Using Electrical Impedance Spectroscopy to Separately Quantify the Effect of Strain on Nanosheet and Junction Resistance in Printed Nanosheet Networks

Many printed electronic applications require strain-independent electrical properties to ensure deformation-independent performance. Thus, developing printed, flexible devices using 2D and other nanomaterials will require an understanding of the effect of strain on the electrical properties of nano-networks. Here, novel AC electrical techniques are introduced to fully characterize the effect of strain on the resistance of high-mobility printed networks, fabricated from of electrochemically exfoliated MoS₂ nanosheets. These devices are initially characterized using DC piezoresistance measurements and show good cyclability and a linear strain response, consistent with a low gauge factor of G ≈ 3. However, AC impedance spectroscopy measurements, performed as a function of strain, allow the measurement of the effects of strain on both the nanosheets and the inter-nanosheet junctions separately. The junction resistance is found to increase linearly with strain, while the nanosheet resistance remains constant. This response is consistent with strain-induced sliding of the highly-aligned nanosheets past one another, without any strain being transferred to the sheets themselves. The approach allows for the individual estimation of the contributions of dimensional factors (G ≈ 1.4) and material factors (G ≈ 1.9) to the total gauge factor. This novel technique may provide insights into other piezoresistive systems.