Recent Developments in Electromechanical Probing on the Nanoscale: Vector and Spectroscopic Imaging, Resolution, and Molecular Orientation Mapping

Strong coupling between electrical and mechanical phenomena and the presence of switchable polarization have enabled applications of ferroelectric materials for nonvolatile memories (FeRAM), data storage, and ferroelectric lithography. Understanding the local functionality of inorganic ferroelectrics including crystallographic orientation, piezoresponse, elasticity, and mechanisms for polarization switching, requires probing material structure and properties on the level of a single ferroelectric grain or domain. Here, I present recent studies on electromechanical, mechanical, and spectroscopic characterization of ferroelectric materials by Scanning Probe Microscopy. Three-dimensional electromechanical imaging, referred to as Vector Piezoresponse Force Microscopy, is presented. Nanoelectromechanics of PFM, including the structure of coupled electroelastic fields and tip-surface contact mechanics, is analyzed. This establishes a complete continuum mechanics description of the PFM and Atomic Force Acoustic Microscopy imaging mechanisms. Mechanism for local polarization switching is analyzed. The hysteresis loop shape is shown to be determined by the formation of the transient domain below the tip, the size of which increases with the tip bias. Spectroscopic imaging that allows relevant characteristics of switching process, such as imprint bias, pinning strength, remanent and saturation response, is introduced. Finally, resolution in PFM and vector PFM imaging of local crystallographic and molecular orientation and disorder is introduced.