Mechanics of Materials at the Extreme Length-Scales

在极小尺度下，传统的材料力学不再有效，新的变形机制出现。例如，金属中基于位错的机制让位于纳米级的基于晶界的机制。本研究的重点是如何在极端长度尺度的机械故障影响其他物理性能。例如，晶界阻碍电流和热载体的几个数量级高于位错。因此，当力学从位错（体）到晶界（纳米）为主的力学变化时，应变的非常小的变化可以引起电导率或热导率的大的变化。该建议的核心概念是，在极小的长度尺度下，机械变形力学与其他物理（热和电）性质强烈耦合。这项研究将提供在材料力学的基本见解在极小的长度尺度，这将允许？调音？热或电性能与应变的增强的能量传输或转换效率。本提案的目的是研究试样尺寸，微观结构和缺陷之间的耦合在纳米尺度上的机械变形和电/热传输的作用。PI将纳米制造新的实验工具，尺寸小于3 mm x 3 mm，用于测量纳米薄膜的机械应力，应变，热导率和电导率。根据数据，PI将构建应变-温度-传输（热和电）图，以验证所提出的耦合概念。在测量热物理性能的同时看到缺陷和变形的演变，将预示着材料表征的范式转变，并减少理论和实验之间的差距。拟议的研究将潜在地影响未来微电子、柔性电子、光电子和激光器件中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.