Scanning impedance microscopy of electroactive interfaces

A scanning probe technique based on the detection of the phase change of cantilever oscillations induced by a lateral bias applied to the sample is developed. This technique is used to investigate Σ5 grain boundary in Nb-doped SrTiO3 bicrystal. Tip bias, frequency, and driving amplitude dependence of cantilever response to sample ac bias were found to be in excellent agreement with the theoretical model. This technique, further referred to as scanning impedance microscopy, allows mapping of the local phase angle of complex microstructures. This technique is complemented by scanning surface potential microscopy (SSPM). Ramping the lateral dc bias during SSPM measurements allows the voltage characteristics of the grain boundary to be reconstructed and dc transport properties to be obtained by an equivalent circuit method. The combination of scanning impedance microscopy and scanning surface potential microscopy allows independent quantification of interface resistivity and capacitance, thus providing spatially resolved impedance spectra of complex microstructures.