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.
