A decade of piezoresponse force microscopy: progress, challenges, and opportunities.

Coupling between electrical and mechanical phenomena is a near-universal characteristic of inorganic and biological systems alike, with examples ranging from piezoelectricity in ferroelectric perovskites to complex, electromechanical couplings in electromotor proteins in cellular membranes. Understanding electromechanical functionality in materials such as ferroelectric nanocrystals and thin films, relaxor ferroelectrics, and biosystems requires probing these properties on the nanometer level of individual grain, domain, or protein fibril. In the last decade, piezoresponse force microscopy (PFM) was established as a powerful tool for nanoscale imaging, spectroscopy, and manipulation of ferroelectric materials. Here, we present principles and recent advances in PFM, including vector and frequency-dependent imaging of piezoelectric materials, briefly review applications for ferroelectric materials, discuss prospects for electromechanical imaging of local crystallographic and molecular orientations and disorder, and summarize future challenges and opportunities for PFM emerging in the second decade since its invention.