Electrets

Abstract Electrets are materials that have a permanent electric field at their surface, analogous to how magnets have a permanent magnetic field. Their electric field arises from a net electrical charge or polarization. This article focuses on the former electrets that bear a net charge. This charge can develop and dissipate in various ways. This article briefly describes advances in our understanding of how charge develops by contact electrification, corona charging, and direct charging from electrodes, and how charge dissipates by electrostatic discharge and charge decay. We also describe ways to pattern charge, including electrical microcontact printing, atomic force microscope‐assisted nanolithography, and new techniques for forming three‐dimensional structures. Lastly, we highlight several relatively new or still‐developing uses for electrets, including electrostatic self‐assembly for sub‐micron xerography, electrostatic generators for harvesting energy or for self‐powered sensing, sources of X‐rays that do not require high‐voltage sources of power, bioactive materials for implants, and electret‐driven chemical reactions.