Films Of Various Thicknesses Research Articles

Using electrical impedance spectroscopy to identify equivalent circuit models of lubricated contacts with complex geometry: In-situ application to mini traction machine

Electrical contact resistance or capacitance as measured between a lubricated contact has been used in tribometers, partially reflecting the lubrication condition. In contrast, the electrical impedance provides rich information of magnitude and phase, which can be interpreted using equivalent circuit models, enabling more comprehensive measurements, including the variation of lubricant film thickness and the asperity (metal-to-metal) contact area. An accurate circuit model of the lubricated contact is critical as needed for the electrical impedance analysis. However, existing circuit models are hand derived and suited to interfaces with simple geometry, such as parallel plates, concentric and eccentric cylinders. Circuit model identification of lubricated contacts with complex geometry is challenging. This work takes the ball-on-disc lubricated contact in a Mini Traction Machine (MTM) as an example, where screws on the ball, grooves on the disc, and contact close to the disc edge make the overall interface geometry complicated. The electrical impedance spectroscopy (EIS) is used to capture its frequency response, with a group of load, speed, and temperature varied and tested separately. The results enable an identification of equivalent circuit models by fitting parallel resistor-capacitor models, the dependence on the oil film thickness is further calibrated using a high-accuracy optical interferometry, which is operated under the same lubrication condition as in the MTM. Overall, the proposed method is applicable to general lubricated interfaces for the identification of equivalent circuit models, which in turn facilitates in-situ tribo-contacts with electric impedance measurement of oil film thickness – it does not need transparent materials as optical techniques do, or structural modifications for piezoelectric sensor mounting as ultrasound techniques do.

Experimental and modeling study on liquid film thickness of horizontal gas-liquid annular flow using ultrasonic method

In horizontal annular flow, the high gas velocity leads to the strong randomness, rapidity and complexity of the structure and dynamic characteristics of gas-liquid interfacial wave. As one of the important parameters to describe the interfacial wave, the liquid film thickness is significant to study the hydrodynamic characteristics of the gas-liquid two-phase flow. In this paper, the ultrasonic echo resonance main frequency (UERMF) method and the ultrasonic reference signal elimination (URSE) method are compared by numerical simulation method. The minimum liquid film thickness measured by these two methods are 0.3 mm and 0.01 mm, respectively. Experiments are conducted on a stainless steel test section with an inner diameter of 50.0 mm to study annular air-water flow under five different pressure conditions (from 0.1 MPa to 0.7 MPa). The experimental data is processed using the URSE method to analyze the characteristics of the liquid film under different operating conditions. In addition, based on the aforementioned experimental dataset, a comparison is made regarding the performance of existing predictive correlations. It is found that the existing correlations have certain limitations in capturing the variations of liquid film thickness in annular flow, particularly at high pressures and for different pipe diameters. Therefore, a new liquid film thickness correlation suitable for different system pressures and pipe diameters is proposed. By expanding the range of fitted data points (220 data points), the 95 % relative error of improved model is within ±25 % error band for all available data (authors' and literature). The mean absolute percentage error (MAPE) is 11.08 %. The improved correlation has the applicability and extrapolation for different system pressure and pipe diameter conditions.

High‐Quality NiFe Thin Films on Oxide/Non‐Oxide Platforms via Pulsed Laser Deposition at Room Temperature

AbstractSoft ferromagnetic permalloy (NiFe) thin films are promising for applications in spintronic devices because of their constituent electrical and magnetic properties. Electron beam evaporation and sputtering techniques have been used to deposit NiFe thin films. For in situ stacking of NiFe with functional complex oxides, the pulsed laser deposition (PLD) method is highly desirable. However, the growth of high‐quality NiFe (and non‐oxide thin films in general) by PLD remains a formidable task. Here, high‐quality NiFe thin films of various thicknesses on oxide/non‐oxide substrates with desirable magnetic properties by PLD at room temperature are reported. The magnetic properties are found to be strongly dependent on the laser fluence of the deposition process. The laser fluence of 4 J cm−2 produces the highest magnetization of ≈547 emu cc−1. The small coercivity (few Oersted) and sharp ferromagnetic switching behavior indicate uniaxial anisotropy with an easy axis along the in‐plane direction. In addition, thickness‐dependent magnetodynamics characterizations are studied via ferromagnetic resonance. These results offer significant insight into the PLD‐based development of thin metal magnetic films.

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.

Hollow-cathode plasma deposited vanadium oxide films: Metal precursor influence on growth and material properties

Due to its different polymorphs, including vanadium pentoxide (V2O5) and vanadium dioxide (VO2), the vanadium oxide (VOX) compound is an immensely interesting material with many important applications. While atomic layer deposition (ALD) is among the possible VOX film synthesis methods, literature reports have majorly utilized thermal-ALD, which reveals as-grown amorphous VOX films. Further post-deposition annealing process is needed to crystallize these films. High-temperature crystallization indeed limits the use of low-temperature compatible materials, processes, and substrates. In this work, we report on the low-temperature crystalline VOX film growth in a hollow-cathode plasma-enhanced atomic layer deposition reactor using two different vanadium precursors, tetrakis(ethylmethylamino)vanadium and vanadium(V) oxytriisopropoxide. Oxygen plasmas were used as co-reactants at a substrate temperature of 150 °C. Along with the purpose of investing in the impact of metal precursors on VOX film growth, we also studied Ar-plasma in situ and thermal ex situ annealing to investigate possible structural enhancement and phase transformation. In situ Ar-plasma annealing was performed with 20 s, 20 SCCM Ar-plasma, while post-deposition ex situ annealing was carried out at 500 °C and 0.5 mTorr O2 pressure. In situ ellipsometry was performed to record instant film thickness variation and several ex situ characterizations were performed to extract the optical, structural, and electrical properties of the films. The outcomes of the study confirm that both metal precursors result in as-grown crystalline V2O5 films at 150 °C. On the other hand, post-deposition annealing converted the as-grown crystalline V2O5 film to VO2 film. Finally, we have also successfully confirmed the metal-to-insulator transition property of the annealed VO2 films via temperature-dependent structural and electrical measurements.

CO2 ultrathin film growth on a monolayer of CO2 adsorbed on the NaCl(100) surface: sticking coefficient and IR-optical signatures in the ν3 region.

CO2 ultrathin molecular films were grown onto a preadsorbed monolayer NaCl(100)/p(2 × 1)-CO2 at 40 K. Polarization infrared spectroscopy (PIRS) reveals that so-prepared films have better quality than directly grown films. A sticking probability of 0.74 ± 0.1 was deduced from the integrated IR absorption. The presence of the monolayer doublet in the film spectra suggests a Stranski-Krastanov film growth with locally varying film thicknesses on the surface. In the region of the ν3(12C16O2) band, fine structure was observed between the well-known transverse-optical (TO) and longitudinal optical (LO) bands. Two independent computational models were applied to analyze the nature of the observed fine structure. Both pair potential calculations in combination with a vibrational exciton model as well as plane-wave density functional theory (DFT) in combination with phonon calculations of IR intensities at the Γ-point reveal that a weak mode visible in s-polarization and p-polarization originates from a vibrational film excitation located near the substrate interface. A series of p-polarized weak bands appearing and partly disappearing upon film-growth is assigned to film stacks of unique local thickness.

Comparison of Deuterium Retention in Tungsten Films of Various Thickness

Comparison of Deuterium Retention in Tungsten Films of Various Thickness

Second Harmonic Generation Versus Linear Magneto-Optical Response Studies of Laser-Induced Switching of Pinning Effects in Antiferromagnetic/Ferromagnetic Films

Composite magnetic nanostructures are a subject of high research interest, as they provide a number of exciting effects absent in live nature. Among others, much attention has been paid to the studies of exchange coupling in antiferromagnetic/ferromagnetic (AFM/FM) films, which leads to the pinning effect. It manifests itself as a widening and shift of the magnetic hysteresis loop with respect to zero value of the external magnetic field oriented along the pinning direction. In this work, we report on comparative studies of linear and nonlinear magneto-optical effects under the laser-induced switching of the pinning effect in IrMn/CoFe films of various thickness of the ferromagnetic CoFe layer. We found that the magneto-optical response of the pinned AFM/FM nanofilms appears with different hysteresis loop parameters in the transverse magneto-optical Kerr effect (MOKE) and interface-sensitive magnetization-induced second harmonic generation (SHG), indicating the diversity of the magnetic effects at interfaces compared to the bulk of the films.

Studying the Crucial Physical Characteristics Related to Surface Roughness and Magnetic Domain Structure in CoFeSm Thin Films

This study investigated the effects of varying film thicknesses and annealing temperatures on the surface roughness and magnetic domain structure of CoFeSm thin films. The results revealed that as the film thickness increased, both the crystalline size and surface roughness decreased, leading to a reduction in coercivity (Hc) and improved magnetic contrast performance. Energy-dispersive X-ray spectroscopy (EDS) analysis confirmed the presence of cobalt (Co), iron (Fe), and samarium (Sm) within the thin films. Notably, the 40 nm Co40Fe40Sm20 thin film annealed at 200 °C exhibited lower sheet resistance (Rs) and resistivity (ρ), indicating higher conductivity and a relatively higher maximum magnetic susceptibility (χac) at 50 Hz. These findings suggest that these films are well suited for low-frequency magnetic components due to their increased spin sensitivity. The 40 nm Co40Fe40Sm20 thin film, subjected to annealing at 200 °C, displayed a distinct stripe domain structure characterized by prominently contrasting dark and bright patterns. It exhibited the lowest Hc and the highest saturation magnetization (Ms), leading to a significant improvement in their soft magnetic properties. It is proposed that the surface roughness of the CoFeSm thin films plays a crucial role in shaping the magnetic properties of these thin magnetic films.

Mask-less Laser Direct Imaging & Adaptive Patterning for Fan-Out Heterogeneous Integration

Mask-less Laser Direct Imaging & Adaptive Patterning for Fan-Out Heterogeneous Integration

Numerical Studies On the Oil Film Thickness in the Case of Stratified Flow with Different Oil-Water Flow Combinations Through Sudden Contraction Tube

Abstract Most of the oil transportation industries deal with liquid-liquid flow considering the adiabatic situation. In such applications, film thickness measurement plays a very significant role in understanding the flow characteristics. The distribution of phases for efficient wall treatment and to understand the phase distribution, measurement of film thickness is very important. Among different flow patterns, stratified flow is most common for low and medium viscous oil-water flow. At lower oil velocities, stratified flow is observed downstream of singularity whereas in the upstream section, stratified flow is observed for low to medium oil velocities and high-water superficial velocity. Variation of oil film thickness for stratified flow has been analyzed in the present study. Results show that oil film thickness decreases with the increase in the superficial velocity of water (Us-Water) for a constant oil superficial velocity (Us-Oil). With the increase in the volume fraction of one phase, the film thickness of that phase increases. As Us-Oil increases, the film thickness of oil also increases for a constant Us-Water. Oil film thickness is directly proportional to the viscosity of oils. This means, the more the viscosity of the oil, the more will be the oil film thickness.

Evaluation of mortar film thickness of dry process crumb rubber modified warm mix asphalt concrete utilizing 2-dimensional images

Asphalt mortar film thickness and its distribution are accepted to be strong parameters that affect the durability and performance of asphalt mixtures. This study focuses on the effects of the Warm Mix Asphalt (WMA) additive, production temperatures, and compaction effort on the distribution of mortar film thickness in dry process crumb rubber modified mixtures. Utilizing image analysis, not only mortar film thickness distribution but also its distribution for each aggregate size fraction was analyzed. It is revealed that the difference in mixture preparation procedures and aggregate size fractions significantly affects the distribution and variation of mortar film thickness. Moreover, to relate between cracking and the mortar film thickness, indirect tensile strength tests are performed at three different temperatures. A good correlation was only built between cracking resistance and average mortar film thickness at −10 °C. Therefore, it can be concluded that the mortar film thickness cannot be solely used as an indicator of performance. However, it can be still generalized that thicker and variable mortar film thickness weakens the aggregate interlock and low-temperature cracking resistance.

Triboelectric behaviors mechanism of continuous rotary friction pairs in liquid lubrication and its potential application

Liquid-solid triboelectric behaviors often involve varied liquid-solid and gas-liquid interfaces. However, applications submerged in lubricants haven not been extensively studied. This paper studies the triboelectric behaviors of continuous rotary friction pairs in liquid lubrication. Triboelectric signals are observed from friction pairs made of graphite and stainless-steel with polytetrafluoroethylene (PTFE) coatings. The mechanism lies in the generated streaming current, with constant circumferential velocities and variable radial velocities induced by the variation of film thickness. Pulse signals of electric outputs of 0.26 V are observed as the film thickness changes suddenly. Further discussions about electrode configurations and sealing mediums are conducted for potential applications in film thickness monitoring of mechanical seals. This work expands theories and applications of conventional liquid-solid triboelectric performances.

Full degree-of-freedom polarization hologram by freeform exposure and inkjet printing

Since the invention of holography by Dennis Gabor, the fabrication of holograms has mainly relied on direct recording of wavefront by engraving the intensity fringes of interfering electric fields into the holographic material. The degree-of-freedom (DoF) is often limited, especially for its usage as a holographic optical element in imaging or display systems, as what is recorded is what to use. In this work, based on the emerging self-assembled photo-aligned liquid crystal, a polarization hologram with full DoF for local manipulation of optical structure is demonstrated. The ability to record an arbitrary wavefront (in-plane DoF) is achieved by freeform surface exposure, while the local adjustment of deposited liquid crystal (out-of-plane DoF) is realized by inkjet printing. The methodology for designing and fabricating such a hologram is exemplified by building a full-color retinal scanning display without color crosstalk. Here, the arbitrary wavefront modulation capability helps to eliminate the aberrations caused by mismatched exposure and display wavelengths. The local liquid crystal adjustment ability enables the suppression of crosstalk by variation of chiral pitch and film thickness to tune the peak and valley of Bragg diffraction band. The demonstrated method is expected to greatly impact the fields of advanced imaging and display, such as augmented reality and virtual reality, that require optics with an ultrathin form factor and high degrees of design freedom simultaneously.

Tunable random laser based on hybrid plasmonic enhancement.

This research investigates the hybridized plasmonic response of silver film combined with dispersed silver (Ag) nanowires (NWs) to random laser emission. The mixture of Rhodamine B (RhB) dye and polyvinyl alcohol (PVA) matrix is taken as the gain medium for random lasing, and the silver combination provides feedback mechanisms for light trapping. Importantly, film roughness and the coupling between localized and extended (delocalized) surface plasmons play a vital role in RL performance evaluation. The laser threshold is strongly influenced by film thickness attributed to surface roughness. Furthermore, the variation in film thickness also supports the wavelength modulation of 9 nm (597 nm to 606 nm), which results from the reabsorption of RhB. Additionally, the intriguing capability of emission wavelength tuning under the variation of temperature facilitates exciting prospects for precise wavelength control in plasmonic devices.

A Highly Transparent β-Ga2O3 Thin Film-Based Photodetector for Solar-Blind Imaging

Ultra-wide bandgap Ga2O3-based optoelectronic devices have attracted considerable attention owing to their special significance in military and commercial applications. Using RF magnetron sputtering and post-annealing, monoclinic Ga2O3 films of various thicknesses were created on a c-plane sapphire substrate (0001). The structural and optical properties of β-Ga2O3 films were then investigated. The results show that all β-Ga2O3 films have a single preferred orientation (2(_)01) and an average transmittance of more than 96% in the visible wavelength range (380–780 nm). Among them, the sample with a 90-minute sputtering time has the best crystal quality. This sample was subsequently used to construct a metal-semiconductor-metal (MSM), solar-blind, ultraviolet photodetector. The resulting photodetector not only exhibits excellent stability and sunblind characteristics but also has an ultra-high responsivity (46.3 A/W) and superb detectivity (1.83 × 1013 Jones). Finally, the application potential of the device in solar-blind ultraviolet imaging was verified.

Mechanical Ventilation Heat Recovery Modelling for AccuRate Home—A Benchmark Tool for Whole House Energy Rating in Australia

To manage energy-efficient indoor air quality, mechanical ventilation with a heat recovery system provides an effective measure to remove extra moisture and air contaminants, especially in bathrooms. Previous studies reveal that heat recovery technology can reduce energy consumption, and its calculation needs detailed information on the thermal performance of exhaust air. However, there are few studies on the thermal performance of bathroom exhaust air during and after showers. This study proposed a detailed thermal performance prediction model for bathroom exhaust air based on the coupled heat and mass transfer theory. The proposed model was implemented into the AccuRate Home engine to estimate the thermal performance of residential buildings with heat recovery systems. The time variation of the water film temperature and thickness on the bathroom floor can be estimated by the proposed model, which is helpful in determining whether the water has completely evaporated. Simulation results show that changing the airflow rate in the bathroom has little effect on drying the wet floor without additional heating. The additional air heater installed in the bathroom can improve floor water evaporation efficiency by 24.7% under an airflow rate of 507.6 m3/h. It also demonstrates that heat recovery can significantly decrease the building energy demand with the fresh air load increasing and contribute about 0.6 stars improvement for the houses in Hobart (heating-dominated region). It may be reduced by around 3.3 MJ/(m2·year) for the houses in other regions. With this study, guidelines for optimizing the control strategy of the dehumidification process are put forward.

Modeling of the Lattice Dynamics in Strontium Titanate Films of Various Thicknesses: Raman Scattering Studies.

While the bulk strontium titanate (STO) crystal characteristics are relatively well known, ultrathin perovskites' nanostructure, chemical composition, and crystallinity are quite complex and challenging to understand in detail. In our study, the DFT methods were used for modelling the Raman spectra of the STO bulk (space group I4/mcm) and 5-21-layer thin films (layer group p4/mbm) in tetragonal phase with different thicknesses ranging from ~0.8 to 3.9 nm. Our calculations revealed features in the Raman spectra of the films that were absent in the bulk spectra. Out of the seven Raman-active modes associated with bulk STO, the frequencies of five modes (2Eg, A1g, B2g, and B1g) decreased as the film thickness increased, while the low-frequency B2g and higher-frequency Eg modes frequencies increased. The modes in the films exhibited vibrations with different amplitudes in the central or surface parts of the films compared to the bulk, resulting in frequency shifts. Some peaks related to bulk vibrations were too weak (compared to the new modes related to films) to distinguish in the Raman spectra. However, as the film thickness increased, the Raman modes approached the frequencies of the bulk, and their intensities became higher, making them more noticeable in the Raman spectrum. Our results could help to explain inconsistencies in the experimental data for thin STO films, providing insights into the behavior of Raman modes and their relationship with film thickness.

Experimental and theoretical study on cooling performance of membrane roof with circulated water film

Membrane roofs are widely used in buildings for excellent daylight and visual effects. Nevertheless, excessive solar penetration results in an overheated indoor thermal environment. The experimental and theoretical study on the cooling performance of circulated water film technology on membrane roofs was conducted. The scale experiment results indicated that with circulated water film the membrane surface temperatures decreased rapidly to a level slightly above the water temperature, where the polyvinylidene fluoride (PVDF) and ethylene tetrafluoroethylene (ETFE) membranes were 0.4 and 2.4 °C higher than water temperature. While the indoor air temperature gradually decreased in instances where PVDF roofs were utilized, the application of ETFE roofs did not yield a significant decrease in temperature. Subsequently, we derived an analytical solution for the dynamic two-dimensional heat and mass transfer process of the water film flowing on the membrane with incident solar radiation, which was validated by experiment. The analysis of influential factors indicated that the temperature drop increased with absorbed solar radiation and outdoor dry-bulb temperature, and decreased with the ambient wet-bulb temperature. Conversely, the cooling performance exhibited minimal sensitivity to variations in water film thickness. The indoor operative temperature dropped by 0.5–0.8 °C in the membrane roofed atrium with water film. The water film effectively cools the indoor thermal environment with membrane roofs.

Oxygen Plasma Treatment to Enable Indium Oxide MESFET Devices

AbstractMetal‐semiconductor field‐effect transistor (MESFET) devices based on pulsed laser deposition (PLD) grown In2O3 thin films with on–off ratios exceeding 6 orders of magnitude and low sub‐threshold swing values close to the thermodynamic limit are reported. Oxygen plasma treatment and compensation doping with Mg are utilized to suppress the accumulation of electrons at the surface of In2O3, which is a major obstacle for its use as an active material in electronic devices. The influence of both methods is investigated on the electrical properties of thin films as determined by Hall effect measurements on samples of varying film thickness. Using the performance of vertical Schottky barrier diodes as a benchmark, fundamental plasma parameters such as input power and background gas pressure are optimized.