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We prepared poly(vinylidene fluoride) (PVDF) and aluminum composite dense films using a tape caster and investigated the microstructural, thermal, and electrical properties and the combustion behavior of the films as a function of nano-aluminum (nAl) solids loading (5–30 wt. %). We found that the addition of nAl facilitates the formation of piezoelectric β and γ phases of PVDF as determined by x-ray diffraction and Fourier transform infrared spectroscopy. At higher nAl solid loadings, the lower onset temperature of the pre-ignition and decomposition reactions have been observed. Moreover, the intentionally incorporated porosity into the films slightly affected the thermal decomposition behavior. While the dielectric constant of the films increases with higher nAl content, the dielectric breakdown strength of the films decreases significantly. The critical active nAl content for the films to exhibit self-propagated reaction was determined to be between 10 and 15 wt. %. Thermochemical calculations using the NASA CEA code showed the maximum flame temperature of 1750 °C near the stoichiometric ratio (∼20 wt. %). The burning rate of the films is enhanced drastically at ambient conditions with further addition of nAl. However, the films with active nAl content over 20 wt. % showed lower flame temperatures, which is due to the reduction of hydrofluoric acid gas generation and the incomplete combustion of Al to form aluminum monofluoride (AlF), instead of aluminum fluoride (AlF3) gas. The fabrication of energetic thin films with tunable properties could enable their use in multifunctional energetic material systems. [ABSTRACT FROM AUTHOR]

Recent studies in complex nanocomposite thin films have brought forth interesting morphologies and physical properties and thus great potential for future devices. This study presents the formation of a nanomushroom structure developed from a complex three-phase nanocomposite system, i.e., the Co–CeO2–BaTiO3 (Co–CeO2–BTO) system. Via varying the oxygen partial pressure during deposition, the Co–CeO2–BTO system growth shows a microstructure tuning of vertically aligned Co nanopillars in a CeO2–BTO composite matrix processed in vacuum to the Co nano-mushroom-like structures under 200 mTorr oxygen. Such morphology tuning results in interesting physical property tuning such as magnetic anisotropy, optical anisotropy, and dielectric function tuning. This study suggests the effectiveness of morphology tuning via complex three-phase nanocomposite designs and processing condition variation. The resultant three-phase nanocomposite structures present great potential to address the needs on multifunctional hybrid materials for nanoscale optical and magnetic device demonstrations. [ABSTRACT FROM AUTHOR]

Silicon (Si) integration is a critical step for implementing functional oxides into Si-based electronic devices, considering the advantages of low-cost and scalability of Si substrates. In the past decade, self-assembled vertically aligned nanocomposites (VANs) have attracted enormous research interest owing to their unique multifunctionalities and highly tunable physical properties as well as their one-step self-assembly process. Most of the VAN thin films have been reported to grow epitaxially on single crystalline oxide substrates, however, with limited systems reported on Si substrates due to the very large lattice mismatch between oxides and Si lattices. In this review, the current progress for self-assembled VAN systems integrated on a Si substrate is summarized. Buffer layered enabled VAN growth has been proven to be an effective approach for improving the epitaxial quality of oxide-oxide and oxide-metal VAN systems, while direct growth is preferred in nitride-metal VAN systems. The material versatility enables the Si-integrated VAN thin films to exhibit distinct physical properties such as ferromagnetism, ferroelectricity, magnetoresistance, as well as unique optical properties. The review also summarizes the various parameters for tuning the growth morphologies and corresponding properties for the VAN systems, including phase molar ratio, deposition frequency, buffer layers, background pressure, etc. Finally, future perspectives are discussed including new VAN system exploration, physical properties tuning, as well as design and fabrication of Si-based nanoelectronics and nanophotonic devices applications. [ABSTRACT FROM AUTHOR]

Dynamic tuning of optical properties is technologically important for the development of future integrated electronic and photonic devices. Here, we demonstrate the electrically tunable permittivity in optical frequency in epitaxial BaTiO3 (BTO) thin films using spectroscopic ellipsometer measurements under DC bias condition. The lattice tetragonal distortion and domain switching of biased BTO is evident based on the increased anisotropy in permittivity in-plane and out-of-plane. Specifically, out-of-plane permittivity, arising from the c-domains, shows a continuous decrease with the applied voltage, relative to the in-plane permittivity, arising from the a-domains. The dielectric constant can also be reversibly adjusted through electric-reset cycles. The current study demonstrates the real-time electrically tunable dielectric permittivity in BaTiO3, probed using spectroscopic ellipsometer at optical frequencies, towards future tunable waveguides, optical components and devices. [ABSTRACT FROM AUTHOR]

Flash sintering has recently been used to sinter various bulk ceramics under reduced sintering temperatures and sintering time by applying an electric field across the sample. In this work, we have demonstrated field‐assisted heating of 10 mol% Gd‐doped CeO2 thin films deposited by pulsed laser deposition. Microstructure analysis revealed the elongated grains aligned in the out‐of‐plane direction which is perpendicular to the direction of electric field. The overall microstructure of the flash‐heated thin film also contained a matrix of porous and clustered regions, which are distributed throughout the thin film from the anode to cathode electrode regions. The flash‐heated thin film showed significantly different conductivity and optical permittivity compared to the as‐grown thin films. This demonstration suggests a feasible approach for post‐deposition synthesis of thin films using field‐assisted heating toward novel morphologies and properties. [ABSTRACT FROM AUTHOR]

Plasmonic oxide‐metal hybrid nanostructures exhibit unprecedented optical properties because of the nanoscale interactions between the oxide and metal components. Precise control of the geometry and arrangement of optical building blocks is key to tailoring system properties toward various nanophotonic applications. Herein, self‐assembled BaTiO3‐Au vertically aligned nanocomposite thin films with a series of thicknesses are fabricated using a one‐step pulsed laser deposition technique. By reducing the film thickness, the geometry of Au phase is effectively tailored from nanopillars to nanodisks, with the aspect ratio (height/width) varied from ≈4.0 to ≈1.0. The experimental optical spectra and numerical simulation results demonstrate that localized surface plasmon resonance and hyperbolic dispersion wavelength can be effectively tuned in the visible to near‐infrared regime by varying the film thickness due to the change of Au aspect ratio and free electron density. This study demonstrates a feasible approach in tuning the optical responses in hybrid oxide‐metal nanostructures, and opens up enormous possibilities in design and fabrication of novel optical components toward all optical integrated devices. [ABSTRACT FROM AUTHOR]

Metallic nanostructures within ceramic matrices provide a unique platform for integrating magnetic, optical, and electrical properties for device applications. Currently, hurdles still exist for the integration of metallic nanostructures within conventional devices, including the incompatible growth conditions between metals and ceramics and control of the overall physical properties. In this study, we demonstrate the tunability of a one-step growth method to fabricate magnetic and metallic nanostructures embedded within an oxide matrix, La0.5Sr0.5FeO3:Fe, from a composite target using pulsed laser deposition. The metal-ceramic nanocomposite films demonstrate tunable nanostructures and anisotropic magnetic response by varying deposition energy, presenting a mechanism for tuning the physical properties of vertically aligned ferromagnetic metallic nanopillars in an oxide matrix. This study also opens avenues towards the integration of nanoscale, vertical, metallic ferromagnetic contacts for anisotropic magnetic tunneling junctions which may not be easily realized by single-phase thin films. [ABSTRACT FROM AUTHOR]

Magnetoacoustic waves generated in piezoelectric and ferromagnetic coupled nanocomposite films through magnetically driven surface acoustic waves present great promise of loss-less data transmission. In this work, ferromagnetic metals of Ni, Co and Co x Ni 1- x are coupled with a piezoelectric ZnO matrix in a vertically-aligned nanocomposite (VAN) thin film platform. Oxidation was found to occur in the cases of ZnO-Co, forming a ZnO-CoO VAN, while only very minor oxidation was found in the case of ZnO-Ni VAN. An alloy approach of Co x Ni 1- x has been explored to overcome the oxidation during growth. Detailed microstructural analysis reveals limited oxidation of both metals and distinct phase separation between the ZnO and the metallic phases. Highly anisotropic properties including anisotropic ferromagnetic properties and hyperbolic dielectric functions are found in the ZnO-Ni and ZnO-Co x Ni 1- x systems. The magnetic metal-ZnO-based hybrid metamaterials in this report present great potential in coupling of optical, magnetic, and piezoelectric properties towards future magnetoacoustic wave devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Integration of highly anisotropic multiferroic thin films on silicon substrates is a critical step towards low-cost devices, especially high-speed and low-power consumption memories. In this work, an oxide-metal vertically aligned nanocomposite (VAN) platform has been used to successfully demonstrate self-assembled multiferroic BaTiO 3 -Fe (BTO-Fe) nanocomposite films with high structural anisotropy on Si substrates. The effects of various buffer layers on the crystallinity, microstructure, and physical properties of the BTO-Fe films have been explored. With an appropriate buffer layer design, e.g. SrTiO 3 /TiN bilayer buffer, the epitaxial quality of the BTO matrix and the anisotropy of the Fe nanopillars can be improved greatly, which in turn enhances the physical properties, including the ferromagnetic, ferroelectric, and optical response of the BTO-Fe thin films. This unique combination of properties integrated on Si offers a promising approach in the design of multifunctional nanocomposites for Si-based memories and optical devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Silicon integration of nanoscale metamaterials is a crucial step toward low-cost and scalable optical-based integrated circuits. Here, a self-assembled epitaxial Au-BaTiO 3 (Au-BTO) hybrid metamaterial with highly anisotropic optical properties has been integrated on Si substrates. A thin buffer layer stack (<20 nm) of TiN and SrTiO 3 (STO) was applied on Si substrates to ensure the epitaxial growth of the Au-BTO hybrid films. Detailed phase composition and microstructural analyses show excellent crystallinity and epitaxial quality of the Au-BTO films. By varying the film growth conditions, the density and dimension of the Au nanopillars can be tuned effectively, leading to highly tailorable optical properties including tunable localized surface plasmon resonance (LSPR) peak and hyperbolic dispersion shift in the visible and near-infrared regimes. The work highlights the feasibility of integrating epitaxial hybrid oxide-metal plasmonic metamaterials on Si toward future complex Si-based integrated photonics.