Treffer: Transmorphic Nucleation of Solids in Liquid Thin Films

This dissertation focuses on identifying and analyzing the mechanism of solid nucleation in liquid thin films. In doing so, we identify and describe a previously unrecognized mechanism of nucleation in condensed systems referred to as transmorphic nucleation. This cluster-shape-change-based mechanism is revealed as a general heterogeneous nucleation mechanism applicable to discontinuous phase transformations occurring in continuous or pre-patterned thin films, as well as in numerous materials systems that possess morphologically and chemically non-trivial heterogeneous-nucleation-catalyzing interfaces (e.g., polycrystalline materials, embedded nano-crystals, and materials with structured interfaces). Identifying, deciphering, and modeling the nature and details associated with how a new phase can nucleate in thin-film materials can be both scientifically meaningful for understanding discontinuous phase transformations in general, and technologically important for engineering various thin-film-based and nano-material-based applications and devices in particular. Classical nucleation theory (CNT) has long been established and regarded as the most practicable treatment that captures the thermodynamic and kinetic essence of the nucleation phenomenon in condensed systems in the simplest and most effective manner. Through a close examination of the theory, we identify and propose morphological equilibrium hypothesis (MEH) as an essential element of CNT. Our shape-transition-based model for transmorphic nucleation in thin films presented in this thesis illustrates that this hypothesis can be violated. As such, the CNT formulation is lacking in capturing the occurrence of the MEH-deviating shape evolution of the clusters, as for instance encountered during the process of transmorphic nucleation. In this dissertation, we conceptually, theoretically, and numerically examine and analyze the kinetic pathway through which nucleation of solids takes place in encapsulated liquid thin films. This example was selected for ...