MRS Bulletin Materials News Podcast: Recent Episodes
MRS Bulletin
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.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Bharat Gwalani from North Carolina State University and Mert Efe from Pacific Northwest National Laboratory about their single-step, energy-efficient method for making a samarium cobalt magnet. Using a process they call “friction stir consolidation,” the researchers apply heat and pressure simultaneously to fuse the two powders together. Their method results in low porosity to make a magnetically stronger, higher quality material than that made by using the conventional method. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Yaroslava Yingling and Joseph Tracy from North Carolina State University about their study on iron oxide colloidal nanoparticles (NPs) coated in oleylamine ligands. By combining experimental work with molecular simulations, their research group determined how to optimize ethanol solvent-mediated ligand stripping in order to control the functionality of the NPs. This work was published in a recent issue of Advanced Materials Interfaces.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Thomas White from the University of Nevada, Reno, about his research group’s work on superheating gold. By hitting the gold foil with 45 femtosecond blue laser pulses, the team heated the foil uniformly up to 14 times hotter than its melting point while maintaining the material’s crystal structure. To confirm the temperature, the group introduced a thermometry technique that derives the temperature based on the velocity of the atoms in the sample. By studying these forms of matter up close in the laboratory, White seeks to better understand what goes on inside planets, stars, and even extreme human-engineered environments, such as nuclear fusion reactors. Furthermore, these experimental results could open new theoretical investigations into superheating. This work was published in a recent issue of Nature.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Sathvik Iyengar, a PhD candidate at Rice University, about the development of a hybrid material called “glaphene.” A hybrid of graphene and two-dimensional (2D) silica glass, glaphene is a semiconductor with a bandgap of ~4 eV. More importantly, Iyengar and colleagues introduce a new method of bandgap engineering using hybrid materials instead of doping, which opens new possibilities for producing electronic components. This work was published in a recent issue of Advanced Materials.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Victor Lopez-Richard from Federal University of São Carlos in Brazil about his memory device called a mem-emitter. Unlike a memresistor (short for “memory resistor”), which made of materials whose electrical resistance can be tuned, the mem-emitter is used to tune optical properties. Experimentally, Lopez-Richard’s research group made the device out of molybdenum diselenide, which is a transition metal dichalcogenide, that was then layered onto a dielectric known as a clinochlore. The researchers found that they were able to tune the intensity of the light emitted according to theoretical predictions. This work was published in a recent issue of Nano Letters.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Ashley Bucsek from the University of Michigan, Ann Arbor about her laboratory-scale three-dimensional (3D) x-ray diffraction (XRD) microscope to replace studies done in synchrotron facilities. A key element of the design is the material used to make the x-rays. Instead of using a solid metal as a target, Bucsek’s research group used a liquid metal source to generate the x-rays, thereby circumventing melting. Among the advantages of miniaturizing the microscope are its immediate availability and the possibility of conducting long-term studies. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Daniel Garcia-Gonzalez from Universidad Carlos III de Madrid in Spain about his research group’s reprogrammable metamaterial. The researchers use a soft polymer, mixed with magnetic particles. By rotating the orientation of the magnets, they tune the softness or compressibility of the material. This work was published in a recent issue of Advanced Materials.
To enable future lunar settlements, researchers are pursuing ways to construct needed devices on the moon to save the expense of shipping them from Earth. In this podcast episode, MRS Bulletin’s Laura Leay interviews Felix Lang from the University of Potsdam, Germany about his group’s development of perovskite solar cells that utilize the moon’s regolith for the substrate. The researchers achieved power conversion efficiency of ~10%, with some device architectures leading to improved efficiencies of ~12%. Calculations show that using resources from the moon resulted in a power-to-weight ratio that outclassed other technologies, even with the low efficiency. Future work will look to improve this efficiency by considering tandem solar cells. This study was published in a recent issue of Device.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Hang Zhang from Aalto University in Finland about his group’s creation of a composite material that is both stiff and self-healing. The composite involves a hydrogel where the long polymer chains are confined between nanosheets of synthetic hectorite. This material mimics skin that is both stiff and self-healing. Applications may be forthcoming in self-healing soft robots or artificial tissues that can self-heal like synthetic skin. This work was published in a recent issue of Nature Materials.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Sheng Xu from Tohoku University, Japan about his lightweight shape memory alloy that retains superelasticity at temperatures as cold as 4 K and as hot as 400°C. This range is about 5 times wider than commercial shape memory alloys. Shape memory alloys are needed for extreme environments such as part of machines in space or deep sea. Xu also sees uses for biomedical applications or for storage containers for liquid fuels like liquid hydrogen, which must be kept at very cold temperatures. This work was published in a recent issue of Nature.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Lane Martin from Rice University about characterization of relaxor ferroelectrics, materials with noteworthy energy-conversion properties used in sensors and actuators. Martin’s research team investigated the material’s behavior at the nanoscale. The researchers found that the specific thin film they studied—the alloy lead magnesium niobate lead titanate—exhibited excellent properties down to 25–30 nm thick before they would start to shift. This work was published in a recent issue of Nature Nanotechnology.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Beth Dickey from Carnegie Mellon University about her new approach to inducing ferroelectricity into a material. Dickey’s research group worked with a class of materials known as wurtzites. The researchers specifically studied aluminum nitride and zinc oxide, which are not ferroelectric in their pristine form at room temperature. However, alloys of these materials are ferroelectric. When the researchers stacked the ferroelectric alloy with a non-ferroelectric wurtzite and applied electric fields to the material, they found that the crystal lattice of the ferroelectric layer began to invert, then switching propagated into the pristine wurtzite, confirming that the entire material was ferroelectric. The results of this study could lead to development of ferroelectric materials for computers where memory and computation can be brought together into a single device, saving energy. This work was published in a recent issue of Nature.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Harry Atwater from the California Institute of Technology about his study on lightsail propulsion in order to understand how the device can be developed to do fly-by space travel riding a beam of laser light. Atwater’s research group made a square prototype device where the researchers incorporated springs at each corner, etched out of a single sheet of silicon nitride, fastening it to the support frame. They tested its behavior in a two-beam interferometry experiment. Their comprehensive analysis provides a thorough understanding of key parameters that are essential for lightsail propulsion and paves the way for the next step of research: untethered flight. This work was published in a recent issue of Nature Photonics.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Ashwin Shahani and Alan Taub from the University of Michigan about their group’s simulations and experimental work detailing the formation mechanisms, morphologies, and microstructures of an in situ Al/TiC metal matrix nanocomposites processed via salt flux reaction. Using these insights, the microstructure of a material can be tuned in order to optimize the materials properties. While the three-dimensional imaging is critical to gaining insight into the structure, computational models can facilitate this optimization. This work was published in a recent issue of Acta Materialia.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Xingchen Ye of Indiana University about his research group’s studies on the fundamental behavior of colloidal materials. Colloidal materials consist of liquids with nanoparticles suspended in them. Ye’s team is interested in how a colloidal material’s properties change as the team spatially rearranges the nanoparticles in the liquid. They looked specifically at the self-assembly of gold nanocubes into a lattice structure. Ye’s team studied how that structure gives rise to the material’s bulk properties. This work was published in a recent issue of Nature Chemical Engineering.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Fabian Meder from the Italian Institute of Technology in Genova and the Sant’Anna School of Advanced Studies in Piza, Italy about his research group’s device that makes use of wind-driven plant leaf motion to generate electricity which can power a chemical delivery system. Their triboelectric nanogenerator involves an artificial leaf made of a 500 μm silicone elastomer layer and an electrode made from indium tin oxide. This is attached to the leaf of a plant. A gold-coated pin electrode inserted in the stem of the plant harvests charges from the plant tissue. This work was published in a recent issue of Bioinspiration & Biomimetic.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Bowen Deng, a graduate student in Gerbrand Ceder’s group at the University of California, Berkeley, about their work on increasing the accuracy of artificial intelligence/machine learning materials prediction models. The use of computer simulations to predict the interaction between atoms in a given molecule is being replaced by machine learning. Researchers describe the atoms’ collective interactions as a quantity of energy, where higher energies correspond to stronger forces holding the molecule together. Now, Deng’s research group studied three machine learning models and found that they tend to predict lower energies than what is accurate by about 20 percent. The researchers have determined that these underpredictions were caused by biased training data and they found a way to remedy the situation. This work was published in a recent issue of NPJ Computational Materials.
In this podcast episode, MRS Bulletin’s Laura Leay interviews David Cahen from the Weizmann Institute of Science, Israel, about the impact surface defects have on bulk properties, specifically in the case of lead halide perovskites. In a perspective he co-authored, Cahen connected numerous experimental data from other researchers that exposed this phenomenon. By understanding how surface defects control the material’s electronic behavior, researchers can pursue new materials for the development of long-lasting devices. This work was published in a recent issue of Advanced Materials.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Gwangmin Bae of Korea University about his work with colleagues on the design of a new smart window system that utilizes compression. Like other smart windows, this window makes use of pores within the material to adjust its transparency. However, instead of using a stretchy material that controls light scattering through the pores, Bae and colleagues used a material that compresses in thickness. That is, the window becomes more transparent when it is compressed. The researchers place this structured porous material made of the polymer polydimethylsiloxane or PDMS between two panes of glass to create the smart window. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Leif Asp of Chalmers University of Technology about his group’s development of an all-carbon fiber-based structural battery. The negative electrode uses carbon fiber and, for the positive electrode, the carbon fiber is coated with lithium iron phosphate. In both cases the carbon fiber takes on the roles of mechanical reinforcement and current collection. This work was published in a recent issue of Advanced Materials.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Nancy Sottos, the Maybelle Leland Swanlund Endowed Chair and head of the Department of Materials Science and Engineering at the University of Illinois–Urbana Champaign (UIUC), and Justine Paul, a former student at UIUC who now holds a position at DuPont, about their work with frontal polymerization. By mimicking patterns in biological materials such as shells, their research group took a multidisciplinary approach to control crystalline patterning, which ultimately enabled them to control mechanical properties of polymers. By applying heat, they made slight changes in the chemical reactions to achieve specific crystalline patterns. This work was published in a recent issue of Nature.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Reza Moini of Princeton University about his group’s development of an enhanced additive manufacturing technique to fabricate cementitious materials with excellent fracture toughness. They based their design of the material on the double-helical or double-bouligand structure of coelacanth fish scales that resist deformation. In order to fabricate the material, Moini’s research team used a two-component robotic additive manufacturing process. The extrusion system was controlled using specialist algorithms. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews postdoctoral research fellow Rohit Pratyush Behera and Prof. Hortense Le Ferrand of Nanyang Technological University in Singapore about their design of a strong and tough ceramic that absorbs energy, inspired from biology. They borrowed microscopic designs found in a mollusk, a mantis shrimp, and the enamel casing surrounding human teeth. The researchers stacked round discs of aluminum oxide particles in horizontal layers in a helical structure, then encased the structure in an extra protective layer made of alumina nanoparticles. The aluminum oxide in the discs is designed to respond to an external magnetic field, modifying the orientation of the discs layer by layer, consequently adjusting the properties of the ceramic composites. This work was published in a recent issue of Cell Reports Physical Science.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Yen-Hung Lin of Hong Kong University of Science and Technology about his work to eliminate defects in perovskite solar cells. Lin’s group treated the perovskites with a category of molecules known as amino-silanes, which bind vacancies in the perovskites, preventing recombination of the electrons and holes. The amino-silane treatment retained the device’s performance at 95% power conversion efficiency for more than 1500 hours. This work was published in a recent issue of Science.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Michael Pettes, deputy group leader and staff scientist at the Center for Integrated Nanotechnologies in Los Alamos National laboratory about a characterization technique that employs a four-dimensional scanning transmission electron microscope (4D-STEM) paired with complex computational data analysis to directly measure the thermal expansion coefficient (TEC) of monolayer epitaxial tungsten diselenide. The standard technique for directly measuring the TEC involves X-ray diffraction, but 2D materials are too thin. 4D-STEM uses a patterned electron probe which enables diffraction positions to be accurately mapped in real space. This method overcomes the challenges of indirect measurements and spatial resolution. This work was published in a recent issue of ACS Nano.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Michael Dickey of North Carolina State University about the discovery and mechanical properties of glassy gels. Dicky credits his postdoc Meixiang Wang who, while studying ionic liquids, created the first glassy gel. Dicky’s group found that the mechanical properties of their glassy gel include shape memory, self-healing, and adhesion. While other materials may demonstrate comparable toughness and stretchiness, the glassy gel offers an advantage because of its simple curing process. This work was published in a recent issue of Nature.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Coskun Kocabas from The University of Manchester in the UK about his development of a metamaterial that can tailor thermal emission. Rather than using a periodic system, which most topological materials employ, his research team borrowed a concept from laser design and created an optical cavity using a dielectric medium sandwiched between two layers that act as mirrors: a metal substrate and a top layer of platinum. The top layer serves as a thermal emitter, and the thickness of the top layer defines the topological property that regulates thermal emissivity. This work was published in a recent issue of Science.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Rasmus Neilsen from the Technical University of Denmark about his fabrication of a monolithic selenium/silicon tandem solar cell. The selenium forms the top cell of the tandem device, with silicon used as the bottom cell. Selenium-based single-junction solar cells have traditionally used fluorine-doped tin oxide. In this work indium-tin oxide was used as a transparent conductive layer that is easier to deposit and its use is more widespread. Neilsen and his research team controlled the thickness of the carrier-selective contacts in the silicon solar cell that protects the silicon layer from the processes used to deposit subsequent layers on top, thus enabling them to deposit the top cell directly onto the substrate. This work was published in a recent issue of PRX Energy.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Mihir Pendharkar of Stanford University about characterizing electronic properties of twistronics materials. Twistronics refers to a type of electronic device consisting of two-dimensional materials layered at a relative twist angle, forming a new periodic structure known as moiré superlattices. Pendharkar and colleagues studied different configurations of graphene layered with hexagonal boron nitride. Determining the twist angle of any particular sample is extremely time-consuming. By developing a characterization technique called torsional force microscopy, Pendharkar and colleagues have reduced the time to a matter of hours. This work was published in a recent issue of Proceedings of the National Academy of Sciences.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Falon Kalutantirige from the University of Illinois Urbana-Champaign and Ying Li from the University of Wisconsin-Madison about their approach and discovery when characterizing nanovoids in polymer films. Using polyamide (PA) membranes as their subject of study, the researchers applied graph theory combined with electron tomography and molecular dynamics simulations to characterize the morphology of the nanovoids. The key to understanding permeance of the membranes lies in understanding the void space that was mapped using electron tomography. Using their mixed-method approach, the researchers were able to relate the nanoscale morphology to membrane function. Taking this beyond the study of PA membranes, the research team showed how nanovoids impact the synthesis‒morphology‒function relationships of complex nanomaterials. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Alexandre Dmitriev from the University of Gothenburg, Sweden about his group’s computational model of a three-dimensional metamaterial exhibiting a magnetoelectric effect—known as the Tellegen effect—when exposed to light. The building blocks of the metamaterial are comprised of disks of silicon, 150 nm in diameter, supporting a cylinder of cobalt. Silicon is chosen for its high refractive index and cobalt for its magnetic properties. These building blocks are randomly distributed in a host medium such as water or a polymer. The metamaterial has applications in areas such as improving the efficiency of solar cells, creating one-way glass, or improving lasers. It also has the potential to revolutionize how the universe is understood and could hold the key to studying dark matter. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Antonio Dominguez-Alfaro from the University of Cambridge, UK about the development of a single-step manufacturing approach for a multimaterial 3D-printing method. The research team created two inks. One ink is a polymeric deep eutectic solvent – polyDES – made by combining and heating two salts to form a deep eutectic monomer and adding a photo-initiator to allow the ink to be cured. This ink is an ionic conductor so can capture signals from neurons inside a biological system. The other ink was based on the polymer Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which is commonly used in bioelectronics as a mixed electronic and ionic conductor. The work resolves many challenges of applying additive manufacturing in the field of bioelectronics. This work was published in a recent issue of Advanced Science.
In this podcast episode, MRS Bulletin’s Elizabeth Wilson interviews postdoctoral researcher M. Iqbal Bakti Utama of Northwestern University about a method allowing single photon production without defect. Aryl diazonium chemistry has been used in the past to functionalize the surface of carbon nanotubes. Utama’s group found that this chemistry also works for tungsten diselenide surfaces. The group immersed tungsten diselenide monolayers into an aqueous solution of 4-nitrobenzene-diazonium tetrafluoroborate. The electrophilic molecules withdraws electrons from the monolayer, creating aryl diazonium radicals. These radicals react with each other to form nitrophenyl oligomer chains. Instead of binding covalently to the monolayer surface, the oligomers form an adlayer that is physisorbed on the tungsten diselenide surface. The spectra of photons generated when the research team irradiated the coated surface was vastly simpler than the uncoated monolayer. This work was published in Nature Communications.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Irmgard Bischofberger of the Massachusetts Institute of Technology about her investigation of how chirality emerges in nature. She uses liquid crystal molecules of disodium chromoglycate in her studies. When the molecules are dissolved in water, they form linear rods. The research group then forces the rods through a microfluidic cell, causing the rods to assemble into spiral structures without mirror symmetry. The achiral structure transformed into a chiral one. What is unique, says Bischofberger, is that the new material is composed of non-chiral building blocks. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Eric Pop, Xiangjin Wu, and Asir Intisar Khan from Stanford University about their work building a phase-change memory superlattice at the nanoscale. They created the superlattice by alternating layers of antimony-tellurium nanoclusters with a nanocomposite made from germanium, antimony, and tellurium (GST467). Each layer is ~2 nm thick and the superlattice consists of 15 periods of these alternating layers. The microstructural properties of GST467 and its high crystallization temperature facilitate both faster switching speed and improved stability. The device operates at low voltage and shows promise for high-density multi-level data storage. This work was published in a recent issue of Nature Communications.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Magalí Lingenfelder from the École Polytechnique Fédérale de Lausanne, Switzerland about her group’s discovery of the switching mechanism behind H-bond-linked two-dimensional networks. The hydrogen bonding ability was tuned by comparing carboxylates to aldehydes. Lingenfelder’s group found that the ability of the structure to switch between an open structure to a close-packed one is governed by a synergistic combination of energetic contributions from both the adsorbate/adsorbate and absorbate/substrate interactions. This work was published in a recent issue of ACS Nano.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Aram Amassian from North Carolina State University about his group’s achievements using RoboMapper, a materials acceleration platform. In researchers’ quest to run environmentally-conscious laboratories, Amassian offers a solution that focuses on characterization of materials. Having found that characterization generates a lot of energy, his group developed an automated approach to screening small samples in order to identify ones that warranted more in-depth study. By using their automated approach, the researchers found quantitative structure–property relationships for wide-bandgap perovskites. This work was published in a recent issue of Matter.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Kaveh Ahadi from The Ohio State University about a material his group developed that maintains superconductivity in a magnetic field. The researchers grew a film of lanthanum manganite on a crystal of potassium tantalate. When lowered to the temperature of 2 Kelvin, the material is a superconductor. When Ahadi’s group applied 25 Teslas of magnetic field, the material stayed superconducting. Even though the material is not of practical use, Ahadi says that studying this material will help researchers better understand the mechanisms that lead to superconductivity. This work was published in Nano Letters.
In this podcast episode, MRS Bulletin’s Elizabeth Wilson interviews Manos Mavrikakis from the University of Wisconsin–Madison about his group’s theoretical work on real-world industrial catalytic conditions. It is often assumed that most catalyst surface atoms stay in place during a reaction, firmly bonded to their metal neighbors. However, Mavrikakis’s theoretical framework shows that under industrial reaction conditions, a surprising amount of metal–metal bond breaking is likely happening during catalytic reactions. This framework predicts that under reaction conditions, some adsorbed molecules have the strength to scavenge metal atoms from the catalyst particle, causing metal atoms to be ejected to a different spot on the metal surface. Bonds between metal atoms in certain geometries such as kinks can also break, even without adsorbed species, due to heat. However, the presence of reaction molecules may greatly increase the frequency of these events. The ejected metal atoms can then move around on the surface, collect together into groups such as trimers, tetramers, hexamers, or larger ensembles, forming entirely new types of active sites. This work was published in Science.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Nathan Gabor from the University of California, Riverside about his group’s work on imaging and directing the flow of electrons in electronic devices. They designed their device by taking a crystal of yttrium iron garnet, which does not conduct electricity, and putting a nanometers-thick layer of platinum, which does conduct electricity, on top of it. When they illuminate the device with a laser, this device produces an electric current. They further discovered that when they combine the crystal with the platinum, the interface between the two materials exhibits magnetic properties. Gabor’s research team used this sensitivity to a magnetic field to steer the electron flow in the device. This work was published in Proceedings of the National Academy of Sciences.
In this podcast episode, MRS Bulletin’s Rahul Rao interviews Fereshte Ghahari of George Mason University about the use of a scanning tunneling microscope (STM) to measure the electronic and magnetic properties of moiré quantum materials. Ghahari and collaborators twisted two layers of graphene at a specific angle, then chilled the material to suppress as much motion as possible. They ran an STM across the material while varying the magnetic field. They could precisely observe how those field changes affected the energy levels of the electrons, realizing that they could use those discrete energy levels as a “quantum ruler.” “We hope these new measurements help researchers to optimize these magnetic and electronic properties of quantum materials for specific applications,” says Prof. Ghahari. By manipulating the electrons in moiré quantum matter and shifting its twist angles, materials researchers may be able to improve on materials that are useful for microelectronics or superconductors, for example. This work was published in a recent issue of Science.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Hamideh Khanbareh and Vlad Jarkov of the University of Bath in the UK about an application they introduced for using piezoelectric materials in tissue engineering. The researchers fabricated a composite by combining polydimethylsiloxane with a piezoelectric material of potassium-sodium-niobate that is compatible with cell lines similar to neurons. They then studied how the composite material would interact with neural stem cells. They found that the piezolectrically activated composites allowed the cells to spread across the surface of the material and saw an increase in the amount of neurons. Usually the use of piezoelectric materials in tissue engineering requires mechanical stimulation from either movement of the body or the application of ultrasound. In this research, no additional mechanical stimulation was required. This work was published in a recent issue of Advanced Engineering Materials.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Professor Jerry Qi and postdoctoral researcher Mingzhe Li of the Georgia Institute of Technology about their new technique to 3D print silica glass. After using two-photon polymerization to cross-link poly-dimethylsiloxane, Qi’s research team used deep UV to convert the polymer into silica glass. The deep UV irradiation is carried out in an oxygen-rich atmosphere. The UV light converts the oxygen to ozone, which then reacts with the polymer, prompting the formation of silica glass. Furthermore, printing of the silica glass is accomplished at the low temperature of 200°C, compared to 1000°C required for current methods of 3D printing. Qi’s group fabricated structures of several tens of micrometers in size, with a resolution of a few hundred nanometers. This work was published in a recent issue of Science Advances.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Surabhi Madhvapathy of Northwestern University about an implantable bioelectronics system that can perform early detection of kidney transplant rejection in rats. Madhvapathy and her colleagues have developed a wireless sensor that attaches to the kidney itself. The biosensor measures the organ’s temperature and its thermal conductivity. These can point toward inflammation in the kidney, which can be a sign of organ rejection. This work was published in a recent issue of Science.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Kento Katagiri, a postdoctoral scholar at Stanford University, about the propagation speed of dislocations in materials. Using an X-ray free electron laser to collect data from single-crystal diamond, Katagiri and colleagues have determined the velocity of wave propagation to be in the transonic region. Katagiri’s work is most applicable to extreme shock events such as missile strikes and shuttle launches where pressures of one terapascal or more might apply. The results are relevant to a type of nuclear fusion known as Inertial Confinement Fusion, which uses intense lasers to compress the fuel. This work was published in a recent issue of Science.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Stanford University’s Jennifer Dionne and her PhD student Fareeha Safir and their colleague Amr. Saleh from Cairo University about their work on identifying bacteria in complex samples. Instead of culturing bacteria then identifying them using specific methods such as a polymerase chain reaction test, which takes hours, Dionne’s research group uses Raman spectroscopy combined with machine learning to detect the presence of two specific bacteria in samples that contained red blood cells. The addition of gold nanorods to the samples further enhanced the signal from the bacteria. Another way the research team accelerated the detection of bacteria signal was by building an acoustic bioprinter for the liquid samples: the specialist printer uses focused soundwaves to break the surface tension of a larger droplet, maintaining cell viability. This work was published in a recent issue of Nano Letters.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Alice Soragni of the University of California, Los Angeles about her work in precision oncology. Rather than sequence the DNA of a patient’s tumor, Soragni uses bioprinting to create organoids from the patient’s cells. She then adds various drugs to the cells to directly test their response to each drug. To check the effectiveness of the drugs, Soragni’s group measures the organoid’s mass with a technique called interferometry. Interferometry is a non-invasive technique that involves shining light on the cells to monitor their response to the drug. This process allows Soragni to characterize the organoid’s response to the drug in fine detail. This work was published in a recent issue of Nature Communications.
While thermodynamics suggests that water sorption is more favorable at a low temperature, MRS Bulletin podcaster Laura Leay interviews post-doctoral researcher Xinyue Liu from the Massachusetts Institute of Technology (MIT) who reports a hydrogel that can adsorb more water at elevated temperatures. Liu and the research team from MIT and the University of Michigan were searching for a way to harvest water from the air without using a lot of energy. They want to tackle the problem of water scarcity and find a way of generating water sustainably. To do so, they tested many different sorbents. Most sorbents, such as zeolite and silica gel, have a structure that does not change much when it has adsorbed water; however, the polyethylene glycol – or PEG – hydrogel that the team synthesized is different. While it is semi-crystalline at 25°C, it becomes amorphous at 50°C. This structural change means that more adsorption sites are available at the higher temperature. As water is absorbed, it caused the hydrogel to swell, opening up further adsorption sites. The PEG hydrogel monomers are star-shaped, forming a network where the molecular weight can be precisely controlled. The shape of the monomer leads to very homogeneous structures, facilitating crystallization. The PEG hydrogel exhibited a water uptake of 0.050 grams per gram of polymer at 50°C and 50% relative humidity, with half this water uptake at 25°C and the same humidity. This work was published in a recent issue of Advanced Materials.
Many industrial processes require heat or create it as a by-product. Now, Takayoshi Katase from the Tokyo Institute of Technology has found a way to harness this heat in an eco-friendly way, as he explains in an interview with MRS Bulletin podcaster Laura Leay. One way to harness this heat is to use thermoelectric devices to produce electricity via the Seebeck effect. Conventional thermoelectric materials, however, are composed of heavy metals such as lead and tellurium, which are toxic. To incorporate hydrogen into the structure, and so replace the toxic elements, Katase’s research team used a rapid thermal sintering process where the starting material—which already includes the hydrogen—is sealed inside a tube. Some of the oxygen sites in strontium titanate are then substituted by the hydrogen. “More than expected, the hydrogen substitution reduces thermal conductivity less than half, and also increases electronic conductivity, resulting in the large enhancement of energy conversion efficiency,” Katase says. This work was published in a recent issue of Advanced Functional Materials.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Xuchen Wang of Karlsruhe Institute of Technology in Germany about his work on photonic time crystals. While conventional crystals are composed of repeating unit cells in space, such as eight carbon atoms arranged in a cube to form a diamond, a photonic time crystal has a structure that repeats in time. Theoretical predictions of photonic time crystals referred to designs consisting of three-dimensional metamaterials whose properties are difficult to manipulate in the laboratory. Wang and his collaborators have adapted the three-dimensional time crystal design to a two-dimensional metasurface. They arranged copper structures on the surface, using conventional printed circuit board technology. The structures look like a forest of mushrooms where the researchers placed a variable capacitor, known as a varactor, between each mushroom. To create the device, the researchers apply changing external voltages to the varactor, modulating the material’s electromagnetic properties in time. Wang then confirmed experimentally that this device amplified microwave signals that he sent across its surface. This work was published in a recent issue of Science Advances.
Little research has been done on the magnetic properties of high-entropy oxides, a challenge taken up by Alannah Hallas at the University of British Columbia in Canada, interviewed by MRS Bulletin podcaster Laura Leay. Hallas’s research group began by choosing five elements that would be magnetic and combining them in oxide form, rendering a spinel structure for further experimentation. To understand how progressive substitution of the magnetic metal cations with non-magnetic gallium would affect the magnetic properties of the spinel, Hallas found that Ga substitution led to precise control of the configurational entropy, which may help to stabilize the spinel structure. Manganese, cobalt, and iron were redistributed throughout the structure whereas nickel and chromium were unaffected. Ga substitution led to the ability to tune the magnetic properties of the material in some unexpected ways that the research team calls “entropy engineering.” The ability to tune the properties may have applications for energy and data storage, for example, and could lead to more sustainable technologies. This work was published in a recent issue of the Journal of the American Chemical Society.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Widi Moestopo, a former graduate student in Julia Greer’s laboratory at the California Institute of Technology (Caltech) and now a postdoc at Lawrence Livermore National Laboratory about their work incorporating microknots in architected materials. Using two-photon lithography, Moestopo scans a resin with a laser to create and shape a three-dimensional (3D) object within foam. Moestopo then used a solvent to wash away the remaining, unconverted resin. In this way, he sculpted the knots out of the resin, rather than tying the knots like shoelaces. This 3D structure is formed from a lattice of 3D rhombuses, where each side of the rhombus consists of three strands of fiber. These fibers are woven around each other to form knots. The result is a materials with high deformability and tensile toughness. This work was published in a recent issue of Science Advances.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Dominic Bresser from the Helmholtz Institute Ulm and the Karlsruhe Institute of Technology in Germany about the suitability of a nanotwinned copper foil as a current collector for the negative electrode in“zero excess” lithium−metal batteries. The nanotwinned copper foil has an essentially pure, single orientation and dense twin boundaries. Bresser’s research group found that lithium deposits more densely and much more homogenously on this nanotwinned copper foil than on commercial foils. This work was published in a recent issue of ACS Applied Energy Materials.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Carmel Majidi from Carnegie Mellon University about an adaptive-responsive soft micro-robot. The key is eliciting a liquid–solid phase transition through electromagnetic induction. In addition to using the magnetic field to induce the phase change, it can also be used to make the machine move. A soft, low-rigidity body is vital for adapting a miniature machine to a variety of applications or a changing environment. This work was published in a recent issue of Matter.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Prof. Esma Ismailova and graduate student Marina Galliani from Mines Saint-Etienne about their work toward creating biocompatible, eco-friendly materials for wearable electronics. For this particular project, they developed a conducting material based on a commercial polymer known as PEDOT-PSS, in a water-based solution. They combined it with various solvents to tune the electrical conductivity, which is dependent on the shape and structure of the polymers in the material as they dry. The researchers tested the material’s conductivity on several substrates, including paper-based substrates and textiles. To make the material printable, they also needed to tune the material’s viscosity. Because the material relies on inkjet printers that are already commonly available, this material is relatively easy to incorporate into industrial processes. This work was published in a recent issue of APL Bioengineering.
In this podcast episode, MRS Bulletin’s Laura Leay interviews Rob Shepherd from Cornell University about an adaptive-responsive self-healing soft robotic system. Shepherd’s research team has developed waveguides made of self-healing polyurethane urea crosslinked with aromatic sulfide bonds. When this material is cut, relatively weak hydrogen bonds quickly form. Disulfide exchange then occurs and, although this takes longer than the formation of hydrogen bonds, results in much stronger bonding and so recovering much of the mechanical strength of the polymer. Light is transmitted down the waveguide and, when the material is cut or punctured, the signal is attenuated. The loss of signal can be acted on by the robot and it can change its pattern of movement until the strong disulfide bonds are formed. This self-healing material absorbs more light than previous versions of the polymer that couldn’t effect a chemical repair. This level of light absorption is actually useful as it makes the robot more sensitive to damage or deformation. This work was published in a recent issue of Science Advances.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Jiahui Li, a graduate student at the University of Illinois Urbana-Champaign about designing structures out of gold nanoparticles. When the nanoparticle structure takes the shape of a pinwheel, different types of light interact with the structure differently due to its chirality. Different wavelengths might be transmitted depending on whether the light’s polarization is rotating clockwise or counterclockwise, which could make this structure useful for filtering light in optical applications. This work was published in a recent issue of Nature (https://doi.org/10.1038/s41586-022-05384-8).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Robert Hovden from the University of Michigan and his graduate student Jonathan Schwartz on development of the freely available tomviz platform (tomviz.org) that enables real-time three-dimensional (3D) visual analysis of materials. Building on the already existing tomviz platform, Schwartz created new algorithms capable of pulling data from transmission and scanning electron microscopes, evolving the 3D image as the experiment progresses. This research is published in a recent issue of Nature Communications (https://doi.org/10.1038/s41467-022-32046-0).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Tao Yang from the City University of Hong Kong in China who focuses on the innovative design of advanced structural materials. In the area of high-strength alloys, Yang’s research team looked specifically at how to stabilize nanoparticles at high temperatures. In an alloy of Ni59.9-xCoxFe13-Cr15Al6Ti6B0.1, Yang’s team achieved ultra-stable nanoparticles at 800–1000°C. They achieved this effect by tailoring the concentration of cobalt. While nanoparticles have already been seen to improve the strength of materials, Yang’s team has provided insight into how this can be achieved at high temperatures. This research is published in a recent issue of Nature Communications (https://doi.org/10.1038/s41467-022-32620-6).
In this podcast episode, MRS Bulletin’s Stephen Riffle interviews Alessandra Scagliarini, a professor of infectious disease at the University of Bologna, and Beatrice Fraboni, a professor of physics at the Department of Physics and Astronomy at the University of Bologna, about their electrical transistor assay that quantifies SARS-CoV-2 for antibodies. The purpose is to determine vaccine efficacy over time. The device is built with the semiconducting material poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The material not only transfers ion signals into electronic signals, but also amplifies it. Without neutralizing antibodies, the virus attacks the cells, causing both macro cracks as well as minor disruptions in the tight junctions of the cells, which the high sensitivity of this device is able to detect. This kind of data is an indirect way to assess whether patient samples have neutralizing antibodies. This work was published in a recent issue of Communications Materials (doi:10.1038/s43246-022-00226-6).
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Murat Onen, a postdoctoral researcher at the Massachusetts Institute of Technology, about analog deep learning that could help lower the cost of training artificial intelligence (AI). The programmable analog device stores information in the same place where the information is processed. The resistor’s main material is tungsten oxide, which can be reversibly doped with protons from an electrolyte material known as phosphosilicate glass, or PSG, layered on top of the tungsten oxide. Palladium is above the PSG layer, which is a reservoir for the protons when they are shuttled out of the tungsten oxide to make it more resistive. “When protons get in, it becomes more conductive. When the protons go out, it becomes less conductive,” says Onen. The resistance of this device responds in about 5 ns. This work was published in a recent issue of Science (doi:10.1126/science.abp8064).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Monica Olvera de la Cruz of Northwestern University and her colleagues who gained insight into biochirality. By analyzing self-assembly for a series of amphiphiles, Cn-K, consisting of an ionizable amino acid [lysine (K)] coupled to alkyl tails with n = 12, 14, or 16 carbons, the researchers found the degree of ionization is what controls the shape. They incorporate this phenomenon into a membrane energetics model. Furthermore, their experimental techniques show that the nanoscale structure of the chiral assemblies can be continuously controlled by solution ionic conditions. The model moves researchers one step closer to building entire cells in the laboratory and could lead to the development of nanotechnology such as drug delivery and electronics. This research is published in a recent issue of ACS Central Science (https://doi.org/10.1021/acscentsci.2c00447).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Sergey Artyukhin from the Istituto Italiano di Tecnologia and Louis Ponet, who is affiliated with both the Istituto Italiano di Tecnologia and Scuola Normale Superiore di Pisa about a topologically protected switching phenomena in ferroic materials. When a multiferroic crystal (GdMn2O5) is placed in a magnetic field at a very particular angle to a crystallographic axis, and the magnetic field is swept up and down twice, the system switches between four magnetic configurations. The interplay between the spin of the gadolinium and manganese ions leads to a unidirectional rotation of the spins and because this rotation is caused by the up-down sweep of the magnetic field, it can be thought of as a crankshaft. This four-state magnetoelectric switching emerges as a topologically protected boundary between different two-state switching regimes. While this magnetoelectric switching has only been observed in one multiferroic material, modelling can help predict other suitable materials from first principles. Eventually this could lead to new technology. This work was published in a recent issue of Nature (doi:10.1038/s41586-022-04851-6).
Victor A. Rodriguez-Toro, a researcher in materials and devices and a science correspondent for MRS Bulletin, interviews Ayse Turak, Associate Professor of Engineering Physics and Director of the Centre for Emerging Device Technologies at McMaster University in Canada, about her group’s research in organic optoelectronics. Turak focuses her research on developing easy, versatile, and inexpensive methods of exploring and tuning interfaces, particularly in organic, perovskite and nanoparticle solar cells, light-emitting diodes, and sensors. Turak discusses her latest work in which her group controlled the reaction kinetics and slowed down the rate of perovskite formation by using diblock copolymer reverse micelle templating. “The slowed reaction,” they write in their article, “allows the use of an unconventional approach, mixing methylammonium iodide (MAI) and lead bromide (PbBr3) to produce pure methylammonium lead bromide MAPbBr3 [nanoparticles].” With this method, Turak’s group achieved two stable phases in a single solution. Turak also talks about challenges to using nanoparticles in devices for wearable electronics and the role of LiF interfaces for high-efficiency organic solar cells. She speculates on which type of optoelectronics will be preferred for commercialization. As an “out” lgbtq+ researcher in the materials science field, Turak provides insights into how universities and research centers can open the doors to help lgbtq+ scientists feel more integrated into the scientific community. She also provides advice to the new generation of researchers coming from different backgrounds representing diversity in science-technology-engineering-mathematics (STEM).
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Bin Ouyang of Florida State University about making a better cathode for lithium ion batteries. The current use of cobalt and nickel in their cathodes causes Li-ion batteries to contract in volume and degrade. Ouyang and his colleagues simulated and then fabricated new cathode materials that do not use cobalt or nickel and also degrade less after being charged and discharged. To achieve this, they found that they needed to design a material with disorder in its crystal structure. They found that replacing cobalt and nickel with vanadium and niobium leads to a battery with a small change of volume. The results provide a model for the further search of viable cathode materials to design lithium-ion batteries that are entirely made of solids. This study is published in Joules (doi:10.1016/j.joule.2022.05.018).
In this podcast episode, MRS Bulletin’s Sophia Chen interviews graduate student John Ahrens of Harvard University about challenges in bioprinting heart tissue. One challenge in particular is aligning the cells. Heart cells are narrow and rectangular in shape. In a natural heart, they line up in parallel to form aligned filaments. Those aligned filaments are built up into a larger tissue with more complex alignment. Cellular alignment correlates with heart function. The research team has programmed the bioprinter to make tissues that are aligned vertically, in a circular pattern, or in the shape of a chevron. This study is published in Advanced Materials (doi:10.1002/adma.202200217).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Laura Rossi from Delft University of Technology (the Netherlands) and Greg van Anders from the University of Michigan (USA) and Queen’s University (Canada) about advances they’ve made in colloidal preassembly in order to gain control in materials structure at a range of length scales. Through experiments and computer simulation, the researchers showed that particle interaction and particle shape can be decoupled through spherical confinement, which – when clustered – assembled differently than those observed in bulk assembly. This work was published in a recent issue of Science Advances (doi: 10.1126/sciadv.abm0548).
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Adam Kubec at Swiss startup XRNanotech and research team member Marie-Christine Zdora of the Paul Scherrer Institut about their proof-of-principle of an x-ray achromatic lens. The lens consist of a focusing diffractive and a defocusing refractive optical element that achieves imaging of a range of wavelengths without having to move the sample. The researchers used two different diffractive lenses, one made from nickel and one with gold. To fabricate the refractive lens, they used a nanoscale 3D printing technique known as two-photon polymerization. This work was published in a recent issue of Nature Communications (doi:10.1038/s41467-022-28902-8).
In this podcast episode, MRS Bulletin’s Stephen Riffle interviews Jennifer Gelinas, an assistant professor in the Department of Neurology and Institute for Genomic Medicine at Columbia University Irving Medical Center, and Dion Khodagholy, an associate professor in the Department of Electrical Engineering at Columbia University, about their ionic communication system for implantable devices. The system involves building a capacitor using water ions and biomolecules. With the placement of two conducting electrodes in the body and introduction of an alternating current, the tissue between the electrode will act as an electrolyte medium. Together, these two electrodes and their electrolyte medium form a capacitor that is capable of generating a detectable electrical field. The ionic communication device is fabricated with materials that have already been shown to be safe in the body, such as gold and a semiconducting plastic—poly(3,4-ethylenedioxythiophene)–polystyrenesulfonate or PEDOT:PSS. This work was published in a recent issue of Science Advances (doi:10.1126/sciadv.abm7851).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Michael Dickey from North Carolina State University about his work manipulating liquid gallium. When submerged in an aqueous solution, liquid gallium will form a sphere. When fed by gravity through a thin nozzle that is surrounded by aqueous solution, it will instead flow into the shape of a wire. Passing an electrical current through the liquid metal wire means that a magnetic field is created, which means the wire can be shaped using external magnets, following the Lorentz force. This research was published in a recent issue of the Proceedings of the National Academy of Sciences (doi:10.1073/pnas.2117535119).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Yang Yang and Yepin Zhao of the University of California, Los Angeles about a dual-function p-type soft interlayer they developed to enhance efficiency of charge transfer in organic solar cells. With the introduction of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the p-type material, the researchers are able to improve the efficiency of the device as well as change its optical distribution. One goal for such a device, they say, is to create a greenhouse that generates its own electricity. This study is published in ACS Nano (doi:10.1021/acsnano.1c09018).
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Kenjiro Fukuda from RIKEN in Japan and Masahito Takakuwa of Waseda University about a technique to connect integrated electronics while maintaining their flexibility. They demonstrated the method on two gold electrodes. To make the two pieces of gold bond, the researchers treated the gold with water vapor plasma. The researchers used this technique to electrically connect the gold electrodes of an organic photovoltaic to an organic light-emitting diode without adding significant thickness, thereby ensuring the flexibility of the device. This study is published in Science Advances (doi:10.1126/sciadv.abl6228).
In this podcast episode, MRS Bulletin’s Stephen Riffle interviews Samuel Herberg from SUNY upstate medical university in Syracuse, New York about a new tool to study cell behavior. According to Herberg, culturing cells in an environment that reflects the materials properties of the human body can help reveal new insights into cell biology and mechanisms of disease. To do that, his research team has created a hydrogel using natural polymers. Through UV and chemically induced crosslinking, Herberg’s team is able to finely tune their hydrogel’s stiffness, which enables them to study diseases like primary open angle glaucoma, the world’s leading cause of vision loss. Their study is published in Frontiers in Cell and Developmental Biology (doi: 10.3389/fcell.2022.844342).
In this podcast episode, MRS Bulletin’s Laura Leay interviews PhD candidate Laura Albero Blanquer and her professor, Jean-Marie Tarascon, from the Collège de France in Paris about their study on what occurs inside the cells of both liquid and solid-state batteries. They embedded the optical Fiber Bragg grating sensor that reflects monochromatic light, revealing a shift in the peak wavelength when there is a change in temperature, pressure, or stress. The sensors were calibrated so that only changes in stress could be detected. This research will lead to new opportunities to look at commercial liquid cells, and to greater insight into the chemo-mechanical processes in electrodes and in all solid-state batteries, which could lead to enhanced performance. Their study is published in Nature Communications (https://doi.org/10.1038/s41467-022-28792-w).
In this podcast episode, MRS Bulletin’s Laura Leay interviews Nate Hohman from The University of Connecticut about the structure of two chalcogenolates his group uncovered. By combining serial femtosecond crystallography —usually used to characterize large molecules—and a clique algorithm, Hohman’s group was able to analyze the structure of small molecules. With serial femtosecond crystallography, large molecules like proteins produce thousands of spots on the detector; in contrast, small molecule crystals only a produce a few spots. The algorithm uses the pattern that the spots make on the detector to determine the orientation of as many crystals in the liquid jet as possible. The data from each crystal can then be merged together to find the structure.
In this podcast episode, MRS Bulletin’s Sophia Chen interviews Carla Gomes, Michael Thompson, and Max Amsler of Cornell University about their robot, SARA—Scientific Autonomous Reasoning Agent. Unlike commonly known artificial intelligence (AI) applications such as the neural networks that enable image recognition, SARA performs within a closed loop system through a type of AI known as active learning, which allows the system to reason without a lot of training data. Within 30 minutes, SARA figured out how to make delta phase bismuth oxide and cool it to room temperature, saving the research team two full days of experiments.
In this podcast episode, MRS Bulletin's Prachi Patel interviews Liangbing Hu of the University of Maryland on research to mold and shape wood — a low-cost, sustainable material. Beginning with basswood, Hu's laboratory removed some of the lignin and fully dried this hardwood. As the wood dries, the cell walls contract. Wood also has hollow fibers and open channels, called vessels, all of which close up as the material dries. The wood is then shocked with water, leaving it with partially open vessels and closely packed fibers. The cells walls expand rapidly and take on an accordion-like wrinkled structure. These wrinkles, and the space created by the partially open vessels, allow the wood to be compressed and stretched, and the closely packed fibers give it enough strength to bend.
In this podcast episode, MRS Bulletin's Sophia Chen interviews Zahra Fakhraai of the University of Pennsylvania on her group's research to better understand how a substance condenses into glass. They studied the liquid–liquid phase transition in vapor-deposited thin films of N,N0-bis(3-methylphenyl)-N,N0-diphenylbenzidine (TPD). They discovered a new high-density supercooled liquid phase in glasses deposited in the thickness range of 25-55 nm. Their findings could lead to more precise theoretical descriptions of glasses.
In this podcast episode, MRS Bulletin's Sophia Chen interviews Nima Rahbar of Worcester Polytechnic Institute on the use of an enzyme, carbonic anhydrase, that initiates self-healing in concrete. The enzyme catalyzes calcium in the cement to react with carbon dioxide from the air to form crystals of calcite, which repairs cracks. Rahbar's research group has demonstrated how the material can heal millimeter-wide cracks. Ubiquitous concrete is responsible for 8% of human-made greenhouse gases, including that used in the repair of existing structures. Rahbar's work is expected to help reduce concrete's carbon footprint, while also speeding up the self-healing compared to the previously used bacteria-based methods.
Omar Fabian: It’s summer and film director James Cameron has just dropped another scorching hit. In Terminator 2: Judgment Day, we find mother-son duo Sarah and John Connor running for their lives, and for the lives of all humankind, with the help of a bad cyborg turned good played by none other than Arnold Schwarzenegger. There are so many undoubtedly cool visual features to take away from this iconic film. Little known fact: it actually won four Academy awards for its sound and visual effects. But if you ask around, more than likely, you’ll find that the coolest has to be the T-1000: the liquid-metal robot sent from the future to destroy John Connor and ensure victory for our machine overlords.
Alireza Dolatshahi-Pirouz: You have this robot that, it’s not electronic but it’s still a robot and it’s because somehow that material that made it is self-healing and it’s animated in some ways that we couldn’t understand back then.
[OF]: That’s Alireza Dolatshahi-Pirouz, a professor in the Department of Micro- and Nanotechnology at the Technical University of Denmark.
You might remember him from a previous episode of our podcast, where he described how his group is developing stretchy, eco-friendly electronics they describe as “fleco”—
[ADP]: “So flexible and eco, fleco”.
[OF]: Now, they’re back with a new material that stretches, conducts electricity, and perhaps most astoundingly, heals itself—not unlike the T-1000 from Terminator 2, which Dolatshahi-Pirouz admits was the inspiration for his lab-work.
The team calls their new wonder material CareGum.
Markus Buehler of the Massachusetts Institute of Technology (MIT) and editor of the Impact section of MRS Bulletin interviews Desirée Plata, the Gilbert W. Winslow Career Development Associate Professor of Civil and Environmental Engineering at MIT about her group’s development of new methods toward functionalization of carbon nanotubes with heteroatoms, which enables covalent attachment, opening up a world of potential materials structures. This research is relevant because common functionalization techniques for carbon nanotube materials (and other, similar nanostructures) are often hazardous, and have adverse environmental impacts, and lack precision. The research group evaluated an in situ functionalization technique utilizing oxygen-containing alkyne precursors, which offers a novel, more sustainable pathway for bottom-up engineering. Through a detailed assessment of the mechanisms by which nanotubes form, the researchers were able to direct new pathways toward bottom-up design of materials while considering sustainability, and especially environmental health, as a parameter during optimization and design. Their work is published in MRS Bulletin (https://doi.org/10.1557/s43577-020-00019-7)
MRS Bulletin’s Impact editor Markus Buehler interviews Huajian Gao of Nanyang Technological University, Singapore and Bo Ni of Brown University on their development of a deep learning method to predict the elastic modulus field based on strain data that may be the result of an experiment. The method is highly efficient and offers real-time solutions to problems that usually require complex numerical methods that rely on variational methods to solve elasticity problems, like finite element analysis. This type of approach may change the way researchers interpret experimental data. See the article “A deep learning approach to the inverse problem of modulus identification in elasticity” (doi:10.1557/mrs.2020.231).
In an interview with Gopal Rao from MRS Bulletin,Cherie Kagan, the 2021 President of the Materials Research Society, discusses changes in the MRS Governance structure that provides greater engagement and empowerment of both volunteers and staff in alignment with the MRS mission. Changes include fewer committees but more “time bound” task forces and an independent nominating committee where MRS looks at the opportunity in this structure to create greater diversity in the leadership of the Society to serve the MRS membership.
As part of the MRS Communications 10th Anniversary event, Gopal Rao, Chief Editor for Technical Content at MRS, interviews David Morse, Executive Vice President and Chief Technology Officer at Corning, about research, development, and innovations at Corning. They discuss Corning’s contributions to addressing the COVID-19 pandemic, the company’s latest version of Gorilla glass, and Corning’s R&D efforts in ceramics as well as the role of industrial R&D labs in the research enterprise.
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 Impactsection 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 Impactsection 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.
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.
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.
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.
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.
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.
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).
TranscriptWelcome 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 for organic synthesis.
Reactions that form carbon–carbon bonds are the basis of synthesizing drugs, plastics, and chemicals. But the reaction procedures are complicated and require expensive noble metal catalysts. A research team led by Yong Yan at San Diego State University found that colloids of methylammonium lead tribromide and cesium lead tribromide are 1000 times as effective as iridium- and ruthenium-based catalysts for catalyzing the α-alkylation of aldehydes, a valuable and widely used chemical reaction. The perovskites cost approximately 100 times less. For the simple one-pot reaction, the researchers mixed organic starting materials into a suspension of the perovskite nanocrystals. Blue-light illumination triggers reactions that generate several products. By tweaking the reaction condition, the researchers can selectively catalyze other important chemical reactions.
This work was published in a recent issue of the Journal of the American Chemical Society. My name is Bob Braughler from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.
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
TranscriptSOPHIA 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. Whereas personalized cooling, like a temperature-regulating outfit, uses tens of watts. Chen isn’t the first to invent clothes that directly cool your skin. For example, you can buy shirts right now that circulate icy water to cool you off. But his team’s design uses a thermoelectric material, which cools via a distinctive mechanism known as the Peltier effect, which creates cooling by passing an electric current between the junction of a semiconductor and metal. When you reverse the current, you create a heating effect. This can achieve much subtler temperature control than the wearables that are commercially available. Chen’s device can cool and heat.
RC: It’s really like the thermostat in the air conditioning system. You can really set the skin temperature.
SC: The highest performing thermoelectric materials are rigid, so Chen’s team needed to configure these materials to make a flexible, wearable device. They used two different commercially available thermoelectric materials. These materials consist of two bismuth telluride alloys: a p-type semiconductor alloyed with antimony, and an n-type semiconductor alloyed with selenium. Both alloys are connected to metal electrodes, and they create a cooling effect by making an electric current flow from the metal to the p-type material, or from the n-type material to the metal. Reversing the direction of the current causes heating. To make their system flexible, Chen and his team made these alloys into pillars and sandwiched them between two sheets of Ecoflex, a flexible silicone rubber.
RC: Even though the pillars by themselves are rigid, the entire device is flexible because of the overall architecture.
SC: They wanted the entire layer of each sheet of Ecoflex to keep at a uniform temperature. So to achieve this, they embedded aluminum nitride particles to increase its thermal conductivity. They also kept a 4 mm air gap between the two sheets for insulation. When the ambient temperature was between 22°C and 36°C, they could maintain the wearer’s skin temperature at 32°C, which they defined as a condition of thermal comfort. Chen wants to develop this into a therapeutic device for people who have medical conditions that make it difficult for them to regulate their skin temperature.
RC: There are patients who are very sensitive or prone to overheating with certain health conditions like multiple sclerosis, or people who are genetically not able to sweat, they are prone to overheating. There are certain occupations, outdoor construction workers or fire fighters, and people who are doing outdoor activities, like athletes for example. For this kind of application, I think our device will also provide good thermal comfort solution.
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.
TranscriptPRACHI 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 conductors is to use nanomaterials like carbon nanotubes, graphene. These are one way where people use these particles and coat it onto a stretchable substrate like silicone rubber or polyurethanes.
PATEL: Another approach is to use metal thin films. Basically, researchers create wavy serpentine patterns of these films so they can stretch with the substrate. But in both approaches, stretching the materials tends to reduce their conductivity. Plus, the thin materials have lower electrical conductivities than bulk metal. So Tee and his colleagues took a different approach.
TEE: We drew inspiration from actually spring-like structures. Spring-like structures are able to withstand strain. If you either stretch on a spring or compress a spring, they return, right?
PATEL: They first made a spring using some off-the-shelf copper wire. Then they embedded it in silicone rubber to make it elastic. But that still wasn’t good enough. The spring started changing shape within the rubber after being stretched a few times.
TEE: And we found out that the reason was that the interface between metal and rubber needs to be well-matched. If you’re talking about metals you have modulus is extremely high in the gigapascals range whereas rubbers typically have a modulus of megapascal range. There’s a three orders of magnitude difference. So we need a way to make sure that these two interface do not slip.
PATEL: And they did that by adding an epoxy to the rubber, which helps bond the metal to the rubber. This did the trick.
TEE: We can stretch it over a 1000 times and these springs stay in the same shape as they were after stretching. What’s interesting is that this electrical conductivity does not change because we’re not changing the crystalline structure of the metal. Our approach basically extends the dimension into 3D as opposed to a planar patterned film. We’re exploiting the bulk property of the metal. The other advantage is it can actually stretch more because we’re going into three dimensions. So I think there is certainly a limit to how much we can scale this down if we want to keep the same good electrical properties that we’re talking about. But that being said when you scale them down to about a micron, they actually become softer and so you can have even greater stretchability. So I think a micron or so is sort of where we want to be if you want to capture bulk properties and still retain the stretchability.
PATEL: The team’s findings are published in APL Materials. My name is Prachi Patel from the Materials Research Society.
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 thousands of frames a second. It becomes unmanageable from a human point, so we have to transition to more automated approaches.
CHEN: So Hexemer and his collaborators decided to try a machine learning approach to quickly classify and process x-ray images. To develop their image classification algorithm, they worked with frequency-space pictures of thin films made of polymers, about 100 nm thick. Scientists image these thin films at the facility. They consist of intricate geometrical patterns on the nanometer scale, which researchers try to engineer to create specific materials properties. For example, Hexemer explains that one future application is a printable solar panel. In the future, people might be able to print photovoltaics made of thin film polymers. But first, they need to figure out what nanometer structures work the best.
HEXEMER: To try to understand the efficiency of the material, we have to understand the morphology.
CHEN: They came up with seven different categories of thin film patterns. One of Hexemer’s computer science collaborators, Dani Ushizima, explains that they had to show the computer millions of examples.
DANIELA USHIZIMA: This neural network base will build a mathematical model that will represent the different patterns.
CHEN: They found they could classify images successfully into the seven categories 94% of the time.
USHIZIMA: The training process might take a long time—hours. But the feedback, to classify a scattering pattern, this is coming on the millisecond.
CHEN: The images they classified were simulations of thin films rather than real data.
HEXEMER: We want to have better and better simulations close to real and partially disordered systems. And that is very difficult.
CHEN: The team brought together experts from materials science and computer science. Shuai Liu, a member of the team, says to expect more collaborations between the disciplines.
SHUAI LIU: We point out a very important direction in future research is to combine machine learning, which has been well developed in recent years, with a lot of characterization techniques.
CHEN: My name is Sophia Chen from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.
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.
TranscriptSOPHIA 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 mechanism as in nature. Both the robot and the plant move fluid around inside them to extend their tendrils. Both the plant and robot push or extract fluid from inside the tendril by exploiting the process of osmosis. Mazzolai’s colleague, Edoardo Sinibaldi, explains how it works in their robot. If you can imagine the curly tip of the robot tendril, that curl is attached to a longer tube contained within a special sleeve made of active carbon cloth electrodes. This sleeve is placed in a solution containing lots of ions.
EDOARDO SINIBALDI: In our implementation we used sodium sulfate. It’s a common electrolyte, and it’s very stable, and it’s not toxic.
CHEN: They’ve made the tendril using two types of plastic. One type, called polysulfone, is permeable to water. Water can flow across this plastic barrier through pores about 50 nm in size. Imagine this part of the tendril, which is soaking inside the solution within the carbon cloth sleeve. At equilibrium, the ion concentration is the same inside and outside the tube. But Sinibaldi applies a voltage to two electrodes on the cloth sleeve, to make ions collect on the electrodes. This causes the liquid outside the tube to have a lower concentration of ions than inside the tube. This concentration gradient causes water to rush into the tube. This inflow of fluid stiffens the tendril tip, making it extend. The tendril tip is made of another type of plastic, ethylene terephthalate, coated with Al, which has been fabricated to achieve the necessary stiffness.
SINIBALDI: This is the basic fluid transport used by plants to, let’s say, swell cells and tissues in a coordinated manner and consistently stiffen tissue while it’s inflating and decreasing the stiffness of tissue while deflating.
CHEN: It takes about a milliliter of fluid to extend the robot tendril. They were able to coil the tendril 500 degrees in 25 minutes. And they can reverse the coiling or uncoiling as needed. Mazzolai also points out that the whole robot, including the tube and the carbon cloth, are made of flexible, soft material with tunable stiffness. These are properties that could be useful for medical applications.
MAZZOLAI: This is the challenge of the soft robotics community, developing something that can operate in the body without any damage to the human, and at the same time to be able to operate and change the stiffness.
CHEN: Mazzolai has also chosen to make plant-like robots because they have unique adaptations for exploring and functioning in harsh conditions. She thinks that they could be useful for exploring new planets, or in more mundane applications on Earth.
MAZZOLAI: These robots, they can move inside very narrow spaces for exploration for recovering objects in wells, or moving debris after a disaster.
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 stress can all make lead and iodide ions more reactive, generating lead and iodine defects that serve as recombination centers for charge carriers and bring down device efficiency and lifetime.
Researchers at Peking University have invented a novel technique for combating these defects. They added a rare-earth europium ion pair to lead-iodide perovskites. The redox pair shuttled electrons in a cyclical fashion from the defects, oxidizing lead and reducing iodine to recover lead and iodine ions. Devices with this redox shuttle have a power efficiency of 21.52%, and they retained more than 90% of this efficiency under 1-sun continuous illumination or heating at 85°C for 1500 hours.
This work was published in a recent issue of Science. My name is Bob Braughler from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.
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).
TranscriptPATEL: 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 metal salts. Heating the slide eliminates the polymer and reduces the metal ions.
CM: The atoms within one nanoreactor will coalesce, aggregate, and form a single nanoparticle. We can make structures with as many as eight different elements within one particle and every combination of those structures. It’s a very, very tiny reactor—a very, very tiny volume. That means you can confine within literally a countable number of atoms, which gives you the ability to precisely control the composition. And then if I control the size of the reactor I can also control particle size. So this is quite sophisticated, and opens the ability to look at the nanomaterial landscape like we’ve never had before. We’ve already used this approach to discover a new catalyst for single-walled carbon nanotubes. That was done with Wright Patterson Air Force Base. There was a sweet spot in terms of the compositional ratio that gave us greatest activity. All of that was refined and figured out by first making a megalibrary that had a systematic variation in particle size and also amounts of copper and gold.
PP: The researchers synthesized these catalysts in larger amounts to test them to make sure they worked. It took less than a week with this process to discover a completely new catalyst. Mirkin’s team has also used megalibraries to identify new catalysts for the hydrogen evolution reaction. These catalysts could help develop next-generation fuel cells that don’t have expensive platinum catalysts.
CM: In this case they were three-element nanoparticles that nobody, again, even contemplated before. So the question is what are you going to discover? “Almost anything” is the answer. Any structure that might lead to a property of interest. This is a way of discovering new nanomaterials with exciting physical properties and chemical properties. This is a completely new territory in terms of materials discovery.
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.
TranscriptFABIÁN: 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 stronger than steel. It’s cheap. It’s readily available in nature. It’s biodegradable. It’s green. It has electronic properties. It is an ionic conductor.
FABIÁN: But silk alone isn’t enough. Films cast from silk fibers are unstable in water. Their unwieldy protein structure, a mixture of random coils and sheets, makes for bad, water-permeable electrodes. To remedy that, a second ingredient is needed, namely, laponite. The nanosized disks that make up this natural ceramic iron out the silk fibers—like pouring hockey pucks on a plate of spaghetti. The result is a water-tight film. And because the disks carry charge of their own, they actually improve the fibers’ ionic conductivity.
DOLATSHAHI-PIROUZ: So it’s pretty amazing, right? You have something that doesn’t work, and then you add something to it, and then suddenly it works. And you get other properties along the way as well.
FABIÁN: Among the most valuable of those properties are low cost and flexibility. Because although electrodes made of gold, copper, or even carbon nanotubes might show higher conductivity, the team’s silk-nanoclay films are much cheaper and able to wrap around almost any curved surface.
DOLATSHAHI-PIROUZ: That’s not something you typically relate with ordinary electronics. Ordinary electronics are expensive, they are rigid. They consume a lot of power. This does not do that. So that’s why I would say we have something pretty fantastic in our hands at the moment.
FABIÁN: As a proof of concept, the researchers have fashioned the hybrid films into wearable electrodes able to track movement throughout the body, such as the flexing of the elbow or the fiddling of the digits. And that could make for interesting applications down the road.
DOLATSHAHI-PIROUZ: We have plans to use this concept inside a glove to develop an electronic glove. An electronic glove, which I think is the exciting thing about the application right now, would entail to have these small thin films inside a glove, and they would then be connected to an amplifier and a wireless unit that can transmit these signals wirelessly to, let’s say, a computer, or a mobile phone, or a portable device. So you have this glove on your hand that is kind of like sending data to the physician so you can, in real time, monitor whether you’re doing these exercises properly or not.
FABIÁN: This concept of an e-glove isn’t new. But the approach is. Co-opting natural materials like silk for advanced electronics applications could help cut cost, time, and, perhaps most importantly, the mountains of electronic waste we generate each year.
DOLATSHAHI-PIROUZ: We need to think simple. Why do we want to do old, complicated chemical syntheses that takes months and years to optimize when we can be smart and look into nature.
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 of sensing feedback.
CHEN: Basically, it works because they’ve invented a stretchable electronic skin covered in sensors that can sense force from multiple directions. It can sense forces perpendicular to the skin, or normal force, as well as forces parallel to the skin, known as shear force. And both forces are necessary for grabbing, holding, and placing objects. Try it. Grab a coin or something between your fingers—you’ll notice how you need to apply pressure to hold it, but also sense shear force to keep it from sliding.
Previously, electronic skins couldn’t sense shear force very effectively. The sensors were fragile and they also could only be placed sparsely on the robot. But Bao has figured out a way for the robot to sense the shear force, and she’s placed those sensors at high density on the skin. The more sensors crammed onto a surface, the better you can control the robot’s sense of touch.
Bao says some of the tactile properties of the electronic skin are comparable to the sensitivity of human skin. For example, if the skin experiences a shear pressure increase of 1 pascal, the electronic signal output of the skin will triple in size. 1 Pascal is about the pressure of a dollar bill resting on a table.
BAO: We are able to use fingertips to feel the most delicate texture and structures on the surface.
CHEN: In fact, to create this electronic skin, she’s borrowed a design element from human skin itself, a structure called the spinosum, which lies between the epidermis and dermis. They’re these little hill-like structures for sensing the direction a force is coming from.
BAO: If you add this hill-like structure, then depending on whether the force comes from left side or right side, because this dome or hill will be pressed from an angle, then only mechanoreceptor that’s on the opposite side of the direction of the force will be pressed and activated. This gives us a sense of direction of the shear force.
CHEN: The hill structures are pretty small—a fraction of a millimeter in size—and she can pack them densely onto the electronic skin. But if you zoom in even further, you can see the other key structural design on their electronic skin. Bao’s group has fabricated tiny pyramids, tens of microns wide at the base.
BAO: After a force is applied, these pyramids allow the elastic material to bounce back to its original shape once the force is removed.
CHEN: And in the future, Bao wants to borrow even more design elements from human physiology. She wants the sensors to pre-process some of the signal, like neurons do.
BAO: This neural-like signal processing lets humans gather a large amount of information and train our brain to learn the patterns of information with very little consumption of energy.
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’s Yuanyuan Zhou and Nitin Padture and their colleagues have made a surprising discovery that provides a solution. They found that simply adding germanium to the lead-free perovskite cesium tin iodide, which degrades easily, makes it air-tolerant. Devices made with the new perovskite show an efficiency of 7.11% and remain highly stable after 500 hours of operation under 1-sun illumination. The key to this behavior is the extremely high oxidation activity of germanium, which forms an ultrathin, uniform oxide layer on the surface, which—as the researchers write—“fully encapsulates and passivates the perovskite surfaces.”
This work was published in a recent issue of Nature Communications. My name is Bob Braughler from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.
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).
TranscriptSOPHIA 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 way it’s progressing, and hope to really see these materials being used, at least, in military garments in the coming years.
SC: They’re working to develop a weaveable material containing the mustard-neutralizing molecules. But one of the molecules is extremely difficult to make from scratch. It’s called protoporphyrin IX.
JD: It’s not a very symmetrical molecule. That means we can’t selectively make the functional groups and so forth to make that molecule.
SC: So they needed a different strategy. Fortunately for them, protoporphyrin IX actually occurs a lot in nature.
JD: Protoporphyrin IX is actually a precursor to heme, which is in our cells for absorbing oxygen, and a precursor for chlorophyll, which is used by plants to absorb light.
SC: And it turns out that E. coli cells make protoporphyrin IX in trace amounts. So DeCoste and his team actually went into the E. coli’s DNA and altered it so that the bacteria would produce it in much larger quantities. Then, they mixed the protoporphyrin IX with another type of molecule called a metal-organic framework. These molecules basically act like absorbent microscopic sponges that other molecules like to stick to.
JD: In a typical solid, the only thing to be exposed to be reacted with is the surface. Inherently if you have a sponge or large porous material, everything is a surface. Everything inside your metal-organic framework is readily available to any application you need, be it detoxification, detection, adsorption.
SC: This sponge-protoporphyrin hybrid collectively is really good at detoxifying mustard gas. So far, DeCoste’s team is working with the material in powder form, but they’re also trying to figure out how to make it into fibers that can be weaved. But the work isn’t just about this one application to mustard gas, says DeCoste. It’s a demonstration of how genetically engineered cells can produce molecules that are difficult to make using conventional chemistry processes. This material would not have been possible without the modified E. coli. DeCoste thinks that this whole field, synthetic biology, has a lot of potential to benefit materials science.
JD: The army and the military in general has a bunch of programs looking at ways to exploiting synthetic biology in general for new materials, making new molecules, and things along those lines. There’s a heavy investment in this area, and it’s a really hot topic right now that’s really started to come into its own.
CHEN: This work was published in a recent issue of MRS Communications.
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).
TranscriptWelcome 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 spectrum. Tandem perovskite/silicon cells are closer to market, but all-perovskite tandem cells would be easier and less costly.
Making an all-perovskite tandem cell that is efficient has been a challenge. The bottom device in a tandem cell is prepared with a low-bandgap material to absorb all of the infrared photons passing through the top device. Despite many efforts, researchers have had difficulty making high-quality low-bandgap perovskite absorber layers.
At the University of Toledo, Yanfa Yan and his colleagues made a high-quality layer by introducing 2.5% chlorine into a mixed tin–lead perovskite. This increased the grain size and crystallinity of the layer and reduced electronic disorder, which quashed the charge-carrier recombinations that produce heat and boost efficiency of the tandem cell. The cell retains 85% of this efficiency after 80 hours.
This work was published in a recent issue of Nature Energy. My name is Bob Braughler from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.
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.
TranscriptPATEL: 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.
PATEL: A failing neuron just leaks all its charge and is unable to collect enough to trigger a signal. And now Ramanathan and his colleagues have made an artificial neuron that can precisely mimic this behavior of normal and faulty neurons in the brain. This could have important implications for neuroscience.
SR: We introduce a quantum material, vanadium dioxide, as a powerful analog of neurons that can be found in the animal brain. We can control the electrical properties of these materials in an exceptionally careful manner. We can, you know, very rigorously grow these materials and also pattern them into devices with very precise geometries. So what we are proposing is we can build these very well defined structures with well defined electrical characteristics and we can emulate the propagation and transmission of signals in these structures which mimic the natural neurons. And so we are hoping that these types of studies will allow neuroscientists to understand, for example, thresholds for resistances or capacitances or electrical leakage across wires and so forth to look at the very, very early stages of breakdown of normal functioning in neural circuits.
PATEL: Why vanadium dioxide? It can undergo a phase transition at room temperature. The material is a semiconductor. But pass enough current through it and at some critical current level it becomes a metal. This property is key for making a simple artificial neuron.
SR: The beauty of this class of materials is that you can couple this type of a phase transition material to a capacitor and you can build an artificial neuron. So it’s really remarkably simple. It just contains this material, the phase transition material, which happens to be a quantum material that’s connected to a capacitor. That’s all it is to build and emulate an individual neuron! It can integrate charge, it can basically collect charge in an insulated state when it’s coupled to this capacitor. And when there is a critical level of charge accumulated or when it hits a certain temperature the material becomes metallic. And so suddenly there is a burst of electrical current through this material because it’s now no longer an insulator; it becomes a metal. So this mimics the integrate-and-fire capability.
PATEL: Then the material returns to its original state and the cycle starts again. Tweaking the material’s oxygen composition ever so slightly changes its conductivity. So the researchers can emulate different types of neurons found in animal brains. And if they make the material really conductive, it cannot integrate charge so it behaves like a faulty neuron. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin.
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).
TranscriptWelcome 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 III-V semiconductors, such as gallium indium phosphide, are often used for such devices.
Could perovskite solar cells, which suffer from instability under light and heat, be used for CPV technology? University of Oxford researchers led by Henry Snaith answer that question. They found that the efficiency of halide perovskite solar cells went up from 21.1% to a peak of 23.6% when simulated sunlight was increased to 14 times the standard irradiance of 1 Sun.
The researchers assessed a range of perovskite materials for their stability under high-intensity light. Perovskites containing a mixed cation formamidinium-cesium composition gave the most stable solar cells under high irradiance, and they chose a compound with a composition of formamidinium, cesium, lead iodide, and bromide for the CPV device. They found that their devices, maintained at room temperature during operation, retained 90% of their original efficiency after 150 hours spent under 10 Suns of concentrated light.
This work was published in a recent issue of Nature Energy. My name is Bob Braughler from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.
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.
TranscriptPRACHI 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 repair spinal cord injuries in rats. The implants are customized to fit the injury. The printer uses a silicon chip with four million microscopic mirrors to shine UV light in a three-dimensional pattern based on a digital MRI image of the wound. The light falls onto a mixture of poly(ethylene) glycol and gelatin methacrylate, which solidifies into the shape of the wound. The method is thousands of times faster than conventional 3D-printing techniques, which makes structures one drop or one layer at a time.
CHEN: So you can imagine we have about 4 million of these traditional printers doing the same work. And the speed is totally different. We can print the similar sized part in a matter of seconds versus 3 or 4 or 6 hours.
PATEL: Chen says the material and the structure of the implant make it unique. Neurons will usually grow around or turn away from foreign materials. But the hydrogel-gelatin combination attracts the cells. The implants have a solid supportive center surrounded by microchannels that are 200 micrometers in diameter. The researchers fill these channels with neural stem cells that urge neurons to grow.
CHEN: So if you put this implant in the gap of the damaged site of the spinal cord you hope, you know, that neurons can grow from both ends, they’d reconnect with the help of this kind of implant just like a bridge.
PATEL: That’s indeed what happened in rats with spinal cord injuries. The animals had no feeling or movement in their legs, but 11 weeks after getting the implants, they could feel their toes and move their knees. When the researchers removed the implants they saw that neurons had grown through the channels. The team is now moving on to test on monkeys. And Chen is doing a lot more with the 3D-printing method.
CHEN: We have been using this technique to print heart tissues, liver tissues, and brain tissue, and also cancer tissue models.
PATEL: Pharmaceutical companies could use those printed human tissues for drug testing, which could drastically cut the time and cost of drug development.
CHEN: They don’t need to wait until, you know, 10 years to see if this compound or this drug is toxic to the heart or liver in a human setting. And, of course, the long-term goal is to have therapeutical uses of this 3D-printed tissue because they can repair, regenerate damaged tissue, for instance heart wall, for instance piece of liver due to cancer you can cut it out and put this 3D-printed liver piece to fix it.
PATEL: The research was published recently in the journal Nature Medicine. My name is Prachi Patel from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin.
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).
TranscriptWelcome 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 the National University of Singapore, and his colleagues have revealed what makes the properties of two-dimensional perovskite differ at molecularly thin dimensions.
The researchers made centimeter-sized crystals of a specific perovskite with four compositions with increasing number of atoms and exfoliated 20–100-micron-thick monolayer sheets from the material. They measured the optical properties of the bulk and monolayer flakes using photoluminescence and optical absorption measurements. To keep the flakes from decomposing under laser irradiation used for these studies, they encapsulated the flakes with a transparent 2D hexagonal boron nitride layer.
The researchers studied the photoresponsivity of the single-crystal 2D perovskites as a function of thickness and discovered that excitons—which are joint states of an electron and a positively charged hole—tunnel across the material interlayers to dissociate at the electrodes, leading to efficient photocurrent generation. With increasing composition – or number of atoms - the luminescence of the materials shifted toward longer, redder wavelengths. The redshift also happened when the material was exposed to the laser for a long time, because thermal fluctuations reoriented the surface organic cations in the monolayer perovskite. The color shift can be reversed by exposing the sample to higher power laser annealing under vacuum. This cycle could be repeated tens of times.
The disordering of the organic cations also creates defects that trap only positively charged carriers, allowing electrons to circulate longer. To test this, the researchers made a photodetector with the monolayer perovskites. The detector had a low current in the dark, but the current increased linearly with laser power because under illumination, excitons tunneled across the interlayers, creating a highly conductive state.
This work was published in a recent issue of Nature Materials. My name is Bob Braughler from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.
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.
Despite being one of the most attractive materials for photovoltaics and light-emitting devices, conventional three-dimensional organic–inorganic perovskites are plagued by instability issues. However, their 2D counterparts, which contain layers of conductive perovskites separated by layers of relatively long organic cations, are much more stable. The cations inhibit charge transport between neighboring conductive inorganic layers. This forms quantum wells, where the charge carriers can freely move in a 2D space, while there is a restriction in the third dimension.
So far, though, not much is understood about their composition or how these materials assemble. To investigate, Edward Sargent and colleagues at the University of Toronto used grazing incidence x-ray scattering on 2D-layered perovskite films as the films formed.
They used methylammonium lead iodide with either phenethylammonium or n-butylammonium cations, and different solvents to make various film samples. They found that intermediate solvent complexes mediated the formation of quantum wells by providing building blocks to grow perovskites as the solvent evaporates out. They also found that changing the cation changed the well distribution.
This understanding could help control the distribution, composition, and orientation of 2D-layered perovskites, properties that influence device performance. The results could be applied to any such material. The researchers say, “This work paves the way toward engineering higher quality materials for more efficient and stable optoelectronic devices.”
This work was published in a recent issue of Nature Materials. My name is Bob Braughler from the Materials Research Society.
For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Thank you for listening.