Unlocking superior fracture resistance in micro-ceramics for architected meta-materials via ALD stress engineering

Abstract

Micro- and nano-architected metamaterials exhibit remarkable mechanical properties, particularly damage tolerance from the interplay between design and material properties, yet their fracture mechanisms remain poorly understood. Strategies to tailor toughness in response to the anisotropic stress distributions experienced are lacking. Here, we demonstrate a novel approach to enhance the fracture toughness of micro-trusses by up to 165% via interface engineering, leveraging the high surface-to-volume ratios in these materials. We investigate the role of residual stress induced by Atomic Layer Deposition (ALD) on fracture behavior using cohesive-zone finite element simulations and advanced experimental techniques, including pillar-splitting indentation cracking and advanced residual stress measurements. Experiments were conducted on fused silica micro-pillars (fabricated via deep reactive ion etching) and glassy carbon micro-pillars (produced via two-photon polymerization and pyrolysis), coated with ALD Al${}_2$O${}_3$ or ZnO thin films. Our results reveal that median crack geometry combined with tensile residual stress in the coating enhances apparent toughness by inducing beneficial compressive stress in the substrate. Due to differences in crack morphology, Al${}_2$O${}_3$ coatings increase the toughness of fused silica by 165% but reduce that of glassy carbon. This study establishes ALD-induced stress modulation as a powerful tool for optimizing fracture resistance in micro-architected ceramics.