Non-uniform Film Research Articles

Electrochemical corrosion behavior and passive film properties of Fe2Ni2CrV0.5Nbx (x=0.2, 0.4, 0.6, 0.8) eutectic high-entropy alloy coating prepared by laser cladding

The phase composition, microstructure morphology, and corrosion behavior of Fe2Ni2CrV0.5Nbx (x=0.2, 0.4, 0.6, 0.8) eutectic high-entropy alloy (EHEA) coatings produced via laser cladding were investigated. The research delved into discerning the phase structures and microstructural variations of the EHEA coatings concerning differing Nb compositions. The findings highlighted a direct correlation between Nb content and the volume fraction of the eutectic structure, specifically the FCC/Laves phases. Electrochemical evaluations, including diverse tests such as potentiodynamic polarization, electrochemical impedance spectroscopy, cyclic polarization, Mott-Schottky measurements, and X-ray photoelectron spectroscopy, revealed distinct corrosion behaviors among the EHEA variants. Notably, the Fe2Ni2CrV0.5Nb0.2 coating exhibited relatively superior corrosion resistance compared with Fe2Ni2CrV0.5Nbx (x=0.4,0.6,0.8) coatings, attributed to its lower corrosion current density (Icorr) and the formation of a thicker passive film with prolonged passivation duration. Conversely, the Fe2Ni2CrV0.5Nb0.8 coating, characterized by increased eutectic structures and grain boundary density, yielded a thicker yet non-uniform passive film with higher vacancy defects. This comprehensive exploration into the corrosion behavior and passive film properties of these EHEA coatings provides a reference for designing materials that hold promising implications for future corrosion-resistant material development in industrial parts repair applications.

CeCl3 concentration effects on cyclic voltammogram overlap in LiCl-KCl eutectic molten salt

In the present study, cyclic voltammetry was performed to investigate CeCl3 in a LiCl-KCl eutectic molten salt at various concentrations. The results indicate that the overlap degree of cyclic voltammograms at different cycles deteriorates with the increasing CeCl3 concentration in the molten salt. This phenomenon was attributed to higher concentrations of CeCl3, which led to a non-uniform film on the electrode surface. This was evidenced by material characterization of the working electrode after cyclic voltammetry (CV) testing and the simulated cyclic voltammograms of a reversible electrochemical reaction. This study will provide new insights that enhance our understanding of the electrochemistry of the CeCl3-LiCl-KCl system and offer valuable reference for other soluble-insoluble electrochemical systems.

Enhancing phase and morphology control of vanadium oxide films for resistive memory applications: A water-assisted chemical approach

This study explores the influence of precursor solution composition and solvent selection on the synthesis of vanadium oxide (VO2) thin films tailored for resistive memory applications. The vanadium pentoxide and oxalic acid molar ratio and the dispersing medium (ethanol, water, and their mixture) were varied. Water content significantly influenced the VO2 phase, morphology, and film thickness. Ethanol yielded mixed vanadium oxide phases VO2 − Tetragonal, V2O5 − Orthorhombic, and Monoclinic) and a film with minor imperfections. Conversely, the active layer prepared using an aqueous medium showed a predominant VO2 − Monoclinic phase, albeit with a non-uniform film. An ethanol–water mixture produced the most uniform morphology and a mixture of vanadium oxide phases (VO2 − Tetragonal, V2O5- Orthorhombic). All devices displayed resistive switching behavior. VO2-containing devices exhibited a more pronounced transition from an ohmic conduction state to a space-charge-limited conduction mechanism. ON-state currents remained consistent, while OFF-state currents varied notably.

Minute‐Scale High‐Temperature Synthesis of Polymeric Carbon Nitride Photoanodes

Polymeric carbon nitride (CN) has emerged as a promising photoanodic material in water‐splitting photoelectrochemical cells (PEC). However, the current deposition methods of CN layers on substrates usually include a long heating process at 500−550 °C, which might cause sublimation or decomposition of the CN monomers and destruction of the substrate, leading to a nonuniform CN film. Herein, a simple, fast, and scalable energy‐economic procedure to synthesize homogenous CN films is introduced. The predesigned CN monomers film is subjected for several minutes to higher temperatures than the standard calcination procedure. The short heating process allows the formation of a uniform CN layer, with excellent contact with the substrate and good activity as a photoanode in PEC. The optimal CN photoanode reaches photocurrent densities of ≈200 μA cm−2 at 1.23 versus reversible hydrogen electrode in neutral and acidic solutions and 120 μA cm−2 in a basic solution.

A droplet-intermixing printing method for high-uniformity pixel ink volume control based on integer programming

Inkjet printing is a promising technology for new display mass production. However, a major challenge in inkjet printing applications is pixel ink volume nonuniformity caused by the volume error of droplets ejected from multiple nozzles. This nonuniformity can lead to nonuniform pixel film thickness and Mura defects in a display panel. To address this issue, an integer programming-based droplet-intermixing printing method for high-uniformity pixel ink volume control is proposed in this study. The printing method is used to homogenize the volume of ink deposited in each pixel by intermixing droplets from different nozzles to improve the whole-panel uniformity. To ensure that the droplet intermixing results meet the printing process requirements, a specific scheduling and printing planning model for the method is established. According to the droplet volume from each nozzle and the printing pattern, the most efficient printing path and nozzle ejection action are obtained by the established model while meeting the volume uniformity requirement of pixel ink. Experiments show that the proposed printing method can realize pixel film thickness error control under ±6 nm on a 400 cm2 display substrate, and the uniformity of different pixels is less than ±4.62 %. Compared with traditional method, the achieved uniformity is improved at 45.4 % under the same conditions. This method has been applied in printed display manufacturing equipment and achieved good results.

Symmetry breaking and high-order instability of telephone cord buckles triggered by in-plane gradients of thin films

Buckle delaminations are ubiquitous in natural and artificial systems including tectonic plates, biological tissues, film structures, and two-dimensional materials. Although the formation and manipulation of various buckle delaminations have been extensively investigated in the past few decades, understanding complex buckle delamination patterns is still a challenge. Here we report on the symmetry breaking and high-order instability of telephone cord (TC) buckles triggered by in-plane gradients of thin films, including strain gradient and thickness gradient. Our experimental observations reveal the unique morphological profile of the asymmetric TC buckle due to the strain gradient. Impact of in-plane strain gradient on morphological changes of TC buckles is elucidated by simulations of buckling and delamination of the thin film. Phase diagrams for five buckle delamination morphologies, i.e., symmetric TC buckle, asymmetric TC buckle, symmetric bilateral branched buckle, asymmetric bilateral branched buckle, and unilateral branched buckle with respect to average strain and strain gradient (or thickness gradient) have been numerically established. This work could promote a better understanding of complex buckle delamination patterns with symmetry breaking and high-order instability and controllable fabrication of ordered buckle delamination patterns by regulating in-plane gradients of thin films.

Prediction of wrinkle patterns in tensioned thin-film structures containing rigid elements

AbstractWith the in-depth study of thin-film structures, nonuniform thin films with rigid elements have been applied in the aerospace and flexible electronics industries. For thin-film structures with rigid elements, there is an interaction force between the rigid element and the thin film; therefore, the wrinkling mode of the thin film changes under the influence of the interaction force. In this study, a wrinkle model was developed to predict the wrinkle morphology of thin-film structures with rigid elements on the diagonal. First, the wrinkle patterns of the rigid elements were observed at different positions using tensile experiments. Then, the relationship between the tilt of the rigid element and the wrinkle wavelength was investigated using a finite-element eigenvalue buckling analysis. Finally, local wrinkling caused by the perturbed stress of the rigid element was introduced, and a wrinkling model of a square thin film with rigid elements on the diagonal under tension was established. The theoretical analysis results were compared with simulation and experimental results, demonstrating that the model can accurately describe the wrinkle patterns of thin-film structures containing rigid elements on the diagonal under tension.

Study on effects of inlet nonuniformities on aerothermal performance of NGV pressure side with different film cooling designs

High pressure (HP) turbine works under nonuniform inlet conditions produced mainly by modern lean burn combustors. This article employed the conjugate heat transfer method to investigate the influences of nonuniform inflow conditions and film hole arrangements on the film coolant coverage and heat transfer characteristics. The researched region is on the pressure side (PS) of the nozzle guiding vane (NGV). A scaled-up model of the GE-E3 engine HP turbine stator vane was used and the film cooling performances of four different film hole arrangement schemes on the PS were discussed. In addition, the results of four nonuniform inflow conditions, including positive/negative swirl aligned with the stator vane leading edge (case PSW-LE and NSW-LE), and positive/negative swirl aligned with the stator vane mid passage (case PSW-PA and NSW-PA), were compared with the uniform inlet condition. The results indicate that the temperature distributions of stator vane PS are dominated by the film hole arrangements and the nonuniform inlet conditions. In the positive swirl (PSW) influenced region, film cooling effectiveness can be improved if the coolant orientation is consistent with the swirl direction. The film cooling effectiveness can be improved by 12%–20% under the Leading Edge (LE) clocking position and 45% under the Passage (PA) clocking position. In contrast, the negative swirl dominates the film cooling effectiveness distribution. Under the PA clocking position, the highest film cooling effectiveness can be enhanced by 45% compared with the LE. In contrast, the design of film holes has a weak contribution to the coolant outflow direction under the negative swirl (NSW) condition. However, the film holes with negative angles can enhance the cooling effectiveness behind the 13th row holes.

Parametric study of water spray cooling on enhanced relatively large surfaces

Spray cooling as an effective cooling technique is widely used in practice. Compared to small heating surfaces, the significantly increase of surface would pose a great challenge to the significant enhancement of spray cooling. Specially, single nozzle spray cooling suffers from non-uniform liquid thin film on a relatively large heating surface, severely inhibiting the formation of efficient thin film evaporation. In this study, two enhanced surfaces such as straight fin surface and cubic fin surface with a relatively large heating surface of 4 cm2 were designed for single nozzle spray cooling. A parametric study was conducted with aims to evaluate the effects of flow rate, spray distance and enhanced surfaces on the formation of thin liquid film and then the performance of spray cooling. Visualization was presented to observe the development of liquid film to elucidate the enhanced mechanism of spray cooling. In this work, spraying height is varying from 20 to 40 mm. Coolant flow rate is ranging from 70 to 100 ml/min. The experimental results show the distribution of liquid film plays an important role in spray cooling, especiallyin the single-phase regime. In two-phase regime, nucleate boiling is significantly boosted on the engineered surfaced. For instance, the cubic fin surface leads to an enhancement of HTC of nearly 24 % compared to that of flat surface.

Sputtering pressure dependence of microstructure and magnetoresistance properties of non-uniform Co–ZnO nanocomposite film

Co-ZnO metal–semiconductor nanocomposite films have become the focus of attention in recent years since their magnetoresistance (MR) effect at room temperature (RT). In this study, non-uniform Co-ZnO nanocomposite films were prepared by magnetron co-sputtering method. With sputtering pressure increasing, the formation of ferromagnetic Co clusters is suppressed effectively, and the metallic-state superparamagnetic Co particles are dispersed, which form the tunneling transport paths in the Co-ZnO films at high Co content. As the sputtering pressure increases from 0.3 Pa to 1.2 Pa, the RT -MR value of the films increases from 0.41 % to 11.85 %, and the saturation magnetization of the films rises from 6.3 kGs to 7.3 kGs and then decreases to 6.7 kGs. It is noteworthy that the low-field MR field sensitivity at 1000 Oe is enhanced by about 10 times from 0.5 Pa to 1.2 Pa. This provides a reference for the application of low-magnetic field detectors.

Optimization of Rotary-Magnet assisted ECSM on borosilicate-glass using machine learning

ABSTRACT Owing to the incapability of the existing techniques, Electrochemical Spark Machining (ECSM) is transpiring to micro machine the glass for potential applications in micro domain. However, in ECSM, the bubble accumulation and poor flushing lead to the generation of a non-uniform gas film, resulting in the deterioration of Hole Circularity (HC) and Surface Roughness (SR). Therefore, present communication is an attempt toward the concept of Rotary-Magnet assisted ECSM (RM-ECSM) to produce the micro holes in the borosilicate glass with better quality characteristics (higher HC and lower SR), which are required for better performance of glass vias in RF-MEMS. The evolutionary algorithm and Machine Learning (ML) have been adopted for optimization. From optimization, the values of optimal input parameters were obtained as follows: Applied voltage = 43.46 V; Electrolyte-temperature = 45.93 ֯ C; Pulse on time = 3.28 ms; Magnetic rotation = 551 rpm with corresponding values of HC and SR as 79.28% and 3 um respectively. Finally, these outcomes were validated by Levenberg-Marquardt algorithm (ML).

Quantifying photoluminescence variability in monolayer molybdenum disulfide films grown by chemical vapour deposition

Monolayer molybdenum disulfide (MoS2) is a promising candidate for inclusion in optoelectronic technologies, owing to its two-dimensional (2D) nature and resultant novel photoluminescence (PL). Chemical vapour deposition (CVD) is an important method for the preparation of large-area films of monolayer MoS2. The PL character of as-prepared monolayer MoS2 must be well understood to facilitate detailed evaluation of any process-induced effects during device fabrication. We comparatively explore the PL emission from four different commercially available CVD-grown MoS2 monolayer films. We characterize the samples via Raman and PL spectroscopy, using both single-spot and mapping techniques, while atomic force microscopy (AFM) is applied to map the surface structure. Via multipeak fitting, we decompose the PL spectra into constituent exciton and trion contributions, enabling an assessment of the quality of the MoS2 monolayers. We find that the PL character varies significantly from sample to sample. We also reveal substantial inhomogeneity of the PL signal across each individual MoS2 film. We attribute the PL variation to non-uniform MoS2 film morphologies that result from the nucleation and coalescence processes during the CVD film development. Understanding the large variability in starting PL behaviour is vital to optimize the optoelectronic properties for MoS2-based devices.

Crystalline and transport characteristics of ferrimagnetic and antiferromagnetic phases in Mn3Ga films

The Mn3Ga material is a promising candidate for memory and computing devices owing to its rich crystalline structures of tunable ferrimagnetic and collinear and non-collinear antiferromagnetic phases. In particular, Mn3Ga with non-collinear antiferromagnetic order exhibits giant anomalous and topological Hall conductivities and is a potential material platform for hosting spin-related quantum phenomena. In this study, we demonstrate Mn3Ga films grown on thermally oxidized Si substrates, with and without the Ta buffer, under different deposition temperatures (Ts). With increasing Ts, the dominant crystalline structure across all Mn3Ga films evolves from a cubic to hybrid tetragonal and hexagonal texture, wherein the crystalline orientation of spins endows the films with in-plane magnetic anisotropy. For Ta/Mn3Ga and Mn3Ga films grown under high Ts, the inhomogeneity in surface energy of the buffer layer results in a non-uniform granular film in the former. Notably, the Mn3Ga films of hexagonal texture exhibit topological Hall signatures. The density functional theory calculations on the hexagonal Mn3Ga phase corroborated with the experimental magnetic, structural, and transport properties. These findings establish an important platform for tailoring Mn3Ga films toward multifunctional applications.

Pulse Electrodeposition of Polycrystalline Si Film in Molten CaCl2 Containing SiO2 Nanoparticles

<p>The high cost of Si-based solar cells remains a substantial challenge to their widespread adoption. To address this issue, it is essential to reduce the production cost of solar-grade Si, which is used as raw material. One approach to achieve this is Si electrodeposition in molten salts containing Si sources, such as SiO<sub>2</sub>. In this study, we present the pulse electrode-position of Si in molten CaCl<sub>2</sub> containing SiO<sub>2</sub> nanoparticles. Theoretically, SiO<sub>2</sub> nanoparticles with a diameter of less than 20 nm in molten CaCl<sub>2</sub> at 850°C have a comparable diffusion coefficient with that of ions in aqueous solutions at room temperature. However, we observed a slower-than-expected diffusion of the SiO<sub>2</sub> nanoparticles, probably because of their tendency to aggregate in the molten CaCl<sub>2</sub>. This led to the formation of a non-uniform Si film with low current efficiency during direct current electrodeposition. We overcome this issue using pulse electrodeposition, which enabled the facile supplementation of SiO<sub>2</sub> nanoparticles to the substrate. This approach produced a uniform and thick electrodeposited Si film. Our results demonstrate an efficient method for Si electrodeposition in molten CaCl<sub>2</sub> containing SiO<sub>2</sub> nanoparticles, which can contribute to a reduction in production cost of solar-grade Si.</p>

Thick film MEMS process using reverse lift-off

The lift-off process is a microfabrication technique that has the capability of forming thin film structures. However, several issues, such as structural shape and burr formation, arise when applying this method to the formation of thick film structures. Thick film structures formed through the lift-off process exhibit a mountainous cross-sectional shape and non-uniform film thickness due to variations in the width of the structure. These challenges make it difficult to apply the method to MEMS. While the reverse lift-off process addresses some of the structural shape problems, its initial development using metal molds makes it challenging to directly apply to MEMS without modification. Therefore, this paper proposes an adaptation to the Si process and presents a method to reduce burrs. The microfabrication characteristics are evaluated by comparing the cross-sectional shapes of thick metallic glass structures formed through both the lift-off and reverse lift-off processes. The structures formed through the reverse lift-off process exhibit a rectangular cross-sectional shape, and the film thickness remains consistent regardless of the structure's width. However, burrs persist on the backside edge of the structure, which hinders its application to MEMS. This paper confirms that pre-etching the underlying Si substrate into an inverse tapered shape effectively reduces burrs. As an illustration of the improved reverse lift-off process applied to MEMS, MEMS mirror structures are fabricated, and their resonance frequency closely aligns with the design value.

Influence of strain path dependent microstructural evolution on corrosion behaviour in Al-Li alloy

This study investigates the corrosion response of Al-Li alloy following deformation along three strain paths, viz. uniaxial, plane strain, and equi-biaxial. The electrochemical studies have revealed that the dissolution behaviour of the as-received and deformed specimens is significantly influenced by grain orientation and grain boundary character distribution. The higher fraction of 〈001〉 // ND grains minimises the dissolution rate by forming a stable film over the specimen. The densely populated sub-grain boundaries, distributed uniformly throughout the microstructure, improve the charge transfer resistance and compensate for the deterioration in corrosion behaviour induced by the presence of higher fraction of 〈011〉 // ND grains. Further, a microstructure consisting of both 〈001〉 // ND and 〈011〉 // ND oriented grains induces micro-galvanic corrosion and forms a highly non-uniform film, degrading the overall corrosion response.

Insight into the decay mechanism of non-ultra-thin silicon film anode for lithium-ion batteries

Silicon thin-film is one of the most promising silicon anode materials for lithium-ion batteries, with the advantages of high cycle stability and initial coulombic efficiency. The excellent performance of silicon thin-films is due to their ultra-thin thickness (< 200 nm), but this results in their areal capacity too low to be compatible with commercial cathode materials, and only films thicker than 500 nm are practical. However, frequent volume changes in non-ultra-thin silicon films during cycling may cause layer misalignment and separation of the film from substrate. In this paper, silicon films with a thickness of ∼700 nm are prepared by magnetron sputtering on the inhomogeneous surface of a copper foil. The properties of the silicon films and mechanisms involved in the cycling process is investigated by combining experimental means during cycling with calculations of the atomic-scale amorphous lithium-silicon Zintl Phases’ structural volumes before and after cycling. The results show that the volume of silicon doesn't recover after delithiation and there is still significant swelling. The cyclic process causes a superimposed expansion of the volume, but the non-uniform film substrate causes the lateral expansion stresses to offset each other, thereby retaining a relatively stable structure. At the end of 100 cycles, the specific capacity of the silicon film electrode is 1461.5 mAh g −1 (areal capacity 0.242 mAh cm−2), with a capacity retention of 64.35%, and the silicon film thickness becomes 8.5 μm. We believe that by reducing the longitudinal expansion volume or stress of the silicon film, the cycle life of the silicon film can be further optimized.

Substrate temperature dependence of microstructure and magnetoresistance field sensitivity of Co–ZnO non-uniform nanocomposite film

Co–ZnO metal-semiconductor nanocomposite films have drawn a growing number of attention due to their significant room temperature (RT) magnetoresistance (MR) effect. In this paper, Co–ZnO non-uniform nanocomposite films with high crystallinity of ZnO matrix have been prepared by controlling substrate temperature. With the increase of substrate temperature, the Co particles grow and gradually aggregated into ferromagnetic clusters, which leads to an increase in saturation magnetization (Ms) from 5.8 to 6.7 kGs. Moreover, the growth of ferromagnetic clusters results in the formation of cluster-particle current paths and isolated magnetic particles, which have less contribution to the MR, causing the separation between MR curve and -(M/Ms)2 curve. This phenomenon induces a broadening of the MR curve, which modulates the shift of the MR field sensitivity (FS) peak toward higher fields. When the substrate temperature is 250 °C, high ZnO matrix crystallinity, -MR value (2.6%) and effective modulation of MR FS in Co–ZnO non-uniform nanocomposite films can be achieved simultaneously. It provides a reference for the application and modification of Co–ZnO MR devices.

Influence of operating conditions on in-tube vapour condensation heat transfer characteristics in the presence of noncondensable gases at high pressure

The in-tube vapour condensation heat characteristics in the presence of noncondensable gas at high pressures are experimentally validated with an error of 20%. Numerical simulations are then conducted to explore heat transfer characteristics at different operating pressures, wall surface temperatures and mass flow rates. The flow and heat transfer characteristics are thoroughly discussed and the buoyancy effects induce a secondary circulation altering flow patterns, changing the water film and heat transfer coefficient distribution. In addition, increasing operating pressures is found to reduce the wall heat transfer rate. Even though the flow pattern is significantly different caused by the increased gas mixture density, the total condensate flow rate is approximately the same at different operating pressures due to the same inlet conditions and temperature difference. The difference in the wall heat transfer rate is attributed to the change of latent heat of vapourisation and falling film at different pressures and is evident at high pressures. At the high temperature difference, a nonuniform film height towards the bottom is emerged, sweeping the condensate upward. Similarly, increasing the mass flow rate can also increase the total wall heat transfer rate and total condensate flow rate.

Two-dimensional computational fluid dynamics modeling of slip-flow heat transfer in the hot filament chemical vapor deposition process

The computational fluid dynamics (CFD) modeling on the hot filament chemical vapor deposition (HFCVD) process used to produce a diamond film has been conducted to anticipate the heat transfer and calculate the generation of H. The effect in the slip-flow regime owing to the low-pressure process should be considered to simulate the heat transfer accurately. In addition, a heterogeneous reaction occurring on the filament should be included to calculate the generation of H. The parameters to simulate such microscopic phenomena were applied in the present work and validated by comparing the results with the previous work. The thermal accommodation coefficient (TAC) for H2 was determined as 0.3, at which the calculated mass fraction and H concentration showed good agreement. In addition, It was confirmed that the value could be applied over various filament temperatures and operating pressure. Further, the behavior of H is analyzed above the substrate; the analysis results indicate that there is a correlation between the gas temperature and the gradient of H concentration on the substrate. The high gas temperature caused a severe gradient; thus, a non-uniform film may be deposited. The developed modeling method suggested that microscopic phenomena could be simulated without experimental materials. This fact implied that it is possible to anticipate the temperature and H concentration regardless of the structural design.