Electret formation in transition metal oxides by electrochemical amorphization

By Yong-Jin Kim, Chan-Ho Yang. NPG Asia Materials, 2020

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AbstractTransition metal oxides (TMOs) are an important class of materials that show a wide range of functionalities involving spin, charge, and lattice degrees of freedom. The strong correlation between electrons in d-orbitals and the multivalence nature give rise to a variety of exotic electronic states ranging from insulator to superconductor and cause intriguing phase competition phenomena. Despite a burst of research on the multifarious functionalities in TMOs, little attention has been paid to the formation and integration of an electret—a type of quasi-permanent electric field generator useful for nanoscale functional devices as an electric counterpart to permanent magnets. Here, we find that an electret can be created in LaMnO3 thin films by tip-induced electric fields, with a considerable surface height change, via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. The temporal evolution of the surface height, charge density, and electric potential are systematically examined by scanning probe microscopy. The underlying mechanism is theoretically analyzed based on a drift-diffusion-reaction model, suggesting that positively charged particles, which are likely protons produced by the dissociation of water, play crucial roles as trapped charges and a catalysis to trigger amorphization. Our finding opens a new horizon for multifunctional TMOs.Electric materials: Finding a sense of permanenceA material that generates its own electric field has been developed by scientists in South Korea. An electret is the electrical equivalent of a magnet in that it is formed of two electric poles rather than two magnetic poles. Just as magnetic dipoles give rise to permanent magnets, electret materials create a quasi-permanent electric field. They are useful for microphones, photocopiers and many other electrical devices. Yong-Jin Kim and Chan-Ho Yang from the Korea Advanced Institute of Science and Technology, Daejeon, have created an electret using transition metal oxides. The researchers used a sharp tip of platinum-coated silicon to “write” a charged pattern with a density similar to that of commercially available electrets into a thin film of lanthanum manganite. These patterns persisted for more than a year.An electret can be created in a complex transition metal oxide LaMnO3 by tip-induced electric fields with a considerable surface height change via solid-state electrochemical amorphization. The surface charge density of the formed electret area reaches ~400 nC cm−2 and persists without significant charge reduction for more than a year. Our finding opens a new horizon for multifunctional transition metal oxides by providing an electric counterpart to permanent magnets.

Subfields: Electronic, Optical and Magnetic Materials, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/16fe6c704799642e62b793b64db128f2aaf6bb12