Disentangling the structural and electronic phase transitions in ultrathin vanadium dioxide

非技术描述：该项目致力于支持在极薄的二氧化钒中从绝缘行为到金属行为的可逆转换的科学基础。这项研究的目标是确定在热驱动的转变过程中纳米级会发生什么，以及如何控制它。了解和控制二氧化钒不同可能阶段之间的过渡将使节能计算机和调节建筑物供暖和制冷的智能窗户的开发取得进展。延长对德国不来梅大学的国际访问，以进行实验，以补充宾厄姆顿大学和不来梅大学之间联合在线课程的发展。来自代表性不足的少数族裔的本科生研究人员参与了研究活动，包括专门到布鲁克海文国家实验室等国家研究机构进行实地考察。为了吸引更年轻的学生进入科学和工程专业，一项K-12教育推广活动采用了在线视频演示和信息图表。技术细节：二氧化钒的突然金属绝缘体转变是电子和晶格之间复杂相互作用的典型例子。伴随着电子相变的是结构相变，这种相变可以由室温附近的微小热扰动来触发。预计在转变过程中会有更多的相存在，或者可以通过应变薄膜来稳定。然而，这些阶段的确切性质和存在是一个热门的辩论话题。高质量超薄膜的出现，新开发的纳米级光谱显微镜技术，以及最近复杂的计算研究，为探索这些相提供了一个理想的机会。纳米分辨率光谱显微镜技术可以准确并同时确定通过二氧化钒相变共存的相分离区域中的电子和几何构型。研究的目标是确定纳米级二氧化钒的结构和电子相变是否像中间态的存在所表明的那样本质上是脱钩的，或者是否可以通过应变和掺杂来定制这种材料。测量的参数，如晶格常数、态密度和钒配位，被用作二氧化钒能带结构计算的输入和约束。研究生和本科生正在美国和国外的国家研究机构接受尖端低能/光电子显微镜和小斑X射线光谱学方面的培训。

NON-TECHNICAL DESCRIPTION: The project addresses the science that underpins the reversible switch from insulating to metallic behavior in extremely thin vanadium dioxide. The goal of this research is to determine what happens at the nanometer scale during the thermally driven transition, and how to control it. Understanding and controlling transitions between the various possible phases of vanadium dioxide will enable advances to be made in the development of energy-efficient computers, and smart windows that regulate the heating and cooling of buildings. Extended international visits to Bremen University in Germany to perform experiments complement the development of joint on-line courses between universities in Binghamton and Bremen. Undergraduate researchers from underrepresented minorities are involved with the research activities, including dedicated field trips to national research facilities, such as Brookhaven National Laboratory. A K-12 educational outreach to attract younger students to science and engineering employs on-line video demonstrations and infographics. TECHNICAL DETAILS: The abrupt metal insulator transition of vanadium dioxide is an archetypal example of the complex interplay between the electrons and the lattice. A structural phase transition accompanies the electronic transition, which can be triggered by small thermal perturbations near room temperature. Additional phases are expected to exist during the transition or may be stabilized by strained thin films. However, the exact nature and presence of these phases is a hot topic of debate. The advent of high quality ultrathin films, newly developed nanoscale spectromicroscopy techniques, and recent sophisticated computational studies present an ideal opportunity to explore these phases. Nanoscale resolution spectromicroscopy techniques can determine exactly and simultaneously the electronic and geometric configurations in phase-separated regions that coexist through the phase transitions of vanadium dioxide. The research objective is to determine whether the structural and electronic phase transitions in nanoscale vanadium dioxide are intrinsically decoupled, as suggested by the presence of intermediate states, or whether the material can be tailored to be so by strain and doping. Measured parameters, such as lattice constants, density of states, and vanadium coordination are used as inputs and constraints for band structure calculations of vanadium dioxide. Students, at both the graduate and undergraduate level, are being trained in cutting-edge low-energy/photoelectron electron microscopy and small-spot X-ray spectroscopy at national research facilities in the US and abroad.