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Markus Buehler of the Massachusetts Institute of Technology and editor of the Impact section of MRS Bulletin interviews Julia Greer, director of the Kavli Nanoscience Institute at the California Institute of Technology about her research on the formation and nanomechanical behavior of electrodeposited lithium for Li-ion batteries. Greer’s group developed an in situ experimental methodology that allows them to electrochemically charge small-scale battery cells and to observe, in real-time, the formation of Li dendrites and to probe their mechanical response. Their work is published in MRS Bulletin (doi:10.1557/mrs.2020.148)

Gopal Rao, chief editor for technical content, interviews Markus Buehler of the Massachusetts Institute of Technology and editor of the Impact section of MRS Bulletin about his research on designing new proteins. Buehler’s group trains a deep learning model whose architecture is composed of several long short-term memory units from data consisting of musical representations of proteins classified by certain features. Their work is published in APL Bioengineering (doi:10.1063/1.5133026). Markus Buehler is also the editor of the new Impact section of MRS Bulletin, that publishes new research: www.mrs.org/impact.

Materials science and engineering has an important role to play in overcoming the current COVID-19 pandemic. Listen to Science Writer Philip Ball talk with three materials researchers, Catherine Fromen (University of Delaware), Thomas Webster (Northeastern University), and George Stylios (Heriott-Watt University, Edinburgh) about their work in different aspects of materials science to mitigate the pandemic. They cover various aspects, including drug delivery for immune engineering for COVID-19, the use of nanoparticles to directly target the virus, vaccines and materials connections, and how materials play a critical role in face mask technologies. For more on this subject, see MRS Bulletin, "The quest for materials solutions to the coronavirus pandemic," by Philip Ball.

Vinayak Dravid, the Abraham Harris Professor of Materials Science and Engineering at Northwestern University and with Vikas Nandwana, who is co-founder and CTO of MFNS Tech, introduce the oleophilic, hydrophobic, and magnetic (OHM) sponge. The OHM smart sponge was awarded 3rd place in the iMatSci Innovation Showcase competition at the 2019 MRS Fall meeting. For more information, see Industrial & Engineering Chemistry Research (doi:10.1021/acs.iecr.0c01493).   

Rigoberto C. Advincula of the University of Tennessee-Knoxville and Oak Ridge National Laboratory, and Editor in Chief of MRS Communications, discusses the role of materials and additive manufacturing on the personal protective equipment (PPE) supply chain during the new coronavirus pandemic. For more information, see “Additive Manufacturing for COVID-19: Devices, Materials, Prospects and Challenges,” MRS Communications. 

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. TranscriptSOPHIA 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.

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.TranscriptCHEN: 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. 

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. TranscriptSOPHIA 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.  

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 .TranscriptSOPHIA 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.   

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. TranscriptSOPHIA 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.   

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. TranscriptSOPHIA 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.   

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. 

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.TranscriptOMAR 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.

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.TranscriptSOPHIA 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. 

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. TranscriptSOPHIA 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.

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.TranscriptSOPHIA 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 these behave like trapped atomic systems within the diamond lattice, they have well-defined electron orbitals and energy states.SC: Using lasers, you can manipulate the NV center into one of two energy states that represent 1, 0, or a superposition of both. Once programmed into quantum states, the NV centers can be manipulated to run computations. However, it’s still difficult to quickly and consistently synthesize NV centers inside diamond. JS: The challenge of creating NV centers is really of creating where you want them within a piece of diamond, and in the conditions that make them perform well as qubits for a quantum computer or quantum device.SC: So Smith and his team have come up with a new technique for implanting these impurities where they want them in a diamond. The technique works like this. They start with a synthetic diamond that already contains nitrogen impurities. They beam an extremely short laser pulse, less than a trillionth of a second long, at the diamond, which knocks out a carbon atom in the diamond lattice, creating a vacancy. Then, they use a less energetic laser to heat up the diamond in a localized spot. JS: We’re annealing the diamond very locally just within the focal spot of the laser. We’re essentially turning up the temperature of the diamond, turning up the heat, encouraging those vacancies to diffuse around the diamond.SC: The vacancies migrate around the diamond randomly. But the researchers sense when they have moved next to a nitrogen atom to create an NV center. They detect this by illuminating the diamond with another laser that causes the NV center to fluoresce. When they detect this fluorescence, they know the NV center has formed.JS: The fluorescence that comes out has a particular spectral signature to it.SC: This technique is much more consistent compared to their previous methods, he says. In the past, they annealed the diamond in an oven to create the NV centers. At most, this only created a defect in the intended lattice site 37% of the time. Using this new technique, they can create an NV center in the intended site just about 100% of the time. Next, they want to try this technique on a synthetic diamond with a lower concentration of nitrogen. The diamond’s nitrogen concentration in their experiment was too high and would create too much noise for actual quantum computing applications. In a diamond with less nitrogen, they want to see if they can make the NV centers at the same rate. The goal, eventually, is to use these techniques to create the much larger processors that are needed for useful quantum computations. Smith says that theoretically, NV centers in diamond should be easier to scale than other types of qubits.JS: A million NV-centered qubits/cm2, the basis for a processor.

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.

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.

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.TranscriptPATEL: 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. These are two metals that are solid at room temperature but when you mix them together they form this eutectic this liquid that has certain nice properties. It’s important that they’re liquid because that allows the droplets to deform with the surrounding rubber as the rubber stretches.  PATEL: Up until now, researchers have tried to make such composites by using mixers that are a bit like kitchen blenders. You essentially throw in the liquid metal alloy along with the molten rubber or plastic. The metal breaks into tiny droplets that disperse through the polymer. But Majidi worked with chemistry professor Krzysztof Matyjaszewski to develop a new technique. They first break up the liquid metal into nanodroplets using high-frequency sound waves. But then, instead of adding the liquid metal to the polymer, they grow the polymer on the tiny metal droplets, like a coating. MAJIDI: You basically start with your nanoscale droplets of liquid metal and then pretty much atom by atom or monomer by monomer you grow these polymer chains from the surface of these droplets—almost like the rays of the sun kind of emanating out. We’re working with these you know gallium indium liquid metal alloys. It wasn’t really obvious whether his polymerization technique would apply to this you know very different and somewhat unique class of materials. So he gave it a shot and it turned out it worked you know pretty much the same way it’s worked for a lot of the other types of metal nanoparticles that he’s worked with. We were delighted that it did. PATEL: The technique, called atom transfer radical polymerization, or ATRP—gives very fine control on the length of the polymer chains so the droplets get evenly suspended in the composite. Plus, it enables the researchers to suspend these droplets in a much wider range of polymers and materials systems than was previously possible. Until now, the researchers could use commercially available materials like silicone rubbers and polyurethanes. MAJIDI: The ability to suspend these liquid metal nanodroplets in virtually any kind of polymer or kind of matrix material opens the door for kind of a wide range of functionalities. A lot of the materials we have been exploring and will continue to explore, they could be used in say wearable or even implantable applications. So we could work with polymers that are biocompatible. We’ve been looking at different types of polyacrylates. Those are materials that are generally kind of popular in engineering. Everything from adhesives to 3D printing. And again using ATRP we’ve been able to show you can suspend liquid metal droplets in those materials. I mean if you just think about just generally where are plastics used and where are rubbers used, there’s a huge spectrum out there. 

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.TranscriptSOPHIA 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 where you effectively combine things like spin degrees of freedom with charge transport or some type of optoelectronic functionality. SC: For spintronics, materials have to exhibit strong magnetism known as a high-spin state. On the microscopic scale, this means that the electrons involved in chemical bonds in the material need to have their spins aligned in the same direction. It has been difficult to make organic high-spin materials that are stable at room temperature. Azoulay and his colleagues have made such a material.  JA: We’ve tested it for a while, and it’s a rock. It’s very stable. SC: The material is a type of macromolecule known as a conjugated polymer, meaning that its constituent molecules are stitched together by a backbone of shared electrons. In the material’s ground state, these electrons align in pairs, thereby collectively creating the desired “high spin state.” JA: The best way to think about it is that we made a polymer organic magnet. SC: The material, which looks like a black powder, behaves like a semiconductor. The flow of these electrons through the material can be turned on and off according to its bandgap energy. In addition, the polymer’s bandgap energy is easy to tune. It consists of alternating molecules of cyclopentadithiophene and thiadiazoloquinoxaline, which are an electron donor and acceptor, respectively. Because of this tunable bandgap and its high spin state, the material is a promising candidate for technologies that integrate both conventional electronics and spintronics. The researchers found that a minimum of 13 donor-acceptor pairs were required in order to create the electron interactions that produce the high-spin state. JA: We’re working on next generation versions of this material. The questions are, can we increase the conductivity? Can we increase the magnetic properties? Can we control the electronic topology? Can we control the properties of the spins. Another fun aspect of it as well, how are these going to interact with electromagnetic fields or stimuli or light. We’re studying their properties because they’re fundamentally new materials.