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

非技术摘要二维晶体形成了一类新的材料，具有强大的机械和电学性能，准备改变我们为计算机、光学探测器以及化学或生物传感器制造电子设备的方式。然而，由于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直接环境更敏感。支撑2D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。2D晶体也对我们对2D中电子输运的基本理解提出了挑战：其中许多材料明显显示出金属行为，但这与非常著名的2D电子输运理论--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2D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2D晶体中存在无序时的行为。该项目正在支持两名研究生和一批本科生的教育和培训。它还通过在新汉普郡大学为高中至研究生举办暑期讲习班，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，了解校园内发生的研究的多样性，以及与同行和主要研究人员亲自联系的机会，降低研究成功的门槛。技术摘要2D晶体非常适合用于下一代电子产品，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性能，包括在某些情况下，高载流子迁移率。它们也提供了一个重新审视我们对2D电子输运的期望的机会：其中许多材料清楚地显示出金属行为，但局域化理论预测2D中普遍存在微弱的局域化。本项目研究了二维材料中金属-绝缘体量子相变的存在和性质，特别是无序和非均匀的作用。该研究小组正在使用扫描隧道显微镜/光谱学与设备规模的输运测量相结合的方法，将二维材料的输运特性与空间不均匀联系起来，因为它们通过调谐无序和载流子浓度被驱动到绝缘相。该团队的目标是揭示无序和不均匀在量子金属-绝缘体转变中的作用，以及不同类型的无序在基于2D晶体的设备中的重要性。

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.