Alternative transducer and optical pumping scheme for nanoscale thermal metrology and imaging

从微电子和电力电子到能量存储设备和热电设备，散热是技术的本质。表征和理解热传递过程的能力可以帮助调节热流，提高设备的功能、效率和稳定性，特别是对于那些由导热性差的材料制成的设备。尽管如此，以高空间分辨率测量低导热材料中的热输运仍然具有挑战性。本文提出了一种新的方法，即利用空间分辨率低至数百纳米的高速摄像机直接成像热流。所提出的方法是基于激光的，因此是非接触的，并将利用有机半导体材料，这种材料在有机发光二极管和显示器中广泛使用。有机半导体将充当下面材料的局部温度报告器，通过观察有机半导体的温度随时间变化的速度，可以评估其热导率。该项目将为研究生和本科生在高时空分辨率综合光学测量系统的构建和改造方面提供广泛的培训机会。来自当地公立高中的K-12学生将获得最先进的热计量实验的理解和经验。缺陷，晶界，以及其他类型的不均匀性是材料的特征，不是单晶或外延薄膜。为了了解这些缺陷对新兴能源相关材料热传输的影响，该团队将探索有机半导体作为光泵探针热反射测量的替代传感器。在广泛的温度范围内，对几种原型有机半导体的形貌、光学性质和热输运性质进行了深入的研究。同时，将建立一个时间分辨的宽视场光学成像装置，这将允许有机换能器的有效热激发和精确的温度监测，以纳秒的时间分辨率。该团队将进行概念验证实验，对异质能材料和二维铁磁材料中的热流进行时空成像。期望本文提出的替代换能器和成像技术可以补充现有的热反射技术，用于研究用于能量转换和存储，光电子等领域的各种技术重要材料的热输运特性。使用后可拆卸换能器的能力是测量不可重复或高值样品的有用功能，以及半导体芯片的故障分析和质量控制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Heat dissipation is intrinsic to technologies ranging from micro- and power-electronics to energy-storage devices and thermoelectrics. The ability to characterize and understand thermal transport processes can help regulate the flow of heat and improve device functionality, efficiency, and stability, especially for those made of materials with poor thermal conductivities. Nonetheless, measuring thermal transport in low thermal-conductivity materials at a high spatial resolution is still challenging. A new approach is proposed here, in which the heat flow will be directly imaged by a high-speed camera with spatial resolution down to hundreds of nanometers. The proposed approach is laser-based, hence non-contact, and will take advantage of organic semiconducting materials, which are abundant and ubiquitously used in organic light-emitting diodes and displays. The organic semiconductors will serve as local temperature reporters of materials underneath, whose thermal conductivity can be assessed by observing how quickly the temperature of the organic semiconductor varies in time. The project will provide extensive training opportunities to graduate and undergraduate students in the construction and modification of comprehensive optical measurement systems with high spatial and temporal resolution. K-12 students from local public high schools will gain understanding and experience in state-of-the-art thermal metrology experiments.Defects, grain boundaries, among other types of inhomogeneities are characteristics of materials that are not single crystals or epitaxial films. To understand the influence of such imperfections on heat transport in emerging energy-related materials, the team will explore organic semiconductors as an alternative type of transducer for optical pump-probe thermoreflectance measurements. The morphology, optical properties, and thermal transport properties of several prototypical organic semiconductors will be thoroughly investigated over a wide temperature range. Meanwhile, a time-resolved, wide-field optical imaging setup will be constructed, which will permit efficient thermal excitation of organic transducers and their accurate temperature monitoring with nanosecond time resolution. The team will perform proof-of-concept experiments to spatiotemporally imaging the flow of heat in heterogeneous energy materials and in prototypical two-dimensional ferromagnetic materials. It is expected that the alternative transducer and imaging technique proposed here can complement the existing thermoreflectance techniques for the investigation of thermal transport properties of a wide range of technologically important materials used for energy conversion and storage, optoelectronics, and beyond. The ability to remove the transducer after their use is a useful feature for measuring unreproducible or high-value samples, and for failure analysis and quality control of semiconductor chips.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.