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

从微电子和电力电子到储能设备和热电技术，散热是一种固有的技术。表征和了解热传输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，特别是对于那些导热性能较差的材料。尽管如此，在高空间分辨率下测量低导热材料中的热传输仍然是具有挑战性的。这里提出了一种新的方法，利用空间分辨率低至数百纳米的高速相机直接对热流进行成像。建议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，有机半导体材料在有机发光二极管和显示器中广泛使用。有机半导体将作为地下材料的局部温度记录器，通过观察有机半导体的温度随时间变化的速度来评估其热导率。该项目将为研究生和本科生提供建造和改装具有高空间和时间分辨率的综合光学测量系统的广泛培训机会。来自当地公立高中的K-12学生将在最先进的热计量实验中获得了解和经验。缺陷、晶界和其他类型的不均匀是材料的特征，不是单晶或外延薄膜。为了了解这种缺陷对新兴能源相关材料中热传输的影响，该团队将探索有机半导体作为光学泵浦-探测热反射测量的替代传感器类型。我们将在较宽的温度范围内深入研究几种典型有机半导体的形态、光学性质和热输运性质。同时，将建立一个时间分辨的广视场光学成像系统，这将使有机换能器的有效热激发和以纳秒时间分辨率精确监测温度成为可能。该团队将进行概念验证实验，以时空成像非均质能量材料和典型的二维铁磁材料中的热流。预计这里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，用于研究广泛的具有重要技术意义的材料的热传输特性，这些材料用于能量转换和存储、光电子等领域。在使用后移除传感器的能力对于测量不可复制或高价值的样品以及半导体芯片的故障分析和质量控制是一个有用的功能。该奖项反映了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。

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.