GOALI: Ultrafast Phase Transition and Critical Issues in Structure-Property Correlations of Vanadium Oxide

该项目对基于测辐射热计成像阵列的红外相机和智能传感器产生了深远的影响，这些传感器可以与硅集成电路单片集成，并在室温或高于室温下工作。通过提高非制冷测辐射热计阵列的可靠性和灵敏度，人们希望战场上的每一个士兵都能有另一种工具。自己的夜晚？保持技术和作战优势。Narayan教授计划与ORNL和Kopin公司密切合作，将基础知识转化为实用设备。这项工作涉及在NCSU的研究生和本科生的培训，并与NC A T大学合作，以吸引少数民族学生进入NCSU的研究生课程。外联活动还将包括ASM国际赞助的每年一度的高中高年级学生暑期学校。这项研究涉及一个非常有趣的现象？氧化钒（VO2）从单斜晶到四斜晶结构的超快相变。主要研究者（PI）将研究外延在确定VO2特性中的作用，VO2是一种在块状形式下表现出急剧的超导体到金属转变的材料。该转变与破坏块体材料的能量释放（至少部分地与和转变相关联的变形相关联）相关。假设是薄膜及其衬底将能够适应转变而不会由于衬底中的热耗散而失效。当然，衬底也将施加机械边界条件，这将影响转变的温度和“锐度”。此外，外延、织构化或非晶膜的详细微结构将影响转变的性质。 该PI将解决钒氧化物薄膜的合成和加工，通过增加晶粒尺寸到高质量的单晶蓝宝石和硅衬底。在具有大晶格失配的衬底上，通过畴匹配外延范例将生长具有受控应变的高质量单晶膜，其中临界厚度小于单层，并且膜从一开始就松弛。这些外延膜应该表现出急剧的转变，大幅度，和非常小的滞后，类似于钒氧化物的块状单晶。为了获得高效可靠的红外摄像头和智能传感器，PI将努力控制和优化过渡的清晰度和幅度，以及加热和冷却时的滞后。

This project impacts profoundly infrared camera and smart sensors based upon bolometer imaging arrays that can be monolithically integrated with silicon integrated circuits and operated at or above room temperature. By improving the reliability and sensitivity of uncooled bolometer arrays, it is hoped that every soldier in the field will have another tool with which to ?own the night? and maintain technological and operational superiority. Professor Narayan plans to work closely with ORNL and Kopin Corporation to transition the basic knowledge into practical devices. This work involves training of graduate and undergraduate students at NCSU, and collaborations with NC A&T University to attract minority students into the graduate program at NCSU. The outreach will also involve an annual ASM International-sponsored Summer School for rising high school seniors. This research deals with the very interesting phenomenon ? an ultrafast phase transition from monoclinic to the tetragonal structure of vanadium oxide (VO2). The principal investigator (PI) will study the role of epitaxy in determining the properties of VO2, a material that exhibits a sharp semiconductor-to-metal transition in bulk form. The transition is associated with energy release (associated, at least in part, with the deformation associated with the transition) that destroys the bulk material. The supposition is that the thin film and its substrate will be able to accommodate the transition without failure due to heat dissipation in the substrate. Of course, the substrate will also impose mechanical boundary conditions that will influence the temperature and "sharpness" of the transition. Furthermore, the detailed microstructure of the epitaxial, textured or amorphous film will influence the nature of the transition. The PI will address the synthesis and processing of vanadium oxide thin films with increasing grain size through to high-quality single-crystal on sapphire and silicon substrates. High-quality single crystal films with controlled strain will be grown by domain matching epitaxy paradigm on substrates with a large lattice misfit, where critical thickness is less than a monolayer and the films are relaxed from the beginning. These epitaxial films should exhibit a sharp transition, large amplitude, and very small hysteresis, similar to bulk single crystals of vanadium oxide. To obtain efficient and reliable infrared camera and smart sensors, the PI will strive to control and optimize the sharpness and amplitude of the transition, and the hysteresis upon heating and cooling.