Principal Investigator Carl Thompson
Co-investigators W Carter , Bilge Yildiz
Solid-state dewetting is a physical phenomenon that disintegrates a continuous film into islands when the film is heated above a characteristic dewetting temperature but kept well below its melting temperature. It is driven by surface energy minimization and mediated via surface diffusion of atoms. Solid-state dewetting has been thought of as an issue in microelectronics, however, it has also demonstrated its potential as a simple patterning method that can be used to generate a complex and reg- ular array of micro- and nano-sized structures in a highly reproducible way. It starts either from edges of the film or in the continuous flat region by forming a natural hole. Various instabilities that develop at retracting edges have been understood via modeling and experimenting over the past years, including “pinch- off,” “corner instability,” and “Rayleigh-like instability.” The fingering instability, which is another instability that creates wire-like structures at retracting edges, is the current focus.
Through experiments, we have found conditions that lead to the fingering instability and have learned that spacing between fingers can be controlled via templating of film edge. We have also found that controlling the period of the fingering process affects the kinetics of the fingering, and we have developed an analytical model that predicts a relationship between the retraction rate and finger period. This model agrees well with experimental results. The increased understanding of the various instabilities at retracting edges can be used to design templates that will lead to specific complex structures during solid-state dewetting.
However, before we can fully exploit our understanding of templated solid-state dewetting to make designed structures, we must understand natural hole formation in thin films. In polycrystalline films, grain boundary triple junctions facilitate hole formation in a well-understood way, but the formation of holes in single-crystal films is not well understood. Studying this phenomenon is critical because holes create new edges from which the film retracts. Furthermore, thinner single-crystal films develop more natural holes per unit area, and the growth of these holes can come to dominate the overall reduction of film surface area. Unsuppressed natural hole formation interrupts edge retraction modes that were intentionally patterned to create a specific structure. If controlled, however, the formation of holes could be used to pattern periodic nanostructures that span large length scales, up to several centimeters. In parallel with studying the fingering instability, we are currently working with both Ni films on MgO substrates and Ru films on sapphire substrates to identify and understand the causes of natural hole formation in single- crystal films. By understanding these mechanisms, we aim to develop templated solid-state dewetting into a powerful and cost-effective method for producing nanostructures.