Step bunching-induced vertical lattice mismatch and crystallographic tilt in vicinal BiFeO3(001) films

TL;DR

This study investigates how step bunching in vicinal BiFeO3(001) films causes vertical lattice mismatch and crystallographic tilt, using X-ray diffraction and an extended Nagai model to quantify strain relaxation effects.

Contribution

It introduces a generalized Nagai model to quantify the impact of step bunching on lattice mismatch and tilt in BiFeO3 thin films.

Findings

Step bunching increases terrace width on the film surface.

Vertical lattice mismatch induces strain relaxation.

Crystallographic tilt correlates with step bunching phenomena.

Abstract

Epitaxial (001) BiFeO3 thin films grown on vicinal SrTiO3 substrates are under large anisotropic stress from the substrates. The variations of the crystallographic tilt angle and the c lattice constant, caused by the lattice mismatch, along the film thickness were analyzed quantitatively using the X-ray diffraction technique. By generalizing the Nagai model, we estimated how step bunching resulted in the vertical lattice mismatch between adjacent BiFeO3 layers, which induced the strain relaxation and crystallographic tilt. The step bunching was confirmed by the increased terrace width on the BiFeO3 surface.