Experimental and Computational Study of Pore Morphology Evolution Mechanisms in Nanoporous Metal Thin Films Under Thermal/Electrical/Mechanical Stress Fields

非技术综述：纳米结构金属对包括电池电极、生物医学植入涂层和生物传感器在内的各种应用产生了巨大的影响。在这些条件下，材料通常会受到各种外部因素(例如，温度、电场和机械应力场)的影响，这些因素会逐渐改变材料的特性和性能。这个项目的目的是用纳米多孔金(NP-Au)作为模型系统，对这些过程有一个基本的了解。NP-Au是一类新兴的纳米多孔金属，其催化、光学、机械和生物医学特性引起了人们的极大兴趣。预期的结果是产生科学知识，允许精确控制纳米多孔金属的形状和结构变化；这将改善对材料性质如何演变的预测，并反过来提高纳米结构金属在应用中的性能。作为该项目的一部分开发的仪器和模拟技术也将广泛适用于其他材料系统，包括其他纳米多孔金属和金属纳米线。该项目的广泛影响包括社会效益和教育机会，例如与主要研究人员一起进行本科研究的机会，以及通过交互式计算机游戏教授微/纳米制造和原子模拟关键概念的互动教育工具。技术摘要：纳米多孔金(NP-Au)的形态通常是通过有选择地溶解合金中不那么贵重的组分来产生双连续多孔结构而产生的，通常通过热退火来调节，其中金原子的表面扩散增强导致韧带粗化。然而，在低温下施加电流和机械应力也会显著影响粗化程度和所产生的形貌，尽管这些影响尚未被研究。该项目假设，通过同时施加加热、电流和机械应力，可以更精细地调制NP-Au中的形态变化，并开发出新的结构特征。一开始，将NP-Au置于不同的温度、电场和机械应力场中，将允许表征各个场的影响。随后的实验和模拟将研究同时施加场的协同效应或紧急效应。该项目的关键科学成果将包括表征加热、电流和机械应力对孔形态演变的解耦效应，识别潜在的机制和相应的动力学，以及一个由实验和模拟支持的模型，以根据这些场的综合影响预测形态演变。对纳米多孔金属形态演变的精确控制将扩大一系列实际可获得的纳米结构和相应的材料特性，这些材料可以作为增强型生物医学设备涂层、催化燃料电池或传感器的等离子体材料来实现。同时，该项目将利用课堂作业开发一个实验程序互动模拟库，强调微/纳米制造，重点是纳米结构金属和相关原子过程的可视化。此外，通过一项计划，本科生撰写一份简短的研究计划书，竞争暑期实习机会，学生将在主要研究人员的指导下受雇于定制项目。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Summary:Nanostructured metals have had a tremendous impact on a variety of applications including battery electrodes, biomedical implant coatings, and biosensors. Materials in these conditions are generally subject to various external factors (e.g., temperature, electric, and mechanical stress fields) that can gradually change the material's properties and performance. The purpose of this project is to develop a fundamental understanding of these processes using nanoporous gold (np-Au) as a model system. The np-Au belongs to the emerging class of nanoporous metals that have attracted significant interest for its catalytic, optical, mechanical, and biomedical features. The expected outcome is the generation of scientific knowledge that allows for precise control of shape and structure changes in nanoporous metals; this will improve predictions of how material properties evolve and in turn enhance the performance of nanostructured metals in applications. The instrumentation and simulation techniques developed as part of the project will be widely applicable to other material systems as well, including other nanoporous metals and metallic nanowires. The broader impacts of this project include societal benefits and educational opportunities, such as undergraduate research opportunities with the principal investigators and interactive educational tools that teach key concepts of micro-/nano-fabrication and atomistic simulations via interactive computer games.Technical Summary:The morphology of nanoporous gold (np-Au), typically produced by selectively dissolving a less noble component of an alloy to create a bicontinuous porous structure, is conventionally modulated via thermal annealing where the enhanced surface diffusion of gold atoms leads to ligament coarsening. However, both the extent of coarsening and the resulting morphologies can also be significantly affected by the application of electrical currents and mechanical stresses at low temperatures, though these effects have not yet been studied. The project hypothesizes that morphological change in np-Au can be more finely modulated, and novel structural features be developed, by applying heating, electrical current, and mechanical stresses in concert. Initially subjecting np-Au to varying temperature, electric, and mechanical stress fields will allow the effects of the individual fields to be characterized. Subsequent experiments and simulations will investigate synergistic or emergent effects from applying the fields simultaneously. Key scientific outcomes of the project will include characterization of the decoupled effects of heating, electrical current, and mechanical stresses on pore morphology evolution, identification of the underlying mechanisms and the corresponding kinetics, and a model supported by experiments and simulations to predict the morphological evolution from the combined influences of these fields. Precise control of morphology evolution in nanoporous metals will expand the set of practically accessible nanostructures and corresponding material properties that can be implemented as enhanced biomedical device coatings, catalytic fuel cells, or as plasmonic materials for sensors. In tandem, the project will employ classroom assignments to develop a library of interactive simulations of experimental procedures that emphasize micro-/nano-fabrication with a focus on nanostructured metals and visualizations of the relevant atomic processes. In addition, through a scheme where undergraduate students write a short research proposal to compete for a summer internship, the students will be employed on customized projects under mentorship of the principal investigators.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.