Phonon Coherence and Scattering Effects in Laterally Periodic Silicon Nanostructures

CBET-1336734 PI：K.E. Goodson斯坦福大学微米和纳米声子/光子晶体已经在许多新兴技术中找到了应用和/或保持了希望，例如纳米光子器件，高ZT热电材料，用于光学冷却的声子-光子晶体，声学绝缘体，微声学元件，例如波导，腔和滤波器，以及NEMS/MEMS热传感器和致动器。 在这些二维周期性多孔（2D-PP）和一维纳米阶梯（1D-NL）结构中的声子相干和散射效应可能导致其有效热导率降低两个数量级以上。探索这些新结构中声子输运的有趣物理学是该项目的主题，通过对硅膜的仔细输运性质测量，由于绝缘体上硅制造技术的改进，硅膜提供了几乎无与伦比的材料质量。 我们探索了一个广泛的关键尺寸，如膜厚度，孔径和间距范围从20到1000 nm，以及表面粗糙度范围从2到10 nm，温度范围从10到800 K。 我们实施新的孔设计，以打破或控制发病周期性和诱导多个声子带隙。 虽然该项目的主要重点是向科学界提供最大的一套准确和充分表征的实验数据，我们还试图开发一个模拟工具/模型，可以帮助指导实验设计，以及改进现有的模型，以扩大其有限的适用范围和准确性。这个项目解决了几个悬而未决的问题的基本声子输运在纳米结构。 例如，我们想知道二维和一维纳米结构热导率极端降低的起源，以及这种降低受孔几何形状和温度影响的方式。 本计画试图找出孔隙与边界上的经典声子散射与声子相干效应（色散）对热传导的相对贡献。 我们应该学习是否有可能在二维结构中使用多个周期性模式来创建多个声子带隙，并能够理解打破周期性模式的影响。 可以直接从拟议研究中受益的其他科学技术领域包括热电能发电和冷却。 潜在地，更有效的热电二维材料可以导致这些装置的显著改进。 理解纳米结构中的输运将极大地有利于纳米制造的热传感器和致动器的性能和可靠性。

CBET-1336734PI: K.E. GoodsonStanford UniversityMicro- and nano-phononic/photonic crystals have found application and/or hold promise in many emerging technologies such as nanophotonic devices, high ZT thermoelectric materials, phononic-photonic crystals for optical cooling, acoustic insulators, micro-acoustic components such as waveguides, cavities and filters, as well as NEMS/MEMS thermal sensors and actuators. Phonon coherence and scattering effects in these two-dimensional periodically porous (2D-PP) and one-dimensional nanoladder (1D-NL) structures may result in more than two orders of magnitude reduction in their effective thermal conductivities. Exploring the intriguing physics of phonon transport in these novel structures is the subject of this project by means of careful transport property measurements on silicon films, which offer nearly unparalleled material quality owing to the refinement of silicon on insulator fabrication technology. We explore a wide range of critical dimensions such as film thickness, hole diameter and separation ranging from 20 to 1000 nm as well as surface roughnesses ranging from 2 to 10 nm and temperatures ranging from 10 to 800 K. We implement novel pore designs to break or control the onset periodicity and induce multiple phononic bandgaps. While the primary focus of this project is to make available the largest set of accurate and well-characterized experimental data to the scientific community, we also attempt to develop a simulation tool/model that can help to guide the experimental design as well as improve upon the existing models to extend their limited range of applicability and accuracy.This project addresses several outstanding questions on the fundamentals of phonon transport in nanostructures. For example, we would like to know the origin of extreme reduction in thermal conductivity two-dimensional and one-dimensional nanostructures and the manner in which this reduction is affected by pore geometry and temperature. This project attempts to identify the relative contributions of classical phonon scattering on pores and boundaries and phonon coherent effect (dispersion) to heat conduction. We should learn if it possible to create multiple phononic bandgaps using multiple periodicity patterns in the 2D structures and be able to understand the impact of breaking the periodicity patterns. Other areas of science and technology that can directly benefit from the proposed research include thermoelectric energy generation and cooling. Potentially, a more efficient thermoelectric two-dimensional material may result in significant improvement of these devices. Understanding of the transport in nanostructures structures will greatly benefit the performance and reliability of nanofabricated thermal sensors and actuators.