A demonstration of the mechanical sensing capability of individually contacted vertical piezoelectric nanowires arranged in matrices

Abstract This paper reports the fabrication of arrays of vertical piezoelectric nanowires which are individually contacted at their base, and demonstrates that an electrical response to strain can be obtained from individual nanowires from the array, without external biasing exploiting the piezotronic effect. Such a technology could thus be used for the fabrication of self-powered sensors for mechanical strain mapping, where each individually contacted nanowire would act as the strain sensing equivalent of a pixel. Lateral mapping resolutions in the micrometer range can be obtained. Here, the hydrothermal method was used to grow vertical ZnO nanowires selectively between two electrodes that had been patterned beforehand. For the sake of demonstration, nanowires deflection was produced by subjecting the array of nanowires to an incident lateral gas flow of controlled rate, which was switched on and off repeatedly across the sample while electrical response was measured. Different experimental configurations were tested in terms of flow rate, flow orientation, or nanowire position with respect to tube outlet. Experiments were carried out with compressed nitrogen and air. The experimental results are fully consistent with the piezoelectric and piezotronic response which can be expected with this geometry. Moreover, it is shown that the electrical response under nitrogen flow is a linear function of flow rate and that its sign provides information about flow direction. These results demonstrate the very promising prospects of this new technology for high-resolution mapping, with potential applications in gas or liquid flow sensing, fingerprints detection or human-machine interfaces.