Understanding Domain Walls in a Two-Dimensional Ferroelectric Material

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Nontechnical Summary:In materials that contain regions with different structures and properties, the interfaces that separate these regions not only influence the overall material characteristics, but also often feature unusual physical properties not present in the surrounding regions. This project investigates interfaces in a unique two-dimensional material consisting of regions characterized by different spatial separations of positive and negative electric charges. Knowledge of the behaviors of these interfaces lays the groundwork for realizing faster computing using high-speed logic and memory devices with large storage density and ultra-low power consumption, as well as for exploring next-generation devices whose functions can be modified on the fly to adapt to different demands and applications. Education and outreach activities are an integral part of this project. In addition to providing research training for students, this project involves the development of classroom demonstrations and experiments that are integrated into an undergraduate physics course. A week-long annual science camp for local middle and high school students is developed by the principal investigator and offered through the Parks and Recreation Department in the City of Pullman. The principal investigator also works with local organizations to integrate the developed activities into science exhibitions and science fairs that are open to the general public. Technical Summary:Two-dimensional indium selenide is a unique ferroelectric material, with the polarization sustained by covalent bonding and with interlinked out-of-plane and in-plane polarizations. The strong covalent bonding leads to highly robust ferroelectricity that persists down to the monolayer limit. The interlinked out-of-plane and in-plane polarizations allow for defining and manipulating charged domain walls using a local electric field. These domain walls have distinctive lattice structures and are expected to exhibit many interesting and novel characteristics. This project aims to develop a fundamental knowledge of the domain wall properties, with the specific objective to understand how the intricate coupling between the local polarization, lattice structure, and charge carriers affects the domain wall electronic and phonon properties. The experimental efforts utilize advanced electron microscopy and multi-functional scanning probe microscopy techniques, such as tip-enhanced Raman spectroscopy and various atomic force microscopy-based measurements with high spatial and temporal resolutions, to probe local properties in individual domain walls. Complementing these experimental investigations, density-functional-theory calculations are used to determine the crystal lattices, electronic and phonon structures, as well as charge carrier transport properties and dynamics in domain walls. The correlation between experimental and theoretical studies enables mechanistic insights and provides a fundamental basis for exploiting unique domain wall properties in electronic applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.