Multilayer Thin Films Research Articles

Lamellar Microphase Separation and Phase Transition of Hydrogen-Bonding/Crystalline Statistical Copolymers: Amide Functionalization at the Interface.

Microphase separation of random copolymers, as well as that of high χ-low N block copolymers, is promising to construct sub-10-nm structures into materials. Herein, we designed statistical copolymers consisting of 2-hydroxyethyl acrylate (HEA) and N-octadecylacrylamide (ODAAm) to produce crystallization and hydrogen bond-assisted lamellar structure materials. The copolymers not only formed a crystalline lamellar structure with 3-4 nm domain spacing but also maintained an amorphous lamellar structure via phase transition above the melting temperature up to approximately 100 °C. The key is to introduce hydrogen-bonding amide junctions between the octadecyl groups and the polymer backbones, by which the polymer chains are physically fixed at the interface of lamellar structures even above the melting temperature. The stabilization of the lamellar structure by the amide units is also supported by the fact that the lamellar structure of all-acrylate random copolymers bearing hydroxyethyl and crystalline octadecyl groups is disordered above the melting temperature. By spin-coating on a silicon substrate, the HEA/ODAAm copolymer formed a multilayered lamellar thin film consisting of a hydrophilic hydroxyethyl/main chain phase and a hydrophobic octadecyl phase. The structure and order-disorder transition were analyzed by neutron reflectivity.

Luminescence enhancement of Y2O3 thin films based on LSPR effect of Ag nanolayers

Based on the local surface plasmon resonance effect of Ag nanolayer, the luminescence enhancement in the visible light range of multilayer thin film has been investigated combined with metal/spacer molecule/photoluminescence material structure. The luminescence enhancement effect of multilayer thin films can be improved by adjusting the spin-coating number of Ag nanolayer and SiO2 spacer in the multilayer structure. At the same time, the mechanism of enhanced luminescence has been analyzed according to the change in fluorescence lifetime. The effect of the coupling between Ag nanolayer and luminescence layer on the radiative transition rate and fluorescence quantum yield have been discussed. The up-conversion luminescence intensity of the noble metal-modified multilayer thin film can be further improved by combining the multilayer structure with sensitized layer.

Investigation of optical and electrical properties of TiO2, SiO2, and Ag single and multilayer thin films using spectroscopic ellipsometry and spectrophotometry methods: prepared by spin coating and DC magnetron sputtering

In this work, spectroscopic ellipsometry was used to study the optical and electrical properties of TiO2 and SiO2 thin films deposited by spin-coating at different coating rotation speeds and annealed at various temperatures. In addition, Ag thin films of different thicknesses were deposited by DC magnetron sputtering at ambient temperature. In this method, the optical band gap for TiO2 thin films is between 3.15–3.85 eV, and for SiO2 thin films, it is between 3.2–3.8 eV. The optical properties, including reflectance, transmittance, and absorbance, of TiO2, SiO2, and Ag thin films in the form of single and multilayer thin films in the wavelength range of 200–2500 nm, were investigated using an ultraviolet-visible-near infrared (UV–vis-NIR) dual-beam spectrophotometer. In the TiO2/Ag/SiO2 multilayer thin film, the rejection was 58.6% −73.6% in the NIR wavelength range (800–2500 nm), and a transmittance of 40%–45% was achieved in the visible light range (400–700 nm).

The influence of a copper spacer on the magnetic properties of Pd/Co/Cu/Pd multilayers with perpendicular anisotropy

The potential for technological applications of systems presenting perpendicular magnetic anisotropy is undeniable. With the advent of spintronics and the possibility to explore spin textures, such as skyrmions, in devices, it becomes fundamental to understand how to finely tune the magnetic properties of nanometric systems. In multilayered thin films, characteristics such as domain structure, saturation magnetization and perpendicular anisotropy may be tailored by modifying the interfaces. In the present study, the impact of a copper spacer of varying thickness on the magnetic properties of Pd/Co/Cu/Pd multilayers is investigated. The evolution of magnetization curves, domain patterns and magnetization reversal processes in terms of the spacers thickness are analyzed.

Effect of rapid/slow annealing routes on the magnetic and photoelectric properties of BiFeO3/CoFe2O4 multilayer thin films

With the development of electronic information technology, the miniaturization of lightweight devices and their integration have increased the requirements for materials, and two-dimensional composite multiferroic materials have become a major research hotspot in recent years. However, it is difficult for traditional solid multiferroic material to directly switch the magnetic/polarization direction under the action of an applied electric/magnetic field, limiting the improvement of the magnetoelectric coupling coefficient. In this study, a series of BiFeO3 (BFO)/CoFe2O4 (CFO) composite film multiferroic materials were prepared by changing the annealing routes and annealing atmosphere, the microstructure, ferroelectric properties, dielectric properties, photovoltaic properties, magnetic properties, and magnetoelectric coupling properties of composite films were routeatically studied. The results showed that under the slow annealing route, the composite film has obvious ellipsoidal grains with distinct grain boundaries and better crystallinity. Moreover, the performance of the film after annealing in different atmospheres of the slow annealing route was improved compared with that of the rapid annealing route after annealing in different atmospheres. Simultaneously, by changing the annealing atmosphere of the composite film, the film exhibited better magnetic optical properties and coupling properties after annealing in oxygen. In addition, this study showed that the dielectric constant and residual polarization value of the film increase under the action of magnetic field and illumination, and the maximum photomagnetic dielectric response (3.19%) and photomagnetic response (1.58%) are observed in the annealed film under the oxygen atmosphere of the slow annealing regime, indicating that the magnetoelectric coupling effect of the film is improved under the action of applied light.

TiN-Au/HfO2 -Au Multilayer Thin Films with Tunable Hyperbolic Optical Response.

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.

Magnetically Reconfigurable Toroidal Metasurfaces

AbstractHarnessing electron spin within limited dimensions under applied magnetic fields can lead to spin‐assisted tunable light‐matter interactions, which form a crucial step in developing frequency‐agile opto‐spintronic structures toward next generation photonic devices. For this purpose, spin‐dependent magneto transport phenomena derived from ferromagnetic (FM)/nonmagnetic (NM) multilayer structures have recently emerged as a useful tool for dynamically tailoring electromagnetic waves. With this pretext, five layers of aluminum (Al)/nickel (Ni) based multilayer thin films in sub skin depth regime are studied in terahertz domain under low‐intensity (0 to 30 mT) magnetic fields while systematically varying the NM spacer layer (sandwiched between the FM layers) from 8 to 18 nm. Such thin multi‐layer films demonstrate conductivity variations up to ≈40% for 30 mT of applied field. Utilizing the same multilayer configurations, magnetic field induced tunability in a metasurface design is investigated that simultaneously manifests toroidal, dipolar, and other higher‐order modes. Further, multipolar analysis reveals that the nonradiative toroidal and radiative dipole modes can be enhanced by almost 56% and 183%, respectively, under 0–30 mT magnetic fields. Such magnetic field‐induced simultaneous control over radiative and non‐radiative resonances can be pivotal for next generation terahertz magnetophotonic devices.

An Edge Detection Algorithm for SEM Images of Multilayer Thin Films

In processing multilayer thin film materials, scanning electron microscopy (SEM) is commonly employed for observation. In images of SEM, backscattered electron (BSE) images is particularly suitable for distinguishing different components and layers of the films. However, at high magnification levels, BSE images often have blurriness and noise, leading to low edge sharpness. This study proposes a method for improving the integrity and accuracy of the edges. First, we segment the image into different contrast regions using the masking algorithm. Second, we enhance the images in separate regions by the enhancement algorithm. Finally, we combine the regions by logical operations. In instantiation, we implement our approach on SEM-BSE images. It was found that the edges are significantly sharpened through the assessment of the edge evaluation algorithm.

Structural robustness and actuation performance of multilayered thin-film actuators based on Ni-Co flexible substrate

This paper presents a comprehensive evaluation of multilayered thin-film actuators based on metal substrates made of Ni and Co alloys. The focus was on improving the structural robustness through appropriate adhesive layers and evaluating their fundamental performance and long-term stability. We conducted nanoscratch testing and scanning electron microscopy to identify the optimal adhesive layers that significantly enhanced the adhesive strength. Following the evaluation, no instances of cracking or peeling were observed in the multilayer thin film where a Ti layer serves as an adhesion mediator between the Ni and Co thin film and the SiO2 and Si3N4 insulating layers. This indicates that this specific layer configuration provides superior structural robustness compared to multilayer thin films with alternative compositions. In addition to enhancing the structural robustness, we comprehensively evaluated the fundamental performance and long-term cyclic stability of the multilayered thin-film actuators. The actuators demonstrated exceptional characteristics including low power consumption, substantial displacements (1.58 mm at 120 mW, corresponding to an input voltage of 5 V), rapid response times, and high operating speeds. The endurance of the actuator was verified through long-term cyclic testing by subjecting it to a sinusoidal excitation for an extensive duration of 1.15 million cycles. This test demonstrated the stability of the actuator in maintaining its functionality and reliability even under prolonged operating conditions. Thereby, the test verified its structural robustness and potential for practical applications.

Prominent ferroelectric properties in multilayered TiO2 Mn-doped BiFeO3 spin-coated thin films

The study investigates the effects of doping on the leakage current and ferroelectric properties of bismuth ferrite (BiFeO3) thin film-based heterostructures. The spin coating method has been employed to deposit thin films of BiFeO3 and heterostructures of TiO2/BiFeO3 and TiO2/BiFe0.95Mn0.05FeO3 on fluorine-doped tin oxide substrates. The ferroelectric behavior of the TiO2/BiFe0.95Mn0.05FeO3 films exhibited better ferroelectric hysteresis loop compared to the other prepared films. The ferroelectric behavior reveals the TiO2/BiFe0.95Mn0.05FeO3 heterostructure showed a significantly lower leakage current density compared to both the BiFeO3 thin film and TiO2/BiFeO3 heterostructure, and the TiO2/BiFe0.95Mn0.05FeO3 heterostructures are likely suitable for solar cell applications. Highlights FTO/TiO2/BiFe0.95Mn0.05FeO3/Au heterostructure thin films prepared by spin coating method. Structure and optical properties of TiO2/BiFe0.95Mn0.05FeO3 heterostructure thin films were investigated. TiO2/BiFe0.95Mn0.05FeO3 heterostructure thin films showed a low optical energy band gap of 2.25 eV. Enhanced ferroelectric property in TiO2 thin film composited with BiFe0.95Mn0.05FeO3 thin films.

Enhanced energy-storage and magnetoelectric properties of Ba0.95La0.05Zr0.4Ti0.6O3/CoFe2O4 multilayer thin films

Multifunctional thin films and devices have gained much interest in both scientific and industrial research for futuristic multifunctional micro- and nano-device applications. Here, we report the development of a multi-layer structure based on relaxor-ferroelectric Ba0.95La0.05Zr0.4Ti0.6O3 (BLZT) and ferrimagnetic CoFe2O4 (CFO) ([BLZT/CFO]3/BLZT or BLZT/CFO) thin-films on Si substrates for enhanced energy-storage density and magnetic properties. An ultrahigh recoverable energy-storage density (Ur) of 137.6 J/cm3 together with an energy efficiency of 76.6 % are achieved for the BLZT/CFO multi-layer, owing to the enhanced breakdown-strength (EBD) of 8.0 MV/cm (BLZT single-layer has an Ur value of 84.7 J/cm3 at EBD of 5.5 MV/cm). Moreover, the saturation magnetization of CFO layers in the BLZT/CFO multi-layer significantly increases from 239.2 kA/m to 276.4 kA/m. This enhancement can be attributed to the enlarged magnetic domains in CFO layers, which follow the piezoelectric domain switching in the BLZT layers induced by applying a dc-bias voltage. These remarkable performances indicate that the BLZT/CFO multi-layer is a promising candidate for multifunctional energy storage and magnetoelectric device applications.

EFFICIENT SYNTHESIS OF ZNO AS AN ELECTRODE OF PIEZOELECTRIC NANOGENERATORS

Piezoelectric nanogenerators (NGs) hold immense promise as self-powered devices for harvesting mechanical energy from the environment. This study introduces an efficient and scalable synthesis method for zinc oxide (ZnO) nanorods, a pivotal material in piezoelectric nanogenerators (NGs), with several key results. A Chemical Bath Deposition technique is employed, optimizing parameters such as growth time, temperature, and precursor concentrations to achieve well-aligned and high-quality ZnO nanorods. The structural and morphological characteristics of the synthesized nanorods are systematically investigated using advanced characterization techniques. The synthesized ZnO nanorods exhibit an average length of 400nm, demonstrating their slender shape. Furthermore, the study determines an energy gap value of 3.5 eV for multilayer zinc oxide thin films, indicating the transition from the valence band to the conduction band. Notably, thermal annealing at 500°C leads to a substantial increase in average output voltage, reaching 1.95 V, a fourfold improvement compared to as-deposited nanopowders. These findings emphasize the efficiency and potential of the proposed synthesis method and underscore its practical applications in enhancing energy harvesting capabilities for sustainable power generation from mechanical sources in piezoelectric NGs.

Investigation of the influence of Al layer and total film thicknesses on structural and related magnetic properties in sputtered Ni/Al multilayer thin films

The effects of parameters of Al layer thickness and total film thickness on the structural and related magnetic properties of Ni/Al multilayer films were investigated. The films were deposited by a dual sputtering. The Ni content decreased gradually while the Al content increased as the Al layer thickness increased. It was also observed that the total film thickness had little effect on the film content. All films have a face-centred cubic structure. And, the surface morphology of Ni/Al films is more uniform and homogeneous than the surface of Ni film. For magnetic analysis, the properties were strongly changed with the parameters. The saturation magnetisation, Ms of Ni film was obtained as 572 emu/cm3 while the Ms of the Ni/Al films decreased from 441 to 298 emu/cm3 with increasing Al content in the films caused by the Al layer thickness. And, the increase of total film thickness resulted in a decrease of Ms value. While the coercivity, Hc value of the Ni film was 90 Oe, Hc of Ni/Al films was decreased to ~ 39 Oe with the formation of multilayer structure. Ni/Al multilayers were obtained magnetically softer than the Ni film. The Ms and Hc values were significantly affected by the variation of the film content and crystal structure caused by the changes in deposition parameters. Therefore, this is a fundamental step for Ni/Al multilayers to improve the properties of these films for their potential applications in microelectronic devices.

Multi-solution inverse design in photonics using generative modeling

The lack of uniqueness poses a common challenge in the inverse design of nanophotonic structures. This issue arises from the presence of multiple sets of design parameters that yield identical output configurations. Several existing machine learning methods offer promising solutions for enabling flexibility in selecting sets of design variables. However, these approaches still face significant challenges like limited output diversity, and training instability. These issues constrain the variety of solutions attainable for a particular target response. To overcome these challenges in the realm of multi-solution inverse design problems in nanophotonics, we have developed a GA-βCVAE architecture based on generative models. This approach effectively tackles such problems, thereby expanding the range of distinct solutions achievable in nanophotonics. Our approach combines a genetic algorithm with a β conditional variational autoencoder neural network based generative model, capturing multiple distinct solutions for a given target. It provides flexibility in selecting design variables. We successfully applied it to design TiO2-SiO2 based multilayer thin films in the visible range (400–750 nm), with layer thickness as the design variable. Experimental verification confirmed the effectiveness of our proposed architecture.

Dynamic electromagnonic crystals based on ferrite-ferroelectric thin film multilayers

Dynamic electromagnonic crystals based on ferrite-ferroelectric thin film multilayers

Effect of the TiSiN interlayer properties on the adhesion and mechanical properties of multilayered TiSiCN thin films

The interlayer design is crucial in optimizing the adhesion of TiSiCN thin films on tool steel. Thus, Ti/TiN/TiSiN interlayer systems were deposited varying the TiSiN interlayer bias voltages (−100 V, −150 V, −200 V) in a magnetron sputtering process to investigate the influence on the mechanical properties and adhesion of the TiSiCN top layer with different thicknesses.A higher bias voltage densifies the TiSiN interlayer structure, thereby increasing its residual stresses (0.11 GPa to 1.46 GPa) and hardness (28.1 GPa to 34.9 GPa). This occurs without affecting the columnar-like microstructure of the TiSiCN top layer and its hardness (25.9 GPa to 29.1 GPa for t = 1.0 μm, 22.6 GPa to 24.8 GPa for t = 2.3 μm). Adhesion classification by Rockwell C indentation of TiSiN declined from HF2 to HF4 due to increased residual stresses, impacting TiSiCN top layer adhesion with a similar deterioration. Scratch tests revealed reduced critical loads Lc2 and Lc3 for the TiSiN interlayer system and also for TiSiCN top layers. The highest critical loads were observed for TiSiCN (1.0 μm) and TiSiCN (2.3 μm) with TiSiN interlayer deposited at a bias voltage of −100 V, measuring (64.4 ± 4.5) N and (73.4 ± 8.3) N for Lc2, and (57.4 ± 5.3) N and (71.6 ± 4.5) N for Lc3, respectively. Increasing bias voltage decreases Lc2 and Lc3 to (23.2 ± 4.5) N and (50.20 ± 2.2) N for TiSiCN (1.0 μm), and (21.4 ± 4.5) N and (58.0 ± 3.6) N for TiSiCN (2.3 μm).Achieving high adhesion strength of TiSiCN multilayered system requires minimizing the residual stress differences between the layers. Therefore, when designing a complex multilayer structure for TiSiCN thin films, careful consideration of the stress state among the layers is crucial, which is achieved by adjusting the bias voltage.

Thermal effusion of water and carbon oxides from multilayered graphene oxide thin films

Thermal effusion of water and carbon oxides from multilayered graphene oxide thin films

Study of the Long-Range Exchange Coupling in Nd-Fe-B/Ti/Fe Multilayered Structure

The exchange coupling between two ferromagnetic thin films, one with magnetically hard and the other with soft phases, separated by a thin non-magnetic layer, is studied. Nd-Fe-B/Ti/Fe thin film heterostructures were fabricated using DC magnetron sputtering on Si substrates, which were heated in situ at 650 °C using a house-built vacuum-compatible heater. The effect of the thickness of the Ti buffer layer and the annealing temperature on the formation of various phases of Nd-Fe-B was investigated. The effect of the thickness of the non-magnetic Ti spacer layer on the exchange coupling strength between the hard phase Nd-Fe-B ferromagnetic thin layer and the soft phase transition metal Fe layer was experimentally investigated. Hysteresis loops of multilayer thin films indicate an antiferromagnetic coupling was observed when the thickness of the spacer layer was 2 nm. This is within the range of an antiferromagnetic coupling calculation based on RKKY theory predictions.

Reduced leakage current and enhanced energy storage performance of BZNT/BTO multilayer structures: Implications in electronic devices

The extremely high recoverable energy density (Wrec) and efficiency (η) of lead-free thin films make them a promising candidate for application in miniature power devices. Here, a stable design of multilayered structures of BaTiO3 (BTO) and Bi[Zn2/3(Nb0.85Ta0.15)1/3]O3 (BZNT) have been fabricated using the pulsed laser deposition (PLD) technique on n-type Si, and Pt/Ti/SiO2/Si (Pt-Si) substrates. The effect of a number of stacking of alternate BTO and BZNT layers on the structural, microstructural, electrical, and ferroelectric properties is investigated. The films exhibited a polycrystalline nature, and the tetra-layer stacked film (BZNT/BTO3) exhibited better crystallinity, improvement in microstructure, and grain growth than that of the bi-layer stacked film (BZNT/BTO1). The improvement in ferroelectric response in the tetra-layer film is well correlated to the low leakage current density (∼10-7 A/cm2 at ±500 kV/cm) owing to reduced defects in the film. The reduced oxygen vacancies and dielectric loss tangent of order 10-3 validate the high quality of BZNT/BTO3 film exhibiting a large Wrec of 52.19 J/cm3 and high energy efficiency of 92.21 % achieved through interface engineering. These findings demonstrate the promising future for BTO-based multilayer thin film in high-power and energy-storage device applications.

TEM Investigations of Multi-Layer Selective Absorber thin films for concentrated solar plant: Structure and composition

TEM Investigations of Multi-Layer Selective Absorber thin films for concentrated solar plant: Structure and composition