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

技术概述：该项目的研究目标是确定导致硅衬底上金属薄膜去湿的原子尺度机制和驱动力。应用原位像差校正的电子显微镜技术与理论研究相结合来研究这种界面脱粘。用原子分辨率和单原子灵敏度在横截面上系统地研究了沉积的薄膜与硅和氧化硅衬底之间的界面结构，同时在显微镜内同时进行了退湿处理。到目前为止，润湿-去湿转变主要是通过微米尺度上的形态变化来研究的。超薄润湿层的除湿动力学和机理以及随后在衬底表面形成的纳米颗粒大多是尚未探索的领域，因此是研究活动的重点。通过对界面结构、局部键合构型和润湿层形貌的原位原子尺度表征，确定了导致纳米级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的研究相结合，提供了对相应的原子尺度过程的基本理解，这些过程可以应用于广泛的其他可能的去湿应用，例如裂纹尖端的扩展。非技术摘要：除湿是自然界中经常观察到的一种基本效应。粘接或焊接后两种材料的任何分裂都是基于润湿-去湿转变，这种转变也发生在金属和陶瓷微观结构演变过程中的烧结和随后的晶粒长大过程中。去湿与产生催化纳米晶体的技术有关，这种纳米晶体是通过解体形成的，即连续的金属薄膜去湿。这类应用通常是催化剂激活生长纳米结构的先决条件，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被用来表征界面脱键的动力学，目的是从根本上理解原子尺度的润湿-去湿转变的驱动力和机制。预期结果将促进对更有效催化剂颗粒的受控制造、机械行为的原子尺度描述(裂纹尖端传播)等方面的新见解。外联和教育活动包括为当地农业社区未被充分代表的少数族裔学生举办特别讲座，为4至8年级的学生提供辅导计划，并为加州大学戴维斯分校工程学院制作研究生通讯。时事通讯将作为研究生的交流和展示平台，以及对未来本科生和研究生的展示和招聘工具。

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.