Ferroelectricity in Niobium Oxide Dihalides NbOX<sub>2</sub> (X = Cl, I): A Macroscopic- to Microscopic-Scale Study.

Liu, Chaofei; Zhang, Xiuying; Wang, Xinyun; Wang, Ziying; Abdelwahab, Ibrahim; Verzhbitskiy, Ivan; Shao, Yan; Eda, Goki et al. · ACS Nano · 2023

basic_science · Level V

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Abstract

2D materials with ferroelectric and piezoelectric properties are of interest for energy harvesting, memory storage and electromechanical systems. Here, we present a systematic study of the ferroelectric properties in NbOX<sub>2</sub> (X = Cl, I) across different spatial scales. The in-plane ferroelectricity in NbOX<sub>2</sub> was investigated using transport and piezoresponse force microscopy (PFM) measurements, where it was observed that NbOCl<sub>2</sub> has a stronger ferroelectric order than NbOI<sub>2</sub>. A high local field, exerted by both PFM and scanning tunneling microscopy (STM) tips, was found to induce 1D collinear ferroelectric strips in NbOCl<sub>2</sub>. STM imaging reveals the unreconstructed atomic structures of NbOX<sub>2</sub> surfaces, and scanning tunneling spectroscopy was used to probe the electronic states induced at defect (vacancy) sites.