An Experimental Study of the Work Hardening Behavior of Metallic Thin Films

技术概述：该项目的目标是开发实验和模型，以阐明材料在小而受限的体积中的机械行为，特别强调材料如何加工硬化以及在自由表面或硬钝化层附近发生的位错过程。许多微电子和微机械设备是由不同的材料组合成复杂的结构。这些设备的部件经常承受非常高的应力。应力如此之高，以至于它们通常不能被相同的材料以散装形式支撑。洞察材料在这些小长度尺度上的机械行为和精确的模型来描述这种行为对于设计和制造可靠的设备至关重要。这一目标将通过微观力学实验和离散位错模拟相结合来实现。实验将集中于测量多晶独立薄膜在一系列钝化条件下的应力-应变行为。恢复机制将通过蠕变和松弛实验进行研究。在自由表面或钝化层附近形成的位错亚结构将在斯坦福同步辐射实验室使用掠射x射线散射和哈佛大学的透射电子显微镜进行研究。多晶薄膜的应力-应变行为将使用离散位错模拟来模拟，该模拟将结合适当的恢复机制来模拟薄膜的硬化行为。非技术总结：该奖项将使人们更好地理解薄膜和涂层的变形行为，从而有可能在微纳米尺度上设计和制造更可靠的设备。受益最大的行业是MEMS和半导体行业。低成本、大面积、柔性电子的新兴领域也将受益于对用作电气互连的金属薄膜的机械行为的基本理解。调查结果将发表在档案期刊上，并将公布在哈佛工程与应用科学学院主办的档案网站www.iMechanica.org上。iMechanica是一个年轻科学家的讨论论坛，旨在加强研究人员之间的交流，使力学和材料更容易被更广泛的公众所了解。该项目也将有助于研究生和本科教育。该奖项将支持一名研究生，并将为几名本科生提供研究机会。长期以来，首席研究员一直让不同背景的本科生参与他的研究项目，这个奖项将确保这种做法继续下去。该奖项下的研究将有助于薄膜力学研究生课程的发展。通过与荷兰代尔夫特技术大学的合作，该项目具有国际组成部分。他们将在离散位错建模方面贡献专业知识，并将这种能力带到哈佛大学。

TECHNICAL SUMMARY:The objective of this project is to develop experiments and models to elucidate the mechanical behavior of materials in small, constrained volumes with a particular emphasis on how a material work-hardens and on the dislocation processes that take place in the vicinity of a free surface or a hard passivating layer. Many micro-electronic and micro-mechanical devices consist of dissimilar materials put together in complex architectures. Components of these devices are often subjected to very high stresses ? stresses so high, that they can often not be supported by the same material in bulk form. Insight in the mechanical behavior of materials at these small length scales and accurate models to describe this behavior are essential to the design and fabrication of reliable devices. This objective will be achieved through a combination of micro-mechanical experiments and discrete dislocation simulations. The experiments will focus on measuring the stress-strain behavior of polycrystalline freestanding thin films under a range of passivation conditions. Recovery mechanisms will be investigated using creep and relaxation experiments. The dislocation substructure that develops in the vicinity of a free surface or a passivating layer will be investigated using grazing incidence X-ray scattering at the Stanford Synchrotron Radiation Laboratory and by means transmission electron microscopy at Harvard. The stress-strain behavior of polycrystalline films will be modeled using discrete dislocation simulations that will incorporate appropriate recovery mechanisms to model the hardening behavior of the films.NON-TECHNICAL SUMMARY:This award will lead to a better understanding of the deformation behavior of thin films and coatings, making it possible to design and fabricate more reliable devices at the micro- and nano-scales. Industries that stand to gain the most are the MEMS and semiconductor industries. The nascent field of low-cost, large-area, flexible electronics will also benefit from a fundamental understanding of the mechanical behavior of the thin metallic films they use as electrical interconnects. Results of the investigation will be published in archival journals and will be posted on the archival web site www.iMechanica.org hosted by the Harvard School of Engineering and Applied Sciences. iMechanica serves as a discussion forum for young scientists with a goal of enhancing communication among researchers and of making mechanics and materials more accessible to a wider public. The project will also contribute to both graduate and undergraduate education. The award will support one graduate student and will provide research opportunities to several undergraduate students. The Principal Investigator has long engaged undergraduate students of diverse background in his research projects and this award will ensure that this practice continues. Research under this award will contribute to the development of a graduate course on thin-film mechanics. The project has an international component through collaboration with the Technical University of Delft in the Netherlands. They will contribute expertise in discrete dislocation modeling and bring this capability to Harvard University.