Multidisciplinarity key to solving today’s problems

Hortense Le Ferrand, the MRS Bulletin Postdoctoral Publication Prize recipient from Nanyang Technological University in Singapore, writes a blog post to Materials Connect on research reported at the 2019 MRS Spring Meeting in Phoenix, Ariz. that “illustrates well why and where multidisciplinarity can foster scientific breakthroughs and technological innovations.”

“For example,” she writes:

“during the characterization of materials at the nanoscopic level, in 3D, and while performing a dynamic motion or a chemical reaction, do we not need to have excellent detectors with ultra-high resolution? To use the new biomarker sensing strategies in a real-life application that can really make a difference in population with limited access to health care, do we not need the advice of medical doctors, health workers and the target population as well? To develop coatings for our boats that prevent the adhesion of barnacles on their hull, do we not need first to understand at a biological, molecular and mechanical levels, how they attach underwater to flat surfaces?” Read more

Symposium ES04: Solid-State Electrochemical Energy Storage

Miaofang Chi, Oak Ridge National Laboratory

Electron Microscopy for All-Solid-State Batteries—Addressing Challenges at Atomic Scale

Written by Aashutosh Mistry

Battery science has seen a fundamental shift in recent years toward the use of solid electrolytes. Conventional liquid electrolytes cause a conformal contact at the electrode–electrolyte interface, which switches to intrinsically nonconformal solid–solid contact in the newer setting. However, the issues with the solid electrolytes extend beyond this geometrical nonconformity, and in order to investigate the fundamental origins of electrochemical limitations the state-of-the-art characterization tools are insufficient since they were designed explicitly for solid–liquid electrochemical contact. Thus, there is an urgent requirement to invent (or modify) a host of characterization techniques for this new class of electrochemistry.

Miaofang Chi and her colleagues at Oak Ridge National Laboratory have been advocating the use of in situ functional imaging—electron-microscopy techniques posing requisite scientific merit. She emphasized that the primary bottleneck in solid-state electrochemistry is the myriad set of interfacial phenomena, namely, instability, impurity, elemental diffusion, and space charge, for instance. In one of the examples, the researchers explored the grain boundary resistivity for two different solid electrolytes (LLTO and LLZO, lithium lanthanum titanium oxide and lithium lanthanum zirconium oxide) and found that the LLZO grain boundaries exhibit similar chemical composition as the grains, while LLTO grain boundaries are lithium-deficient which explains a greater grain boundary resistance in LLTO. Another puzzling observation had been the relative stability of Li–LiPON (another solid electrolyte) interface. The researchers’ in situ observation of Li and LiPON contact showed that a chemical reaction takes place upon contact between the two solids which results in a new interphase between the two. This interphase is stable over the electrochemical operation and is the root cause for extended cycling. Upon elemental mapping using EELS (electron energy-loss spectroscopy), it was revealed that this interphase represents the decomposition of LiPON into Li3N, Li2O, and Li3P. The developed techniques are suitable for different types of 4D (space and time) in situ investigations of solid–solid electrochemistry.


Symposium CP04: Interfacial Science and Engineering—Mechanics, Thermodynamics, Kinetics and Chemistry

Ricardo Castro, University of California-Davis

Nano-scale Effects on Grain Growth—Grain Boundary Energy and Velocity in Magnesium Aluminate

Written by Aashutosh Mistry

Most of the materials of engineering relevance are polycrystalline in nature. Desired properties of such materials strongly depend on the underlying grain structure, making the study of grain formation and growth scientifically important. With advances, it has become possible to create a grain structure with nanosized grains. Nanograins possess lucrative characteristics of increased grain boundary density, greater resistance to dislocation movement, and equivalently higher mechanical strength. At such small dimensions, interfacial effects are expected to play a crucial role; however, such effects remain poorly understood.

Ricardo Castro and his research group have been investigating the nanoscale effects on grain growth. The essential question is: do nanosized grains grow differently than the microsized ones? The researchers studied MgAl2O4 spinel as a model system. Since the grain growth is a thermally activated process, they carried out DSC (differential scanning calorimetry) measurements over different temperature ranges to obtain different average grain sizes. Over the course of such experiments, the heat release due to grain growth recorded which in turn gives a measure of surface energies for different grain sizes. Their experiments demonstrate higher surface energies for smaller grains and approaching to the nominal value for microsized grains. Their ongoing work deals with identifying the origins of such excess surface energy.

Symposium SM01: Materials for Biological and Medical Applications

Caroline Ajo-Franklin, Lawrence Berkeley National Laboratory

Living Foundations: Programming Cells to Synthesize Hierarchically Ordered Materials

Written by Gargi Joshi

Structural hierarchy found in nature imparts several survival characteristics to organisms including high toughness as observed in shells, bones, and teeth to prevent crack propagation. The components involved are a mix of hard and soft features across multiple length scales. We as researchers learn from such examples and try to mimic nature by synthesizing such materials but understanding of the key processes has not been unveiled. Caroline Ajo-Franklin is trying to assess the mechanisms by using a bottom-up synthesis of assembling engineered living systems similar to nacre (pearl from mollusks). Synthetic biology provides this scope as two strains having different properties of surface attachment were associated together by artificial engineering. The designed combination demonstrated behavior of a hydrogel similar to that in living systems. Not only this, but the behavior can be dynamically modified by altering the crosslinking densities in the hydrogel to display switchable mechanical properties.

Symposium QN03: 2D Materials—Tunable Physical Properties, Heterostructures and Device Applications

Clarissa Towle, University of California, Berkeley and Lawrence Berkeley National Laboratory

4D STEM Study of Au-Induced Epitaxial Strain in Few- and Monolayer MoS2

Written by Bharati Neelamraju

Associated with both UC Berkeley and Lawrence Berkeley National Lab (LBNL), most of Clarissa Towle’s work was done at LBNL using the four-dimensional (4D) scanning transmission electron microscope (STEM). Towle explains that this microscopy is 4D because the microscope scans a 2D array of 2D diffraction patterns of a given sample. She works on the epitaxial growth of gold on 2D transition metal dichalcogenides (TMDCs) to understand the role of strain on the top layer of a stack for opto-electronic device fabrications. Towle emphasized the fact that this technique uses about 2000 images or more to provide precise useful data. The researchers also use neural networks to increase the pace of their “Big Data” set analysis. They teach the neural network about the diffraction patterns of the gold on TMDCs. While the neural network gives the basic lattice diffraction peaks, it still does not understand all the nuances and says the same. Her excitement connected with the 4D STEM images and the data they have so far was contagious.

Symposium ES15: Fundamental Understanding of the Multifaceted Optoelectronic Properties of Halide Perovskites

James Sadighian, University of Oregon

In Situ Transient Absorption Spectroscopy of Perovskite Nanocrystal Formation and Growth

Written by Gargi Joshi

Perovskite nanocrystals (NC) have attracted significant interest due to their tunable properties and applicability in light-emitting diodes, lasers, and optical sensors. Usually it is difficult to use time-resolved spectroscopy techniques with the fast synthesis rate of preparation of NCs as well as the unstable nucleation centers behaving as nascent nanocrystals. In order to modulate the functional electronic properties of these particles it is of utmost importance to be able to clarify development of the excited stable dynamics during their formation. James Sadighian prepared methylammonium lead halide perovskite NCs by a ligand-mediated NC synthesis comprising of reaction timescales favorable for study via transient absorption spectroscopy. With this room temperature synthesis initiated by solvation of the precursors with passivating ligands, Sadighian has done first known characterization of immature perovskite NCs in the dynamic unstable state. Future work includes measurement of the growth of these NCs in real-time using the single-shot transient absorption spectrometer, which can give entire transient results in a few seconds.

Symposium ES04: Solid-State Electrochemical Energy Storage

Jan Allen, US Army Research Laboratory

Synthesis and Characterization of Fast Li-ion Conducting Solid State Electrolytes

Written by Aashutosh Mistry

Solid electrolytes represent a key research area in lithium batteries for a safer future. Many different solid electrolytes have been invented in recent years with the primary aim of matching ionic conductivity to their liquid counterparts. Most of the electrolytes are poor ion conductors in their pristine form, and elemental doping appears to be an effective strategy to advance these materials. Toward that end, Jan Allen and his collaborators have studied various different solid electrolytes and their subsequent substitutions to assess the relative usefulness. They identified that a reduction of titanium Ti4+ is an issue for perovskite (e.g., LLTO lithium lanthanum titanium oxide) and NaSICON (e.g., LATP lithium aluminum titanium phosphate) type electrolytes. On the contrary, zirconium-based solid electrolytes, specifically LZP (lithium zirconium phosphate) and LLZO (lithium lanthanum zirconium oxide) are more stable. Both these materials are amenable to substitution via other cations (calcium, yttrium, aluminum, tantalum, gallium, etc.) and provide increased conductivity. For example, consider substitution to LLZO structure via Ta, Al, and Ga. Ta replaces Zr sites and changes the unit cell, Ga has an octahedral site preference, and Al prefers tetrahedral sites (which competes with Li). Ta-doped LLZO has higher conduction than Ga-doped and Al-doped is inferior given the competition of Al with Li distribution. Such experiments provide valuable design rules for choosing solid electrolytes and appropriate substitutions.

Symposium CP04: Interfacial Science and Engineering—Mechanics, Thermodynamics, Kinetics and Chemistry

Shen Dillon, University of Illinois

Oxide Grain Boundary Deformation and Failure Characterized by In Situ TEM

Written by Gargi Joshi

Along with synthesis and preparation of metal oxide incorporating materials comes defects and dislocations. In this regard the grain boundaries in these metal oxides tend to significantly affect the final mechanical response. The major concern is their weak presence in the bulk, which causes deformations/fractures. The influence is observed in bulk polycrystalline measurements and poses difficulty in assessing individual contributions. Shen Dillion has done single interface measurements at a small scale using the technique of in situ TEM. This contributed in determining the fracture energies from real interfaces in the polycrystals and answers the characterization of interface mechanics. Dillon specially focused on the factors of grain boundary sliding and grain rotation inversing the stress response (Hall-Petch strengthening) in such materials.

Symposium QN04: Nanoscale Heat Transport—Fundamentals

Pierre-Olivier Chapuis, CNRS - INSA Lyon

Scanning Thermal Microscopy—Probing Temperature and Heat Dissipation Down to the Few-Nanometers Scale

Written by Bharati Neelamraju

Pierre-Olivier Chapuis covered the use of scanning thermal microscopy, which is based on the concept of atomic force microscopy but with heat. This technique has applications at micro- and nanoscale levels of samples where the researchers can characterize local thermal conductivity, local melting temperature, and local heating in ICS, for example. Some other uses of this technique include nano-lithography and data storage. This technique competes with other optical methods and has a shortcoming when the sample roughness is too high. Chapuis showed that in their laboratory, SThM is used under varying environments that include vacuum, a homemade SEM system, and a homemade cryo cooled sample. Chapuis discussed the sensitivities of a microprobe and a nanoprobe with varying materials and emphasized the need for proper calibration. He showed that as of now, thinner samples had a higher error bar while thicker samples had very precise measurements. He emphasized that SThM makes measurements in the cross plane direction while most other techniques only do it in the in-plane direction of the sample. The final dream of this project is to be able to take precise thermal conductivity measurements with no contact under vacuum. From theoretical calculations the researchers compute a flux between probe and sample that gives a spatial resolution for non-contact SThM to be approximately 10 nm.

Symposium EP13: Thermoelectrics—Materials, Methods and Devices

Hyejeong Lee, Gwangju Institute of Science and Technology

Enhanced Thermoelectric Performance of PEDOT:PSS Nanotubes via AAO Template-Assisted Growth

Written by Bharati Neelamraju

Hyejeong Lee works with Ji Young Jo on using variations of PEDOT:PSS for thermoelectric applications. Lee addressed how conducting polymers are a good choice for wearable thermoelectric devices like thermoelectric generators (TEG). She said PEDOT:PSS is one of the highest conductivity polymers but that it still suffers from low thermoelectric efficiencies compared to their inorganic counterparts. The researchers fabricated PEDOT:PSS nanotubes in a template for enhanced thermoelectric efficiencies. They saw an increase in electrical conductivity due to the stretching of PEDOT chains as well as the decrease in thermal conductivity through phonon scattering in these nanotubes made in their laboratory. They achieved better efficiencies by adding post processing treatments and adding a solvent to these thin films. Lee concluded her talk by explaining to the audience why heading toward low-dimensional nanotubes is an interesting path forward for these materials.