Growth of copper oxide at V2O5/Cu interface and its impact on the performance of piezoresistive pressure sensors using V2O5 films

Though various two-dimensional (2D) materials have been identified as useful candidates for piezoresistive pressure sensors, layered vanadium pentoxide (V2O5) has been negligibly explored. Here, simple drop cast films of ultrasonicated V2O5 on copper (Cu) substrates, stacked face-to-face, are demonstrated to exhibit remarkable piezoresistive pressure sensing behaviour over a pressure range of 250-2000 Pa, as impacted by the growth of copper oxide (CuO) at V2O5/Cu interface. Significant and accelerated growth of CuO at the interface, in ambient conditions, was observed with the addition of deionized (DI) water in the solvent used for drop casting V2O5 films, while it was negligible for those deposited without DI water. The strong growth of CuO interface layer in the former, attributed to the enhanced interaction between V2O5 and Cu in the acidic medium provided by DI water, was found to induce microcracks in V2O5 films. These microcracks could be causing reduced sensitivity of the pressure sensors (similar to 0.36 kPa(-1)) with these films, compared to the sensors with films deposited without DI water (similar to 2.57 kPa(-1)). The results suggest the tunable pressure sensing performance of V2O5 films owing to their readiness to transfer electrons with other materials. In-situ impedance spectroscopic measurements under an applied pressure are also demonstrated, which revealed the major contribution of V2O5/V2O5 interface on sensor response, thereby offering insight into the sensing mechanism. Additionally, V2O5 films are demonstrated as flexible pressure/strain sensors for detecting human physiological activities like finger bending, blinking, swallowing etc.