Mechanics of Materials at the Extreme Length-Scales

在极小的长度尺度上，传统的材料力学不再有效，新的变形机制出现。例如，在纳米尺度上，金属中基于位错的机制让位错为基于晶界的机制。这项研究的重点是极长尺度下的机械击穿如何影响其他物理特性。例如，晶界阻碍电流和热载流子的作用比位错高几个数量级。结果表明，当力学行为由位错(体相)转变为晶界(纳米)为主时，极小的应变变化就会引起电导率或热导率的较大变化。这一建议的核心概念是，在极小的长度尺度上，机械变形力学与其他物理(热和电)性质强烈耦合。这项研究将在极小的长度尺度上提供材料力学的基本见解，这将使？调谐？提高能量传输或转换效率的热或电性能的应变。该方案的目的是在纳米尺度上研究样品尺寸、微结构和缺陷对机械变形和电/热传输之间的耦合的作用。PI将使尺寸小于3 mm x 3 mm的新型实验工具纳米丰富，以测量纳米级薄膜的机械应力、应变、导热系数和导电率。根据数据，PI将构建应变-温度-传输(热和电)图来验证所提出的耦合概念。在测量热物性的同时观察缺陷和变形的演变将预示着材料表征的范式转变，并缩小理论和实验之间的差距。这项拟议的研究可能会影响未来微电子、柔性电子、光电子和激光设备等领域的机械可靠性和热管理问题。

At the extremely small length-scales, the conventional mechanics of materials cease to be effective and new deformation mechanisms emerge. For example, dislocation based mechanisms in metals give way for grain boundary based mechanisms at the nanoscale. The focus of this research is on how mechanical breakdown at the extreme length-scales influence other physical properties. For example, grain boundaries impede current and heat carriers several orders of magnitude higher than dislocations do. As a result, when the mechanics change from dislocation (bulk) to grain boundary (nano) dominated one, very small change in strain can cause large changes in electrical or thermal conductivity. The core concept of this proposal is that at the extremely small length-scales, the mechanical deformation mechanics is strongly coupled with other physical (thermal and electrical) properties. The research will provide fundamental insights in the mechanics of materials at the extremely small length-scales, which will allow ?tuning? of thermal or electrical properties with strain for enhanced energy transport or conversion efficiency. The objective of this proposal is to study the role of specimen size, microstructure and defects on the coupling between mechanical deformation and electrical/thermal transport at the nanoscale. The PI will nanofabricate novel experimental tools with less than 3mm x 3mm size footprint to measure mechanical stress, strain, thermal conductivity and electrical conductivity of nanoscale thin films. From the data, the PI will construct the strain-temperature-transport (thermal and electrical) map to validate the proposed coupling concept. Seeing the defects and deformation as they evolve while measuring the thermo-physical properties will herald a paradigm shift in materials characterization and reduce the gap between theory and experiments. The proposed research will potentially impact the mechanical reliability and thermal management issues in future micro-electronics, flexible electronics, opto-electronics and laser devices, to name a few.