Probing Charge, Spin and Thermoelectric Transport in Atomically Thin Materials

非技术摘要：硅晶体管是现代电子产品的基本组成部分，在过去的几十年里，硅晶体管的不断缩小推动了计算能力的指数级增长。当晶体管的尺寸接近原子大小时，这种趋势不能继续下去。硅以外的新电子产品需要新的操作原理，这些原理与传统晶体管的操作原理截然不同，传统晶体管通过控制载流子的电荷来控制电流。对当今社会同样重要的是能量收集材料和设备的发展，这些材料和设备可以有效地将热量转化为电能。原子薄层材料是由原子层组成的，每层原子层之间的键结很强，但层与层之间的键结很弱，为解决这两个挑战提供了极好的机会。该项目的第一个目标是了解一种叫做“自旋”的电子的量子力学特性是如何在原子薄的材料中传播的，并开发一种新型的阀门，通过控制载流子的自旋来控制电流的流动。该项目的第二个目标是了解电流如何在原子级薄材料中传输和消散，以及如何设计材料的表面化学成分，使其成为高效的热电转换器。在这项研究中获得的知识预计将对下一代纳米电子学和能量收集设备的发展产生重大影响。这些研究活动训练各级学生掌握必要的技能，以推进纳米科学和纳米技术，并促进代表性不足的群体的参与。技术摘要：本项目旨在显著推进对原子薄过渡金属二硫化物（TMDs）中电荷、自旋和热电输运的基本认识，并探索其独特的应用潜力。可能导致低功耗电子应用的tmd的一个显着特性是这些材料中的自旋，谷和层自由度的互锁。该项目的第一个重点是利用磁输运测量系统地研究几层tmd中的自旋和谷弛豫路径。所获得的知识用于设计和实现双层tmd中的新型自旋谷层阀，利用PI？的实验室。测量旨在了解其操作原理并评估其性能。该项目的第二个重点是了解和控制TMD材料中的电荷和热电输运，以实现热电应用。该推力的一项活动旨在通过研究高载流子密度下材料的温度依赖片电阻，建立对TMD材料中电子-声子相互作用急需的定量理解。第二种活动利用它们的能带结构和表面性质来设计所需的热电响应。实验试图通过表面共价功能化来提高TMD材料的热功率。测量是由计算支持的。在这个项目中进行的研究预计将产生及时和关键的知识，以刺激和支持TMD材料潜在的电子、自旋电子和热电应用的发展。研究活动为学生提供必要的STEM技能，而夏令营活动则促进科学领导能力，旨在扩大科学对弱势群体的影响。

Non-technical abstract: The silicon transistor is the fundamental building block of modern electronics, the continued shrinking of which propelled the exponential growth of computing power over the past several decades. This trend cannot continue as the size of a transistor approaches that of an atom. New electronics beyond silicon calls for new operational principles that are drastically different from that of a conventional transistor, which controls the current flow by controlling the charge of the carriers. Equally important to today's society is the development of energy-harvesting materials and devices that could convert heat to electricity efficiently. Atomically thin layered materials, which consist of layers of atoms strongly bonded within each layer but weakly bonded between layers, offer excellent opportunities to tackle both challenges. The first objective of this project is to understand how a quantum mechanical property of an electron called 'spin' propagates in atomically thin materials and to develop a new type of valve that controls an electric current flow by controlling the spin of the carriers. The second objective of this project is to understand how electric current transports and dissipates in atomically thin materials and how to engineer the surface chemistry of the materials to make them efficient heat-to-electricity converters. Knowledge gained in this research is expected to have significant impact on the development of next-generation nanoelectronics and energy-harvesting devices. The research activities train students of all levels with necessary skills to advance nanoscience and nanotechnology and promote the participation of under-represented groups. Technical abstract: This project seeks to significantly advance the fundamental understandings of charge, spin and thermoelectric transport in atomically thin transition metal dichalcogenides (TMDs) and explore their unique application potentials. One distinguishing property of TMDs that may lead to low-power electronic applications is the interlocking of the spin, valley and layer degrees of freedom in these materials. The first thrust of the project aims to systematically study spin and valley relaxation pathways in few-layer TMDs using magneto-transport measurements. The knowledge acquired is used to design and implement a novel spin-valley-layer valve in bilayer TMDs, leveraging the extensive device fabrication expertise of the PI?' lab. Measurements seek to understand its operation principles and evaluate its performances. The second thrust of the project focuses on understanding and controlling the charge and thermoelectric transport in TMD materials towards thermoelectric applications. One activity of this thrust aims to establish a much-needed quantitative understanding of the electron-phonon interactions in TMD materials by studying the temperature-dependent sheet resistance of the materials in the high-carrier density regime. A second activity exploits their band structures and surface nature to engineer desired thermoelectric responses. Experiments seek to enhance the thermopower of TMD materials using surface covalent functionalization. Measurements are supported by computations. Research carried out in this project is expected to produce timely and critical knowledge to stimulate and underpin the development of potential electronic, spintronic and thermoelectric applications of TMD materials. The research activities equip students with necessary STEM skills while summer camp activities promote science leadership and aim to broaden the reach of science to under-represented groups.