Search

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. [ABSTRACT FROM AUTHOR]

Freestanding oxide nanomembranes have promising applications because of their novel electronic states and flexible crystalline structures. Several materials have been developed as sacrificial layers to exfoliate thin films from substrates via wet‐etching. However, these materials face great challenges in terms of either complicated crystalline structures or corrosive solutions. Here, a new sacrificial material, SrCoO2.5, is presented, which can be coherently grown with wide‐range strains and crystalline orientations and is also soluble in eco‐friendly solutions such as acetic acid, vinegar, and even carbonated drinks. With SrCoO2.5 as the sacrificial layer, high‐quality freestanding ferromagnetic SrRuO3 membranes are achieved from wide‐range epitaxial strains and different crystalline orientations. By investigating the evolution of the magnetic properties of these samples, it is discovered that epitaxial strain causes a distinct modification of the magnetic anisotropy of (001)pc‐oriented SrRuO3 samples, while its influence on the (110)pc and (111)pc samples is insignificant. This study not only demonstrates the freestanding SrRuO3 as a promising material for flexible spintronic devices, but also offers a great opportunity to engineer a wide range of strained and oriented complex oxides for novel freestanding electronics using this newly developed sacrificial material. [ABSTRACT FROM AUTHOR]

BiFeO3, a single-phase multiferroic material, possesses several polymorphs and exhibits a strong sensitivity to strain. Recently, emergent strain engineering in BiFeO3 thin films has attracted intense interest, which can overcome the confines of traditional strain engineering introduced through the mismatch between the film and substrate. In this review, we discuss emerging non-traditional strain engineering approaches to create new ground states and manipulate novel functionalities in multiferroic BiFeO3 thin films. Through fabricating freestanding thin films, inserting an interface layer or utilizing thermal expansion mismatch, continuously tunable strain can be imposed beyond substrate limitations. Nanostructured evolution and defect introduction are discussed as efficient routes to introduce strain, promising for the development of new nanodevices. Ultrafast optical excitation, growth conditions and chemical doping driven strain are summarized as well. We hope this review will arouse the readers’ interest in this fascinating field.

With their promising enhanced magnetoelectric (ME) effects and multifunctional properties, 2D ME materials are garnering considerable research interest. However, experimental studies regarding ME effects are sparse. In order to enhance ME properties, it may be important to develop a strategy to prepare ordered ME thin film materials on suitable substrates. Materials ought to possess high surface area and less area of contact with the substrate. We investigate ME thin films consisting of CoFe2O4 (CFO)/Pb(Zr0.52Ti0.48)O3 (PZT)/LaNiO3·(LNO) on a Pt/Ti/SiO2/Si substrate that were prepared using a radio-frequency magnetron sputtering technique. The method helps to relax the in-plane constraint force and enhances the coexistence of the ferromagnetic and ferroelectric phases at the interface of the materials. Interestingly, the freestanding hemispherical ME thin films exhibited huge changes in magnetic field-induced polarization. Compared with planar CFO/PZT thin films of similar dimensions, the measured polarization was more than twice as large in the freestanding hemispherical ME thin films. This facile physicochemical technique for preparing highly efficient, hierarchically ordered micro/nano-magnetoelectric thin films may be used for the fabrication of miniaturized devices. [ABSTRACT FROM AUTHOR]

We report the growth of high-quality GaN epitaxial thin films on graphene-coated c -sapphire substrates using pulsed-mode metalorganic vapor-phase epitaxy, together with the fabrication of freestanding GaN films by simple mechanical exfoliation for transferable light-emitting diodes (LEDs). High-quality GaN films grown on the graphene-coated sapphire substrates were easily lifted off by using thermal release tape and transferred onto foreign substrates. Furthermore, we revealed that the pulsed operation of ammonia flow during GaN growth was a critical factor for the fabrication of high-quality freestanding GaN films. These films, exhibiting excellent single crystallinity, were utilized to fabricate transferable GaN LEDs by heteroepitaxially growing In x Ga 1- x N/GaN multiple quantum wells and a p -GaN layer on the GaN films, showing their potential application in advanced optoelectronic devices.

Abstract: Manipulation of self-assembly processes to construct predesigned supramolecular architectures in a controllable manner is of utmost importance in the field of nanotechnology for the development of application-oriented devices. We here summarize recent progress in the current strategies for the manipulation of thin film assemblies on solid surfaces and at interfaces, as well as in freestanding thin film structures. We also highlight our recent progress including a description of the concept of hand-operating nanotechnology for controlling thin film assemblies at dynamic interfaces. This review is organized into three sections: (i) functionalization and manipulation of solid surfaces to assist molecular self-assembly; (ii) manipulation of freestanding ultrathin films by self-assembly; and (iii) molecular assembly at dynamic interfaces. [Copyright &y& Elsevier]

Highlights from the article: Freestanding Thin-Films: Water-Assisted Liftoff of Polycrystalline CdS/CdTe Thin Films Using Heterogeneous Interfacial Engineering (Adv. Keywords: electron microscopy; freestanding thin films; liftoff; polycrystalline CdTe; solar cells Electron microscopy, freestanding thin films, liftoff, polycrystalline CdTe, solar cells.

Recent advances in device design and process optimizations have enabled the production of CdTe devices on flexible substrates, but the necessary high‐temperature processing (>450 °C) to recrystallize grains limits the use of alternative lightweight substrates. Here, a new synthesis method is reported to create a freestanding CdS/CdTe film by combining high‐temperature depositions (CdS/CdTe on Si/SiO2) and a simple lift‐off process in a water environment at room temperature. Analysis of the results indicate that the delamination is facilitated by the innate lattice mismatch as well as the presence of an unexpected Te‐rich layer (≈20 nm), which accumulates on the SiO2 surface. High‐resolution electron microscopy and spectroscopy measurements confirm that the CdS/CdTe film is physically liberated from the substrate without leaving any residue, while also preserving their initial structural and compositional properties. [ABSTRACT FROM AUTHOR]