Nanoscale electromechanical coupling in atomically thin materials

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Nontechnical Description: Structural deformation of materials, such as bending or wrinkling, can lead to dramatic changes in their electronic properties. The project explores these effects in so-called two-dimensional materials, such as molybdenum disulfide and tungsten diselenide, that are only a few atoms thick, and that therefore inevitably suffer from structural deformation due to their extreme mechanical flexibility. The research focuses on using advanced microscopy techniques to measure and analyze electric charge and voltage distributions that arise in the presence of deformations in two-dimensional materials through effects such as piezoelectricity. These effects play a central role in devices and technologies for computing and communications that are based on such materials, including proposed approaches for quantum information processing. Research on this topic is closely integrated with activities in education and outreach. In particular, an activity focusing on design and construction of simple optical microscopes based on Legos or three-dimensional printed components combined with extremely inexpensive, readily purchased plastic optical components provides diverse populations of elementary school students with a new window into both the power of imaging in exploring their worlds, and modern manufacturing technologies such as three-dimensional printing.Technical Description: The project focuses on fundamental studies of electromechanical coupling phenomena - piezoelectricity and flexoelectricity - in atomically thin transition metal dichalcogenide materials. Three primary directions are emphasized. First, the project explores characterization and analysis of electromechanical coupling, in both in-plane and out-of-plane directions, in mono- to several-layer thick transition metal dichalcogenides using piezoresponse force microscopy. Second, the project uses exfoliation and layer transfer techniques to create bilayer transition metal dichalcogenide homojunctions and heterojunctions with reduced symmetry compared to the corresponding bulk materials to assess possibilities for engineering electromechanical response via control over the composition and symmetry of bilayer van der Waals homostructures and heterostructures. Proximal probe characterization of these structures provides insight into nanoscale electromechanical response associated with local symmetry in bilayers with different layer compositions and rotational alignments. And third, the project combines computational modeling with experimental measurements to analyze the implications of electromechanical coupling at the nanoscale for functional electronic and photonic structures based on atomically thin transition metal dichalcogenide materials in which highly inhomogeneous strain distributions are present. By exploring fundamental issues pertaining to piezoelectricity and flexoelectricity at nanoscale dimensions, the research provides new information about and insights into the nature, magnitude, and technological implications of these effects through direct experimental characterization combined with computational modeling.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.