Thin-film Configuration Research Articles

Hybrid Ag-mesh/Ta-doped TiO2 thin film configuration as a visible and near-infrared transparent electrode

This study focuses on the fabrication of a hybrid Ag-mesh/Ta-doped TiO2 (TTO) electrode that has a low sheet resistance and high transparency in the visible and near-infrared region, thereby holding significant commercialization potential. Here, ∼82 nm thick TTO film is deposited on the glass substrate using radio frequency magnetron sputtering technique, over which Ag mesh is carved using the metal aerosol jet printing method. As compared to TTO, sheet resistance of the entire hybrid configuration is found to show a 2-3 order improvement, with the loss of a mere ∼12 % in the visible and ∼8 % in NIR transmittance. The electronic structure of the Ag/TTO interface demonstrates the formation of an ohmic junction, thereby making it suitable for the fabrication of a network-based transparent electrode. Moreover, the overall functionality and preparation route of this electrode makes it more promising as compared to those of the conventional metal mesh and metal-oxide electrodes.

Operando Stress Evolution in Hard Carbon Anodes – Insight into the Mechanical Degradation Induced Failure Mode in Rechargeable Sodium Ion Batteries

Microstructural instabilities in electrodes arising from cycling induced stress is a primary failure mode in rechargeable batteries. Therefore, a quantitative knowledge of the cycling induced stress evolution in rechargeable battery electrodes is important for understanding the electrode microstructural instabilities during cycling that can potentially inform the electrode design to prolong battery cycle life. The cycling induced stress in electrodes typically arises from the volume changes associated with insertion/extraction of the electroactive species in the electrode matrix. For example, operando measurement of lithiation-delithiation induced stress in graphite electrodes that typically show 10% volume change has previously resulted in useful information that correlates well with the lithiation-delithiation mechanism in graphite anodes1. The size of the shuttling-electroactive species can be taken as an indicator of the cycling induced stress magnitude that drives the electrode microstructural instabilities. In this regard, quantification of the cycling induced stress in rechargeable Na-ion battery electrodes is warranted for understanding mechanical degradation induced failure modes owing to the larger size of the electroactive species, i.e., Na ions (vs. Li-ion).Hard carbons as potential anodes in rechargeable sodium ion batteries has gained considerable attention in the recent past due to their superior Na-ion storage capability (vs. graphite that is a canonical anode in rechargeable lithium-ion batteries). However, hard carbon anodes typically show significant capacity fade that can potentially arise from cycling induced mechanical degradation of the anodes. Operando stress measurements coupled with comprehensive electrode microstructural characterization will provide valuable insights in this context. Here we report on the operando stress evolution in hard carbon anodes in rechargeable sodium ion batteries as probed by Multiple Optical-beam Sensing (MOS) technique that basically involves monitoring the spacings among a group of laser spot (Fig. 1). Preliminary measurements have shown that the stress correlates with the potential with a maximum around 12 MPa in compression during sodiation and tensile stress of ~ 2MPa during desodiation. Operando stress measurements are performed in hard carbon anodes in two different electrode configurations – typical composite anodes (with binder and conductive agents) and hard carbon thin film anodes (without binder and conductive agents). The thin film configuration is considered to evaluate intrinsic stress response in hard carbon anodes in absence of any secondary phase. A comparison of operando stress response in these two types of hard carbon anodes along with comprehensive electrode microstructural characterization will be presented. Additionally, attempts will be made to shed light on the current debate in the mechanism of sodium storage in hard carbon anodes by comparing operando stress response of hard carbons from multiple sources along with their structural characterization (Raman, XPS, surface area etc.). V. A. Sethuraman, N. Van Winkle, D. P. Abraham, A. F. Bower, and P. R. Guduru, Journal of Power Sources, 206, 334–342 (2012). Figure 1

Wrinkled metal-organic framework thin films with tunable Turing patterns for pliable integration.

Flexible integration spurs diverse applications in metal-organic frameworks (MOFs). However, current configurations suffer from the trade-off between MOF loadings and mechanical compliance. We report a wrinkled configuration of MOF thin films. We established an interfacial synthesis confined and controlled by a polymer topcoat and achieved multiple Turing motifs in the wrinkled thin films. These films have complete MOF surface coverage and exhibit strain tolerance up to 53.2%. The enhanced mechanical properties allow film transfer onto various substrates. We obtained membranes with large H2/CO2 selectivity (41.2) and high H2 permeance (8.46 × 103 gas permeation units), showcasing negligible defects after transfer. We also achieved soft humidity sensors on delicate electrodes by avoiding exposure to harsh MOF synthesis conditions. These results highlight the potential of wrinkled MOF thin films for plug-and-play integration.

P‐109: Investigation of Low Residual Stress Anti Reflection Coating with High Hardness for Display Applications

Anti reflection coating with high hardness on the OLED display surface was studied to improve the wear resistance and visibility of OLED. However, the high residual stress inside the multilayer thin film configuration of anti reflection coating has been a problem and the improvement is necessary. In this study, the residual stress and optical properties variation on various deposition conditions on the thin film were investigated. In addition, we suggested new coating structure using nanocomposites to overcome the residual stress of films.

Fabrication of Bi2Te3 and Sb2Te3 Thermoelectric Thin Films using Radio Frequency Magnetron Sputtering Technique.

Through various studies on thermoelectric (TE) materials, thin film configuration gives superior advantages over conventional bulk TEs, including adaptability to curved and flexible substrates. Several different thin film deposition methods have been explored, yet magnetron sputtering is still favorable due to its high deposition efficiency and scalability. Therefore, this study aims to fabricate a bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thin film via the radio frequency (RF) magnetron sputtering method. The thin films were deposited on soda lime glass substrates at ambient temperature. The substrates were first washed using water and soap, ultrasonically cleaned with methanol, acetone, ethanol, and deionized water for 10 min, dried with nitrogen gas and hot plate, and finally treated under UV ozone for 10 min to remove residues before the coating process. A sputter target of Bi2Te3 and Sb2Te3 with Argon gas was used, and pre-sputtering was done to clean the target's surface. Then, a few clean substrates were loaded into the sputtering chamber, and the chamber was vacuumed until the pressure reached 2 x 10-5 Torr. The thin films were deposited for 60 min with Argon flow of 4 sccm and RF power at 75 W and 30 W for Bi2Te3 and Sb2Te3, respectively. This method resulted in highly uniform n-type Bi2Te3 and p-type Sb2Te3 thin films.

Performance prediction of a novel solar power tower system based on spectral beam splitting

Photovoltaic technology is currently the most widely used solar generation technology in engineering. The particular spectral response band of PV cells cannot convert all solar radiation into electricity. Meanwhile, some radiation will become heat, leading to an increase in cell temperature and a decrease in the conversion efficiency of photovoltaic cells. Spectral splitting technology is an effective technology to improve electrical generation efficiency and can achieve full spectrum utilization of solar energy. The current work involved (1) proposing a novel solar power tower comprehensive utilization system based on spectral splitting; (2) developing a spectral splitting thin film configuration by using the Needle method whose transmittance is higher than 90% against the band range of 510 nm-1, 020 nm; (3) setting up a spectral splitting PV panel whose cover glass is coated the developed film, and replacing the heliostat of SPT system by using such spectral splitting PV panels; (4) predicting the electrical power generation of the spectral splitting-based tower type concentrating solar power system. The results demonstrate that the power generation efficiency of the proposed system is 5.5% and 3.46% higher than PV power generation and SPT systems respectively.

Investigating the dielectric and ferroelectric properties of (Bi4Ti3O12)0.4–(CaCu3Ti4O12)0.6 nanocomposite ceramics, thin films and thick films for microwave and microelectronic applications

The (Bi4Ti3O12)0.4–(CaCu3Ti4O12)0.6{(BTO)0.4–(CCTO)0.6} nanocomposite was fabricated in powder, thin film, and thick film configurations employing sol-gel, spin coating, and screen printing techniques. The weight loss observed in TGA and the presence of an exothermic peak in the DTA results confirm that 900°C is the optimal temperature for preparing a high-purity dual-phase composite. The XRD patterns and phase fraction analysis substantiate the formation of distinct orthorhombic structured BTO and cubic structured CCTO phases. FESEM images depict an irregular shape, dense microstructure with minimal pores, and a bimodal distribution. The EDAX results provide direct evidence of the formation of nanocomposites according to the stoichiometric ratio. The confirmation of good compatibility between both constituent phases is affirmed by the observation of vibration modes in the Raman spectra. The nanocomposite thin film demonstrates superior dielectric properties (with a dielectric constant of approximately 3534 and a lower dielectric loss of about 2.41), as well as optimal ferroelectric properties (including a remnant polarization of around 12.37 µC/cm2 and coercivity of approximately 0.95 kV/cm) compared to its powder and thick film counterparts. These observed characteristics of (BTO)0.4–(CCTO)0.6 nanocomposite materials strongly correlate with their practical suitability for use in technologically advanced microwave and microelectronic devices.

Performance study of a thin film cation exchange membrane on carbon electrode for supercapacitor application

In this work we report a green procedure for the infiltration of a SPEEK solution into a porous carbon electrode resulting in a thin-film cation exchange membrane. The electrodes have been investigated by a morphological point of view, showing the formation of a thin coating infiltrated into the porous carbonaceous matrix, while mechanical peeling of a tape demonstrated the adhesion of the proposed layer. The fabricated electrodes have been analyzed by electrochemical measurement. The 3-electrode cyclic voltammetry measurements allowed to verify the voltage window resulting in an improved negative potential, while the electrochemical impedance spectroscopy showed a reduction of the electrical resistance. The SPEEK electrode was used in a supercapacitor and deeply characterized by electrochemical analysis. The reported findings demonstrate for the first time the possibility to exploit a cation exchange material in thin film configuration for supercapacitor application with improved performance of the device and exclusively involving the use of nontoxic reagents.

Comparative Performance Evaluation of Transparent Conducting Oxides With Different Mobilities for All-Optical Switching in Silicon

All-optical switching is an appealing approach for signal processing, optical communications or sensing systems. In this work, we compare the performance of doped cadmium oxide, aluminum doped zinc oxide, and indium tin oxide as transparent conducting oxide (TCO) materials with different mobilities in thin-film configuration integrated into a hybrid silicon photonic waveguide. Our results reveal the best operational parameters and trade-offs for enabling high-performance and energy-efficient switching by using TCOs with moderate mobility but more environmental-friendly. Extinction ratios of 10 dB∙μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and insertion losses of 2 dB∙μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> are achieved by an AZO/Si amplitude switch with an energy consumption of only 90 fJ. These results reveal that cadmium-free TCO materials can also be leveraged to build high-performance all-optical switches in silicon.

Trilayered Block Copolymer Nanostructures Formed by an Iterative Layering Strategy

AbstractNanostructured block copolymer (BCP) thin films enable the formation on‐demand of a variety of periodic patterns at the nanometer scale by tuning the macromolecular BCP characteristics and annealing processes. Significant progress in the control of the self‐assembly has been witnessed over the past decade with the implementation of robust directed self‐assembly methods. However, the self‐assembled structural patterns obtained at equilibrium are limited and methods to expand the range of structural configurations are required to harness additional functionalities. Here, this work demonstrates how polystyrene‐b‐poly(methyl methacrylate) BCP thin layers can be stacked to produce a library of complex 3D hierarchical heterostructures. In this iterative assembly process based on simple building bricks (i.e., immobilized BCP patterns forming Holes, Lines and Dots), the stacking configuration (i.e., self‐assembly and registration) of a BCP thin film is directed with respect to the previous layer using confinement effects and interfacial energy tuning. This responsive layering can lead to intricate 3D Al2O3 structures and opens the way to a broad variety of structural designs toward functional applications.

Highly Efficient Switchable Underwater Adhesion in Channeled Hydrogel Networks

AbstractThe ability to switch adhesion strength is a highly desirable property for adhesives applied in a wet environment. The major challenges involve the presence of a water layer between the substrate and adhesive, and the incorporation of efficient switching mechanisms. Despite the recent progresses in devising such systems, there exist several intrinsic limitations in the current strategies, such as high residual adhesion, the use of solid–liquid transition, or thin film configurations. Herein, a channeled poly(N‐isopropylacrylamide) (PNIPAm) hydrogel containing bio‐inspired dopamine‐comonomers is reported, which undergoes temperature‐controlled reversible switching of underwater adhesion on both hydrophilic and hydrophobic surfaces. The introduction of microscopic channels inside the hydrogel, achieved by removing a sacrificial agarose network, greatly facilitates water removal from the interface and thus promotes underwater adhesive strength. On glass, the maximum adhesive stress of the channeled hydrogel can reach six times that of hydrogels without channels. Additionally, high switching efficiency and low residual adhesion can be achieved by the thermal phase transition of the PNIPAm network, also demonstrated by the capture and release of lightweight, irregular, fragile, and biological objects using the hydrogel. The channeling strategy provides implications for designing future underwater adhesive systems for, e.g., soft robotics or biomedical applications.

Investigation of inverse design of multilayer thin-films with conditional invertible neural networks

In this work, we apply conditional invertible neural networks (cINN) to inversely design multilayer thin-films given an optical target in order to overcome limitations of state-of-the-art optimization approaches. Usually, state-of-the-art algorithms depend on a set of carefully chosen initial thin-film parameters or employ neural networks which must be retrained for every new application. We aim to overcome those limitations by training the cINN to learn the loss landscape of all thin-film configurations within a training dataset. We show that cINNs can generate a stochastic ensemble of proposals for thin-film configurations that are reasonably close to the desired target depending only on random variables. By refining the proposed configurations further by a local optimization, we show that the generated thin-films reach the target with significantly greater precision than comparable state-of-the-art approaches. Furthermore, we tested the generative capabilities on samples which are outside of the training data distribution and found that the cINN was able to predict thin-films for out-of-distribution targets, too. The results suggest that in order to improve the generative design of thin-films, it is instructive to use established and new machine learning methods in conjunction in order to obtain the most favorable results.

Micromagnetic modeling of columnar thin films by ultra-dense arrays of nano-columns

We investigate the magnetostatic properties of nanostructured thin film through micromagnetic simulations using the NMAG modeling package. This work focuses on nanostructured columnar structures observed in the oblique growth of soft magnetic thin films which strongly modify the magnetic properties of the material. We report on how micromagnetic calculations give crucial information on the reversal mechanisms depending on the morphology of such a magnetic film. Micromagnetic simulations include periodic boundary conditions that are shown to be needed to describe correctly the magnetization configurations of nanostructured thin films.

Monitoring of the conductivity properties with respect to the development of geopolymer network

In this work, we focused on the chemical and (micro)structural changes that occur during curing at different temperatures of geopolymers (GP) prepared with a mullite-based precursor obtained by sol-gel synthesis. Several factors, such as the Si-to-Al ratio in the precursors and the curing temperatures, affect geopolymerisation. While potassium, sodium and even lithium are the most commonly studied cations, for this study, we examined geopolymers with sodium cations only. The H2O:Na2O ratio was set high at 22.80 to allow good workability of the paste having in mind the intended thin film application, i.e. the water-to-geopolymer binder ratio was set at 0.64. We performed extensive structural (diffraction and vibrational spectroscopy), morphological (electron microscopy) and electrical (impedance spectroscopy) characterisation, to facilitate an understanding of the conditions behind the optimal geopolymerisation. Particular attention was paid to the study of the evolution of the GP system as a function of curing temperature using solid-state magic angle spinning nuclear magnetic resonance. This allowed us to better understand the influence of the chemical composition of the constituents and their homogeneity, on the evolution of the organizational domains and electrical properties of the GP samples. We have explored the feasibility of moving from a relatively porous bulk to a thin film configuration, highlighting the applicability of geopolymers as constituents in photovoltaic facade systems.

Charge-transfer interface of insulating metal-organic frameworks with metallic conduction

Downsizing materials into hetero-structured thin film configurations is an important avenue to capture various interfacial phenomena. Metallic conduction at the interfaces of insulating transition metal oxides and organic molecules are notable examples, though, it remained elusive in the domain of coordination polymers including metal-organic frameworks (MOFs). MOFs are comprised of metal centers connected to organic linkers with an extended coordination geometry and potential void space. Poor orbitals overlap often makes these crystalline solids electrical insulators. Herein, we have fabricated hetero-structured thin film of a Mott and a band insulating MOFs via layer-by-layer method. Electrical transport measurements across the thin film evidenced an interfacial metallic conduction. The origin of such an unusual observation was understood by the first-principles density functional theory calculations; specifically, Bader charge analysis revealed significant accumulation and percolation of charge across the interface. We anticipate similar interfacial effects in other rationally designed hetero-structured thin films of MOFs.

Utilization of conventional PXRD apparatus for characterization of thin-films using reconsidered equations for XRR

Conventional powder X-ray diffraction (PXRD) device in Bragg-Brentano configuration was utilized to derive X-ray reflectivity (XRR) measurements of a thin-film without technical specifications provided by the supplier. XRR was reviewed as one of the methods for fast thin-film characterization on behalf of modified equations for quantification of thin-film parameters. We evaluated the feasibility of a conventional PXRD device for an acceptable description of thin-films using the equations for assessment of density, thickness and roughness, modified in manner to address incomplete angular data. We correlated approximations to relative errors. The PXRD-obtained thickness for the sample was 27 nm. The PXRD results were compared with the results obtained using methods that presume some knowledge on the thin-film composition. Ellipsometry considers the thin-film as 61 nm thick metallic-metallic oxide bilayer. Scanning electron microscopy (FESEM) pointed out to homogeneous Ni,Cr-based thin-film sample with a thickness of about 50 nm. Ambiguous FESEM results were corrected with atomic force microscopy (AFM), suggesting a monolayer thickness of 28 nm. Finally, synchrotron XRR allowed the best possible geometry and signal acquisition quality confirming the monolayer with thickness of 27 nm. In conclusion, we find the PXRD setup to be an equally precise method. However, the method shows limitations for complex multilayer thin-film configurations having similar refraction properties. The method can be recommended for thin-film characterization, however, it is not completely self-standing.

Investigation of a High-Pressure Turbine Stage in a High-Speed Rotating Transient Test Facility for Rotor Tip Study and a Parametric Study for Improved Heat Transfer Calculation

Abstract The first part of the paper presents commissioning of a single-stage high-pressure (HP) turbine employed in a series of extensive experiments to study the aerodynamics and heat transfer on the rotor surface and casing liner. The Oxford Turbine Research Facility (OTRF), a high-speed rotating transient test facility has the capability to take unsteady aerodynamic and heat transfer measurements at engine representative conditions with a variety of inlet temperature profiles including radial distortion and swirl. A temperature profile survey was conducted at the inlet of the HP nozzle guide vane (NGV). Static and total pressure and temperature measurements have been taken at various locations on the rig including NGV surface, inlet and exit, and rotor exit to establish rig operating conditions. Detailed description of mass flow rate measurements along with calculation of heat loss factor in the rig is presented. The second part of the paper presents a parametric study performed to improve heat transfer measurement calculations from high-frequency response thin-film gauges. The effect of parameters like material properties and thickness of substrate on heat flux has been studied. A detailed uncertainty analysis for heat flux is also presented. A thermal model calibrated with analytical solutions has been developed to optimize thin-film gauge configurations and to study side-conduction effects.

Plasmonic enhanced ultraviolet photodetection performance of n-TiO2/p-Si anisotype heterojunction with aluminum patterned array

The demand for efficient and power-saving photodetectors provides new opportunities for the rapid development of ultraviolet (UV) photodetectors. Thus, we designed and fabricated self-powered UV photodetectors using an n-TiO2/p-Si heterojunction and two different configurations of an Al-hexagonal plasmonic array. X-ray diffraction, high-resolution transmission electron microscope, and X-ray photoelectron spectroscopy analyses of the microstructural, compositional, and core level electronic characteristics of the TiO2 nanoparticles indicated their nanocrystalline structure with a valence band maximum at 3.29 eV. The optical absorption spectra obtained for the two alternative configurations of TiO2 thin films decorated with Al-arrays demonstrated their remarkable absorption properties. Decoration of the TiO2 film with Al-arrays at the top and bottom positions increased the absorption intensities at a wavelength of 280 nm by 344.5% and 414.9%, respectively. We also evaluated how the two distinct Al-array decorations affected the electrical characteristics of the fabricated virgin TiO2/p-Si heterojunction. The plasmonic enhanced device exhibited ideal diode behavior with a tunable barrier height and improved rectification ratio. In addition, self-biased evaluation of the photodetection performance of the three designed photodetectors indicated notable improvements in the figures of merit for the plasmonic decorated devices in terms of R (70.8 mA W−1), D* (3.86 × 1011 Jones), signal to noise ratio (16805), linear dynamic range (84.51 dB), external quantum efficiency (159.9%), and trise/tfall (50.2 ms/52.8 ms). Our results demonstrate the improved UV photodetection capacities of TiO2/p-Si heterojunctions decorated with hexagonal aluminum dot arrays.

Post-buckling evolution of compressed thin films adhered to rigid substrates

Compressing a thin film adhered to a substrate can yield delaminated blisters, if the interface adhesion is relatively weak. In this work, through the combination of theoretical modeling and numerical simulations, we investigate the mechanics governing the buckle-delamination and post-buckling evolution of compressed thin films adhered to rigid substrate, where the interface adhesion is attributed by van der Waals interactions. The deformed configurations of thin films can be categorized into five deformation modes depending on the material, geometric and interfacial parameters and the in-plane compressive strain. Through the energy-variational approach, large-deformation beam models are constructed to describe the deformed configurations and energy variations of the arc-shape and self-contact buckling modes. The phase diagrams related to the equilibrium buckling state are constructed by energy analysis, based on which the evolution of the post-buckling behavior is analyzed. Our results may find potential applications in the controlled compressive-buckling assembly of micro-/nano-scale thin films.

Improving Photoelectrochemical Activity of Magnetron-Sputtered Double-Layer Tungsten Trioxide Photoanodes by Irradiation with Intense Pulsed Ion Beams.

The photoelectrochemical (PEC) activity of metal oxide photoelectrodes for water-splitting applications can be boosted in several different ways. In this study, we showed that PEC activity can be significantly improved with a double-layer (crystalline-amorphous) configuration of WO3 thin films irradiated with intense pulsed ion beams (IPIB) of a nanosecond duration. It was found that IPIB irradiation promotes the formation of crystalline and sponge-like WO3 structures on the surface. Due to an increase in the active surface and light scattering in irradiated samples, photocurrent generation increased by ~80% at 1.23 reversible hydrogen electrodes (RHE).