Films Of Various Thicknesses Research Articles

Numerical Study of Comparison of Thrust Bearing Slip - No Slip Condition on Acoustic Performance

The acoustic power level (APL) produced by a thrust bearing during operation has a major effect on its performance. Therefore, this research aimed to investigate the impact of slip engineered on the noise generated by thrust bearings. A numerical approach was used to simulate open pocket bearings with varying film thickness depths. At the initial location of the slip area, three bearing models were analyzed: pocket slip, pocket no slip, and smooth slip. The results show that implementing slip can reduce noise levels, turbulence kinetic energy (TKE), and turbulence eddy dissipation (TED) rate. The average APL, TKE, and TED values were the lowest at the high film thickness

Comparative analysis of analytical and numerical approximations for the flow and heat transfer in mixed convection stagnation point flow of Casson fluid

A mathematical description of non-Newtonian mixed convective Casson fluid stagnation point flow and transfer of heat exists in terms of partial differential equations. We considered the same to study it further under the effects of unsteadiness and varied film thickness parameters. For inclusion of these parameters in the flow model study we modified the available similarity transformations. The governing equations with three independent variables are converted into ordinary differential equations by employing the modified invertible transformations. For the mass and heat transfer in the mixed convection stagnation point unsteady flow of Casson fluid over a stretching sheet, a detailed comparative analysis is carried out in this paper, of the analytical and numerical approximation techniques. The Homotopy Analysis Method is applied for the analytical solutions while the Runge-Kutta with a Shooting Method (RKF45) and Finite Difference Method are used for obtaining the numerical solutions. With these solution schemes we present an analysis of velocity and temperature profiles under the effects of embedded parameters such as the Casson fluid parameter, unsteadiness parameter, mixed convection parameter, Prandtl number, Eckert number, and stretching ratio. The results are presented in both graphical and tabulated forms and they illustrate the dependence of mass and heat transfer characteristics of Casson fluid upon the embedded parameters. Further, we have shown an agreement between the analytical and the approximate solutions for the considered flow and heat transfer which reflects a validation of the results presented here.

Close-contact melting of shear-thinning fluids

This study aims at establishing a model for close-contact melting (CCM) of shear-thinning fluids. We presented a theoretical framework for predicting the variation of liquid melt film thickness and motion of unmelted solid for both Carreau and power-law fluids. We identified the appropriate energy equation considering the convective effect and derived an analytical temperature profile across the liquid film. Using the lubrication approximation, force equilibrium relationships and the corresponding numerical approaches were built. By using laser interferometry and photographic recording methods, we found excellent agreement between numerical solutions and experimental results for Carreau liquids, revealing that the convective effect weakens heat transfer and melting rate. We identified the critical liquid film thickness that determines three situations of CCM in the theoretical model for Carreau fluids. Numerical prediction demonstrated that the CCM of Carreau fluids can be almost equivalent to that of power-law fluids if the initial film thickness is greater than the critical value. Finally, approximate analytical models were developed for both Carreau and power-law models. For the applicability of the approximate analytical solutions, we derived two- and three-dimensional dimensionless phase diagrams of validity range and identified a key dimensionless group $(\varLambda Re)^{4/3}{Re}\left [3\ln (Ste+1)\right ]^{1/3}{Pe}^{-1/3}$ , where $\varLambda$ is dimensionless characteristic time, Re is Reynolds number, Ste is Stefan number and Pe is Peclect number. The reliability of the approximate solutions was verified by comparing with the numerical results. These approximate solutions enable convenient and low-cost computational prediction of the dynamic CCM process of shear-thinning fluids.

On the analysis of time-dependent drainage of Sisko fluid film slowly down a vertical belt

Theoretical analysis of time-dependent drainage of Sisko fluid film slowly down a stationary vertical belt is presented in this paper. Employing [C. Gutfinger and J. A. Tallmadge, AIChE J. 10, 774 (1964)] approach the subsequent nonlinear partial differential equation is simplified. The Adomian decomposition method is then used to solve the simplified nonlinear partial differential equation to obtain the analytic expression for velocity. The analytic expressions for volume flow rate, shear stress, average film velocity, surface profile and film mean thickness are also derived. It is delineated that the velocity decreases by an increment in the Sisko fluid parameter and time while it increases by an increment in the fluid behavior index. The elevation of the Sisko surface profile decreases when the values of Sisko fluid parameter are increased, whereas it increases when the values of fluid behavior index and time are increased. The variable film thickness of four different lubricating greases is estimated by using experimental values of material constants and fluid behavior index [A. W. Sisko, Ind. Eng. Chem. Res. 50, 1789 (1958) and M. A. Delgado et al., Chem. Eng. Process. 44, 805 (2005)]. Furthermore, the flow variables studied for the Sisko fluid are also studied for the Newtonian fluid, and comparisons between both are provided.

Exploring hafnium oxide's potential for passivating contacts for silicon solar cells

We investigate the potential of ultra-thin HfO2 films grown by atomic layer deposition for passivating contacts to silicon focusing on variations in film thickness and post-deposition annealing temperature. A peak in passivation quality – as assessed by carrier lifetime measurements – is reported for 2.2 nm thick films annealed at 475 °C, for which a surface recombination velocity <1 cm/s is determined. For films <2.2 nm thick, there is a marked decrease in passivation quality. X-ray diffraction highlights a change from crystallised monoclinic to amorphous HfO2 as film thickness decreases from 12 nm to 2.2 nm. Kelvin probe results indicate that as-deposited 2.2–12 nm films have similar effective work functions, although the work function of 1 nm films is considerably lower. Upon post-deposition annealing in vacuum, all films exhibit a reduction in effective work function at temperatures coincident with the onset of passivation in air-annealed samples. An initial investigation into the contact resistivity in a passivating contact structure utilizing HfO2 reveals a strong post-deposition annealing temperature dependence, with the lowest resistance achieved below 375 °C, followed by a decrease in performance as temperature increases towards the optimal temperature for passivation (475 °C). Limitations of the contact structure used are discussed.

Highly Sensitive and Selective Hydrogen Gas Sensor with Humidity Tolerance Using Pd-Capped SnO2 Thin Films of Various Thicknesses

Detecting and identifying hydrogen gas leakage before a potential disaster is a critical safety concern. To address this issue, a low-cost and simple-design sensor is required with high response and fast sensing time, capable of detecting hydrogen gas even at low concentrations of 5–500 ppm. This study investigates the use of magnetron-sputtered SnO2 thin films with palladium as a catalytic layer to achieve better sensing output. The developed Pd-caped SnO2 thin film sensors showed increased sensitivity with increasing thickness, up to 246.1 nm at an operating temperature of 250 °C. The sensor with a thickness of 246.1 nm exhibited excellent selectivity for H2 gas, even in humid conditions, and was able to distinguish it from other gases such as CO, NH3, and NO2. The sensor demonstrated high response (99%) with a response/recovery time of 58 s/35 s for (5–500 ppm) hydrogen gas. The sensor showed linear response to H2 gas concentration variation (5–500 ppm) at 250 °C. The sensor was found to be mechanically stable even after 60 days in a high-humidity environment. The LOD of sensor was 151.6 ppb, making it a suitable candidate for applied sensing applications. The Pd-caped SnO2 thin film sensor with thickness of ~245 nm could potentially improve the safety of hydrogen gas handling.

Effect of graphene film thickness on photoluminescence properties of ZnO/graphene composite films

As an excellent reinforcing material, graphene is widely utilized to composite with various functional materials, such as ZnO with hexagonal wurtzite structure. Due to their high lattice fitting degree, numerous properties of ZnO material are reinforced, such as conductivity and photoluminescence (PL) characteristics, etc. However, the mechanism of the influence of graphene film thickness on PL in composite films remains to be explored. Moreover, it remains to be explored how thick graphene film is more suitable for composite with ZnO film to achieve the best PL performance enhancement effect. The motivations of this study are based on the above two points, under the constant optimal ZnO sputtering process, the ZnO film was compounded with five kinds of graphene films with different thickness, and the surface morphology and growth quality of the grown ZnO films were analyzed in detail, to obtain the effect mechanism of the variation of graphene film thickness on the growth quality of ZnO; and to explore the optimal preparation parameters, dimension parameters, and the crystalline information of the graphene film, which can be most appropriately composite with ZnO film to make the strongest ultraviolet PL properties.

A Study on Optimal Indium Tin Oxide Thickness as Transparent Conductive Electrodes for Near-Ultraviolet Light-Emitting Diodes.

This research study thoroughly examines the optimal thickness of indium tin oxide (ITO), a transparent electrode, for near-ultraviolet (NUV) light-emitting diodes (LEDs) based on InGaN/AlGaInN materials. A range of ITO thicknesses from 30 to 170 nm is investigated, and annealing processes are performed to determine the most favorable figure of merit (FOM) by balancing transmittance and sheet resistance in the NUV region. Among the films of different thicknesses, an ITO film measuring 110 nm, annealed at 550 °C for 1 min, demonstrates the highest FOM. This film exhibits notable characteristics, including 89.0% transmittance at 385 nm, a sheet resistance of 131 Ω/□, and a contact resistance of 3.1 × 10-3 Ω·cm2. Comparing the performance of NUV LEDs using ITO films of various thicknesses (30, 50, 70, 90, 130, 150, and 170 nm), it is observed that the NUV LED employing ITO with a thickness of 110 nm achieves a maximum 48% increase in light output power at 50 mA while maintaining the same forward voltage at 20 mA.

Photo-electrocatalytic performance of poly(3,4-ethylenedioxythiophene)/TiO2 nano-tree films deposited by oCVD/CVD for H2 production

The hydrogen production from photo-electrocatalytic water splitting attracts extensive attention as a direct way to convert solar energy into chemical fuels. In this work, innovative photo-anodes composed of TiO2 which has a preferable growth orientation [211] conjugated with PEDOT as bi-layers are prepared by a dry process strategy, combining oxidative and metalorganic chemical vapor deposition (CVD). Pure anatase, dendritic TiO2 films of variable thickness are obtained at 500 °C by varying the deposition time. Increase of films thickness from 474 to 2133 nm results in morphologies that evolve from dense and angular structures to isolated and nanostructured tree-like columns with a concomitant decrease of the charge transfer resistance due to the enhancement of active facets of anatase structure. The PEDOT/TiO2 bi-layer with an overall thickness of 1350 nm and a 50 nm thick upper-PEDOT layer exhibits the highest photocurrent response (0.26 mA cm−2 at 1.8 V/RHE), a fast photocurrent response under illumination, and the best hydrogen yield up to 4.1 µmol cm-2h−1 with electronic conductivity being three order of magnitude higher than pristine TiO2.

The Effects of mmW and THz Radiation on Dry Eyes: A Finite-Difference Time-Domain (FDTD) Computational Simulation Using XFdtd.

The importance of investigating the health effects of RF radiation on the cornea cannot be overstated. This study aimed to address this need by utilizing a mathematical simulation to examine the absorption of millimeter wave (mmW) and terahertz (THz) waves by the cornea, considering both normal and pathological conditions. The simulation incorporated variations in tear film thickness and hydration levels, as these factors play a crucial role in corneal health. To assess the impact of RF radiation on the cornea, the study calculated temperature rises, which indicate heating effects for both dry and normal eyes. XFdtd, a widely used commercial software based on the Finite-Difference Time Domain (FDTD) method, was employed to evaluate the radiation absorption and resulting temperature changes. The outcomes of this study demonstrated a crucial finding, i.e., that changes in the water ratio and thickness of the tear film, which are associated with an increased risk of dry eye syndrome, directly impact the absorption of mmW and THz waves by the cornea. This insight provides valuable evidence supporting the interconnection between tear film properties and the vulnerability of the cornea to RF radiation.

Multilayer amorphous-crystalline high-entropy metal films

High-entropy alloys (HEA) are multi-element materials and contain at least five elements of similar concentration. HEA are, as a rule, single- phase thermodynamically stable substitutional solid solutions, mainly based on a body-centered cubic and face-centered cubic crystal lattice. Solid solution stabilization during the crystallization of a high-entropy alloy is provided by the interaction of a number of factors, namely, a high mixing entropy and low diffusion rate of components, and a low growth rate of crystallites from the melt. The purpose of this work was to obtain new knowledge about the structure and properties of high-entropy films synthesized on a metal substrate during deposition of a multi-element metal plasma in argon atmosphere. The plasma was formed as a result of independent plasma-assisted electric arc cathodes of the following metals: Ti, Al, Cu, Nb, Zr sputtering. As a result of the performed studies, the deposition mode was revealed, which allows the formation of films of various thicknesses of close to equiatomic composition. Transmission electron microscopy methods have established that the films are multilayer formations and have nanoscale amorphous-crystalline structure. Microhardness of the films significantly depends on the ratio of number of the forming elements and varies from 12 to 14 GPa, Young’s modulus – from 230 to 310 GPa. Crystallization of the films was carried out by irradiation with a pulsed electron beam. As a result of processing, a two-phase state is formed. The main phase is α-NbZrTiAl with a volume-centered cubic crystal lattice with a parameter of 0.32344 nm; the second phase of CuZr composition has a simple cubic lattice.

Phase evolution in epitaxial Gd2O3 due to anneal temperature for silicon on insulator application

Epitaxial growth of Si on rare-earth oxides on Si wafer using sputter technology promises cheaper and high-volume manufacturing of Silicon-on-insulator (SOI) wafers over costly solutions like the smart-cut method. Further, rapid thermal annealing (RTA) in standard complementary metal–oxide–semiconductor (CMOS) processing affects the performance of SOI substrate through chemical and crystal phase change. Herein, we present a systematic study on the rich physical and chemical phase evolution of epitaxial Gd2O3 grown on Si (111) using RF sputtering subjected to RTA temperatures (850−1050 °C). First, X-ray diffraction analysis shows a significant enhancement of the epitaxial cubic phase in as-deposited Gd2O3 at an optimum RTA temperature of 850 °C, which is partially explained by epitaxial-regrowth of an amorphous layer at Gd2O3/Si interface as observed in Transmission Electron Microscopy. Secondly, the degradation of crystallinity beyond 900 °C is correlated with temperature-dependent Si diffusion into Gd2O3 that becomes observable by X-ray photoelectron spectroscopy. The Gd2O3 crystallinity is completely quenched into the amorphous gadolinium silicate phase at 1050 °C. Eventually, we employed X-ray reflectivity modeling to evaluate the film thickness variation with RTA. This study provides a detailed insight into the structural and chemical dynamics occurring in epitaxial-Gd2O3 film for CMOS-relevant temperatures.

A theoretical model on unfrozen water content in soils and verification

Phase transition of pore water is a fundamental reason for frost heave in cold regions. Therefore, studying the variation in unfrozen water content is of great significance for understanding the freezing process of pore water and revealing the freezing mechanism in soils. In this study, a prediction model for unfrozen water content was established based on a probabilistic ice-forming model. To determine the heterogeneous nucleation rate, which is the key variation in the probabilistic model, the relationship between the water film thickness and temperature variation in the soil was characterized based on the improved premelting theory. In this process, the equivalent particle size and density of impurities on the surface of the particles were determined by introducing the particle size distribution curve and average accumulation mode of the particles. Based on the heterogeneous nucleation mechanism of ice crystals and the variation in the water film, a relationship between the heterogeneous nucleation rate and temperature was established. Subsequently, a method for calculating the equivalent contact angle related to pore water in soils was presented. The results showed that the heterogeneous nucleation rate and equivalent contact angle are positively and negatively correlated with the equivalent particle size at the same temperature, respectively, and the angle decreases with increasing solution concentration. Furthermore, the experimental data of 10 different soils showed that the variation in water content obtained by our model was in good agreement with the experimental values, particularly during the stage of rapid water phase change. The study developed an effective correlation among heterogeneous nucleation rate and equivalent contact angle of pore water and physical properties of soil, by combining crystallization theory and premelting theory, which provided a new way to explain water freezing and predict unfrozen water content in soils.

The impact of temperature on heated liquid films: Crater and jetting impact dynamics

The droplet impact phenomena onto liquid films are a field extensively researched for over a century, which are driven by many practical applications such as heat exchangers, internal combustion engines and spray cooling. Despite the extensive work on wetted surfaces, the influence of temperature on droplet outcome, local evaporation/boiling effects, and liquid film stability has been overlooked in the literature. Therefore, the main objective of this work is to evaluate the influence of the liquid film temperature on the crater and jet dynamics. The experimental setup was designed for this purpose, in which a borosilicate glass surface that contains the liquid film is placed over an aluminium block with embedded cartridge heaters, heating it by conduction. Water, n-decane and n-heptane are the fluids adopted for the experiments due to their differences in thermophysical properties and saturation temperature. Different conditions are considered, which include two dimensionless thicknesses, h∗=1.0 and h∗=1.5, and a range of dimensionless temperatures, θ=0, θ=0.2, θ=0.4 and θ=0.6. Qualitative and quantitative analyses are performed regarding crater evolution, and central jet height and breakup measurements, respectively. Evaporation rate measurements are required due to the influence on the liquid film thickness variation. Qualitative results show that temperature differences promote the formation of recirculation zones near the impact surface and the crater boundaries, as well as the influence on the crater shape and curvature. In terms of the quantitative analysis, the central jet height measurements for the n-heptane and n-decane reveal that higher values of the dimensionless temperature lead to an increase in the jet height, as well as promoting and increasing the occurrence and number of secondary droplets, respectively. Water follows a similar trend with the exception of θ=0.2, which can be explained by a time scale analysis.

Electron transport properties and free electron density evolution during the phase change in VO2 thin films

The experimental results on the phase change behavior of vanadium dioxide (VO2) as a function of temperature are invariably examined in the light of the strong electron correlation-based Mott-Hubbard model or the periodic lattice distortion based Peierls model with limited success. Further, the experimental conditions-based nanostructure imparted to the VO2 thin films also plays an important role. Hence, it has been suggested that the theoretical model that best suits the experimental conditions needs to be applied. In this work, we have examined the electron transport properties of VO2 thin films of various thicknesses all along the reversible phase change cycle. These results have led us to carefully examine the free electron density (ne) evolution all along the phase transition cycle and to establish for the first time the reversible hysteresis cycles of this important parameter. The intimate correlation between the degree of change in ne and the resistance seen in our samples leads us to believe that our results may be in favor of the Mott-Hubbard model of phase transition.

Latent fingerprint imaging by spectroscopic optical coherence tomography

Optical coherence tomography (OCT) is a non-contact and non-invasive optical method for evaluating semitransparent and scattering objects. Its unique features, such as non-destructive 3D measurements of tested objects with a fast scanning rate, make this technique interesting for latent fingerprint reading, which is the subject of this paper. So far, OCT has not found widespread use for reading fingerprints directly from surfaces due to its insufficient axial resolution. This problem has been overcome by applying spectroscopic analysis to the OCT measurements, which is based on retrieving the spatially resolved spectral characteristics of the recorded backscattered light directly from the OCT measurement data. The spectroscopic analysis is very sensitive to thin film thickness variations, improving the readability of the latent fingerprints by OCT, which is reported here as well. This study includes a description of spectroscopic analysis in combination with OCT and indicates the benefits for thin film evaluation, in particular, latent fingerprints. The example of latent fingerprint OCT measurements enhanced by spectroscopic analysis has been shown, as well as a brief discussion of the method's applicability. Finally, improving fingerprint OCT imaging contrast and readability by applying spectroscopic analysis have been confirmed.

Vacuum Thermoforming for Packaging Flexible Electronics and Sensors in E-Textiles

Packaging of flexible electronics is essential for e-textile applications to reduce degradation of the performance caused by mechanical stress, environmental effects and to have increased durability. Conformal coatings for packaging have the advantage of reducing rigidity and can be seamlessly integrated into fabrics. Vacuum forming is a technique for packaging electronic devices with thermoplastic films of various thicknesses providing uniform coating. Polyurethane is a widely used thermoplastic material in e-textile and can be easily processed by vacuum forming for packaging. In this paper, a detailed explanation of the working of Formech 450DT vacuum former is discussed for packaging small electronic chip for e-textile application with thermoplastic polyurethane (TPU). Two types of flexible circuits were packaged; a Carbon monoxide gas sensor and a series of resistors on flexible PCB. The packaged CO flexible sensor and series resistors endured 5.3 times and 1.7 times respectively, more bending cycles than unpackaged flexible electronic filament samples. For the washing cycles, the packaged flexible strips with CO sensor and series resistors endured 1.5 times.

Plasmon mediated extra-ordinary optical transmission through an apertureless plasmonic metagrating

Extra-ordinary optical transmission (EOT) through subwavelength plasmonic nanoapertures is possible due to the funneling of light via surface plasmons (SPs) at the resonant wavelengths through the apertures. In this Letter, we experimentally demonstrate EOT through a plasmonic metagrating which does not have any open apertures. The plasmonic metagrating was fabricated by deposition of silver (Ag) on a one-dimensionally patterned flexible and transparent polydimethylsiloxane grating obtained via pattern imprinting and subsequent peeling off a commercially available blue ray disk. For normal incidence of transverse magnetic-polarized light on the top surface of plasmonic metagrating, transmission of light through it was obtained in the visible wavelength range of electromagnetic spectrum. Control experiments on variation of Ag film thickness were performed to attain optimal parameters for maximum transmission, followed by polarization and refractive index (RI) dependent performance of the plasmonic metagrating. Electric fields and Poynting vector profiles were simulated using a finite element method to explain the interaction of light with the plasmonic metagrating and the mechanism of plasmon mediated optical transmission. Such a large optical transmission is possible because the SP modes generated at metal–air interface penetrate through metagrating and couple with those supported by the metal–substrate interface. As a model application, RI sensing using the plasmonic metagrating was demonstrated. The present study shows that optical transmission is possible from apertureless structures and enriches literature with better understanding of EOT. Moreover, it opens avenues for development of flexible, cost-effective plasmonic metagratings for sensors, spectral filters, polarizers, etc.

Ultrathin Micellar Foam Films of Sodium Caseinate Protein Solutions

Sodium caseinates (NaCas), derived from milk proteins called caseins, are often added to food formulations as emulsifiers, foaming agents, and ingredients for producing dairy products. In this contribution, we contrast the drainage behavior of single foam films made with micellar NaCas solutions with well-established features of stratification observed for the micellar sodium dodecyl sulfate (SDS) foam films. In reflected light microscopy, the stratified SDS foam films display regions with distinct gray colors due to differences in interference intensity from coexisting thick-thin regions. Using IDIOM (interferometry digital imaging optical microscopy) protocols we pioneered for mapping nanotopography of foam films, we showed that drainage via stratification in SDS films proceeds by the expansion of flat domains that are thinner than surrounding by a concentration-dependent step-size, and nonflat features (nanoridges and mesas) form at the moving front. Furthermore, stratifying SDS foam films show stepwise thinning, such that the step-size and terminal film thickness decrease with concentration. Here we visualize the nanotopography in protein films with high spatiotemporal resolution using IDIOM protocols to address two long-standing questions. Do protein foam films formulated with NaCas undergo drainage via stratification? Are thickness transitions and variations in protein foam films determined by intermicellar interactions and supramolecular oscillatory disjoining pressure? In contrast with foam films containing micellar SDS, we find that micellar NaCas foam films display just one step, nonflat and noncircular domains that expand without forming nanoridges and a terminal thickness that increases with NaCas concentration. We infer that the differences in adsorbing and self-assembling unimers triumph over any similarities in the structure and interactions of their micelles.

High-speed low-coherence interferometry of fuel films in impinging gasoline direct injection sprays

Quantitative experimental characterization of dynamic fuel film deposition processes is critical to developing better understanding and modeling of cold-start behavior in gasoline direct injection engines. Low-Coherence Interferometry (LCI) offers a quantitative fuel film thickness diagnostic that is immune or resistant to major confounding influences that limit other optical diagnostics in engine-relevant environments. This work describes an extension of spectral LCI techniques to high-speeds (10 kHz) that are capable of resolving the dynamics of fuel film deposition and evaporation in impinging gasoline sprays. Two approaches to LCI, Michelson interferometry and Fizeau interferometry, were tested and results demonstrate the superiority of the Fizeau configuration for enclosed vessel experiments. Experiments were performed at cold start conditions in an enclosed spray chamber with a gasoline spray impinging on a transparent wall. High-speed LCI was used to measure fuel film thicknesses and dynamic changes in thickness. The measurements were used to observe variation in film thickness and behavior with changes in system temperature and fuel composition.