Coupled Electronic and Lattice Structures in Thin Crystalline Films

摘要：材料中的电子效应和现象是许多应用的基础；值得注意的例子包括现代电子学中使用的各种半导体和金属，其中超薄薄膜和微/纳米晶体通常用作基本构建块。本研究项目的重点是通过控制拉伸或压缩使这些基本设备构建块承受应变，从而对其进行修改、改进和创造新特性的实验。其目的是建立对应变效应的基本理解，从而建立所需的指导原则，以建立卓越的设备和新的应用系统类别。实验工作利用国家设施的尖端仪器，并在材料制备、制造、表征和优化的科学和艺术方面为研究生和博士后研究人员提供严格的培训。技术摘要：超薄膜和微纳米晶体是现代器件的关键组成部分；它们的优点包括最少的材料资源使用，易于制造和集成，减少电子散射和耗散，以及可通过分层和量子相干和限制实现功能化的可定制和涌现特性。该项目研究了选定模型系统的电子结构和原子行为，重点关注应力/应变对这些系统的影响，这些系统可能会改变费米表面附近的详细电子结构，并改变晶格的整体对称性，从而产生重要后果。特别感兴趣的案例包括拓扑绝缘体薄膜中的非平凡电子态，Dirac/Weyl半金属等，超导体和电荷密度波材料的转变温度，以及金属微晶体的表面化学和催化性质。应变是通过力学方法在实验中引入的。测量电子结构和原子位移的实验技术包括角分辨光发射光谱和x射线衍射，这两种技术都是在家庭实验室和同步辐射设施中进行的。

Non-Technical Abstract:Electronic effects and phenomena in materials underlie many applications; notable examples include the wide variety of semiconductors and metals employed in modern electronics, where ultrathin films and micro/nano crystals are often used as the basic building blocks. This research project focuses on experimentation at modifying, improving, and creating novel properties of these basic device building blocks by subjecting them to strain realized by controlled stretching or compression. The aim is to establish a basic understanding of strain effects and thereby to establish the guiding principles needed for building superior devices and new classes of systems for applications. The experimental work utilizes cutting-edge instruments at national facilities and offers rigorous training to graduate students and postdoctoral research associates in the science and art of materials preparation, fabrication, characterization, and optimization. Technical Abstract:Ultrathin films and micro/nano crystals are key building blocks for modern devices; their advantages include minimal usage of material resources, ease of fabrication and integration, reduction of electronic scattering and dissipation, and tailorable and emergent properties amenable to functionalization through layering and quantum coherence and confinement. This project examines the electronic structure and atomistic behavior of selected model systems, with a focus on the effects of stress/strain upon these systems that may alter the detailed electronic structure near the Fermi surface and transform the overall symmetry of the lattice with important consequences. Cases of special interest include nontrivial electronic states in films of topological insulators, Dirac/Weyl semimetals, etc., transition temperatures of superconductors and charge density wave materials, and surface chemical and catalytic properties of metallic microcrystals. Strain is introduced experimentally by mechanical means. Experimental techniques for the measurements of the electronic structure and atomic displacements include angle-resolved photoemission spectroscopy and x-ray diffraction both in the home laboratories and at synchrotron radiation facilities.