Fig. 3: VGS performance and sensing mechanism.
From: Vertical graphene on flexible substrate, overcoming limits of crack-based resistive strain sensors
a Gauge factor as a function of strain, estimated from Fig. 2c. Except for 2% strain, no noticeable changes at each strain are observed, indicating highly reversible behavior. The width of highlighted color bars indicates the difference between averaged gauge factors when stretching and releasing at specific strains. b Resistance measured between 0 and 2% strain for 10,000 consecutive cycles with a strain sweep rate of 1 mm/s and 0.1 s hold time at the peak. The response and recovery times are approximately 200 and 100 ms from the enlarged curves in blue box. c, d Gap size between cracks and crack density versus applied strain for VGS-V (c) and VGS-H (d). In e the ‘vertical’ cracks are those formed initially during removal from the SiO2 substrate and the ‘horizontal’ cracks are those newly formed during stretching. e Resistance as a function of time with applied stepwise strain when the elongated direction is parallel to the cracks on the BFG (upper illustration). The resistance approaches infinity when the applied strain reaches up to 40%, namely, the current path is broken. But, the resistance recovers to the initial value during release, and the post-overload resistance is almost the same to the pre-overload resistance at each strain. Right panel of e In situ SEM images of VGS-H during stretching (I (0%), green box and II (35%), yellow box)/release (III (15%), purple box and IV (0%), blue box). Scale bars, 200 μm. Inset in I, enlarged SEM image, clearly showing vertical cracks on the BFG. Scale bar, 50 μm.
