  In this paper, we describe the modification of Nanoscale Impedance Microscopy
(NIM), namely, a combination of contact-mode atomic force microscopy with local
impedance measurements. The postulated approach is based on the application of
multifrequency voltage perturbation instead of standard frequency-by-frequency
analysis, which among others offers more time-efficient and accurate
determination of the resultant impedance spectra with high spatial resolution.
Based on the impedance spectra analysis with an appropriate electric equivalent
circuit, it was possible to map surface resistance and contact capacitance.
Polycrystalline heavy boron-doped diamond (BDD) electrodes were the research
object. Recent studies have shown that the exposure of such electrodes to
oxidizing environment may result in the modification of termination type, and
thus it is a key factor in describing the electric and electrochemical
properties of BDD. We have successfully applied multifrequency NIM, which
allowed us to prove that the modification of termination type is selective and
occurs with different propensity on the grains having specific crystallographic
orientation. Furthermore, our approach enabled the detection of even subtle
submicroscopic surface heterogeneities, created as a result of various
oxidation treatments and to distinguish them from the surface heterogeneity
related to the local distribution of boron at the grain boundaries.
