Epitaxially Grown Single-Crystalline SrTiO3 Membranes Using a Solution-Processed, Amorphous SrCa2Al2O6 Sacrificial Layer

TL;DR

This paper demonstrates a hybrid MBE process to grow epitaxial SrTiO3 membranes using a solution-processed amorphous SrCa2Al2O6 sacrificial layer, enabling free-standing membranes with tunable ferroelectric properties.

Contribution

It introduces a novel hybrid MBE method with solution-processed sacrificial layers for epitaxial SrTiO3 membrane fabrication, overcoming stoichiometry challenges.

Findings

Successful epitaxial growth of SrTiO3 on amorphous sacrificial layer

Creation of free-standing membranes via water dissolution

Ferroelectric-like behavior in Sr-deficient membranes

Abstract

Water-soluble sacrificial layers based on epitaxially-grown, single crystalline (Ca, Sr, Ba)3Al2O6 layer are widely used for creating free-standing perovskite oxide membranes. However, obtaining these sacrificial layers with intricate stoichiometry remains a challenge, especially for molecular beam epitaxy (MBE). In this study, we demonstrate the hybrid MBE growth of epitaxial, single crystalline SrTiO3 films using a solution processed, amorphous SrCa2Al2O6 sacrificial layer onto SrTiO3 (001) substrates. Prior to the growth, the oxygen plasma exposure was used to first create the crystalline SrCa2Al2O6 layer with well-defined surface crystallinity. Utilizing reflection high energy electron diffraction, x-ray diffraction, and atomic force microscopy, we observe an atomic layer-by-layer growth of epitaxial, single crystalline SrTiO3 film on the SrCa2Al2O6 layer with atomically smooth surfaces. The SrCa2Al2O6 layer was subsequently dissolved in de-ionized water to create free-standing SrTiO3 membranes that were transferred onto a metal-coated Si wafer. Membranes created with Sr-deficiency revealed ferroelectric-like behavior measured using piezo force microscopy whereas stoichiometric films remained paraelectric-like. These findings underscore the viability of using ex-situ deposited amorphous SrCa2Al2O6 for epitaxial, single crystalline growth, as well as the importance of point defects in determining the ferroic properties in membranes.