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Tuning spin and charge degrees of freedom of complex oxide materials can enable significant advancements in future spintronics. In this study, by three dimensional strain engineering, we demonstrate room temperature ferroelectricity and magnetoelectricity in a vertically aligned nanocomposite thin film structure, composed of vertical nanopillars of SmFeO3 (SFO) embedded within the NiFeO4 (NFO) matrix. A three-dimensional tensile strain is induced in the SFO as a result of the unique film architecture. The tensile strain in SFO produces strong room temperature ferroelectric response instead of the normally very weak ferroelectricity of unstrained SFO, which is an improper ferroelectric. The induced ferroelectricity in SFO enables self-biased magnetoelectric coupling to be achieved between the two phases (magnetoelectric coupling coefficient ∼4 × 10−11 sm−1 at room temperature). The magnetoelectric coupling is facilitated by strain transfer across the vertical interfaces of the two phases. We additionally observe an exchange bias of ∼200 Oe (at 2 K) surviving up to the room temperature, indicating strongly coupled interfaces of SFO and NFO. These findings represent a step forward in future magnetoelectric RAM devices. 

Abstract Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high‐quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO₃(STO), MgO, LaAlO₃, a‐Al₂O_3,and many others. Recent successes in transferring these complex oxides as free‐standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost‐effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high‐resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre‐strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y₃Fe₅O₁₂) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high‐quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices. 

The unique redox properties and high oxygen capacity of nanostructured CeO₂demonstrate a wide range of applications, such as electrolytes for solid oxide fuel cells, gas sensors, and catalysis for automotive exhaust gas. Most CeO₂nanomaterials are prepared by chemical synthesis or hard templating methods. An effective way to obtain highly textured, small‐radius dimensions with high specific surface area remains challenging. Here, highly textured CeO₂nanostructures with various shapes ranging from nanowires to nanoporous thin films are successfully synthesized. Vertically aligned nanocomposites (VANs) of Sr₃Al₂O₆(SAO) and CeO₂are synthesized first while varying concentration ratio between them. Once the SAO is dissolved in water, the remaining CeO₂forms distinct nanostructures. The thermal stability of the nanostructured CeO₂is evaluated byin situheating XRD and thermal annealing tests. This method provides an alternative approach to preparing nanostructured CeO₂without toxic chemical solutions or complex micro/nanofabrication techniques. These results present a novel approach to prepare nanostructured CeO₂for future sensing and energy device applications. 

Abstract Vertically aligned nanocomposite (VAN) thin films offer exceptional physical properties through diverse material combinations, providing a robust platform for designing complex nanocomposites with tailored performance. Considering materials compatibility issues, most of oxide‐metal VANs have focused on noble metals as the secondary phase in the oxide matrix. Here, an oxide‐metal hybrid metamaterials in the VAN form has been designed which combines ferroelectric BaTiO₃(BTO) with two immiscible non‐noble metal elements of Co and Cu, resulting in a three‐phase BTO‐Co‐Cu (BTO‐CC) VAN film. This film exhibits a characteristic nanopillar‐in‐matrix nanostructure with three distinct types of nanopillar morphologies, i.e., Co‐rich cylindrical nanopillars, Cu‐Co‐nanolaminated Co rectangular nanopillars and Co‐Cu‐core–shell cylindrical nanopillars. Phase field modeling indicates the constructed structure is resulted from the interplay between thermochemical, chemomechanical, and interfacial energy driving forces. The strong structural anisotropy leads to anisotropic optical and magnetic properties, presenting potential as hyperbolic metamaterial (HMM) with transverse‐positive dispersion in the near‐infrared region. The inclusion of non‐noble Cu nanostructure induces surface plasmon resonance (SPR) in the visible region. Additionally, ferroelectric properties have been demonstrated in a BTO/BTO‐CC bilayer, confirming room‐temperature multiferroicity in the film. The complex three‐phase VANs offer a novel platform for exploring electro‐magneto‐optical coupling along vertical interfaces toward future integrated devices. 

A “lab‐to‐fab” transition is described that enables the semiautomated production of thin‐film potentiometric pH electrodes, designed for use in sterile single‐use bioreactors. Manual methods of materials deposition and film casting are replaced with spray coating on a moving web and the production of membranes with a programmable dispenser operating at constant rates. These provide a greater degree of control over membrane thickness and a reduction in voltage spread between electrodes, which are evaluated in batches using a multichannel analyzer. γ‐ray ionization of the pH electrodes introduces a predictable voltage drift that follows a log decay function on the day timescale; the voltage decay rate correlates with membrane thickness and can be modeled as a parallel diode–capacitor circuit. Batches of radiation‐sterilized pH electrodes are tested in cell culture media and yield mean pH values within 0.05 units relative to a commercial meter (ground truth) following a single‐point calibration protocol. Quantitative uncertainty analysis attributes more than half of total error to variations caused by ionizing radiation and yields novel insights into strategies for reducing uncertainty. 

Abstract Flexible and wearable sensors show enormous potential for personalized healthcare devices by real‐time monitoring of an individual's health. Typically, a single functional material is selected for one sensor to sense a particular physical signal while multiple materials will be selected for multi‐mode sensing. Vertically aligned nanocomposites (VANs) have recently demonstrated various material combinations and novel coupled multifunctionalities that are hard to achieve in any single‐phase material alone, including multiphase multiferroics, magneto‐optic coupling, and strong magnetic and optical anisotropy. Integrating these novel VANs into wearable sensors shows enormous potential in multi‐mode sensing owing to their multifunctional nature. In this work, the transfer of VANs onto polydimethylsiloxane as a novel flexible chemical and pressure sensor is demonstrated. For this demonstration, the classical BaTiO₃‐Au VAN with combined plasmonic and piezoelectric properties is used to demonstrate a multi‐sensing mechanism. A thin water‐soluble buffer of Sr₃Al₂O₆serves as a buffer layer for the epitaxial growth and transfer process. The electrical output based on the piezoelectric responses and identifying 4‐mercaptobenzoic acid by surface‐enhanced Raman spectroscopy reveal great potential for free‐standing VANs in a wearable multifunctional sensing platform.