CAREER: Mean Free Path Spectroscopy - Experimental determination of the mean free path distribution in solids

职业：平均自由程光谱 - 固体中平均自由程分布的实验测定

• 批准号: 1358370
• 负责人: Chris Dames
• 金额: $ 28.72万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1358370&HistoricalAwards=false
• 关键词: CAREER; Mean; Free; Path; Spectroscopy

1055317DamesEngineering the conduction of heat in solid materials is essential for numerous applications ranging from thermal management and insulation, to power generation, to information technology. Many modern systems including lasers, thermoelectric energy converters, and transistors are based on materials containing structures much smaller than one micron. These structures can cause very large reductions in the thermal conductivity, sometimes by a factor of ten or more, as compared to the familiar bulk values reported in handbooks. To predict and engineer the thermal conductivity in both bulk and microstructured materials, it is essential to understand the mean free paths of the energy carriers, that is, the average distance between their collisions. Although various models of the thermal conductivity have been used widely for more than half a century, when these models are applied to microstructures they often exhibit large disagreements with each other. The heart of the model disagreements is their different mean free path calculations, yet direct experimental measurements of the full distribution of mean free paths have not been reported to date for any material. Therefore, the primary goal of this CAREER proposal is to experimentally measure the full distribution of mean free paths in several standard materials. To accomplish this objective, this project will pursue two complementary experimental strategies, designed to cover a very large range of length and time scales. The first approach involves systematic measurements of steady-state conduction in microstructures with sizes ranging from around 50 nm to around 100 microns. The data will then be transformed into mean free path spectra using a new Fredholm integral equation. The second approach involves measuring ultrafast thermal transients ranging from around 0.1 ns to around 10 microseconds, and analyzed using the Boltzmann transport equation. The intellectual merit of this CAREER proposal is in advancing the fundamental understanding of thermal conductivity. By experimentally quantifying the real mean free path distributions, these measurements will help identify which of the standard models in use today can actually be correct. This project will also test a postulate recently introduced by Y. K. Koh and D. Cahill to relate their observed frequency-dependent thermal conductivity to a mean free path distribution. The project also proposes to develop an all-electrical pump-probe apparatus that should be more accessible and less costly than the important optical pump probe experimental technique. The broader impacts of this project include both engineering relevance and an education/outreach component. The fundamental knowledge gained will be relevant for a wide range of materials systems including alloys, crystalline materials, and amorphous materials, and for thermal engineering of numerous applications including lasers, transistors, and thermoelectric energy conversion. The outreach activities are built around workshops at regional high schools based on thermoelectric energy conversion and visualizing the nanoworld at the human scale. At the end of each workshop the workshop materials will be donated to the classroom for their future use. The workshop content has already been strengthened by two iterations with the intended high school science teachers, and one teacher will be recruited and supported for a summer to optimize the workshop content and disseminate it on a website.

1055317Dameseginering在固体材料中的热传导对于从热管理和绝缘，到发电到信息技术的许多应用至关重要。 许多现代系统在内，包括激光器，热电能转换器和晶体管都基于包含比一微米小得多的结构的材料。 与手册中报道的熟悉的散装值相比，这些结构会导致热导率的降低，有时甚至增加十倍或更多。 为了预测和设计大量和微结构材料的热导率，必须了解能量载体的平均自由路径，即碰撞之间的平均距离。 尽管多种模型的热导率模型已被广泛使用了半个多世纪，但是当将这些模型应用于微观结构时，它们经常表现出很大的分歧。 模型分歧的核心是其不同的平均自由路径计算，但尚未报告任何材料的平均自由路径的完整分布的直接实验测量。 因此，这项职业建议的主要目标是实验测量几种标准材料中平均自由路径的完整分布。 为了实现这一目标，该项目将采用两种互补的实验策略，旨在涵盖非常范围的长度和时间尺度。 第一种方法涉及对微观结构的稳态传导的系统测量，尺寸范围从约50 nm到约100微米。 然后，使用新的Fredholm积分方程将数据转换为平均自由路径光谱。 第二种方法涉及测量从约0.1 ns到10微秒左右的超快热瞬变，并使用Boltzmann传输方程进行分析。这项职业建议的智力优点在于促进对导热性的基本理解。 通过实验量化实际平均自由路径分布，这些测量结果将有助于确定当今使用的标准模型实际上是正确的。 该项目还将测试Y. K. Koh和D. Cahill最近引入的一个假设，以将其观察到的频率依赖性导热率与平均自由路径分布联系起来。 该项目还提议开发一种全电动泵探针设备，该设备应该比重要的光学泵探针实验技术更容易访问和成本更低。 该项目的更广泛影响包括工程相关性和教育/外展部分。 获得的基本知识将与多种材料系统有关，包括合金，结晶材料和无定形材料，以及许多应用的热工程，包括激光器，晶体管和热电能量转换。 外展活动是基于热电能量转换的区域高中研讨会建立的，并以人尺度的方式可视化纳米界。 在每个研讨会结束时，研讨会材料将捐赠给教室以供未来使用。 与预期的高中科学老师的两次迭代已经加强了研讨会的内容，将在一个夏季招募和支持一位老师，以优化研讨会内容并在网站上进行传播。