Strain engineering in single-crystalline oxide membranes offers a versatile platform to tailor functional properties beyond thin films or bulk materials. However, accurately determining strain transfer and distribution within these membranes remains challenging, limiting direct correlations between structural distortion and functional response and hindering the rational design of flexible devices. Here, high-resolution synchrotron x-ray diffraction is used for in situ monitoring of strain in (001)-oriented La 0.7 Sr 0.3 MnO 3 membranes on flexible polymer substrates under stretching and bending. This approach enables quantitative determination of in-plane strain as both macroscopic averages and spatially resolved maps. Macroscopic analysis shows that strain transfer is most efficient in thinner films and leads to distinct strain symmetries under stretching and bending. Spatially resolved measurements reveal local strain heterogeneity that increases with applied stress beyond macroscopic averages. Correlating strain distribution with estimated Curie temperature shifts illustrates how such heterogeneity could translate into spatially non-uniform functional behavior. Additionally, the setup's sensitivity to crystallographic orientation enables analysis of stacked and twisted architectures, where interlayer strain transfer is effective yet attenuated with distance from the substrate. Altogether, this framework establishes a robust approach for probing oxide membranes, opening pathways toward strain-engineered flexible devices, multilayer heterostructures, and operando investigations.

Single-crystalline perovskite oxide membranes provide a powerful platform to access physical properties that are inaccessible in bulk crystals and substrate-clamped thin films. Within this context, the deliberate fabrication of tailored corrugations provides a reliable mean to impose local curvature enabling deterministic modulation of functional properties. Here, we demonstrate controlled topographic patterning in (00l)-oriented La_0.7Sr_0.3MnO_3 (LSMO) membranes with thicknesses ranging from 4 to 100 nm where they spontaneously form sinusoidal wrinkles with thickness-dependent periodicity and amplitude. The wrinkle morphology directly modulates membrane stiffness and generates exceptionally large local strains exceeding 5% with strain gradients approaching ∼ 2.5 x 10^7 m^-1 in the thinnest membranes. These extreme deformations suppress antiferrodistortive octahedral rotations and stabilize polar distortions, evidencing a curvature-driven symmetry transformation. The surface potential variation reinforces the formation of wrinkled-induced polar patterns being strongly modulated with thickness. The variation of Mn oxidation state from ∼ 3.2+ to ∼ 2.85+ provides a direct chemical signature of a thickness-controlled electronic transition. These results demonstrate that corrugation-induced strain gradients in oxide membranes with different thicknesses can drive coupled structural, nanomechanical and electronic transformations, offering a singular route to engineer their functional states for next-generation electronic devices.

Controlling material functionalities via external stimuli is a cornerstone of modern science and technology. One effective strategy involves tuning mechanical strain, which can be induced through lattice mismatch, electric fields, or applied mechanical force. Recent advances in fabricating freestanding single-crystalline complex oxide membranes have opened new opportunities for integrating these materials onto previously incompatible platforms such as metals and flexible polymers for next-generation device applications. A key step in strain engineering is understanding and controlling the integration of such materials with flexible substrates. In this study, the integration and adhesion of freestanding single-crystalline La0.7Sr0.3MnO3 (LSMO(001)) membranes onto metallic surfaces (Au, Pt, and TiN) coated on flexible polymer substrates is demonstrated. It is found that the choice of metal underlayer significantly influences the ability to strain the membrane. Using TiN-coated polymer support, a uniform strain of approximate to 1% in LSMO membranes, along with strong adhesion between the membrane and substrate, is achieved. Theoretical calculations reveal that strong Ti & horbar;O bonding and compact in-plane lattice matching at the LSMO(001)/TiN(111) interface lower the interface formation energy compared to noble metals. These findings offer valuable insights for selecting suitable platforms to apply external mechanical stress to freestanding oxide membranes, facilitating their integration into flexible electronic systems.

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.

Photoferroelectric BiFeO3 (BFO) has attracted renewed interest to be integrated into thin film photovoltaic (PV) devices as a stable, lead-free, and versatile photoabsorber with simplified architecture. While significant efforts have been dedicated toward the exploration of strategies to tailor the properties of this photoabsorber to improve the device performance, efficiencies still remain low. The modification of the BFO interface by the incorporation of transport-selective layers can offer fresh opportunities to modify the properties of the device. Identifying an optical and electrically suitable selective layer while ensuring easy device processing and controlled film properties is challenging. In this work, we determine the influence of incorporating a ZnO layer on the ferroelectric and photoresponse behavior of an epitaxial BiFe0.9Co0.1O3 (BFCO)-based heterostructure. The device is completed with Sn-doped In2O3 (ITO) and La0.7Sr0.3MnO3 (LSMO) electrodes. This all-oxide system is stable under ambient conditions and displays robust ferroelectricity. The coupled ferroelectricity-photoresponse measurements demonstrate that the short circuit current can be modulated by ferroelectric polarization in up to 68% under blue monochromatic light. Also, the responsivity of the system with the ZnO-modified interface is larger than that of the system with no ZnO. Complementary band energy alignment studies reveal that the observed increase in the short circuit current density of the device with ZnO is attributed to lower Fermi level energy at the ZnO/BFCO interface compared to the ITO/BFCO interface, which reduces charge recombination. Therefore, this study provides useful insights into the role of the ZnO interface layer in stable BFO-based devices to further explore their viability for potential optoelectronic applications.

The ability to prepare single crystalline complex oxide freestanding membranes has opened a new playground to access new phases and functionalities not available when they are epitaxially bound to the substrates. The water-soluble Sr3Al2O6 (SAO) sacrificial layer approach has proven to be one of the most promising pathways to prepare a wide variety of single crystalline complex oxide membranes, typically by high vacuum deposition techniques. Here, we present solution processing, also named chemical solution deposition (CSD), as a cost-effective alternative deposition technique to prepare freestanding membranes identifying the main processing challenges and how to overcome them. In particular, we compare three different strategies based on interface and cation engineering to prepare CSD (00l)-oriented BiFeO3 (BFO) membranes. First, BFO is deposited directly on SAO but forms a nanocomposite of Sr-Al-O rich nanoparticles embedded in an epitaxial BFO matrix because the Sr-O bonds react with the solvents of the BFO precursor solution. Second, the incorporation of a pulsed laser deposited La0.7Sr0.3MnO3 (LSMO) buffer layer on SAO prior to the BFO deposition prevents the massive interface reaction and subsequent formation of a nanocomposite but migration of cations from the upper layers to SAO occurs, making the sacrificial layer insoluble in water and withholding the membrane release. Finally, in the third scenario, a combination of LSMO with a more robust sacrificial layer composition, SrCa2Al2O6 (SC2AO), offers an ideal building block to obtain (001)-oriented BFO/LSMO bilayer membranes with a high-quality interface that can be successfully transferred to both flexible and rigid host substrates. Ferroelectric fingerprints are identified in the BFO film prior and after membrane release. These results show the feasibility to use CSD as alternative deposition technique to prepare single crystalline complex oxide membranes widening the range of available phases and functionalities for next-generation electronic devices.

Abstract In this work, we review recent progress achieved in the use of chemical solution deposition (CSD) based on fluorinated metalorganic precursors to grow superconducting REBa2Cu3O7 (REBCO) films and coated conductors (CCs). We examine, first of all, the advances in optimizing the steps related to the solutions preparation, deposition and pyrolysis based on novel low-fluorine metalorganic solutions. We show that a new type of multifunctional colloidal solutions including preformed nanoparticles (NPs), can be used to introduce artificial pinning centers (APCs). We analyze how to disentangle the complex physico-chemical transformations occurring during the pyrolysis with the purpose of maximizing the film thicknesses. Understanding the nucleation and growth mechanisms is shown to be critical to achieve a fine tuning of the final microstructure, either using the spontaneous segregation or the colloidal solution approaches, and make industrially scalable this process. Advanced nanostructural studies have deeply modified our understanding of the defect structure and its genealogy. It is remarkable the key role played by the high concentration of randomly distributed and oriented BaMO3 (M = Zr, Hf) NPs which enhance the concentration of APCs, such as stacking faults and the associated partial dislocations. Correlating the defect structure with the critical current density Jc (H,T,θ) allows to reach a tight control of the vortex pinning properties and to devise a general scheme of the vortex pinning landscape in the whole H–T phase diagram. We also refer to the outstanding recent achievements in enhancing the vortex pinning strength by shifting the carrier concentration in REBCO films towards the overdoped state, where the pinning energy is maximum and so, record values of critical current densities are achieved. This confirms the performance competitiveness of nanocomposite CCs prepared through the CSD route. We conclude with a short summary of the progress in scaling the CC manufacturing using fluorinated solutions.

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 Sr 3 Al 2 O 6 (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 (Sr 3−x Ca x Al 2 O 6 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 La 0.7 Sr 0.3 MnO 3 (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.

[This corrects the article DOI: 10.1021/acs.chemmater.2c03831.].

Piezoelectric force microscopy (PFM) has demonstrated to be a powerful tool to characterize ferroelectric materials. However, extrinsic effects, most notably, those resulting from surface charges, often mask or mirror genuine piezoelectric response, challenging PFM data understanding. The contribution of surface charges to PFM signal is commonly compensated by using appropriate external bias voltage, which is ad-hoc selected and sample dependent. Here, we determine the compensating voltage in thin films of different ferroelectric materials and we compare with the corresponding I-V characteristics recorded using suitable electrodes. It turns out that the sign and magnitude of the bias voltage required to compensate the surface charges are related to the asymmetry of the I-V characteristics. We propose that this relation results from the fact that the semiconducting properties of the material determine both the I-V dependence, and the sign of charged adsorbates. We show how to make use of this correlation to predict the required compensation voltage of a non-ferroelectric material and we show that spurious piezoelectric-like contributions are largely cancelled. The results provide guidelines to mitigate common extrinsic contributions in PFM imaging.

Oxides offer unique physical and chemical properties that inspire rapid advances in materials chemistry to design and nanoengineer materials compositions and implement them in devices for a myriad of applications. Chemical deposition methods are gaining attention as a versatile approach to develop complex oxide thin films and nanostructures by properly selecting compatible chemical precursors and designing an accurate cost-effective thermal treatment. Here, upon describing the basics of chemical solution deposition (CSD) and atomic layer deposition (ALD), some examples of the growth of chemically-deposited functional complex oxide films that can have applications in energy and electronics are discussed. To go one step further, the suitability of these techniques is presented to prepare freestanding complex oxides which can notably broaden their applications. Finally, perspectives on the use of chemical methods to prepare future materials are given.

The preparation and manipulation of crystalline yet bendable functional complex oxide membranes has been a long-standing issue for a myriad of applications, in particular, for flexible electronics. Here, we investigate the viability to prepare magnetic and crystalline CoFe2O4 (CFO) membranes by means of the Sr3Al2O6 (SAO) sacrificial layer approach using chemical deposition techniques. Meticulous chemical and structural study of the SAO surface and SAO/CFO interface properties have allowed us to identify the formation of an amorphous SAO capping layer and carbonates upon air exposure, which dictate the crystalline quality of the subsequent CFO film growth. Vacuum annealing at 800 °C of SAO films promotes the elimination of the surface carbonates and the reconstruction of the SAO surface crystallinity. Ex-situ atomic layer deposition of CFO films at 250 °C on air-exposed SAO offers the opportunity to avoid high-temperature growth while achieving polycrystalline CFO films that can be successfully transferred to a polymer support preserving the magnetic properties under bending. Float on and transfer provides an alternative route to prepare freestanding and wrinkle-free CFO membrane films. The advances and challenges presented in this work are expected to help increase the capabilities to grow different oxide compositions and heterostructures of freestanding films and their range of functional properties.

Compositional engineering of BiFeO3can significantly boost its optoelectronic properties.

The growth of complex oxide thin films with atomic precision offers bright prospects to study improved properties and novel functionalities.

The growth of epitaxial complex oxides has been essentially limited to specific substrates that can induce epitaxial growth and stand high temperature thermal treatments. These restrictions hinder the opportunity to manipulate and integrate such materials into new artificial heterostructures including the use of polymeric and silicon substrates and study emergent phenomena for novel applications. To tackle this bottleneck, herein, a facile chemical route to prepare water‐soluble epitaxial Sr 3 Al 2 O 6 thin films to be used as sacrificial layer for future free‐standing epitaxial complex oxide manipulation is described. Two solution processes are put forward based on metal nitrate and metalorganic precursors to prepare dense, homogeneous and epitaxial Sr 3 Al 2 O 6 thin films that can be easily etched by milli‐Q water. Moreover, as a proof of concept, a basic heterostructure consisting of Al 2 O 3 /Sr 3 Al 2 O 6 on SrTiO 3 is fabricated to subsequently exfoliate the Al 2 O 3 thin film and transfer it to a polymer substrate. This is a robust chemical and low‐cost methodology that could be adopted to prepare a wide variety of thin films to fabricate artificial heterostructures to go beyond the traditional electronic, spintronic, and energy storage and conversion devices.

The growth of complex oxide thin films with atomic precision offers bright prospects to study improved properties and novel functionalities.