Ruddlesden-Popper faults in LaNiO3/LaAlO3 superlattices

TL;DR

This study uses advanced microscopy and spectroscopy to analyze atomic-level defects in LaNiO3/LaAlO3 superlattices, revealing two types of Ruddlesden-Popper faults and their origins, which influence the material's properties.

Contribution

It identifies and characterizes two distinct Ruddlesden-Popper fault types in superlattices and links their formation to substrate steps and growth processes.

Findings

Two types of Ruddlesden-Popper faults identified

Faults induced by substrate steps and growth faults

Microstructure largely independent of layer thickness

Abstract

Scanning transmission electron microscopy in combination with electron energy-loss spectroscopy is used to study LaNiO3/LaAlO3 superlattices grown on (La,Sr)AlO4 with varying single-layer thicknesses which are known to control their electronic properties. The microstructure of the films is investigated on the atomic level and the role of observed defects is discussed in the context of the different properties. Two types of Ruddlesden-Popper faults are found which are either two or three dimensional. The common planar Ruddlesden-Popper fault is induced by steps on the substrate surface. In contrast, the three-dimensionally arranged Ruddlesden-Popper fault, whose size is in the nanometer range, is caused by the formation of local stacking faults during film growth. Furthermore, the interfaces of the superlattices are found to show different sharpness, but the microstructure does not depend substantially on the single-layer thickness.