Soft Vibration Sensor Based on Atomically Thin MoS₂ Nanoribbon Networks

Soft, low-profile, and conformal vibration sensors that can simultaneously and continuously measure and differentiate weak, complex physiological activities from human body are highly desired. Most of the commercially available vibration sensors are bulky and rigid and have limited form factors, which largely limit the implementation in human-interfacing applications requiring seamless integration, safer interaction, improved signal quality, and continuous long-term recording. Low-dimensional materials such as carbon nanotubes, metal nanowires, and two-dimensional materials (e.g., graphene and transition metal dichalcogenides (TMDs)) have been emerging as potential candidates for soft vibration sensors. However, they still suffer the drawbacks of low sensitivities to small mechanical stimuli, structural non-uniformity, and poor mechanical robustness over repeated deformation. In this work, we present an ultrathin and soft vibration sensor made of directly grown single atomic layer MoS₂ nanoribbon networks (NRNT) as an active sensing material and styrene-ethylene-butylene-styrene (SEBS) thermoplastic elastomer. In contrast to the same MoS₂ NRNT on rigid polyethylene terephthalate (PET) that shows typical negative piezoresistive gauge factor (GF) upon bending, the MoS₂ NRNT/SEBS system is a crack-based sensor, which renders a positive GF with a much higher absolute value (~1500 at 1.5% strain) compared to the MoS₂/PET system (~200 at 1.5% strain) and other low-dimension materials based sensor under similar strain. Compared to continuous MoS₂ film, the NRNT shows much higher mechanical robustness, ideal for long-term sensing with bending-unbending cycles upon vibration. The MoS₂/SEBS is able to sense acoustic vibration up to 500 Hz with a signal-to-noise of up to 40 dB and differentiate frequencies of mixed vibration signals. The MoS₂/SEBS vibration sensor shows great potential for soft electronics in health monitoring, biomedical, and clinical applications.