Micro-/nano-voids guided two-stage film cracking on bioinspired assemblies for high-performance electronics

Current metal film-based electronics, while sensitive to external stretching, typically fail via uncontrolled cracking under a relatively small strain (~30%), which restricts their practical applications. To address this, here we report a design approach inspired by the stereocilia bundles of a cochlea that uses a hierarchical assembly of interfacial nanowires to retard penetrating cracking. This structured surface outperforms its flat counterparts in stretchability (130% versus 30% tolerable strain) and maintains high sensitivity (minimum detection of 0.005% strain) in response to external stimuli such as sounds and mechanical forces. The enlarged stretchability is attributed to the two-stage cracking process induced by the synergy of micro-voids and nano-voids. In-situ observation confirms that at low strains micro-voids between nanowire clusters guide the process of crack growth, whereas at large strains new cracks are randomly initiated from nano-voids among individual nanowires. Metal film-based electronics usually fail via uncontrolled cracking at small strains. Here, the authors design a micro-/nano-structured surface with bundled flexible nanowires onto which a metal film can stretch more than a regular flat surface, retard penetrating cracks and remain sensitive.