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The switching dynamics of antiferroelectric lead zirconate (PbZrO3) freestanding capacitors compared to their epitaxial counterparts is reported. Frequency dependence of hysteresis indicates that freestanding capacitors exhibit a lower dispersion of switching fields, lower residual polarization, and faster switching response as compared to epitaxially‐clamped capacitors. As a consequence, freestanding capacitor membranes exhibit better energy storage density and efficiency. [ABSTRACT FROM AUTHOR]

Freestanding membranes provide a unique opportunity to integrate complex oxides with mature semiconductor technologies and flexible electronics. It is known that the physical functionalities of complex oxides can be modified by epitaxial strain induced by the underneath substrates. The strain release may degrade the physical properties of the freestanding oxide membranes. Here, we demonstrate that various strain states in the pristine epitaxial films can be well preserved in the freestanding single-crystal SrRuO3 (SRO) membranes using the sacrificial layers with high lattice flexibility. Tensile and compressive strains are induced by the water-soluble sacrificial layers of Sr3Al2O6 (SAO) and Sr2CaAl2O6 (SCAO) on SrTiO3 substrates, respectively. An atomically flat surface morphology and initial strain states are maintained in the freestanding SRO membranes after etching the SAO and SCAO layers in water. In light of this, the electrical and magnetic properties of the SRO membranes are comparable to those of the corresponding strained films before exfoliation but completely different from those of the fully relaxed SRO films. The robust strain in the freestanding membranes offers the ability to integrate the strain-modified functionality of complex oxides with the conventional silicon-based semiconductor or flexible electronics. [ABSTRACT FROM AUTHOR]

Abstract The switching dynamics of antiferroelectric lead zirconate (PbZrO3) freestanding capacitors compared to their epitaxial counterparts is reported. Frequency dependence of hysteresis indicates that freestanding capacitors exhibit a lower dispersion of switching fields, lower residual polarization, and faster switching response as compared to epitaxially‐clamped capacitors. As a consequence, freestanding capacitor membranes exhibit better energy storage density and efficiency.

Germanium (Ge) is a critical material for applications in space solar cells, integrated photonics, infrared imaging, sensing, and photodetectors. However, the corresponding cost and limited availability hinder its potential for widespread applications. However, using Ge freestanding membranes (FSMs) allows for a significant reduction in the material consumption during device fabrication while offering additional advantages such as lightweight and flexible form factor for novel applications. In this work, we present the Ge FSM production process involving sequential porous Ge (PGe) structure formation, Ge membrane epitaxial growth, detachment, substrate cleaning, and subsequent reuse. This process enables the fabrication of multiple high-quality monocrystalline Ge FSMs from the same substrate through efficient substrate reuse at a 100 mm wafer scale by a simple and low-cost chemical cleaning process. A uniform, high-quality PGe layer is produced on the entire recovered substrate. By circumventing the use of conventional high-cost chemical–mechanical polishing or even substantial chemical wet-etching, and by using an optimized PGe structure with reduced thickness, the developed process allows for both cost and an environmental impact reduction in Ge FSMs production, lowering the amount of Ge used per membrane fabrication. Moreover, this process employs large-scale compatible techniques paving the way for the sustainable production of group IV FSMs for next-generation flexible optoelectronics. [ABSTRACT FROM AUTHOR]

Chronic skin wounds place a heavy burden on patients and healthcare systems. To address this problem, we have developed a novel composite material consisting of an electrospun fleece and a free-standing multilayer film that combines the wound healing benefits of both materials. In detail a combination of spray coating and electrospinning is used to create a layer-by-layer film on top of a gelatin fleece, with a final thickness of about 1 mm. A gelatin fleece is partially crosslinked in formaldehyde vapor and 30 pH-sensitive bonding bilayers of partially oxidized hyaluronic acid (HA) and chitosan, followed by 120 bilayers of alginate and chitosan are sprayed on top. The resulting composite is crosslinked with genipin. Uncrosslinked and genipin crosslinked composites are compared to the unprocessed fleece and free-standing multilayer film. The spray coating method produces a stable composite, allows a fast growth of the film part und most importantly retains the nano-topography of the fleece side as confirmed by electron microscopy, profilometry, nano-tomography and dynamic mechanical analysis. To test biocompatibility, cell proliferation experiments with human dermal fibroblasts and THP-1 derived macrophages are performed, proliferative assays are accompanied by immunohistochemical staining and a pro/anti-inflammatory cytokine assay. The composite shows no cytotoxicity and is biocompatible in vitro. Furthermore, the electrospun fibers of the fleece act as a scaffold to highly promote cell adhesion and proliferation, while the modular design of the multilayer free-standing film, in combination with genipin crosslinking, allows the tuning of the anti-inflammatory effect by HA. Overall, the composite seems to be a promising starting point for the design of a novel wound dressing.

[Display omitted] Integration of ultralow surface energy and surface functionality on one surface coatings is highly desirable in chemical and biomedical applications. However, it is a fundamental challenge to reduce surface energy without cost of surface functionality and vice versa. To address this challenge, the present work made use of the rapid and reversible change of surface orientation conformations of weak polyelectrolyte multilayers to create ionic, perfluorinated surfaces. Poly(allylamine hydrochloride) (PAH) chains and the micelles of sodium perfluorooctanoate (SPFO) were layer-by-layer (LbL) assembled into (SPFO/PAH) n multilayer films, which readily exfoliated to freestanding membranes. The static and dynamic surface wetting behaviors of the resulting membranes were studied by sessile drop technique and their surface charge behaviors in water by electrokinetic analysis. As-prepared (SPFO/PAH) n membranes exhibited ultralow surface energy in air; the lowest surface energy is 2.6 ± 0.5 mJ/m2 for PAH-capped surfaces and 7.0 ± 0.9 mJ/m2 for SPFO-capped surfaces. They readily became positively charged in water, which allowed not only effective adsorption of ionic species for further functionalization with subtle change in surface energy, but effective adhesion onto various solid substrates such as glass, stainless steel, and polytetrafluoroethylene to endorse the wide applicability of (SPFO/PAH) n membranes. [ABSTRACT FROM AUTHOR]

Inorganic/organic dielectric composites are very attractive for high energy density electrostatic capacitors. Usually, linear dielectric and ferroelectric materials are chosen as inorganic fillers to improve energy storage performance. Antiferroelectric (AFE) materials, especially single‐crystalline AFE oxides, have relatively high efficiency and higher density than linear dielectrics or ferroelectrics. However, adding single‐crystalline AFE oxides into polymers to construct composite with improved energy storage performance remains elusive. In this study, high‐quality freestanding single‐crystalline PbZrO3 membranes are obtained by a water‐soluble sacrificial layer method. They exhibit classic AFE behavior and then 2D–2D type PbZrO3/PVDF composites with the different film thicknesses of PbZrO3 (0.1‐0.4 µm) is constructed. Their dielectric properties and polarization response improve significantly as compared to pure PVDF and are optimized in the PbZrO3(0.3 µm)/PVDF composite. Consequently, a record‐high energy density of 43.3 J cm−3 is achieved at a large breakdown strength of 750 MV m−1. Phase‐field simulation indicates that inserting PbZrO3 membranes effectively reduces the breakdown path. Single‐crystalline AFE oxide membranes will be useful fillers for composite‐based high‐power capacitors. [ABSTRACT FROM AUTHOR]

Complex oxide thin films exhibit intriguing phenomena due to the coupling between multiple degrees of freedom through interfacial structural engineering. Atomic tailoring of structural parameters determines unique band structure and phonon modes, regulating emergent magnetic and electrical properties of oxide films. However, the construction of different strained and oriented domains in one intact oxide thin film is impossible using conventional means. Here we report the fabrication and quantitative structural analysis of La0.7Sr0.3MnO3 (LSMO) homostructures assisted by atomic-flat freestanding membranes. Pristine substrates and suspended membranes regulate the epitaxial strain and orientation of subsequently grown films. Our results demonstrate an ultrathin transition layer (∼ 4 atomic layers) between freestanding membranes and LSMO films is formed due to the strain relaxation. This work offers a simple and scalable methodology for fabricating unprecedented innovative functional oxide homostructures through artificially controlled synthesis routes. [ABSTRACT FROM AUTHOR]

Articular cartilage injuries are currently one of the world's top health concerns owing to its limited capacity of self‐renewal, thus raising to the economic burden in the healthcare system. Cell implantation strategies resorting to a suitable delivery platform hold a great promising approach to increase cell retention to be further supplied in a sufficient amount to the cartilage defects. So far, macromolecular engineering toolboxes for designing cell‐carrier devices with on‐demand cell delivery efficiency are rarely reported. Herein, anisotropically patterned mussel‐inspired membranes, comprising oppositely charged marine‐origin biopolymers (e.g., chitosan and alginate) combined in a multilayered fashion with catechol‐functionalized hyaluronic acid (DOPA‐HA), through electrostatically driven layer‐by‐layer (LbL) assembly approach, are developed. The seamless combination of nanotopography and catechol molecular cues in one single platform significantly augments ASC/TERT1 adhesion at the patterned DOPA‐HA membrane surface. These highest cell density membranes are further applied onto human chondral discs ex vivo models to evaluate their capability to act as cell delivery vehicles. Results show the successful cell migration and retention at cartilage surface, wherein they spread to inhabit both superficial empty lacunae and furrows. Therefore, the present study supplies an important strategy for designing cell delivery vehicles to be applied on cell‐based therapies.

Semiconductor-based freestanding membranes (FSM) have recently emerged as a highly promising area of advanced materials research. Their unique properties, such as lightweight and flexibility, make them attractive for a wide range of disruptive device applications. However, the production of high-quality, single-crystalline FSM, especially from elemental materials such as germanium (Ge), remains a significant challenge. In this work, we report on the formation of easily detachable wafer-scale Ge FSM on porous Ge (PGe) substrate. The proposed method relies on low-temperature Ge epitaxy, allowing to preserve the porous structure's integrity during the FSM formation, and an easy substrate preparation for multiple reuses. Analysis of the surface morphology as a function of the deposited Ge thickness reveals that the FSM formation occurs in two distinct regimes. During the initial epitaxial regime, the Ge growth is governed by 3D nucleation on the PGe top surface. The nanoscale islands size increase, and consequent coalescence are found to increase the surface roughness up to a critical thickness, allowing full coalescence of islands into a 2D epilayer. The analysis of the membrane's surface morphology for various thicknesses shows continuous improvement, achieving sub nanometer surface roughness. Moreover, we demonstrate that the FSM formation process is applicable regardless the PGe porosity and thickness, while offering facile and sustainable substrate reconditioning for multiple FSM generation from the same substrate. Our findings open new opportunities to produce lightweight and flexible, high-performance optoelectronics based on Ge FSM, while ensuring reduction of both cost and critical materials consumption.

The bulk photovoltaic effect (BPVE), which uniquely exists in non-centrosymmetric materials, has been received extensive attention recently due to its potential to overcome the theoretical Shockley-Queisser limit in traditional p-n junction solar cells. Here, freestanding single-domain BiFeO 3 membranes are exfoliated from miscut SrTiO 3 substrates by dissolving Sr 3 Al 2 O 6 sacrificial layers, and transferred on SiO 2 /Si substrates. This study finds that the freestanding BiFeO 3 membranes maintain the single-domain structure and exhibits the significantly enhanced bulk photovoltaic response (≈200% enhancement), compared to the strained BiFeO 3 films. The comprehensive atomic imaging analyses manifest that the freestanding BiFeO 3 membrane demonstrates the bigger noncentral ion (Fe) displacement, which results in the larger in-plane ferroelectric polarization and substantial increase in the BPVE photocurrent. This work not only provides an effective approach to enhance the BPVE of ferroelectric oxide films, but also can potentially promote the exploration of BPVE of oxide membranes integrated with silicon-based or 2D electronics., (© 2024 Wiley‐VCH GmbH.)

Amphiphilic nanoparticles can adsorb at interfaces between immiscible phases and form membranes. The ability to handle nanoparticle monolayers/bilayers as freestanding membranes independently from the interfaces on which they form can be of significant practical interest. Janus nanoparticles (JNPs) could generate membranes that have tunable pore size and are amphiphilic. Here it is shown how freestanding membranes from JNPs can be generated. First, strongly amphiphilic Janus nanoparticles that generate foams in surfactant‐free conditions are synthesized. Upon drying the foam lamellae remain as freestanding membranes consisting of perfectly oriented bilayers or monolayers of JNPs, thus providing direct evidence of structural organization of amphiphiles in foam lamellae. The wet foam lamellae can be picked up on grids and upon drying generate freestanding membranes. Sturdy freestanding membranes by transferring monolayers of JNPs from the air–water interfaces onto grids with fine openings are also prepared. [ABSTRACT FROM AUTHOR]

Complex oxides offer a wide range of functional properties, and recent advances in the fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, photoactuation is demonstrated in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO 3 ) and paraelectric Strontium Titanate (SrTiO 3 ). The free-standing films, transferred onto perforated supports, act as nano-drums, oscillating at their natural resonance frequency when illuminated by a frequency-modulated laser. The light-induced deflections in the ferroelectric BaTiO 3 membranes are two orders of magnitude larger than in the paraelectric SrTiO 3 ones. Time-resolved X-ray micro-diffraction under illumination and temperature-dependent holographic interferometry provide combined evidence for the photostrictive strain in BaTiO 3 originating from a partial screening of ferroelectric polarization by photo-excited carriers, which decreases the tetragonality of the unit cell. These findings showcase the potential of photostrictive freestanding ferroelectric films as wireless actuators operated by light., (© 2024 Wiley‐VCH GmbH.)

In this study, graphene oxide (GO) was synthesized using Hummers, modified Hummers and improved Hummers methods, and then freestanding membranes were prepared based on these materials. Effects of different GO preparation methods on C/O ratio and interlayer spacing of freestanding membranes were studied. Structure of these membranes was studied by X-ray diffraction, contact angle, XRF, FT-IR, and FESEM methods. Also, permeability of ammonia, dichloromethane, and water vapor was investigated through these membranes. Results showed that, the sample prepared by the Hummers method had lower C/O ratio, smoother surface and lower permeability for polar species, such as water and ammonia vapors, than nonpolar materials. Membranes prepared using Improved Hummers method showed the least permeability against nonpolar vapors such as dichloromethane. [ABSTRACT FROM AUTHOR]

The discovery of 2D conductivity at the LaAlO3/SrTiO3 interface has been linking, for over a decade, two of the major current research fields in materials science: correlated transition‐metal‐oxide systems and low‐dimensional systems. Notably, despite the 2D nature of the interfacial electron gas, the samples are 3D objects with thickness in the mm range. This prevented researchers so far from adopting strategies that are only viable for fully 2D materials, or from effectively exploiting degrees of freedom related to strain, strain gradient and curvature. Here a method based on pure strain engineering for obtaining freestanding LaAlO3/SrTiO3 membranes with micrometer lateral dimensions is demonstrated. Detailed transmission electron microscopy investigations show that the membranes are fully epitaxial and that their curvature results in a huge strain gradient, each layer showing a mixed compressive/tensile strain state. Electronic devices are fabricated by realizing ad hoc circuits for individual micro‐membranes transferred on silicon chips. The samples exhibit metallic conductivity and electrostatic field effect like 2D‐electron systems in bulk heterostructures. The results open a new path for adding oxide functionalities into semiconductor electronics, potentially allowing for ultra‐low voltage gating of a superconducting transistors, micromechanical control of the 2D electron gas mediated by ferroelectricity and flexoelectricity, and on‐chip straintronics. [ABSTRACT FROM AUTHOR]

Advanced heterogeneous integration technologies are pivotal for next-generation electronics. Single-crystalline materials are one of the key building blocks for heterogeneous integration, although it is challenging to produce and integrate these materials. Remote epitaxy is recently introduced as a solution for growing single-crystalline thin films that can be exfoliated from host wafers and then transferred onto foreign platforms. This technology has quickly gained attention, as it can be applied to a wide variety of materials and can realize new functionalities and novel application platforms. Nevertheless, remote epitaxy is a delicate process, and thus, successful execution of remote epitaxy is often challenging. Here, we elucidate the mechanisms of remote epitaxy, summarize recent breakthroughs, and discuss the challenges and solutions in the remote epitaxy of various material systems. We also provide a vision for the future of remote epitaxy for studying fundamental materials science, as well as for functional applications.

Aqueous organic redox flow batteries (AORFBs) are attractive for energy storage applications, benefiting from the high safety and low cost. Covalent organic frameworks (COFs) with uniformly arranged rigid nanochannels are suitable for fabricating membranes implemented into AORFBs. However, most freestanding COF membranes are challenging to apply directly to flow batteries due to their insufficient mechanical strength. This work proposes a mechanochemistry-based method for fabricating freestanding COF membranes and a corresponding macromolecular suturing strategy to prepare membranes with excellent mechanical properties and enhanced proton conductivity. Through the steric hindrance effect of the introduced sulfonic acid group (-SO 3 H) functionalized chains, the ability of the membrane to block the crossover of redox couples is strengthened. Meanwhile, the –SO 3 H groups provide additional active sites, constructing a more continuous proton pathway. The optimized membrane exhibits a high voltage efficiency of 79.06% at 40 mA cm−2 and retains nearly 100% of its discharge capacity even after 100 cycles at 80 mA cm−2, outperforming the TpAzo membrane. This work offers a novel strategy to promote the utilization of COF membranes in flow battery applications. [Display omitted] • Freestanding covalent organic framework (COF) membranes modulated by sulfonated Polyetheretherketone were constructed. • The macromolecular suturing strategy was proposed to improve the membrane's mechanical properties and proton conductivity. • Efficient nanochannels of COF and introduced sites for proton conduction affect the ion transmembrane process. • The membrane achieved high efficiency in an acidic aqueous quinone-based redox flow battery. [ABSTRACT FROM AUTHOR]

To avoid the epitaxy dilemma in various thin films, such as complex oxide, silicon, organic, metal/alloy, etc., their stacking at an atomic level and secondary growth are highly desired to maximize the functionality of a promising electronic device. The ceramic nature of complex oxides and the demand for accurate and long-range-ordered stoichiometry face severe challenges. Here, the transport and magnetic properties of the La 0.7 Ca 0.3 MnO 3 (LCMO) secondary growth on single-crystal freestanding SrTiO 3 (STO) membranes are demonstrated. It has been experimentally found that on an only 10 nm thick STO membrane, the LCMO can offer a bulk-like Curie temperature ( T C ) of 253 K and negative magnetoresistance of -64%, with a weak dependence on the thickness. The resurrected conductivity and ferromagnetism in LCMO confirm the advantages of secondary growth, which benefits from the excellent flexibility and transferability. Additionally, this study explores the integration strategy of complex oxides with other functional materials.

[Display omitted] • The ionic COF had an high gold capture capacity from diluted aqueous solutions. • The gold capture process on the COF was extremely fast and highly selectively. • Freestanding nanopapers consisting of cellulose fibers and COF were prepared. • The nanopapers enabled efficient gold recovery from E-waste leaching solution. • The CF-COF nanopapers can be prepared with a relatively low cost. The ever-increasing production of electronic devices generates a huge amount of electronic waste (E-waste). Therefore, there is an urgent need for advanced recycling technology for E-waste that provides both economic and environmental benefits. Herein, we describe the preparation of flexible, freestanding CF-COF nanopapers consisting of cellulose fibers (CFs) and guanidinium-based ionic covalent organic framework (COF) that can be used for recovering gold from E-waste leaching solutions via a membrane separation technique. Due to the synergetic effects of physical adsorption, ion exchange and chemical reduction, the COF has an extremely high capture capacity (up to 1,794 mg of Au per gram of COF), is highly selective and has fast kinetics for adsorbing trace amounts of [AuCl 4 ]− in aqueous solution. The high COF loadings (∼50 wt%) and hierarchical porosity of the CF-COF nanopapers resulted in excellent performance when capturing gold species from the E-waste leaching solution. This study provides new possibilities for developing sustainable membrane materials, and highly efficient and cost-effective techniques for the recovery of precious metals from E-waste. [ABSTRACT FROM AUTHOR]

Interfaces formed by correlated oxides offer a critical avenue for discovering emergent phenomena and quantum states. However, the fabrication of oxide interfaces with variable crystallographic orientations and strain states integrated along a film plane is extremely challenging by conventional layer-by-layer stacking or self-assembling. Here, the creation of morphotropic grain boundaries (GBs) in laterally interconnected cobaltite homostructures is reported. Single-crystalline substrates and suspended ultrathin freestanding membranes provide independent templates for coherent epitaxy and constraint on the growth orientation, resulting in seamless and atomically sharp GBs. Electronic states and magnetic behavior in hybrid structures are laterally modulated and isolated by GBs, enabling artificially engineered functionalities in the planar matrix. This work offers a simple and scalable method for fabricating unprecedented innovative interfaces through controlled synthesis routes as well as providing a platform for exploring potential applications in neuromorphics, solid-state batteries, and catalysis., (© 2022 Wiley-VCH GmbH.)

Hafnia-based compounds have considerable potential for use in nanoelectronics due to their compatibility with complementary metal-oxide-semiconductor devices and robust ferroelectricity at nanoscale sizes. However, the unexpected ferroelectricity in this class of compounds often remains elusive due to the polymorphic nature of hafnia, as well as the lack of suitable methods for the characterization of the mixed/complex phases in hafnia thin films. Herein, the preparation of centimeter-scale, crack-free, freestanding Hf 0.5 Zr 0.5 O 2 (HZO) nanomembranes that are well suited for investigating the local crystallographic phases, orientations, and grain boundaries at both the microscopic and mesoscopic scales is reported. Atomic-level imaging of the plan-view crystallographic patterns shows that more than 80% of the grains are the ferroelectric orthorhombic phase, and that the mean equivalent diameter of these grains is about 12.1 nm, with values ranging from 4 to 50 nm. Moreover, the ferroelectric orthorhombic phase is stable in substrate-free HZO membranes, indicating that strain from the substrate is not responsible for maintaining the polar phase. It is also demonstrated that HZO capacitors prepared on flexible substrates are highly uniform, stable, and robust. These freestanding membranes provide a viable platform for the exploration of HZO polymorphic films with complex structures and pave the way to flexible nanoelectronics., (© 2022 Wiley-VCH GmbH.)