Electronic tattoos based on large-area Mo₂C grown by chemical vapor deposition for electrophysiology

Tattoo electronics has attracted intensive interest in recent years due to its comfortable wearing and imperceivable sensing, and has been broadly applied in wearable healthcare and human–machine interface. However, the tattoo electrodes are mostly composed of metal films and conductive polymers. Two-dimensional (2D) materials, which are superior in conductivity and stability, are barely studied for electronic tattoos. Herein, we reported a novel electronic tattoo based on large-area Mo₂C film grown by chemical vapor deposition (CVD), and applied it to accurately and imperceivably acquire on-body electrophysiological signals and interface with robotics. High-quality Mo₂C film was obtained via optimizing the distribution of gas flow during CVD growth. According to the finite element simulation (FES), bottom surface of Cu foil covers more stable gas flow than the top surface, thus leading to more uniform Mo₂C film. The resulting Mo₂C film was transferred onto tattoo paper, showing a total thickness of ~ 3 μm, sheet resistance of 60–150 Ω/sq, and skin-electrode impedance of ~ 5 × 10⁵ Ω. Such thin Mo₂C electronic tattoo (MCET in short) can form conformal contact with skin and accurately record electrophysiological signals, including electromyography (EMG), electrocardiogram (ECG), and electrooculogram (EOG). These body signals collected by MCET can not only reflect the health status but also be transformed to control the robotics for human–machine interface.