Background-free Piezoresponse Force Microscopy with high sensitivity

Piezoresponse Force Microscopy (PFM) detects small mechanical deformation of a specimen by applying an AC voltage between a conductive AFM tip (as a top electrode) and the bottom electrode. It is widely used for visualizing ferroelectric domain patterns with high lateral resolution. In nominal or commercial setups, the PFM signal is contaminated by the so-called ``system-inherent background'' with a complex frequency spectrum which consists of many cross-talk resonances with peak amplitude over 10 pm/V [1]. The presence of the system-inherent background will severely distort the PFM contrast (especially the phase signal) and the domain pattern in PFM images of ferroelectrics with weak piezoelectric response ($<$1 pm/V). Although the system-inherent background can be subtracted out by proper calibration using a non-piezoelectric material (e.g. glass slides), it is highly desirable to eliminate it directly from PFM setup for background-free measurements. Here we demonstrate that the system-inherent background can be eliminated using carefully designed electric wiring of PFM setup. Results of background-free PFM detection with excellent sensitivity($\le$0.1 pm/V) will be presented. \\[4pt] [1] Jungk et al, Appl. Phys. Lett. 89 163507 (2006).