Revealing the role of inhomogeneities and disorder in 2D materials: Correlating transport with spatial and electronic topography

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Non-technical AbstractTwo-dimensional crystals form a new class of materials with robust mechanical and electrical properties, primed to change the way we build electronic devices for computers, optical detectors, and chemical or biological sensors. However, because they are only a single crystalline layer (1-3 atoms thick), their properties are more sensitive to their immediate environment than their three-dimensional counterparts. Substrates that support the 2D crystal, and impurities introduced by processing or adsorbed from the air degrade the performance of the material, and threaten the success of applications. 2D crystals also present a challenge to our fundamental understanding of electronic transport in 2D: many of these materials clearly show metallic behavior, but this is in contradiction with a very well-known theory of 2D electron transport called weak localization. The goals of this project are to understand the impact of defects and disorder on device performance and to investigate the roots of metallic behavior in 2D crystals. The research team will use a combination of electronic transport measurements and atomic-scale imaging to determine how electrons behave in the presence of disorder in 2D crystals. This project is supporting the education and training of two graduate students and a number of undergraduate students. It also supports the development of the next generation of researchers through summer workshops at University of New Hampshire for high school through graduate students. The goal of the workshops is to lower the barrier to success in research through topics that give new researchers practical information and advice, opportunities to hear about the diversity of research happening on campus, and a chance to personally connect with peers and principle investigators.Technical Abstract2D crystals are very attractive for use in next-generation electronics because they are as thin as physically possible, mechanically flexible, and still have robust electronic properties including, in several cases, high carrier mobility. They also present an opportunity to reexamine our expectations for electronic transport in 2D: many of these materials clearly show metallic behavior, but localization theory predicts weak localization universally in 2D. This project investigates the existence and properties of a metal-insulator quantum phase transitions in 2D materials, specifically focusing on the role of disorder and inhomogeneities. The research team is using scanning tunneling microscopy/spectroscopy coupled with device-scale transport measurements to correlate transport properties with spatial inhomogeneities in 2D materials as they are driven into the insulating phase by tuning disorder and carrier concentration. The team aims to uncover the role of disorder and inhomogeneities in quantum metal-insulator transitions and also the importance of different types of disorder in 2D crystal-based devices.