MRS Bulletin Materials News Podcast
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Materials News podcast by MRS Bulletin provides breakthrough news & interviews with researchers on hot topics including biomaterials, quantum materials, artificial intelligence, sustainability, perovskites, and robotics. Produced by the Materials Research Society.
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Apr 29, 2020
Episode 8: Atomic defects form quantum emitters in hBN
Sophia Chen of MRS Bulletin interviews Jennifer Dionne from Stanford University about the origin of photonic emissions in the quantum material hexagonal boron nitride (hBN). Read the article in Nature Materials.
Transcript
SOPHIA CHEN: Many researchers are hotly anticipating quantum technology, a new paradigm that exploits the mathematics of quantum mechanics. But researchers are still developing the so-called quantum materials to build these devices and connect them in a future quantum internet. Jennifer Dionne, a materials scientist at Stanford University, is investigating one such material called hBN, or hexagonal boron nitride. hBN could be useful for quantum machines because it can be made to emit single photons of light to compute and transmit information. When you illuminate hBN with light the material will emit a spectrum of colors ranging from the red to the green. Dionne’s team wanted to understand what microscopic property or defect in the material was responsible for the different colors.
JD: What we wanted to do was address where those different colors were coming from, because in a future quantum optical network, ideally you’d be able to control what color is coming out where and be able to use that wavelength multiplexing of photonic communications.
SC: To identify which light came from what defect, they used a combination of two different techniques.
JD: By interrogating with an optical microscope, we can see broadly where there were different defects and use the electron microscope to zoom into those defects and map them out with much higher resolution and to also look at their atomic scale structure.
SC: They were able to identify that the colors arise from four classes of defects in the hexagonal boron nitride.
JD: So we now know with certainty there are at least four different types of atomic defects that are responsible in the main spectral windows. If you want light predominantly in the green, you would use one type of atomic defect. If you want light in the red, you use a different type of atomic defect.
SC: Combining their experimental studies with theory, Dionne’s team was able to deduce more details about the defects themselves.
JD: We found that it seems like most of the defects that are emitting are not simple atomic defects, but rather complexes. So hexagonal boron nitride, like I said, is this layered material. You need to think not only about a missing atom in one layer but perhaps a missing atom or a substitutional atom in a neighboring layer, and basically a series of missing atoms between one layer and a next form something like its own independent molecule in the material.
SC: By understanding the specific defects in a material, eventually, researchers should be able to implant specific impurities that can be independently controlled to emit light in a quantum device.
JD: We’re excited to get higher spatial imaging resolution and start positioning those emitters and see how we might be able to modulate the emission, to be able to turn the emission on off, which would be the same in a transistor. You want to be able to turn the electrical current on and off and be able to get gain. Trying to create a suite of quantum optical devices based on these emitters would be very exciting and next step.
SC: But this technique, where they combine optical and electron microscopy to study quantum materials, is useful beyond just hexagonal boron nitride.
JD: More so than learning about hexagonal boron nitride, I think the significance of our paper is that it provides a technique to be able to do this correlation of the atomic scale structure of quantum materials with their optical properties.
Apr 14, 2020
Episode 7: Microneedle array key to deliver vaccine against COVID-19
Sophia Chen of MRS Bulletin interviews Stephen Balmert of the University of PIttsburgh about a patch delivery method of a vaccine to counter COVID-19. Read the article in EBioMedicine.
Transcript
CHEN: To prevent the spread of Covid-19 in the long term, we will almost certainly need a vaccine against the disease. Stephen Balmert, a biomedical engineer from the University of Pittsburgh, is part of an international collaboration that has made such a candidate vaccine for Covid-19. They’ve tested their vaccine in mice and gotten promising results.
BALMERT: I think everybody really wants to know, when is this going to be in humans? We’re putting together [a form] to get approval from the FDA to begin a clinical trial.
SC: Under the microscope, the pathogen resembles a sphere adorned with spikes, known as spike proteins. Balmert’s vaccine is made of these spike proteins. To produce the spike, they introduce the genetic instructions for making the proteins into human embryonic kidney cell lines. These cells make the proteins. Then, the idea is to introduce the spike proteins into the human body, which teaches the immune system to recognize these proteins and produce antibodies that neutralize the virus. Their Covid-19 vaccine piggybacks off previous research on a similar coronavirus. Balmert’s colleague, Andrea Gambotto, had previously studied the MERS virus in his lab.
SB: They had already identified at that point there’s a particular part of the virus, which is called the S protein or the spike protein, they’d identified that was a good target for vaccines.
SC: Targeting the spike protein is a popular approach. But Balmert’s team uses a distinctive delivery method. Instead of injecting the vaccine via the traditional needle, they package their vaccine as a small, fingertip-sized patch covered in very small, short needles. The needles are made of a material called carboxymethyl cellulose, a hydrogel that dissolves in the skin. Each one is 225 µm in width, 750 µm in length, with a pointy tip shaped like a tiny Washington monument.
SB: Each of those needles has the vaccine in the tips, so in the pyramidal part at top, and there’s a flat backing underneath that you use for the application. We say the application of the microneedle feels a little bit like Velcro, the hook part of the Velcro. So you can feel the pressure, but it’s not painful in the sense of a traditional injection is.
SC: In addition, the patch deposits the spike proteins into the skin, as opposed to muscle like many traditional vaccines. This offers potential benefits as well. The skin contains a high concentration of immune cells because it protects the body from foreign particles.
SB: So you have potentially somewhat of a dose sparing effect, where you get a stronger immune response with the same dose. Or you can use less dose for the same immune response than a regular injection. In that sense, it requires potentially less vaccine.
SC: They could also be easier and cheaper to store compared to other vaccines.
SB: With these microneedle arrays, the carboxymethyl cellulose in the hydrogel material around the vaccine itself kind of maintains the structure of the vaccine. It maintains its bioactivity so you don’t have to keep them refrigerated. You don’t have to have refrigerated shipping or store them in a refrigerator necessarily, so that’s another potential advantage.
SC: They’ve published peer-reviewed results indicating the vaccine produces antibodies in mice. Now, they’re running tests to confirm that their results are reproducible and are working to gain approval from the Food and Drug Administration to begin clinical trials in humans.
Mar 30, 2020
Episode 6: Catalyst design speeds up CO2 conversion to carbon products
Sophia Chen of MRS Bulletin interviews Pelayo Garcia de Arquer of the University of Toronto in Canada about a catalyst-ionomer architecture his group designed to quickly convert CO2 into useful hydrocarbons. Read the abstract in Science.
Transcript
SOPHIA CHEN: The challenge for the world to reduce carbon emissions is steep. To reduce these emissions in the long run, some scientists believe it will be necessary to extract carbon dioxide from the air. But once you extract all that carbon dioxide, what do you do with it? Pelayo Garcia de Arquer, a materials scientist at the University of Toronto in Canada, has a potential answer. He’s working on technology for converting carbon dioxide into useful hydrocarbons, such as plastics, fabrics and fuels that are now produced by the petrochemical industry. In other words, he’s trying to turn lemons into lemonade.
PELAYO GARCIA DE ARQUER: Our approach is to decarbonize this process by taking existing CO2 in the atmosphere, in the exhaust of an industry for example, and using electricity, which could come from renewables, and using water, and upgrade the CO2 into other molecules that can be used in these production systems, for example upgrading CO2 into ethylene, which is the precursor to a lot of polymers.
SC: To convert carbon dioxide into ethylene, they pump CO2 gas to a spongelike catalyst interface, where the CO2 breaks down and ultimately reacts with water and an electrolyte. But it’s difficult to orchestrate this reaction quickly and efficiently, at the rates needed to make this technology economically viable. On their own, the individual reactants don’t tend to move to the right location very quickly.
PGDA: You need to have all the ingredients of your cake in the right place and in the right time.
SC: The difficulty is that CO2 does not like to dissolve in water. It also tends to undergo undesired reactions with the electrolyte to produce hydrogen molecules, for example. This makes the reactions proceed slowly. So their lab’s innovation was to include an extra ingredient on the surface of the catalyst known as an ionomer, a polymer that conducts ions. The ionomer had both hydrophobic and hydrophilic parts, which in effect created distinct channels for carbon dioxide, water, and the other ingredients to travel through separately to reach the catalyst. Monitoring the electric activity in their system, which is an indication of how quickly the chemical reaction is proceeding, they measured an electric current density of more than one ampere per square centimeter, which Garcia de Arquer says is about 10x improvement compared to the state-of-the-art just 2 years ago.
PGDA: This is enabled, we believe, because of this phenomenon, like CO2 can travel faster through these more dry channels that do not have water.
SC: They also achieved an efficiency of 45%, meaning that 45% of the energy they put in created the ethylene. It’s not clear yet what metrics will make this system commercially viable, as the economics depend on many outside factors, such as the cost of electricity. But Garcia de Arquer says that the field is moving closer to a deployable technology.
PGDA: Achieving current densities in the realm of amperes per square centimeter, together with energy efficiencies above 60%, that’s the threshold we predict with the numbers we have right now, where we think things will become more and more interesting.
Mar 16, 2020
Episode 5: Coupled-QD system in graphene reveals puzzling charging patterns
Sophia Chen of MRS Bulletin interviews Dan Walkup of the National Institute of Standards and Technlogy about an unusual concentric quantum dot structure created in graphene. Read the abstract in Physical Review B .
Transcript
SOPHIA CHEN: Physicist Dan Walkup has a mystery on his hands. Working at the National Institute of Standards and Technology in Gaithersburg, Maryland, his team has engineered a strange phenomenon in the 2D material graphene using a scanning tunneling microscope, or STM. They created the phenomenon by accident playing around with the STM, whose very sharp tip manipulates single atoms on a material. In the graphene it created a quantum dot (QD).
DAN WALKUP: Historically we weren’t trying to study coupled QDs per se. We were trying to figure out how to tune the properties of the graphene with STM tip. In that way we came eventually to this QD study.
SC: You can visualize the QD as an island in the graphene, where electric charges are confined and isolated from the rest of the material. At the QD, negative electrons gather around positive electron holes. They can also do the charge inverse of this, where the positive holes go around a negatively charged nucleus. From this, you might get the sense why QDs are sometimes known as artificial atoms. Like atoms, quantum dots consist of one type of charge going around a nucleus of the opposite charge. The researchers have taken the graphene, stuck it on a substrate of hexagonal boron nitride, and manipulated the electric charges with the STM inside these two materials to create the QD.
DW: We create a little pocket of charge in the hexagonal boron nitride, and that charge pocket attracts oppositely charged electrons in the graphene and makes a little charge pocket in the graphene, which becomes a QD.
SC: But this isn’t your garden variety QD. The geometry of this particular island has never been seen in graphene. By using the STM and applying a strong magnetic field to the material, Walkup’s team has made a nested QD, one island of charge stacked on the other. From overhead it looks like a bulls’ eye, with one island of charge at the center, and another forming a ring around it.
DW: The two dots are like the two tiers of this wedding cake.
SC: They’re two concentric quantum dots: one dot is in the center and the other dot is the ring around the first. These two structures are distinct quantum dots because electrons from one island are generally confined to that island. Walkup’s team ran some experiments in which they added electrons to each quantum dot. They did this by applying a voltage to the back of the material, causing electrons to move toward each dot. The researchers can then monitor where the electrons go using the scanning tunneling microscope. And what they found was puzzling. They found that as they added electrons to either of the two quantum dots, they behaved in a way that can’t be explained by accepted models of quantum dot physics. Walkup says you would expect the two dots to repel each other as you add electrons to them, since negative charges repel each other. But the inner dot only cared about its own charge. It did not care about the charge of the outer dot. Whereas the outer dot responded to the combined charge of both dots. They want to figure out why.
DW: Part of this paper is an open invitation to the theorists in the world to figure out why it is this way instead of some other way.
SC: A better understanding of the basic physics of this bizarre quantum dot configuration could help the development of applications such as quantum computing, in which information is stored in the way quantum dots share electrons. This work was published in a recent issue of Physical Review B.
Feb 27, 2020
Episode 4: Toxic bromate removed from drinking water
Sophia Chen of MRS Bulletin interviews Tina Škorjanc, a PhD student at New York University in Abu Dhabi in the United Arab Emirates, and her professor Dinesh Shetty at Khalifa University, Abu Dhabi, about porphyrin–based covalent organic frameworks they developed that remove the toxic substance bromate from drinking water. Read the article in Chemical Science.
Transcript
SOPHIA CHEN: Drinking water: Whether it’s out of the tap, the refrigerator, or a bottle, we expect it to be clean. Water treatment plants oblige, with a complicated sequence of filtration and purification processes. During a last purification step, the treatment plants add ozone to disinfect the water. The ozone removes odor, color, and taste, and it does this all quickly. But a potential dangerous side effect of the ozone turns harmless, naturally occurring bromine ions in the water into the toxic substance bromate. Tina Škorjanc, a PhD student at New York University in Abu Dhabi in the United Arab Emirates, is working on methods to remove bromate from drinking water.
TINA ŠKORJANC: It has been linked to a whole series of health conditions in humans and has been linked to cancer, which is why we think it is important to remove it.
SC: Škorjanc’s team has developed a new material that can remove bromate much faster than any other existing method.
TS: We really outperformed other materials which were of different classes. This list included inorganic materials, activated carbons, metal organic frameworks, a couple of other polymers, our rates really surpassed the ones reported for these other materials.
SC: Dinesh Shetty, Škorjanc’s colleague and a professor at Khalifa University, also in Abu Dhabi, says that their group is the first to create a covalent organic framework specifically for bromate removal.
DINESH SHETTY: Compared to normal polymers, covalent organic frameworks are ordered structures. It has defined structure, you can study exactly what is happening within this framework, you know exactly where bromate is going, how it is interacting with this material.
SC: Bromate likes to stick to this material, because the material is positively charged and electrostatically attracts the negatively charged bromate.
DS: If you think about other covalent organic frameworks, you have to synthesize COF first and then introduce positive charges. We are reducing one step, synthetically, if you think about it.
TS: We can do our bromate adsorption experiment, take that material which has bromate on its surface and in its pores, remove those molecules by simple treatment with sodium hydroxide followed by neutralization, and we can reuse that same batch for bromate adsorption again. What’s important in the second step is the efficiency doesn’t drop. We’re still able to remove the same amount of bromate that was removed in the first cycle.
SC: It’s still unclear whether this material will be economically viable for adoption by existing water treatment plants. But their work opens the door to further development of covalent organic frameworks that remove bromate. And in the meantime, their team is working to figure out how to scale up their experiment and eventually test it in a water research center in Abu Dhabi.
DS: We are dealing with something which can directly impact society. If our plan works, if it becomes water purification material for bromate removal, we are helping millions all around the world. That’s real motivation for us.
SC: My name is Sophia Chen from the Materials Research Society. Follow us on twitter, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.
Feb 13, 2020
Episode 3: E.coli evolved to eat CO2
Sophia Chen of MRS Bulletin interviews Ron Milo of the Weizmann Institute of Science in Israel about a strain of E. coli his team developed that generates all its biomass from carbon dioxide. Their work was achieved through a technique called adaptive laboratory evolution, that is, evolutionary selection. Read the article in Cell.
Transcript
SOPHIA CHEN: Inside a lab at the Weizmann Institute of Science in Israel, biologist Ron Milo and his team have engineered a strain of E.coli with an unusual diet. Natural E.coli is a heterotroph, meaning that it can only consume organic carbon compounds—like glucose. But Milo’s team converted the bacteria into an autotroph, an organism such as a plant that can consume inorganic carbon. They essentially changed the bacteria’s metabolic process.
RON MILO: What we did in this study is show that we could take an organism of the second type, a heterotroph, in this case E.coli, that is used to having its diet coming from glucose in the media, and being able to transform it into the first type, the autotrophs, which build all their biomass directly from CO2.
SC: To do this, Milo’s team had to enable E.coli to perform carbon fixation. Carbon fixation is a capability found in plants where inorganic forms of carbon are converted into organic compounds. This process involves first by adding electrons to the inorganic carbon, or reducing it, which allows the carbon to form an organic molecule. Then, the organic carbon is converted into biomass such as proteins and carbohydrates inside the cell. They did this by adding some genes into the bacteria’s DNA. One gene, for example, enabled the E.coli to reduce the carbon by taking electrons from a compound called formate. They also put in other genes.
RM: So we put in the gene that takes carbon dioxide and incorporates it into biomass. It’s a gene called rubisco. We also put in a gene that builds a substrate for rubisco, it’s called PRK.
SC: The engineered bacteria still ate sugar, so to make bacteria that ate only CO2, they turned to a technique known as adaptive laboratory evolution. They placed the engineered bacteria in a container with very little sugar and a high concentration of CO2, an environment which basically starved the cells. In this low sugar environment, they let the bacteria reproduce several hundred times for nearly a year. Eventually, they found that these later generations of E.coli generated all their biomass from CO2.
RM: The process of carbon fixation aims to find ways to deal with the challenge of how do you produce transportation fuels that will not harm the environment as well as how to increase the yields in agriculture, and more generally, to see if there’s ways to sequester CO2 from all sorts of concentrated sources or even directly from the air.
SC: The bacteria produced CO2 in addition to consuming it. In total, it created a net gain of CO2. So in its current form, the bacteria would not be useful for many applications. But they’ve come a long way since Milo started the project about a decade ago.
RM: I remember when I presented this work, people thought it was somewhere between naive and crazy to think that one could actually change a heterotroph into an autotroph. We did most of our experiments in an atmosphere of 10% CO2. We could also show we could grow bacteria in lower CO2 levels of say, about 1 percent. But what we have in the atmosphere around us is about 400 parts per million, and we want to see if we can evolve the bacteria to grow in that.
SC: Thank you for listening.
Jan 29, 2020
Episode 2: AI steers autonomous x-ray scattering experiments
Prachi Patel of MRS Bulletin interviews Kevin Yager and Masafumi Fukuto of Brookhaven National Laboratory about an artificial intelligence algorithm they designed that analyzes data and then decides what should be measured next. In their first autonomous experiment, the researchers used x-ray scattering to map the boundaries of a droplet where nanoparticles segregate. Read the article in Scientific Reports.
PRACHI PATEL: Discovering new materials takes an enormous amount of time. You make a material, measure its properties, analyze the data, and then repeat the process all over again. Automation has sped things up. But now scientists have made this automation smarter. In a recent paper published in the journal Scientific Reports, researchers presented an artificial intelligence algorithm that can analyze data and then decide what to measure next. Here’s Kevin Yager, a scientist at Brookhaven National Laboratory.
KEVIN YAGER: I think its important to make a distinction between automation and autonomous. It’s autonomous in the sense that you tell it a goal and it, you know, starts conducting the experiments and updating its experimental plan on each iteration.
PATEL: The goal is to speed up every step in the materials discovery process, improve those steps, and couple them better to each other. And eventually, make the entire experimental workflow autonomous.
YAGER: Not to replace the human experimenter but really to liberate the scientist to think about the data at a higher level because the tool is automatically making decisions about what to measure, doing that measurement, and then updating its experimental plan in a loop. So the human can think about the meaning of the data as its being collected and intervene as necessary.
PATEL: The researchers start by defining a set of goals for their experiment. The algorithm then works in a multidimensional parameter space. Those parameters can be things like material composition, temperature, and pressure. And the algorithm explores how material properties vary throughout that space, Yager says.
YAGER: The algorithm treats it as a very abstract mathematical problem. Which is saying ok I have some data points in this space and what I’m going to do is I’m going to interpolate between the existing data to create what’s called a surrogate model that sort of tries to represent the data. And then along with that surrogate model I can compute a corresponding uncertainty. So how certain or uncertain my model is across that space. Where I’ve measured a lot of data my model is pretty certain. Where I’ve measured not very much data my model is very uncertain. So the algorithm essentially says wherever my uncertainty is high, that’s probably where I should measure next because I’m going to gain the most information.
PATEL: For their first autonomous experiment, the team used x-ray scattering to map the boundaries of a droplet where nanoparticles segregate. They compared the standard approach with the new AI algorithm explains Masafumi Fukuto, a scientist at Brookhaven and co-author on the paper.
MASAFUMI FUKUTO: The first test that we did was to compare a simple grid search, a grid scan of this material as a function of spatial coordinates vs AI-driven search of these spatial coordinates. We found features like the boundaries of this heterogeneous material much more quickly than you do with a simple grid scanning method.
PATEL: The algorithm could be applied to any other materials research and discovery method.
FUKUTO: The brain part, the AI part, the decision algorithm part is completely independent of the technique that you use.
PATEL: This is Prachi Patel for MRS Bulletin’s Materials News Podcast.
Jan 13, 2020
Episode 1: Strain engineering guided by machine learning
Omar Fabián of MRS Bulletin interviews Ju Li of Massachusetts Institute of Technology about applying machine learning to elastic strain engineering of semiconductor materials at the nanoscale. The research team presents a framework for guiding strain engineering whereby materials properties and performance could be designed. Read the article in Proceedings of the National Academy of Sciences.
Transcript
OMAR FABIÁN: There are innumerable ways to alter a material’s properties. For crystalline materials it comes down to lattice structure, to the shape of the unit cell. That’s the key to unlocking new macroscopic properties from the same old material.
JU LI: We think we know silicon…But what is interesting is if you put 5% tension on silicon or 5% shear that becomes a different material.
OF: That’s Prof. Ju Li, a professor of nuclear science and engineering at MIT, talking about elastic strain engineering.
JL: This is not, you know, you take a piece of metal and you can bend it 30, 50%. Those are plastic strain. The amount of elastic strain that a conventional metal can sustain is no more than 0.2, 0.3%. But with nanomaterials, we can talk about more than 1% elastic strain. And not just near defects or near some special locations, but throughout the entire component that you are using.
OF: Going nano opens up new degrees of freedom for accessing bandgaps that are otherwise off limits. One percent strain, for example, is enough to bump silicon’s bandgap such that the material’s electron mobility jumps by more than 50%. But at about 15% strain, you’re able to wipe out silicon’s bandgap altogether—transforming it into a metal. Prof. Li’s team is using neural networks to learn the quickest, lowest-energy pathways to get from a set of strain conditions to different bandgap energies in materials like silicon and diamond.
JL: It turns out that if you want to make silicon a metal, then the strain path you impose should not be a straight line. So perturbation theory doesn’t work. The best way to make silicon in the least amount of energy to reduce its bandgap is actually a pretty curved path. And so that’s sort of the power of ML. It’s a fast-acting model, it can do all kinds of projections or visualizations that you simply cannot do on a point-by-point calculation. You can also ask other questions, like how do I improve its thermoelectric figure of merit? Or what’s the fastest way to make it have this kind of optical signature? This is kind of like Alice in Wonderland. There is suddenly a big space that opens up and that can be a little bewildering at the beginning because we are sort of looking at each other and saying what is the first device we’re going to design. It’s quite a big space, and we feel that just on our own group, our own power, we probably cannot explore it all. So we’d really like the community to jump in and help in this effort of strain engineering because it’s going to have long-term consequence on human civilization—just as much as chemical metallurgy has.
Dec 18, 2019
Episode 24: Gold nanoparticles modify electrical behavior inside living cells
Sophia Chen of MRS Bulletin interviews Frankie Rawson of the University of Nottingham, UK, about wirelessly manipulating the electrical behavior of living cells. His research group does so by applying an external voltage to Au nanoparticles inserted into the cell. The voltage causes a molecule attached to each Au nanoparticle to undergo a redox reaction, in which atoms give up or accept electrons from each other. Read the abstract in Applied Nano Materials.
Transcript
SOPHIA CHEN: Tiny electrical currents flow in many parts of the human body. For example, ions moving inside cells or crossing cell membranes. Many instances of these electrical currents occur because of a type of chemical reaction in the cell known as a redox reaction, in which atoms give up or accept electrons from each other.
FRANKIE RAWSON: Ultimately, redox reactions underpin how cells make energy.
SC: Frankie Rawson is a bioengineer at the University of Nottingham in the UK. He’s designing materials that can be placed into a live cell—and modify its electrical behavior.
FR: Biology is largely underpinned by electrical behavior, and we’re starting to realize that if we can merge and develop materials that seamlessly integrate with that biology we can control the electrical input and output on a really targeted scale.
SC: In the past, to manipulate a cell’s electrical behavior, researchers would have to place nanowires inside the cell. Rawson and his team have recently demonstrated that they can do this wirelessly. Essentially, they drove a redox reaction in the cell, and they did it like this. They inserted modified gold nanoparticles into the cell. Then, they applied an external voltage. They applied a relatively low 150 volts compared to the kilovolts used in prior experiments. This basically causes a molecule attached to each gold nanoparticle to undergo a redox reaction. The nanoparticle helps direct the external electric field.
FR: The gold nanoparticle acts as an electrical antennae, effectively.
SC: The researchers confirmed that the redox reaction occurred using two different methods. First, they illuminated the molecule attached to the gold nanoparticle, a type of molecule known as zinc porphyrin, with yellow light and monitored its fluorescence. Zinc porphyrin’s fluorescence changes depending on its number of electrons. When the molecule gains an electron, its fluorescence dims, signifying that the redox reaction has occurred. At the same time, the researchers also performed a measurement known as cyclic voltammetry, in which they measure electrical behavior of the nanoparticle while changing an applied voltage. These two methods collectively indicated that they had triggered a redox reaction at the surface of the gold nanoparticle inside the cell wirelessly.
FR: What that means is, that’s moving toward that step where you don’t need a physical wire connection inside the cell to actuate electrochemical behavior inside the cell.
SC: Ultimately, the bigger goal is to use the zinc porphyrin redox reaction to drive other reactions inside the cell. Rawson wants to trigger redox reactions in a cell that would kill it.
FR: If everything goes to plan, the research hypothesis is that you can use this as a bioelectronic drug. You put this in an organism; you can target the electric field in a location in that organism, and switch on cell death. Our hypothesis is to use this to kill cancer cells.
SC: For more news, log onto MRS Bulletin and follow us on twitter.
Nov 21, 2019
Episode 23: Spin-triplet superconductivity discovered in uranium ditelluride
Sophia Chen of MRS Bulletin interviews Nicholas Butch of the National Institute of Standards and Technology about the evidence of topological states found in UTe2. These could possibly function as topological qubits, a favorable “hardware” for quantum computers that should not require error correction. Read the article in Science.
Transcript
SOPHIA CHEN: Recently, you may have heard that Google’s quantum computer executed an algorithm a billion times faster than a conventional computer. But their machine is far from being broadly useful. No existing quantum computer is. One of the biggest challenges that the technology faces is that the computer hardware—its so-called qubits—interacts with the environment in unwanted ways. This results in computing errors, and no one knows how to correct these errors yet. That’s why researchers are investigating new materials for building qubits that might avoid these errors altogether. Nicholas Butch, a physicist at the National Institute of Standards and Technology, researches a class of materials that can be manipulated into something known as a topological state. A topological state occurs when the material’s electrons are collectively manipulated to behave in a specific correlated way.
NICHOLAS BUTCH: Topological states are in principle robust, or at least more strongly defendant, against that kind of coupling to the noise in the environment.
SC: Materials that harbor these quantum states could then be built into topological qubits, which shouldn’t need error correction. So you could build a comparably powerful computer with much fewer qubits compared to devices like Google’s quantum computer. The company Microsoft is pursuing a quantum computer made of topological qubits. However, it’s been difficult to create these quantum states. So far, researchers have only found indirect evidence of topological states in materials. Recently, Butch and his colleagues synthesized another promising candidate, UTe2, which looks like a silvery crystal.
NB: These are basically the size of typical, let’s say, table salt grains.
SC: While the researchers haven’t directly confirmed that UTe2 is a topological material, they’ve observed properties in it that are associated with topological states. The researchers ran a current through the crystal and found its resistivity went to zero as they cooled it to 1.6 Kelvin.
NB: Even though we know about thousands of superconductors, there’s a very short list of spin triplet superconductors that we know about.
SC: They still have to confirm this, but they suspect it’s this rare type because its properties differ from those of typical superconductors. The heat capacity of typical superconductors usually goes to zero as the material becomes superconducting, but this material’s heat capacity does not. In addition, most superconductors lose their superconductivity if you put them in a magnetic field of around 1 Tesla. In this material, it took 35 Tesla. These properties hint that the electrons in UTe2 pair up in different configurations than they do in a typical superconductor. Theory suggests that if a material shows this distinctive electron pairing, it should also harbor topological states. Butch and his team plan to study how the material responds under increasingly high pressure. They also want to definitively find the topological states. They’ve also found that once you suppress the material’s superconductivity in a 35 Tesla magnetic field, that if you turn the field even higher, the superconductivity comes back between 40 and 60 Tesla. They don’t know why.
NB: We’re in the midst of trying to determine exactly how weird it is.
Nov 21, 2019
Episode 22: NV center qubits engineered optically for quantum computers
Sophia Chen of MRS Bulletin interviews Jason Smith of the University of Oxford about using ultrashort pulse laser processing to engineer nitrogen-vacancy centers in diamond that can then perform as qubits in quantum computers. Read the article in Optica.
Transcript
SOPHIA CHEN: Quantum computers promise to be much faster than conventional computers at solving certain problems, such as in chemistry and machine learning. But it’s still unclear what material to build them from. One promising candidate is a type of synthetic diamond containing an impurity known as a nitrogen vacancy center, or NV center. These impurities consist of a nitrogen atom and a vacancy, next to each other, inside a lattice of carbon atoms. Jason Smith, a materials scientist at the University of Oxford, explains how the defects would work as quantum bits, or qubits.
JASON SMITH: When you put these two defects next to each other, the nitrogen and the vacancy, they form a stable complex called the NV center, and t…
Oct 29, 2019
Episode 21: Cold fusion revisited
Philip Ball of MRS Bulletin interviews Yet-Ming Chiang of the Massachusetts Institute of Technology about their Google-sponsored elaborate study on cold fusion. The investigations have provided new insights into highly hydrided metals and low-energy nuclear reactions, with much interesting science yet to be explored. Read the multi-authored Perspective in Nature.
Oct 15, 2019
Episode 20: Research highlights: Perovskites
Researchers at the University of North Carolina at Chapel Hill stabilize solar cells by converting the surfaces of lead halide perovskites to water-insoluble lead oxysalt, as reported in Science. Researchers at Weizmann Institute of Science open a new path to defect management in materials by providing insight into the low defect density of halide perovskites, as reported in Materials Horizon. Researchers at the University of Oxford add ionic liquids to perovskites which markedly improves the devices’ long-term stability, as reported in Nature. Researchers at Kyushu University make exceptionally thick organic light-emitting diodes by combining thin organic light-emitting films with hybrid perovskite charge-transport layers, as reported in Nature.
Sep 19, 2019
Episode 19: Polymer grown on liquid metal nanodroplets
Prachi Patel of MRS Bulletin interviews Carmel Majidi of Carnegie Mellon University about utilizing atom transfer radical polymerization to create liquid metal–polymer hybrid materials with high stability, excellent dispersibility, and tunable mechanical and optical properties. Read the article in Nature Nanotechnology.
Transcript
PATEL: Rubbers and plastics have snuck into hundreds of products we use every day. They have excellent mechanical properties for these applications. But they are terrible at transporting heat and electricity. That’s a problem if you are an engineer who’s trying to make soft robots or artificial skin, like Carmel Majidi of Carnegie Mellon University. He is trying to create new kinds of composites by tailoring the electrical and thermal properties of polymers. He and his colleagues recently found a way to do this by filling polymers with nanoscale droplets made of liquid metals.
MAJIDI: And the liquid metal itself is an alloy of gallium and indium. T…
Sep 11, 2019
Episode 18: Organic high-spin material conducive for quantum computing
Sophia Chen of MRS Bulletin interviews Jason Azoulay of the University of Southern Mississippi about his conjugated polymer semiconductor, a promising candidate for technologies that integrate both conventional electronics and spintronics. Read the article in Science Advances.
Transcript
SOPHIA CHEN: Conventional electronics like your smartphone or computer use the voltage and current of electrons in a material to encode and transmit information. Spintronics aims to exploit the quantum spin of those electrons as an additional signal. Jason Azoulay of the University of Southern Mississippi, develops materials that might be useful for spintronics combined with conventional electronics.
JASON AZOULAY: People are looking at controlling electron correlations and spin and magnetism for emerging types of technologies. There’s a wide variety of technologies, whether it’s something as far off as quantum computing or new types of magnetic materials, or even multifunctional activities wher…
Aug 26, 2019
Episode 17: Lead-halide perovskites make effective catalysts for organic synthesis
Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field.
Read the abstract in the Journal of the American Chemical Society (doi:10.1021/jacs.8b08720).
Transcript
Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler.
While lead-halide perovskites have revolutionized photovoltaics, they have also shown promise for lasers, light-emitting diodes, and transistors. Now, researchers show that perovskite nanocrystals are also highly effective catalysts…
Aug 16, 2019
Episode 16: Thermoelectrics enables clothes with adjustable temperature
Sophia Chen of MRS Bulletin interviews Renkun Chen of the University of California, San Diego about his flexible thermoelectric devices that can provide personalized cooling and heating effects in clothing. Read the article in Science Advances.
Transcript
Transcript
SOPHIA CHEN: If you’ve ever had to pay an air conditioning bill during the summer, you know how expensive it gets. Renkun Chen is a mechanical engineer at UCSD with an energy-saving idea: clothes with adjustable temperature. He and his team have designed and fabricated a material you can wear that directly cools the skin.
RENKUN CHEN: Instead of having a centralized air conditioning system in a building, where you need to cool down a large volume of space for building occupants, we use our system to cool down a much smaller volume at a personal level. By doing so, we can save energy by at least an order of magnitude.
SC: The power consumption per person of a conventional AC system is a few kilowatts, he says. Where…
Aug 7, 2019
Episode 15: 3D stretchable electronics achieves ultrahigh conductivity
Prachi Patel of MRS Bulletin interviews Benjamin C.-K. Tee of the National University of Singapore about an interfacial design for stretchable electronics that uses three-dimensional helical copper micro-interconnects embedded in an elastic rubber substrate. Read the article in APL Materials.
Transcript
PRACHI PATEL: Metals are excellent at conducting electricity but not the best at being stretched or bent. For electronics that can be worn or wrapped around curved surfaces, stretchable conductors are key.
BENJAMIN TEE: One good example is a smart patch that you can wear to record your heartbeat, or your ECG and so on.
PATEL: That’s Benjamin Tee at the National University of Singapore. He and his colleagues have come up with a new way to make stretchable conductors that stay strong and remain highly conductive when stretched to almost twice their length. Their strategy overcomes two main challenges of previous stretchable conductors.
TEE: So one approach to make stretchable…
Jul 22, 2019
Episode 14: Thin film patterns classified by machine learning
Sophia Chen of MRS Bulletin interviews Alex Hexemer of Lawrence Berkeley National Laboratory in California, and Daniela Ushizima and Shuai Liu of the University of California, Berkeley about their design of multiple Convolutional Neural Networks (CNN) to classify nanoparticle orientation in a thin film by learning scattering patterns. Read the article in MRS Communications.
Transcript
SOPHIA CHEN: Materials researchers come from around the world to study their samples in the beamline at the Advanced Light Source facility, located at Lawrence Berkeley National Laboratory in California. Alex Hexemer, a senior scientist at the facility, tells me that they’re currently upgrading the machine, so that it can take much more data, much more quickly.
HEXEMER: The amount of data you’re going to create is so large that A, you can’t take it home on a hard drive anymore, nor can you start looking at the data anymore. It’s just too big. Some of the detectors here are going to run at tho…
Jul 2, 2019
Episode 13: Tendril-like robot inspired by plants
Sophia Chen of MRS Bulletin interviews Barbara Mazzolai and Edoardo Sinibaldi of the Italian Institute of Technology about their robot made from two types of polymers, enabling it to extend and retract like the tendrils of a plant. Read the article in Nature Communications.
Transcript
SOPHIA CHEN: Barbara Mazzolai is designing robots inspired by plants. Recently, she and her research team at the Italian Institute of Technology have made a robot that looks like a plant tendril, similar to the ones that ivy plants might use to climb a trellis. She says they want to develop a robot that can explore an unknown area just like a plant does.
BARBARA MAZZOLAI: Plants could be the model to develop the robot for a very harsh environment, for colonizing a very difficult environment, to explore a harsh situation. Tendril is one of the ways, one of the strategies that they use to anchor the body.
CHEN: The robot doesn’t just look like a plant tendril. It also moves according to the same m…
Jun 25, 2019
Episode 12: Europium thwarts reactivity in metal-halide perovskite solar cells
Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field. Read the abstract in Science (doi:10.1126/science.aau5701).
Transcript
Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler.
Metal-halide perovskite solar cells degrade when exposed to oxygen and moisture. Encapsulating the devices makes them more stable and long-lasting, but it does not solve one issue that crops up during regular device operation. Light, electric field, and thermal stres…
Jun 12, 2019
Episode 11: Nanoparticle megalibraries enable materials discovery
Prachi Patel of MRS Bulletin interviews Chad Mirkin of Northwestern University about the use of his polymer pen lithography technique combined with an ink spray-coating method to ultimately create a megalibrary of nanoparticles that speeds up the discovery of new materials. Read the abstract in Proceedings of the National Academy of Sciences (PNAS).
Transcript
PATEL: Mirkin and his colleagues are trying to dramatically speed up materials discovery. They have created a tool: a “megalibrary.” It’s an array of millions of little nanoparticles that fits on a microscope slide. Each nanoparticle has a different structure and composition.
CM: We’ve made libraries with as many as 5 billion particles and a million different variants, compositional and size variants.
PP: They make the libraries using a technique called polymer pen lithography. They use hundreds of thousands of tiny, sharp tips to deposit dots of polymer on the slide. Each dot is a little reactor, loaded with different…
May 7, 2019
Episode 10: Protein-based polymer achieves green electronics
Omar Fabián of MRS Bulletin interviews Alireza Dolatshahi-Pirouz of the Technical University of Denmark about the use of silk to fabricate eco-friendly electronics. Read the article in Advanced Science.
Transcript
FABIÁN: We have an electronic waste problem. While the development of recyclable plastics has helped curb that problem, currently only about 15% of e-waste is actually recycled. So how can we make a bigger dent? Materials researchers from Denmark are looking to the silkworm for answers.
ALIREZA DOLATSHAHI-PIROUZ: Who can do it better than Mother Nature, right?
FABIÁN: That’s Prof. Alireza Dolatshahi-Pirouz. His research team at the Technical University of Denmark is developing a new class of thin-film electronics they’ve dubbed “fleco-ionics.” That’s short for flexible, eco-friendly electronics. And they’re doing it using cocoons woven by silkworms.
DOLATSHAHI-PIROUZ: Silk is one of the strongest materials out there. It has strength that is many times…
May 3, 2019
Episode 9: E-skin detects direction of applied pressure
Sophia Chen of MRS Bulletin interviews Zhenan Bao of Stanford University about her research team’s development of a biomimetic soft electronic skin (e-skin) composed of an array of capacitors capable of effectively measuring and discriminating shear force in real time. Read the abstract in Science Robotics.
CHEN: Zhenan Bao is a professor at Stanford University whose research team developed this robot. She says the key design of the robot is a network of force sensors on its fingertip that tell the robot when to retract.
BAO: Without sensor feedback, the robot would not know how much it can press on an object before it should stop.
CHEN: They’ve also shown that the robot can respond to feedback to place a ping-pong ball into an arrangement of different round holes. She says that this type of tactile robot could be useful in all sorts of situations.
BAO: Any robot that will need to have the ability to manipulate objects and being in contact with objects will need this type…
Apr 19, 2019
Episode 8: Ge added to lead-free perovskite improves efficiency
Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field.
Read the article in Nature Communications (doi:10.1038/s41467-018-07951-y).
Transcript
Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler.
The presence of lead in state-of-the-art perovskite solar cells could hold back their commercialization. Lead-free alternatives based on tin compounds have shown promise, but they typically suffer from low efficiency and stability.
Brown University…
Apr 12, 2019
Episode 7: Synthetic biology exploited to neutralize mustard gas
Sophia Chen of MRS Bulletin interviews Jared DeCoste, a researcher with the US army, about the research team's work to counter the effect of mustard gas. First, the researchers alter E. coli’s DNA to produce an abundance of the molecule protoporphyrin IX. They then mix the protoporphyrin IX with another type of molecule called a metal-organic framework, which then behaves like an absorbent microscopic sponge that detoxifies sulfur mustard, or mustard gas. Read the abstract in MRS Communications (doi: 10.1557/mrc.2019.22).
Transcript
SOPHIA CHEN: Today we’re talking about new research out of the military on sulfur mustard, or as it’s more commonly known: mustard gas. Researchers are wondering, could you make some sort of clothing protection for a soldier that basically neutralizes the chemical upon contact? Jared DeCoste is a researcher with the US Army developing these smart uniforms.
JARED DECOSTE: We’re doing a lot of research in this area, and we’re excited about the…
Mar 25, 2019
Episode 6: Chlorine boosts efficiency of tandem solar cell
Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field.
Read the abstract in Nature Energy (doi:10.1038/s41560-018-0278-x).
Transcript
Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler.
Researchers have made an all-perovskite tandem solar cell with a record high power-conversion efficiency of 21%.
Tandem solar cells are more efficient than a single cell because each device in the stack can be tailored to absorb a different part of the light…
Mar 11, 2019
Episode 5: Artificial neuron made from VO2
An artificial neuron made from vanadium dioxide precisely mimics the behavior of normal and faulty neurons in the brain. This could have important implications for neuroscience. Read the abstract in Frontiers in Neuroscience.
Transcript
PATEL: Our brains conduct information through electrical signals. Little voltage spikes that neurons pass around. And the frequency of those little spikes encodes information. But disorders like depression or ADHD can weaken these signals or alter their frequency. Here’s Shriram Ramanathan at Purdue University, with a materials engineer’s take.
SHRIRAM RAMANATHAN: Basically you can think of the neuron as a material that integrates charge. So imagine the neuron is collecting charge as it receives charge. And then at some critical charge level it fires a signal. So this can be referred to as a leaky integrate fire function. So the neuron is integrating charge but it’s not a perfect insulator so it leaks a little bit of charge as it’s collecting.…
Feb 21, 2019
Episode 4: Can metal-halide perovskite solar cells be used for concentrated PV devices?
Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field.
Read the abstract in Nature Energy (doi:10.1038/s41560-018-0220-2).
Transcript
Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler.
Concentrated photovoltaic devices – also called CPV, which use lenses and mirrors to focus sunlight onto small, highly efficient solar cells, can have power-conversion efficiencies as high as 46%. Very expensive multi-junction solar cells made with groups I…
Feb 13, 2019
Episode 3: 3D-printed implant designed to repair spinal injuries
A silicon chip with 4 million microscopic mirrors is used to shine UV light in a 3D pattern based on a digital MRI image of the spinal cord wound in rats. The light falls onto a mixture of poly(ethylene) glycol and gelatin methacrylate, which solidifies into the shape of the wound.
Transcript
PRACHI PATEL: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Prachi Patel.
Over 250,000 people around the world suffer a spinal cord injury every year.
SHAOCHEN CHEN: Spinal cord damage turns out to be a very devastating disease. You know people cannot walk, they feel nothing below the hip and other parts of the body.
PATEL: Shaochen Chen, a nanoengineer at the University of California in San Diego, worked with neuroscientists to 3D-print implants that can…
Jan 25, 2019
Episode 2: Optoelectronic properties of perovskites tunable due to reversible surface relaxation
Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field.
Read the abstract in Nature Materials (doi:10.1038/s41563-018-0164-8).
Transcript
Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler.
The layered nature of Ruddlesden–Popper perovskites means that the materials can be shaved down to a single layer or just a few layers. The properties of any material at the molecular level are different from those at larger scales. Kian Ping Loh, at th…
Jan 15, 2019
Episode 1: How reduced-dimensional metal halide perovskites are formed
Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field. Read the abstract in Nature Materials (doi:10.1038/s41563-018-0154-x).
Transcript
Welcome to the first episode of the MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler.
A new study offers key insights into the formation of layered two-dimensional perovskite films known as Ruddlesden–Popper phases, a class of materials that hold promise for stable light-harvesting and light-emitting devices.
Desp…