Compositionally-Driven Formation Mechanism of Hierarchical Morphologies in Co-Deposited Immiscible Alloy Thin Films

Abstract

Co-deposited immiscible alloy systems will form hierarchical microstructures under specific processing parameters that accentuate the difference in constituent element mobility. The formation mechanism of these unique hierarchical morphologies during the deposition process is hard to identify since the characterization of these structures is typically done post-deposition. The present work employs a combination of phase-field modeling for the evolution of microstructure during deposition with microscopy characterization of experimentally-deposited thin films to reveal the origin of the formation mechanism of hierarchical morphologies in co-deposited immiscible alloy thin films. Our results show the significant influence of a local compositional driving force that triggers the simultaneous evolution across multiple length scales, necessary for hierarchical formation. We reveal that there must be a threshold local phase concentration near the surface of the thin film in order to generate distinct hierarchical morphologies in a single domain.