Probing Highly Non-equilibrium Thermal Transport in Nanostructures and Devices

李石（U Texas, Austin）在纳米电子器件、激光材料加工和热输运测量中，不同的电子和声子种群可以被驱动出局部热平衡。更好地理解高度非平衡输运现象对于设计具有更高性能和可靠性的下一代器件和材料结构是必要的。然而，目前的实验能力不足以探测这些不同能量激发的局部温度。尽管最近在扫描热显微镜（SThM），红外光谱和微拉曼光谱方面取得了进展，但缺乏实验方法来解决主导热传导的声子的局部温度，以及纳米结构中可能处于弹道传输状态的低频声子。本研究的目的是探索在纳米结构和器件中高度非平衡输运过程中探测声子局部温度的新实验方法。研究的技术包括一种基于微布里渊光散射（BLS）的新方法，用于探测低频(0.5 GHz至100？5 GHz)空间分辨率为亚微米的声子。基于BLS对玻璃中局部声子温度的初步测量，该技术将进一步用于探测硅纳米结构中电偏激或光激发的局部声子温度。得到的声子温度将与微拉曼光谱、红外光谱和SThM测量的温度相关联，以量化电子、声子和光学声子之间的局部不平衡。微bls技术作为低频声子的热显微镜工具的演示将对实验热输运研究界有价值。同时，测量数据可以被理论和计算热输运研究人员用来更好地理解一些有趣和重要的非平衡输运现象。这样的理解可以影响纳米电子器件、激光材料加工和热测量技术的进一步发展。此外，本研究将为学生提供最先进实验技术的训练机会，并为本科和研究生课程提供新的范例材料。它还将产生新的示范材料，用于推广活动，以吸引代表性不足的群体的学生进入工程和科学专业，并向德克萨斯州的K-12学生、家长和教师展示大学的研究成果。

CBET-1336968PI: Li Shi (U Texas, Austin)Different electron and phonon populations can be driven out of local thermal equilibrium in nanoelectronic devices, laser materials processing, and thermal transport measurements. A better understanding of the highly non-equilibrium transport phenomena is necessary for the design of next-generation devices and material structures with enhanced performance and reliability. However, current experimental capabilities are inadequate for probing local temperatures of these different energy excitations. Despite the recent progresses in scanning thermal microscopy (SThM), infrared spectroscopy, and micro-Raman spectroscopy, there is a lack of experimental methods for resolving the local temperature of the acoustic phonons that dominate heat conduction, as well as low-frequency acoustic phonons that may be in the ballistic transport regime in nanostructures. The objective of this research is to investigate new experimental methods for probing the local temperature of acoustic phonons during highly non-equilibrium transport processes in nanostructures and devices. The techniques to be investigated include a new method based on micro-Brillouin light scattering (BLS) for probing the local temperature of low-frequency (0.5 GHz to 100?s GHz) acoustic phonons with sub-micron spatial resolution. Based on preliminary BLS measurements of local acoustic phonon temperatures in glass, this technique will be investigated further for probing the local acoustic phonon temperature in silicon nanostructures that are either electrically biased or optically excited. The obtained acoustic phonon temperature will be correlated with those measured by micro-Raman spectroscopy, infrared spectroscopy, and SThM to quantify local non-equilibrium between electrons, acoustic and optical phonons.The demonstration of the micro-BLS technique as a thermal microscopy tool for low-frequency phonons will be of value for the experimental thermal transport research community. Meanwhile, the measurement data can be used by theoretical and computational thermal transport researchers to establish a better understanding of several intriguing and important non-equilibrium transport phenomena. Such understanding can impact further advances in nanoelectronic devices, laser materials processing, and thermal measurement techniques. In addition, this research will provide student training opportunities in state-of-the-art experimental techniques, and result in new example materials for undergraduate and graduate courses. It will also generate new demonstration materials to be used in outreach activities for attracting students from underrepresented groups to engineering and science professions, and for exposing university research to K-12 students, parents, and teachers in Texas.