applications? There are so many scientific and technological questions.

Sun: Our group [with professor of chemistry Keith Nelson] strives to push the limits of what is experimentally achievable for impact testing, and we are always excited by a new challenge. Recently, we have been venturing into the area of high-speed mechanics, testing novel materials spanning polymers, thin films, and nanoarchitected materials using a laser accelerator facility designed by our lab to impinge tiny particles on target surfaces at speeds exceeding 1 kilometer per second.

When the idea emerged to test a material capable of detecting impact signatures in low Earth orbit and beyond, there was immediate interest on our side since it is fundamentally different from our previous research focus. These experiments are certainly more difficult and complex than what we are used to, with many more active parts to maintain. I think we were all quite pleasantly surprised when our preliminary impact experiments were successful and encouraging.

Cherston: While space launches are exciting, in reality some of our most convincing data to date has come from impact testing on the ground. Initially, it was not at all obvious that a fabric sensor with sparsely integrated sensing elements could actually detect such small and fast particles. There were a really great few minutes at our first serious impact testing campaign during which Yuchen gradually increased the number of particles accelerated onto our sensor, while holding all other aspects of the experiment constant. The growing signal was a smoking gun indication that we were seeing a true impact signature. 

On a personal level, I’m really fascinated by the idea of leveraging very unconventional technology like fabric for questions of scientific significance. And I think the idea of feeling right through a pressurized spacesuit is delightful!

David L. Chandler | MIT News Officeback to newsletter
Publication Date: November 25, 2020

Tuesday, 24 September 2019 10:45

3 Questions: Why sensing, why now, what next?

Brian Anthony, co-leader of SENSE.nano, discusses sensing for augmented and virtual reality and for advanced manufacturing.
Brian Anthony,  MIT Nano
Brian Anthony

Sensors are everywhere today, from our homes and vehicles to medical devices, smart phones, and other useful tech. More and more, sensors help detect our interactions with the environment around us — and shape our understanding of the world.

SENSE.nano is an MIT.nano Center of Excellence, with a focus on sensors, sensing systems, and sensing technologies. The 2019 SENSE.nano Symposium, taking place on Sept. 30 at MIT, will dive deep into the impact of sensors on two topics: sensing for augmented and virtual reality (AR/VR) and sensing for advanced manufacturing. 

MIT Principal Research Scientist Brian W. Anthony is the associate director of MIT.nano and faculty director of the Industry Immersion Program in Mechanical Engineering. He weighs in on why sensing is ubiquitous and how advancements in sensing technologies are linked to the challenges and opportunities of big data.

Q: What do you see as the next frontier for sensing as it relates to augmented and virtual reality?

A: Sensors are an enabling technology for AR/VR. When you slip on a VR headset and enter an immersive environment, sensors map your movements and gestures to create a convincing virtual experience.

But sensors have a role beyond the headset. When we're interacting with the real world we're constrained by our own senses — seeing, hearing, touching, and feeling. But imagine sensors providing data within AR/VR to enhance your understanding of the physical environment, such as allowing you to see air currents, thermal gradients, or the electricity flowing through wires superimposed on top of the real physical structure. That's not something you could do any place else other than a virtual environment.

Another example: MIT.nano is a massive generator of data. Could AR/VR provide a more intuitive and powerful way to study information coming from the metrology instruments in the basement, or the fabrication tools in the clean room? Could it allow you to look at data on a massive scale, instead of always having to look under a microscope or on a flat screen that's the size of your laptop? Sensors are also critical for haptics, which are interactions related to the sensation of touch. As I apply pressure to a device or pick up an object — real or virtual — can I receive physical feedback that conveys that state of interaction to me?

You can’t be an engineer or a scientist without being involved with sensing instrumentation in some way. Recognizing the widespread presence of sensing on campus, SENSE.nano and MIT.nano — with MIT.nano’s new Immersion Lab providing the tools and facility — are trying to bring together researchers on both the hardware and software sides to explore the future of these technologies.

Q: Why is SENSE.nano focusing on sensing for advanced manufacturing?

A: In this era of big data, we sometimes forget that data comes from someplace: sensors and instruments. As soon as the data industry as a whole has solved the big data challenges we have now with the data that's coming from current sensors — wearable physiological monitors, or from factories, or from your automobiles — it is going to be starved for new sensors with improved functionality.

Coupled with that, there are a large number of manufacturing technologies — in the U.S. and worldwide — that are either coming to maturity or receiving a lot of investment. For example, researchers are looking at novel ways to make integrated photonics devices combining electronics and optics for on-chip sensors; exploring novel fiber manufacturing approaches to embed sensors into your clothing or composites; and developing flexible materials that mold to the body or to the shape of an automobile as the substrate for integrated circuits or as a sensor. These various manufacturing technologies enable us to think of new, innovative ways to create sensors that are lower in cost and more readily immersed into our environment.

Q: You’ve said that a factory is not just a place that produces products, but also a machine that produces information. What does that mean?

A: Today’s manufacturers have to approach a factory not just as a physical place, but also as a data center. Seeing physical operation and data as interconnected can improve quality, drive down costs, and increase the rate of production. And sensors and sensing systems are the tools to collect this data and improve the manufacturing process.

Communications technologies now make it easy to transmit data from a machine to a central location. For example, we can apply sensing techniques to individual machines and then collect data across an entire factory so that information on how to debug one computer-controlled machine can be used to improve another in the same facility. Or, suppose I'm the producer of those machines and I've deployed them to any number of manufacturers. If I can get a little bit of information from each of my customers to optimize the machine’s operating performance, I can turn around and share improvements with all the companies who purchase my equipment. When information is shared amongst manufacturers, it helps all of them drive down their costs and improve quality.

back to newsletter– MIT.nano | MIT News Office
September 20, 2019

Wednesday, 01 November 2017 17:43

A magical dimension

Engineering at the nanoscale opens new doors to control optical, electronic and magnetic behaviors of materials and enable new multi-functional devices

Materials Day Panel 9584 DP Web
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.back to newsletter

Denis Paiste, Materials Research Laboratory
November 27, 2017

Related: Poster Highlights

Interdisciplinary materials science model offers key to progress

Monday, 23 October 2017 15:07

A new approach to ultrafast light pulses

Unusual fluorescent materials could be used for rapid light-based communications systems.

MIT FastLight Emit 1 Daily
In this image, light strikes a molecular lattice deposited on a metal substrate. The molecules can quickly exchange energy with the metal below, a mechanism that leads to a much faster response time for the emission of fluorescent light from the lattice. Courtesy of the researchers

Two-dimensional materials called molecular aggregates are very effective light emitters that work on a different principle than typical organic light-emitting diodes (OLEDs) or quantum dots. But their potential as components for new kinds of optoelectronic devices has been limited by their relatively slow response time. Now, researchers at MIT, the University of California at Berkeley, and Northeastern University have found a way to overcome that limitation, potentially opening up a variety of applications for these materials.

The findings are described in the journal Proceedings of the National Academy of Sciences, in a paper by MIT associate professor of mechanical engineering Nicholas X. Fang, postdocs Qing Hu and Dafei Jin, and five others.

The key to enhancing the response time of these 2-D molecular aggregates (2DMA), Fang and his team found, is to couple that material with a thin layer of a metal such as silver. The interaction between the 2DMA and the metal that is just a few nanometers away boosts the speed of the material’s light pulses more than tenfold. 

Read more at the MIT News Office.

David L. Chandler | MIT News Office
Sept. 18, 2017

Study of minerals widely used in industrial processes could lead to discovery of new materials for catalysis and filtering.

Zeolites are a class of natural or manufactured minerals with a sponge-like structure, riddled with tiny pores that make them useful as catalysts or ultrafine filters. But of the millions of zeolite compositions that are theoretically possible, so far only about 248 have ever been discovered or made. Now, research from MIT helps explain why only this small subset has been found, and could help scientists find or produce more zeolites with desired properties.

The new findings are reported in the journal Nature Materials, in a paper by MIT graduate students Daniel Schwalbe-Koda and Zach Jensen, and professors Elsa Olivetti and Rafael Gomez-Bombarelli.

MIT Zeolite Structure Web
Traditional structure-based representations of the many forms of zeolites, some of which are illustrated here, provide little guidance as to how they can convert to other forms, but a new graph-based system does a much better job. Illustration courtesy of the researchers.

Previous attempts to figure out why only this small group of possible zeolite compositions has been identified, and to explain why certain types of zeolites can be transformed into specific other types, have failed to come up with a theory that matches the observed data. Now, the MIT team has developed a mathematical approach to describing the different molecular structures. The approach is based on graph theory, which can predict which pairs of zeolite types can be transformed from one to the other.

This could be an important step toward finding ways of making zeolites tailored for specific purposes. It could also lead to new pathways for production, since it predicts certain transformations that have not been previously observed. And, it suggests the possibility of producing zeolites that have never been seen before, since some of the predicted pairings would lead to transformations into new types of zeolite structures.

Interzeolite tranformations

Zeolites are widely used today in applications as varied as catalyzing the “cracking” of petroleum in refineries and absorbing odors as components in cat litterbox filler. Even more applications may become possible if researchers can create new types of zeolites, for example with pore sizes suited to specific types of filtration.

All kinds of zeolites are silicate minerals, similar in chemical composition to quartz. In fact, over geological timescales, they will all eventually turn into quartz — a much denser form of the mineral — explains Gomez-Bombarelli, who is the Toyota Assistant Professor in Materials Processing. But in the meantime, they are in a “metastable” form, which can sometimes be transformed into a different metastable form by applying heat or pressure or both. Some of these transformations are well-known and already used to produce desired zeolite varieties from more readily available natural forms.

Currently, many zeolites are produced by using chemical compounds known as OSDAs (organic structure-directing agents), which provide a kind of template for their crystallization. But Gomez-Bombarelli says that if instead they can be produced through the transformation of another, readily available form of zeolite, “that’s really exciting. If we don’t need to use OSDAs, then it’s much cheaper [to produce the material]. The organic material is pricey. Anything we can make to avoid the organics gets us closer to industrial-scale production.

Traditional chemical modeling of the structure of different zeolite compounds, researchers have found, provides no real clue to finding the pairs of zeolites that can readily transform from one to the other.

Compounds that appear structurally similar sometimes are not subject to such transformations, and other pairs that are quite dissimilar turn out to easily interchange. To guide their research, the team used an artificial intelligence system previously developed by the Olivetti group to “read” more than 70,000 research papers on zeolites and select those that specifically identify interzeolite transformations. They then studied those pairs in detail to try to identify common characteristics.

What they found was that a topological description based on graph theory, rather than traditional structural modeling, clearly identified the relevant pairings. These graph-based descriptions, based on the number and locations of chemical bonds in the solids rather than their actual physical arrangement, showed that all the known pairings had nearly identical graphs. No such identical graphs were found among pairs that were not subject to transformation.

The finding revealed a few previously unknown pairings, some of which turned out to match with preliminary laboratory observations that had not previously been identified as such, thus helping to validate the new model. The system also was successful at predicting which forms of zeolites can intergrow — forming combinations of two types that are interleaved like the fingers on two clasped hands. Such combinations are also commercially useful, for example for sequential catalysis steps using different zeolite materials.

Ripe for further research

The new findings might also help explain why many of the theoretically possible zeolite formations don’t seem to actually exist. Since some forms readily transform into others, it may be that some of them transform so quickly that they are never observed on their own. Screening using the graph-based approach may reveal some of these unknown pairings and show why those short-lived forms are not seen.

Some zeolites, according to the graph model, “have no hypothetical partners with the same graph, so it doesn’t make sense to try to transform them, but some have thousands of partners” and thus are ripe for further research, Gomez-Bombarelli says.

In principle, the new findings could lead to the development of a variety of new catalysts, tuned to the exact chemical reactions they are intended to promote. Gomez-Bombarelli says that almost any desired reaction could hypothetically find an appropriate zeolite material to promote it.

“Experimentalists are very excited to find a language to describe their transformations that is predictive,” he says.

This work is “a major advancement in the understanding of interzeolite transformations, which has become an increasingly important topic owing to the potential for using these processes to improve the efficiency and economics of commercial zeolite production,” says Jeffrey Rimer, an associate professor of chemical and biomolecular engineering at the University of Houston, who was not involved in this research.

Manuel Moliner, a tenured scientist at the Technical University of Valencia, in Spain, who also was not connected to this research, says: “Understanding the pairs involved in particular interzeolite transformations, considering not only known zeolites but also hundreds of hypothetical zeolites that have not ever been synthesized, opens extraordinary practical opportunities to rationalize and direct the synthesis of target zeolites with potential interest as industrial catalysts.”

This research was supported, in part, by the National Science Foundation and the Office of Naval Research.

– David L. Chandler | MIT News Office
October 7, 2019

Tuesday, 25 June 2019 11:38

A very good ring resonator

MIT, SUTD researchers show high-quality photonic device based on amorphous silicon carbide
ACS Photonics Cover 05152019 Web
Researchers at MIT and Singapore University of Technology (SUTD) have demonstrated a micro ring resonator made of amorphous silicon carbide with the highest quality factor to date. Illustration, Dawn Tan, SUTD. Reproduced with permission of ACS Photonics.

Researchers at MIT and Singapore University of Technology (SUTD) have demonstrated a micro ring resonator made of amorphous silicon carbide with the highest quality factor to date. The resonator shows promise to be used as an on-chip photonic light source at the infrared telecom wavelength of 1,550 nanometers.

Ordinary daylight will pass through a window unaltered, which is called linear transmission, but the same light passing through a prism will split into a rainbow of colors. Similarly in photonic devices, infrared light from a laser can pass through in linear fashion without changing its “color,” but at high intensity, the light can exhibit nonlinear behavior, generating additional colors, or wavelengths. For example, a single yellow laser coupled to a photonic device can generate blue, green, yellow or orange colors.

Researchers led by MIT Materials Research Laboratory Research Scientist Anuradha M. Agarwal fabricated the amorphous silicon carbide ring resonators and researchers at SUTD led by Associate Professor Dawn T.H. Tan analyzed the device’s linear and nonlinear properties.

“We are able to show one order of magnitude higher nonlinear effect than measured before in any of the silicon carbide substrates,” Agarwal says.

Their findings are described in a paper, featured on the cover of ACS Photonics, by Agarwal, Tan, MIT materials science and engineering graduate student Danhao Ma, and three others in Singapore and Malaysia.

Quality factor is a measure of how strongly the resonator produces nonlinear effects. “The larger the quality factor, the better the nonlinear effect,” says Tan, who leads the Photonics Devices and Systems Group at SUTD. “So in this case, the quality factor was pretty good. It was actually much better than we expected.”

Resonator advantage

High intensity of light is needed to trigger nonlinear properties for photonic devices, which can be achieved either by ramping up the power of the laser or using a device such as a ring resonator. “A ring allows for that high intensity because it traps the photons for a long time,” Agarwal explains. “More and more photons build up to like a crescendo and that allows for the evaluation of nonlinear optical properties.”

Like a fiber optic cable, which transmits light by wrapping one material that carries the light inside a different material that won’t allow the light to escape through it, the amorphous silicon carbide ring resonator and straight waveguide for carrying the infrared light are surrounded by a layer of silicon oxide that minimizes the amount of light that can escape. The refractive indices of different materials determine how well they work together as the carrier layer and protective outer layer.

“We are trying to create this kind of a fiber optic waveguide on chip,” Agarwal explains. “So it’s like a fiber, but on a chip, and therefore what we need is a core with a high (refractive) index and a cladding with a low index.” Silicon carbide and silicon oxide have a large enough difference in their refractive indices that they work together well as the core and cladding for a waveguide.

The researchers achieved the record quality factor in this study using the plasma enhanced chemical (PECVD) process to deposit the silicon carbide, at a temperature that is compatible with CMOS silicon chip processing, and developing a method to pattern and etch the silicon carbide ring resonator, which is coupled to a straight waveguide.

Overcoming challenges

MIT graduate student Ma overcame several processing challenges to make the high-quality resonator. When Ma began working on silicon carbide materials for this study about three years ago, there was no existing recipe for how to etch a pattern into the amorphous silicon carbide material when it is deposited on a silicon dioxide substrate. “Silicon carbide is a very rigid and physically and chemically hard material, so in other words, it’s very difficult for it to be removed or etched,” Ma says.

To deposit and etch the silicon carbide waveguide on silicon oxide, Ma first used electron beam lithography to pattern the waveguides and reactive ion dry etching to remove excess silicon carbide. But his first attempts using a typical polymer-based mask didn’t work because the process removed more of the mask than it removed of the silicon carbide. Ma then tried a metal mask, but grain boundaries from the mask carried over to the silicon carbide leaving behind rough sidewalls in the waveguides. Roughness is undesirable because it increases photon scattering and light loss. To resolve the issue, Ma developed a technique using a silicon dioxide-based mask for the reactive ion etching. During the process development, Ma worked closely with his colleague Postdoctoral Associate Qingyang Du and Mark K. Mondol, assistant director, NanoStructures Laboratory, Research Laboratory of Electronics.

“We came up with the right type of chemistries in this reaction and controlled the gas flows and the plasma, or in other words, the details of the processing recipe,” Ma says. “This recipe is really selective to etch silicon carbide compared to silicon dioxide which made it possible for us to shape the silicon carbide photonic devices and have a smooth waveguide sidewall,” Ma says. The smooth sidewall is critical for maintaining the optical signals in the photonic device, he notes.

MRL Anu Agarwal 0523 DP Web
MIT Materials Research Laboratory Research Scientist Anuradha M. Agarwal partnered with Singapore University of Technology and Design Assistant Professor Dawn T.H. Tan to demonstrate a high-quality amorphous silicon carbide ring resonator. Photo, Denis Paiste, Materials Research Laboratory.

The main sources of light loss in these resonators are absorption of photons in the ring material and/or scattering of photons caused by edge roughness of the ring device. “Danhao’s processing yielded smooth sidewalls, which enabled low loss and a high Q (Quality) factor resonator,” Agarwal explains.

“The beauty of this silicon carbide material and the technique that we used here in the paper is that the PECVD process of silicon carbide is an inexpensive process, standard in the silicon microelectronics industry,” says Ma, whose research concentration is materials design and engineering for integrated photonics. “Use of the existing microelectronics processes will make the adoption of silicon carbide into the integrated photonic and integrated electronic platforms easier.” The PECVD and reactive dry ion etching processes he used don’t require the lattice matching and other critical demands of epitaxial growth on silicon, and is substrate-agnostic, Ma says.

Better performance

Tan has studied silicon nitride materials and other complementary metal-oxide semiconductor (CMOS) materials for their nonlinearity for several years. “For (amorphous) silicon carbide, you would have a better enhancement when cast as a resonator compared to ultra-silicon-rich nitride (USRN), and it also has a higher nonlinear refractive index than stoichiometric silicon nitride which is prolific in nonlinear optics,” Tan says.

Several kinds of photon absorption known as two-photon and three-photon absorption are typically present in these devices. In this study, Tan says, loss was dominated by three-photon absorption, which is a relatively weak nonlinear loss mechanism, while two-photon absorption, which can be a problem in many crystalline silicon and amorphous silicon materials, was suppressed.

Agarwal and Tan began collaborating while Tan was a visiting scholar at MIT from August 2013 through August 2014. “We were very fortunate to be paired with Prof. Tan’s team, and we benefited a great deal from this collaboration, and we continue to collaborate,” Agarwal says. Agarwal’s team previously worked on using silicon carbide in a sensor for harsh environments.

For the current work, the Singapore team measured the additional wavelengths of light generated in the ring resonator – a phenomenon called spectral broadening which is quantified by a term called Kerr nonlinearity. The researchers found the Kerr nonlinearity of their silicon carbide film to be almost 10 times that of previously reported crystalline and amorphous silicon carbide.

“With this you see a spectral broadening effect, which we can leverage to our advantage because now instead of having just one frequency, we are generating several other frequencies which can provide a super continuum light source,” Agarwal says.

Exciting development

Professor David J. Moss, director of the Centre for Micro-Photonics at Swinburne University of Technology in Australia, who studies photonic materials, says, “This paper presents new results for amorphous silicon carbide as a promising CMOS compatible platform for nonlinear optics, particularly focused on the important telecommunications window.”

“The achievement of a high Kerr nonlinearity – comparable to crystalline silicon – along with negligible two-photon absorption, together with record high (for silicon carbide) Q factor ring resonators, is an exciting development in the continuing quest for ever more efficient platforms for nonlinear optics at 1,550 nanometers,” adds Moss, who was not involved in this research.

Associate Professor Andrea Melloni, who heads the Photonics Devices Group at Politecnico di Milano in Italy, says, “Amorphous SiC (silicon carbide) deposited with PECVD is of great interest. The refractive index is extremely appealing (2.45 is not a common value) because it is high enough to allow large-scale integration, but not as high as silicon, thus minimizing problems associated with the very high index contrast of SOI (silicon-on-insulator) structures.” Melloni, who also did not participate in this research, published a paper last year on Silicon Oxycarbide Photonic Waveguides.

Looking ahead, Ma hopes to make a thicker silicon carbide waveguide for a broader set of applications, for example, creating more wavelengths (multiplexing) within the single waveguide.

“As a first demonstration of what we’ve done together, I think it’s a very promising platform where if we can continue refining the platform and device design, I think we probably would be able to demonstrate very good resonator enhancement because we have demonstrated very good quality factors,” Tan says. “If we wanted to do something like a frequency comb or an optical parametric oscillator, the threshold power becomes a lot smaller if the quality factor is large.”

“If this work can be jointly funded then we can think about making an integrated light source, sensor and detector, so there are a lot of exciting next steps in this,” Agarwal says.

This work was supported by SUTD–MIT International Design Center, the Singapore National Research Foundation and the Singapore Ministry of Education.

back to newsletterDenis Paiste, Materials Research Laboratory
June 27, 2019


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