Changes In Film Thickness Research Articles

Enhanced compressive strength by Ti[sbnd]Cr coating on cBN particle surface using vacuum vapor deposition

In order to enhance compressive strength of the coating on cBN particles, this study proposes using vacuum vapor deposition to achieve a Titanium-Chromium (TiCr) co-deposited coating on the surface of cBN particles. Base on deposition process of the TiCr coating using vacuum vapor deposition technology, it proposed a simulation model by an Angular Coefficient Method(ACM), and conducts compressive strength experiments on the TiCr coating of cBN particles. Using the simulation and analysis model, the effect of temperature on the formation of TiCr coating during the reaction process was systematically analyzed, the molecular flow, the change of film thickness, and the deposition rate at different temperature stages was got, and verify the simulation results through experiments. The formation mechanism of TiCr co-deposited coatings was derived by SEM, XRD characterization and reaction thermodynamic analysis. Experiments show that TiCr co-deposited coatings are effective in increasing compressive strength, and the experimental results can be a guidance in controlling Ti/Cr amount in the coatings. In addition, it was found in experiments that by using vacuum vapor deposition technique, Ti/Cr powder mixing ratio of 1:1 provided the best compressive strength, and the compressive strength increased with higher Cr content in the coating after heating. This achievement is of significant importance for the formation of alloyed coatings on superhard materials, enhancing the wettability between the surfaces of superhard materials and their substrates under high-temperature conditions.

Heat transfer characteristics of vertical condensers under unsteady boundary conditions: Dynamic modeling, experiment validation, and parametric analysis

A dynamic model has been developed to predict the coupled heat transfer characteristics of vertical condensers under varying boundary conditions. The model predictions closely matched the experimental data, with normalized mean bias error and root mean square error metrics below 3%. It was observed that variations in the inlet temperature of the secondary-side coolant did not immediately affect the outlet coolant temperature, exhibiting a noticeable lag phase before gradually adjusting to new conditions. Even after the inlet coolant stabilized, the outlet coolant temperature continued to rise until reaching a steady state after a defined period. The dynamic changes in the condensate film thickness and local heat flux density were categorized into three stages: lag, transitional, and steady. These stages showed differing response and transition times across various locations of the condenser. The bottom of the condenser pipeline demonstrated the shortest response time for condensate film thickness variation but the longest transition time. Additionally, the study investigated the influence of geometric parameters on the dynamic response characteristics of condensers. It was found that longer condenser tubes, lower wall thermal diffusivity, and thicker condensing walls resulted in extended transition times for condensate mass flow at the condenser bottom.

Novel Approach to Analyzing Friction Losses by Modeling the Microflow of Lubricating Oil between the Piston Rings and Cylinder in Internal Combustion Engines

This work focuses on the evolution of lubrication wedge shaping in internal combustion piston engines, taking into account liquid microflows on curved surfaces and coating microgeometries. It introduces a new approach to the analysis of friction losses by simulating the microflow of lubricating oil between the surfaces of piston rings cooperating with the cylinder surface. The models used take into account three types of microgeometry and material expansion. Key results indicate that microirregularities with a stereometry of 0.1–0.2 µm significantly influence the distribution of oil film thickness in the phase of maximum working pressure, which is critical for the functioning of the seal ring. The innovation of the work consists of demonstrating that, despite small changes in the friction force and power in the piston rings, changes in the minimum values of the oil film thickness are significant. The work highlights the failure to take into account microgeometry parameters in friction models, which leads to significant errors in the simulation results, especially in terms of oil film continuity and the contribution of mixed friction. The simulations also indicate that advanced geometric models with high mesh resolution are necessary only for the assessment of changes in oil film thickness during the highest pressure increase in the combustion chamber and taking into account various mixed friction conditions. The results suggest significant progress in engine design and performance, confirming the importance of advanced fluid and mixed friction models in piston engine lubrication research.

Extraction of nanometer-scale displacements from noisy signals at frequencies down to 1 mHz obtained by differential laser Doppler vibrometry

Abstract. A method is presented by which very small, slow, anharmonic signals can be extracted from measurement data overlaid with noise that is orders of magnitude larger than the signal of interest. To this end, a multi-step filtering process is applied to a time signal containing the time-dependent displacement of the surface of a sample, which is determined with a contactless measurement method, differential laser Doppler vibrometry (D-LDV), at elevated temperatures. The time signal contains the phase difference of the measurement and reference laser beams of the D-LDV, already greatly reducing noise from, e.g., length fluctuations, heat haze, and mechanical vibrations. In postprocessing of the data, anharmonic signal contributions are identified and extracted to show the accurate displacement originating from thickness changes of thin films and related sample bending. The approach is demonstrated on a Pr0.1Ce0.9O2−δ (PCO) thin film deposited on a single-crystalline ZrO2-based substrate. The displacement extracted from the data is ca. 38 % larger and the uncertainty ca. 35 % lower than those calculated directly from the D-LDV spectrum.

Analysis of wheel-rail contact under oil lubrication conditions

Abstract This investigation centers on the characteristics of the contact between the wheel and rail when lubricated with oil, with a consideration of the impact of surface roughness. Confronting significant challenges related to low adhesion, a thorough examination is undertaken to analyze the changes in film thickness under oil lubrication, investigating trends at varying vehicle speeds and axle loads. Employing detailed modeling based on micro-elastohydrodynamic theory, the distribution of oil film thickness under diverse operational conditions is determined. The findings indicate that, under oil lubrication, a film thickness in the range of several tens of micrometers is established, effectively insulating the surfaces of the wheel and rail, thereby reducing adhesion. With increasing vehicle speed, the thickness of the oil film also rises, whereas an elevation in axle load results in a marginal decrease in film thickness. This research contributes to a comprehensive comprehension of the wheel-rail contact mechanism in oil lubrication scenarios, providing theoretical backing to address concerns related to low adhesion. The implications are substantial for improving the safety and economic efficiency of efficient railway transportation.

Coupling Study on Quasi-Static and Mixed Thermal Elastohydrodynamic Lubrication Behavior of Precision High-Speed Machine Spindle Bearing with Spinning

In this work, a modified numerical algorithm that couples the quasi-static theory with the mixed thermal elastohydrodynamic lubrication (mixed-TEHL) model is proposed to examine the mechanical properties and lubrication performance of the spindle bearing that is used in a high-speed machine tool with spinning. The non-Newtonian fluid characteristics of the lubricant and the non-Gaussian surface roughness are also considered. Moreover, the mechanical properties and lubrication state of the bearing are examined in various service environments. The results indicate that the temperature reduces the lubrication efficiency, which in turn exerts a significant impact on the mechanical properties. The lubrication that either behaves in the manner of Newtonian or non-Newtonian fluid has a relatively negligible influence on the bearing working state, while the non-Gaussian surface roughness significantly alters the oil film thickness and temperature. Calculations with different operating conditions demonstrate that the operating parameters (i.e., axial load, rotation speed) will directly affect the performance of the bearings via the changes in the oil film thickness and the temperature.

Numerical modeling of a confined falling liquid film sheared by a gas flow in a plate heat exchanger of an NH3/H20 absorption chiller

In recent years, the demand for cooling has seen a substantial increase, primarily due to rising summertime temperatures. Conventional mechanical compression air conditioners have played a predominant role in fulfilling this demand, albeit at the cost of significant electricity consumption. In response, absorption chillers have emerged as an eco-friendly alternative, powered by sustainable heat sources like solar energy or industrial waste heat. The present work is conducted within the framework of developing compact absorption chillers incorporating plate heat exchangers. It builds upon prior research by improving an existing numerical model for falling film plate heat exchangers within an NH3/H2O absorption chiller. This former numerical model evaluates the coupled heat and mass transfer between the liquid film and the vapor flow while excluding hydrodynamic interactions at the liquid-vapor interface. The current investigation aims to address compactness and cost-efficiency limitations in absorption chillers. The consequences of operation within confined spaces were numerically evaluated. An innovative analytical model was developed to quantify the influence of the interactions at the liquid-vapor interface. Shear stress and interfacial perturbations were considered compared to the classical Nusselt model, enabling the evaluation of the changes in the average film thickness and the flooding phenomenon. This analytical model was then added to the previously developed heat and mass transfer model. The numerical model was applied to both the desorber and absorber units. The results show that increased confinement has minimal effects on the transfer coefficients. Additionally, an approach is suggested for estimating flooding in confined spaces and the results are compared with various correlations available in the literature.

Dynamic Characterization of Grease-Lubricated Ball Screws

According to the lubrication characteristics of grease and lubrication mechanism, concerning the Hamrock-Dowson minimum film thickness formula, this paper analyses the trend and size of oil film thickness change of grease-lubricated ball screw sub under different aviation working conditions to identify the lubrication status. ABAQUS software is used to carry out dynamic simulation and the friction coefficient is selected according to the lubrication state and Stribeck curve to define the contact conditions to obtain the friction torque change curve and the fluctuation curve of axial velocity of the nut under different aerospace working conditions. Finally, a test bench is set up to test and calculate the friction torque of grease-lubricated ball screws to analyze the influence of different aviation working conditions on the dynamic characteristics of grease-lubricated ball screws and to investigate the reasons for the change of dynamic characteristics.

Terahertz Sensing of Å‐scale Thin Dielectric Film Via Electron Tunnelling

AbstractPrecise sensing of ultrathin dielectric films is paramount in various fields including nanoscale dielectric characterization, advanced material development, and quality control in microelectronics manufacturing. However, achieving this with conventional detection techniques within the terahertz (THz) frequency range has remained challenging due to their limited sensitivity and resolution. In this study, a novel approach is reported that utilizes Fowler‐Nordheim (FN) tunnelling at a metal‐dielectric junction, which drastically improves the sensitivity to changes in dielectric film thickness down to the Angstrom scale. Through a detailed analysis of both experimental and simulated data, it is demonstrated that the FN tunnelling‐based THz sensing technique exhibits exceptional sensitivity. This finding not only overcomes the limitations of traditional detection techniques, but also paves the way for novel ultrathin film sensing capabilities in the rapidly advancing field of THz technology.

GeSe ovonic threshold switch: the impact of functional layer thickness and device size

Three-dimensional phase change memory (3D PCM), possessing fast-speed, high-density and nonvolatility, has been successfully commercialized as storage class memory. A complete PCM device is composed of a memory cell and an associated ovonic threshold switch (OTS) device, which effectively resolves the leakage current issue in the crossbar array. The OTS materials are chalcogenide glasses consisting of chalcogens such as Te, Se and S as central elements, represented by GeTe6, GeSe and GeS. Among them, GeSe-based OTS materials are widely utilized in commercial 3D PCM, their scalability, however, has not been thoroughly investigated. Here, we explore the miniaturization of GeSe OTS selector, including functional layer thickness scalability and device size scalability. The threshold switching voltage of the GeSe OTS device almost lineally decreases with the thinning of the thickness, whereas it hardly changes with the device size. This indicates that the threshold switching behavior is triggered by the electric field, and the threshold switching field of the GeSe OTS selector is approximately 105 V/μm, regardless of the change in film thickness or device size. Systematically analyzing the threshold switching field of Ge–S and Ge–Te OTSs, we find that the threshold switching field of the OTS device is larger than 75 V/μm, significantly higher than PCM devices (8.1–56 V/μm), such as traditional Ge2Sb2Te5, Ag–In–Sb–Te, etc. Moreover, the required electric field is highly correlated with the optical bandgap. Our findings not only serve to optimize GeSe-based OTS device, but also may pave the approach for exploring OTS materials in chalcogenide alloys.

A Study on the Oil Film Thickness Between the Lower Rail of Oil Control Ring and Lower Flank of Oil Control Ring Groove of an Engine

Abstract Lubricating oil consumption (LOC) of engines causes particulate matter in exhaust gas and abnormal combustion like pre-ignition which becomes a serious problem in hydrogen engines. Lubricating oil transports upward into the combustion chamber of an engine via the sliding surface, the gap, and the side and back of a piston ring. The target of this study was to clarify the mechanism of oil flowing between an oil control ring lower flank and the groove which was the first entrance of lubricating oil supplied from the crankshaft. Oil film thickness at the lower flank of the oil control ring was measured by laser-induced fluorescence method using optical fibers embedded in the lower flank of the ring groove. The measured oil film thickness was compared with forces acting on the lower rail of three-piece type oil control ring. The oil film thickness change was well explained using those forces and it was found that friction force at the sliding surface and pressure in the ring groove were dominant on the oil film thickness under all operating conditions tested in this study.

Advanced Characterization Methodology to Unravel the Biodegradability of Metal-Organic Framework Nanoparticles in Extremely Diluted Conditions.

Porous iron(III) carboxylate metal-organic frameworks (MIL-100; MIL stands for Material of Institute Lavoisier) of submicronic size (nanoMOFs) have attracted a growing interest in the field of drug delivery due to their high drug payloads, excellent entrapment efficiencies, biodegradable character, and poor toxicity. However, only a few studies have dealt with the nanoMOF degradation mechanism, which is key to their biological applications. Complementary methods have been used here to investigate the degradation mechanism of Fe-based nanoMOFs under neutral or acidic conditions and in the presence of albumin. High-resolution STEM-HAADF coupled with energy-dispersive X-ray spectroscopy enabled the monitoring of the crystalline organization and elemental distribution during degradation. NanoMOFs were also deposited onto silicon substrates by dip-coating, forming stable thin films of high optical quality. The mean film thickness and structural changes were further monitored by IR ellipsometry, approaching the "sink conditions" occurring in vivo. This approach is essential for the successful design of biocompatible nano-vectors under extreme diluted conditions. It was revealed that while the presence of a protein coating layer did not impede the degradation process, the pH of the medium in contact with the nanoMOFs played a major role. The degradation of nanoMOFs occurred to a larger extent under neutral conditions, rapidly and homogeneously within the crystalline matrices, and was associated with the departure of their constitutive organic ligand. Remarkably, the nanoMOFs' particles maintained their global morphology during degradation.

Investigating the thickness of patterned polyethylene layers by changing the line speed and temperature in the embossing machine

Patterned polyethylene films are mandatory products in the rubber tire industry. They are used as protective lining to prevent contamination of the rubber. This pattern geometry (2D and 3D) prevents the rubber from sticking to each other. The film is desired to be homogeneous, precise in thickness, and have sufficient mechanical strength. The speed and the temperature of the pattern-forming machine are among the factors that determine this relationship between the thickness of the film and its mechanical properties for sustainable quality production. In this study, the effect of the speed and the temperature of the pattern machine on the pattern thickness during the creation of the pyramid-shaped pattern applied on a 100 ± 5 µm thick polyethylene film were examined. Four different machine speeds (24, 26, 28, and 30 m/min) and three different temperatures (100, 110, and 120 °C) were studied as variables. The impact of parameters on film thicknesses and tensile properties was assessed. Film thickness varied from ~ 375 to ~ 340 µm at higher machine speed, strength-at-break values decreased from 28 to 22 MPa, and elongation values dropped from 575 to 437% with the increment in speed. On the other hand, at higher temperatures, thickness rose from ~ 360 to ~ 390 µm, and elongation values reduced from 440 to 410%. Within the scope of the experimental studies, it was observed that the film thickness changes and the mechanical properties can be controlled by changing the line speed or process temperature.Graphical abstract

Surface coverage ratio of contaminated Taylor bubbles in a square microchannel

Experiments on contaminated Taylor flows in a microchannel were carried out to investigate the surface coverage ratio for different surfactant properties. Nitrogen and water were used for the gas and liquid phases, respectively. Triton X-100, sodium dodecyl sulfate (SDS) of 90% purity and SDS of 99% purity were used as surfactant. The cross section of the microchannel was square and its width was 200μm. The gas and liquid volumetric fluxes were 0.54 and 0.50 m/s, respectively. Taylor flows were formed by mixing the two phases at the T-junction. Shapes of Taylor bubbles were observed using a microscope and a high-speed video camera. The liquid film thickness changed in the film region, demonstrating that a steep gradient of the interfacial surfactant concentration was formed there. The interface was therefore separated into the clean interface region and the immobilized region by detecting the change in the liquid film thickness. The surface coverage ratio estimated from bubble shapes agreed with that measured from the reduction in the bulk concentration due to surfactant separation by bubbles. The surface coverage ratio increased with increasing the bulk concentration and the increasing rate was smaller than that for the adsorption–desorption equilibrium because of the presence of interfacial advection. The data, however, could be fitted by modifying the functional form for the ad-desorption equilibrium. The bulk concentration normalized by the concentration for the breakdown of the logarithmic relation between the surface tension and the concentration given by the isotherm worked for correlating the surface coverage ratio for the three different surfactants, which can be understood from the order of magnitude of the Marangoni stress.

Atomic-Scale Structural Properties in NiCo2O4/CuFe2O4 Bilayer Heterostructures on (001)-MgAl2O4 Substrate Regulated by Film Thickness.

Changing film thickness to manipulate microstructural properties has been considered as a potential method in practical application. Here, we report that atomic-scale structural properties are regulated by film thickness in an NiCO2O4(NCO)/CuFe2O4(CFO) bilayer heterostructure prepared on (001)-MgAl2O4 (MAO) substrate by means of aberration-corrected scanning transmission electron microscopy (STEM). The misfit dislocations at the NCO/CFO interface and antiphase boundaries (APBs) bound to dislocations within the films are both found in NCO (40 nm)/CFO (40 nm)/MAO heterostructures, contributing to the relaxation of mismatch lattice strain. In addition, the non-overlapping a/4[101]-APB is found and the structural transformation of this kind of APB is resolved at the atomic scale. In contrast, only the interfacial dislocations form at the interface without the formation of APBs within the films in NCO (10 nm)/CFO (40 nm)/MAO heterostructures. Our results provide evidence that the formation of microstructural defects can be regulated by changing film thickness to tune the magnetic properties of epitaxial bilayer spinel oxide films.

Flow and thermo-hydrodynamic characteristics in supercritical CO2 lubrication

Supercritical CO2 is used as an important lubricant in Brayton cycle turbomachinery, and the study of lubricant flow and heat transfer mechanisms plays a crucial role in the lubrication performance of Supercritical CO2. To improve the thermal environment and load capacity performance of lubrication in turbomachinery, the turbulence models and real gas models were used in this work to numerically simulate the evolution of lubrication flow and thermal characteristics of CO2 from low pressure to supercritical condition. Simulations were conducted under various operating parameters and lubrication conditions. The rarefaction effect, viscous heat, compression heat and tribological performance were analyzed. The findings indicate that the lubrication film temperature characteristics of low operating pressure depended on the viscous heat dissipation. Under the effect of rarefaction, the CO2 lubrication pressure maximum decreased of 3.0 %. As the operating pressure increased to the supercritical condition, the compression heat effect of SCO2 lubricating film increased and dominated the temperature distribution characteristics of the lubricating film. High operating pressure enhanced the pressure and load capacity of the lubrication film, and reduced the maximum lubrication temperature by 7.2 K. However, it was observed that near the critical temperature, fluctuations in the load capacity and friction torque of the lubricating film damaged the stable operation of the rotor. The change in lubrication film thickness has a significant impact on the load capacity and viscous heat dissipation, with variations as high as 81.4 % and 82.6 %, respectively. The research results provide guidance for the selection of operating pressure and temperature within the lubrication film, thereby improving the thermal working environment and operational stability of the rotor and stator.

Low energy ion irradiation induced Au/Ag multilayer nanostructured substrates for SERS-based molecular sensing

Au and Ag are the most prominent plasmonic materials to study Surface-Enhanced Raman Spectroscopy (SERS) because of their wide tuning of localized surface plasmon resonance in the broad wavelength range. In the present work, the formation of nanostructures of Au single-layer, Au/Ag bi-layer, and Au/Ag/Au/Ag four-layer thin films on silicon substrates by low energy Kr++ ion irradiation with fluences of 1 × 1015 and 3 × 1015 ions/cm2 was systematically studied and were used for the detection of dye molecules. The surface morphology and microstructural analysis indicated the formation of different nanostructures with different ion fluences by atomic force microscopy and field emission scanning electron microscopy. Rutherford backscattering spectrometry results indicate a considerable change in film thickness after ion irradiation, mainly due to the removal of surface atoms due to sputtering. The maximum enhancement in Raman intensity of R6G was observed in the Bi-layer Au–Ag substrate compared to other substrates with an enhancement factor of 4.78 × 106 corresponding to a 1516 cm−1 characteristic peak in SERS analysis. Coumarin 343 molecules trace amount were detected to determine the versatility of the substrate. A finite-difference time-domain simulation was performed to provide a better understanding of the nanostructure hot-spots formation and support the obtained SERS results.

Film thickness-induced optical and electrical modifications in large-area few-layer 2H-MoSe2 grown by MBE.

Here, we report on a detailed study of film thickness-induced effects on optical and electrical characteristics of ultra-thin MoSe2 films grown using molecular beam epitaxy (MBE) on a c-plane sapphire substrate. The layer-dependent optical and electrical responses are investigated for MoSe2 films with different thicknesses (1, 2, 4 and 7 layers). Spectroscopic ellipsometry (SE) reveals significant variation in optical constants with film thickness in the spectral range of 5.04 eV to 0.73 eV. As the thickness increases from 1 layer to 7 layers, the band gap of the materials also changes from 1.62 eV to 1.19 eV. The layer-dependent band diagram analysis shows that the conduction band to Fermi level energy gap changes from 0.50 eV to 0.40 eV as the film thickness changes from 1 layer to 7 layers, making thicker films more n-type than thinner ones. I-V measurement shows an increase in current from the order of 10-9 to 10-5 ampere at a voltage of 3 V as the film thickness increases from 1 layer to 7 layers, which is explained by the corresponding change in the band diagram and supported by a temperature-dependent I-V study. The findings of the study offer a pathway to tune the optical and electrical characteristics of MoSe2 by controlling the layer number which can be valuable for its electronic and optoelectronic device applications.

The impact of thickness-related grain boundary migration on hole concentration and mobility of p-type transparent conducting CuI films.

CuI films present promising optoelectronic properties for transparent conductors. However, the high hole concentration in CuI films hinders the controllable modulation of hole mobility, limiting their application in low-dimensional thin-film transistors. In this study, CuI films were prepared through a Cu film iodination method at room temperature, and a systematic investigation was conducted on the modulation of hole concentration and mobility with varying film thickness. The films exhibited a zinc blende structure (γ-phase) with increasing grain size as the thickness increased. The transmittance and optical bandgap of the films decreased with increasing thickness. The correlation of vacancy concentration with changing film thickness was analyzed through photoluminescence spectroscopy, revealing the influence of grain boundary migration on vacancy formation. The reduction in film thickness diminishes the migration of CuI grain boundaries, consequently reducing the probability of Cu vacancy and I vacancy formation, resulting in diminished hole concentration and enhanced hole mobility and film conductivity. The film with a thickness of 20 nm demonstrated optimal performance, with a transmittance of 90%, hole concentration of 4.09 × 1017 cm-3, hole mobility of 506.50 cm2 V-1 s-1, and conductivity of 33.19 S cm-1. This work deepens the understanding of hole transport such as hole concentration and mobility modulation in CuI films, highlighting the importance of controlling grain boundary migration during the film growth process.

Coalescence of biphasic droplets embedded in free standing smectic A films.

We investigate micrometer-sized flat droplets consisting of an isotropic core surrounded by a nematic rim in freely suspended smectic A liquid-crystal films. In contrast to purely isotropic droplets which are characterized by a sharp edge and no long-range interactions, the nematic fringe introduces a continuous film thickness change resulting in long-range mutual attraction of droplets. The coalescence scenario is divided in two phases. The first one consists in the fusion of the nematic regions. The second phase involves the dissolution of a thin nematic film between the two isotropic cores. The latter has many similarities with the rupture of thin liquid films between droplets coalescing in an immiscible viscous liquid.