Applications of piezoresponse force microscopy in materials research: from inorganic ferroelectrics to biopiezoelectrics and beyond

Piezoresponse force microscopy (PFM) probes the mechanical deformation of a sample in response to an electric field applied with the tip of an atomic force microscope. Originally developed more than two decades ago to study ferroelectric materials, this technique has since been used to probe electromechanical functionality in a wide range of piezoelectric materials including organic and biological systems. Piezoresponse force microscopy has also been demonstrated as a useful tool to detect mechanical strain originating from electrical phenomena in non-piezoelectric materials. Parallelling advances in analytical and numerical modelling, many technical improvements have been made in the last decade: switching spectroscopy PFM allows the polarisation switching properties of ferroelectrics to be resolved in real space with nanometric resolution, while dual ac resonance tracking and band excitation PFM have been used to improve the signal-to-noise ratio. In turn, these advances have led to increasingly large multidimensional data sets containing more complete information on the properties of the sample studied. In this review, PFM operation and calibration are described, and recent advances in the characterisation of electromechanical coupling using PFM are presented. The breadth of the systems covered highlights the versatility and wide applicability of PFM in fields as diverse as materials engineering and nanomedicine. In each of these fields, combining PFM with complementary techniques is key to develop future insight into the intrinsic properties of the materials as well as for device applications.