Piezoresponse force microscopy (PFM) is one of the most widespread methods for investigating and visualizing ferroelectric domain
structures down to the nanometer length scale. PFM makes use of the direct coupling of the piezoelectric response to the crystal lattice, and
hence, it is most often applied to spatially map the three-dimensional (3D) near-surface domain distribution of any polar or ferroic sample.
Nonetheless, since most samples investigated by PFM are at least semiconducting or fully insulating, the electric ac field emerging from the
conductive scanning force microscopy (SFM) tip penetrates the sample and, hence, may also couple to polar features that are deeply buried
into the bulk of the sample under investigation. Thus, in the work presented here, we experimentally and theoretically explore the contrast
and depth resolution capabilities of PFM, by analyzing the dependence of several key parameters. These key parameters include the depth
of the buried feature, i.e., here a domain wall (DW), as well as PFM-relevant technical parameters such as the tip radius, the PFM drive
voltage and frequency, and the signal-to-noise ratio. The theoretical predictions are experimentally verified using x-cut periodically poled
lithium niobate single crystals that are specially prepared into wedge-shaped samples, in order to allow the buried feature, here the DW, to
be “positioned” at any depth into the bulk. This inspection essentially contributes to the fundamental understanding in PFM contrast analysis and to the reconstruction of 3D domain structures down to a 1 μm-penetration depth into the sample