Formation of twins during epitaxial growth of alpha -iron films on silicon (111)

Synthesis of Heterostructured Metallic Films with Precisely Defined Multimodal Microstructures

Heterostructured materials (e.g., metals with multimodal microstructures) offer the promise of unprecedented functionality and performance by avoiding trade-offs between competing properties such as strength and ductility. However, methods to reproducibly synthesize heterostructured materials with explicit microstructural control are still elusive, and therefore optimizing their mechanical and functional properties via microstructural engineering is presently infeasible. Here, we describe a broadly applicable method to synthesize metallic films with precisely defined multimodal microstructures. This method enables explicit control of the size, volume fraction, and spatial connectivity of fine and coarse grains by exploiting two distinct forms of film growth (epitaxial and Volmer-Weber) simultaneously. We fabricated Cu and Fe films with bimodal and multimodal microstructures using this method and investigated their mechanical properties, which reveals a hitherto unknown breakdown in the strength-ductility synergy produced by such microstructures at small sample dimensions. Our approach enables systematic design of multimodal microstructures to tailor the mechanical properties of metallic materials and provides a platform to create functional thin films and 2D materials with prescribed phase morphologies and microstructures.