Solution-processed negative gauge factor PtSe strain sensors.

We undertake electrochemical exfoliation of a 2D semiconductor platinum diselenide, PtSe and investigate the piezoresistance response of a solution-processed network. Due to the large PtSe aspect ratios, exceeding 300, we achieve conformal flake-to-flake junctions and good inter-flake electrical coupling. Our measured piezoresistive gauge factor is negative (-5.45), consistent with the intrinsic negative gauge factor of PtSe. This negative network gauge factor implies that strain is transferred from the substrate to the nanosheets. However, detailed modelling shows that the strain transferred to the nanosheets is much smaller than the applied strain, showing that conformal junctions do not necessarily lead to good mechanical coupling between nanosheets. Our model implies that this gauge factor is consistent with a strain transfer efficiency of 8.5%. Our strain sensor also demonstrated a cyclic response for over 1000 cycles, enabling the sensor to be used in future flexible optoelectronics applications.