Synthesis and Properties of Heterostructures Containing Magnetic 2d Layers Not Found As Bulk Compounds

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NON-TECHNICAL SUMMARYThe 2010 Nobel prize in physics was awarded for the discovery of novel properties in monolayers of compounds with two dimensional (2D) structures that are not present in the bulk compounds. The resulting field of science - 2D materials and stacked layers of 2D materials known as heterostructures - has exponentially expanded as theorists proposed new exotic properties and experimentalists discovered new properties in monolayers and heterostructures. Currently the preparation of heterostructures is done by cleaving bulk materials to the monolayer limit and stacking them in designed sequences. This approach is limited to constituents that are stable as bulk compounds which are cleavable. New synthesis approaches are needed that enable preparation of heterostructures at a wafer scale, that provide a wider selection of constituent layers, and that provide control over the nanoarchitecture (stacking sequence and thickness of constituent layers). In this project, with the support of the Solid State and Materials Chemistry and Ceramics Programs in the Division of Materials Research, Dr. David Johnson and his research group at the University of Oregon, will develop new synthetic approaches to preparing heterostructures containing 2D magnetic constituent layers with structures and compositions that are not thermodynamically stable as isolated compounds. Three different strategies, all of which use precursors with targeted composition profiles that match that of the targeted heterostructures, are being tested. This research program provides a broad technical background for graduate students in deposition technologies, thin film characterization techniques, and physical phenomena that occur in 2D heterostructures. This training enables them to thrive in a variety of future careers (high tech industries, academia, or national laboratories). Internships will provide an opportunity for graduate students to “test drive” future careers while expanding their knowledge base, leading to more productive researchers. Engaging undergraduate students in this research enables them to apply principles learned in classes to solve research challenges. Providing undergraduate research opportunities is a critical tool to increase the number and diversity of students pursuing science as a career. TECHNICAL SUMMARYWith the support of the Solid State and Materials Chemistry and Ceramics Programs in the Division of Materials Research, Dr. David Johnson and his research group at the University of Oregon will develop synthetic approaches to preparing heterostructures containing 2D magnetic constituent layers with structures and compositions that are not thermodynamically stable as isolated compounds. Synthetic targets include diselenides (TSe2) and rock salt structured Pb2+nT1+mSe3+n+m layers, where T = Cr, Mn, Fe and Ni. Three synthesis strategies, which use precursors with targeted local composition and nanoarchitecture to control nucleation and growth, are being tested. One strategy is to prepare a precursor designed such that one layer crystalizes as 2D sheets separated by amorphous layers of controlled composition. The resulting 2D form factor and composition of the interleaved amorphous layers as well as the structure of adjacent crystalline layers will be used to control the nucleation and growth of the metastable constituent layers. A second strategy will be to seed nucleation of the desired structures by controlling local composition. A third strategy will be to use charge transfer from an adjacent layer to stabilize the targeted structures. The companion constituents in the targeted heterostructures will be critical to controlling the reaction pathways for each of these strategies, and our list of potential constituents include piezoelectric (GeSe, SnSe), topological insulating (Bi2Se3, Bi2Te3), semiconducting (PbSe, MoSe2, SnSe2) and/or superconducting (NbSe2) layers. A rich collection of new materials with diverse and tunable emergent properties is anticipated.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.