Synthesis of single-crystal La0.67Sr0.33MnO3 freestanding films with different crystal-orientation

Abstract

We report the synthesis of single-crystal La0.67Sr0.33MnO3 (LSMO) freestanding films with different crystal orientations. By using pulsed laser deposition, water soluble perovskite-like sacrificial layers Sr3Al2O6 (SAO) followed by LSMO films are grown on differently oriented SrTiO3 substrates. Freestanding LSMO films with different orientations are obtained by etching the SAO in pure water. All the freestanding films show room-temperature ferromagnetism and metallicity, independent of the crystal orientation. Intriguingly, the Curie temperature (TC) of the freestanding films is increased due to strain relaxation after releasing from the substrates. Our results provide an additional degree of freedom to tailor the properties of freestanding perovskite oxide heterostructures by crystal orientation and an opportunity to further integrate different oriented films together.

High Yield Transfer of Clean Large-Area Epitaxial Oxide Thin Films

“…This contrasts with other reports which show larger increases in resistivity (e.g. 80% in LSMO reported by Di Lu et al [32], ~ 700% in LSMO reported by Zengxing Lu et al [46]).…”

“…The first step in the process of getting a perfect freestanding film is to grow the target single-crystal oxide thin film with a well-defined orientation. Several studies using pulsed laser deposition (PLD) and molecular-beam epitaxy (MBE) have demonstrated growth of single crystalline films on Sr 3 Al 2 O 6 sacrificial layers [32,39,46,47]. The layer is coherently strained to the STO when it is very thin (around 10 nm).…”

Oxidic 2D Materials

“…2D materials are defined as sheet-like solid crystals composed of a single or few atomic layers [2]. They are typically free-standing [22,39,40] and have a thickness of 1-10 Å. Ramesh et al define three types of thin-film architectures, including (i) single-phase epitaxial thin films, i.e., single-crystalline films having their growth orientation dictated by the orientation of a single-crystalline substrate material, (ii) horizontal heterostructures in which a magnetic phase is epitaxially interleaved with a ferroelectric (piezoelectric) phase and (iii) nanoscale 'vertical heterostructures' as the vertical analogue [16]. An additional subdivision into three classes, that can be prepared in the form of single-atom-or single-polyhedral-thick layers, is given by Butler et al [22]: (i) layered van der Waals solids contain individual layers bonded together by van der Waals forces, in which the atoms are covalently or ionically bonded, (ii) layered ionic solids represent crystal structures consisting of charged 2D polyhedral layers held together by ionic bonding, and (iii) multilayer assemblies produced by electrostatic layer-by-layer deposition or self-assembly processes.…”

“…The wide range of properties results from the high flexibility of the chemical composition due to incorporation of different cations [83]. Since crystalline orientation and perovskite properties are closely related [39], physical characteristics such as the band structure, electron and hole transport properties, photoluminescence and dielectric behaviour may be affected by the degrees of tilting of the octahedra [151,152], the influence of strain relaxation or the preparation of free-standing thin films [39]. For instance, orientation-dependent ferroelectric and magnetic anisotropy have been detected in bulk BiFeO 3 [153] and SrRuO 3 [154,155].…”

“…Epitaxial growth of water-soluble buffer layers using MBE [26] or PLD [39] represents another promising substrate pre-treatment for the fabrication of free-standing oxide membranes (Figure 6b). Subsequently, thin layers of the material to be deposited can be grown on the buffer layer via MBE or PLD.…”