Multilayer Thin Films Research Articles

Deposition Temperature Induced Texture and Strengthening of Ti/Ni Multilayer Thin Films

Abstract Strong thermal effect on microstructure and mechanical properties of Ti/Ni multilayer thin films was observed from in situ heating during deposition and subsequent annealing. Films deposited at low-temperature show preferred crystallographic texture for both Ti and Ni layers, with columnar structure extending through the layers. The columnar structure becomes more distinct and complete with the increase of temperature up to 300 °C, and meanwhile, more atomic diffusion and intermixing occur along the Ti/Ni interfaces, promoting the formation of Ti-Ni intermetallic precipitates. High-temperature deposition causes disintegration of the layered structure. Columnar Ti-Ni alloys and further recrystallized alloys were detected with the preferred crystallographic texture. For material strength, an increased hardness trend was observed with increasing deposition temperature even with much larger grain size compared to room temperature case. Furthermore, for multilayer systems deposited under low temperature, post-annealing resulted in higher hardness with minimal microstructure modification, with more strengthening observed in lower deposition temperature case.

Tuning Ionic Conductivity in Fluorite Gd-Doped CeO2-Bixbyite RE2O3 (RE = Y and Sm) Multilayer Thin Films by Controlling Interfacial Strain.

Interfacial strain in heteroepitaxial oxide thin films is a powerful tool for discovering properties and recognizing the potential of materials performance. Particularly, facilitating ion conduction by interfacial strain in oxide multilayer thin films has always been seen to be a highly promising route to this goal. However, the effect of interfacial strain on ion transport properties is still controversial due to the difficulty in deconvoluting the strain contribution from other interfacial phenomena, such as space charge effects. Here, we show that interfacial strain can effectively tune the ionic conductivity by successfully growing multilayer thin films composed of an ionic conductor Gd-doped CeO2 (GDC) and an insulator RE2O3 (RE = Y and Sm). In contrast to compressively strained GDC-Y2O3 multilayer films, tensile strained GDC-Sm2O3 multilayer films demonstrate the enhanced ionic conductivity of GDC, which is attributed to the increased concentration of oxygen vacancies. In addition, we demonstrate that increasing the number of interfaces has no impact on the further enhancement of the ionic conductivity in GDC-Sm2O3 multilayer films. Our findings demonstrate the unambiguous role of interfacial strain on ion conduction of oxides and provide insights into the rational design of fast ion conductors through interface engineering.

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).

Nondestructive initial-profile-free 3D elemental mapping inmultilayer thin film structures based onEDX anda quadratic programming problem.

We have demonstrated a new data analysis method that enables nondestructive depth profiling of a multilayer thin-film sample from energy-dispersive X-ray spectroscopy (EDX) data without the assumption of initial profiles. This method is based on a quadratic programming problem and allows for three-dimensional elemental mapping in the sample without destroying it, by performing depth profiling for all the pixels in the EDX two-dimensional mapping data. In this paper, first nondestructive depth profiling of two samples with different multilayer structures was performed using the proposed method. The results were compared with those obtained by cross-sectional observation to validate the accuracy and usefulness of the proposed method. Next, an example of the three-dimensional elemental mapping based on the proposed method was demonstrated. This method allows us to nondestructively obtain three-dimensional elemental distribution within a sample over a wide area on the order of mm, which is impossible to obtain using other analytical methods. The way to determine the hyperparameters, which significantly affects the calculation results, is fully described in this paper.

A novel selenization-free chalcopyrite CIGSSe formation in a heat-treated Cu2Se/S/Ga3Se2/S/In3Se2 multilayer thin film (ML) and ML/n-Si heterojunction characteristics

Selenization or sulphurization is a standard method for developing copper-selenium-based ternary to quinary compounds. The route proved effective, but there are concerns about the high-risk management and potential explosion if mishandled. This article discusses a selenization/sulphurization-free fabrication of a CIGSSe thin film structure. Instead of selenization, a Cu2Se/S/Ga3Se2/S/In3Se2 multilayer thin film structure is chosen, and a simple post-annealing in high vacuum is used. The x-ray diffraction analysis hinted at a composite structure in as-deposited and a phase pure dominant chalcopyrite structure in the annealed film. The bandgap of 1.71 eV with a high absorption coefficient of 104/cm with smaller Urbach energy of 59 meV supports the dominant microstructure of the annealed thin film. Room temperature hall measurements also ensured the charge carrier transformation of n-type to p-type during annealing with the carrier concentration of 1016/cm3. The Au/p-CIGS/n-Si/Au heterojunction is developed, and current-voltage measurements are investigated.

Annealing effects on Al/polyimide adhesion in flexible optical solar reflectors

Flexible optical solar reflectors are made of single and multi-layered metal thin films on polymer substrates and will encounter around 6000 thermal cycles exceeding +/-100°C during one year of operation in low earth orbit. The candidate thin film system of Inconel/silver (Ag)/Teflon (FEP) recently demonstrated early damage formation (cracks and voids) after only a few thermal cycles, most likely due to the poor interfacial properties between Ag and FEP. An alternative material system that could be used is colourless polyimide, Tormed, instead of FEP. Additionally, aluminium (Al) has demonstrated very good interfacial properties with polyimide even after thermal cycling and has suitable optical properties. The adhesion of the Al/Tormed and Ag/Tormed interfaces were evaluated with tensile induced delamination. Generally, Al/Tormed has a much higher interface adhesion energy compared to Ag/Tormed, and there is no significant degradation after bake-out in vacuum (200°C, 10-6 mbar) for 10 and 24 hrs. Thus, the Al/Tormed system could be a more robust coating system for future flexible solar reflectors.

Influence of zirconium and copper sub-layer in cell integrations on femtosecond laser-processed Ti thin films

The creation of novel biocompatible Ti-based thin films with a Zr or Cu sub-layer modified by ultrafast laser processing is studied. To prepare bioactive surfaces, ultrafast laser processing is focused on the formation of laser-induced periodic surface structures (LIPSS) with the production of oxide phases at the surfaces. Two differently designed multilayer thin films Ti/Cu/Ti and Ti/Zr/Ti were deposited on the silicon using the ion sputtering method. The Ti thin film contains Cu or Zr sub-layer (thickness of 10 nm) at the 10 nm below the surface. The composition and surface morphology variations for these systems, deposited and laser-processed under the same experimental conditions, were caused only by different thermo-physical properties of the sub-layer (Cu or Zr). The surface morphology in the form of LIPSS, led to improved cell adhesion and stable cells/thin films interface compared to as-deposited samples. Field-emission scanning electron microscopy and MTT analysis revealed that laser processing of both systems increased cell adhesion, proliferation, and metabolical activity of L929 mouse fibroblast cells compared to non-modified flat surfaces. Overall, the biocompatibility of Zr-containing thin films is better than Ti/Cu/Ti system. Further, laser processing and formation of LIPSS makes Ti/Zr/Ti thin films excellent candidate for biomedical .

Commercial optical coatings in space

The use of commercial optical coatings for space applications for the aptly named “New Space” missions is a state-of-the-art trend. These products are generally less costly and time-consuming in their production and therefore, there is a much wider range of optical coatings available compared to custom-made products. However, the reliability of commercial manufacturing processes is a key concern. Additionally, the resistance of commercial products against space environmental degradation mechanism at operating temperatures needs to be evaluated. In this study, seven commercial products with multi-layer thin film optical coatings consisting of filters, mirrors and windows have been selected from various manufacturers and the results with regards to process verification and space environmental exposure testing are presented. The impact of space environmental effects on the optical performance of the coatings is evaluated, with particular emphasis on the performance at cryogenic temperature. Finally, guidelines and precautions for use of commercial optical coatings for space applications.

Sidewall patterning of organic–inorganic multilayer thin film encapsulation by adhesion lithography

A simple sidewall patterning process for organic–inorganic multilayer thin-film encapsulation (TFE) has been proposed and demonstrated. An Al2O3 thin film grown by atomic layer deposition (ALD) was patterned by adhesion lithography using the difference in interfacial adhesion strength. The difference in interfacial adhesion strength was provided by the vapor-deposited fluoro-octyl-trichloro-silane self-assembled monolayer (SAM) patterns formed by a shadow mask. The sidewall patterning of multilayer TFE was shown possible by repeating the adhesion lithography and the vapor deposition of organic polymer and SAM patterns using shadow masks. The proposed process has the advantage of being able to pattern the blanket ALD-grown Al2O3 thin films by adhesion lithography using a SAM pattern that can be more accurately predefined with a shadow mask.

Antireflective properties of Al2O3/SiO2 multilayer stacks for GaAs solar cells.

Multilayer (ML) thin films are an optical engineering strategy to address reflectivity losses in GaAs photovoltaic devices, enhancing the power conversion of light around a single wavelength. Inspired by the enhanced response of periodic ML Bragg mirrors, the authors introduce quite simple antireflective designs based on two periods and single periods of A l 2 O 3/S i O 2 bilayer stacks. The reflectivity losses of the systems are evaluated with the aid of numerical simulations, and their dimensions are optimized to enhance the transmission of plane waves towards GaAs substrates. Reflectivity losses are evaluated at angles off the normal for s- and p-polarized light, exhibiting gains at broader angles and the quenching of undesired s-t o-p optical anisotropy, inherent to GaAs substrates. ML stacks were fabricated by RF sputtering deposition on G a A s-n and p+ type substrates and characterized by UV-Vis spectroscopy techniques to evaluate the role of carriers on coating performance.

Realizing an Optical Micro‐Cavity in a CuCo2O4‐W‐CuCo2O4 Thin Film Stack for Spectrally Selective Solar Absorbers

AbstractTapping the potential of solar thermal energy requires spectrally selective solar absorber coatings, which lead to high photothermal efficiency. Micro‐cavities are known to dramatically enhance or suppress light absorption and emission in a directional manner and are used in nanophotonics, photodetectors, lasing, etc. Here, a dielectric‐metal‐dielectric multilayer stack with an optical micro‐cavity of a 12 nm tungsten layer formed between two dielectric layers of transition metal oxide CuCo2O4 (CCO) is designed. The CCO‐W‐CCO thin film multilayers deposited on stainless steel substrate by DC‐radio frequency magnetron sputtering achieve a 90% solar absorptance for the entire solar spectrum and a thermal emittance of 19% for the infrared spectrum. Optimization of thicknesses of individual layers is achieved by numerical simulations done in COMSOL Multiphysics, thereby reproducing the optical properties of each layer. The simulation results satisfactorily reproduce the experimental reflectance and demonstrate maximum power dissipation in the metallic layer in visible as well as NIR regions. Nevertheless, CCO material characterizations reveal that the enhanced absorption over the entire solar spectrum could be attributed to the underlying spinel crystal structure and the nanostructure film morphology.

Probing of three-dimensional spin textures in multilayers by field dependent X-ray resonant magnetic scattering

In multilayers of magnetic thin films with perpendicular anisotropy, domain walls can take on hybrid configurations in the vertical direction which minimize the domain wall energy, with Néel walls in the top or bottom layers and Bloch walls in some central layers. These types of textures are theoretically predicted, but their observation has remained challenging until recently, with only a few techniques capable of realizing a three dimensional characterization of their magnetization distribution. Here we perform a field dependent X-ray resonant magnetic scattering measurements on magnetic multilayers exploiting circular dichroism contrast to investigate such structures. Using a combination of micromagnetic and X-ray resonant magnetic scattering simulations along with our experimental results, we characterize the three-dimensional magnetic texture of domain walls, notably the thickness resolved characterization of the size and position of the Bloch part in hybrid walls. We also take a step in advancing the resonant scattering methodology by using measurements performed off the multilayer Bragg angle in order to calibrate the effective absorption of the X-rays, and permitting a quantitative evaluation of the out of plane (z) structure of our samples. Beyond hybrid domain walls, this approach can be used to characterize other periodic chiral structures such as skyrmions, antiskyrmions or even magnetic bobbers or hopfions, in both static and dynamic experiments.

A high strength and flexible multilayered thin film laser induced graphene heater for thermal applications

Increasing demand for wearable sensors and heating elements has occurred recently. Herein, graphene has been observed as a biocompatible, cost effective, and multidimensional material catering to both sensing and heating applications. However, it still lacks essential features such as high temperature performance with low power usage, high strength, and robustness of thin films in tough environments such as heating elements in thermal socks. Hence, in this paper, we demonstrated laser induced graphene (LIG) as a suitable candidate for wearable thermal applications. LIG heaters were fabricated using a cost effective and environmentally friendly technique based on photothermal ablation of polyimide substrate using a 50 W CO2 laser. The heat flux of LIG heater was improved by stacking multiple films while their electrical connections are made in parallel. Upon joule heating, the heaters had excellent electrothermal performance, fast and stable response, achieving temperature of 195 °C using a relatively low DC voltage of 10 V. Most importantly, they showed good durability after bending, washing and repeated heating and cooling cycles. Due to these advantages, the LIG-based thin film heaters have potential as reliable and low-cost heating elements for variety of tough applications such as defrosting and wearable thermal pads.

Phase intensity nanoscope (PINE) opens long-time investigation windows of living matter

Fundamental to all living organisms and living soft matter are emergent processes in which the reorganization of individual constituents at the nanoscale drives group-level movements and shape changes at the macroscale over time. However, light-induced degradation of fluorophores, photobleaching, is a significant problem in extended bioimaging in life science. Here, we report opening a long-time investigation window by nonbleaching phase intensity nanoscope: PINE. We accomplish phase-intensity separation such that nanoprobe distributions are distinguished by an integrated phase-intensity multilayer thin film (polyvinyl alcohol/liquid crystal). We overcame a physical limit to resolve sub-10 nm cellular architectures, and achieve the first dynamic imaging of nanoscopic reorganization over 250 h using PINE. We discover nanoscopic rearrangements synchronized with the emergence of group-level movements and shape changes at the macroscale according to a set of interaction rules with importance in cellular and soft matter reorganization, self-organization, and pattern formation.

Novel Gas Phase Route Toward Patterned Deposition of Sputter‐Free Pt/Al Nanofoils

AbstractThis article reports a new approach toward fabrication and directed assembly of nanoparticulate reactive system (Nanofoils) on patterned substrates. Different from current state‐of‐the‐art, gas phase electrodeposition uses nanoparticles instead of atoms to form densely packed multilayered thin films at room temperature‐pressure. On ignition, the multilayer system undergoes an exothermic self‐propagating reaction. The numerous contact points between two metallic nanoparticulate layers aid in high heat release. Sub‐10‐nm Platinum (Pt) and Aluminum (Al) particles are synthesized through cathode erosion of metal electrodes in a flow of pure nitrogen gas (spark ablation). Pt/Al bilayer stacks with total thickness of 3–8 µm undergo self‐propagating reaction with a 10.3 mm s−1 wavefront velocity on local ignition. The reaction wavefront is captured using high speed videography. Calorimetry studies reveal two exothermic peaks suggesting Pt/Al alloy formation. The peak at 135 °C has a higher calorific value of 150 mW g−1 while the peak at 400 °C has a 12 mW g−1 exothermic peak. X‐ray diffraction study shows reaction‐products are cubic Al2Pt with small quantities of orthorhombic Al6Pt and orthorhombic AlPt2. Electron microscopy studies help draw a correlation between film morphology, bimetallic interface, nanoparticle oxidation, and self‐propagating reaction kinetics that is significant in broadening our understanding towards nanoparticulate reactive systems.

Investigation of Interfacial and Interdiffusion Study of Ti2N MXene Phase from TiN/Ti multilayers

Ti2N MXene phase was synthesized by interdiffusion of TiN/Ti multilayers by dc-magnetron sputtering at 698 K. The Atomic force microscopy (AFM) reveals the root mean square (RMS) roughness of the TiN/Ti multilayer was ∼4.78 nm of pristine samples which increased to ∼5.74 nm after annealing. The total thickness of (TiN10 nm/Ti10 nm), (TiN5 nm/Ti5 nm), and (TiN2.5 nm/Ti2.5 nm) multilayers was 200 nm as estimated by X-ray reflectivity (XRR). The secondary ion mass spectroscopy (SIMS) data reveals the diffusivity of N2 in the (TiN/Ti) multilayer is ∼10−18 m2s−1 at 698 K. The X-ray diffraction (XRD) planes of (112), (200), (220), (224) are at 36.95⁰, 42.89⁰, 62.25⁰, and 78.53⁰ 2θ values respectively confirming the Ti2N MXene phase and the X-ray photoelectron spectroscopy (XPS) confirmed Ti(2p) and N(1s) core orbitals are at 457.14 eV and 397.17 eV on the surface of TiN/Ti multilayer thin films. The X-ray absorption spectroscopy (XAS) of N and Ti L-edges were found at 404.51 eV, and 462.38 eV respectively which were shifted towards the right and left respectively after annealing indicating an increase and decrease in the oxidation state. Raman bands TA, LA, and TO were shifted towards higher wave numbers to 238, 337, and 634 cm−1 respectively for annealed TiN/Ti multilayer thin films.

Deep learning-based inverse design optimization of efficient multilayer thermal emitters in the near-infrared broad spectrum.

This study proposes a deep learning architecture for automatic modeling and optimization of multilayer thin film structures to address the need for specific spectral emitters and achieve rapid design of geometric parameters for an ideal spectral response. Multilayer film structures are ideal thermal emitter structures for thermophotovoltaic application systems because they combine the advantages of large area preparation and controllable costs. However, achieving good spectral response performance requires stacking more layers, which makes it more difficult to achieve fine spectral inverse design using forward calculation of the dimensional parameters of each layer of the structure. Deep learning is the main method for solving complex data-driven problems in artificial intelligence and provides an efficient solution for the inverse design of structural parameters for a target waveband. In this study, an eight-layer thin film structure composed of SiO2/Ti and SiO2/W is rapidly reverse engineered using a deep learning method to achieve a structural design with an emissivity better than 0.8 in the near-infrared band. Additionally, an eight-layer thin film structure composed of 3 × 3 cm SiO2/Ti is experimentally measured using magnetron sputtering, and the emissivity in the 1-4 µm band was better than 0.68. This research provides implications for the design and application of micro-nano structures, can be widely used in the fields of thermal imaging and thermal regulation, and will contribute to developing a new paradigm for optical nanophotonic structures with a fast target-oriented inverse design of structural parameters, such as required spectral emissivity, phase, and polarization.

Magnetic field driven magnetic domains and ferromagnetic resonances in multilayer thin films Ta/FeGaB/Ta for microwave application

Magnetic field driven magnetic domains and ferromagnetic resonances in multilayer thin films Ta/FeGaB/Ta for microwave application

Modeling of a novel chikungunya virus detector based on silicon and titanium nitride multilayer thin films

About 60 countries around the world have been found to have the chikungunya virus (ChV). It causes the human body to become fatigued and causes joint pain, muscular soreness, headaches, and joint swelling. As a result, the scientific community puts a lot of effort into creating reliable, quick, highly sensitive, and affordable methodologies for ChV detection. This study suggests a novel biosensor for the detection of ChV in components of blood including platelets and plasma that is using a binary photonic crystal (BiPC). The structure of the BiPC is (Si/ TiN)NP/SM/(Si/ TiN)NP, where NP = 5 is the number of unit cells and SM is the sensing medium. The proposed system has been examined via the transfer matrix approach (TMA), and the proposed sensor's operating principle is the defect mode shift. BiPC's reflectance spectra are displayed and investigated. The best incidence angle is 80°, and the desired defect layer thickness is 15(h1 +h2). In comparison to earlier published papers, a higher maximum sensitivity of 2306 and 2833 nm/RIU was found for platelets and plasma cells. Additionally, its straightforward design and nanoscale size make it a viable device for ChV detection.

Highly stable, ultra-thin Au embedded zinc tin oxide multilayer transparent conductive thin films

Transparent conducting thin films (TCFs) with excellent stability and good mechanical properties, room temperature processing, as well as owing high transparency and conductivity, have become an essential requirement in numerous applications. Here, we report the fabrication of room temperature processed Au-embedded zinc tin oxide (ZTO) multilayer transparent conducting thin films on glass and polycarbonate substrates by radio frequency magnetron sputtering. A detailed investigation on the correlation of optical and electrical properties of the ZTO/Au/ZTO (ZGZ) multilayer thin films, with the thickness of individual layers was carried out. The ZGZ thin films showed excellent performance under various stability tests. To evaluate the commercial application capabilities in aircraft canopies and other optoelectronic devices, the fabricated ZGZ multilayer TCFs was subjected to electromagnetic interference (EMI) shielding studies. The ZGZ thin film exhibited EMI shielding effectiveness of 24.75 dB in the X-band region, yielding 99.66% power attenuation.