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Mapping Ions and Polarons at the Nanoscale with Photoinduced Force Microscopy (PiFM)

Professor Connor G. Bischak

The ability to spatially resolve ionic and electronic species is important for understanding energy transport in heterogeneous materials at the nanoscale. This capability is particularly important in organic mixed ionic-electronic conductors (OMIECs), which are emerging materials for applications such as bioelectronics, energy storage, and neuromorphic computing. OMIECs are typically semiconducting polymers with conjugated backbones that enable electron transport and side chains that facilitate ion transport. The complex nanoscale arrangement of amorphous and crystalline regions in OMIECs dictates their performance, impacting both ion and electron transport in the polymer matrix. Because these domains are much smaller than the diffraction limit of light, new imaging methods are necessary to resolve electronic and ionic species. Here, we demonstrate how nanoscale imaging with photoinduced force microscopy (PiFM) can resolve local ion and polaron densities in OMIECs. Using PiFM, we find that ions and polarons localize preferentially in crystalline regions of OMIECs. Overall, we show that PiFM is a powerful tool for resolving both ionic and electronic species at the nanoscale.