Oxygen vacancy-induced topological nanodomains in ultrathin ferroelectric films

Wei Peng,Tae Won Noh,Lingfei Wang,Miyoung Kim,Qidong Xie,Junsik Mun,Jingsheng Chen

doi:10.1038/s41535-021-00349-y

Abstract

Oxygen vacancy in oxide ferroelectrics can be strongly coupled to the polar order via local strain and electric fields, thus holding the capability of producing and stabilizing exotic polarization patterns. However, despite intense theoretical studies, an explicit microscopic picture to correlate the polarization pattern and the distribution of oxygen vacancies remains absent in experiments. Here we show that in a high-quality, uniaxial ferroelectric system, i.e., compressively strained BaTiO3 ultrathin films (below 10 nm), nanoscale polarization structures can be created by intentionally introducing oxygen vacancies in the film while maintaining structure integrity (namely no extended lattice defects). Using scanning transmission electron microscopy, we reveal that the nanodomain is composed of swirling electric dipoles in the vicinity of clustered oxygen vacancies. This finding opens a new path toward the creation and understanding of the long-sought topological polar objects such as vortices and skyrmions.

Highlights

In the past 10 years, an intriguing query in ferroelectricity studies has been the existence of topological arrangement of electric dipoles such as vortices and skyrmions in magnetic systems[1,2,3,4,5,6,7,8,9,10]
BaTiO3 (BTO) films with a bottom SrRuO3 (SRO) electrode layer were grown on TiO2-terminated SrTiO3 (001) substrates by pulsed laser deposition (PLD)[29]
The high quality of BTO films grown under 5 mTorr ( 5-BTO) was inferred from the diffraction fringes of X-ray diffraction (XRD) and the step-terrace morphology with unit-cell step height by atomic force microscopy (AFM, Fig. 1a, b)

Summary

Introduction

In the past 10 years, an intriguing query in ferroelectricity studies has been the existence of topological arrangement of electric dipoles such as vortices and skyrmions in magnetic systems[1,2,3,4,5,6,7,8,9,10]. Scanning transmission electron microscopy (STEM) further reveals that oxygen vacancies clusters give rise to polarization vortices without any extended lattice defects. Fresh BTO films grown in lower oxygen pressures, namely 5-BTO, exhibit a uniformly opposite self-polarization in average, namely pointing from the top surface down to the bottom electrode (Fig. 1d).

Results

Conclusion