Multilayer Thin Films Research Articles

Dissolution of Mg(OH)2 by swift heavy ion irradiation in CoFe2O4/MgO/ZnFe2O4 multilayer thin films

In-situ system for metallic multilayer thin films used for magnetic tunnel junction (MTJ) required a multi-target system to avoid the formation of impurities which make these devices very costly. In this work, the study was performed to resolve this issue by using a single target system for multilayer formation and impurity phases were dissolved by swift heavy ion (SHI) irradiation. A pristine MgO/Si(100) and CoFe2O4/MgO/ZnFe2O4/Si(100) (CFMZF) multilayer thin film were prepared via radio frequency (RF) sputtering technique. These structures were irradiated by 75 MeV oxygen-ion (O-ion) fluence (5x1011, 1x1012, and 5x1012 ions/cm2) and 200 MeV silver-ion (Ag-ion) fluence (1x1012 ions/cm2) for the investigation of structural changes. The high-resolution X-ray diffraction (HRXRD) reveals that MgO and CFMZF thin films have impurity peaks, dissolved via O-ion and Ag-ion irradiation. Further HRXRD analysis confirmed that Ag-ion irradiation dissolves more peaks leaving one small intensity peak of (400) corresponding to MgO. The multilayer stack of CFMZF irradiated via Ag-ion shows that Mg(OH)2 phase were completely dissolved and appears only (311) less intense peak corresponding to the ferrite structure. The findings are also corroborated by cross-sectional field emission scanning electron microscopy of CFMZF multilayer thin film showing damaged layers with Ag-ion irradiation. Therefore, the SHI irradiation technique can be used to dissolve the impurity peaks and improve the interface of the multilayer stacks.

Environmentally Sustainable and Multifunctional Chrome-like Coatings Having No Chromium Designed with Reinforcement Learning.

Decorative chrome plating (DCP) continues to be ubiquitous in creating highly appealing metal finishings and coatings, beating out other organic dye-based finishes. However, the hazardous chrome plating process is fraught with adverse health effects for the workers involved and causes significant environmental damage. In this work, we present a multilayer thin film structure to mimic the chrome appearance. To find a design efficiently, we employ a reinforcement learning (RL) algorithm to perform an automatic inverse design. This results in structures composed of environmentally friendly materials that not only have the chrome color but can also achieve additional functions beyond decoration. As an example, one structure is designed to have high transmission in the radio frequency regime, a property that general metals cannot have, which can broaden the decorative chrome applications to include microwave operating devices. The experimental structures are fabricated by physical vapor deposition to demonstrate the indistinguishable chrome color and validate the effectiveness of the RL inverse design approach.

Resonant dynamics of three-dimensional skyrmionic textures in thin film multilayers

Skyrmions are topological magnetic solitons that exhibit a rich variety of dynamics, such as breathing and gyration, which can involve collective behavior in arrangements like skyrmion lattices. However, such localized excitations typically lie in the gap of the spin wave spectrum and do not couple to propagating modes. By combining magnetic force microscopy, broadband ferromagnetic resonance, and micromagnetics simulations, we show that in thin-film multilayers of [Pt/FeCoB/AlOx]20 a high-frequency (>12 GHz) mode accompanies the skyrmion lattice phase, which involves the coherent precession of the skyrmion cores that results in the generation of 50–80 nm wavelength spin waves flowing into the uniformly magnetized background. This observation is made possible by a Gilbert damping constant of ∼0.02, which is nearly an order of magnitude lower than in similar ultrathin materials. The simulations also reveal a complex three-dimensional spin structure of the skyrmion cores, which plays a key role for spin wave generation.

Deposition of Nanocrystalline Multilayer Graphene Using Pulsed Laser Deposition

The wide application of graphene in the industry requires the direct growth of graphene films on silicon substrates. In this study, we found a possible technique to meet the requirement above. Multilayer graphene thin films (MLG) were grown without a catalyst on Si/SiO2 using pulsed laser deposition (PLD). It was found that the minimum number of laser pulses required to produce fully covered (uninterrupted) samples is 500. This number of laser pulses resulted in samples that contain ~5 layers of graphene. The number of layers was not affected by the laser fluence and the sample cooling rate after the deposition. However, the increase in the laser fluence from 0.9 J/cm2 to 1.5 J/cm2 resulted in a 2.5-fold reduction in the MLG resistance. The present study reveals that the PLD method is suitable to produce nanocrystalline multilayer graphene with electrical conductivity of the same magnitude as commercial CVD graphene samples.

Transient guided-mode resonance metasurfaces with phase-transition materials.

We investigate transient, photo-thermally induced metasurface effects in a planar thin-film multilayer based on a phase-transition material. Illumination of a properly designed multilayer with two obliquely incident and phase-coherent pulsed pumps induces a transient and reversible temperature pattern in the phase-transition layer. The deep periodic modulation of the refractive index, caused by the interfering pumps, produces a transient Fano-like spectral feature associated with a guided-mode resonance. A coupled opto-thermal model is employed to analyze the temporal dynamics of the transient metasurface and to evaluate its speed and modulation capabilities. Using near-infrared pump pulses with peak intensities of the order of 100 MW/cm2 and duration of a few picoseconds, we find that the characteristic time scale of the transient metasurface is of the order of nanoseconds. Our results indicate that inducing transient metasurface effects in films of phase-transition materials can lead to new opportunities for dynamic control of quality (Q)-factor in photonic resonances, and for light modulation and switching.

Highly transparent multilayer organic thin film for effective antistatic and electromagnetic interference shielding applications

Highly transparent multilayer organic thin film for effective antistatic and electromagnetic interference shielding applications

Effect of Multilayers CdS Nanocrystalline Thin Films on the Performance of Dye-Sensitized Solar Cells

Due to relatively low price and nontoxicity of photovoltaic (PV) systems, dye-sensitized solar cells (DSSCs) recently gained a lot of attention in terms of improving their performance and longevity. Because most of the major elements are impacted by their separate production and layering procedures, the substances in DSSCs are critical to achieving these goals. Methylene blue dye sensitizer-based solar cells were effectively constructed in this work, and DSSC performance was assessed. The morphologies of nanocrystalline CdS thin films were investigated by the FE-SEM machine, and then XRD patterns of 1 layer, 2 layers, and 3 layers of nanocrystalline CdS thin films were analyzed. The thicknesses of the prepared samples were about 391 nm, 457 nm, and 912 nm for 1, 2, and 3 layers of nanocrystalline CdS thin film, respectively. J-V characteristics of the multilayer CdS thin films have been studied under a 100 mW/cm2 sunlight source. The experimental results revealed that the highest power conversion efficiency of a 3 layer porous-nanowall CdS/MB device was about 0.47%.

Interfacial reaction and phase formation in Pd/ZrO/Pd/TiO/Pd multilayer stack on silicon substrate: Investigated by ion beam techniques

The influence of the annealing temperature on the stability of the multilayer stack Pd/Zr/Pd/Ti/Pd thin films system, with both Zirconium (Zr) and Titanium (Ti) layers containing oxygen (O), deposited on silicon substrate was investigated. Using the in-situ real-time Rutherford backscattering spectrometry (RBS) analysis, the multilayer stacked thin film systems were linearly heated, at a constant heating rate, from room temperature up to 600 °C and found to be stable up to ∼370 °C whereby the inter-diffusion of Palladium (Pd), from both the third and the fifth layer, towards the forth layer comprising of Ti and O in 2:1 ratio, was observed. Moreover, the Ti, from the Ti–O layer, was found to spread to low and higher channels during Pd diffusion. Above 480 °C the second reaction was observed between Pd and silicon substrate, forming a hexagon silicide phase (Pd2Si) confirmed by X-ray diffraction. The thickness of the Pd2Si layer increased with increasing temperature and its activation energy was estimated to be 2.30 eV, which is about 1.10 eV and 0.65 eV higher than the activation energy of the Pd2Si phase formation at 100 °C and 250 °C, respectively. Therefore, the activation energy of the Pd2Si phase depends on the temperature at which the phase is growing.

Effect of oxygen flow rate on properties of multilayer aluminum-doped indium saving ITO thin films produced by sputtering method

Multilayer aluminum-doped indium saving indium-tin oxide (ITO) thin films with low volume resistivity and high transmittance in the visible spectrum have been designed and fabricated by sputtering method. Double-layered structures consisting of very thin layer of conventional indium tin oxide (In2O3-10 mass % SnO2) and aluminum-doped indium saving indium-tin oxide layer with reduced to 50 mass % In2O3 content are discussed. Multilayer aluminum-doped ITO were deposited on glass substrates preheated at 523 K. Thin films deposited in pure argon demonstrate volume resistivity of 445 µΩcm, mobility of 26 cm2/V·s, carrier concentration of 5.6 × 1020 cm−3 and average transmittance larger than 85% in the visible range. Introducing oxygen to sputtering gas allowed increasing average transmittance of as-deposited multilayer aluminum-doped indium saving ITO thin films over 90% in the visible range. As-deposited multilayer aluminum-doped ITO thin films showed significantly higher transmittance in comparison with undoped ML ITO50/ITO90 and crystallized in In4Sn3O12 structure.

Ion migration in GaSb/Mn multilayers for memories applications: Study of Mn diffusion into the GaSb layers

This work presents a study of bilayer and multilayer systems of GaSb/Mn, obtained via DC magnetron sputtering at room temperature for memories applications. These architectures were observed through HR-SEM, which determined that the GaSb and Mn layers had an average thickness of 186,01±5,582 nm and 10,71±0,323 nm, respectively. Through the deconvolution of AES spectra, it was possible to identify the chemical element concentration profiles for each system and propose a model of diffusion layers. The GaSb/Mn systems were analyzed in two cases; in the cases of Mn deposited on the surface of GaSb wafer and bilayer systems, the Mn diffusion process was studied by the conventional Fick’s second law, considering the Mn layer as a constant source, and the Mn diffusion coefficient values correspond to 1,6×10−15cm2/s and 5,8×10−15cm2/s, respectively. The superposition of Fick´s second law solutions in each section of the multilayer architecture was used to describe the experimental concentration profile. Through, the model proposed to calculate the different diffusion coefficients of Mn layers, the description of the diffusion process in the bilayer and multilayer systems and their correlation with synthesis parameters, such as deposition time, has been satisfactory. In the multilayer architecture case, the Mn diffusion coefficients have been reported, considering the Mn layer position, and their values corresponding are 1,105×10−14cm2/s and 6,5×10−15cm2/s for Mn inner and middle layer respectively. Finally, the resistive behavior of the multilayers was studied through I-V curves. It was possible to establish the bipolar resistive behavior of the multilayer and contribution to the formation of conductive filaments or the space charge limited current like conductive mechanism of the multilayer thin films.

The influence of defects on hydrogen sorption from Mg–V thin films

In this paper hydrogen sorption properties of Mg–V multilayer thin films are studied. Thin films are synthesized by means of RF magnetron sputtering. Further modification of material is done using low energy H ion irradiation. The hydrogen sorption properties and kinetics are assessed using TOF-ERDA, in situ optical microscopy coupled with TDS, and TEM analysis. The results of TOF-ERDA indicate full hydrogenation of samples, although the presence of oxygen throughout the film is observed. It corresponds to the formation of MgO, also confirmed by EELS results with hydride plasmon peak hindered by MgO peak. Hydrogenation causes severe damage to the surface of the film and fragmentation of the V layer. TDS and optical analysis indicate lower desorption temperatures for thinner films. The desorption onset does not depend on defects concentration. The kinetic analysis further shows that the apparent activation energy for the thinner film is two times lower.

Giant Magnetoimpedance Effect of Multilayered Thin Film Meanders Formed on Flexible Substrates.

The giant magnetoimpedance effect of multilayered thin films under stress has great application prospects in magnetic sensing, but related studies are rarely reported. Therefore, the giant magnetoimpedance effects in multilayered thin film meanders under different stresses were thoroughly investigated. Firstly, multilayered FeNi/Cu/FeNi thin film meanders with the same thickness were manufactured on polyimide (PI) and polyester (PET) substrates by DC magnetron sputtering and MEMS technology. The characterization of meanders was analyzed by SEM, AFM, XRD, and VSM. The results show that multilayered thin film meanders on flexible substrates also have the advantages of good density, high crystallinity, and excellent soft magnetic properties. Then, we observed the giant magnetoimpedance effect under tensile and compressive stresses. The results show that the application of longitudinal compressive stress increases the transverse anisotropy and enhances the GMI effect of multilayered thin film meanders, while the application of longitudinal tensile stress yields the opposite result. The results provide novel solutions for the fabrication of more stable and flexible giant magnetoimpedance sensors, as well as for the development of stress sensors.

Nanosecond pulsed laser annealing of Cu/Ag/AZO multilayer thin films for performance improvement and transparent heater application

Nanosecond pulsed laser annealing was performed to improve optical and electrical properties of the Cu/Ag/AZO multilayer films. Different laser fluences (L) and scanning speeds (S) were selected to investigate their influences on optical transparency and electrical conductivity of the films. The results revealed that laser annealing under L = 1.0 J/cm2 and S = 10 mm/s effectively promoted grain growth in the film and caused formation of significantly enlarged particles with a more uniform distribution on the film surface. The as-obtained Cu/Ag/AZO multilayer film possessed the optimal comprehensive property with the highest figure of merit of 3.58 × 10–2 Ω−1, far outperforming the unannealed Cu/Ag/AZO multilayer film (1.92 × 10–2 Ω−1). Subsequently, this film was chosen to fabricate a transparent heater, which exhibited excellent heating performance (saturated temperature: 104.9 ℃; response time: 120 s; applied voltage: 5 V) and heating stability. Its deicing availability was also shown by a deicing test.

Improvement of Saturation Magnetization of Sputtered Fe/Al Multilayer Thin Films Using Taguchi Method Supported by ANOVA, Response Surface Methodology and Regression Analysis

Improvement of Saturation Magnetization of Sputtered Fe/Al Multilayer Thin Films Using Taguchi Method Supported by ANOVA, Response Surface Methodology and Regression Analysis

Optical modelling of TCO based FTO/TiO2 multilayer thin films and simulation in hydrogenated amorphous silicon solar cell

Hydrogenated Amorphous silicon (a:Si:H) has low amounts of defects making it attractive for photovoltaic applications. To improve power conversion efficiency (PCE) of a:Si:H solar cells, this study investigated the effect of introducing FTO/TiO2 multilayer thin films into its structure to serve as antireflection coating. The multilayer thin films were characterized and optimized by optical simulations using a computer program, GLSIM (glazing simulator). The program was written in FORTRAN and implemented in MATLAB. The multi-Fresnel equations were employed to create the GLSIM program. Then using the program, together with the pairs of real and imaginary values of complex refractive index, n and k respectively, the transmittance and reflectance data of FTO/TiO2 multilayer thin films on glass substrate were computed. The optimized FTO/TiO2 multilayer thin films were then incorporated into silicon solar cell with structure glass/FTO/TiO2/n-a-Si:H/i-a-Si:H/p-a:Si:H/P+-BSF and characterized using SCAPS-1D software. The effect of varying layer thickness on the solar cell performance was also investigated. The optimized solar cell had a thickness of 100 nm, 50 nm, 900 nm, 100 nm, 10μm and 5μm for FTO, TiO2, n-a-Si:H, i-a-Si:H, p-a-Si:H and P+-BSF respectively. The device output performance were 37.96 mA/cm2, 1.34 V, 56.37% and 28.72% for Jsc, Voc, FF and η respectively showing a remarkable improvement in the solar cell performance. These results show potential of fabricating an improved hydrogenated silicon solar cell.

Primary and Secondary Reflective Color Realized by Full‐Solution‐Processed Multi‐Layer Structures

AbstractA full solution‐based method is reported to fabricate multilayer thin film stacks for structural color applications. This is in contrast to the conventional fabrication methods that require high vacuum processes such as physical vapor deposition and magnetron sputtering, which significantly limits their practical use due to the high cost and long processing time. Copper/silicon dioxide/copper (Cu/SiO2/Cu) and copper/titanium dioxide/copper (Cu/TiO2/Cu) are chosen as the model system due to their simple structure and wide color tunability. A systematic investigation is carried out for each layer to ensure good film quality as well as its compatibility with all previous layers. Especially, a particulate Cu layer having optical properties distinct from that of bulk is obtained through such solution deposition, where the refractive index of Cu can be continuously tuned with deposition time. Both primary and secondary colors are achieved with a continuous manipulation of both the dielectric thickness and top Cu morphology on different substrates (e.g., silicon, glass, plastics, etc.).

Thermoluminescence properties of TiO2/Cu/TiO2 multilayer thin films fabricated by (RF/DC) sputtering for radiation dosimetry

The most popular TLDs are composed of phosphors, ceramics, and crystals. Despite having a high light output per unit of absorbed dose, they suffer from rapid signal fading, light scattering, saturation at higher doses, and difficulties annealing for re-use. Here, we report the characteristics of a novel TiO2/Cu/TiO2 multilayer thin film dosimeter fabricated using radio-frequency (RF) and direct current (DC) sputtering methods with a faster deposition rate, high purity, and uniformity. The multilayer sequence was set to TiO2 (150 nm)/Cu (x)/TiO2 (50 nm), at varying Cu thicknesses (x = 5, 10, 25, 40, and 50 nm). The structure, morphology, elemental composition, and optical properties of the films were characterized by the XRD, FESEM, EDX, and UV–Vis, respectively. Next, the best TiO2 multilayer films with 5 nm Cu were tested for morphological, structural, and optical properties at 600 and 1200 mGy of x-ray radiation. The dosimetric properties of samples irradiated with X-ray doses ranging from 100 to 1500 mGy were then investigated. The best annealing time, reproducibility, fading, low minimum detectable dose as well as the effect of different heating rates on the TL glow curve have all been studied. Our results indicate that the films are amorphous, porous with spherically shaped nanoparticles, have a uniform distribution of elements, and are transparent in the visible region. The optimum TL intensity was found at TiO2 (445 nm)/14.2 nm Cu/TiO2 (130 nm) sequence. The dose-response has a good linear correlation to x-ray radiation with a sensitivity that is 0.444 times less than that of TLD-100 sensitivity within the dose range 100–1500 mGy. Upon irradiation, the band gap decreases, crystallinity increases, pores increase, films become rougher, and the absorption band edge extends to higher wavelengths. The single and multilayer TiO2 films have high-intensity peaks at 270 and 274 ∘C, respectively, which is typical of TL glow curve peaks used in TLD applications. There were no significant changes in the TL reading after six times of reuse, and the fading was observed at 49.57% after 15 days of irradiation. The findings indicate that TiO2/Cu/TiO2 multilayer films are appropriate for thermoluminescence dosimetric applications.

Nanostructured multilayer CAE-PVD coatings based on transition metal nitrides on Ti6Al4V alloy for biomedical applications

Titanium alloys possess poor resistance to friction and this adversely affects the corrosion behavior and osseointegration of the implants made from these alloys. Nanostructured PVD coatings with biocompatibility, anti-wear and anti-corrosion characteristics have attracted much attention in biomedical applications. In this study, TiN and ZrN single layer and CrN/TiN and CrN/ZrN nanostructured multilayer thin films were applied on a Ti6Al4V substrate by means of cathodic arc PVD technique. The physical-chemical characterization of the coatings was conducted using FE-SEM, EDS, and XRD analyses. Their surface topography and wettability were measured. In addition, the hardness and adhesion strength were evaluated by means of Knoop microhardness and scratch tests, respectively. Also, the apatite-forming ability of the coatings was investigated through SEM, EDS and, FTIR. The corrosion performance of the coatings was studied using PDP and EIS assessments in SBF solution. According to the findings, the multilayer coatings have higher hardness and scratch resistance than single layers. The coating delamination tacked place in Lc equal 39.6 (N) and 39.3 (N) for CrN/TiN and CrN/ZrN coatings, respectively. The corrosion assessments revealed that the CrN/ZrN multilayer coating exhibited the best corrosion resistance due to its smoother surface and more dense structure in addition to its specific architecture. The ZrN single layer and CrN/ZrN multilayer coatings showed a better hydroxyapatite precipitation; however, all surfaces had satisfactory bioactivity. In all, this study showed that CrN/ZrN nanostructured multilayer thin film is potentially suitable candidate for orthopedic and dental implants.

Mechanical behaviors of high-strength fabric composite membrane designed for cardiac valve prosthesis replacement

Bovine pericardium has been commonly used as leaflets in cardiac valve prosthesis replacement for decades because of its good short-term hemocompatibility and hemodynamic performance. However, fatigue, abrasion, permanent deformation, calcification, and many other failure modes have been reported as well. The degradation of the performance will have a serious impact on the function of valve prostheses, posing a risk to the patient's health. This study aimed to introduce a flexible fabric composite with better mechanical performance such that it can be employed as a substitute material for bioprosthetic valve leaflets. This composite has a multilayered thin film structure made of ultrahigh molecular weight polyethylene (UHMWPE) fabric and thermoplastic polyurethane (TPU) membranes. The mechanical properties of three specifications with different design parameters were tested. The tensile strength, shear behavior, tear resistance, and bending stiffness of the composites were characterized and compared to those of bovine pericardium. A constitutive model was also established to describe the composites' mechanical behaviors and predict their strength. According to the results of the tests, the composite could maintain a flexible bending stiffness with high in-plane tensile strength and tear strength. Therefore, bioprosthetic valve made of this substitute material can withstand harsher loads in the blood flow environment than those made of bovine pericardium. Moreover, all these test results and constitutive models can be used in future research to evaluate hemodynamic performance and clinical applications of fabric composite valve prostheses.

Influence of Repeated Bending Loading on the Residual Stresses in Multilayer Coating Materials

The technology of multilayer thin films to improve performance is widely used in the fields of semiconductors and functional composite materials. However, each layer of the multilayer film generates a residual stress during deposition due to differences in Young's modulus and coefficient of thermal expansion. In addition, the residual stress of the coating material is significantly affected by the mechanical load during use. In this study, the coated materials with deposited multilayer thin films were subjected to repeated bending loads, and the effects on the residual stresses in the thin films and substrates were investigated. Carbon steel (JIS: S45C) was used as the substrate material for the specimens. The thin films were deposited by sputtering. Three kinds of specimens were used, in which Cu, TiN and SiO2 films were deposited as a single Cu layer, a Cu/TiN double layer and a SiO2/Cu/TiN multilayer. The residual stress values of the Cu layer within the thin films were evaluated by X-ray stress measurement method using 311 and 222 diffractions of Cu. As a result, the tensile residual stress values in the Cu layers within each thin film were approximately 60~70 MPa for the single layer and 110~120 MPa for the double and multi-layer films. The residual stress values in the substrate, carbon steel, were evaluated using 211 diffractions of α-Fe. As a result, a tensile residual stress of about 30 MPa is existed. When all the coated materials were subjected to repeated bending loads, the change in the residual stress values of Cu layer showed that the residual stresses relaxed rapidly after several cycles of repeated loading and saturated to a value of about 30 MPa after 100 cycles. On the other hand, the residual stress evaluation by 222 diffractions of Cu showed that for all coated materials the residual stress values increased and decreased repeatedly with increasing number of repeated loadings. For the carbon steel substrate, the residual stress values hardly changed due to repeated loading.