Symposium EQ03: Plasmonics, Nanophotonics and Metamaterials—From Design to Applications

Teri W. Odom, Northwestern University

Beyond Band-Edge Lasing: Plasmonic Lattices with High-Gain Materials

Written by Rosemary Calabro

Lasers are an important tool that provide large amplifications of light. In general, they require a gain material to amplify light as well as a cavity to confine the gain length of radiation prior to emission. Nanoscale lasing has potential for many applications such as facial recognition, virtual reality displays, and integrated circuits; however, their implementation requires control of the properties of the emitted light including the phase, intensity, and polarization. Teri Odom presented research from her group that combined arrays of metal nanoparticles combined with quantum dot films. The metal nanoparticles exhibit a phenomenon called localized surface plasmon resonance (LSPR) which allows for fields to be highly localized at the particle surface. The quantum dot films act as promising gain medium due to their high photoluminescent quantum yields, size control and tunability, and processability from solution phase. Odom’s group explored various parameters such lattice spacing of the metal nanoparticles, quantum dot film thickness, the addition of shells, and alternative gain materials such as perovskites, and they demonstrated control over properties such as lasing direction and polarization of the emitted radiation. In conclusion, Odom addressed how moving forward her group aims to produce continuous wave electrically pumped nanoscale lasers.

Symposium NM03: Colloidal Quantum Dots for Emerging Technologies

Rafik Naccache, Concordia University

Carbon Quantum Dots—A Sustainable Nanoplatform in Sensing and Energy Applications

Written by Rosemary Calabro

Carbon quantum dots are a unique class of optically emissive nanomaterials that are composed mainly of carbon, oxygen, and hydrogen. Unlike their inorganic quantum dot counterparts, carbon dots do not require ligands to coordinate and stabilize them, and they are highly dispersible in water, very stable, can be dried, and can have low cytotoxicity and good biocompatibility. The emission mechanism has puzzled researchers for some time as they try to answer the question of whether carbon dots are molecule like or quantum dot like. It turns out that they can be both and their emissive properties depend highly on their synthesis conditions that include both top-down or bottom-up strategies. Additionally, the fluorescence properties can be further tuned by incorporating other atoms such as nitrogen, sulfur, and boron, and also by changing the precursor materials. Rafik Naccache presented a type of carbon dot that his group synthesized that has both blue and red emission bands when excited at 405 nm. He determined that the carbon dots had a core–shell like structure and that the blue emission originated from the core, while the red emission originated from the shell. Interestingly, the red band was able to be quenched upon exposure to different metals, while the blue band remained unchanged which allowed these carbon dots to be used for applications such as ratio-metric sensing. Certain samples also showed selectivity toward sensing metal cations such as mercury or lead which shows promise for applications such as water purification and water sensing. The carbon dots also showed ratio-metric temperature selective photoluminescence which could be used for monitoring temperatures in cells. Naccache also presented data showing promise for using the surface states of the carbon dots for catalyst applications. In general, this talk highlighted the broad range of applications of carbon dots as well as challenges in both characterization understanding the emission mechanism.

Symposium EQ01: Progress in Thermoelectrics—From Traditional to Novel Materials

Leah Borgsmiller, Northwestern University  

Low Thermal Conductivity and Thermoelectric Performance of Zintl Yb₁₀MnSb₉

Written by Mohamed Atwa

Leah Borgsmiller gave an informative talk detailing novel transport measurements on a newly discovered Zintl phase. She highlighted the complexity of the Yb-Mn-Sb phase space. The goal of her work was to explore the thermoelectric properties of this newly discovered phase. She detailed the synthesis process of the Yb₁₀MnSb₉ using a solid state reaction route that employed both ball milling and hot pressing. Measurements of the electronic properties revealed that Yb₁₀MnSb₉ was a small bandgap semiconductor, consistent with the limited existing literature on this material. She also presented on the thermal conductivity of this phase, showing that the Yb₁₀MnSb₉ had exceptionally low thermal conductivity, a favorable property for thermoelectric performance. Using the electrical, thermoelectric, and thermal conductivity data, Borgsmiller showed an experimentally determined figure of merit for the Yb₁₀MnSb₉. She used the quality factor metrics of Yb₁₀MnSb₉ to illustrate that further enhancement of the thermoelectric performance of Yb₁₀MnSb₉ was possible. Borgsmiller concluded by detailing her discovery of a Yb-free Mg analog of this phase. She gave a future outlook of zT enhancements that may be possible in Yb₁₀MnSb₉ through Na-doping.

Shaping Policy as a Scientist - MRS Government Affairs Committee

MRS TV talks to Loucas Tsakalakos, Chair of the MRS Government Affairs Committee and Glenn Ruskin, MRS Government Affairs Principal, about the role of MRS and materials scientists in developing effective public policy. MRS encourages those in the materials science and engineering community to contact their governmental representatives via Materials Voice at https://www.mrs.org/materials-voice.

 

MRS Award Recipients Lightning Talks and Panel Discussion

Written by Don Monroe

Suveen Mathaudhu of the Colorado School of Mines, chair of the MRS Awards Committee, moderated the Lightning Talks session featuring award recipients. The MRS awards encompass eminent researchers with a lifetime of achievements as well as researchers just embarking on their careers. Mathaudhu encouraged listeners to consider nominating deserving colleagues, especially those from underrepresented groups.

Each of the six award recipients presented eight-minute highlights of the recognized research. These presentations were followed by a brief panel discussion.

Lightning Talks

Chad A. Mirkin of Northwestern University was awarded the MRS Medal “for the invention and implementation of nanoparticle mega-libraries for materials discovery.” He and his colleagues have developed a “new approach to materials discovery”: scanning-probe techniques to deposit huge arrays of attoliter or smaller “polymer nanoreactors,” whose composition or size systematically varies with position. Thermal treatment produces nanoparticles of metal alloys, metal oxides, sulfides, and other materials. The resulting “megalibraries” contain millions or even billions of compositions, more than have been characterized in history, Mirkin said, with “a lot of shots on goal.” Among the successes to date are the identification of new catalysts for nanotube growth and metal-alloy nanoparticles with two distinct phases. Taking full advantage of the libraries also requires corresponding automated characterization tools. The resulting high-quality “first-person” data is now being used to train machine-learning systems to help explore the “matterverse,” Mirkin said.

The Materials Theory Award was granted to George Schatz of Northwestern University “for pioneering theoretical advances in the properties of plasmonic nanostructures, self-assembly models for soft materials, and the discovery of lattice plasmon polaritons.” Plasmons, the collective oscillations of conduction electrons, give rise to dramatic absorption peaks for colloids of metal particles. The size dependence of this effect is well-predicted by Mie Theory, Schatz said. Arrays of nanoparticles also show a sharp spectral feature determined by their spacing, which can even lead to laser action. The resonant field enhancement associated with nanoparticles also leads to the well-known surface-enhanced Raman scattering, and affects absorption, fluorescence, resonant energy transfer, and nonlinear optics. For small nanoparticles, “Classical electrodynamics is sometimes not enough,” Schatz said. Quantum mechanics calculations can pick up the job for particles a few nanometers in size, however. These calculations are helping drive research in plasmon-driven chemistry, in which the optical energy is transferred to electrons to drive photochemical reactions.

Kelsey A. Stoerzinger of Oregon State University received the MRS Nelson “Buck” Robinson Science and Technology Award for Renewable Energy. Although renewable energy sources such as solar and wind are being much more affordable, getting their full benefits demands dealing with many other challenges, Stoerzinger said. One important aspect is storage of the intermittent energy, for example through liquid fuels or hydrogen generated from electrolysis. The efficiency of water splitting is limited by the oxygen evolution reaction at the anode, which currently drives the use of precious metal catalysts. Using an alkaline electrolyte “opens up a world of different transition-metal oxides that you can look at to drive this reaction instead,” Stoerzinger said, typically based on abundant metals like nickel, iron, and cobalt. She has been using surface-science tools to study highly controlled surfaces to clarify the role of crystal orientation, defects, and other details on the activity of potential catalysts.

The Kavli Foundation Early Career Lectureship in Materials Science went to Aaswath Raman, University of California, Los Angeles, who devoted his short talk to “thermal photonics.” The thermal radiation is “omnipresent,” but manipulating the spectral or direction dependence of materials’ emissivity makes new applications possible. For example, thermal emission aligned with the atmospheric transmission window, at wavelengths around 8 to 13 microns, can cool an object well below the ambient temperature. “This is not just research,” Raman said, but is being pursued for commercial use in cooling water. Such passive cooling could even be used to desalinate water through freezing, as opposed to the familiar but energy-intensive distillation. “There is actually hope for this technology to compete,” Raman said, with the familiar, energy-intensive distillation. Multiscale metamaterials can also enhance infrared emissivity of ultralight laser-propelled sails being explored for interstellar exploration. Raman also described layered structures exploiting epsilon-near-zero materials to control the direction of emissivity.

The MRS Postdoctoral Award is granted to two early-career researchers. One award went to Kenji Yasuda of the Massachusetts Institute of Technology “for the discovery of atomically-thin interfacial ferroelectricity in van der Waals heterostructures.” These structures are created from layers of two-dimensional materials, including combining different compositions. “We can stack these materials…to create artificial heterostructures that do not exist in nature,” Yasuda said. In particular, a pair of boron nitride layers, stacked in parallel, develops an out-of-plane electrical polarization whose direction depends on the alignment between the layers. Interlayer sliding switches the polarization, a mechanism he described as “quite unique.” This ferroelectricity persists up to room temperature, and nanosecond-scale switching suggests possible application as a memory. Ferroelectricity was also observed in layered dichalcogenides.

The other MRS Postdoctoral Award was given to Liang Feng of Northwestern University “for discovery of mechanisorption, a fundamentally new mode of adsorption.” Unlike physisorption and chemisorption, this new mechanism can operate far from equilibrium, Feng said. “Mechanisorption is totally different,” and can load a surface with very high, nonequilibrium concentrations of a molecule. Feng likened this nonequilibrium pumping to biological ATP-driven pumps that transport ions against concentration gradients. The work uses molecular rings that have a “mechanical bond” to a linear molecule that passes through them. Loading a ring is controlled by a chemical group on the chain whose charge state can be modified electrochemically or electrically. Feng and his colleagues have demonstrated one-way transfer process as well as the ability to transfer up to 10 rings onto a long collecting chain.

Panel Discussion

In response to an audience question in the brief panel discussion following the talks, the speakers all described failures they had experienced in their research. Such failures happen “every day,” Mirkin said.

But research surprises can also lead to serendipitous discoveries, they said in response to a query from Mathaudu. Mirkin noted that his well known dip-pen lithography technique was adapted from the frequently troublesome condensation of water in the vicinity of scanning-probe microscope tips. Schatz said that the initial study of arrays of metal particles was started to explore their interactions in close proximity. The wider spacings that led to dramatic polariton effects were investigated only for completeness. Researchers should not ignore unexpected results, Feng said, because they “might be something interesting.”

MRS acknowledges the generosity of Dr. Gwo-Ching Wang and Dr. Toh-Ming Lu  in endowing the MRS Medal and the Materials Theory Award. MRS acknowledges the generosity of Sophie Robinson for endowing this award in memory of her father, Nelson "Buck" Robinson. The Kavli Foundation is dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research and supporting scientists and their work. MRS acknowledges the Jiang Family Foundation and MTI Corporation for their generous contribution to support of the MRS Postdoctoral Award.

 

Symposium CH03: Advanced Characterizations of Heterogeneities in Electrochemical Energy Storage Materials

Binguyan Ma, Washington University in St. Louis

Microscopic Operando Diagnosis of Li Plating During Full Cell Fast Charging

Written by Aashutosh Mistry

While lithium-ion batteries have been commercialized for decades, in recent years, they are being deployed in unknown scenarios such as a very fast charging time of a few minutes as compared to more traditional charging that takes place over hours. The behavior of the underlying battery materials is still not fully understood under such new operating conditions. In this talk, Binguyan Ma and his colleagues show optical measurements of what happens to the graphite electrode, a typical negative electrode for lithium-ion batteries, when operated at faster rates. As lithium intercalates in graphite, it changes color and thus lithium intercalation in graphite can be probed via optical measurements. Ma’s experiments show the expected behavior at slow rates. But as faster rates are probed, distinct compositional gradients are observed along the electrode thickness. Additionally, they observe appreciable side reactions at the graphite–electrolyte interface in the form of irregular lithium deposition at this interface in addition to lithium intercalation in graphite. It would be interesting to use such optical experiments to see how different materials modifications change this behavior.

Symposium EN05: Solid-State Batteries—Life, Safety and Scalability

Gerbrand Ceder, University of California, Berkeley

The Complex Mechanisms that Create High Li-ion Mobility in Oxides and Sulfides

Written by Aashutosh Mistry

In recent years, there is a lot of buzz about solid electrolytes and how they are poised to replace the liquid electrolytes in state-of-the-art lithium batteries. While there have been considerable breakthroughs in materials development largely based on intuition, a game-changing idea is being able to systematically design such materials by picking atomic constituents. To be able to pursue such a rational design approach, we need to understand the connection between the underlying materials structure and the resultant lithium conduction behavior. Gerbrand Ceder and his group have been pursuing such overarching research using theoretical calculations. In this talk, based on detailed studies of exemplar lithium conducting solid electrolytes, Ceder outlined some of the principles that correlate specific geometrical features in the crystal structures of these materials that translate to superior conduction. Such principles are powerful as they can be easily used to accurately screen many solid electrolyte materials for conductivity without having to run expensive simulations to predict conductivity. With such formal rules, we expect a new theme of materials discovery for solid electrolytes.

Symposium SF04: Integrated Experimental and Modeling Approaches for Understanding Interfacial Effects at Different Physical Scales in Crystalline Materials

Avanish Mishra, Los Alamos National Laboratory

Analysis of Grain Boundary (GB) Structure and Dislocation – GB Interactions using Unsupervised Machine Learning

Written by Yasir Mahmood

The mechanical response of structural materials is influenced by grain boundary (GB) interaction with the dislocations. Naturally, this interaction is a function of local atomic environment, which has been characterized across several studies using structural units. Avanish Mishra and his team took a novel approach to the problem and characterized GB structures using strain functional descriptors (SFD). They coupled this characterization with unsupervised learning methods. Using SFDs, the researchers were able to decompose almost 5000 GBs into 6 classes. The dislocation interactions are analyzed using these classes. The researchers also looked at structural motifs within a cutoff distance for the GB structures and are currently building a database for motifs across different misorientation angles and respective metastable states.

Symposium EQ01: Progress in Thermoelectrics—From Traditional to Novel Materials

Dylan Kirsch, National Institute of Standards and Technology and University of Maryland

Discovery and Characterization of an Off-Stoichiometric Stability Region in Combinatorial (Nb,Ta)FeSb Half Heusler Thin Films

Written by Mohamed Atwa

Dylan Kirsch explored Ta-doped NbFeSb Heusler alloys as a compositionally complex alloy for thermoelectric applications. He employed a natural spread combinatorial deposition system together with high throughput thermoelectric characterization technique to test the thermoelectric properties of different compositions of his thin films. In addition, he reported on phase and stochiometric mapping of his spatially-varying film compositions using x-ray diffraction and µX-ray fluorescence spectroscopy, respectively. Using Rietveld refinement, Kirsch highlighted the key role of Fe and Sb excess or deficiency on the resulting electrical and thermoelectric properties of the thin films. A region of off-stoichiometric phase was identified having properties that agree well with the values of bulk (Nb,Ta)FeSb from literature. He then detailed his efforts to more tightly control the compositions of his films using a more sophisticated deposition technique known as discreet pad combinatorial sputtering. Kirsch is interested in developing a scanning frequency domain thermoreflectance (FDTR) instrument to measure the thermal conductivity of the films and intends to conduct height profiling of the thin films to determine the thickness-dependence of the bulk properties.

Symposium EN03: Beyond Li-Ion Batteries—Low Cost Alternatives Based on Other Chemistries

Louis Sieuw, Empa—Swiss Federal Laboratories for Materials Science and Technology

Influence of Cathode Processing on Cycle Life and Performance of Sodium-Zinc Chloride Batteries

Written by Aashutosh Mistry

As the global demand for batteries increases due to our push for a more sustainable future, we have to discover new materials for many commercially existing technologies. Molten sodium nickel chloride battery (colloquially referred to as ZEBRA batteries) is one such successful battery, operating around 250^oC and offering stable operation over 4500 charge-discharge cycles. Interestingly nickel is 25% of the cell cost and with uncertainty in its supplies, we wish to replace nickel with cheaper, more abundant alternatives like zinc. However, this is not just as simple as swapping a red lego brick with a yellow one of the same type. We have to rethink multiple aspects of such batteries like reactions, stability, and performance. Louis Sieuw and his colleagues have been examining such aspects. In this talk, Sieuw showed how different zinc content alters the pathways for ionic and electronic transport. Interestingly, the commonly available particle morphology changes from filamentary to spherical once nickel is swapped for zinc. This morphological change further complicates the electrode microstructure, transport pathways, and cell performance. As the research progresses, it would be curious to see how the design of zinc electrodes differs from the present-day nickel electrodes for these batteries.