Electromechanics on the Nanometer Scale: Emerging Phenomena, Devices, and Applications
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on the Nanometer Scale: Emerging Phenomena, Devices, and Applications Sergei V. Kalinin, Nava Setter, and Andrei L. Kholkin, Guest Editors
Abstract Coupling between mechanical and electrical phenomena is ubiquitous at the nanoand molecular scales, with examples ranging from piezoelectricity and flexoelectricity in perovskites to complex molecular transformations in redox active molecules and ion channels. This article delineates the field of nanoelectromechanics enabled by recent advances in scanning probe, indentation, and interferometric techniques and provides a unified outlook at a number of related topics, including membrane and surface flexoelectricity, local piezoelectricity in ferroelectrics and associated devices, and electromechanical molecular machines. It also summarizes experimental and theoretical challenges on the pathway to visualize, control, and manipulate electromechanical activity on the nanoscale and molecular levels.
Electromechanical Coupling in Nature: Phenomena, Materials, and Devices Coupling between electrical and mechanical phenomena is one of the fundamental natural processes manifested in materials and systems ranging from simple electrostriction in dielectrics to more complicated effects in piezoelectrics and ferroelectrics and to far more complex phenomena in electroactive polymers and biomimetic/biological systems.1 Electromechanics refers to a broad class of phenomena in which mechanical deformation is induced by an external electric field, or, conversely, electric charge separation is generated by the application of an external force. Linear piezoelectric coupling is present in approximately 30% of all inorganic materials, including technologically important oxides (e.g., ZnO), III–V nitrides, quartz, various minerals and polar dielectrics, and ferroelectrics (as exemplified by ABO3 perovskites). 634
In most materials, electromechanical activity is directly related to their structure and both electrical and mechanical functionalities. In polar compounds, local piezoelectric properties are strongly affected by structural defects, local electric and stress fields, and disorder. In ferroelectrics and multiferroics, electromechanical behavior can be used to study a wide range of phenomena, including polarization reversal mechanisms, domain wall propagation, cross-coupled phenomena (e.g., in multiferroics), and electron-lattice coupling. The basis of functionality in many biological and biomimetic systems is electromechanics—from nervecontrolled muscle contraction on the macroscale, to cardiac activity and hearing on the microscale, to energy storage in mitochondria and electromotor proteins on the nanoscale. This has led to the
development of biomimetic electromechanically active materials such as “artificial muscles” and may pave the way for high-energy density capacitors and fuel cells. Finally, electromechanical coupling is a key component of virtually all electrochemical transformations, in which changes in oxidation state are associated with changes in molecular shape and bon
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