Scalable Thin-Film Fabrication for THz Optical Switching Devices in Vanadium Dioxide

技术描述：二氧化钒表现出一种可逆的绝缘体到金属的转变，可以用飞秒激光光学启动，因此是高速电子、光子和存储设备的潜在理想选择。本研究项目解决了实现这一潜力的两个挑战：首先，绝缘体到金属的转变是快速的（亚皮秒），但金属到绝缘体的转变是缓慢的（亚纳秒），因为它需要晶体结构的重新排列。其次，可扩展的低温薄膜制造还没有证明在技术上有用的衬底上外延二氧化钒薄膜。该活性通过将材料特性（薄膜形态、衬底相互作用、掺杂剂浓度、晶格匹配、应变和晶相）与薄膜结构的静态和动态光学常数以及与时间相关的电子响应和控制转变速度的晶格振动相关联来解决这些问题。评价了溅射、电子束和原子层薄膜沉积技术的相对优点，并通过椭偏、x射线衍射和高分辨率透射电子、拉曼和x射线光电子显微镜对薄膜的平衡光学和物理性质进行了表征。通过可见光、红外和太赫兹泵浦探测光谱、时变椭偏、干涉自相关和光电子显微镜，以飞秒时间分辨率测量了其动态光学特性。非技术描述。二氧化钒是一种非凡的材料，当被短暂的激光照射时，它能在万亿分之一秒内从绝缘体变成金属，这使它成为电信、电子和光学计算应用的理想材料。该项目的目标是优化二氧化钒的性能，以最快的速度制造光开关，同时开发制造工具，使二氧化钒薄膜器件的尺寸适合实际应用。该项目通过培养研究生在科学和工程之间的跨学科边界上思考和工作，促进未来科学和工程劳动力的发展。这项研究通过招募一名研究生，并与两所大学的研究人员合作，促进了劳动力的多样性，这两所大学为代表性不足的人群提供服务。参与研究的本科生通过范德比尔特学生科学志愿者向当地高中生介绍光交换的概念。研究生和每年一次的田纳西州州长新兴技术学院之间的长期互动促进了全州范围内对未来科学和工程本科生的影响。该研究项目还推动了与正在开发基于二氧化钒技术的工业伙伴的持续对话。

Technical Description: Vanadium dioxide exhibits a reversible insulator-to-metal transition that can be initiated optically with femtosecond lasers, and is thus potentially ideal for high-speed electronic, photonic and memory devices. This research project addresses two challenges to the realization of this potential: First, the insulator-to-metal transition is fast (sub-picosecond), but the metal-to-insulator transition is slow (sub-nanosecond) because it requires a rearrangement of crystal structure. Second, scalable low-temperature thin-film fabrication has not been demonstrated for epitaxial vanadium-dioxide films on technologically useful substrates. The activity addresses these issues by correlating materials properties (film morphology, substrate interactions, dopant concentration, lattice match, strain and crystalline phases) to the static and dynamic optical constants of the thin-film structures and to the time-dependent electronic response and lattice vibrations that govern the speed of the transition. The relative merits of sputter, electron-beam and atomic-layer film-deposition techniques are assessed and the equilibrium optical and physical properties of the films are characterized by ellipsometry, X-ray diffraction and by high-resolution transmission-electron, Raman and X-ray photoelectron microscopy. Dynamical optical properties are measured with femtosecond time resolution by visible, infrared and THz pump-probe spectroscopy, time-dependent ellipsometry, interferometric autocorrelation and photoelectron electron microscopy.Non-technical Description. Vanadium dioxide is a remarkable material that changes from an insulator to a metal in about a trillionth of a second when illuminated by a short burst of laser light, making it ideal for applications in telecommunications, electronics and optical computing. The goal of this project is to optimize vanadium dioxide properties to make the fastest possible optical switch while developing fabrication tools to make vanadium dioxide thin-film devices on a size scale suitable for real-world applications. The project promotes the development of the future science and engineering work force by training graduate students to think and work at the interdisciplinary boundary between science and engineering. The research fosters work-force diversity by recruiting a graduate student from, and collaborating with researchers at, two universities that serve underrepresented populations. Undergraduate students involved in the research present the concept of optical switching to local high school students through Vanderbilt Students Volunteering for Science. Statewide impact on future science and engineering undergraduates is fostered by a long-standing interaction between the graduate students and the annual Tennessee Governor's School for Emerging Technologies. The research project also motivates ongoing dialogue with industrial partners who are developing technologies based on vanadium dioxide.