Flexible Zinc Oxide Nanowire Array/Graphene Nanohybrid for High-Sensitivity Strain Detection

Abstract

A fully flexible strain sensor consisting of vertically aligned ZnO nanowires on graphene transferred on polyethylene terephthalate with prefabricated Au/Ti electrodes (ZnO-VANWs/Gr)/PET) has been obtained. The ZnO-VANWs were grown in solution using a seedless hydrothermal process and are single-crystalline of (0001) orientation that provides optimal piezoelectric gating on graphene when deformed mechanically. The change of the graphene channel conductance under such a piezoelectric gating through transduction of the mechanical deformation on the ZnO-VANWs/Gr was used to detect the strain induced by the deformation. Under applied normal forces of 0.30, 0.50, and 0.70 N in a dynamic manner, the ZnO-VANWs/Gr/PET strain sensors exhibited a high response and response times of ∼0.20 s to both force on and off were achieved. Under mechanical bending curvatures of 0.18, 0.23, 0.37, and 0.45 cm –1 , high sensitivity of the gauge factors up to ∼248 and response times of 0.20 s/0.20 s (rise/fall) were achieved on the ZnO-VANWs/Gr/PET strain sensors. Moreover, the response changes polarity when the directions of bending alters between up and down, corresponding to the polarity change of the space charge on the ZnO-VANWs/Gr interface as a consequence of the compressive and tensile strains along the ZnO-VANWs. This result shows that the low-cost and scalable ZnO-VANWs/Gr/PET strain sensors are promising for applications in stress/strain monitoring, wearable electronics, and touch screens.

Low-Temperature Growth of ZnO Nanowires from Gravure-Printed ZnO Nanoparticle Seed Layers for Flexible Piezoelectric Devices

“…Flexible piezoelectric transducers make the development of innovative devices possible, especially in the energy and sensor fields [1]. Several piezoelectric materials have been studied and integrated into flexible substrates, including organic materials, such as poly(vinylidene fluoride) (PVDF) [2] and its co-polymers [3][4][5]; inorganic materials, like lead zirconate titanate (PZT) [6], potassium sodium niobate (KNN) [7], lead magnesium niobate-lead titanate (PMN-PT) [8], barium titanate (BaTiO 3 ) [9], zinc stannate (ZnSnO 3 ) [10], and bismuth ferrite (BiFeO 3 ) [11]; and semiconductors like zinc oxide (ZnO) in the shape of nanowires (NWs) [12,13]. Among those materials, ZnO has attracted a of 15 great deal of attention because it is biocompatible, abundant, and sustainable, making it interesting for future applications while reducing the use of critical and toxic materials [14].…”

Metal-Oxide Nanomaterials Synthesis and Applications in Flexible and Wearable Sensors

“…MONs are used as piezoresistive materials, , piezoelectric materials, and fillers enhancing piezoelectric characteristics in flexible/wearable sensor fabrication, detecting diverse mechanical deformations including bending, stretching, and compression . In particular, ZnO is the most common material used for mechanical sensors because of its magnificent piezoelectric and piezoresistive performance.…”

“…The sensor detected mercury electrochemically as well . A piezoelectric mechanical sensor was established by vertically growing ZnO NWs on the transferred graphene on PET . The vertically aligned (0001) orientation single-crystalline ZnO NWs provide optimal piezoelectric behavior under mechanical deformation, resulting in high strain sensitivity and response speed.…”

Elucidation of Strain-Dependent, Zinc Oxide Nanorod Response for Nanorod-Guided Fluorescence Intensity

“…They include changing chemical compositions through doping [ 16 , 17 , 18 ], altering crystalline structures [ 19 , 20 , 21 , 22 ], and applying a magnetic field [ 23 ]. More recently, mechanical strain has also been used to modulate ZnO properties [ 24 , 25 , 26 , 27 , 28 , 29 ]. For example, strain-altered ZnO NRs have been shown to alter their Schottky barrier height [ 25 , 26 ] and electrical conductance [ 27 , 28 , 29 ].…”