Haiyan Wang

Nanoscale metamaterials based on transition metal nitrides, e.g., TiN, TaN, and HfN, have recently attracted significant attention for photonic devices owing to their unique optical and plasmonic properties and high‐temperature stability. With the very recent demonstration of nitride‐metal vertically aligned nanocomposite (VAN) thin films, enormous potentials are presented in these complex hybrid metamaterials with well controlled light‐matter interactions. Most of the epitaxial VAN growth requires a lattice‐matched single‐crystalline oxide substrate and high deposition temperatures, which significantly limit the device integration potentials of VANs. In this work, a freestanding TiN‐Au VAN is synthesized on a water‐soluble Sr₃Al₂O₆ buffer layer. A very thin TiN buffer layer is incorporated to improve the overall VAN growth quality. The microstructure and optical properties of the VAN samples are compared before and after transfer to evaluate the transfer properties. The results suggest that minimal impacts on film morphology and properties are found in the transferred samples. This study demonstrates the potential to obtain high‐quality freestanding TiN‐Au VAN thin film for flexible and transferable hybrid metamaterials and metasurfaces for plasmonics and integrated photonic devices.

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.

The unique redox properties and high oxygen capacity of nanostructured CeO₂ demonstrate a wide range of applications, such as electrolytes for solid oxide fuel cells, gas sensors, and catalysis for automotive exhaust gas. Most CeO₂ nanomaterials 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 CeO₂ nanostructures with various shapes ranging from nanowires to nanoporous thin films are successfully synthesized. Vertically aligned nanocomposites (VANs) of Sr₃Al₂O₆ (SAO) and CeO₂ are synthesized first while varying concentration ratio between them. Once the SAO is dissolved in water, the remaining CeO₂ forms distinct nanostructures. The thermal stability of the nanostructured CeO₂ is evaluated by in situ heating XRD and thermal annealing tests. This method provides an alternative approach to preparing nanostructured CeO₂ without toxic chemical solutions or complex micro/nanofabrication techniques. These results present a novel approach to prepare nanostructured CeO₂ for future sensing and energy device applications.

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.

Alumina (α‐Al₂O₃) is one of the most versatile engineering ceramics, and its mechanical properties have been extensively studied. However, the micromechanical properties of Al₂O₃ with a fine microstructure are less well understood. Here, we present one of the first investigations that probe the micromechanical properties of fine‐grained polycrystalline Al₂O₃ fabricated via spark plasma sintering, employing in situ microcompression tests inside a scanning electron microscope. This study explores the influence of temperature variations on the deformation mechanisms, particularly the involvement of microcracks and dislocation activities throughout the deformation process. As temperature rises, substantial deformability occurs in the inherently brittle Al₂O₃ at intermediate temperature, where the improved plastic deformability mainly arose from prominent dislocation activities accompanied by grain boundary sliding. This study sheds light on understanding the relationship between defect evolution and mechanical behavior in Al₂O₃ with fine grain sizes.

Resistive switching devices are promising candidates for the next generation of nonvolatile memory and neuromorphic computing applications. Despite the advantages in retention and on/off ratio, filamentary-based memristors still suffer from challenges, particularly endurance (flash being a benchmark system showing 10 ⁴ to 10 ⁶  cycles) and uniformity. Here, we use WO ₃ as a complementary metal-oxide semiconductor–compatible switching oxide and demonstrate a proof-of-concept materials design approach to enhance endurance and device-to-device uniformity in WO ₃ -based memristive devices while preserving other performance metrics. These devices show stable resistive switching behavior with >10 ⁶  cycles, >10 ⁵ -second retention, >10 on/off ratio, and good device-to-device uniformity, without using current compliance. All these metrics are achieved using a one-step pulsed laser deposition process to create self-assembled nanocomposite thin films that have regular guided filaments of ≈100-nanometer pitch, preformed between WO ₃ grains and interspersed smaller Ce ₂ O ₃ grains.

Emerging non-volatile memristor-based devices with resistive switching (RS) materials are being widely researched as promising contenders for the next generation of data storage and neuromorphic technologies. Titanium nitride (TiN_x) is a common industry-friendly electrode system for RS; however, the precise TiN_x properties required for optimum RS performance is still lacking. Herein, using ion-assisted DC magnetron sputtering, we demonstrate the key importance not only of engineering the TiN_x bottom electrodes to be dense, smooth, and conductive, but also understoichiometric in N. With these properties, RS in HfO₂-based memristive devices is shown to be optimised for TiN_0.96. These devices have switching voltages ≤ ±1 V with promising device-to-device uniformity, endurance, memory window of ~40, and multiple non-volatile intermediate conductance levels. This study highlights the importance of precise tuning of TiN_x bottom electrodes to achieve robust performance of oxide resistive switching materials.

Nanocomposite thin films, comprising two or more distinct materials at nanoscale, have attracted significant research interest considering their potential of integrating multiple functionalities for advanced applications in electronics, energy storage, photonics, photovoltaics, and sensing. Among various fabrication technologies, a one-step pulsed laser deposition process enables the self-assembly of materials into vertically aligned nanocomposites (VANs). The demonstrated VAN systems include oxide–oxide, oxide–metal, and nitride–metal VAN films and their growth mechanisms are vastly different. These complexities pose challenges in the designs, materials selection, and prediction of the resulted VAN morphologies and properties. The review examines the key roles that surface energy plays in the VAN growth and provides a generalized materials design guideline combining the two key factors of surface energy and lattice strain/mismatch, along with other factors related to growth kinetics that collectively influence the morphology of VAN films. This review aims to offer valuable guidelines for future material selection and microstructure design in the development of self-assembled VAN films.

Neutron irradiation poses a substantial challenge in the development and application of tungsten (W) and its alloys, predominantly in the framework of nuclear fusion and fission environments. Although W is well-acknowledged for its unique properties like its high melting temperature and higher resistance to sputtering, transmutation products, such as Re and Os, form and impact the alloy properties as a result of neutron irradiation. This transmutation effect accompanied by significant microstructure damage due to neutron irradiation can lead to the significant degradation of mechanical properties. This review surveys the literature focusing on the microstructural modifications post-irradiation and its impacts on the irradiation hardening. This review provides insights into the elaborative understanding on the neutron radiation damage on W and W alloys by exploring the microstructural evolution and hardness changes post-irradiation. The gaps and future opportunities for understanding neutron radiation damage in W are briefly summarized

Hyperbolic metamaterials (HMM) possess significant anisotropic physical properties and tunability and thus find many applications in integrated photonic devices. HMMs consisting of metal and dielectric phases in either multilayer or vertically aligned nanocomposites (VAN) form are demonstrated with different hyperbolic properties. Herein, self‐assembled HfO₂‐Au/TiN‐Au multilayer thin films, combining both the multilayer and VAN designs, are demonstrated. Specifically, Au nanopillars embedded in HfO₂ and TiN layers forming the alternative layers of HfO₂‐Au VAN and TiN‐Au VAN. The HfO₂ and TiN layer thickness is carefully controlled by varying laser pulses during pulsed laser deposition (PLD). Interestingly, tunable anisotropic physical properties can be achieved by adjusting the bi‐layer thickness and the number of the bi‐layers. Type II optical hyperbolic dispersion can be obtained from high layer thickness structure (e.g., 20 nm), while it can be transformed into Type I optical hyperbolic dispersion by reducing the thickness to a proper value (e.g., 4 nm). This new nanoscale hybrid metamaterial structure with the three‐phase VAN design shows great potential for tailorable optical components in future integrated devices.

High critical current (Ic) in high magnetic fields (B) with minimal variations with respect to the orientation of the B field is demanded by many applications such as high-field magnets for fusion systems. Motivated by this, this work studies 6 vol. % BaZrO3/YBa2Cu3O7 (BZO/YBCO) multilayer nanocomposite films by stacking two 10 nm thick Ca0.3Y0.7Ba2Cu3O7 (CaY-123) spacers with three BZO/YBCO layers of thickness varied from 50 to 330 nm to make the total film thickness of 150–1000 nm. The Ca diffusion from the spacers into BZO/YBCO was shown to dramatically enhance pinning efficiency of c-axis aligned BZO nanorods, which yields high and almost thickness independent critical current density (Jc) in the BZO/YBCO multilayer nanocomposite films. Remarkably, enhanced Jc was observed in these multilayer samples at a wide temperature range of 20–80 K and magnetic fields up to 9.0 T. In particular, the thicker BZO/YBCO multilayer films outperform their thinner counterparts in both higher value and less anisotropy of Jc at lower temperatures and higher fields. At 20 K and 9.0 T, Ic is up to 654 A/cm-width at B//c in the 6% multilayer (1000 nm) sample, which is close to 753 A/cm-width at B//ab due to the intrinsic pinning. This result illustrates the critical role of the Ca cation diffusion into the YBCO lattice in achieving high and isotropic pinning in thick BZO/YBCO multilayer films.

Microlattices hold significant potential for developing lightweight structures for the aeronautics and astronautics industries. Laser Powder Bed Fusion (LPBF) is an attractive method for producing these structures due to its capacity for achieving high-resolution, intricately designed architectures. However, defects, such as cracks, in the as-printed alloys degrade mechanical properties, particularly tensile strength, and thereby limit their applications. This study examines the effects of microlattice architecture and relative density on crack formation in the as-printed 718 superalloy. Complex microlattice design and higher relative density are more prone to large-scale crack formation. The mechanisms behind these phenomena are discussed. This study reveals that microlattice type and relative density are crucial factors in defect formation in LPBF metallic alloys. The transmission electron microscopy observations show roughly round γ″ precipitates with an average size of 10 nm in the as-printed 718 without heat treatment. This work demonstrates the feasibility of the additive manufacturing of complex microlattices using 718 superalloys towards architectured lightweight structures.

The integration of nanocomposite thin films with combined multifunctionalities on flexible substrates is desired for flexible device design and applications. For example, combined plasmonic and magnetic properties could lead to unique optical switchable magnetic devices and sensors. In this work, a multiphase TiN-Au-Ni nanocomposite system with core–shell-like Au-Ni nanopillars embedded in a TiN matrix has been demonstrated on flexible mica substrates. The three-phase nanocomposite film has been compared with its single metal nanocomposite counterparts, i.e., TiN-Au and TiN-Ni. Magnetic measurement results suggest that both TiN-Au-Ni/mica and TiN-Ni/mica present room-temperature ferromagnetic property. Tunable plasmonic property has been achieved by varying the metallic component of the nanocomposite films. The cyclic bending test was performed to verify the property reliability of the flexible nanocomposite thin films upon bending. This work opens a new path for integrating complex nitride-based nanocomposite designs on mica towards multifunctional flexible nanodevice applications.

Hybrid metamaterials (HMs) have attracted significant research interests owing to their unique optical properties and their ability to manipulate light‐matter interaction in a novel and controlled fashion beyond what any single material offers. Especially 3D HMs are of great interest due to their potential to provide advanced and precise control of such light‐matter interaction in nanoscale. In this study, a set of 3D HM nanocomposite films are designed by integrating three phases, i.e., vertically aligned CoFe₂ nanosheets within the matrix of TiN/TaN multilayers. By increasing the number of TiN/TaN multilayers from 2 to 19, a high degree of tunability in optical property has been demonstrated, including well‐tailored optical permittivity, and tunable hyperbolic dispersion from Type‐II to Type‐I. Ferromagnetic CoFe₂ nanosheets introduces novel magnetic responses, such as magnetic anisotropy and enhanced coercivity. Furthermore, in situ heating X‐ray diffraction (XRD) suggests good thermal stability of the 3D nanocomposite films up to the measured temperature of 600 °C. This three‐phase 3D nanocomposite design offers more flexibility in HM designs, multifunctionalities, and phase stability, compared with the typical two‐phase HMs toward future metamaterials by design.

Magnetic and ferroelectric oxide thin films have long been studied for their applications in electronics, optics, and sensors. The properties of these oxide thin films are highly dependent on the film growth quality and conditions. To maximize the film quality, epitaxial oxide thin films are frequently grown on single‐crystal oxide substrates such as strontium titanate (SrTiO₃) and lanthanum aluminate (LaAlO₃) to satisfy lattice matching and minimize defect formation. However, these single‐crystal oxide substrates cannot readily be used in practical applications due to their high cost, limited availability, and small wafer sizes. One leading solution to this challenge is film transfer. In this demonstration, a material from a new class of multiferroic oxides is selected, namely bismuth‐based layered oxides, for the transfer. A water‐soluble sacrificial layer of Sr₃Al₂O₆is inserted between the oxide substrate and the film, enabling the release of the film from the original substrate onto a polymer support layer. The films are transferred onto new substrates of silicon and lithium niobate (LiNbO₃) and the polymer layer is removed. These substrates allow for the future design of electronic and optical devices as well as sensors using this new group of multiferroic layered oxide films.

Multiferroic materials, where ferroelectric and magnetic orders coexist, have ignited substantial research interest due to the achievable manipulation of magnetic orders using external electric fields, a feature that has garnered serious interest for memory storage applications. Nonetheless, naturally occurring single-phase multiferroic materials are scarce, thus constraining options for practical use. Over the last decade, bismuth-based layered supercell (LSC) oxides have emerged as novel candidates for multiferroics, catalyzing extensive investigations in this domain. Additionally, these LSC systems are known for their anisotropic structures and optical properties, making them promising for application in optics such as polarizers, beam splitters, and modulators. This thorough review explores the development and current advancements in multiferroic bismuth-based LSC materials. It covers the diverse nature of LSCs, detailing their microstructure, properties, and the mechanics of self-assembly formation. It also highlights the remarkable multifunctional characteristics of LSC-based nanocomposites, with a particular focus on their applications in electronics and optics. Moreover, this review examines the significant potential of LSCs in practical applications, particularly through their integration onto silicon and flexible substrates via heteroepitaxy and film transfer techniques. Finally, it offers insights into potential future research avenues and the broader implications of these versatile LSC materials.

Functional thin films of nanoscale metal pillars in oxide or nitride matrices known as vertically aligned nanocomposite (VAN) have gained much interest owing to their unique strain-coupled and highly anisotropic properties. So far, the deposition of these films has been explored mostly experimentally. In this work, a density functional theory (DFT)-based kinetic Monte Carlo simulation model using Bortz–Kalos–Lebowitz algorithm was developed to understand the growth of VAN films deposited by pulsed laser technique on mismatching substrates. The model has been parameterized and applied to understand the kinetics of growth thin films consisting of Au pillars in CeO2 matrix deposited on SrTiO3 substrates. The effects of pulsed laser deposition (PLD) conditions including the pulse frequency, deposition flux, and substrate temperature were explored. The simulations indicate that the Au pillar size and shape exhibit significant dependence on the PLD conditions. Namely, increasing the temperature increases the average pillar size and lowers the pillar density, and vice versa. In addition, the simulations revealed that increasing the deposition rate results in lowering the average pillar size and increasing the density. Particularly, the DFT results suggest that Au pillar size can be tuned during the initial growth of the first monolayer due to the significantly low activation barrier. Our analysis showed that the relationship between the average pillar size and pillar density is influenced by the kinetics. Furthermore, autocorrelation analysis showed that pillars self-organize in quasi-ordered patterns at certain windows of the deposition conditions, which is attributed to the complex nature of the chemical interactions in the system, the kinetics, and the deposition parameters.

Bi₂NiMnO₆ (BNMO) epitaxial thin films with a layered supercell (LSC) structure have emerged as a promising single‐phase multiferroic material recently. Because of the required strain state for the formation of the LSC structures, most of the previous BNMO films are demonstrated on rigid oxide substrates such as SrTiO₃ and LaAlO₃. Here, the potential of BNMO films grown on muscovite mica substrates via van der Waals epitaxy, spotlighting their suitability for cutting‐edge flexible device applications is delved. Comprehensive scanning transmission electron microscopy/energy‐dispersive X‐ray analyses reveal a layered structure in the BNMO film and a pristine interface with the mica substrate, indicating high‐quality deposition and minimal interfacial defects. Capitalizing on its unique property of easily cleavable layers due to weak van der Waals forces in mica substrates, flexible BNMO/mica samples are fixed. A standout feature of the BNMO film grown on mica substrate is its consistent multiferroic properties across varied mechanical conditions. A novel technique is introduced for thinning the mica substrate and subsequent transfer of the sample, with post‐transfer analyses validating the preserved structural and magnetic attributes of the film. Overall, this study illuminates the resilient multiferroic properties of BNMO films on mica, offering promising avenues for their integration for next‐generation flexible electronics.

ZnO-Au nanocomposite thin films have been previously reported as hybrid metamaterials with unique optical properties such as plasmonic resonance properties and hyperbolic behaviors. In this study, Au composition in the ZnO-Au nanocomposites has been effectively tuned by target composition variation and thus resulted in microstructure and optical property tuning. Specifically, all the ZnO-Au nanocomposite thin films grown through the pulsed laser deposition (PLD) method show obvious vertically aligned nanocomposite (VAN) structure with the Au nanopillars embedded in the ZnO matrix. Moreover, the average diameter of Au nanopillars increases as Au concentration increases, which also leads to the redshifts in the surface plasmon resonance (SPR) wavelength and changes in the hyperbolic behaviors of the films. As a whole, this work discusses how strain-driven tuning of optical properties and microstructure resulted through a novel Au concentration variation approach which has not been previously attempted in the ZnO-Au thin film system. These highly ordered films present great promise in the areas of sensing, waveguides, and nanophotonics to name a few.

This study demonstrates the use of Cold atmospheric plasma-assisted deposition of conductive PPy–Ag nanocomposite coatings onto fabric electrodes, for enhancing the long-term antibiofouling performance of e-textile-based electronics.

Plastic wastes produced graphitic carbon shell encapsulation on cobalt nanoparticles and the derived composite materials showed ferromagnetism and superior Li⁺ ion storage of 377 mA h g^–1 (Co-GNP-ZipC) and 509 mA h g^–1 (Co-GNP-FmC) at the 250^th cycle.

Laser-assisted surface alloying (LSA) process to modify orthopedic implant surfaces with Ti–Ag alloy for enhanced antibacterial and osteoinduction properties.

We report a milestone in achieving large-scale, ultrathin (~5 nm) superconducting NbN thin films on 300 mm Si wafers using a high-volume manufacturing (HVM) industrial physical vapor deposition (PVD) system. The NbN thin films possess remarkable structural uniformity and consistently high superconducting quality across the entire 300 mm Si wafer, by incorporating an AlN buffer layer. High-resolution X-ray diffraction and transmission electron microscopy analyses unveiled enhanced crystallinity of (111)-oriented δ-phase NbN with the AlN buffer layer. Notably, NbN films deposited on AlN-buffered Si substrates exhibited a significantly elevated superconducting critical temperature (~2 K higher for the 10 nm NbN) and a higher upper critical magnetic field or Hc2 (34.06 T boost in Hc2 for the 50 nm NbN) in comparison with those without AlN. These findings present a promising pathway for the integration of quantum-grade superconducting NbN films with the existing 300 mm CMOS Si platform for quantum information applications.

Thermophotovoltaics (TPVs) are devices that convert thermal radiation into electricity using a low-bandgap photovoltaic (PV) cell. While the theoretical efficiency can approach the Carnot limit, designing a TPV selective emitter that is spectrally matched with the PV cell's bandgap and is stable at high temperatures is critical for achieving high-efficiency systems. Photonic crystal (PhC) emitters can provide excellent spectral control, but prior experimental designs lack the thermal stability required for high-performance TPVs. In this study, a tri-phase PhC emitter design is proposed and optimized. The tri-phase design introduces an additional material in one of the alternating layers of an existing 1D PhC emitter, potentially stabilizing it at high temperatures. BaZrO3 is introduced in the CeO2 layers of a CeO2/MgO PhC emitter. Stanford Stratified Structure Solver (S4) is used to model the emittance of multiple tri-phase PhC variations. The parameter for optimization is the spectral efficiency of the emitter. The structure with the highest spectral efficiency is only 0.02% less efficient than the original design. The structure with the lowest spectral efficiency is only 0.28% less efficient. Therefore, any tri-phase variation can be applied to existing PhC emitters without compromising on their spectral efficiency. Without the need for manufacturing specific parameters, the tri-phase PhC can be an inexpensive emitter for real world applications that may improve thermal stability without compromising on the spectral efficiency, making the practical applications of TPVs feasible.

CeO₂ is a rare-earth refractory material with high refractive index, high thermal stability and infrared transparency; this knowledge can be utilized to develop practical thin films for high temperature thermophotovoltaics (TPVs) and thermal barrier coatings (TBCs). Here, we report ellipsometric measurements of a CeO₂ thin film in the wavelength range 210 nm–2500 nm from room temperature to 500 ^∘C. Because most previous spectroscopic studies of CeO₂ evaluated its optical properties only at room temperature, our findings provide insights into the potential impacts of temperature change on the aforementioned applications, induced by the changes in its electronic structure. We also provide the reflectance and transmittance measurements of the same CeO₂ thin film at room temperature using Fourier transform infrared (FTIR) spectroscopy. This knowledge can be leveraged to develop TPV and TBC designs. Finally, we used a software package called Stanford Stratified Structure Solver (S4) to simulate the angle-dependent reflectance spectrum. The optical properties of CeO₂ films measured by ellipsometry are used as inputs to predict reflectance spectra. Comparison of the experimental FTIR reflectance with simulated reflectance in S4 shows strong agreement at three different angles.

Currently, metallic powders for laser powder bed fusion (LPBF) primarily come in two commercially available powder size distributions (PSDs): 15+/45− for non-reactive powders and 15+/63− for reactive powders. These powders are generally produced via gas atomization processes that create highly spherical particles with a Gaussian PSD. Because of the standard deviation within a Gaussian distribution, only small portions of the total product are used for LPBF applications. This screening process makes the other particle sizes a waste product and, thus, increases processing costs. The non-reactive 718 powder was printed with both the typical PSD of 15+/45− and a wider bimodal experimental PSD. Compared to conventional 718, the 718 alloys with bimodal PSD shows less than a 0.2% difference in density, and insignificant change in mechanical behavior. Electron backscattered diffraction studies revealed that grain sizes and morphology were similar between the two sample sets, but bimodal 718 alloy has a slightly greater degree of large grains. The study suggests that particles with wide or bimodal size distributions show promise in producing equivalent high-quality products without sacrificing mechanical properties.

Metamaterials have gained great research interest in recent years owing to their potential for property tunability, multifunctionality, and property coupling. As a new group of self‐assembled thin films, vertically aligned nanocomposite (VAN)‐based hybrid metamaterials have been demonstrated with significant anisotropic physical properties and a broad range of property tailorability, such as optical anisotropy, magnetic anisotropy, hyperbolic dispersion, and enhanced second harmonic generation properties. Herein, self‐assembled ZrO₂‐Co nanocomposite films, with high epitaxial quality and ultra‐fine vertically aligned Co nanopillars (with an average diameter of ≈2 nm) embedded in a ZrO₂ matrix, are fabricated using a pulsed laser deposition (PLD) method. The Co pillar density can be effectively tuned by varying the Co concentration in the target, which results in tunable optical properties and magnetic properties. Specifically, a high saturation magnetization of 100 emu cm⁻³, strong out‐of‐plane magnetic anisotropy and tailorable magnetization properties are achieved via tuning the Co nanopillar density. Coupled with hyperbolic dispersion of dielectric constant from 950 to 1500 nm in wavelength, plasmonic Co metal nanopillars, and the unique dielectric ZrO₂ matrix, this new nanoscale hybrid metamaterial shows great potential for future integrated optical and magnetic device designs.

A design concept of phase-separated amorphous nanocomposite thin films is presented that realizes interfacial resistive switching (RS) in hafnium-oxide-based devices. The films are formed by incorporating an average of 7% Ba into hafnium oxide during pulsed laser deposition at temperatures ≤400°C. The added Ba prevents the films from crystallizing and leads to ∼20-nm-thin films consisting of an amorphous HfO_xhost matrix interspersed with ∼2-nm-wide, ∼5-to-10-nm-pitch Ba-rich amorphous nanocolumns penetrating approximately two-thirds through the films. This restricts the RS to an interfacial Schottky-like energy barrier whose magnitude is tuned by ionic migration under an applied electric field. Resulting devices achieve stable cycle-to-cycle, device-to-device, and sample-to-sample reproducibility with a measured switching endurance of ≥10⁴cycles for a memory window ≥10 at switching voltages of ±2 V. Each device can be set to multiple intermediate resistance states, which enables synaptic spike-timing–dependent plasticity. The presented concept unlocks additional design variables for RS devices.

Cu-to-Cu thermal compression bonding (TCB) has emerged as a promising solution for ultrafine pitch packaging in 3D integrated circuit technologies. Despite the progress made by conventional Cu-to-Cu TCB methods in achieving good mechanical strength of the Cu bonds, the bonding processes generally require high temperature and high pressure, which may degrade the performance and reliability of the device. Therefore, it is imperative to investigate the processing parameters to understand the bonding mechanism and achieve effective TCB at a low temperature and low pressure. Here, we developed an in situ TCB technique inside a scanning electron microscope. The in situ TCB method enables a real-time observation of bonding development, which provides critical insights into how the texture and microstructure of Cu bumps may influence the creep and surface diffusion during the bonding process. This work features a strategy to advance our understanding of the bonding mechanisms and provides insight into tailoring the microstructure of Cu for bonding at a low temperature and low pressure.

Nanostructured metallic materials with abundant high-angle grain boundaries exhibit high strength and good radiation resistance. While the nanoscale grains induce high strength, they also degrade tensile ductility. We show that a gradient nanostructured ferritic steel exhibits simultaneous improvement in yield strength by 36% and uniform elongation by 50% compared to the homogenously structured counterpart. In situ tension studies coupled with electron backscattered diffraction analyses reveal intricate coordinated deformation mechanisms in the gradient structures. The outermost nanolaminate grains sustain a substantial plastic strain via a profound deformation mechanism involving prominent grain reorientation. This synergistic plastic co-deformation process alters the rupture mode in the post-necking regime, thus delaying the onset of fracture. The present discovery highlights the intrinsic plasticity of nanolaminate grains and their significance in simultaneous improvement of strength and tensile ductility of structural metallic materials.

Twinned Al–Mg alloys have been reported. However, the role of Mg solute in facilitating the formation of growth twins remains unclear. By using a precession-assisted crystal orientation mapping technique (PACOM) coupled with transmission electron microscopy (known as ASTAR), we examined the evolution of twin boundaries in Al, Al–1Mg, and Al–2.2Mg (at. %) films. The twinned grain fraction elevates with increasing film thickness until it reaches a peak when the film thickness is 120–160 nm. The Al–Mg alloys exhibited greater twinned grain fractions than pure Al. To investigate the fluctuation of twinned grain fraction, two types of twin boundaries were classified including intergranular and intragranular twins. The initial increase in twin density is attributed to the impingement of twinned grains during island coalescence and the twinned grains are more likely to survive during the grain growth process. Whereas the decrease in twinned grain fraction in thicker films is related to the removal of intragranular twins, and a lack of formation mechanisms of new twins.

Oxide-dispersion-strengthened (ODS) alloys have long been considered for high temperature turbine, spacecraft, and nuclear reactor components due to their high temperature strength and radiation resistance. Conventional synthesis approaches of ODS alloys involve ball milling of powders and consolidation. In this work, a process-synergistic approach is used to introduce oxide particles during laser powder bed fusion (LPBF). Chromium (III) oxide (Cr2O3) powders are blended with a cobalt-based alloy, Mar-M 509, and exposed to laser irradiation, resulting in reduction–oxidation reactions involving metal (Ta, Ti, Zr) ions from the metal matrix to form mixed oxides of increased thermodynamic stability. A microstructure analysis indicates the formation of nanoscale spherical mixed oxide particles as well as large agglomerates with internal cracks. Chemical analyses confirm the presence of Ta, Ti, and Zr in agglomerated oxides, but primarily Zr in the nanoscale oxides. Mechanical testing reveals that agglomerate particle cracking is detrimental to tensile ductility compared to the base alloy, suggesting the need for improved processing methods to break up oxide particle clusters and promote their uniform dispersion during laser exposure.

Defect engineering in valence change memories aimed at tuning the concentration and transport of oxygen vacancies are studied extensively, however mostly focusing on contribution from individual extended defects such as single dislocations and grain boundaries. In this work, the impact of engineering large numbers of grain boundaries on resistive switching mechanisms and performances is investigated. Three different grain morphologies, that is, “random network,” “columnar scaffold,” and “island‐like,” are realized in CeO₂ thin films. The devices with the three grain morphologies demonstrate vastly different resistive switching behaviors. The best overall resistive switching performance is shown in the devices with “columnar scaffold” morphology, where the vertical grain boundaries extending through the film facilitate the generation of oxygen vacancies as well as their migration under external bias. The observation of both interfacial and filamentary switching modes only in the devices with a “columnar scaffold” morphology further confirms the contribution from grain boundaries. In contrast, the “random network” or “island‐like” structures result in excessive or insufficient oxygen vacancy concentration migration paths. The research provides design guidelines for grain boundary engineering of oxide‐based resistive switching materials to tune the resistive switching performances for memory and neuromorphic computing applications.

Nanotwinned metals have exhibited many enhanced physical and mechanical properties. Twin boundaries have recently been introduced into sputtered Al alloys in spite of their high stacking fault energy. These twinned Al alloys possess unique microstructures composed of vertically aligned Σ3(112) incoherent twin boundaries (ITBs) and have demonstrated remarkable mechanical strengths and thermal stability. However, their strain rate sensitivity has not been fully assessed. A modified nanoindentation method has been employed here to accurately determine the strain rate sensitivity of nanotwinned Al–Zr alloys. The hardness of these alloys reaches 4.2 GPa while simultaneously exhibiting an improved strain rate sensitivity. The nanotwinned Al–Zr alloys have shown grain size-dependent strain rate sensitivity, consistent with previous findings in the literature. This work provides insight into a previously unstudied aspect of nanotwinned Al alloys.

Colloidal Ag particles decorated with Fe₃O₄islands can be electrochemically or photochemically activated as inverse catalysts for C(sp²)–H heteroarylation.

The insertion of strain re-seeding CeO₂ layers allows for thick growth of strain-dependent Aurivillius supercell phases.

This study presents an efficient method to deposit silver-doped glass-ceramic coatings on polypropylene meshes using cold atmospheric plasma and laser surface texturing. The optimal process offers sustained antibacterial properties and high biocompatibility.

Multiferroic materials have generated great interest due to their potential as functional device materials. Nanocomposites have been increasingly used to design and generate new functionalities by pairing dissimilar ferroic materials, though the combination often introduces new complexity and challenges unforeseeable in single-phase counterparts. The recently developed approaches to fabricate 3D super-nanocomposites (3D‐sNC) open new avenues to control and enhance functional properties. In this work, we develop a new 3D‐sNC with CoFe₂O₄ (CFO) short nanopillar arrays embedded in BaTiO₃ (BTO) film matrix via microstructure engineering by alternatively depositing BTO:CFO vertically-aligned nanocomposite layers and single-phase BTO layers. This microstructure engineering method allows encapsulating the relative conducting CFO phase by the insulating BTO phase, which suppress the leakage current and enhance the polarization. Our results demonstrate that microstructure engineering in 3D‐sNC offers a new bottom–up method of fabricating advanced nanostructures with a wide range of possible configurations for applications where the functional properties need to be systematically modified.

Nanocomposite thin film materials present great opportunities in coupling materials and functionalities in unique nanostructures including nanoparticles-in-matrix, vertically aligned nanocomposites (VANs), and nanolayers. Interestingly the nanocomposites processed through a non-equilibrium processing method, e.g., pulsed laser deposition (PLD), often possess unique metastable phases and microstructures that could not achieve using equilibrium techniques, and thus lead to novel physical properties. In this work, a unique three-phase system composed of BaTiO3 (BTO), with two immiscible metals, Au and Fe, is demonstrated. By adjusting the deposition laser frequency from 2 Hz to 10 Hz, the phase and morphology of Au and Fe nanoparticles in BTO matrix vary from separated Au and Fe nanoparticles to well-mixed Au-Fe alloy pillars. This is attributed to the non-equilibrium process of PLD and the limited diffusion under high laser frequency (e.g., 10 Hz). The magnetic and optical properties are effectively tuned based on the morphology variation. This work demonstrates the stabilization of non-equilibrium alloy structures in the VAN form and allows for the exploration of new non-equilibrium materials systems and their properties that could not be easily achieved through traditional equilibrium methods.

Nanocomposite thin film materials present great opportunities in coupling materials and functionalities in unique nanostructures including nanoparticles-in-matrix, vertically aligned nanocomposites (VANs), and nanolayers. Interestingly the nanocomposites processed through a non-equilibrium processing method, e.g., pulsed laser deposition (PLD), often possess unique metastable phases and microstructures that could not achieve using equilibrium techniques, and thus lead to novel physical properties. In this work, a unique three-phase system composed of BaTiO3 (BTO), with two immiscible metals, Au and Fe, is demonstrated. By adjusting the deposition laser frequency from 2 Hz to 10 Hz, the phase and morphology of Au and Fe nanoparticles in BTO matrix vary from separated Au and Fe nanoparticles to well-mixed Au-Fe alloy pillars. This is attributed to the non-equilibrium process of PLD and the limited diffusion under high laser frequency (e.g., 10 Hz). The magnetic and optical properties are effectively tuned based on the morphology variation. This work demonstrates the stabilization of non-equilibrium alloy structures in the VAN form and allows for the exploration of new non-equilibrium materials systems and their properties that could not be easily achieved through traditional equilibrium methods.

Nanotwinned metals have demonstrated the capacity for concomitant high strength and ductility. However, metals with high stacking fault energies, such as aluminum (Al), have a low propensity for twin formation. Here, we show the fabrication of supersaturated solid-solution Al–Zr alloys with a high density of growth twins. Incoherent twin boundaries (ITBs) are strong barriers to dislocation motion, while mobile partial dislocations promote plasticity. These deformable nanotwinned Al–Zr alloys reach a flow stress of ∼1 GPa, as demonstrated using in situ micropillar compression tests. Density functional theory calculations uncover the role Zr solute plays in the formation and deformation of the nanotwinned microstructure. This study features a strategy for incorporating ITBs and 9R phase into Al alloys for simultaneous benefits to strength and deformability.

Transition metal nitrides such as titanium nitride (TiN) possess exceptional mechanical-, chemical-, and thermal-stability and have been utilized in a wide variety of applications ranging from super-hard, corrosion-resistive, and decorative coatings to nanoscale diffusion barriers in semiconductor devices. Despite the ongoing interest in these robust materials, there have been limited reports focused on engineering high-aspect ratio TiN-based nanocomposites with anisotropic magnetic and optical properties. To this end, we explored TiN–Fe thin films with self-assembled vertical structures integrated on Si substrates. We showed that the key physical properties of the individual components (e.g., ferromagnetism from Fe) are preserved, that vertical nanostructures promote anisotropic behavior, and interactions between TiN and Fe enable a special magneto-optical response. This TiN–Fe nanocomposite system presents a new group of complex multifunctional hybrid materials that can be integrated on Si for future Si-based memory, optical, and biocompatible devices.

Manufacture and characterizations of perovskite-mica van der Waals epitaxy heterostructures are a critical step to realize the application of flexible devices. However, the fabrication and investigation of the van der Waals epitaxy architectures grown on mica substrates are mainly limited to (111)-oriented perovskite functional oxide thin films up to now and buffer layers are highly needed. In this work, we directly grew La_0.7Sr_0.3MnO₃ (LSMO) thin films on mica substrates without using any buffer layer. By the characterizations of x-ray diffractometer and scanning transmission electron microscopy, we demonstrate the epitaxial growth of the (110)-oriented LSMO thin film on the mica substrate. The LSMO thin film grown on the mica substrate via van der Waals epitaxy adopts domain matching epitaxy instead of conventional lattice matching epitaxy. Two kinds of domain matching relationships between the LSMO thin film and mica substrate are sketched by Visualization for Electronic and STructural Analysis software and discussed. A decent ferromagnetism retains in the (110)-oriented LSMO thin film. Our work demonstrates a new pathway to fabricate (110)-oriented functional oxide thin films on flexible mica substrates directly.

In this work, we demonstrate vertically stacked multilayer sub-1-nm In2O3 field-effect transistors (FETs) with surrounding gate in a back-end-of-line (BEOL) compatible low-temperature fabrication process. A typical bottom-gated single layer In2O3 FET with maximum on-state current (ION) of 890 μA/μm at VDS = 0.8 V and an on/off ratio over 106 is achieved with a channel length (Lch) of 100 nm. The effects of HfO2 capping and O2 annealing are systematically studied, which is critical to realizing the multilayer FETs. Each atomically thin In2O3 channel layer with a thickness (TIO) of 0.9 nm is realized by atomic layer deposition (ALD) at 225 °C. Multilayer FETs with a number of In2O3 layers up to 4 and 1.2 nm-thick HfO2 between each individual layer are fabricated. An enhancement of on-state current (ION) from 183 μA in a single layer In2O3 FET to 339 μA in a 4 layer device with an on/off ratio of 3.4 × 104 is achieved, demonstrating the key advantage of the multilayer FETs to improve the current. Several critical features, such as large-area growth, high uniformity, high reproducibility, ultrathin body, flexibility, and BEOL compatibility, have turned ALD In2O3 into a noteworthy candidate for next-generation oxide semiconductor channel materials.

Vertically aligned nanocomposite (VAN) thin films have shown strong potential in oxide nanoionics but are yet to be explored in detail in solid-state battery systems. Their 3D architectures are attractive because they may allow enhancements in capacity, current, and power densities. In addition, owing to their large interfacial surface areas, the VAN could serve as models to study interfaces and solid-electrolyte interphase formation. Here, we have deposited highly crystalline and epitaxial vertically aligned nanocomposite films composed of a LixLa0.32±0.05(Nb0.7±0.1Ti0.32±0.05)O3±δ-Ti0.8±0.1Nb0.17±0.03O2±δ-anatase [herein referred to as LL(Nb, Ti)O-(Ti, Nb)O2] electrolyte/anode system, the first anode VAN battery system reported. This system has an order of magnitude increased Li+ ionic conductivity over that in bulk Li3xLa1/3−xNbO3 and is comparable with the best available Li3xLa2/3−xTiO3 pulsed laser deposition films. Furthermore, the ionic conducting/electrically insulating LL(Nb, Ti)O and electrically conducting (Ti, Nb)O2 phases are a prerequisite for an interdigitated electrolyte/anode system. This work opens up the possibility of incorporating VAN films into an all solid-state battery, either as electrodes or electrolytes, by the pairing of suitable materials.

Hyperbolic metamaterials are a class of materials exhibiting anisotropic dielectric function owing to the morphology of the nanostructures. In these structures, one direction behaves as a metal, and the orthogonal direction behaves as a dielectric material. Applications include subdiffraction imaging and hyperlenses. However, key limiting factors include energy losses of noble metals and challenging fabrication methods. In this work, self-assembled plasmonic metamaterials consisting of anisotropic nanoalloy pillars embedded into the ZnO matrix are developed using a seed-layer approach. Alloys of AuxAl1−x or AuxCu1−x are explored due to their lower losses and higher stability. Optical and microstructural properties were explored. The ZnO-AuxCu1−x system demonstrated excellent epitaxial quality and optical properties compared with the ZnO-AuxAl1−x system. Both nanocomposite systems demonstrate plasmonic resonance, hyperbolic dispersion, low losses, and epsilon-near-zero permittivity, making them promising candidates towards direct photonic integration.

Hyperbolic metamaterials are a class of materials exhibiting anisotropic dielectric function owing to the morphology of the nanostructures. In these structures, one direction behaves as a metal, and the orthogonal direction behaves as a dielectric material. Applications include subdiffraction imaging and hyperlenses. However, key limiting factors include energy losses of noble metals and challenging fabrication methods. In this work, self-assembled plasmonic metamaterials consisting of anisotropic nanoalloy pillars embedded into the ZnO matrix are developed using a seed-layer approach. Alloys of AuxAl1−x or AuxCu1−x are explored due to their lower losses and higher stability. Optical and microstructural properties were explored. The ZnO-AuxCu1−x system demonstrated excellent epitaxial quality and optical properties compared with the ZnO-AuxAl1−x system. Both nanocomposite systems demonstrate plasmonic resonance, hyperbolic dispersion, low losses, and epsilon-near-zero permittivity, making them promising candidates towards direct photonic integration.

One-dimensionalc-axis-aligned BaZrO₃(BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa₂Cu₃O_7−x(BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to inducec-axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca_0.3Y_0.7Ba₂Cu₃O_7−x(CaY-123) spacers as the Ca reservoir in 2–6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement ofJ_c(B) at magnetic fieldB= 9.0 T//c-axis and 65 K–77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart’s. This has led to a record high pinning force densityF_ptogether with significantly enhancedB_maxat whichF_preaches its maximum valueF_p,maxfor BZO 1D-APCs atB//c-axis. At 65 K, theF_p,max∼158 GN m⁻³andB_max∼ 8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement overF_p,max∼ 36.1 GN m⁻³andB_max∼ 5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs.

Electric field control of magnetism (EFCM) at low voltage (≤5 V) and high temperature (≥353 K) is crucial to micro-integrated magnetoelectric devices. In this work, the BaFe10.2Sc1.8O19 (BFSO)/BaTiO3(BTO) bilayer epitaxial thin films are fabricated. Results show that compared to the single BFSO film, there are significant increases in magnetic susceptibility, multiferroic transition temperature (Tcone), and EFCM in BFSO/BTO bilayer films. The room temperature magnetoelectric coupling coefficient in BFSO (80 nm)/BTO (300 nm) bilayer films (189.6 ns/m) is 14.7 times higher than that in the single layer BFSO film and 345 times larger than single crystalline BiFeO3. A change in magnetization ΔM% about 38% at 20 K and 7.1% at 390 K is obtained in the BFSO (80 nm)/BTO (300 nm) bilayer film. Moreover, repeatable low voltage (≤4 V) EFCM with a high signal-to-noise ratio in the BFSO/BTO bilayer film device is verified at temperatures ranging from 20 K to above 390 K. This high temperature EFCM is mainly contributed by the high Tcone of BFSO and strong piezoelectric/magnetostrictive coupling at the BFSO/BTO interface. The above findings enable the potential usage and integration of BFSO/BTO bilayer films into micro-integrated microwave devices.

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.

First time demonstration of epitaxially stabilised δ-Bi₂O₃phase in vertically aligned nanocomposite thin films, exhibiting very high ionic conductivities of up to 10⁻³S cm⁻¹at 500 °C.

A stacking scheme for solution-processable electrochromic polymers is presented with the integration of direct photolithography patterning to realize full colors, layered textures, and controllable color switching.

Oxide-metal-based hybrid material of HfO₂-Au have been demonstrated and shown novel anisotropic optical and plasmonic properties.

An Aurivillius-phase multiferroic material Bi_1.25AlMnO_3.25embedded with Au NPs displays tunable functionalities at various deposition temperatures.

BaZrO₃(BZO) one-dimensional artificial pinning centers (1D-APCs) aligned along thec-axis of the YBa₂Cu₃O₇(YBCO) have been adopted to enhance the magnetic vortex pinning in BZO/YBCO nanocomposite films. However, the pinning force densityF_pof the BZO 1D-APCs remains moderate at temperatures near 77 K. A hypothesis of the major limiting factor is the defective BZO 1D-APCs/YBCO interface as a direct consequence of the large interfacial strain originated from the BZO/YBCO lattice mismatch of ∼7.7%. Herein, we explore enlarging thec-axis of the YBCO dynamically to reduce the lattice mismatch and hence to prevent formation of the defective BZO 1D-APCs/YBCO interface. Specifically, thec-axis enlargement was achieved by partial replacement of Cu with Ca on the YBCO lattice using strain-directed Ca diffusion into YBCO from two Ca_0.3Y_0.7Ba₂Cu₃O_7−x(CaY-123) spacers of only 10 nm in thickness inserted into the 2 vol% BZO 1D-APC/YBCO nanocomposite thin films of ∼150 nm in total thickness. The achieved elongatedc-axis is attributed to the formation of stacking faults induced by Ca-replacement of Cu on YBCO lattice. The reduced BZO/YBCO lattice mismatch allows formation of a coherent BZO 1D-APC/YBCO interface with negligible defects. This leads to an enhancedF_pvalue up to 98 GN m⁻³at 65 K, which is 70% higher than that of the reference 2 vol% BZO 1D-APC/YBCO sample. Furthermore, the benefit of the enhanced pinning of the BZO 1D-APCs with a coherent interface with YBCO can be extended to a large angular range of the magnetic field orientation. This study reveals the significant effect of the BZO/YBCO interface on the pinning efficiency of BZO 1D-APCs and provides a promising approach to achieve a coherent interface in BZO/YBCO nanocomposite films.

Ferroelectric HfO₂-based materials hold great potential for widespread integration of ferroelectricity into modern electronics due to their robust ferroelectric properties at the nanoscale and compatibility with the existing Si technology. Earlier work indicated that the nanometer crystal grain size was crucial for stabilization of the ferroelectric phase of hafnia. This constraint caused high density of unavoidable structural defects of the HfO₂-based ferroelectrics, obscuring the intrinsic ferroelectricity inherited from the crystal space group of bulk HfO₂. Here, we demonstrate the intrinsic ferroelectricity in Y-doped HfO₂ films of high crystallinity. Contrary to the common expectation, we show that in the 5% Y-doped HfO₂ epitaxial thin films, high crystallinity enhances the spontaneous polarization up to a record-high 50 µC/cm² value at room temperature. The high spontaneous polarization persists at reduced temperature, with polarization values consistent with our theoretical predictions, indicating the dominant contribution from the intrinsic ferroelectricity. The crystal structure of these films reveals the Pca2₁ orthorhombic phase with a small rhombohedral distortion, underlining the role of the anisotropic stress and strain. These results open a pathway to controlling the intrinsic ferroelectricity in the HfO₂-based materials and optimizing their performance in applications.

We report on the fabrication of a complex gear‐shaped 3 mol.% yttria‐stabilized zirconia via a combination of additive manufacturing and flash sintering. The gear was printed via direct ink printing technique. Flash sintering was performed at an electric field of 150 V/cm and the specimens were rapidly densified within a few seconds at a furnace temperature of 1200°C. The flash‐sintered gear has a 95% relative density and shows no obvious warping or cracking after the rapid densification. Microstructure analysis and hardness measurement revealed grain size gradients and hardness variation along both thickness and lateral directions of the flash‐sintered gear. This study demonstrates a possible route to produce dense complex‐shaped parts using the flash sintering technique.

Nanometer thick grain boundaries enable room temperature deformability in conventional brittle intermetallics.

Developing reliable and tunable metamaterials is fundamental to next-generation optical-based nanodevices and computing schemes. In this review, an overview of recent progress made with a unique group of ceramic-based functional nanocomposites, i.e., vertically aligned nanocomposites (VANs), is presented, with the focus on the tunable anisotropic optical properties. Using a self-assembling bottom-up deposition method, the as-grown VANs present great promise in terms of structural flexibility and property tunability. Such broad tunability of functionalities is achieved through VAN designs, material selection, growth control, and strain coupling. The as-grown multi-phase VAN films also present enormous advantages, including wafer scale integration, epitaxial quality, sharp atomic interface, as well as designable materials and geometries. This review also covers the research directions with practical device potentials, such as multiplex sensing, high-temperature plasmonics, magneto-optical switching, as well as photonic circuits.

We demonstrate p-type thin-film transistors (TFTs) on copper(I) oxide (Cu₂O) grown by plasma-enhanced atomic layer deposition (PEALD) with bis(N,N′-di-sec-butylacetami-dinato)dicopper(I) as the Cu precursor and oxygen (O₂) plasma as an oxidant. PEALD provides many if the advantages of other ALD processes, including uniformity and conformality, but with the additional ability to actively generate reactants and to add substantial energy from the plasma which may be important in defect control, low-temperature deposition. In this letter, Cu₂O films were grown on SiO₂/Si substrates under different substrate temperatures (160 ∼ 240 °C) and post-deposition annealing was carried out under various temperatures (300 ∼ 1100 °C) to improve the growth rate and crystallinity of the Cu₂O films. The fabricated p-channel bottom-gate Cu₂O transistors with a controlled thickness of 12 nm have high transparency over 90% and exhibit a subgap density of states (g(E)) of 7.2 × 10¹⁸ eV⁻¹·cm⁻³ near the valence band (E _V), contact resistivity (R _C) of 14 kΩ·mm, I _ON/I _OFF ratio of 2 × 10³, and field-effect mobility of 0.1 cm²/V·s.

The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of functional materials with enhanced electrochemical properties. Here we report on the realization of vertically aligned nanocomposites of lanthanum strontium manganite and doped ceria with straight applicability as functional layers in high-temperature energy conversion devices. By a detailed analysis using complementary state-of-the-art techniques, which include atom-probe tomography combined with oxygen isotopic exchange, we assess the local structural and electrochemical functionalities and we allow direct observation of local fast oxygen diffusion pathways. The resulting ordered mesostructure, which is characterized by a coherent, dense array of vertical interfaces, shows high electrochemically activity and suppressed dopant segregation. The latter is ascribed to spontaneous cationic intermixing enabling lattice stabilization, according to density functional theory calculations. This work highlights the relevance of local disorder and long-range arrangements for functional oxides nano-engineering and introduces an advanced method for the local analysis of mass transport phenomena.

We present a simple liquid-assisted processing (LAP) method, to be used in situ during pulsed laser deposition growth to give both rapid growth rates (50 Hz deposition leading to >250 nm min⁻¹ with a single plume) and strong pinning (improved ×5–10 at 30 K and below, over plain standard YBCO films grown at similar rates). Achieving these two important features simultaneously has been a serious bottleneck to date and yet for applications, it is critical to overcome it. The new LAP method uses a non-stoichiometric target composition, giving rise to a small volume fraction of liquid phase during film growth. LAP enhances the kinetics of the film growth so that good crystalline perfection can be achieved at up to 60× faster growth rates than normal, while also enabling artificial pinning centres to be self-assembled into fine nanocolumns. In addition, LAP allows for RE mixing (80% of Y with 20% of Yb, Sm, or Yb + Sm), creating effective point-like disorder pinning centres within the rare earth barium cuprate lattice. Overall, LAP is a simple method for use in pulsed laser deposition, and it can also be adopted by other in situ physical or vapour deposition methods (i.e. MOCVD, evaporation, etc) to significantly enhance both growth rate and performance.

Even a century after the discovery of ferroelectricity, the quest for the novel multifunctionalities in ferroelectric and multiferroics continues unbounded. Vertically aligned nanocomposites (VANs) offer a new avenue toward improved (multi)functionality, both for fundamental understanding and for real-world applications. In these systems, vertical strain effects, interfaces, and defects serve as key driving forces to tune properties in very positive ways. In this Perspective, the twists and turns in the development of ferroelectric/multiferroics oxide–oxide and unconventional metal–oxide VANs are highlighted. In addition, the future trends and challenges to improve classic ferroelectric/multiferroic VANs are presented, with emphasis on the enhanced functionalities offered by existing VANs, as well as those in emerging systems.

One-dimensional ZnO nanostructures have shown great potential in electronics, optoelectronics and electromechanical devices owing to their unique physical and chemical properties. Most of these nanostructures were grown by equilibrium processes where the defects density is controlled by thermodynamic equilibrium. In this work, flash sintering, a non-equilibrium field-assisted processing method, has been used to synthesize ZnO nanostructures. By applying a high electric field and limiting a low current flow, ZnO nanorods grew uniformly by a vapor–liquid–solid mechanism due to the extreme temperatures achieved near the hot spot. High density basal stacking faults in the nanorods along with ultraviolet excitonic emission and a red emission under room temperature demonstrate the potential of defect engineering in nanostructures via the field-assisted growth method.

The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of superior energy materials. Vertically aligned nanocomposites are characterized by a coherent, dense array of vertical interfaces, which allows for the extension of local effects to the whole volume of the material. Here, we use such a unique architecture to fabricate highly electrochemically active nanocomposites of lanthanum strontium manganite and doped ceria with unprecedented stability and straight applicability as functional layers in solid state energy devices. Direct evidence of synergistic local effects for enhancing the electrochemical performance, stemming from the highly ordered phase alternation, is given here for the first time using atom-probe tomography combined with oxygen isotopic exchange. Interface-induced cationic substitution, enabling lattice stabilization, is presented as the origin of the observed long-term stability. These findings reveal a novel route for materials nano-engineering based on the coexistence between local disorder and long-range arrangement.

Gradient structures containing nanograins in the surface layer have been introduced into Inconel 718 (IN718) nickel-based alloy using the surface mechanical grinding treatment technique. The thermal stability of the gradient IN718 alloy was investigated. Annealing studies reveal that nanograins with a grain size smaller than 40 nm exhibited significantly better thermal stability than those with larger grain size. Transmission electron microscopy analyses reveal that the enhanced thermal stability was attributed to the formation of grain boundaries with low energy configurations. This study provides new insight on strategies to improve the thermal stability of nanocrystalline metals.

Amorphous molybdenum disulfide (MoS ₂ ) is a promising electrochemical catalyst for hydrogen evolution reaction (HER) due to more active sites exposed on the surface compared to its crystalline counterpart. In this study, a novel fast three-minute one-pot method is proposed to prepare the single-wall carbon nanotube- (SWCNT-) supported amorphous MoS ₂ via a microwave heating process. Compared to traditional hydro- or solvent thermal methods to prepare MoS ₂ which usually consume more than 10 hours, it is more promising for fast production. An overpotential at 10 mA/cm ² of amorphous MoS ₂ @SWCNT is 178 mV, which is 99 mV and 22 mV lower than crystalline MoS ₂ @SWCNT and pure amorphous MoS ₂ , respectively. After running 1000 cycles of polarization, ~2% increase in overpotential is observed, indicating its good stability. The enhanced performance results from the beneficial combination of the SWCNT substrate and the amorphous microstructures. The introduction of SWCNT increases catalyst conductivity and prevents MoS ₂ aggregation. The amorphous microstructures of MoS ₂ prepared by a microwave heating method lead to more Mo edges or active sites exposed.

ZnO–Ag_xAu_1−x oxide–nanoalloy vertically aligned nanocomposite thin films have been grown via pulsed laser deposition and the film morphology and optical properties were tuned through oxygen partial pressure.

Ti_1−xCr_xO_2−x/2−δ (0 ≤ x ≤ 0.05) ceramics show high electronic conductivity at low x attributed to oxygen vacancy compensation by co-doping with Ti³⁺ and Cr³⁺ ions. At intermediate x, p-type conductivity is attributed to hole location on under-bonded oxygen.

Recent works of epitaxial nanotwinned metals and alloys with different stacking fault energies are reviewed to elaborate the relationship among synthesis conditions, intrinsic factors, twin structure and various properties.

Ag nanostructures exhibit extraordinary optical properties, which are important for photonic device integration.

A tuneable laser-induced oxidation technique was demonstrated for the fabrication of binder-free and robust electroactive copper oxide film as a highly sensitive non-enzymatic glucose sensor.

Locally intensified, low energy electromagnetic fields can directly affect atomic arrangements through defect-driven structural distortions.

This review summarizes the recent progress in self-assembled oxide-metal nanocomposites, their design criteria using the in-plane strain compensation model, functionalities, and the coupling between electrical, magnetic and optical properties

Ultrathin BFMO layered oxide films were demonstrated to achieve tunable ferromagnetic and ferroelectric properties, dielectric permittivity, and optical bandgap.

The emergent phenomena in complex oxide thin films are strongly tied to the oxygen content, which is often engineered by the oxygen partial pressure during growth. However, such oxygen control by the growth pressure is challenging to synthesize for some oxide films, which requires a subtle control of the oxygen content. A parameter of controlling the oxygen content independent of the growth pressure is desired. Here, we propose a method of controlling the oxygen content of films by engineering the substrate before the growth. The oxide substrate serves as an oxygen sponge, which provides a tunable oxygen environment ranging from oxygen-rich to oxygen-poor for the film growth, depending on the pre-substrate annealing (PSA) conditions. Using manganite as a model system, we demonstrate that this simple PSA method leads to remarkable changes in the structure and physical properties of the as-grown films. This substrate oxygen sponge effect, driven by the large oxygen concentration gradient at high temperatures, can be applied to explore not only emergent interfacial phenomena but also the growth of a variety of functional oxide thin films and nanocomposites.

In situ utilization of available resources in space is necessary for future space habitation. However, direct sintering of the lunar regolith on the Moon as structural and functional components is considered to be challenging due to the sintering conditions. To address this issue, we demonstrate the use of electric current-assisted sintering (ECAS) as a single-step method of compacting and densifying lunar regolith simulant JSC-1A. The sintering temperature and pressure required to achieve a relative density of 97% and microhardness of 6 GPa are 700 °C and 50 MPa, which are significantly lower than for the conventional sintering technique. The sintered samples also demonstrated ferroelectric and ferromagnetic behavior at room temperature. This study presents the feasibility of using ECAS to sinter lunar regolith for future space resource utilization and habitation.

We studied the microstructural evolution and magnetism of ferroelastic La0.9Sr0.1MnO3 (LSMO) epitaxial thin films grown on SrTiO3 (001) substrates with different miscut angles. The substrate miscut angle plays a critical role in controlling the in-plane magnetic anisotropy. The microscopic origin of such magnetic anisotropy is attributed to the formation of anisotropic stripe domains along the surface step terraces. The magnetization in the LSMO films was found to be selectively modulated by the antiferrodistortive phase transition of the SrTiO3 substrate. This phenomenon has been qualitatively explained by a strain modified Stoner–Wohlfarth model. We conclude that the magnetization modulation by the SrTiO3 phase transition depends on h, the ratio of applied magnetic field to the saturation field. Such modulation is only visible with h < 1. The established domain microstructure–anisotropy–magnetism correlation in manganite films can be applied to a variety of complex oxide thin films on vicinal substrates.

To investigate the role of interlayers on the growth, microstructure, and physical properties of 3D nanocomposite frameworks, a set of novel 3D vertically aligned nanocomposite (VAN) frameworks are assembled by a relatively thin interlayer (M) sandwiched by two consecutively grown La_0.7Sr_0.3MnO₃ (LSMO)‐ZnO VANs layers. ZnO nanopillars from the two VAN layers and the interlayer (M) create a heterogeneous 3D frame embedded in the LSMO matrix. The interlayer (M) includes yttria‐stabilized zirconia (YSZ), CeO₂, SrTiO₃, BaTiO₃, and MgO with in‐plane matching distances increasing from ≈3.63 to ≈4.21 Å, and expected in‐plane strains ranging from tensile (≈8.81% on YSZ interlayer) to compressive (≈–6.23% on MgO interlayer). The metal‐insulator transition temperature increases from ≈133 K (M = YSZ) to ≈252 K (M = MgO), and the low‐field magnetoresistance peak value is tuned from ≈36.7% to ≈20.8%. The 3D heterogeneous frames empower excellent tunable magnetotransport properties and promising potentials for microstructure‐enabled applications.

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.

Light coupling with patterned subwavelength hole arrays induces enhanced transmission supported by the strong surface plasmon mode. In this work, a nanostructured plasmonic framework with vertically built‐in nanohole arrays at deep‐subwavelength scale (6 nm) is demonstrated using a two‐step fabrication method. The nanohole arrays are formed first by the growth of a high‐quality two‐phase (i.e., Au–TiN) vertically aligned nanocomposite template, followed by selective wet‐etching of the metal (Au). Such a plasmonic nanohole film owns high epitaxial quality with large surface coverage and the structure can be tailored as either fully etched or half‐way etched nanoholes via careful control of the etching process. The chemically inert and plasmonic TiN plays a role in maintaining sharp hole boundary and preventing lattice distortion. Optical properties such as enhanced transmittance and anisotropic dielectric function in the visible regime are demonstrated. Numerical simulation suggests an extended surface plasmon mode and strong field enhancement at the hole edges. Two demonstrations, including the enhanced and modulated photoluminescence by surface coupling with 2D perovskite nanoplates and the refractive index sensing by infiltrating immersion liquids, suggest the great potential of such plasmonic nanohole array for reusable surface plasmon‐enhanced sensing applications.

Binder-free thin film cathodes have become a critical basis for advanced high-performance lithium ion batteries for lightweight device applications such as all-solid-state batteries, portable electronics, and flexible electronics. However, these thin film electrodes generally require modifications to improve the electrochemical performance. This overview summarizes the current modification approaches on thin film cathodes, where the approaches can be classified as single-phase nanostructure designs and multiphase nanocomposite designs. Recent representative advancements of different modification approaches are also highlighted. Besides, this review discusses the existing challenges regarding the thin film cathodes. The review also discusses the future research directions and needs towards future advancement in thin film cathode designs for energy storage needs in advanced portable and personal electronics.

Combined strain + doping method is used in a VAN system to realise exemplary properties which cannot be realised in plain films.

Pt : VO₂nanocomposite design to achieve bidirectional tuning of phase transformationviasize dependent work function of nanoparticles.

Sm-doped BiFeO₃ (Bi₀.₈₅Sm_0.15FeO₃) thin films were fabricated on (001) SrTiO₃ substrates by PLD over a range of deposition temperatures. The Sm dopants are clearly detected by high-resolution scanning transmission electron microscopy.

Inducing new phases in thick films via vertical lattice strain is one of the critical advantages of vertically aligned nanocomposites (VANs).

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 self-assembled vertically aligned nanocomposite (VAN) thin films of La₂CuO_4+δ + LaCuO₃, we find from DC magnetic susceptibility measurements, weak signatures of superconductivity at ∼120 K.

Negative pressure enhances the ferroelectric Curie temperature and piezoelectric coefficient in lead-free monoclinic BaTiO₃ films for high-temperature ferroelectric applications.

Bi₃MoM_TO₉ (M_T, transition metals of Mn, Fe, Co and Ni) thin films with pillar-in-matrix form have been deposited. Room temperature multiferroism as well as anisotropic ferromagnetic and optical properties have been demonstrated.

Self-assembled nitride–metal nanocomposites offering flexible geometrical control and tunable functionalities towards metamaterial design and nanophotonic devices.

Thermal stability of an ordered three-phase Au–BaTiO₃–ZnO vertically aligned nanostructure by both ex situ annealing under air and vacuum conditions, and in situ heating in TEM in vacuum has been demonstrated.

Morphology tuning of Bi-based layered structures by varying the Al : Mn molar ratio leads to tunable magnetic and optical properties.

An SbO_x–GNP hybrid anode is synthesised with the aid of ultrafast dry microwave superheating in 30 seconds.

A new vertically aligned nanocomposite BaTiO₃(BTO):La_0.7Sr_0.3MnO₃(LSMO) was synthesized using a one-step pulsed laser deposition technique and anisotropic magnetic and optical properties were achieved due to the ultra thin LSMO pillars embedded in BTO matrix microstructure.

The ultrafast measurements of polarization switching dynamics on ferroelectric (FE) and antiferroelectric (AFE) hafnium zirconium oxide (HZO) are studied. The transient current during the polarization switching process is probed directly on the nanosecond scale. The switching time is determined to be as fast as 10 ns to reach fully switched polarization with characteristic switching times of 5.4 ns for FE HZO and 4.5 ns for AFE HZO by the nucleation limited switching model. The limitation by the parasitic effect on capacitor charging is found to be critical in the correct and accurate measurements of intrinsic polarization switching speed of HZO.

Vertically aligned nanocomposite (VAN) (La0.7Ca0.3MnO3)1−x:(CeO2)x thin films have been deposited on SrTiO3 (001) substrates by pulsed laser deposition. Enhanced low-field magnetoresistance properties and tunable metal-insulator transition temperature (TMI) have been demonstrated via modulating the composition of (La0.7Ca0.3MnO3)1−x:(CeO2)x (x = 0, 0.05, 0.1, and 0.2). By increasing the atomic percentage of the CeO2 phase to 20%, a maximum magnetoresistance value of 51.8% can be achieved and the TMI value can be tuned from 113 K to 210 K. The enhanced magnetoresistance properties are attributed to the disordered grain boundary and tunneling structure generated by the insulating CeO2 phase. The change in the TMI value is attributed to the strain state in the La0.7Ca0.3MnO3 phase. Furthermore, high ferromagnetic anisotropy and enhanced magnetization have been demonstrated in the VAN system. This work demonstrates the power of multifunctionalities and property tuning in VAN thin films.

Complex multiphase nanocomposite designs present enormous opportunities for developing next‐generation integrated photonic and electronic devices. Here, a unique three‐phase nanostructure combining a ferroelectric BaTiO₃, a wide‐bandgap semiconductor of ZnO, and a plasmonic metal of Au toward multifunctionalities is demonstrated. By a novel two‐step templated growth, a highly ordered Au–BaTiO₃–ZnO nanocomposite in a unique “nanoman”‐like form, i.e., self‐assembled ZnO nanopillars and Au nanopillars in a BaTiO₃ matrix, is realized, and is very different from the random three‐phase ones with randomly arranged Au nanoparticles and ZnO nanopillars in the BaTiO₃ matrix. The ordered three‐phase “nanoman”‐like structure provides unique functionalities such as obvious hyperbolic dispersion in the visible and near‐infrared regime enabled by the highly anisotropic nanostructures compared to other random structures. Such a self‐assembled and ordered three‐phase nanocomposite is obtained through a combination of vapor–liquid–solid (VLS) and two‐phase epitaxy growth mechanisms. The study opens up new possibilities in the design, growth, and application of multiphase structures and provides a new approach to engineer the ordering of complex nanocomposite systems with unprecedented control over electron–light–matter interactions at the nanoscale.

Aluminum nitride (AlN)-based two-phase nanocomposite thin films with plasmonic Au and Ag nanoinclusions have been demonstrated using a one-step thin film growth method. Such AlN-based nanocomposites, while maintaining their wide bandgap semiconductor behavior, present tunable optical properties such as bandgap, plasmonic resonance, and complex dielectric function. Depending on the growth atmosphere, the metallic nanoinclusions self-organized into different geometries, such as nano-dendrites, nano-disks, and nanoparticles, providing enhanced optical anisotropy in-plane and out-of-plane. The infrared transmission measurements demonstrate the signature peaks of AlN as well as a broad transmission window attributed to the plasmonic nanoinclusions. This unique AlN-metal hybrid thin film platform provides a route to modulate the optical response of wide bandgap III-V nitride semiconductors towards infrared sensing or all optical based integrated circuits.

Field‐assisted processing techniques can enhance the kinetics of powder synthesis, accelerate sintering processes, and drive phase transformations at significantly lower temperatures compared to conventional methods. However, the exact nature of this nonthermal interaction between field and matter remains vastly speculative. A 2‐day workshop on “Electromagnetic Effects in Materials Synthesis” was organized at Carnegie Mellon University (Pittsburgh, USA) in June 2017, jointly sponsored by the U.S. National Science Foundation and the U.S. Office of Naval Research. This workshop gathered the scientific community working on field‐assisted techniques of materials processing. Inspired by the discussions held at the workshop, this paper summarizes the advancements to date and opens scientific questions and research opportunities in the three major field‐assisted sintering techniques (laser, microwave, and flash sintering). Significant challenges remain in (a) experimental design, measurements, and computational simulations to distinguish the nonthermal effects of the externally applied fields from conventional thermal phenomena; and (b) identifying fundamental mechanisms behind low temperature, nonthermal effects that produce phase transitions and microstructural evolution in materials under externally applied fields. We also present the recent developments in multiscale characterization techniques and the theory and modeling efforts, which aim to tackle the aforementioned grand multidisciplinary challenges facing researchers.

Mo enriched thick GBs in nanocrystalline Ni alloy are stronger barriers than conventional GBs to the transmission of dislocations.

Ferromagnetic nanostructures with tunable, strong anisotropic properties are highly desired for their potential integration into spintronic devices.

Flash sintering has attracted significant attention as its remarkably rapid densification process at low sintering furnace temperature leads to the retention of fine grains and enhanced dielectric properties. However, high-temperature mechanical behaviors of flash-sintered ceramics remain poorly understood. Here, we present high-temperature (up to 600 °C) in situ compression studies on flash-sintered yttria-stabilized zirconia (YSZ). Below 400 °C, the YSZ exhibits high ultimate compressive strength exceeding 3.5 GPa and high inelastic strain (~8%) due primarily to phase transformation toughening. At higher temperatures, crack nucleation and propagation are significantly retarded, and prominent plasticity arises mainly from dislocation activity. The high dislocation density induced in flash-sintered ceramics may have general implications for improving the plasticity of sintered ceramic materials.

Self-assembled vertically aligned metal–oxide (Ni–CeO₂) nanocomposite thin films with novel multifunctionalities have been successfully deposited by a one-step growth method.

Strain-induced suppression of the miscibility gap in solid solutions of Mg₂Si and Mg₂Sn was studied to reduce lattice thermal conductivity.

A novel three-dimensional (3D) framework with integrated lateral and vertical interfaces, enables the power of 3D strain tuning and improves its electrical transport properties.

Twin boundaries have been proven effective for strengthening metallic materials while maintaining plasticity.

We report on nanoengineered SrTiO₃–Sm₂O₃ nanocomposite thin films with the highest reported values of commutation quality factor (CQF or K-factor) of >2800 in SrTiO₃ at room temperature.

Aluminium typically deforms via full dislocations due to its high stacking fault energy. Twinning in aluminium, although difficult, may occur at low temperature and high strain rate. However, the 9R phase rarely occurs in aluminium simply because of its giant stacking fault energy. Here, by using a laser-induced projectile impact testing technique, we discover a deformation-induced 9R phase with tens of nm in width in ultrafine-grained aluminium with an average grain size of 140 nm, as confirmed by extensive post-impact microscopy analyses. The stability of the 9R phase is related to the existence of sessile Frank loops. Molecular dynamics simulations reveal the formation mechanisms of the 9R phase in aluminium. This study sheds lights on a deformation mechanism in metals with high stacking fault energies.

Chip-scale chemical detection is demonstrated by using mid-Infrared (mid-IR) photonic circuits consisting of amorphous silicon (a-Si) waveguides on an epitaxial barium titanate (BaTiO₃, BTO) thin film. The highly c-axis oriented BTO film was grown by the pulsed laser deposition (PLD) method and it exhibits a broad transparent window from λ = 2.5 μm up to 7 μm. The waveguide structure was fabricated by the complementary metal–oxide–semiconductor (CMOS) process and a sharp fundamental waveguide mode has been observed. By scanning the spectrum within the characteristic absorption regime, our mid-IR waveguide successfully perform label-free monitoring of various organic solvents. The real-time heptane detection is accomplished by measuring the intensity attenuation at λ = 3.0–3.2 μm, which is associated with -CH absorption. While for methanol detection, we track the -OH absorption at λ = 2.8–2.9 μm. Our monolithic Si-on-BTO waveguides establish a new sensor platform that enables integrated photonic device for label-free chemical detection.

Resistive switches are non-volatile memory cells based on nano-ionic redox processes that offer energy efficient device architectures and open pathways to neuromorphics and cognitive computing. However, channel formation typically requires an irreversible, not well controlled electroforming process, giving difficulty to independently control ionic and electronic properties. The device performance is also limited by the incomplete understanding of the underlying mechanisms. Here, we report a novel memristive model material system based on self-assembled Sm-doped CeO₂ and SrTiO₃ films that allow the separate tailoring of nanoscale ionic and electronic channels at high density (∼10¹² inch⁻²). We systematically show that these devices allow precise engineering of the resistance states, thus enabling large on–off ratios and high reproducibility. The tunable structure presents an ideal platform to explore ionic and electronic mechanisms and we expect a wide potential impact also on other nascent technologies, ranging from ionic gating to micro-solid oxide fuel cells and neuromorphics.

Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO₂ embedded in supporting matrices of SrTiO₃. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO₂ films. By using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO₂ nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness.

Defect sinks, such as grain boundaries and phase boundaries, have been widely accepted to improve the irradiation resistance of metallic materials. However, free surface, an ideal defect sink, has received little attention in bulk materials as surface-to-volume ratio is typically low. Here by using in situ Kr ion irradiation technique in a transmission electron microscope, we show that nanoporous (NP) Ag has enhanced radiation tolerance. Besides direct evidence of free surface induced frequent removal of various types of defect clusters, we determined, for the first time, the global and instantaneous diffusivity of defect clusters in both coarse-grained (CG) and NP Ag. Opposite to conventional wisdom, both types of diffusivities are lower in NP Ag. Such a surprise is largely related to the reduced interaction energy between isolated defect clusters in NP Ag. Determination of kinetics of defect clusters is essential to understand and model their migration and clustering in irradiated materials.

Vertically aligned nanocomposites (VAN) combined ferrimagnetic CoFe2O4 with non-magnetic CeO2 ((CoFe2O4)x:(CeO2)1−x) in different phase ratios (x = 10%, 30% to 50%) have been grown by a pulsed laser deposition technique. Various unique magnetic domain structures form based on the VAN compositions and growth conditions. Anisotropic and tunable ferrimagnetic properties have been demonstrated. These ordered ferrimagnetic nanostructures have been incorporated into YBa2Cu3O7−δ thin films as both cap and buffer layers to enhance the flux pinning properties of the superconducting thin films. The results suggest that the ordered magnetic VAN provides effective pinning centers by both defect and magnetic nanoinclusions.

Nanotwinned metals have rare combinations of mechanical strength and ductility. Previous studies have shown that detwinning occurs in plastically deformed nanotwinned metals. Although molecular dynamics simulations have predicted that fine nanotwins can migrate at low stress, there is little in situ evidence to validate such predictions. Also it is unclear if detwinning occurs prior to or succeeding plastic yielding. Here, by using in situ nanoindentation in a transmission electron microscope, we show that a non-elastic detwinning process in nanotwinned Cu occurred at ultra-low indentation stress (0.1 GPa), well before the stress necessary for plastic yielding. Furthermore, the in situ nanoindentation technique allows us to differentiate dislocation-nucleation dominated microscopic yielding preceding macroscopic yielding manifested by dislocation-transmission through twin boundaries. This study thus provides further insights for understanding plasticity in nanotwinned metals at microscopic levels.

Self‐assembled nanocomposite films and coatings have huge potential for many functional and structural applications. However, control and manipulation of the nanostructures is still at very early stage. Here, guidelines are established for manipulating the types of composite structures that can be achieved. In order to do this, a well studied (YBa₂Cu₃O_7‐δ)_1‐x:(BaZrO₃)_x ‘model’ system is used. A switch from BaZrO₃ nanorods in YBa₂Cu₃O_7‐δ matrix to planar, horizontal layered plates is found with increasing x, with a transitional cross‐ply structure forming between these states at x = 0.4. The switch is related to a release in strain energy which builds up in the YBa₂Cu₃O_7‐δ with increasing x. At x = 0.5, an unusually low strain state is observed in the planar composite structure, which is postulated to arise from a pseudo‐spinodal mechanism.

The photocarrier relaxation dynamics of EuTiO3 films have been investigated using femtosecond transient absorption spectroscopy. Two kinds of EuTiO3 films, with and without strain, have been included. In both films, the decay dynamics of 2p-3dt2g transition has a fast (∼2 ps) and slow (ns) components which are independent of the strain. Remarkably, the transient photobleaching of 4f-3dt2g transition is found to be enhanced considerably in the strained film, accompanied with a subnanosecond carrier lifetime. This behavior can be linked to the strain induced band structure modulation. Our results reveal the dynamical interactions in EuTiO3, identifying the critical roles of strain in photo induced phenomena.

Self-assembled BiFeO3:CoFe2O4 (BFO:CFO) vertically aligned nanocomposite thin films have been fabricated on SrTiO3 (001) substrates using pulsed laser deposition. The strain relaxation mechanism between BFO and CFO with a large lattice mismatch has been studied by X-ray diffraction and transmission electron microscopy. The as-prepared nanocomposite films exhibit enhanced perpendicular magnetic anisotropy as the BFO composition increases. Different anisotropy sources have been investigated, suggesting that spin-flop coupling between antiferromagnetic BFO and ferrimagnetic CFO plays a dominant role in enhancing the uniaxial magnetic anisotropy.

In pulsed laser deposited YBa2Cu3O7−x thin films containing 5 mol. % Ba2YNbO6 pinning additions, we show that a growth rate of 1 nm/s (10 Hz laser repetition rate with an instant rate ∼0.1 nm/pulse) gives remarkably strong c-axis correlated pinning which is associated with the presence of Ba2YNbO6 nanocolumns. This is different to the behaviour of other well-studied pinning additions where only random nanoparticles of the pinning phase are present at high growth rates and is an important finding for industrial fabrication of coated conductors where fast growth is required.

We report on compositional tuning to create excellent field-performance of Jc in “self-doped,” GdBa2Cu3O7−y (GdBCO) coated conductors grown by ultrafast reactive co-evaporation. In order to give excess liquid and Gd2O3, the overall compositions were all Ba-poor and Cu-rich compared to GdBCO. The precise composition was found to be critical to the current carrying performance. The most copper-rich composition had an optimum self-field Jc of 3.2 MA cm−2. A more Gd-rich composition had the best in-field performance because of the formation of low coherence, splayed Gd2O3 nanoparticles, giving Jc (77 K, 1 T) of over 1 MA cm−2 and Jc (77 K, 5 T) of over 0.1 MA cm−2.

Textured metastable VO2 (B) thin films with a layered structure were grown on SrTiO3 (001) by pulsed laser deposition. The X-ray diffraction and transmission electron microscopy results indicate that VO2 (B) films exhibit c-axis out-of-plane, while the films have 4 possible in-plane matching relations. In addition, a small amount of VO2 (M) phase can co-grow in the VO2 (B) phase when the film thickness exceeds a threshold. The thick VO2 films on STO exhibit a sharp metal-insulator transition with an increase of electrical conductivity in two orders of magnitude. This study may provide an alternative approach to enhance the performance of insulating VO2 (B) based batteries with increased electrical conductivity by incorporating VO2 (M) phase in the VO2 (B) phase layered network.

Unimorph cantilevers are made from 0.5BaTiO₃‐0.5Sm₂O₃ (BTO‐SmO) self‐assembled vertical heteroepitaxial nanocomposite thin films, grown by PLD on (001) SrTiO₃ single crystal substrates. The films remain piezoelectric up to at least 250 °C without losing any actuation. The longitudinal piezoelectric coefficient, d₃₃, is ≈45 to 50 pm V⁻¹ measured from room temperature to 250 °C. The transverse piezoelectric coefficient, d₃₁, a key parameter of actuator performance, exceeds PZT (Pb_1–xZr_xTiO₃) films at >200 pm V⁻¹. Since the d₃₁ coefficient was found to be positive, this opens up exciting new applications opportunities. The possible reasons for d₃₁ > 0 are discussed in the light of 3D strain control in the nanocomposites.

Nanotwinned metals received significant interest lately as twin boundaries may enable simultaneous enhancement of strength, ductility, thermal stability, and radiation tolerance. However, nanotwins have been the privilege of metals with low-to-intermediate stacking fault energy (SFE). Recent scattered studies show that nanotwins could be introduced into high SFE metals, such as Al. In this paper, we examine several sputter-deposited, {111} textured Ag/Al, Cu/Ni, and Cu/Fe multilayers, wherein growth twins were observed in Al, Ni, and face-centered cubic (fcc) Fe. The comparisons lead to two important design criteria that dictate the introduction of growth twins in high SFE metals. The validity of these criteria was then examined in Ag/Ni multilayers. Furthermore, another twin formation mechanism in high SFE metals was discovered in Ag/Ni system.

Heterostructures and interfacial defects in a 40-nm-thick SrTiO₃ (STO) film grown epitaxially on a single-crystal MgO (001) were investigated using aberration-corrected scanning transmission electron microscopy and geometric phase analysis. The interface of STO/MgO was found to be of the typical domain-matching epitaxy with a misfit dislocation network having a Burgers vector of ½ a_STO ⟨100⟩. Our studies also revealed that the misfit dislocation cores at the heterogeneous interface display various local cation arrangements in terms of the combination of the extra-half inserting plane and the initial film plane. The type of the inserting plane, either the SrO or the TiO₂ plane, alters with actual interfacial conditions. Contrary to previous theoretical calculations, the starting film planes were found to be dominated by the SrO layer, i.e., a SrO/MgO interface. In certain regions, the starting film planes change to the TiO₂/MgO interface because of atomic steps at the MgO substrate surface. In particular, four basic misfit dislocation core configurations of the STO/MgO system have been identified and discussed in relation to the substrate surface terraces and possible interdiffusion. The interface structure of the system in reverse—MgO/STO—is also studied and presented for comparison.

Ultrafast, spatial atmospheric atomic layer deposition, which does not involve vacuum steps and is compatible with roll‐to‐roll processing, is used to grow high quality TiO₂ blocking layers for organic solar cells. Dense, uniform thin TiO₂ films are grown at temperatures as low as 100 °C in only 37 s (~20 nm/min growth rate). Incorporation of these films in P3HT‐PCBM‐based solar cells shows performances comparable with cells made using TiO₂ films deposited with much longer processing times and/or higher temperatures. Copyright © 2013 John Wiley & Sons, Ltd.

Superconducting FeSe_0.5Te_0.5thin films are deposited on amorphous substrates, i.e., glass substrates by a pulsed laser deposition (PLD) technique. Microstructural characterizations show that the films are highly textured along (00l) with good crystallinity. The superconducting critical transition temperature (T_c) ranges from ∼8 to ∼10 K. The self-field critical current density (J_c^sf) at 4 K is ∼1.2×10⁴A/cm². The in-field critical current density (J_c^infield) decreases slowly under high magnetic field confirmed by both transport and magnetization measurements. The growth of high quality superconducting FeSe_0.5Te_0.5thin films on amorphous substrates demonstrates a low cost architecture for future Fe-based superconductor coated conductors.

NiCoMnAl thin films were deposited onto unheated substrates using dc magnetron co-sputtering. The microstructure of as-deposited films consisted of nanocrystals in an amorphous matrix and did not exhibit a martensitic phase transformation. After heat treatment, films crystallized into a B2 austenite phase, which exhibited a magnetic field induced martensitic phase transformation. The level of the change in the martensitic transformation temperatures in the magnetic field was determined to be ∼2.1 K/T. The films exhibited non-reversible magnetic field induced martensite to austenite transformation due to the large thermal hysteresis.

A unique quasi-one-dimensionally channeled nanomaze structure has been self-assembled in the (La0.7Sr0.3MnO3)1−x:(ZnO)x vertically aligned nanocomposites (VANs). Significantly enhanced magnetotransport properties have been achieved by tuning the ZnO composition x. The heteroepitaxial VAN thin films, free of large angle grain boundaries, exhibit a maximum low-field magnetoresistance (LFMR) of 75% (20 K and 1 T). The enhanced LFMR close to the percolation threshold is attributed to the spin-polarized tunneling through the ferromagnetic/insulating/ferromagnetic vertical sandwiches in the nanomazes. This study suggests that the phase boundary in the nanomaze structure is an alternative approach to produce decoupled ferromagnetic domains and thus to achieve enhanced magnetoresistance.

The microstructure evolution of heteroepitaxial BaTiO3 (BTO) thin films grown on single crystal (001) SrTiO3 (STO) under Ne irradiation at room temperature was systematically investigated with special attention given to the behavior at the BTO/STO interface. Cross sectional transmission electron microscope investigations reveal that amorphization occurs at the top BTO film region. BTO grains in the dimensions of 10–20 nm survived the irradiation damage and maintained their original crystal orientation. Other irradiation-induced defects such as dislocation loops and defect clusters were observed only at the portion of the BTO thin film near the interface, but not at the STO side of the bilayer. Atomic calculations find that the energetics of defects are very similar on each side of the BTO/STO interface, suggesting that the interface will not significantly modify radiation damage evolution in this system, in agreement with the experimental observations. These results support the hypothesis we presented in previous work about the role of coherent interfaces on radiation damage evolution.

Here, we report detailed strain mapping analysis at heterointerfaces of a new multiferroic complex oxide Bi3Fe2Mn2Ox(BFMO322) supercell and related layered structures. The state-of-the-art aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and the modified geometric phase analysis (GPA) have been used to characterize the self-assembled transitional layers, misfit defects, and, in particular, the biaxial lattice strain distributions. We found that not only a sufficient lattice misfit is required through substrate selection and to be preserved in initial coherent epilayer growth, but also an appropriate interfacial reconstruction is crucial for triggering the growth of the new BFMO322 supercell structure. The observation of new transitional interfacial phases behaving like coherent film layers within the critical thickness challenges the conventional understanding in existing epitaxial growth model.

We report the synthesis and systematic Raman study of twisted bilayer graphene (tBLG) with rotation angles from below 10° to nearly 30°. Chemical vapor deposition was used to grow hexagon-shaped tBLG with a rotation angle that can be conveniently determined by relative edge misalignment. Rotation dependent G-line resonances and folded phonons were observed by selecting suitable energies of excitation lasers. The observed phonon frequencies of the tBLG superlattices agree well with our ab initio calculation.

Outstanding phase transition properties of vanadium dioxide (VO2) thin films on amorphous glass were achieved and compared with the ones grown on c-cut sapphire and Si (111) substrates, all by pulsed laser deposition. The films on glass substrate exhibit a sharp semiconductor-to-metal transition (∼4.3 °C) at a near bulk transition temperature of ∼68.4 °C with an electrical resistance change as high as 3.2 × 103 times. The excellent phase transition properties of the films on glass substrate are correlated with the large grain size and low defects density achieved. The phase transition properties of VO2 films on c-cut sapphire and Si (111) substrates were found to be limited by the high defect density.

The oxygen pressure effect on the structural and ferroelectric properties have been studied in epitaxial BaTiO3 (BTO)/SrRuO3/SrTiO3 (001) heterostructures grown by pulsed laser deposition. It is found that oxygen pressure is a sensitive parameter, which can influence the characteristics of oxide films in many aspects. The out-of-plane lattice parameter, tetragonality, (c/a) and Ti/Ba ratio monotonously decrease as the oxygen pressure increases from 5 mTorr to 200 mTorr. Microstructural study shows that the growth of BaTiO3 varies from a dense large grained structure with a smooth surface to a small columnar grain structure with rough surface as the deposition pressure increases. Electrical measurements show that the 40 mTorr deposited BTO films present maximum remanent polarization (Pr) (14 μC/cm2) and saturation polarization (Ps) (27 μC/cm2) due to the stoichiometric cation ratio, very smooth surface, and low leakage current. These results demonstrate that the controlling of cation stoichiometry, surface morphology, and leakage current by oxygen pressure is one of very important prerequisites for device applications in the BaTiO3 films.

Self-assembled, nanocomposite heteroepitaxial films of BiFeO3 + Fe3O4 (x BiFeO3 + (1 − x) Fe3O4), where x = 0.5 or 0.9, were grown on (011) SrTiO3. Depending on the value of x and on the film thickness, either exchange bias or exchange enhancement of coercivity was demonstrated. In epitaxially and highly strained (7%) films of 250 nm thickness, and for x = 0.9, exchange bias (HEB) values of 40 Oe and HEB/HC ratios of 0.5 were achieved. Most crucially, these effects were measured at room temperature, showing the high potential of chemically compatible BiFeO3 + Fe3O4 for achieving room temperature magnetoelectricity.

High density nanotwins with average twin thickness varying from 3 to 6 nm are formed in sputtered highly (111) textured Cu/Ni multilayers, when individual layer thickness is 25 nm or less. Twin interfaces are normal to growth direction. Both maximum twin thickness and volume fraction of twins vary with the individual layer thickness. Coherency stress plays an important role in tailoring the formation of nanotwins. Nanotwins compete with misfit dislocations in accommodating elastic strain energy in epitaxial Cu/Ni multilayers.

To investigate leakage current density versus electric field characteristics, epitaxial EuTiO3 thin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition and were post-annealed in a reducing atmosphere. This investigation found that conduction mechanisms are strongly related to temperature and voltage polarity. It was determined that from 50 to 150 K, the dominant conduction mechanism was a space-charge-limited current under both negative and positive biases. From 200 to 300 K, the conduction mechanism shows Schottky emission and Fowler-Nordheim tunneling behaviors for the negative and positive biases, respectively. This work demonstrates that Eu3+ is one source of leakage current in EuTiO3 thin films.

We review He ion induced radiation damage in several metallic multilayer systems, including Cu/V, Cu/Mo, Fe/W, and Al/Nb up to a peak dose of several displacements per atom (dpa). Size dependent radiation damage is observed in all systems. Nanolayer composites can store a very high concentration of He. Layer interfaces promote the recombination of opposite type of point defects and hence reduce the accumulative defect density, swelling, and lattice distortion. Interfaces also alleviate radiation hardening substantially. The chemical stability of interfaces is an important issue when considering the design of radiation tolerant nanolayer composites. Immiscible and certain miscible systems possess superior stability against He ion irradiation. Challenge and future directions are briefly discussed.

Phase pure, dense Cu2O thin films were grown on glass and polymer substrates at 225°C by rapid atmospheric atomic layer deposition (AALD). Carrier mobilities of 5 cm2V−1s−1 and carrier concentrations of ∼1016 cm−3 were achieved in films of thickness 50 - 120 nm, over a &gt;10 cm2 area. Growth rates were ∼1 nm·min−1 which is two orders of magnitude faster than conventional ALD.. The high mobilities achieved using the atmospheric, low temperature method represent a significant advance for flextronics and flexible solar cells which require growth on plastic substrates.

Epitaxial Ag/Al multilayer films have high hardness (up to 5.5 GPa) in comparison to monolithic Ag and Al films (2 and 1 GPa). High-density nanotwins and stacking faults appear in both Ag and Al layers, and stacking fault density in Al increases sharply with decreasing individual layer thickness, h. Hardness increases monotonically with decreasing h, with no softening. In comparison, epitaxial Cu/Ni multilayers reach similar peak hardness when h ≈ 5 nm, but soften at smaller h. High strength in Ag/Al films is primarily a result of layer interfaces, nanotwins, and stacking faults, which are strong barriers to dislocation transmission.

ZnO thin films were grown on sapphire (0001) substrates by pulsed-laser deposition at 700 °C. 70 keV N+ ion implantation was performed under various temperatures and fluences in the range of 300−460 °C and 3.0×1014−1.2×1015 cm−2, respectively. Hall measurements indicate that the ZnO films implanted at 460 °C are p-type for all fluences used herein. Hole-carrier concentrations lie in the range of 2.4×1016−5.2×1017 cm−3, hole mobilities in the range of 0.7−3.7 cm2 V−1 s−1, and resistivities between 18−71 Ωcm. Transmission-electron microscopy reveals major microstructural differences between the n-type and p-type films. Ion implantation at elevated temperatures is shown to be an effective method to introduce increased concentrations of p-type N dopants while reducing the amount of stable post-implantation disorder.

The structure, metal-insulator transition (MIT), and related Terahertz (THz) transmission characteristics of VO2 thin films obtained by sputtering deposition on c-, r-, and m-plane sapphire substrates were investigated by different techniques. On c-sapphire, monoclinic VO2 films were characterized to be epitaxial films with triple domain structure caused by β-angle mismatch. Monoclinic VO2 β angle of 122.2° and the two angles of V4+–V4+ chain deviating from the am axis of 4.4° and 4.3° are determined. On r-sapphire, tetragonal VO2 was determined to be epitaxially deposited with VO2 (011)T perpendicular to the growth direction, while the structural phase transformation into lower symmetric monoclinic phase results in (2¯11) and (200) orientations forming a twinned structure. VO2 on m-sapphire has several growth orientations, related with the uneven substrate surface and possible inter-diffusion between film and substrate. Measurements of the electrical properties show that the sample on r-sapphire has MIT property superior to the other two samples, with a resistivity change as large as 9 × 104 times and a transition window as narrow as 3.9 K, and it has the highest resistivity with the lowest free carrier density in the insulating phase. THz transmission measurements on VO2 films grown on r-plane sapphire substrates revealed intensity modulation depth as large as 98% over a broadband THz region, suggesting that VO2 films are ideal material candidates for THz modulation applications.

Epitaxial La0.67Ca0.33MnO3:SrTiO3 (LCMO:STO) composite thin films have been grown on single crystal LaAlO3(001) substrates by a cost effective polymer-assisted deposition method. Both x-ray diffraction and high-resolution transmission electron microscopy confirm the growth of epitaxial films with an epitaxial relationship between the films and the substrates as (002)film||(002)sub and [202]film||[202]sub. The transport property measurement shows that the STO phase significantly increases the resistivity and enhances the magnetoresistance (MR) effect of LCMO and moves the metal-insulator transition to lower temperatures. For example, the MR values measured at magnetic fields of 0 and 3 T are −44.6% at 255 K for LCMO, −94.2% at 125 K for LCMO:3% STO, and −99.4% at 100 K for LCMO:5% STO, respectively.

The diffusion behavior of elements constituting Hastelloy C-276 (C, Si, Mn, Co, W, Fe, Cr, Mo, and Ni) in alumina films was investigated using secondary ion mass spectroscopy. The films were deposited by ion-beam-assisted deposition and annealed in vacuum over a temperature range of 500–1000 °C. Characterization of film microstructure was performed using transmission electron microscopy and selected area diffraction analyses. The films were predominantly amorphous with alumina nanocrystallites nonuniformly dispersed throughout the volume both before and after annealing. A relatively wide interface region between the Hastelloy substrate and alumina film was formed in the as-deposited sample due to ion beam mixing. No diffusion of any of the substrate elements was observed after annealing, except for Mn, Cr, and Ni. The impurity depth distributions consisted of two components, which differed by several orders of magnitude with respect to diffusion coefficient and solubility. Activation energies and temperature dependencies of the diffusion coefficients were determined, and a diffusion mechanism was discussed.

TaN has become a very promising diffusion barrier material for Cu interconnections, due to the high thermal stability requirement and thickness limitation for next generation ULSI devices. TaN has a variety of phases and Cu diffusion characteristics vary with different phases and microstructures. We have investigated the diffusivity of copper in single-crystal (NaCl-structured) and polycrystalline TaN thin films grown by pulsed laser deposition. The polycrystalline TaN films were grown directly on Si(100), while the single crystal films were grown with TiN buffer layers. Both of poly and single-crystal films with Cu overlayers were annealed at 500 °C, 600 °C, 650 °C, and 700 °C in vacuum to study the copper diffusion characteristics. The diffusion of copper into TaN was studied using STEM-Z contrast, where the contrast is proportional to Z (atomic number), and TEM. The diffusion distances are found to be about 5nm at 650°C for 30 min annealing. The diffusivity of Cu into single crystal TaN follows the relation D = (160±9.5)exp[-(3.27 ±0.1)eV/k_BT]cm²s^-1 in the temperature range of 600°C to 700°C. We observe that Cu diffusion in polycrystalline TaN thin films is nonuniform with enhanced diffusivities along the grain boundary.

Previous work on YBa₂Cu₃O_7−x (YBCO) + BaSnO₃ (BSO) films with a single composition showed significant critical current density (J_c) improvements at higher fields but lowered J_c in low fields. A detailed study on BSO concentrations provided here demonstrates that significant J_c enhancement can occur even up to 20 mol% BSO inclusion, where typical particulate inclusions in these concentrations degrade the YBCO performance. YBCO + BSO films were processed on (100) LaAlO₃ substrates using premixed targets of YBa₂Cu₃O_7-x (YBCO) with additions of 2, 4, 10, and 20 mol% BSO. The critical transition temperature T_c of the films remained high (>87 K), even with large amounts (20 mol%) of BSO. YBCO + BSO films showed a gradual increase in J_c at high fields as the amount of BSO was increased. More than an order of magnitude increase in J_c was measured in YBCO + BSO samples as compared to regular YBCO at 4 T. YBCO + 10 mol% BSO films showed overall improvement at all the field ranges while YBCO + 20 mol% BSO was better only at high fields. Transmission electron microscopy revealed the presence of ∼7–8-nm-diameter BSO nanocolumns, the density of which increased with increasing BSO content correlating well with the observed improvements in J_c.

The deformation behaviors of YBa2Cu3O7−x (YBCO) thin films with twinning structures were studied via in situ nanoindentation experiments in a transmission electron microscope. The YBCO films were grown on SrTiO3 (001) substrates by pulsed laser deposition. Both ex situ (conventional) and in situ nanoindentation were conducted to reveal the deformation of the YBCO films from the directions perpendicular and parallel to the twin interfaces. The hardness measured perpendicular to the twin interfaces is ∼50% and 40% higher than that measured parallel to the twin interfaces ex situ and in situ, respectively. Detailed in situ movie analysis reveals that the twin structures play an important role in deformation and strengthening mechanisms in YBCO thin films.

ZnO and Ag-doped ZnO films were grown on sapphire (0001) substrates by pulsed-laser deposition in vacuum both with and without oxygen at 700 °C. N+ ions were implanted in these films at room temperature and at 300 °C to a dose of 1×1014 cm−2 at 50 keV. Hall measurements indicate that ZnO films deposited in vacuum without oxygen and implanted with N+ at elevated temperatures are p-type with a hole-carrier concentration of 6×1016 cm−3, a mobility of 2.1 cm2 V−1 s−1, and a resistivity of 50 Ω cm. Both scanning-electron microscopy and transmission-electron microscopy studies on the implanted films reveal microstructural differences in grain size, surface roughness, and the nature of defects, which may impact the activation of N atoms as p-type carriers. Low-energy ion implantation at elevated temperatures is shown to be an effective method to introduce p-type N dopants into ZnO, which minimizes defect clustering and promotes defect annihilation during implantation.

In this paper, we report low-field magnetoresistance observed in preferentially c-axis oriented La0.67Sr0.33MnO3:MgO composite films fabricated on (001) LaAlO3 substrates using a hybrid solution route. Addition of MgO in the composite film results in lowering of Curie temperature (∼300 K) from that of the pure film (∼360 K). The resistivity increases and temperature of highest resistivity of the composite films decrease with the addition of MgO. This behavior is attributed to a small substitution of Mg2+ in the manganite lattice and the presence of MgO near the manganite grain boundaries, thus building tunneling barriers and enhancing the spin polarized tunneling in the composite films. The values of low-field magnetoresistance increase with MgO addition and the composite film with highest amount of MgO exhibits maximum MR of −33% at 0.5 T (5000 Oe) and 10 K.

In this paper, we report the growth of ZnO films on silicon substrates using a pulsed laser deposition technique. These films were deposited on Si(111) directly as well as by using thin buffer layers of AlN and GaN. All the films were found to have c-axis-preferred orientation aligned with normal to the substrate. Films with AlN and GaN buffer layers were epitaxial with preferred in-plane orientation, while those directly grown on Si(111) were found to have random in-plane orientation. A decrease in the frequency of the Raman mode and a red shift of the band-edge photoluminescence peak due to the presence of tensile strain in the film, was observed. Various possible sources for the observed biaxial strain are discussed.

A free charge layer forms at the LaAlO3/SrTiO3 interface. We show the influence of the SrTiO3 (001) substrate miscut angle on its electronic and transport properties. Highly miscut substrates lead to a substantial mobility enhancement and a carrier density decrease at low temperature consistent with a two-carrier type model.

Thin films of Pr0.5Ca0.5MnO3 were fabricated on (001) oriented SrLaAlO4, NdGaO3, and SrTiO3 substrates using a hybrid solution route and spin coating techniques. Good crystalline and epitaxial quality of the films was confirmed with X-ray diffraction and transmission electron microscopy studies. Strain in the film grown on NdGaO3 substrate did not relax during annealing process and the film exhibited charge-ordered insulator phase at low temperatures even with magnetic fields up to 9 T. However, the films on SrLaAlO4 and SrTiO3 substrates (with partially relaxed compressive and tensile strain, respectively) displayed melting of the charge-ordered phase with applied magnetic fields of less than 5 T. The results suggest that strain-relaxation rather than only the type of strain plays an important role in lowering critical melting magnetic fields in these films.

Epitaxial (La0.7Sr0.3MnO3)0.7:(Mn3O4)0.3 (LSMO:Mn3O4) nanocomposite thin films were grown on SrTiO3 (001) substrate by a pulsed laser deposition technique. The nanocomposite structures vary from triangular domains, to vertically aligned columns, and finally to smaller spherical domains as the deposition frequency varies from 1, 5, to 10 Hz, respectively. The strain in LSMO is systematically tuned, but that of the Mn3O4 phase is relatively stable as the deposition frequency increases. The tunable strain is found directly related to the different domain and grain boundary (GB) structures. Physical properties including saturation magnetization, Curie temperature (TC), magnetoresistance and metal–insulator transition temperature (TMI), all show systematic trends as the deposition frequency varies. This study reveals that the domain/GBs tunability achieved in nanocomposite thin films can affect the lattice strain and further tune their ferromagnetic properties.

Nanostructured Cu/304 stainless steel (SS) multilayers were prepared by magnetron sputtering at room temperature. 304SS has a face-centered cubic (fcc) structure in bulk. However, in the Cu/304SS multilayers, the SS layers exhibited fcc structure for layer thickness of less than or equal to 5 nm. For 304SS layer thickness larger than 5nm, bcc 304SS grains were observed to grow on top of the initial ≈ 5 nm of fcc SS. The maximum hardness of Cu/304SS multilayers was ≈ 5.5 GPa (factor of two enhancement compared to rule of mixtures hardness) achieved at a layer thickness of 5nm, with a decrease in hardness with decreasing layer thickness below 5 nm. The hardness of fcc/fcc Cu/304SS multilayers (layer thickness ≤ 5 nm) is compared with Cu/Ni, another fcc/fcc system, to gain insight on how the mismatch in physical properties such as lattice parameters and shear moduli of the constituent layers affect the peak hardness achieved in these nanoscale systems.

We have synthesized novel diamondlike carbon coatings with silver nanoparticles embedded into the DLC film. The size of silver nanoparticles that are confined into layered structures has been varied from 5 nm to 50 nm using an ingenious pulsed laser deposition technique. The size of nanoparticles was found to be remarkably uniform within 15%. We have characterized these samples using high-resolution cross-section TEM and STEM-Z contrast techniques, electron energy loss spectroscopy (EELS), Raman, nanohardness, adhesion, and biocompatibility measurements. In the STEM-Z, where the contrast is proportional to atomic number², we have obtained the details of the atomic structure of silver particles. We have correlated the microstructure with hardness and adhesion properties. The EELS was used in conjunction with STEM-Z to obtain sp³/sp² bonding ratio. This ratio was compared with Raman result to provide an average bulk value. The role of silver nanoparticles is surmised to provide a reservoir of electrons for antimicrobial activity on the surface, as revealed by our biocompatibility tests.

We have successfully grown epitaxial cubic (B1-NaCl structure) tantalum nitride films on Si (100) and (111) substrate using a pulsed laser deposition technique. A thin layer of titanium nitride was used as a buffer medium. We characterized these films using X-ray diffraction, high resolution transmission electron microscopy and scanning transmission electron microscopy (Zcontrast). X-ray diffraction and high-resolution transmission electron microscopy confirmed the single crystalline nature of these films with cubic-on-cubic epitaxy. The epitaxial relations follow TaN(100)//TiN(100)//Si(100) on Si(100) and TaN(111)//TiN(111)//Si(111) on Si(111). We observed sharp interfaces of TaN/TiN and TiN/Si without any indication of interfacial reaction. Rutherford backscattering experiments showed these films to be slightly nitrogen deficient (TaN_0.95). High precision electrical resistivity measurements showed excellent metallic nature of these films. We also tried to deposit TaN directly on silicon, the films were found to be polycrystalline. In our method, TiN plays a key role in facilitating the epitaxial growth of TaN. This method exploits the concept of lattice matching epitaxy between TaN and TiN and domain matching epitaxy between TiN and Si. We studied the diffusion barrier properties of these films by growing a thin layer of copper on the top and subsequently annealing the films at 500°C and 600°C in vacuum. Cu diffusion layer was about 2nm after 600°C annealing for 30min. This work explores a promising way to grow high quality TaN diffusion barrier on silicon for copper interconnection.

We report highly resistive strongly ferromagnetic strained thin (∼30 nm) films of BiFe0.5Mn0.5O3 (BFMO) grown on (001) SrTiO3 substrates using pulsed laser deposition. The films are tetragonal with high epitaxial quality and phase-purity. The magnetic moment and coercivity values at room temperature are 90 emu/cc (0.58μB/B-site ion) at H=3 kOe and 274 Oe, respectively. The magnetic transition temperature is strongly enhanced up to ∼600 K, which is ∼500 K higher than for pure bulk BiMnO3. Strained BFMO is a potential room temperature spin filter material for magnetic tunnel devices.

We present the details of epitaxial growth interface structure of single wurtzite AlN thin films on (111) Si substrates by laser-molecular-beam-epitaxy. High quality AlN thin films with atomically sharp interfaces can be obtained by Laser-MBE at a substrate temperature of 650 ±10°C. X-ray diffraction and high resolution transmission electron microscopy was used to study the details of epitaxial growth of AlN on Si(111) substrate. The orientation-relationship of AlN on Si(111) was studied from Si <110> and <112> zone axis and determined to be AlN [2110]|Si[110] and AlN [0110]|Si[211]. The atomic structure of the interface was studied by high-resolution transmission electron microscopy and Fourier filtered image of cross-sectional AlN/Si(111) samples from both Si<110> and <112> zone axis. The results revealed the domain matching epitaxy of 4:5 ratio between the interplanar distances of Si(110) and AlN [2110]. We also present similarities and differences between the growth mechanism of AlN/Si(111) and GaN/Si(111) heterostructures.

Response to irradiation of nanocrystalline 3C–SiC is studied using 2 MeV Au²⁺ ions at elevated temperatures and is compared to the behavior of its monocrystalline counterpart under the identical irradiation conditions. The irradiated samples are characterized using in‐situ ion channeling, ex‐situ X‐ray diffraction, and helium ion microscopy. Compared to monocrystalline 3C–SiC, a faster amorphization process in the nanocrystalline material (average grain size = 3.3 nm) is observed at 500 K. However, the nanograin grows with increasing ion fluence at 550 K and the grain size tends to saturate at high fluences. The striking contrast demonstrates a sharp transition from irradiation‐induced interface‐driven amorphization at 500 K to crystallization at 550 K. The results could potentially have a positive impact on nuclear fuel cladding and structural components of next‐generation nuclear energy systems.

Tunable and enhanced low‐field magnetoresistance (LFMR) is observed in epitaxial (La_0.7Sr_0.3MnO₃)_0.5:(ZnO)_0.5 (LSMO:ZnO) self‐assembled vertically aligned nanocomposite (VAN) thin films, which have been grown on SrTiO₃ (001) substrates by pulsed laser deposition (PLD). The enhanced LFMR properties of the VAN films reach values as high as 17.5% at 40 K and 30% at 154 K. They can be attributed to the spin‐polarized tunneling across the artificial vertical grain boundaries (GBs) introduced by the secondary ZnO nanocolumns and the enhancement of spin fluctuation depression at the spin‐disordered phase boundary regions. More interestingly, the vertical residual strain and the LFMR peak position of the VAN films can be systematically tuned by changing the deposition frequency. The tunability of the physical properties is associated with the vertical phase boundaries that change as a function of the deposition frequency. The results suggest that the tunable artificial vertical GB and spin‐disordered phase boundary in the unique VAN system with vertical ferromagnetic‐insulating‐ferromagnetic (FM‐I‐FM) structure provides a viable route to manipulate the low‐field magnetotransport properties in VAN films with favorable epitaxial quality.

Irradiation-induced amorphization in nanocrystalline and single-crystal 3C-SiC has been studied using 1 MeV Si⁺ ions under identical irradiation conditions at room temperature and 400 K. The disordering behavior has been characterized using in situ ion channeling and ex situ x-ray diffraction methods. The results show that, compared with single-crystal 3C-SiC, full amorphization of small 3C-SiC grains (˜3.8 nm in size) at room temperature occurs at a slightly lower dose. Grain size decreases with increasing dose until a fully amorphized state is attained. The amorphization dose increases at 400 K relative to room temperature. However, at 400 K, the amorphization dose for 2.0 nm grains is about a factor of 4 and 8 smaller than for 3.0 nm grains and bulk single-crystal 3C-SiC, respectively. The behavior is attributed to the preferential amorphization at the interface.

10% Fe3O4–90% BiFeO3 nanocomposite thin films of 180 nm thickness were grown by pulsed laser deposition on SrTiO3 (011) single crystals. A 3–4 nm nanolamella structure of Fe3O4 and BiFeO3 was formed. While BiFeO3 has the expected epitaxial relationship with the substrate, Fe3O4 grew epitaxially and highly strained (7%). Compared to pure Fe3O4 films of similar thickness, the nanolamella structure of Fe3O4 gives rise to a greatly enhanced saturation magnetization of 900 emu/cc, and, after field cooling, an enhanced coercivity of 450 Oe. Piezoresponse force microscopy measurements show similar polar switching properties between the nanocomposite and pure BiFeO3 films.

A much simplified template, i.e., two nonsuperconducting layers between the superconducting YBa2Cu3O7−δ (YBCO) and the polycrystalline metal substrate, has been developed for high-performance coated conductors by using biaxially aligned TiN as a seed layer. A combination of a thin TiN (∼10 nm by ion-beam assisted deposition) layer and an epitaxial buffer LaMnO3 layer (∼120 nm) allows us to grow epitaxial YBCO films with values of full width at half-maximum around 3.5° and 1.7° for the ϕ-scan of (103) and rocking curve of (005) YBCO, respectively. The YBCO films grown on electropolished polycrystalline Hastelloy using this two-layer template exhibited a superconducting transition temperature of 89.5 K, a critical current density of 1.2 MA/cm2 at 75.5 K, and an α value (proportional factor of critical current density Jc∼H−α) of around 0.33, indicating a high density of pinning centers and an absence of weak links.

Epitaxial c-axis oriented BiFeO3 (BFO) films were fabricated on (001) oriented SrTiO3 substrates by pulsed laser deposition. Nuclear resonance backscattering spectrometry was used to directly measure the oxygen concentration of as-deposited and annealed BFO films. Compared to the ideal stoichiometry of BFO, the as-deposited BFO film shows more than 10% oxygen deficiency. However, postannealing the as-deposited BFO films reduces the oxygen deficiency almost half. The reduced oxygen vacancies in annealed BFO films are believed to be responsible for the different leakage mechanisms and the two orders of magnitude drop in leakage current density.

We investigate size dependent strengthening mechanisms in sputtered Fe/W multilayers with individual layer thickness, h, varying from 1 to 200 nm. Microstructure analyses reveal that Fe/W has incoherent bcc/bcc interface when h is greater than 5 nm. When h decreases to 1–2.5 nm, the interface becomes semicoherent, and Fe and W show significant lattice distortions comparing to their bulk counterpart due to interface constraint. The layer thickness dependent drastic variations in x-ray diffraction profiles are simulated well by using an analytical model. Film hardness increases with decreasing h, and approaches a maximum value of 12.5 GPa when h is 1 nm. The layer thickness dependent film hardnesses are compared with analytical models. Koehler’s image force plays a major role in determining the maximum strength of composites at smaller h.

We investigate the evolution of microstructure and mechanical properties of sputter-deposited Al∕Nb multilayers with miscible fcc/bcc type interface and individual layer thickness, h, of 1–200nm, subjected to helium ion irradiations: 100keV He+ ions and a fluence of 6×1016∕cm2. Helium bubbles, 1–2nm in diameter, are observed. When h is greater than 25nm, hardnesses of irradiated multilayers barely change, whereas radiation hardening is more significant at smaller h. Transmission electron microscopy and scanning transmission electron microscopy studies reveal the formation of a thin layer of Nb3Al intermetallic phase along the Al∕Nb interface as a consequence of radiation induced intermixing. The dependence of radiation hardening on h is interpreted by using a composite model considering the formation of the hard Nb3Al intermetallic layer.

Film studies: Epitaxial films of BaZrN₂ (see TEM image) and BaHfN₂ are grown by polymer‐assisted deposition on SrTiO₃ (STO) substrates. The films are phase‐pure, allowing the intrinsic physical properties of the ternary nitrides to be studied. From 5 to 300 K, the films exhibit metallic‐like resistivity–temperature behavior, with large residual resistivity ratios.magnified image

Nanocomposite (YBa2Cu3O7−x)0.5:(BaZrO3)0.5 thin films were fabricated on (001) oriented SrTiO3 substrates by pulsed laser deposition using a single uniformly mixed target. Both x-ray diffraction and transmission electron microscopy revealed remarkable, spontaneous formation of YBa2Cu3O7−x (YBCO) and BaZrO3 (BZO) multilayers. The high integrity and continuity of the multilayer made it possible to achieve a critical temperature of 88 K, given that the BaZrO3 fraction in the films is 50 mol %. The unique self-assembled microstructure led to a surprising field dependent critical current density along the ab plane.

Epitaxial nanotwinned Cu films, with an average twin spacing ranging from 7 to 16 nm, exhibit a high ratio of strength-to-electrical resistivity, ∼400 MPa(μΩ cm)−1. The hardness of these Cu films approaches 2.8 GPa, and their electrical resistivities are comparable to that of oxygen-free high-conductivity Cu. Compared to high-angle grain boundaries, coherent twin interfaces possess inherently high resistance to the transmission of single dislocations, and yet an order of magnitude lower electron scattering coefficient, determined to be 1.5–5×10−7 μΩ cm2 at room temperature. Analytical studies as well as experimental results show that, in polycrystalline Cu, grain refinement leads to a maximum of the strength-to-resistivity ratio, ∼250 MPa(μΩ cm)−1, when grain size is comparable to the mean-free path of electrons. However, in twinned Cu, such a ratio increases continuously with decreasing twin spacing down to a few nanometers. Hence nanoscale growth twins are more effective to achieve a higher strength-to-resistivity ratio than high-angle grain boundaries.

Unique epitaxial two-phase vertically aligned nanocomposite (VAN) (BiFeO3)x:(Sm2O3)1−x thin films were deposited on SrTiO3(001) substrates by pulsed laser deposition. The VAN thin films exhibit a highly ordered vertical columnar structure with high epitaxial quality. We demonstrate that the strains of the two phases in both out-of-plane and in-plane directions can be tuned by the deposition parameters during growth, e.g., deposition frequency and film composition of the nanocomposite. The strain tunability is found to be directly related to the systematic variation in the column widths in the nanocomposite. The dielectric property measurement shows that increasing vertical strain control will lead to a systematic dielectric loss reduction in the VAN thin films. This study suggests a promising avenue in achieving tunable strain in functional oxide thin films by using VAN structures.

A thin layer of a vertically aligned nanocomposite (VAN) structure is deposited between the electrolyte, Ce_0.9Gd_0.1O_1.95 (CGO), and the thin‐film cathode layer, La_0.5Sr_0.5CoO₃ (LSCO), of a thin‐film solid‐oxide fuel cell (TFSOFC). The self‐assembled VAN nanostructure contains highly ordered alternating vertical columns of CGO and LSCO formed through a one‐step thin‐film deposition process that uses pulsed laser deposition. The VAN structure significantly improves the overall performance of the TFSOFC by increasing the interfacial area between the electrolyte and cathode. Low cathode polarization resistances of 9 × 10⁻⁴ and 2.39 Ω were measured for the cells with the VAN interlayer at 600 and 400 °C, respectively. Furthermore, anode‐supported single cells with LSCO/CGO VAN interlayer demonstrate maximum power densities of 329, 546, 718, and 812 mW cm⁻² at 550, 600, 650, and 700 °C, respectively, with an open‐circuit voltage (OCV) of 1.13 V at 550 °C. The cells with the interlayer triple the overall power output at 650 °C compared to that achieved with the cells without an interlayer. The binary VAN interlayer could also act as a transition layer that improves adhesion and relieves both thermal stress and lattice strain between the cathode and the electrolyte.

Cubic HfN (B1-NaCl) thin films were grown epitaxially on Si(001) substrates by using a TiN (B1-NaCl) buffer layer as thin as ∼10nm. The HfN∕TiN stacks were deposited by pulsed laser deposition with an overall thickness below 60nm. Detailed microstructural characterizations include x-ray diffraction, transmission electron microscopy (TEM), and high resolution TEM. The electrical resistivity measured by four-point probe is as low as 70μΩcm at room temperature. Preliminary Cu diffusion tests show a good diffusion barrier property with a diffusion depth (2Dτ) of 2–3nm after annealing at 500°C for 30min in vacuum.

We report on the synthesis of epitaxial (single-crystal-like), nanotwinned Cu films via magnetron sputtering. Increasing the deposition rate from 1 to 4 nm/s decreased the average twin lamellae spacing from 16 to 7 nm. These epitaxial nanotwinned Cu films exhibit significantly higher ratio of hardness to room temperature electrical resistivity than columnar grain (nanocrystalline), textured, nanotwinned Cu films.

In this paper, we report a strong correlation between the stacking fault (SF) density and the critical current density of YBa2Cu3O7−δ (YBCO) thin films in applied field (Jcin-field). We found that the Jcin-field (H∥c) increases as a clear linear dependence of the density of SF identified in the as-grown samples deposited on both SrTiO3 (STO) and LaAlO3 substrates. Detailed microstructural studies including cross-section transmission electron microscopy (TEM) and high resolution TEM were conducted for all the films deposited on STO substrates. This work suggests that the YBCO SF density plays an important role in the YBCO in-field transport performance.

Nanocomposite (BiFeO3)0.5:(Sm2O3)0.5 films were deposited on (001) oriented Nb-doped SrTiO3 substrates by pulsed laser deposition. The leakage current density versus electric field characteristics were investigated and compared with those of as-deposited and annealed pure BiFeO3 (BFO) thin films. The dominant leakage mechanisms of nanocomposite films were space-charge-limited current and Poole–Frenkle emission for positive and negative biases, respectively. The leakage current density of nanocomposite films was reduced three orders of magnitude in comparison with the as-deposited pure BFO films. The less oxygen vacancies in the BFO phase in the nanocomposite is believed to contribute to the leakage reduction.

In thin films of rare‐earth manganites, RE_1−xM_xMnO₃ (RE=rare earth, M=Ca, Sr, Ba), with mixed‐valence perovskite structure, the transport properties highly depend on the deposition technique, processing conditions, and the substrate used. Chemical solution deposition techniques provide many advantages, such as low cost, easy setup, and coating of large areas. However, the crystalline quality, uniformity, and reproducibility of the film depend on the reactivity of the chemical used for solution preparation. In this paper, we report a novel process to grow rare‐earth manganite films using low‐cost polymer‐assisted deposition technique. In this process, polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and a uniform film. These solutions were stable, and crack‐free films were obtained using these solutions. In this paper, thin films of La_1−xSr_xMnO₃, La_1−xCa_xMnO₃, and Pr_0.5Ca_0.5MnO₃ were grown on (001) LaAlO₃ substrates. The La_1−xSr_xMnO₃ and La_1−xCa_xMnO₃ films were highly c‐axis oriented and epitaxial, and showed high magnetoresistance near their Curie temperature. Charge ordering was observed in the Pr_0.5Ca_0.5MnO₃ film at 220 K and high magnetoresistance of nearly −100% was obtained at low temperatures. The structural, transport, and magnetic properties of these films were similar to those obtained for films grown by physical vapor deposition.

Epitaxial c-axis oriented BiFeO3 (BFO) thin films were deposited on (001) Nb-doped SrTiO3 (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies caused the BFO thin film to evolve to a p-type semiconductor and formed a p-n heterojunction with an n-type semiconductor Nb-STO. The current density versus voltage (J-V) and capacitance versus voltage (C-V) characteristics of the heterojunction were investigated. A typical rectifying J-V effect was observed with a large rectifying ratio of 5×104. Reverse C-V characteristics exhibited a linear 1∕C2 versus V plot, from which a built-in potential of 0.6V was deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics.

Epitaxial Sm2O3 thin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition. The structural and dielectric properties were investigated. Microstructural studies by x-ray diffraction and transmission electron microscopy showed that the Sm2O3 thin films have a cubic structure and an epitaxial relationship of (004)Sm2O3∥(002)SrTiO3 and [440]Sm2O3∥[200]SrTiO3. A high dielectric constant of 30.5 was found, which can be attributed to the cubic structure and the high crystalline quality and shows a potential application of epitaxial Sm2O3 thin film for high-k material.

We have investigated the thermal stability of sputter-deposited Cu thin films with a high density of nanoscale growth twins by using high-vacuum annealing up to 800 °C for 1 h. Average twin lamella thickness gradually increased from approximately 4 nm for as-deposited films to slightly less than 20 nm after annealing at 800 °C. The average columnar grain size, on the other hand, rapidly increased from approximately 50 to 500 nm. In spite of an order of magnitude increase in grain size, the annealed films retained a high hardness of 2.2 GPa, reduced from 3.5 GPa in the as-deposited state. The high hardness of the annealed films is interpreted in terms of the thermally stable nanotwinned structures. This study shows that nanostructures with a layered arrangement of low-angle coherent twin boundaries may exhibit better thermal stability than monolithic nanocrystals with high-angle grain boundaries.

The thickness dependence was studied for the critical current density (Jc) of YBa2Cu3O7−x(YBCO)+BaSnO3 (BSO) nanocomposite films. These films showed a significantly reduced decline of the Jc with thickness, especially at high magnetic fields. For example, a 2 μm thick YBCO+BSO film had a Jc∼3×105 A/cm2 at 5 T as compared to a typical Jc of 2.4×103 A/cm2 at 5 T for a 300 nm thick YBCO film. The thick YBCO+BSO films maintained high Tc (&gt;88 K) and had a high density (2.5×1011/cm2) of continuous BSO nanocolumns that likely contributed for the observed Jc enhancements.

This study shows that biaxially textured Sm_xZr_1−xO_y(SZO) with a wide range of compositions (0.06 <x< 0.75) can be grown directly on ion-beam-assisted deposition (IBAD) MgO template using reactive cosputtering. The SZO crystal structure can be changed, and the lattice parameter can be tailored (from 5.23 to 5.49 Å) by changing the composition. We have developed a simplified high-temperature superconducting coated conductor using SZO as the buffer layer. YBa₂Cu₃O_7−δ(YBCO) films grown by pulsed laser deposition on the SZO buffered IBAD MgO have self-field critical current densities (J_c) in the 2–4 MA/cm²range. The in-field measurements demonstrate that high-quality YBCO films can be grown on SZO buffered IBAD MgO. The present results are especially important because they were obtained on coated conductors with the simpler architecture by eliminating the additional homoepitaxial layer of MgO. This translates in faster production and lower manufacturing cost.

Y Ba 2 Cu 3 O 7 − x (YBCO) films with nanoparticles of BaSnO3 (BSO) were processed using pulsed laser ablation of a special target made with dual phase sectors of YBCO and BSO. Transport critical current density (Jct) of these YBCO+BSO films in applied magnetic fields and angular dependence of Jct on the applied field orientation was measured. It was observed that in the YBCO+BSO films, the Jct (H‖c orientation) increased considerably as compared to regular YBCO films and was 1.3 times higher than Jct in H‖ab orientation. Cross-sectional transmission electron microscopy images on YBCO+BSO films showed the presence of high density (3.5×1011cm−2) of nanoparticles (∼10nm size) and nanocolumns that extended throughout the thickness of the films with high density of dislocations and stacking faults (1000μm−2). The observed results of enhancements in Jct in H‖c and Jct in H‖ab orientations were discussed in the light of the observed microstructural details.

Highly tunable films of dielectric PbxSr1−xTiO3 (with x=0.3 and 0.4) have been deposited on conductive LaNiO3 coated LaAlO3 substrates using a sol-gel technique. The processing condition was found to greatly influence the microstructure as well as the dielectric and electrical properties of the films. At room temperature, dielectric tunability values as high as 70% and 78.6% at an applied electric field of 223kV∕cm were achieved for the Pb0.3Sr0.7TiO3 and Pb0.4Sr0.6TiO3 films, respectively.

The authors have studied the influence of deposition rate on the formation of growth twins in sputter-deposited 330 austenitic stainless steel thin films. Transmission electron microscopy shows that the volume fraction of twinned grains increases with increasing deposition rate, whereas the average columnar grain size and twin spacing stay approximately unchanged. These experimental results agree qualitatively with their analytical model that predicts deposition rate dependent formation of growth twins. The film hardness increases monotonically with increasing volume fraction of twinned grains.

We report on the thermal stability of sputter-deposited Cu∕304 stainless steel nanoscale multilayer films. For individual layer thickness of approximately 70nm, the layered morphology was stable up to 600°C with no significant change in the hardness. The stainless steel layer had a duplex bcc+fcc structure that was also preserved in annealed films. After annealing at temperatures of 650°C or higher, the hardness of these multilayer films decreased from 4.75to3.4GPa due to morphological evolution from layers to equiaxed grains and coarsening of the nanolayers.

Bulk Cu foils have been synthesized via magnetron sputtering with an average twin spacing of 5nm. Twin interfaces are of {111} type and normal to the growth direction. Growth twins with such high twin density and preferred orientation have never been observed in elemental metals. These Cu foils exhibited tensile strengths of 1.2GPa, a factor of 3 higher than that reported earlier for nanocrystalline Cu, average uniform elongation of 1%–2%, and ductile dimple fracture surfaces. This work provides a route for the synthesis of ultrahigh-strength, ductile pure metals via control of twin spacing and twin orientation in vapor-deposited materials.

( La 0.7 Sr 0.3 Mn O 3 ) 0.5 : ( Zn O ) 0.5 nanocomposite thin films were deposited on c-cut sapphire substrates via pulsed laser deposition. The as-grown films were composed of fine grains of 20–50nm size. The epitaxial orientation relationships between the La0.7Sr0.3MnO3 (LSMO) and the sapphire was (111)LSMO∕∕(0003)Al2O3 and ⟨112¯⟩LSMO∕∕⟨101¯0⟩Al2O3. A low field magnetoresistance (LFMR) of ∼12% was achieved at an external magnetic field of H=1T at 77K, possibly due to enhanced grain boundary effects. The postannealed film had columnar structures with well-crystallized large grains (∼200nm), and showed a low resistivity and consequently negligible LFMR similar to that of single crystal LSMO.

Epitaxial YXBa2Cu3O7−δ (YXBCO) thin films were deposited by pulsed laser deposition on both single crystal SrTiO3 (100) and buffered polycrystalline metal substrates, where X=0.9, 1.0, 1.1, 1.2, and 1.3. The self-field critical current density (Jc) of YXBCO exhibits the best performance at X=1.1 for the samples on both single crystal substrates and metal substrates. Epitaxial Y2O3 nanoparticles were observed in Y-rich samples (X&gt;1.0) by X-ray diffraction and cross-sectional transmission electron microscopy. The field-dependence and angular-dependence measurements show that Y2O3 nanoparticles improve the in-field Jc performance, especially in the low field regime, without reducing self-field Jc of YBCO films.

The critical currents of coated conductors fabricated by metal-organic deposition (MOD) on rolling-assisted biaxially textured substrates (RABiTS) and by pulsed laser deposition (PLD) on ion-beam assisted deposition (IBAD) templates have been measured as a function of magnetic field orientation and compared to films grown on single crystal substrates. By varying the orientation of magnetic field applied in the plane of the film, we are able to determine the extent to which current flow in each type of conductor is percolative. Standard MOD/RABiTS conductors have also been compared to samples whose grain boundaries have been doped by diffusing Ca from an overlayer. We find that undoped MOD/RABiTS tapes have a less anisotropic in-plane field dependence than PLD/IBAD tapes and that the uniformity of critical current as a function of in-plane field angle is greater for MOD/RABiTS samples doped with Ca.

We conducted a comparative study of microstructural properties for YBa₂Cu₃O₇ (YBCO) films on single-crystal MgO and polycrystalline Ni-based metal substrates with ion-beam-assisted deposited (IBAD) MgO as a template. The film grown on the metal substrate shows more crystalline imperfections with density of screw dislocations four times higher than that of the film on single-crystal MgO, as revealed by high-resolution x-ray diffraction (HRXRD). These high-density screw dislocation cores connect well and form bigger clustered grains as detected by scanning tunneling microscopy. Transmission electron microscopy studies confirm that the structural quality of YBCO on the Ni-based alloy is comparable to that on single-crystal MgO. All these factors contribute to our routine fabrication of high-quality YBCO films on metal substrates with critical current densities in self-field as high as those for the films grown on single-crystal MgO substrates. Superconducting properties in fields are also discussed.

By inserting a thin YBa2Cu3O7−δ (Y123) seed layer, high quality EuBa2Cu3O7−δ (Eu123) films can grow with epitaxial c-axis orientation on SrTiO3 (STO) substrate without increasing the growth temperature. The interfacial structures of Eu123∕STO and Eu123∕Y123∕STO were investigated using scanning transmission electron microscopy. Results show that the Eu mobility on the STO substrate is very low at the regular deposition temperature. This leads to nonuniform composition distribution at the Eu123∕STO interface and a mixture of c-axis and a-axis growth. A thin Y123 seed layer greatly improves the Eu mobility and therefore facilitates high quality c-axis growth.

We have explored the influence of sputtering parameters on the structural, mechanical, and electrical properties of nanoscale twinned 330 stainless steel thin films. As the residual stress in the film is changed from tensile to compressive by varying the growth conditions, the nanoscale twinned structure, the average columnar grain size and texture of the film show little or no change. Hardness of the film in compression reaches 7GPa, compared to about 5.5GPa in films with high residual tension, and an order of magnitude higher than that of bulk 330 stainless steel. Molecular dynamics simulations indicate that twin boundaries pose a strong barrier to glide dislocation transmission under applied in-plane biaxial loading, consistent with the GPa level strengths measured in these films. The increase in the room temperature electrical resistivity of these films, compared to bulk 330 stainless steel, is found to be small, indicating that nanoscale twinned structures may provide the best combination of high mechanical strengths and high electrical conductivity.

Liquid-mediated growth of YBa2Cu3O7−x has the potential to be high rate and low cost. However, the reported critical current densities (Jc) are generally lower than for films deposited by physical vapor deposition processes. We report the deposition of thick high-Jc films (1.2MAcm−2 in self-field) on (001) SrTiO3 by high-rate hybrid liquid phase epitaxy, and show angular-dependent transport critical current as a function of applied field for these films, as well as microstructural measurements by transmission electron microscopy.

Remarkable progress has been made in the development of YBa2Cu3O7−δ (YBCO)-based coated conductors, and the problems of continuous processing of commercially viable tape lengths are being rapidly solved by companies around the world. However, the current carried by these tapes is presently limited to about 100A for a 1-cm-wide tape, and this is due to a rapid decrease of critical current density (Jc) as the coating thickness is increased. We have now overcome this problem by separating relatively thin YBCO layers with very thin layers of CeO2. Using this multilayer technology, we have achieved Jc values on metal substrates of up to 4.0MA∕cm2 (75K, self-field) in films as thick as 3.5μm, for an extrapolated current of 1400A∕cm width.

The influence of rare earth (RE) ion size on critical current density (Jc) in epitaxial films of superconducting REBa2Cu3O7−x was studied, where RE is the mixture of two or three rare earth ions. No systematic dependence of Jc on RE ion size was found. However, strongly enhanced critical current densities (Jc’s) were found for the composition Y2∕3Sm1∕3Ba2Cu3O7−x (YSmBCO). In ∼1-μm-thick films, Jc’s as high as 4.7×106Acm−2 (75.5K,0T) and 11×104Acm−2 (75.5K,5T) were obtained on single crystals and 6×104Acm−2 (75.5K,5T) on buffered metal. The values are up to a factor of 3 higher than for comparative YBCO samples.

We report our detailed studies of the microstructures of EuBa2Cu3O7−x (Eu123) films by using high-resolution x-ray diffraction. Reciprocal space maps show that the growth rate plays an important role in nucleation of a-axis Eu123 films on SrTiO3 (STO) substrates at a given deposition temperature. It is further revealed that a pseudotetragonal distortion often occurs in Eu123 films. This distortion, however, can be eliminated by decreasing the deposition rate. The low mobility of Eu atoms on the STO substrate is suggested to be the main reason for these phenomena.

We have explored the thermal stability of nanoscale growth twins in sputter-deposited 330 stainless-steel (SS) films by vacuum annealing up to 500°C. In spite of an average twin spacing of only 4nm in the as-deposited films, no detectable variation in the twin spacing or orientation of twin interfaces was observed after annealing. An increase in the average columnar grain size was observed after annealing. The hardness of 330 SS films increases after annealing, from 7GPa for as-deposited films to around 8GPa for annealed films, while the electrical resistivity decreases slightly after annealing. The changes in mechanical and electrical properties after annealing are interpreted in terms of the corresponding changes in the residual stress and microstructure of the films.

We compare the angular-dependent critical current density (Jc) in YBa2Cu3O7 films deposited on MgO templates grown by ion-beam-assisted deposition (IBAD), and on single-crystal substrates. We identify three angular regimes in which pinning is dominated by different types of correlated and uncorrelated defects. Those regimes are present in all cases, but their extension and characteristics are sample dependent, reflecting differences in texture and defect density. The more defective nature of the films on IBAD turns into an advantage as it results in higher Jc, demonstrating that the performance of the films on single crystals is not an upper limit for the IBAD coated conductors.

Bulk austenitic stainless steels (SS) have a face-centered cubic (fcc) structure. However, sputter deposited films synthesized using austenitic stainless steel targets usually exhibit body-centered cubic (bcc) structure or a mixture of fcc and bcc phases. This paper presents studies on the effect of processing parameters on the phase stability of 304 and 330 SS thin films. The 304 SS thin films with in-plane, biaxial residual stresses in the range of approximately 1 GPa (tensile) to approximately 300 MPa (compressive) exhibited only bcc structure. The retention of bcc 304 SS after high-temperature annealing followed by slow furnace cooling indicates depletion of Ni in as-sputtered 304 SS films. The 330 SS films sputtered at room temperature possess pure fcc phase. The Ni content and the substrate temperature during deposition are crucial factors in determining the phase stability in sputter deposited austenitic SS films.

Critical current density Jc as a function of temperature T and magnetic field H was studied for high quality YBa2Cu3O7−δ (YBCO) films with thickness d=0.2, 1, and 3 μm by means of magnetization measurements of a circular disk in perpendicular field. We found that the thickness dependence of Jc(H) for the YBCO thick films crossovers at high fields for T&gt;50 K, where the 0.2-μm-thick film carries significantly lower Jc(H) than the 3-μm-thick film at high fields, even though the zero- or low-field Jc for the 0.2-μm-thick film is more than twice the value for the 3-μm-thick film.