Resistance measurements at the nanoscale: scanning probe ac impedance spectroscopy

We report a novel nanoscale method for measuring the alternating current (AC) impedance of conducting polymer electrolyte films using an atomic force microscope (AFM). The use of a conductive AFM probe provides direct impedance measurements at localized sites allowing interfaces and surface areas the size of the cantilever tip to be examined. This proves useful in the examination of polymer electrolytes where conduction is known to be heterogeneous across the surface of the film. Using the AFM we are able to sequentially image the surface then measure the resistance across various regions of the surface. The localized nature of this technique allows clear differentiation between highly conductive amorphous regions and less conductive crystalline regions of the film. Direct comparison of these impedances is consistent with bulk polymer film measurements. The results show the AFM to be a powerful method for ac impedance measurements at the nanoscale