Dispersed VO2 phases in a flexible sensor for recognizing tensile and compressive stress

Stress recognition has been exploited in flexible sensors and has attracted considerable attention in the fields of electronic skins and intelligent robots towards artificial intelligence. Inspired by human skin, to identify the direction of external stresses or forces is one of the urgent and challenging issues in strain sensors. Here we present a sensor for recognizing tensile and compressive stress by the way of the stress-induced multiphase in VO2 microwires on flexible substrates. Direction-dependent resistance responses are utilized for identifying whether external tensile or compressive stress is applied to microwire-based sensors. The stress-triggered monoclinic M2 phase is stress-triggered and radially distributed in the VO2 microwire of monoclinic M1 phase. Discrete phases are stress-dependent and confirmed by phonon vibration modes and are further exploited to detect and distinguish the exertion direction of external stress. We expected that the stress-induced homogeneous junctions would help in constructing intelligent strain sensors and understanding stress recognition.