Mechanical Loss Mechanisms in c-axis Gallium Nitride Nanowires

该研究的主要目标是通过实验测量c轴取向氮化镓（GaN）纳米线（NWs）在NW维度上的质量(Q)因子，同时开发新的多尺度耦合物理计算模型来量化主要损耗机制。将特别强调在技术相关的长度尺度范围内，对单个损失机制的相对重要性的大小和表面影响的理解。在实验上，这将通过首次提供关于大型c轴GaN NWs集合的机械共振位置和共振线宽的综合实验数据来实现，并且在NW长度（1至20微米），直径（10至100纳米），振动频率（100 kHz至100 MHz）和温度（4 K至400 K）的广泛范围内。新的多尺度建模方法，包括表面Cauchy-Born模型和耦合的纳米尺度能量和动量方程，将首次捕获表面应力对热和机械场的影响，以模拟和定量预测由于NWs的固有表面损失和热弹性阻尼而导致的q因子退化。如果成功的话，这项研究将对理解表面如何与氮化镓NWs的机械损失有关做出原创性贡献。它还将阐明控制尺寸的基本机制，以及温度对氮化镓NWs能量耗散的影响，同时描述每种损耗机制占主导地位的长度尺度。如果将忽略表面效应的标准体连续体模型缩小到纳米尺度，该项目将首次进一步量化NW模型中引入的误差。该项目进一步关注代表性不足的少数民族在纳米工程研究和教育过程中的参与。它将利用未来纳米工程师在纳米尺度建模和实验方面的培训，通过将拟议的研究整合到课程中。结果和见解将通过专业和物理教育网站广泛传播。

The key goal of the proposed research is to experimentally measure quality (Q)-factors for c-axis oriented Gallium Nitride (GaN) nanowires (NWs) over a large ensemble of NW dimensions, while simultaneously developing novel multiscale, coupled physics computational models to quantify the dominant loss mechanisms. A particular emphasis will be placed on understanding size and surface effects on the relative importance of the individual loss mechanisms across a technologically relevant range of length scales. Experimentally, this will be achieved by providing, for the first time, a comprehensive body of experimental data on mechanical resonance position and resonance linewidth for a large ensemble of c-axis GaN NWs, and over a wide range of NW lengths (1 to 20 microns), diameters (10 to 100 nm), vibrational frequencies (100 kHz to 100 MHz), and temperature (4 K to 400 K). Novel multiscale modeling approaches, including the surface Cauchy-Born model and coupled nanoscale energy and momentum equations that capture, for the first time, surface stress effects on both the thermal and mechanical fields, will be developed to simulate and quantitatively predict Q-factor degradation due to intrinsic surface losses and thermoelastic damping of NWs.If successful, this research will make original contributions in the understanding of how surfaces are implicated in the mechanical losses of GaN NWs. It will additionally elucidate the fundamental mechanisms governing size, and temperature effects on energy dissipation in GaN NWs, while delineating the length scales at which each loss mechanism dominates. This project will further quantify, for the first time, the errors introduced in NW modeling if standard bulk continuum models that neglect surface effects are scaled down to the nanoscale. The project further focuses on the involvement of under-represented minorities in the nanoengineering research and education process. It will leverage the training of future nanoengineers in both nanoscale modeling and experiment by the integration of the proposed research into the curriculum. Results and insights will be broadly distributed through professional and physics educational websites.