Experimental Investigation of Phonon Localization in Nanostructures

声子是固体中原子的集体振动，是半导体等材料中的主要热载体。声子输运物理学是重要的，因为它决定了材料的热和其他相关性质。正常情况下，声子要么以扩散的方式传播，从晶格杂质中随机散射，要么以直线的方式传播。 这个项目的目的是调查一个新的制度的声子运输称为“声子本地化”的声子的波动性质，防止他们传播。这项研究可能会导致新的方法来设计超越当前范式的热性能，特别是实现超低导热率，这对于广泛的热技术，如隔热和热能到电能的转换非常重要。该项目通过为研究生和本科生提供跨学科教育和培训机会，同时吸引代表性不足的群体进入科学领域，扩大了其影响。综合推广活动为大圣地亚哥地区的弱势第一代高中生提供纳米和能源技术的教育和研究机会。安德森局域化已经在费米子和玻色子中得到实验证明，包括电子、光子（光），最近还在超声波中得到证实。理论研究已经预测了热声子的局域化，但直到现在还没有实验验证这些预测，可能是由于与感知实验相关的艰巨挑战。本项目旨在克服这些实验挑战，并首次对低维无序系统中的声子局域化进行系统研究。声子本地化制度的实验探索的热输运测量的半导体纳米线精确控制的表面形貌和杂质浓度。声子本地化签名进行调查，包括依赖于纳米线的几何形状，表面粗糙度，缺陷浓度以及温度的热导。

Non-Technical Abstract:Phonons are collective vibrations of the atoms in a solid and are the dominant heat carriers in materials such as semiconductors. Phonon transport physics is important as it dictates thermal and other related properties of materials. Normally phonons either travel diffusively, randomly scattering from lattice impurities, or ballistically, in a straight line. This project aims to investigate a new regime of phonon transport termed "phonon localization" where the wave nature of the phonons prevents them from propogating. The study could lead to new approaches to engineer thermal properties beyond the current paradigm, in particular achieving ultra-low thermal conductivity, which is important for a wide range of thermal technologies such as thermal insulation and thermal to electrical energy conversion. The project broadens its impacts by providing interdisciplinary education and training opportunities to graduate and undergraduate students while attracting underrepresented groups into science. The integrated outreach activities provide education and research opportunities in nano- and energy technologies for disadvantaged, first generation high school students in the greater San Diego area. Technical AbstractAnderson localization has been experimentally demonstrated in both fermions and bosons, including electrons, photons (light), and recently with ultrasound. Theoretical studies have already predicted localization of thermal phonons, but until now there has been no experimental verification of these predictions, presumably due to the daunting challenges associated with the perceived experiments. This project aims to overcome these experimental challenges and carry out the first systematic study of phonon localization in low dimensional systems with disorders. The phonon localization regime is experimentally probed by thermal transport measurements of semiconductor nanowires with precisely controlled surface morphology and impurity concentration. Phonon localization signatures to be investigated include the dependence of thermal conductance on the nanowire geometry, surface roughness, and defect concentration as well as the temperature.