Ferroelectricity in Niobium Oxide Dihalides NbOX2 (X = Cl, I): A Macroscopic- to Microscopic-Scale Study

Chaofei Liu; Xiuying Zhang; Xinyun Wang; Ziying Wang; Ibrahim Abdelwahab; Ivan Verzhbitskiy; Yan Shao; Goki Eda; Wanxin Sun; Lei Shen; Kian Ping Loh

doi:10.1021/acsnano.2c09267

Ferroelectricity in Niobium Oxide Dihalides NbOX₂ (X = Cl, I): A Macroscopic- to Microscopic-Scale Study

ACS Nano. 2023 Apr 25;17(8):7170-7179. doi: 10.1021/acsnano.2c09267. Epub 2023 Apr 10.

Authors

Chaofei Liu¹, Xiuying Zhang², Xinyun Wang¹, Ziying Wang¹, Ibrahim Abdelwahab¹, Ivan Verzhbitskiy², Yan Shao¹, Goki Eda^{1

2

3}, Wanxin Sun⁴, Lei Shen⁵, Kian Ping Loh^{1

3}

Affiliations

¹ Department of Chemistry, National University of Singapore, Singapore 117543, Singapore.
² Department of Physics, National University of Singapore, Singapore 117542, Singapore.
³ Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore.
⁴ Bruker Nano Surface Division, 30 Biopolis Street 09-01, The Matrix, Singapore 138671.
⁵ Department of Mechanical Engineering, National University of Singapore, Singapore 117575, Singapore.

PMID: 37036127
DOI: 10.1021/acsnano.2c09267

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 NbOX₂ (X = Cl, I) across different spatial scales. The in-plane ferroelectricity in NbOX₂ was investigated using transport and piezoresponse force microscopy (PFM) measurements, where it was observed that NbOCl₂ has a stronger ferroelectric order than NbOI₂. A high local field, exerted by both PFM and scanning tunneling microscopy (STM) tips, was found to induce 1D collinear ferroelectric strips in NbOCl₂. STM imaging reveals the unreconstructed atomic structures of NbOX₂ surfaces, and scanning tunneling spectroscopy was used to probe the electronic states induced at defect (vacancy) sites.

Keywords: 1D collinearity; NbOX2; defect bound states; ferroelectricity; van der Waals materials.