Ferroelectric Polarization-Modulated Interfacial Fine Structures Involving Two-Dimensional Electron Gases in Pb(Zr,Ti)O3/LaAlO3/SrTiO3 Heterostructures

Shuangbao Wang; Yuhang Bai; Lin Xie; Chen Li; Julian D Key; Di Wu; Peng Wang; Xiaoqing Pan

doi:10.1021/acsami.7b14712

Ferroelectric Polarization-Modulated Interfacial Fine Structures Involving Two-Dimensional Electron Gases in Pb(Zr,Ti)O₃/LaAlO₃/SrTiO₃ Heterostructures

ACS Appl Mater Interfaces. 2018 Jan 10;10(1):1374-1382. doi: 10.1021/acsami.7b14712. Epub 2017 Dec 19.

Authors

Shuangbao Wang^{1

2}, Yuhang Bai¹, Lin Xie¹, Chen Li¹, Julian D Key², Di Wu¹, Peng Wang¹, Xiaoqing Pan³

Affiliations

¹ National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences and Collaborative Innovation Center of Advanced Microstructures, Nanjing University , Nanjing 210093, China.
² Collaborative Innovation Center of Sustainable Energy Materials, Guangxi University , Nanning 530004, China.
³ Department of Physics and Astronomy and Department of Chemical Engineering and Materials Science, University of California , Irvine, California 92697, United States.

PMID: 29226675
DOI: 10.1021/acsami.7b14712

Abstract

Interfacial fine structures of bare LaAlO₃/SrTiO₃ (LAO/STO) heterostructures are compared with those of LAO/STO heterostructures capped with upward-polarized Pb(Zr_0.1,Ti_0.9)O₃ (PZT_up) or downward-polarized Pb(Zr_0.5,Ti_0.5)O₃ (PZT_down) overlayers by aberration-corrected scanning transmission electron microscopy experiments. By combining the acquired electron energy-loss spectroscopy mapping, we are able to directly observe electron transfer from Ti⁴⁺ to Ti³⁺ and ionic displacements at the interface of bare LAO/STO and PZT_down/LAO/STO heterostructure unit cell by unit cell. No evidence of Ti³⁺ is observed at the interface of the PZT_up/LAO/STO samples. Furthermore, the confinement of the two-dimensional electron gas (2DEG) at the interface is determined by atomic-column spatial resolution. Compared with the bare LAO/STO interface, the 2DEG density at the LAO/STO interface is enhanced or depressed by the PZT_down or PZT_up overlayer, respectively. Our microscopy studies shed light on the mechanism of ferroelectric modulation of interfacial transport at polar/nonpolar oxide heterointerfaces, which may facilitate applications of these materials as nonvolatile memory.

Keywords: ferroelectric polarization; interface; microstructures; oxide heterostructure; transmission electron microscopy.