Properties Of Multilayer Thin Films Research Articles

Improved performance of AZO/Ag/AZO transparent conductive films by inserting an ultrathin Ti layer

Multilayer thin films of titanium-embedded Al-doped ZnO/Ag/Al-doped ZnO (AZO/Ag/AZO) structures have been designed and deposited onto polyethylene terephthalate (PET) substrates to develop an indium-free transparent flexible electrode. The effect of Ti layer on the morphological, structural, optical and electrical properties of multilayer thin films was investigated. The insertion of ultra-thin Ti layers enhances the near-infrared transmittance of AZO/Ag/AZO thin films, widens the spectral transmission window of AZO/Ag/AZO thin films, and improves the conductivity and surface roughness of AZO/Ag/AZO thin films. As the Ag thickness increases from 8 nm to 12 nm, the sheet resistance of the AZO/Ti/Ag/AZO thin film decreases from 16.22 Ω sq-1 to 7.17 Ω sq-1. AZO/Ti/Ag/AZO with an Ag thickness of 8 nm exhibits excellent optoelectronic properties with an average transmittance of 80.3 % and 61.7 % in the wavelength range of 400–1100 nm and 400–2000 nm, as well as a sheet resistance of 16.22 Ω Sq-1. It is demonstrated that AZO/Ti/Ag/AZO multilayer flexible films have great potential in various fields.

Energy storage properties of multilayer thin films based on relaxor-ferroelectric (Ba0.9Sr0.1)(Zr0.4Ti0.6)O3 and paraelectric Sr(Zr0.1Ti0.9)O3 layers

Lead-free dielectric film capacitors with high recoverable energy-storage density (Ur) and large energy efficiency (η) are highly desired for the development of next-generation energy-storage devices for environmental sustainability. In this work, the impact of inserting SrZr0.1Ti0.9O3 layers in the structure and properties of [(Ba0.9Sr0.1)Zr0.4Ti0.6O3/SrZr0.1Ti0.9O3]N = 4/(Ba0.9Sr0.1)Zr0.4Ti0.6O3 ([BSZT/SZT]N = 4/BSZT) multilayer films was systematically investigated. The results indicated that both maximum polarization and breakdown strength are enhanced in the multilayer structure. This is attributed to the strain gradient, dielectric constant gradient, and interface blocking effect in the interfaces between relaxor BSZT and paraelectric SZT layers. Consequently, a high Ur of about 107.3 J/cm3 and an excellent η of about 84.2% were achieved in the multilayer films (Ur and η values were about 73.7 J/cm3 and 73.1%, and 40.9 J/cm3 and 89.6%, respectively, for the single-layered BSZT and SZT films).

Effects of Vacuum and Air Annealing on Structural, Morphological, Optical, and Electrical Properties of Multilayer CdZnS Thin Films for Photovoltaic and Optoelectronic Applications.

Multilayer CdZnS (CZS) thin film was deposited on soda lime glass substrates. After deposition, the films were vacuum and air annealed at 100 °C, 200 °C, 300 and 400 °C for 1 h. Effects of vacuum and air annealing on structural, morphological, optical, and electrical properties of multilayer CZS films with increasing annealing temperature (IAT) were studied. The structural analysis revealed that the films were polycrystalline with hexagonal structure having a prominent/intensive peak along the (002) plane at 300 and 400 °C. The crystallite size of nanoparticles increased from 18.4 to 20.5 nm under air annealing and from 18.4 to 26.9 nm under vacuum annealing, showing the significance of annealing on nanoparticle grain growth. According to morphological analysis, the multilayer technique provides homogeneous film distribution over the substrate. The transmittance graphs of films revealed that it increased up to 92% in the visible and NIR regions under vacuum annealing and up to 52% under air annealing. Vacuum annealing enhanced the band gap energies more significantly than air annealing. The electrical resistivity increased with IAT, showing that structural, morphological, optical, and electrical properties of the multilayer thin films of CZS were strongly dependent on vacuum and air annealing.

Parameterized reinforcement learning for optical system optimization

Engineering a physical system to feature designated characteristics states an inverse design problem, which is often determined by several discrete and continuous parameters. If such a system must feature a particular behavior, the mentioned combination of both, discrete and continuous, parameters results in a challenging optimization problem that requires an extensive search for an optimal system design. However, if the corresponding inverse design problem can be reformulated as a parameterized Markov decision process, reinforcement learning (RL) provides a heuristic framework to solve it. In this work, we use multi-layer thin films as an example of the aforementioned optimization problems and consider three design parameters: Each of the thin film layer’s dielectric material (discrete) and thickness (continuous), as well as the total number of layers (discrete). While recent methods merely determine the optimal thicknesses and—less commonly—the layers’ materials, our approach optimizes the total number of stacked layers as well. In summary, we further develop a Q-learning variant to solve inverse design optimization and thereby outperform human experts and current approaches like needle-point optimization or naive RL. For this purpose, we propose an exponentially transformed reward signal that eases policy search and enables constrained optimization. Moreover, the learned Q-values contain information about the optical properties of multi-layer thin films, which allows us a physical interpretation or what-if analysis and thus enables explainability.

Effect of zincone ratio on mechanical reliability of aluminum-doped zinc oxide-zincone multilayer thin films grown on flexible substrate using atomic/molecular layer deposition hybrid techniques

The combination of atomic and molecular layer deposition techniques enables the fabrication of various functional organic-inorganic multilayer thin-film structures. The alloys in metal oxide thin films and organic metalcone thin films demonstrate many technical advantages over conventional metal oxide single-layer thin films in terms of mechanical and electrical properties. This study investigates the effect of multilayer thin-film structures, which are fabricated as zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) single thin films and ZnO-zincone and AZO-zincone multilayer thin films, on the mechanical and electrical properties of multilayer thin films. Various multilayer thin films are fabricated with variations in composition ratios between the inorganic and organic materials by controlling the process cycles. To analyze the reliability of thin multilayer films under external deformations, the variations in the electrical resistivity and crack generation of the thin films are measured using micro-tensile specimens. In addition, the variations with respect to the optical transmittance and surface morphology of multilayer thin films are analyzed using various composition ratios, and the results are compared with those obtained from single metal oxide thin films.

Magnetic domain size tuning in asymmetric Pd/Co/W/Pd multilayers with perpendicular magnetic anisotropy

Magnetic multilayers presenting perpendicular magnetic anisotropy (PMA) have great potential for technological applications. On the path to develop further magnetic devices, one can adjust the physical properties of multilayered thin films by modifying their interfaces, thus determining the magnetic domain type, chirality, and size. Here, we demonstrate the tailoring of the domain pattern by tuning the perpendicular anisotropy, the saturation magnetization, and the interfacial Dzyaloshinskii-Moriya interaction (iDMI) in Pd/Co/Pd multilayers with the insertion of an ultrathin tungsten layer at the top interface. The average domain size decreases around 60% when a 0.2 nm thick W layer is added to the Co/Pd interface. Magnetic force microscopy images and micromagnetic simulations were contrasted to elucidate the mechanisms that determine the domain textures and sizes. Our results indicate that both iDMI and PMA can be tuned by carefully changing the interfaces of originally symmetric multilayers, leading to magnetic domain patterns promising for high density magnetic memories.

Electro-mechanical properties of multilayered aluminum nitride and platinum thin films at high temperatures

In this study, the electro-mechanical properties of multilayered thin films consisting of 10 bi-layers of 7 nm aluminum nitride (AlN) and 3 nm platinum (Pt) are investigated in the as deposited state and after different post deposition annealing steps. The multilayers are deposited using direct current magnetron sputtering on thermally oxidized silicon wafers or sapphire substrates and are annealed in Ar atmosphere at 800, 900 and 1000 °C up to 24 h. The electro-mechanical properties are characterized from room temperature up to 500 °C using Van-der-Pauw as well as gauge factor measurements. Furthermore, transmission electron microscopy and energy dispersive X-ray analyses are used to investigate the microstructure and the chemical composition of the multilayers before and after thermal loading. The influence of the annealing on the crystalline structure is examined by X-ray diffraction analyses. Annealing in this high temperature range causes an intermixture of the individual Pt and AlN sub-layers as well as a recrystallization of the Pt thin films. Annealing the multilayered thin film system at 900 °C for 1 h in Argon atmosphere results in a multilayer which is electrically stable up to 500 °C in air and which exhibits a 3 times lower temperature coefficient of resistance at a similar gauge factor when compared to pure Pt thin films.

The role of Al concentration on improving the photocatalytic performance of nanostructured ZnO/ZnO:Al/ZnO multilayer thin films

Nanostructured ZnO, ZnO/AZO, and ZnO/AZO/ZnO multilayer thin films were deposited on glass substrates by the sol-gel spin coating method. Structural, optical and photocatalytic properties of multilayer thin films as a function of Al doping concentration were studied. Field emission scanning electron microscopy (FESEM) images showed that surfaces of ZnO multilayer thin films have granular character. X-ray diffraction (XRD) analysis indicated that all multilayer thin films are polycrystalline with a hexagonal Wurtzite structure, and the crystallinity of multilayer thin films deteriorate with an increase in the Al doping concentration. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy showed that oxygen vacancies in ZnO/AZO/ZnO thin films are higher than in ZnO/AZO thin films. The DRS result showed that the band-gap energy of ZnO multilayer thin films increases with increasing Al doping concentration. The prepared samples were examined by the photodegradation reaction of methylene blue (MB) under visible light irradiation. The AZO as the middle layer in the ZnO/AZO/ZnO thin films was found to improve the photocatalytic activity of the samples. The maximum photocatalytic activity (95.2%) was obtained at 20% Al concentration, and the photocatalytic activity of this sample stayed nearly unchanged after three cycles.

A computational approach for engineering optical properties of multilayer thin films: Particle swarm optimization applied to Bruggeman homogenization formalism

An algorithm based on Particle Swarm Optimization (PSO) and Bruggeman Homogenization Formalism was presented to design a model structure for a thin film with various sublayers to obtain a desired optical reflectance/transmittance spectrum. In principle, the results showed that the designed structure is strongly affected by the input parameters of the algorithm such as film thickness, number of sublayers, incident light characteristic wavelength and utilized materials, and the method has its ability to find the best optimized structure based on desired optical properties. The results of calculations were in good agreement with the physical principles of classical optics and the method could be useful in both design and characterization purposes.

Determination of thin metal film’s thickness and optical constants based on SPR phase detection by simulated annealing particle swarm optimization

Abstract Simulated annealing particle swarm optimization (SAPSO) method for inverse model of optical properties of multilayer thin films based on surface plasmon resonance (SPR) experimental results is introduced in this paper. The purpose is to extract unknown parameters from the phase difference between P- and S- polarizations of the reflected light occurred at the metal/dielectric interface. The results of both the metallic and bimetallic layer derived from our method are in better agreement with the experiment data than particle swarm optimization (PSO) method. Therefore, the approach reveals the possibility of retrieving the thickness and optical constants from the measurement results of the phase difference for multilayers, and makes it be a much better option to be employed for further film’s parameter analysis applications.

Uniaxial mechanical properties of multi-layer thin films in use for scientific balloons

Essential and accurate mechanical parameters of multi-layer thin films for scientific balloons are indispensable for performing structural analysis. This study focuses on the determination of uniaxial mechanical properties of a new multi-layer thin film and the understanding of the effects of mechanical properties on structural behavior and altitude with three-dimensional numerical models. For uniaxial monotonic mechanical properties, a method to determine yield stress is proposed in combination of geometrical and energetic principles. It is found that average yield stresses are 20.5 MPa and 15.0 MPa for machine and transverse directions. The cyclic mechanical properties in terms of elastic modulus and ratcheting strain tend to be stable after certain cycles. Moreover, the Poisson’s ratios of 0.31 and 0.15 in machine and transverse directions are determined with digital image correlation (DIC) technique. Furthermore, these mechanical properties are utilized to analyze a 12 m diameter spherical superpressure balloons floating at the altitude of 20 km. A corresponding three-dimensional numerical model is developed to understand the effects of mechanical properties on structural behavior and altitude. The numerical results in terms of elastic moduli show that the effects of mechanical properties on structural behavior and altitude are relatively apparent and slight, respectively.

Measuring Elastic Properties of the Constituent Multilayer Coatings for Different Modulation Periods

This paper is developed to characterize mechanical properties of multilayer coatings for different modulation periods. To that end, Dimensional Analysis Method (DAM) and Finite Element Method (FEM) are applied. Based on these methodologies, two dimensionless forms for the new model are expressed. Numerical nanoindentation tests are carried out for different set properties of multilayer coatings in order to validate the proposed model. Therefore, the mechanical properties of multilayer thin films are identified according to the reverse analysis algorithm. Hence, the input and the identified properties are consistent which ensure the effectiveness and the reliability of the proposed model. Moreover, a case study of Ti-TiN multilayer coating deposited on Zr-based metallic glasses was considered. As a result, the new model is useful for multilayer coatings for different modulation periods and can be used for technological applications.

Investigation of Magnetic Properties of Multilayer Thin Films with Spin-Wave Resonance

A theory has been developed to simulate spin-wave resonance (SWR) modes in the multilayer systems consisting of alternate magnetic and nonmagnetic layers. An equation of motion of magnetization with Gilbert-type damping parameter for simulating SWR modes was used. It has been realized that the theory developed for the magnetic multilayer films is suitable to study the spin dynamics and extract various magnetic parameters. It has been shown that SWR modes strongly depend on an effective magnetic anisotropy constant (K eff), interlayer exchange coupling constant (A 12) and effective magnetization (M eff). The nature of the effective magnetic anisotropy and interlayer exchange coupling constants has been investigated by using the developed SWR theory in detail. The separation between optic and acoustic modes strongly depends on the magnitude of the interlayer exchange coupling constant, whereas the relative position of the acoustic and optic modes depends on the sign of $A_{12}$ . With increasing the interlayer exchange coupling constant, the resonance field of the optic mode decreases (increases) for ferromagnetic (antiferromagnetic) coupling. When the effective magnetic anisotropy constant increases, the resonance field of the acoustic and optic modes increases for both the ferromagnetic and antiferromagnetic couplings. The increasing of the effective magnetization results in decreasing of the resonance field of SWR mode at parallel geometry, whereas that of SWR mode increases at the perpendicular geometry. The results are compatible to the other theories and experimental results.

Improved performance of transparent-conducting AZO/Cu/AZO multilayer thin films by inserting a metal Ti layer for flexible electronics.

In order to improve the performance of transparent conductive Al-doped ZnO (AZO)/Cu/Al-doped ZnO multilayer thin films, multilayer thin films of titanium-embedded AZO/Cu/AZO structures have been designed and deposited onto flexible polycarbonate substrates to develop an indium-free transparent flexible electrode. The effect of Ti layer on the structural, optical, and electrical properties of multilayer thin films was investigated. The experiments reveal that the AZO/Ti/Cu/AZO fabricated in argon-oxygen mixtures has the best performance (commutation quality factor of 422.0): resistivity of 3.85×10-5 Ω·cm, sheet resistance of 4.31 Ω/sq, carrier concentration of 1.65×1022 cm-3, mobility of 9.87 cm2/Vs, and acceptable luminous transmittance of above 82% in the visible range.

Influence of Graphene Reduction and Polymer Cross-Linking on Improving the Interfacial Properties of Multilayer Thin Films.

Graphene is a versatile composite reinforcement candidate due to its strong mechanical, tunable electrical and optical properties, and chemical stability. However, one drawback is the weak interfacial bonding, which results in weak adhesion to substrates. This could be overcome by adding polymer layers to have stronger adherence to the substrate and between graphene sheets. These multilayer thin films were found to have lower resistance to lateral scratch forces when compared to other reinforcements such as polymer/clay nanocomposites. Two additional processing steps are suggested to improve the scratch resistance of these films: graphene reduction and polymer cross-linking. Graphene/polymer nanocomposites consisting of polyvinylamine (PVAm) and graphene oxide (GO) were fabricated using the layer-by-layer assembly (LbL) technique. The reduced elastic modulus and hardness of PVAm/GO films were measured using nanoindentation. Reducing GO enhances mechanical properties by 60-70% while polymer cross-linking maintains this enhancement. Both graphene reduction and polymer cross-linking show significant improvement to scratch resistance. Particularly, polymer cross-linking leads to films with higher elastic recovery, 50% lower adhesive and plowing friction coefficient, 140 and 50% higher adhesive and shear strength values, respectively, and lower material pileup and scratch width/depth.

Magnetic properties of single-layer and multilayer structured Co40Fe40B20 thin films

We report systematic investigations of thickness dependent magnetic properties of amorphous Co40Fe40B20 (x nm) single-layer films and effects of number of multilayers and thickness of spacer layer on the magnetic properties of multilayer structured [Co40Fe40B20 (y nm)/Ta (z nm)]n=1–3/Co40Fe40B20 (y nm) films prepared directly on thermally oxidized Si substrate using magnetron sputtering technique. All the as-deposited films at ambient temperature exhibit amorphous structure. For single-layer films, coercivity (HC) and field required for saturation (HS) increase gradually with increasing x from 10 to 30nm, but exhibit a rapid increase when x≥67nm. This behaviour was attributed to the change in the magnetic domain structure from in-plane magnetization to stripe domains caused by the development of effective magnetic anisotropy instigated by stress accumulated during the deposition. High temperature thermomagnetization data show the Curie temperature of Co40Fe40B20 (20nm) film as 512K. On the other hand, the introduction of thin Ta spacer layers in multilayer films helps reducing HC and HS substantially, but magnitude of the reduction depends strongly on the values of n and z. The increase of n diminishes the development of effective magnetic anisotropy in CoFeB film. This is due to the reduction in the thickness of the ferromagnetic layers, which changes the magnetic domain structure, and the optimum value of z enhancing interlayer coupling between CoFeB layers. Hence, the magnetic properties of the multilayer thin films are improved. The observed results are elucidated on the basis of change in the magnetic domain structure with increasing film thickness in single-layer films, and with increasing number of multilayers and spacer layer thickness dependent interlayer coupling in multilayer structured thin films.

Properties of nano-thick BaSnO3/Cu/BaSnO3 multilayer thin films: the role of substrate temperature

The nano-thick BaSnO3/Cu/BaSnO3 multilayer thin films have been designed and fabricated on glass by magnetron sputtering. The thickness of BaSnO3, Cu, and BaSnO3 layer in the multilayer thin films was set at 50, 10, and 50 nm, respectively. The structural, electrical, and optical properties of multilayer thin films were investigated with respect to the variation of substrate temperature. The average optical transmittance in the visible range of wavelengths (400–800 nm) shows an increase for the multilayer thin films grown at a temperature below 250 °C. A low resistivity (<10−4 Ω cm) for the multilayer thin films is found to be retained until 200 °C, followed by a quickly increase as the substrate temperature further increases to 300 °C. In addition, a mechanism for the variation of electrical and optical properties with the substrate temperature was proposed.

Preparation, Surface Morphology and Electrical Properties of Multilayer Antireflection Thin Films

In this study we have prepared different designs of thin films by physical vapour deposition with the help of MgF2 and YF3 materials of high and low refractive index on BK-7 glass substrate at 684 nm wavelength. To study the electrical properties, Silver electrodes have been coated between the top and bottom of different multilayer structures with the help of aluminum masking on the BK-7 glass substrate. The electrical and surface properties of multilayer thin films produced by PVD technique have been investigated. The surface morphology of Roughness (Ra) and grain size were systematically investigated by Atomic Force Microscope (AFM). The electrical conductivity at room temperature was obtained by using Four probe method. Electrical resistance is found to vary with the thickness of the layer thickness. In order to understand the composition and microstructures of the thin films were investigated systematically by SEM where the films have been grown on BK-7 glass substrate using PVD technique with the substrate temperature of 300K during the deposition process.

Thickness-Dependent Magnetocapacitance of Ni0.98Co0.02Fe2O4/BaTiO3/Ni0.98Co0.02Fe2O4 Trilayers

We report the fabrication of a multilayer magnetocapacitor from the highly magnetostrictive material Ni0.98Co0.02Fe2O4. To fabricate the magnetocapacitor, Ni0.98Co0.02Fe2O4/BaTiO3/Ni0.98Co0.02Fe2O4 sandwich-type multilayer thin films were deposited on Pt/TiO2/SiO2/Si(100) substrates by pulsed laser deposition. We studied the crystal structures, the surface and interface microstructures, and the magnetic and electric properties of multilayer thin films with different thickness of Ni0.98Co0.02Fe2O4 (20, 60, and 150 nm) and BaTiO3 (100, 300, and 1000 nm).

Plasmonics Properties of ZnO/Ag/ZnO Multilayer Thin Films

The optical properties of ZnO (Zinc Oxide)/Ag (silver)/ZnO (Zinc Oxide)/glass multilayer structure have been investigated. These properties could be tuned using the plasmonic properties of the intermediate Ag layer. ZnO thin film of 80 nm thickness has been deposited using Spray Pyrolysis on Glass Substrate. Prior to the deposition of approximately same thickness of ZnO like the previous one, a thin layer of Ag with thicknesses varying from 0.5 nm to 10 nm have been deposited using Vacuum Deposition. We have correlated the properties of multilayer thin film with thickness and morphology of the intermediate silver layer. Crystallographic properties of thin films have been characterized using XRD (X-ray Diffraction). Surface Morphology of Ag layer on ZnO has been studied using AFM (Atomic Force Microscopy). UV-VIS Spectrometer has been used to measure the optical transparency of these multilayer thin films. It has been observed that optical transparency of ZnO/Ag/ZnO/Glass thin film on glass substrate slightly enhanced compared to ZnO/ZnO/Glass. We interpret these experimental results with Maxwell-Garnett theory. The simulated and experimental SPR (Surface Plasmon Resonance) positions of ZnO/Ag/ZnO thin films are well matched. We expect that MG Theory interpretation of these kind Dielectric/Metal/Dielectric multilayer thin films were applicable only for Metallic Island thin films deposited using Vacuum coating method. We also describe the influence of Ag thickness on optical properties of the ZnO/Ag/ZnO composite and suggest a mechanism of tunability influenced by surface plasmons.