EAGER: Nanoscale Elastocaloric Effect in Phase-Change Nanowires for Solid-State Cooling

目前，大多数冷却设备(冰箱、空调机组)使用对环境有害的液体，称为制冷剂。它们也很难小型化，阻碍了它们在电子设备中的实施，由于持续的小型化和处理能力的增加，需要新的冷却机制来保持半导体行业的进步。这项拟议的研究旨在研究纳米级的弹热效应，这是一种冷却机制，变形导致固体中原子能级的变化，从而导致其温度的显著变化。这种效应有望消除用作制冷剂的有害流体，并适用于集成在电子芯片中的小型化冷却设备，以及自冷却织物和智能涂料等消费产品。这项提议还将为研究生、本科生和K-12学生提供辅导、研究和推广机会。研究生将指导在调查员实验室接待的本科生和高中生。通过与这个项目相关的有意义的研究，他们将受到激励，追求科学和技术方面的职业生涯。总体目标是通过评估纳米结构在模型系统：二氧化钒(VO2)纳米线中的前景，率先探索纳米结构中的弹性热效应。这项拟议的研究是实验性的，旨在通过红外成像直接表征该效应的输出(温度变化)，从而证明它在VO2中的存在。同样，测量纳米线的变形随温度的变化将提供衡量标准，以确定VO2中影响的大小，从而评估这种材料用于新型冷却设备的前景，以及进行更深入研究的必要性。纳米线将通过自组装和微流控图案化的方法沉积在柔性衬底上，以使它们在一个方向上排列，从而获得宏观尺度的纳米结构薄膜。然后，这些薄膜将沿排列方向变形，以触发弹性热效应。由此产生的温度变化将使用红外成像进行测量。最后，使用最先进的纳米机械测试，单个纳米线将被变形，以表征它们在两个代表性温度下的响应，从而量化相变的能量学界限(即其熵变)。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Currently, most cooling devices (refrigerators, air-conditioning units) employ environmentally-harmful fluids, known as refrigerants. They are also hard to miniaturize, preventing their implementation in electronic devices, which due to continued miniaturization and increase of processing power, necessitate novel cooling mechanisms for the semiconductor industry to keep progressing. The proposed research aims to investigate the nanoscale elastocaloric effect, a cooling mechanism where deformation causes an atomic-level change in a solid, which results in significant changes in its temperature. This effect promises to eliminate the need for harmful fluids used as refrigerants, and to be applicable both in miniaturized, cooling devices integrated inside electronic chips, and in consumer products such as self-cooling fabrics and smart coatings. Mentoring, research and outreach opportunities for graduate, undergraduate and K-12 students will also be enabled by this proposal. The graduate students will mentor undergraduates and high-school students hosted in the investigator’s lab. By doing meaningful research related to this project, they will be inspired to pursue careers in science and technology.The overall goal is to pioneer the exploration of the elastocaloric effect in nanoscale structures by assessing its promise in a model system: vanadium dioxide (VO2) nanowires. The proposed research is experimental and aims to directly characterize the effect’s output (temperature change) by infrared imaging, thus proving its existence in VO2. Similarly, measurements of the deformation of the nanowires as a function of temperature will provide metrics to put bounds on the magnitude of the effect in VO2, thus assessing the promise of the material for novel cooling devices, and the need for deeper investigations. Nanowires will be deposited in flexible substrates by self-assembly and microfluidic patterning methods, in order to align them in one direction and obtain a macroscale nanostructured film. These films will then be deformed along the alignment direction to trigger the elastocaloric effect. The resulting temperature changes will be measured using infrared imaging. Finally, using state-of-the-art nanomechanical testing, individual nanowires will be deformed in order to characterize their response at two representative temperatures, thereby quantifying bounds for the energetics of the phase transformation (i.e. its entropy change).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.