The Materials Research Society held its Spring Meeting on April 17-21 in Phoenix, Arizona. See the highlights reported on social media by participants, presenters, and others as well as reports from additional MRS news sources.
David Prendergast, Lawrence Berkeley National Laboratory
Understanding the Nature of Chemical and Electrochemical Stability of Electrolytes at Mg Anode Surfaces
Written by Aashutosh Mistry
With depleting reserves for lithium, there has been an active interest in making successful secondary batteries using other alkali and alkaline metals. Magnesium is one of the competitors, given reasonably smaller size and high but not extreme reactivity (making it safer). In addition, experimentally no dendrites are observed on magnesium surfaces, in contrast to lithium metal where dendrite-free electrodeposition is more of a dream than reality.
There are two long-standing problems with Mg—unavailability of a good cathode host and search of a suitable electrolyte that would lead to desired Mg/electrolyte interface. David Prendergast of Lawrence Berkeley National Laboratory and his colleagues have been investigating the science of the Mg/electrolyte interface using a three-pronged approach that involves Ab initio molecular dynamics (AIMD) simulations, x-ray spectral interpretation of in situ chemical/electrochemical tests and condensed phase interfacial modeling. The research question addressed in this talk was whether a combination of good electrode (Mg) and good electrolyte would lead to a good interface, and possibly an interphase as well. They experimented with Mg symmetric cells using Mg(AlCl2BuEt)2 salt in tetrahydrofuran (THF) electrolyte. They found out that even under no electrochemical bias (i.e., open circuit situation), there is a formation of different magnesium compounds on the electrode surface—for example, oxides MgO, hydroxides Mg(OH)2, and carbonate MgCO3. From molecular simulations, the researchers revealed that such reactions are only possible given surface defects on the electrode and which can subsequently lead to electrolyte decomposition. At this stage, they are involved in further electrochemical testing and equivalent modeling. The overall study is of extreme importance and should help identify suitable materials for Mg battery.
Andres Vasquez Quintero, Ghent University
Fabrication of Fixed-Shape Soft Smart Objects by Thermoplastic Forming of Flat Stretchable Circuits
Written by Akshay Phadnis
An increasing interest in stretchable, controlled shape polymer has inspired Andres Vasquez Quintero of Ghent University to develop shape-retaining electronic circuits. These circuits are based on elastic circuits with substitution by thermoplastic polymer carrier. Most importantly, these circuit systems are supposed to take a predetermined shape in the absence of any external force, for example, smart lenses (to replace the bi-focal glasses) or shoe in-soles. A flexible electronic circuit capable of stretching and deforming is first developed and then molded into the desired shape using a thermoforming process using suitable molds. Smart lenses developed using this methodology were demonstrated. Various challenges faced in the development of these lenses such as wrinkling were discussed in detail. These dynamic lenses can be tuned to be adaptable to environmental condition using LCD monitors to develop tunable lenses.
Kenneth C. Manning, Arizona State University
Super-absorbing Polymers for Breathable and Self-Sealing Smart Hazmat Suits
Written by Akshay Phadnis
Superabsorbent polymers are a special class of stimuli-sensitive polymers that undergo multifold swelling upon contact with the suitable solvents. Kenneth C. Manning of Arizona State University proposes to use such polymers in developing breathable, self-cleaning hazmat suits for use in chemically hazardous environments. If the polymer is tuned to be swelling when in contact with these chemicals, the swelling property of the polymers can be utilized to reduce the permeability of the chemicals. Since the suits will be “breathable” at all other times, there is no need of separate cooling mechanics to regulate the body temperature, which otherwise is needed in the case of current hazmat suits. The swelling phenomenon of the polymer is characterized experimentally in terms of swelling ratio, swelling time, and repeatability for selected choice of solvents. A finite element-based mathematical model is also implemented to represent the swelling. Using this model, various configurational studies can be done to design the shape and size of the polymer matrix. Also, since these polymers need to be combined with the wearable suits, an optimized method to develop a polymer-fiber matrix can be designed using this model. Use of this selective, self-breathable hazmat suit will bring a new future to the hazmat suits in chemical warfare.
Chong-Yu Ruan, Michigan State University
In situ imaging of complex phase transitions in functional transition metal compounds at ultrafast timescales
Written by Trevor Clark
In high speed imaging only a small amount of the light/electron information can be captured. A high intensity brightness is required to be able to distinguish what is in the image. This is easy enough to do for light imaging by just adding more photons; however, it is not as simple for electrons: if packed into high densities their charges repel each other resulting in greatly reduced spatial resolution. This space-charge effect can be corrected by radio frequency (RF) longitudinal lenses, and allows for the capability of imaging extremely fast processes. These RF cavities allow for correction of temporal and spatial anomalies by changing the high-volume electron flow from turbulent to laminar. This retains benefits of increased brightness from increased dose, while limiting the negative resolution impacts from the space-charge effect. This lens setup has been used to study the ultrafast phase transitions in transition metal dichalcogenide systems, and is a promising tool for advanced materials characterization at the ultrafast time scale.
Khalid Hattar, Sandia National Laboratories, Boise, Idaho
In situ Ion Irradiation Dynamic TEM
Written by Trevor Clark
Understanding radiation effects at a microstructural level is important on many scales. A microchip in close proximity to a nuclear reactor needs to be very reliable and components on spacecraft also have the need for reliability. Khalid Hattar of Sandia National Laboratories in Boise, Idaho is working with industry to develop setups to allow for radiation sources within a transmission electron microscope (TEM) to dynamically, in real time, view the effects of radiation on the microstructure at the nanometer scale. The radiation is ionic gold particles that are accelerated to high speeds within the machine; this means that the particle–material interactions can occur at very short time scales, on the order of 10–100s of nanoseconds. Hattar and his team have made many optimizations to retain the high spatial resolution, tune the radiation to single particle events, and have a high time resolution. The camera and detectors are optimized for stability and resolution. This set up allows for many in situ TEM experiments that will offer much needed insight into a variety of nanoscale processes.
Yan-qing Lu, Nanjing University, China
Microfiber-Based Microcavities and Miniaturized Fiber Stereo Devices
Written by Akshay Phadnis
Microcavities based on optical microfibers are significant in fiber electronics because of their strong confinement, large evanescent field, flexibility, low-loss connection, and configurability. The one-dimensional (1D) approach involves methods such as Bragg grating for producing micro-cavities on the microfiber surface. Yan-qing Lu of Nanjing University explains the importance of optical force in these fibers, wherein force due momentum change of photons is considered. As compared to 1D, the three-dimensional resonator can be developed by a 2D graphene sheet coiled and put inside a 3D cavity of spiral microfibers. These kinds of special resonators, miniaturized fiber stereo device (MFSD), result in increased interaction length, with high modulation efficiency and hence find applications in optical modulation for optical signal processing. This type of miniaturized fiber stereo, in-line, all-optical modulator has potential in fiber optical communications, in which there are demands for high-speed, wideband, low-cost, and integrated methods to modulate information.
Gerald Brady, University of Wisconsin-Madison
Pengcheng Chen, Northwestern University
Fudong Han, University of Maryland
Won-Kyu Lee, Northwestern University
Qiyang Lu, Massachusetts Institute of Technology
Ye Shi, The University of Texas at Austin
Aditya Sood, Stanford University
Ye Zhang, Fudan University
Swetha Barkam, University of Central Florida
Nigel Becknell, University of California, Berkeley
Michael Christiansen, Massachusetts Institute of Technology
Sujay Desai, University of California, Berkeley
Arko Graf, Heidelberg University
Won Jun Jo, Massachusetts Institute of Technology
Yanxi Li, Virginia Tech
Jinxing Li, University of California, San Diego
YunHui Lin, Princeton University
Siying Peng, California Institute of Technology
Tyler Schon, University of Toronto
Yude Su, University of California, Berkeley
Lixin Sun, Massachusetts Institute of Technology
Katalin Szendrei, Max Planck Institute for Solid State Research, Ludwig-Maximilians-Universität Munich
Achim Woessner, ICFO - The Institute of Photonic Sciences
Shuozhi Xu, Georgia Institute of Technology
Zichao Ye, University of Illinois at Urbana-Champaign
Zhengshan Yu, Arizona State University
Jie Zhao, Stanford University
Electron Microscopy and Spectroscopy of Low-Dimensional Materials at the Single Atom Level
Written by Aditi Risbud
On Thursday afternoon, Kazutomo Suenaga of the National Institute of Advanced Industrial Science and Technology in Japan gave the last Symposium X presentation of the week. His talk focused on single-atom spectroscopy and single-molecule imaging of low-dimensional (1D, 2D) materials.
Suenaga uses electron microscopy and spectroscopy to characterize materials atom by atom. What began as his “science dream from a long time ago” has now become a set of analytical tools to understand the physical and chemical properties of single atoms.
In particular, Suenaga and his team use electron energy-loss spectroscopy (EELS) to discriminate between individual atoms in low-dimensional materials, whether they are different atoms, or identical atoms in excited states or with different spin properties.
Unlike in 3D or bulk materials, defects have significant impact on the properties of low-dimensional materials. Without accurate characterization techniques, the behavior of devices based on low-dimensional materials such as graphene cannot be understood or controlled.
During his talk, Suenaga outlined several examples in various carbon nanostructures using EELS to examine structural imperfections such as defects, impurities, edges, or boundaries. EELS provides an “atomic size probe” to image a material and if the sample is thin enough, obtain some optical absorption information as well.
There are challenges to single-atom spectroscopy, including weak inelastic scattering from electrons, localized signals, and specimen damage. To overcome these difficulties, Suenaga has designed a high-resolution, low-voltage electron microscope that produces high-quality images without destroying a sample. This microscope can resolve a carbon–carbon bond at 30 keV and generate spectroscopic data from individual molecules or atoms.
“Low-voltage microscopes are very good for low-dimensional materials characterization because we can identify each element, even lighter elements such as lithium,” Suenaga concluded.
Symposium X lectures are aimed at a broad audience to provide meeting attendees with an overview of leading-edge topics.