In this review paper, recent progress in the fabrication, transfer, and fundamental physical properties of freestanding oxide perovskite thin films is discussed. First, the main strategies for the synthesis and transfer of freestanding perovskite thin films are analyzed. In this initial section, particular attention is devoted to the use of water‐soluble (Ca,Sr,Ba)3Al2O6 thin films as sacrificial layers, one of the most promising techniques for the fabrication of perovskite membranes. The main functionalities that have been observed in freestanding perovskite thin films are then reviewed. In doing so, the authors begin by describing the emergence of new phenomena in ultrathin perovskite membranes when released from the substrate. They then move on to a summary of the functional properties that are observed in freestanding perovskite membranes under the application of strain. Indeed, freestanding thin films offer the unique possibility to actively control the strain state far beyond what can be observed with traditional methods, allowing the investigation of the profound interplay between structural and electronic properties in oxides. Overall, this review highlights the potential of oxide‐based freestanding thin films to become the preferred platform for the study of novel functionalities in perovskite oxide materials.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/andp.202200084

Freestanding Perovskite Oxide Films: Synthesis, Challenges, and Properties

Enhanced conductivity and stability of Cu-embedded zinc tin oxide flexible transparent conductive thin films

The formation energies and electronic and optical properties of anatase titanium dioxide doped with high‐valence transition metals (niobium, tantalum, tungsten, and molybdenum) were studied through first‐principles calculations based on density functional theory. The results showed that the doped titanium dioxide systems exhibited a typical n‐type metallic characteristic and high transmittance within the visible light spectrum. The high‐valence transition metal‐doped anatase titanium dioxide films should be formed under oxygen‐rich conditions and the niobium‐doped anatase titanium dioxide film is easier to synthesize and more stable than the other three films. Moreover, the band gaps of the doped titanium dioxide systems decrease due to the hybridization of transition metal d, tantalum 3d and oxygen 2p states. Niobium‐ and tantalum‐doped titanium dioxide have lower effective mass and higher electron mobility than tungsten‐ and molybdenum‐doped titanium dioxide, hence are more suitable for transparent conductive oxide materials.

First principles study of the electronic and optical properties of high‐valence transition metal‐doped anatase titanium dioxide

In an effort to explore new electronic devices with multiple functionalities, there are numerous studies of depositing perovskite oxides on flexible substrates to replace rigid silicon‐based wafer in device applications. In this study, the growth of pseudocubic SrRuO 3 single‐crystal thin film on a transparent and flexible muscovite is established. The experimental results confirm that the Curie temperature T C and the magnetic properties can be effectively tuned via the mechanical strain due to the facilitation of flexible substrate. It is found that the tensile strain increases while the compressive strain decreases the spontaneous magnetization for the thin film suffering the same ±0.24% strain. Based on the study of critical behavior, the critical exponents β  = 0.543(19) and γ  = 1.262(1) with the critical temperature T C = 159.04(5) K and T C = 159.10 K, respectively, are obtained by the modified Arrott plot. The set of critical exponents matches well with Widom scaling relation and the scaling equation, indicating these critical exponents are intrinsic for SrRuO3 thin films. Moreover, it is achieved that the SrRuO3 thin films exhibit a long‐range interaction coupled with 3D‐Heisenberg type.

Mechanically Modulated Ferromagnetism and Critical Properties of Flexible Perovskite SrRuO3 Thin Film

Ferromagnetic insulators play a crucial role in the development of low‐dissipation quantum magnetic devices for spintronics. Epitaxial LaCoO3 thin film is a prominent ferromagnetic insulator, in which the robust ferromagnetic ordering emerges owing to epitaxial strain. Whereas it is evident that strong spin‐lattice coupling induces ferromagnetism, the reported ferromagnetic properties of epitaxially strained LaCoO3 thin films are highly consistent. For example, even under largely modulated degree of strain, the reported Curie temperatures of epitaxially strained LaCoO3 thin films lie in a narrow range of 80–85 K, without much deviation. In this study, substantial enhancement (≈18%) in the Curie temperature of epitaxial LaCoO3 thin films is demonstrated via crystallographic orientation dependence. By changing the crystallographic orientation of the films from (111) to (110), the crystal‐field energy is reduced and the charge transfer between the Co and O orbitals is enhanced. These modifications lead to a considerable enhancement of the ferromagnetic properties (including the Curie temperature and magnetization), despite the identical nominal degree of epitaxial strain. The findings of this study provide insights into facile tunability of ferromagnetic properties via structural symmetry control in LaCoO3.

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Fengjiao Qian

Papers

High stability of flexible perovskite transparent conductive oxide film via van der Waals heteroepitaxy

Scaling analysis of magnetic-thermal behaviors in ferromagnetic insulator LaCoO3 thin film

Critical Behavior of the (111)‐Oriented LaCoO 3 /SrTiO 3 Thin Film