Ionic and electronic impedance imaging using atomic force microscopy

Localized alternating current (ac) impedance measurements are acquired directly through a conductive atomic force microscope (AFM) tip. Both a spectroscopy mode (where full impedance spectra are obtained at fixed locations on a sample surface) and an imaging mode (where single frequency impedance maps are acquired across a sample) are used to characterize Au/Si3N4 test structures, ZnO varistors, and Nafion membrane (an ion conductor). Both modulus and phase information are acquired simultaneously. The use of an ac technique permits the study of electrochemical systems and ion conductors in addition to electronic systems. The capabilities and limitations of the AFM impedance imaging technique are discussed in detail.