Growth of Tensile Germanium Nanowires Embedded in a III-V Matrix

非技术描述：电子和光子材料的许多性质是由其化学键的长度和夹角决定的。应力和应变可以轻微改变这些键，但会导致材料与光和电荷相互作用的方式发生深刻变化。在这方面，锗特别值得注意。键长改变2%使其能够非常有效地发光，而在其正常状态下，Ge是一个很差的发光体。这个项目试图通过将锗纳米结构嵌入到会产生应力的基质中来改变它们的性质。由嵌入在异质宿主中的Ge纳米结构形成的纳米复合材料使新的光学和电学性能成为可能。该研究项目与教育和外联活动相结合。除了在研究生和本科生层面提供跨学科研究培训外，PI还定期与工程学初级教员举行会议，讨论K-12外展如何改善工作与生活的平衡，这是学术科学家日益关注的问题。通过这些外展活动，他用自己的亲身经历鼓励初级教员开展创新的外展活动。另一项活动涉及威尔伯·克罗斯高中(Wilbur Cross High School)对有才华的高年级学生的大学前推广活动。威尔伯·克罗斯高中是一所种族和经济多元化的公立高中。技术描述：该项目旨在展示由嵌入III-V矩阵的拉伸应变Ge纳米线组成的新型纳米复合材料。最近的研究表明，Ge纳米膜、纳米线、微盘和微桥的性能可以通过施加大的双向或单轴拉伸应变的外部应力来调节。在本项目中，研究了分子束外延生长过程中的表面介质相分离，作为一种新的方法来生长嵌入在高拉伸应变的III-V基质中的外延Ge纳米结构。具体地说，任务1试图找出Ge/III-V纳米复合材料的生长条件、结构和性能之间的联系，包括对界面应变耦合的基本了解；任务2侧重于基质组成和晶格常数对Ge相分离动力学和由此产生的微结构的耦合影响。最后，任务3试图了解当纳米线被调制成纳米棒或量子点时结构和性质的变化。设计和生长具有以前无法达到的应变状态的Ge/III-V纳米复合材料的能力可能导致Ge具有一系列前所未有的材料特性，例如从间接带隙到直接带隙的转换，甚至成为一种半金属材料。此外，对外延纳米复合材料的基本理解可以应用于广泛的其他材料系统，如复合氧化物、稀磁半导体和高度不匹配的合金。

Non-technical Description:Many of the properties of electronic and photonic materials are determined by the length of and the angle between their chemical bonds. Stress and strain can slightly alter these bonds, but cause profound changes in the way that materials interact with both light and electrical charge. Germanium is particularly noteworthy in this regard. A 2% change in bond length enables it to emit light very efficiently while in its normal state, germanium is a poor light emitter. This project seeks to engineer the properties of germanium nanostructures by embedding them into a matrix that induces stress. Nanocomposites formed from Ge nanostructures embedded in a foreign host enable new optical and electrical properties. The research project is integrated with the education and outreach activities. Besides interdisciplinary research training provided at the graduate and undergraduate levels, the PI schedules regular meetings with junior faculty in engineering to discuss how K-12 outreach can improve work-life balance, a growing concern among academic scientists. Through these outreach activities, he uses his personal experience to encourage junior faculty members in developing innovative outreach activities. Another activity involves pre-college outreach to talented seniors at Wilbur Cross High School, a racially and economically diverse public high school in New Haven.Technical Description:This project aims to demonstrate novel nanocomposite materials consisting of tensile-strained Ge nanowires embedded in III-V matrices. Recent research has shown that the properties of Ge nanomembranes, nanowires, microdisks, and microbridges can be tuned using external stressors to apply large biaxial or uniaxial tensile strains. In this project, surface-mediated phase separation during molecular beam epitaxy growth is investigated as a new approach to grow epitaxial Ge nanostructures embedded in a III-V matrix with high tensile strain. Specifically, Task 1 seeks to draw connections between growth conditions, structure, and properties of Ge/III-V nanocomposites, including basic understanding of interfacial strain coupling; Task 2 focuses on the coupled effects of matrix composition and lattice constant on the kinetics of Ge phase separation and the resulting microstructures. Finally task 3 seeks to understand the changes in structure and properties when the nanowires are modulated into nanorods or quantum dots. The ability to design and grow Ge/III-V nanocomposites with previously unattainable strain states may lead to a range of unprecedented material properties for Ge, such as the indirect-gap to direct-gap conversion or even becoming a semi-metallic material. Moreover, the fundamental understanding of epitaxial nanocomposites could apply to a wide range of other material systems such as complex oxides, dilute magnetic semiconductors, and highly mismatched alloys.