Ultra-conformable liquid metal particle monolayer on air/water interface for substrate-free E-tattoo

Abstract Gallium-based liquid metal has gained significant attention in conformal flexible electronics due to its high electrical conductivity, intrinsic deformability, and biocompatibility. However, the fabrication of large-area and highly uniform conformal liquid metal films remains challenging. Interfacial self-assembly has emerged as a promising method, but traditional approaches face difficulties in assembling liquid metal particles. Here, we realized the multi-size universal self-assembly (MUS) for liquid metal particles with various diameters (<500 μm). By implementing a z-axis undisturbed interfacial material releasing strategy, the interference of gravitational energy on the stability of floating particles is avoided, enabling the fabrication of ultra-conformable monolayer films with large areas (>100 cm 2 ) and high floating yield (50–90%). Moreover, the films can be conformally transferred onto complex surfaces such as human skin, allowing for the fabrication of substrate-free flexible devices. This eliminates interference from traditional substrate mechanical responses, making the liquid metal e-tattoo more user-friendly.