CAREER: Dewetting Atom-by-Atom: Identification of Driving Forces for Interfacial Debonding using In Situ Electron Microscopy

技术概述：本项目的研究目标是确定导致硅衬底上金属薄膜脱湿的原子尺度机制和驱动力。原位像差校正电子显微镜技术的应用与理论研究相一致，以研究这种界面脱粘。利用原子分辨率和单原子灵敏度对沉积薄膜与硅和氧化硅衬底之间的界面结构进行了系统的研究，同时在显微镜内进行了同步退火来进行脱湿。到目前为止，对润湿-脱湿转变的研究大多是在微米尺度上的形态变化。超薄润湿层的脱湿动力学和机制以及随后在衬底表面形成的纳米颗粒大多是未开发的领域，因此是研究活动的重点。界面结构、局部键构型和润湿层形貌的原位原子尺度表征用于识别导致纳米尺度脱湿的驱动力和局部脱粘机制。实验研究与分子动力学和密度泛函理论研究相结合，提供了对相应的原子尺度过程的基本理解，可以应用于广泛的其他可能的脱湿应用，例如裂纹尖端扩展。非技术总结：脱湿是自然界中经常观察到的一种基本效应。两种材料在粘合或焊接后的任何分裂都是基于润湿-脱湿转变，这也发生在烧结和随后的金属和陶瓷微观结构演变中的晶粒生长过程中。脱湿在技术上与产生由解体形成的催化纳米晶体有关，即连续金属薄膜的脱湿。这类应用通常是催化激活纳米结构生长的先决条件，如半导体纳米线、碳纳米管和纳米纤维等。原位像差校正电子显微镜技术用于表征界面脱键的动力学，目的是实现对润湿-脱湿转变的原子尺度驱动力和机制的基本理解。预期的结果将促进新的见解，例如，更有效的催化剂颗粒的控制制造，机械行为的原子尺度描述（裂纹尖端扩展）等。外展和教育活动包括为当地农业社区中代表性不足的少数民族学生提供特别讲座，为4至8年级学生提供指导计划，以及为加州大学戴维斯分校工程学院制作研究生通讯。该通讯将作为研究生交流和展示的平台，同时也是向未来的本科生和研究生展示和招聘的工具。

TECHNICAL SUMMARY: The research objective of this project is to identify atomic-scale mechanisms and driving forces that cause dewetting of thin metal films on silicon substrates. In situ aberration-corrected electron microscopy techniques applied in concert with theoretical investigations to study such interfacial debonding. The interface structure between as-deposited thin films and silicon and silicon oxide substrates is systematically investigated in cross-section with atomic resolution and single atom sensitivity while dewetting is enforced by simultaneous annealing inside the microscope. Wetting-dewetting transitions have so far mostly been studied by morphological changes on the micron length-scale. Dewetting dynamics and mechanisms for ultra-thin wetting layers and the subsequent formation of nanoparticles on the substrate surface is mostly unexplored territory and is therefore in the focus of the research activities. The in situ atomic-scale characterization of interface structures, local bonding configurations and morphologies of the wetting layer are used to identify driving forces and local debonding mechanisms that lead to nano-scale dewetting. The combination of experimental studies with molecular dynamics and density functional theory investigations provides a fundamental understanding of the corresponding atomic-scale processes that can be applied to a wide range of other possible applications of dewetting, such as crack-tip propagation. NON-TECHNICAL SUMMARY: Dewetting is a fundamental effect frequently observed in nature. Any splitting apart of two materials after gluing or soldering is based on wetting-dewetting transitions, which also occur during sintering and subsequent grain growth in the evolution of microstructures of metals and ceramics. Dewetting is technologically relevant for generating catalytic nano-crystals formed by the disintegration, i.e. dewetting of continuous thin metal films. Such applications are often the prerequisite to catalyst-activated growth of nanostructures, such as semiconductor nanowires, carbon nanotubes and nanofibers, etc. In situ aberration-corrected electron microscopy techniques are used to characterize the dynamics of interfacial de-bonding with the goal to achieve a fundamental understanding of the atomic-scale driving forces and mechanisms for wetting-dewetting transitions. The anticipated results will foster new insights to, e.g., the controlled fabrication of more efficient catalyst particles, the atomic-scale description of mechanical behaviors (crack-tip propagation), etc. Outreach and educational activities cover special lectures to underrepresented minority students in local farming communities, mentoring programs for 4th through 8th grade pupils, and the generation of a graduate student newsletter for the College of Engineering at UC Davis. The newsletter will serve as a communication and presentation platform for graduate students, as well as a showcase and recruitment tool to and for future undergraduate and graduate students.