MRL summer interns tackle materials science challenges, contributing to MIT faculty research labs, overcoming obstacles and gaining new skills.
MIT Materials Research Laboratory interns this summer covered a wide gamut of challenges working with materials as soft as silk to as hard as iron and at temperatures from as low as that of liquid helium [minus 452.47 F] to as high as that of melted copper [1,984 F].
Summer Scholars and other interns participated on the MIT campus in Cambridge, Mass., through the MIT MRL’s Materials Research Science and Engineering Center, with support from the National Science Foundation, AIM Photonics Academy, MRL Collegium, and the Guided Academic Industry Network [GAIN] program.
Simon Egner, from the University of Illinois at Urbana-Champaign, made samples of lead tin telluride to detect mid-infrared light at wavelengths from 4 to 7 microns for integrated photonic applications. Working with Materials Science and Engineering graduate student Peter Su, Egner measured several materials properties of the samples, including the concentration and mobility of electrons. “One thing we have come up with recently is adding lead oxide to try to decrease the amount of noise we get when sensing light with our detectors,” Egner says.
Lead tin telluride is an alloy of lead telluride and tin telluride, Su explains in the lab of MIT Materials Research Laboratory Principal Research Scientist Anuradha Agarwal. “If you have a lot of carriers already present in your material, you get a lot of extra noise, a lot of background signal, above which it’s really hard to detect the new carriers generated by the light striking your material,” Su says. “We’re trying to lower that noise level by lowering the carrier concentration and we’re trying to do that by adding lead oxide to that alloy.”
Juan Hincapie, from Roxbury Community College, took current and voltage measurements of samples in the lab of Riccardo Comin, assistant professor of physics. Wendy Moy, Physical Science teacher at Diamond Middle School in Lexington, Mass., also interned in the Comin lab, growing crystals. Comin’s lab studies superconductors as well as more traditional insulating and metallic semiconductor materials.
“In order to study their properties, we need to measure their electrical transport properties, which in simple terms, means their resistance, or if you like, resistivity, which is an intrinsic version of the resistance, and in order to do that we need to do measurement in a special geometry where we place four contacts on these samples and then we source and sample the current and the voltage,” Comin explains. The tests are conducted using a cryostat at extremely cold temperatures down to a temperature of about 4 kelvins [roughly the temperature of liquid helium]. These current and voltage measurements reveal the resistivity of the material.
“We need to place the samples in an environment whose temperature we can control from very low temperatures, say a few kelvins, up to room temperature and above,” Comin explains. “And then we want to track the resistance as it changes as a function of temperature and we want to see at which point it drops to zero, because that’s the defining feature of a superconductor. It has zero resistance.”
Hincapie says his summer internship was his first research experience and he learned how to program in Python and how to operate equipment in the lab. He hopes to attend a four-year college this fall to study civil engineering.
|Video: Creating Thin Films with Non-Linear Optical Properties|
Thin films for photonics
Summer Scholar Alvin Chang, from Oregon State University, created chalcogenide thin films with non-linear properties for photonics applications. He worked with Postdoctoral Fellow Samuel Serna in the lab of Associate Professor of Materials Science and Engineering Juejun (JJ) Hu. Chang varied the thickness of two different compositions, creating a gradient, or ratio, between the two across the length of the film. “We have two different materials. One is GSS, or germanium antimony and then sulfur, and the other is GSSE, which is germanium, antimony and then selenium,” Chang explains.
“The GSS and GSSE both have different advantages and disadvantages. We're hoping that by merging the two together in a film we can sort of optimize both their advantages and disadvantages so that they would be complementary with each other.” These materials, known as chalcogenide glasses, can be used for infrared sensing and imaging.
Superconducting thin films
Elizabeth [Lily] Hallett, from the University of Arkansas-Fayetteville, made 60 samples of molybdenum nitride thin films on different substrates [silicon oxide, magnesium oxide, silicon] and studied their electrical and superconducting properties in Professor of Electrical Engineering Karl K. Berggren’s lab. She examined the films in a four-probe instrument that measures electrical resistance and in a closed-cycle cryostat that measures the critical temperature. The hope is to develop single photon detectors based on the superconducting property of this material. Molybdenum nitride is predicted to transition to a superconducting state at a higher temperature than similar materials. “This is desirable because it takes less energy to cool the device down to its operating temperature,” Hallett says.
“I’ve been working to optimize deposition conditions for molybdenum nitride in the sputtering system in our lab, by varying all the parameters like temperature, pressure, substrate, gas flow and discharge currents,” she says. A thinner sample looks different from thicker samples with their mirror-like surface, she points out. “Thin films are essential for nanowire single photon detectors, so I have been working on increasing the critical temperature of films that are essentially 5 nanometers thick,” Hallett says.
“Something that I’ve learned that is extremely important is to do a lot of background reading on your project,” Hallett notes. “I tried to find every paper I could on molybdenum nitride. I wanted to know who else had tried to make this material and what results they achieved. Learning how to organize and understand this information was important in making decisions about what experiments to perform.”
Quantum dots for solar
Quantum dots were the focus of summer research for Sarai Patterson from the University of Utah. She synthesized the perovskite quantum dots in the lab of William A. Tisdale, ARCO Career Development Professor of Chemical Engineering, then examined them under a transmission electron microscope [TEM] in MIT MRL MRSEC program’s shared facilities.
After placing a sample in the TEM, Patterson says, “This is one of the samples I made yesterday, and I’m looking to see if I have quantum dots or if I just made nanoplatelets. So far I don’t see anything that looks very much like quantum dots. But we’ll see.”
“The beam is such high energy that a lot of the time it will start burning the sample before you can get a really good image of it and then that just degrades the focus and the image. So it’s kind of difficult,” Patterson says of the TEM work. Quantum dots can be used in LEDs and liquid crystal displays such as in TVs and cell phones. “The perovskite quantum dots that I’m working with have shown a lot of promise for solar technology which is primarily why I’m interested in quantum dots,” Patterson says.
In the Tisdale Lab, she varied the amount of each chemical ingredient to determine the best combination of materials. The quantum dots glow under ultraviolet light, a greenish color in the case of Patterson’s perovskite materials.
Protecting lasers from back splash
Brown University rising senior Ekaterina [Stella] Tsotsos studied cerium-doped iron garnet thin films in the lab of Caroline A. Ross, Toyota Professor of Materials Science and Engineering and Associate Head of the Department of Materials Science and Engineering. “These films are around 100 nanometers thick and they are 10 millimeters by 10 millimeters square. We’re testing their magnetic properties and their optical properties. The machine we’re using right now is called a VSM [vibrating sample magnetometer] and it vibrates the sample and magnetizes it and because it’s vibrating, it generates a current and you measure the current to see how much you can magnetize the sample,” Tsotsos says. “The value you’re measuring is how much can I magnetize this material by putting a magnetic field on it. My specific experiments are about temperature dependent measurements.”
The Ross lab is developing materials that can be used in photonic devices as isolators that protect the laser from any back reflection. “So light can go through forward but can’t come back and hit the laser, which would break it,” Tsotsos says.
Tsotsos worked with Materials Science and Engineering graduate student Takian Fakhrul. Besides magnetic measurements Tsotsos also did optical measurements of her garnet samples. Condensation at low temperatures became a challenge, she explains. “Once we get down to negative 60 degrees C, condensation starts forming on the film and it alters the light that we are trying to pass through it, so we get bad measurements then. But we’ve been working through it, heating it up first to try to dry it out, shooting a bunch of nitrogen through the stage, to try to make sure there is not water vapor in there. Yea, we’re trying to see what will work.”
Strengthening aerospace composites
Abigail Nason, from the University of Florida, studied the potential benefits of incorporating carbon nanotubes into carbon fiber reinforced plastic [CFRP] via a process termed “nanostitching” in the lab of Brian L. Wardle, Professor of Aeronautics and Astronautics. Bundles of carbon microfibers are known as tows and are used to make sheets of aerospace-grade carbon fiber reinforced plastic. Working with graduate student Reed Kopp, Nason took 3D scans of composite laminate samples to reveal their structure. “We’re working with 10 millimeter by 4 millimeter by 2 millimeter little rectangular composites and some of them have nano-stitch[ing] in them and some of them do not,” Nason explains.
Areas between sheets of the laminate are called the interlaminar region, and are weaker because they lack the added strength from mechanical reinforcement that fibers provide. Traditional composites have no reinforcement in this interlaminar region, and carbon nanotubes provide nano-scale fiber reinforcement in the nano-stitch version. Kopp notes that despite the high level of resolution required to elucidate an intricate architecture of micro-scale features, the 3D scans can’t distinguish the carbon nanotubes from the epoxy resin because they have similar density and elemental composition. “Since they absorb X-rays similarly, we can’t actually detect X-ray interaction differences that would indicate the locations of reinforcing carbon nanotube forests, but we can visualize how they affect the shape of the interlaminar region, such as how they may push fibers apart and change the shape of inherent resin-rich regions caused during carbon fiber reinforced plastic layer manufacturing.”
Nason adds that “It’s really interesting to see that there isn’t a lot of information out there about how composites fail and why they fail the way they do. But it’s really cool and interesting to be at the forefront of seeing this new technology and being able to look so closely at the composite layers and quantifying critical micro-scale material features that influence failure.”
Astatke Assaminew, a biotechnology student at Roxbury Community College, and Heather Giblin, a biology teacher at Brookline High School, interned in the lab of Katharina Ribbeck, associate professor of biological engineering.
Working with Postdocs Miri Krupkin and Gerardo Cárcamo-Oyarce and Research Scientist Bradley Turner, Assaminew investigated the effects of purified mucin polymers on the opportunistic bacterial pathogen, Pseudomonas aeruginosa, using live confocal microscopy. Giblin, who worked with biology graduate student Julie Takagi, investigated the effects of mucin polymers purified from saliva on biofilm formation in the opportunistic fungal pathogen, Candida albicans. Assaminew and Giblin learned to purify mucin polymers from native mucus tissues using size exclusion chromatography.
Both Roxbury Community College Chemistry and Biotechnology Professor Kimberly Stieglitz and Roxbury Community College student Credoritch Joseph worked in the lab of Assistant Professor in Materials Science and Engineering Robert J. Macfarlane. The Macfarlane Lab grafts DNA to nanoparticles, which enables precise control over self-assembly of molecular structures. The lab also is creating a new class of chemical building blocks that it calls Nanocomposite Tectons, or NCTs, which present new opportunities for self-assembly of composite materials.
Joseph learned the multi-step process of creating self-assembled DNA-nanoparticle aggregates, and used the ones he prepared to study the stability of the aggregates when exposed to different chemicals. Additionally, Joseph began to optimize a silica-embedding procedure for removing DNA-nanoparticle crystals from solution. Stieglitz created NCTs consisting of clusters of gold nanoparticles with attached polymers and examined their melting behavior in polymer solutions. She learned a multi-step process to produce NCTs, including how to spin the compounds in vials of water-based liquid, containing either DAP [diaminopyridine] or Thymine, each of which has hydrogen donor/acceptor pairs. After the spinning step, water and dimethylformamide [DMF] are removed, and the nanoparticles are re-suspended in toluene before being combined to assemble into NCTs. “They’re actually nanoparticles that are linked together through hydrogen bonding networks,” Stieglitz explains, “and the nanoparticles have gold which reacts with the S-H [sulfur-hydrogen end].”
Spinning particles with magnetism
Summer Scholar Ryan Tollefsen from Oregon State University joined Associate Professor of Materials Science and Engineering Alfredo Alexander-Katz’s lab to explore the dynamics of neutral colloidal particles spinning in a magnetic field. These simulations model generic neutral beads but show behavior similar to living cells, such as bacteria. “The goal with the spinners is to achieve self-assembly, which is when the active particles just by themselves create a structure,” Tollefsen says.
Tollefsen learned to write simulations in the Fortran programming language, adapting a freely available code for dissipative particle dynamics simulation known as CAMUS. “Before this summer, I had never created a piece of software that had more than probably 200 lines of code,” Tollefsen says. “Now I’m working with software that has over 4,000 lines of code. So one of the biggest skills I’ve learned is just keeping track of something that has so many moving parts.”
Applying a magnetic field that repeatedly crosses back and forth from positive to negative, Tollefsen says, causes the spinners first to spin in one direction, then to slow down and stop, and lastly to spin in the other direction. “When the spinners are kind of spinning like this, they form these little clusters but they don’t completely phase separate. They form little groups and then start to push other little groups away, and so you get kind of these clusters which are neatly organized with each other and that’s called a microphase separation,” Tollefsen explains.
“When we learn the rules of these systems, we start to get the idea of how we can use it to engineer synthetic living systems. I think when that technology is fully realized, it will define its era,” he says. “We kind of have living buildings where they’ll read the temperature and they’ll open and close windows automatically but imagine if you could have that kind of responsiveness and functionality within a material, microscopically. That’s the goal in my mind, when I study these spinners,” he says.
Activating silk fibers
Summer Scholar Sabrina Shen, from Johns Hopkins University, carried out molecular dynamics simulations of how different forms of carbon affect silk in the lab of Civil and Environmental Engineering Department Head Markus J. Buehler. “If we can put activated carbon inside silk and make conductive membranes with it, then it can be conductive, and then it can be used for flexible electronics or sensors,” Shen explains. The lab is interested in obtaining activated carbon from biomass, she says. Compared to pure carbon materials, like graphite or carbon nanotubes, biomass-derived activated carbons often contain oxygen and nitrogen, and this affects their interaction with silk proteins. “Previous studies have shown that graphene can disrupt hydrogen bonding within the silk beta crystals, which would decrease the mechanical strength of the silk. Now we want to see how biomass-derived carbons populated with different functional groups including both oxygens and nitrogens will interact with the silk, and how this affects the mechanical properties,” Shen says.
“I’ve never done computational research before so all of it is fairly new to me,” Shen says. “I was fairly set on graduate school before coming here, but I’m even more certain now, especially after I’ve had opportunities to talk to the other graduate students in my lab and to hear about their experiences.”
While she previously worked with biomaterials for the medical field, Shen says she finds the Buehler lab’s focus on bio-inspired materials and hierarchical design to be fascinating. “I like it a lot, and it’s definitely something I would consider for graduate research,” Shen says.
Analyzing cobalt supply and demand
Working in the research group of Elsa A. Olivetti, Atlantic Richfield Associate Professor of Energy Studies, Summer Scholar Danielle Beatty from the University of Utah, says she experienced an entirely different side of materials science and engineering from the experimental work she previously did.
Beatty developed scenarios to analyze the balance between supply and demand for cobalt, particularly in the face of increasing demand for lithium ion batteries in electric vehicles. “We’re focusing on how demand is going to change out to 2030,” Beatty explains. “We’re doing a short-term analysis, how demand is going to change, how supply of cobalt coming from both primary sources and recycling may have an impact on that demand-supply ratio.”
Beatty learned new coding skills in Python and gained a broader perspective on materials availability. “It’s opened up a whole new side of things for me. I never had really considered the computational side of materials science much, but coming into this, that’s definitely a possibility for me now and something I’d be really interested in pursuing further or at least incorporating more into my experimental work as well,” she says.
Creating neuro fibers
Bunker Hill Community College student Minhua Mei worked with Postdoc Mehmet Kanik in the lab of Associate Professor in Materials Science and Engineering Polina Anikeeva on a project to develop a flexible fiber probe. The goal is develop a neuro probe for recording brain activity in mice as part of an autism study. Mei worked with the polymer PMMA to create blocks about 10 inches long with electrodes melded into them that can be drawn out to a hundred times their length in a fiber drawing tower.
Improving flow batteries
Summer Scholar Julianna La Lane from the University of Puerto Rico at Mayagüez and Bunker Hill Community College student Zhirong [Justin] Fan worked on aqueous flow batteries in the lab of Fikile R. Brushett, the Cecil and Ida Green Career Development Chair, Associate Professor of Chemical Engineering.
Fan used electrochemical diagnostics to compare the microstructure and the performance of different commercial electrodes in flow batteries. La Lane created hierarchically porous electrodes derived from polyacrylonitrile, optimizing the fabrication procedure to tune properties including porosity, hydrophilicity [ease of wetting by water], and electrical conductivity. “We’re trying to make it as porous as possible,” La Lane explains.
Synthesizing electronic materials
Summer Scholar Michael Molinski, from the University of Rhode Island, and Roxbury Community College student Bruce Quinn worked in the lab of Assistant Professor of Materials Science and Engineering Rafael Jaramillo. Working with graduate students Stephen Filippone and Kevin Ye, both Molinski and Quinn made solid materials, producing powders of compounds such as barium zirconium sulfide, which are desirable for their optical and electrical properties.
The process involves mixing together the chemical ingredients to produce the powders in a quartz tube in the absence of air and sealing it. “In the reaction, you don’t want any oxygen to create an oxide, so he seals them in the tube, then he puts them in the furnace, heats them up and hopefully creates barium zirconium sulfide when it comes out,” Filippone explains.
The first GAIN program participant, Quinn hot pressed the powders into pellets. He expects to complete an associate degree in biotechnology next spring. Molinski also grew crystals. Both examined their powders with X-Ray diffraction.
Developing multiple sclerosis models
Summer Scholar Fernando Nieves Muñoz, from the University of Puerto Rico, Mayagüez, worked in the lab of Krystyn Van Vliet, the Michael (1949) and Sonja Koerner Professor of Materials Science and Engineering, to develop mechanical models of multiple sclerosis [MS] lesions. Nieves Muñoz worked closely with Research Scientist Anna Jagielska and chemical engineering graduate student Daniela Espinosa-Hoyos. “We are trying to find a way to stimulate repair of myelin in MS patients so that neurological function can be restored. To better understand how remyelination works, we are developing polymer-based materials to engineer models of MS lesions that mimic mechanical stiffness of real lesions in the brain,” Jagielska explains.
Nieves Muñoz used stereolithography 3D printing to create cross-linked polymers with varying degrees of mechanical stiffness and conducted atomic force microscopy studies to determine the stiffness of his samples. “Fernando has been optimizing a commercial 3D printer to generate stiffness maps by changing the gray scale values of digital masks and in this way change the extent of cross-linking of the polymer within a given model,” Espinosa-Hoyos says.
“Our long-term goal is to use these models of lesions and brain tissue to develop drugs that can stimulate myelin repair,” Nieves Muñoz says. “As a mechanical engineering major, it has been exciting to work and learn from people with diverse backgrounds.”
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