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

二维晶体形成了一类具有强大机械和电气性能的新材料，将改变我们制造计算机、光学探测器、化学或生物传感器等电子设备的方式。然而，因为它们只是一个单晶层（1-3个原子厚），它们的性质比它们的三维对应物对周围环境更敏感。支撑二维晶体的衬底，以及加工过程中引入或从空气中吸附的杂质会降低材料的性能，并威胁到应用的成功。二维晶体也对我们对二维电子输运的基本理解提出了挑战：许多这些材料清楚地显示出金属行为，但这与众所周知的二维电子输运理论（称为弱局域化）相矛盾。该项目的目标是了解缺陷和无序对器件性能的影响，并研究二维晶体中金属行为的根源。研究小组将结合电子输运测量和原子尺度成像来确定电子在二维晶体中无序存在时的行为。该项目支持两名研究生和多名本科生的教育和培训。它还通过在新罕布什尔大学为高中生和研究生举办的暑期研讨会来支持下一代研究人员的发展。研讨会的目标是通过为新研究人员提供实用信息和建议的主题，降低研究成功的障碍，有机会了解校园研究的多样性，并有机会亲自与同行和主要研究者联系。技术摘要：二维晶体在下一代电子产品中非常有吸引力，因为它们在物理上尽可能薄，机械上灵活，并且仍然具有强大的电子特性，包括在某些情况下，高载流子迁移率。它们也提供了一个机会来重新审视我们对二维电子输运的期望：许多这些材料清楚地显示出金属行为，但局域化理论预测二维中普遍存在弱局域化。本项目研究二维材料中金属-绝缘体量子相变的存在和性质，特别关注无序和非均质性的作用。该研究团队正在使用扫描隧道显微镜/光谱学与设备尺度的传输测量相结合，将二维材料的传输特性与空间不均匀性联系起来，因为它们被调谐无序和载流子浓度驱动到绝缘阶段。该团队的目标是揭示无序和非均匀性在量子金属-绝缘体转变中的作用，以及不同类型的无序在二维晶体器件中的重要性。

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.