Tailoring the Properties of Heterostructures of Monolayers: Epitaxial Growth and Doping

定制单层异质结构的特性：外延生长和掺杂

• 批准号: 1734017
• 负责人: Lian Li
• 金额: $ 39.97万
• 依托单位: West Virginia University Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-16 至 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1734017&HistoricalAwards=false
• 关键词: Tailoring; Properties; Heterostructures; Monolayers; Epitaxial

Nontechnical Description: Heterostructures of semiconductor materials, which provide enhanced electrical and optical characteristics well beyond that of each individual constituent material, have been the key enabling element in modern telecommunication, energy-efficient displays, and energy harvesting technologies. This project explores a new approach to synthesize heterostructures made of sheets of two-dimensional materials, in which atoms within a sheet form strong bonds but interactions between the layers are very weak. Atomic-resolution imaging and calculations are carried out to understand how this characteristic anisotropic bonding facilitates the growth and assembling of the single atomic layers similar to LEGO blocks, thus allowing the design and synthesis of new materials with tailored properties and functionalities beyond the limits of materials that currently exist in nature. This project provides graduate and undergraduate students interdisciplinary training in areas of materials synthesis and characterization at the atomic scale, as well as electronic structure calculations. The open source distribution of electronic structure codes continues to provide the scientific community the benefits of our team's code development efforts. An ongoing Research Experience for Teachers outreach program brings cutting-edge research on two-dimensional materials to high-school students to inspire their interest in science and engineering.Technical Description: This project aims to gain an atomic scale understanding of 1) the inherent grain boundary formation during the van der Waals (vdW) epitaxial growth of two-dimensional transition-metal dichalcogenides, and 2) the doping and bandgap engineering of their heterostructures. Leveraging the capability of integrating molecular beam epitaxy, scanning tunneling microscopy (STM) and atomic force microscopy (AFM), the intrinsic materials properties such as band offsets across lateral junctions and work functions are determined by in-situ tunneling spectroscopy and force-bias spectroscopy, respectively. Layer thickness, doping, and band gaps are further accessed by ex-situ Raman spectroscopy and photoluminescence. The information obtained by these spatially averaged spectroscopic measurements is correlated with atomic scale structural information such as the alignment of vertical junctions, interface intermixing, local strain, and disorder obtained by in-situ atomic resolution STM/AFM imaging, as well as ex-situ transmission electron microscopy. Density functional theory calculations are tightly coupled to the experimental systems of interest, addressing issues related to structural properties (e.g., energetics of the modified vdW growth and the impact of defects and impurities) and electronic properties (interface states, band offsets, charging effects at grain boundaries, and work functions). This integrated approach enables the controlled growth, bandgap engineering, and characterization of heterostructures of monolayers at the atomic scale, all necessary steps towards tailoring their electronic and optical properties.

非技术描述：半导体材料的异质结构提供了远远超出每种单独组成材料的增强的电气和光学特性，已成为现代电信、节能显示器和能量收集技术的关键实现元件。该项目探索了一种合成由二维材料片材制成的异质结构的新方法，其中片材内的原子形成牢固的键，但层之间的相互作用非常弱。进行原子分辨率成像和计算，以了解这种特征性的各向异性键合如何促进类似于乐高积木的单原子层的生长和组装，从而允许设计和合成具有超越材料限制的定制特性和功能的新材料目前存在于自然界中。该项目为研究生和本科生提供原子尺度材料合成和表征以及电子结构计算领域的跨学科培训。电子结构代码的开源分发继续为科学界提供我们团队代码开发工作的好处。正在进行的教师研究体验推广计划为高中生带来了二维材料的前沿研究，激发他们对科学和工程的兴趣。技术描述：该项目旨在获得对 1) 固有晶粒的原子尺度理解二维过渡金属二硫属化物范德华 (vdW) 外延生长过程中边界的形成，以及 2) 异质结构的掺杂和带隙工程。利用集成分子束外延、扫描隧道显微镜 (STM) 和原子力显微镜 (AFM) 的能力，通过原位隧道光谱和力偏置光谱确定材料的固有特性，例如跨横向结的能带偏移和功函数， 分别。通过异位拉曼光谱和光致发光进一步了解层厚度、掺杂和带隙。通过这些空间平均光谱测量获得的信息与原子尺度结构信息相关，例如通过原位原子分辨率 STM/AFM 成像以及异位获得的垂直结的排列、界面混合、局部应变和无序。透射电子显微镜。密度泛函理论计算与感兴趣的实验系统紧密耦合，解决与结构特性（例如，改进的 vdW 生长的能量学以及缺陷和杂质的影响）和电子特性（界面态、能带偏移、充电效应）相关的问题。晶界和功函数）。这种集成方法能够在原子尺度上实现单层的受控生长、带隙工程和异质结构表征，这是定制其电子和光学特性的所有必要步骤。