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: 1508560
• 负责人: Lian Li
• 金额: $ 51万
• 依托单位: University of Wisconsin-Milwaukee
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2017-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1508560&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，它们提供了增强的电气和光学特性，远远超出了每种单独的组成材料，它一直是现代电信，能源效率显示和能源收集技术的关键促成元素。该项目探讨了一种新的方法来合成由二维材料片制成的异质结构，其中纸张中的原子形成牢固的键，但层之间的相互作用非常薄弱。进行原子分辨率成像和计算，以了解这种特征性各向异性键如何促进与乐高积木相似的单个原子层的生长和组装，从而允许设计和合成具有量身定制的特性和功能的新材料，超出了当前在自然界中存在的材料的极限。该项目为原子量表的材料综合和表征以及电子结构计算提供了研究生和本科生的跨学科培训。电子结构代码的开源分布继续为科学界提供了我们团队代码开发工作的好处。 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异质结构。利用整合分子束外延，扫描隧道显微镜（STM）和原子力显微镜（AFM）的能力，分别由横向连接功能和工作功能的固有材料特性分别由固有的材料（例如带偏移）来确定。层厚度，掺杂和带隙通过前静脉拉曼光谱和光致发光进一步访问。这些空间平均的光谱测量获得的信息与原子尺度的结构信息相关，例如垂直连接，界面相互混合，局部应变和由原子原子原子分辨率STM/AFM成像获得的疾病的比对，以及其他电源传输电子显微镜。密度功能理论的计算与感兴趣的实验系统紧密耦合，以解决与结构特性有关的问题（例如，修改后的VDW增长的能量学以及缺陷和杂质的影响）和电子特性（接口状态，界面状态，带偏移，晶粒边界处的充电效应以及工作功能）。这种综合方法使单层以原子量表的异质结构的受控生长，带隙工程和表征能够受到控制，这是为了调整其电子和光学特性的所有必要步骤。