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Room-Temperature Ferroelectricity in Croconic Acid Films

Molecular ferroelectrics have the potential to become viable material alternatives to inorganic ferroelectrics. Unlike traditional oxide ferroelectrics, molecular ferroelectrics are structurally flexible, can be engineered at the molecular level, and can be assembled on nearly any surface, including flexible sheets and fabrics. The application of molecular ferroelectrics hinges, however, on the availability of strategies to fabricate thin films with defined structure and morphology on a large scale, which at the same time preserve their ferroelectric properties.
Nebraska MRSEC researchers have demonstrated for the first time the successful growth of a continuous nanometer thin film of a proton transfer ferroelectric organics, croconic acid, solvent-free from the vapor phase, while fully maintaining the material’s ferroelectric properties. The key to success has been the careful sublimation of croconic acid powder at temperatures that are far below the melting point. Ferroelectric testing of the films at room temperature shows a polydomain structure which can be manipulated locally, at the level of individual nanocrystals, by applying a voltage pulse to the tip of an atomic force microscope. The application of the solvent-free growth protocol to molecular ferroelectric thin films is scalable and may be key to the development of flexible and bendable ferroelectric thin films for electronics applications.