On the Role of the Sr_3−xCa_xAl₂O₆ Sacrificial Layer Composition in Epitaxial La_0.7Sr_0.3MnO₃ Membranes

Abstract

The possibility to fabricate freestanding single crystal complex oxide films has raised enormous interest to be integrated in next‐generation electronic devices envisaging distinct and novel properties that can deliver unprecedented performance improvement compared to traditional semiconductors. The use of the water‐soluble Sr3Al2O6 (SAO) sacrificial layer to detach the complex oxide film from the growth substrate has significantly expanded the complex oxide perovskite membranes library. Nonetheless, the extreme water sensitivity of SAO hinders its manipulation in ambient conditions and restricts the deposition approaches to those using high vacuum. This study presents a pioneering study on the role of Ca‐substitution in solution processed SAO (Sr3−xCaxAl2O6 with x ⩽ 3) identifying a noticeable improvement on surface film crystallinity preserving a smooth surface morphology while favoring the manipulation in a less‐restricted ambient conditions. Then, the study focuses on the effect of the sacrificial composition on the subsequent ex situ deposition of La0.7Sr0.3MnO3 (LSMO) by pulsed laser deposition, to obtain epitaxial films with a variable degree of strain. Finally, epitaxial and strain‐free LSMO membranes with metal‐insulator transition at 290 K are delivered. This study offers a hybrid and versatile approach to prepare and easily manipulate crystalline perovskite oxide membranes by facilitating ex situ growth on SAO‐based sacrificial layer.

Chemical synthesis of complex oxide thin films and freestanding membranes

“…This extreme SAO sensitivity to ambient humidity is a strong limitation for easy manipulation of the sacrificial layer in air and restricted the deposition of epitaxial oxides to in situ approaches. Vacuum thermal annealing under an oxygen atmosphere can successfully recrystallize the SAO surface 143 and obtain epitaxial complex membranes, 147 but a more robust sacrificial layer would facilitate exploiting its full potential. Considering that the SAO fast hydrolysis is mostly determined by the ionicity of the Sr–O bond, performing cation nanoengineering in solution processed SAO, i.e.…”

“…Therefore, the Ca-substitution favors the manipulation of the SAO sacrificial layer under less-restricted ambient conditions. 147…”

“…crystallinity and surface morphology (dictated by the Ca substitution) influences the properties of the LSMO grown on top. 147 The SCAO films with large Ca loads produces strained and biaxially textured LSMO films that upon lift-off result in a relaxed membrane with cracks and wrinkles. The electrical transport properties of the LSMO grown on SCAO are better than those of LSMO grown on pristine SAO and it is mostly attributed to the reduced cation interdiffusion between LSMO and SCAO.…”

“…Finally, epitaxial and strain-free LSMO membranes exfoliated from SCAO and transferred on silicon or glass substrates show a metal–insulator transition at 290 K. Therefore, we demonstrate that CSD offers a facile route to deliver a series of sacrificial layer compositions by appropriate intermixing of chemical precursors and can deliver different complex oxides membranes including CFO, LSMO, and can be extended to many more opening new venues to study the behavior of these freestanding oxides. 147,149–151…”

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers

“…To put this into context, we show, in Figure a, the number of publications on membrane synthesis using an epitaxial sacrificial layer since its report in 2016. While there have been more than 60 publications on the growth of complex sacrificial layers using PLD, there have been only limited publications using other growth approaches like chemical solution deposition (only 3) − and MBE (only 7). ,− This shows that PLD has been most successful in creating single-crystalline membranes using a sacrificial layer. In part, this can be attributed to the difficulty associated with MBE for growing a complex sacrificial layer.…”