  Coupling between electrical and mechanical phenomena is a near-universal
characteristic of inorganic and biological systems alike, with examples ranging
from ferroelectric perovskites to electromotor proteins in cellular membranes.
Understanding electromechanical functionality in materials such as
ferroelectric nanocrystals, 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 a powerful tool for nanoscale imaging, spectroscopy, and
manipulation of ferroelectric and piezoelectric 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.
