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.
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.
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.