Scientists from the US Department of Energy’s Ames lab and their collaborators at Iowa State University have developed a new approach to generate hard-to-combine, layered heterostructured solids. Heterostructured materials, composed of layers of dissimilar building blocks, exhibit unique electronic and magnetic transport properties that are governed by quantum interactions between their structurally different building blocks, and open new avenues for electronic and energy applications.
The technique for making them is simple and counter-intuitive: it consists of breaking up virgin materials to build new ones. Called mechanochemistry, the technique uses ball milling to separate structurally immeasurable solids – those that have no corresponding atomic arrangements – and reassemble them into three unique three-dimensional (3D) “misfit” heterogeneous assemblages. Breaking things together by milling appears to be the least plausible way to achieve atomic order, but it turned out to be more effective than the scientists themselves had imagined.
“A colleague of mine pointed out that our ideas would be either naïve or brilliant,” said Viktor Balema, senior scientist at the Ames lab. “Some time ago, we discovered the stochastic rearrangement of layered metal dichalcogenides (TMDCs) into 3D hetero-assemblies during mechanical milling. This completely surprised us and sparked our curiosity about the possibility of atomic ordering by mechanochemical processing. “
Metal chalcogenides are often unique in their properties and uses. They can display remarkable electron transport behaviors ranging from complete absence of electrical conductivity to superconductivity, photo- and thermoelectric properties, mechanical flexibility and, in particular, the ability to form stable two-dimensional monolayers, heterostructures three-dimensional and other quantum materials at the nanoscale. .
‘Mismatched layered compound nanostructures (MLCs) in the form of nanotubes, nanofilms (ferecrystals) and exfoliated sheets have been studied for over a decade and offer a rich area of research and possibly exciting applications as well. in renewable energy, catalysis and optoelectronics, said Reshef Tenne of the Weizmann Institute of Science, Israel, and expert in the synthesis of nanostructures. “One obstacle to their large-scale application is the high temperature and lengthy growth processes, which are prohibitive for large-scale applications. The mechanochemical process developed by the Balema group at Ames Lab, in addition to being scientifically stimulating, brings us one step closer to the realization of concrete applications for these intriguing materials.
Typically, these complex materials, especially those with the more unusual structures and properties, are made using two different synthetic approaches. The first, known as top-down synthesis, uses two-dimensional (2D) building blocks to put them together, using additive manufacturing techniques. The second approach, broadly defined as bottom-up synthesis, uses step-by-step chemical reactions involving pure elements or small molecules that deposit individual monolayers on top of each other. Both are laborious and have other drawbacks such as poor scalability for use in real world applications.
The Ames lab team combined these two methods into a single mechanochemical process that simultaneously exfoliates, disintegrates and recombines the starting materials into new heterostructures even though their crystal structures do not fit well (i.e. unsuitable). Theoretical calculations (DFT), supported by the results of X-ray diffraction, scanning transmission electron microscopy, Raman spectroscopy, electron transport studies and, for the first time, resonance experiments solid state nuclear magnetic resonance (NMR), explained the mechanism of the reorganization of precursor materials and the driving forces for the formation of new 3D heterostructures during mechanical processing.
“Solid state NMR spectroscopy is an ideal technique for the characterization of powdered materials obtained from mechanochemistry,” said Aaron Rossini, scientist in the Ames laboratory and professor of chemistry at Iowa State University. “By combining the information obtained from solid state NMR spectroscopy with other characterization techniques, we are able to obtain a complete picture of 3D heterostructures. ”
Reference: “Unprecedented generation of 3D heterostructures by mechanochemical disassembly and reorganization of immeasurable metal chalcogenides” by Oleksandr Dolotko, Ihor Z. Hlova, Arjun K. Pathak, Yaroslav Mudryk, Vitalij K. Pecharsky, Prashant Singh, Duane D. Johnson, Brett W. Boote, Jingzhe Li, Emily A. Smith, Scott L. Carnahan, Aaron J. Rossini, Lin Zhou, Ely M. Eastman and Viktor P. Balema, June 12, 2020, Nature Communication.
DOI: 10.1038 / s41467-020-16672-0
The experimental synthesis work was carried out under the auspices of the 2019 Laboratory-Led Research and Development Program (LDRD) at the Ames Laboratory. Theoretical support, solid state NMR spectroscopy, efforts to characterize structural and physical properties were funded by the US Department of Energy (DOE) Office of Science.
Ames Laboratory is a national laboratory of the United States Department of Energy, managed by Iowa State University. The Ames laboratory creates innovative materials, technologies and energy solutions. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global problems.
The DOE’s Office of Science is the largest supporter of basic research in the physical sciences in the United States and works to address some of the most pressing challenges of our time.