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，这种成像阵列可以与硅集成电路单片集成，并在室温或更高温度下运行。通过提高非制冷测辐射热计阵列的可靠性和灵敏度，希望战场上的每一名士兵都能有另一种工具来拥有夜晚？保持技术和作战优势。纳拉扬教授计划与ORNL和Kopin Corporation密切合作，将基础知识转化为实际设备。这项工作包括对NCSU研究生和本科生的培训，以及与NC A&T大学的合作，以吸引少数族裔学生进入NCSU的研究生课程。外展还将包括一年一度的ASM国际赞助的暑期学校，面向正在崛起的高中高年级学生。这项研究涉及到一个非常有趣的现象？氧化钒(VO2)从单斜晶系到四方系结构的超快相变。首席研究员(PI)将研究外延在决定VO2性能方面的作用，VO2是一种在体相中表现出从半导体到金属的急剧转变的材料。转变与破坏主体材料的能量释放(至少部分地与与转变相关的变形)相关联。假设薄膜及其衬底将能够适应这种转变，而不会因为衬底中的散热而失效。当然，衬底也会施加机械边界条件，影响过渡的温度和“锐度”。此外，外延、织构或非晶态薄膜的详细微结构将影响转变的性质。PI将致力于合成和加工晶粒度不断增大的氧化钒薄膜，直至在蓝宝石和硅衬底上获得高质量的单晶。在晶格失配较大的衬底上，临界厚度小于1个单层且薄膜从一开始就松弛的衬底上，可以采用区域匹配外延模式生长出高质量的应变可控单晶薄膜。这些外延薄膜应该表现出类似于大块氧化钒单晶的急剧跃迁、大幅度和非常小的磁滞。为了获得高效可靠的红外摄像机和智能传感器，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.