Film Thickness Uniformity Research Articles

Leidenfrost levitation of a spherical particle above a liquid bath: Evolution of the vapour-film morphology with particle size

We consider a spherical particle levitating above a liquid bath owing to the Leidenfrost effect, where the vapour of either the bath or sphere forms an insulating film whose pressure supports the sphere’s weight. Starting from a reduced formulation based on a lubrication-type approximation, we use matched asymptotics to describe the morphology of the vapour film assuming that the sphere is small relative to the capillary length (small Bond number) and that the densities of the bath and sphere are comparable. We find that this regime is comprised of two formally infinite sequences of distinguished limits which meet at an accumulation point, the limits being defined by the smallness of an intrinsic evaporation number relative to the Bond number. These sequences of limits reveal a surprisingly intricate evolution of the film morphology with increasing sphere size. Initially, the vapour film transitions from a featureless morphology, where the thickness profile is parabolic, to a neck–bubble morphology, which consists of a uniform pressure bubble bounded by a narrow and much thinner annular neck. Gravity effects then become important in the bubble leading to sequential formation of increasingly smaller neck–bubble pairs near the symmetry axis. This process terminates when the pairs closest to the symmetry axis become indistinguishable and merge. Subsequently, the inner section of that merger transitions into a uniform-thickness film that expands radially, gradually squishing increasingly larger neck–bubble pairs into a region of localised oscillations sandwiched between the uniform film and what remains of the bubble whose radial extent is presently comparable to the uniform film; the neck–bubble pairs farther from the axis remain essentially intact. Ultimately, the uniform film gobbles up the largest outermost bubble, whereby the morphology simplifies to a uniform film bounded by localised oscillations. Overall, the asymptotic analysis describes the continuous evolution of the vapour film from a neck–bubble morphology typical of a Leidenfrost drop levitating above a flat solid substrate to a uniform-film morphology which resembles that in the case of a large liquid drop levitating above a liquid bath.

Uniform growth of MoS2 films using ultra-low MoO3 precursor in one-step heating chemical vapor deposition

In chemical vapor deposition (CVD), homogeneous molybdenum vapor concentration is important in synthesizing uniform thickness and large coverage of two-dimensional molybdenum disulfide (2D-MoS2) films. Here, we synthesize few-layer MoS2 films with uniform thickness and adequate coverage over 50 mm2 size area using ultra-low molybdenum trioxide (MoO3) precursor placed directly under a face-down silicon dioxide/silicon (SiO2/Si) substrate in one-step heating CVD. The precursor mass is controlled by dispersing MoO3 powder in ethanol (C2H5OH) and varying the volume of MoO3/C2H5OH solution coated on SiO2/Si substrates into 10, 20 and 25 µL. Field emission scanning electron microscopy images reveal that 20 µL MoO3/C2H5OH solution produces ∼93% area coverage of 2D-MoS2 films. The average Raman spectra show the typical presence of MoS2 peaks around 378.8 cm−1 and 404 cm−1 referring to the E12g and A1g modes, respectively. The difference between the two Raman modes for all samples is ∼25 cm−1, indicating few-layer MoS2 films. The thickness of MoS2 films is estimated at around 2.8 ± 0.44 nm and 3.2 ± 0.43 nm (∼6 layers) using atomic force microscopy analysis. These findings suggest that ultra-low MoO3 precursor is useful to produce uniform thickness and high coverage few-layer MoS2 films using one-step heating CVD.

Effect of magnetic field on the thickness uniformity of thin film deposited on inner surface

In order to improve the thickness uniformity of thin film deposited on inner surface, an auxiliary magnetic field was set inside the arc ion plating device and applied during thin film deposition. Effect of magnetic field on the film thickness uniformity was studied through simulation and experiments. Simulation results revealed that magnetic field significantly increased the amount of ions deposited in the pipe. Along the axis of the pipe, the number of deposited ions first decreased and then increased. Experiment results proved that magnetic field changed the trend of the film thickness along the axis of the pipe and raised the ratio of the minimum to the maximum of the film thickness, thereby improving the film thickness uniformity. When magnetic field was applied together with bias, both the film thickness and thickness uniformity increased with the magnetic field intensity. • An auxiliary magnetic field was set inside the arc ion plating device and applied to assist the deposition. • Thin films were prepared onto the inner surface of a pipe. • Magnetic field significantly increased the amount of ions deposited in the pipe. • Magnetic field changed the trend of the film thickness along the axis of the pipe and improved the film thickness uniformity.

Uniformity of Surface Film Thickness of Meniscus Lens in Third-Order Common Rotation Planetary System

Uniformity of Surface Film Thickness of Meniscus Lens in Third-Order Common Rotation Planetary System

Process optimization & reactive extrusion of high-molecular weight Poly(butylene-adipate-co-terephthalate) (PBAT) polymer for film blowing application

The present study demonstrates a novel approach of the process optimization for the synthesis of Poly(butylene-adipate-co-terephthalate) polymer, and its exclusive reactive extrusion for the film blowing application. The polymers have been synthesized under different processing conditions in order to determine the effect of different variables on the kinetics and optimize the system to obtain biopolymers. The catalytic chemistry of tetra-isopropyl titanate (TIPT) and zinc acetate in the optimal dosage resulted in the development of very high molecular weight PBAT, which is very essential for a polymer to have superior mechanical properties. The polymers were characterized using gel permeation chromatography (GPC), FT-IR, and calorimetry (DSC) analysis to investigate their properties. Furthermore, the polymer compounding was conducted using a unique reactive extrusion process which resulted in the compound with physiochemical property retention at the reduced polymer dosage level. This novel extrusion process reduced the polymer consumption in the compounding by up to 25% with intact properties. Mechanical and thermal properties were enhanced using metal complex-based inorganic coupling agents and fluoropolymers during the process. In the blowing, a flexible and thin film of uniform thickness was obtained in the continual run on the machine. The films were tested for mechanical properties which were at par with commercially available bags. With the ever-increasing demand for environmental-friendly products in plastics & polymers and stricter regulations against the use against conventional plastics, these polymer-based bio-films can be extensively used in the packaging and plastic bag applications due to their biodegradability and the superior strength in terms of mechanical properties which are comparable to the one exhibited by conventional polyethylene bags.

Investigation of film thickness uniformity on tablets by handheld Raman spectrometer

Investigation of film thickness uniformity on tablets by handheld Raman spectrometer

Film thickness uniformity of deep ultraviolet large aperture aspheric mirror

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed

Optimization of coating uniformity in a simple rotation system by using a rotating shadow mask.

A theoretically designed rotating shadow mask is proposed to optimize the uniformity of a simple rotation system, which makes full use of the width of the coating chamber. This method can fabricate a large-aperture optical component, the diameter of which is more than half the width of the coating machine. The rotating shadow mask is applied to correct the film thickness uniformity near the center point of simple plane substrate. The factors influencing the effect of the rotating shadow mask are simulated and discussed. Then the shape of the rotating shadow mask is theoretically designed, and the uniformity within a corresponding radius is well corrected. After determining the shape of the rotating shadow mask, an additional fixed shadow mask is calculated and used to improve the uniformity of the entire substrate. Through the application of the two shadow masks together, uniformity about 99.5% is obtained in the diameter of 640 mm on a 1100 mm coating machine.

Numerical investigation on heat transfer enhancement and surface temperature non-uniformity improvement of spray cooling

Heat dissipation and uniform temperature distribution are crucial to the operational reliability of electronic devices. In this study, the heat transfer enhancement and surface temperature non-uniformity (STNU) improvement of spray cooling are numerically investigated by CFD. The simulated results match well with experimental data under verification conditions with the maximum relative deviation below 7%, which demonstrates the numerical reliability of the two-phase flow model based on Euler-Lagrangian approach. The results of adjusting spray height reveal that there are different optimal spray heights for the heat transfer (4 mm) and the STNU (12.81 mm), indicating that the heat transfer enhancement and STNU improvement cannot be realized simultaneously. Based on this, two methods to enhance heat transfer and reduce STNU are developed. One method is to reduce the tangent angle θ and increase the tangent height H accordingly. It shows that the θ = 30°, H = 27.59 mm case has a maximum enhancement of 24.03% in heat flux relative to the θ = 100°, H = 6.21 mm case. Moreover, for all nozzles (θ = 30°∼100°), the lower STNU is attained at respective tangent heights. The other method is spray-array jets cooling, in which 132 micro-hole jets are added around the spray. It is found that the minimum STNU is obtained by spray-array jets cooling compared with all cases of spray cooling. In addition, it weakens the evaporation, but promotes the forced convection dramatically. Based on the analysis of several average liquid film microscopic characteristics and the droplet distribution, it is concluded that the mean film velocity, thickness and droplet coverage uniformity are the keys to determine heat transfer and STNU.

Study on thickness uniformity of Ta2O5 film evaporated on the inner-face of a hemispherical substrate

Study on thickness uniformity of Ta2O5 film evaporated on the inner-face of a hemispherical substrate

Indentation behavior of suspended single-walled carbon nanotube films

Suspended thin film carbon nanotubes with suitable mechanical strength are in high demand for applications such as sensors, particle filters, or thermoacoustic speakers. However, researchers working on the production and development of applications for thin films have found difficulty in evaluating their mechanical strength. This research shows the nano-indentation behavior of thin (<26 nm thickness) single-walled carbon nanotube suspended films, to evaluate their mechanical strength. Indentation tests, scanning electron microscopy, and Raman, infrared, reflection spectroscopy showed that the high crystallinity of carbon nanotubes and film thickness uniformity are important for achieving high mechanical strength.

Asymmetric Sawtooth Microstructure-Induced Vapor Mobility for Suppressed Buoyancy Conditions: Terrestrial Experiment and Design for ISS Experiments

The lack of buoyancy forces in microgravity stagnates vapor bubbles on heated electronic surfaces, raising local surface temperatures above device operating limits. Though flow boiling can help dissipate higher heat fluxes, the addition of pumps and regulated flow loops increases design complexity for electronic systems. Passive directional motion of the fluid using an asymmetric sawtooth microstructure has demonstrated motion along the surface due to viscous forces. The current study explores the sawtooth microstructure in the nucleate boiling regime for a horizontal upward- and downward-facing orientation with varying sawtooth profiles (60°–30° and 75°–15°) in terrestrial gravity conditions as a precursor to the International Space Station (ISS) experiments. A laser powder bed fusion metal additive manufacturing technique was used to fabricate the test surfaces with 250- $\mu \text{m}$ nucleation sites located on the long slopes. For the test surface with cavities spaced 2-mm apart, the wall superheat was ~4 K lower compared to cavities spaced 1 mm apart in the upward-facing orientation. The downward-facing surface induced passive vapor mobility in the direction of the long slope, and a thin liquid film was observed between the vapor mass and microstructure. This liquid film thickness was predicted using a simplified force balance model modified from a prior parabolic flight experiment. The model predicted a uniform liquid film thickness of $49~\mu \text{m}$ for a vapor slug moving at 13.7 mm/s with the input heat flux at 1.25 W/cm2. These terrestrial tests in the adverse orientation suggest that the sawtooth microstructure will successfully induce vapor mobility in upcoming ISS microgravity experiments. Elements of the final flight ampoule, including the cooling zone, the two-stage pressure relief system, and the high-speed imagery setup, are discussed.

Photoresponsive polymers with dangling triptycene units as efficient receptor for fullerene‐C60

AbstractWe report herein a new triptycene derivative (1) with an azo functional group. This molecule has been used as a monomer to yield two linear polymers (TAFPs) that have several triptycene units dangling from the linear polymer chain. TAFPs are soluble in organic solvents and are thermally stable. TAFPs can be cast into thin films. Further, these polymers are fluorescent with emission intensity increasing upon irradiation with ultraviolet light due to photoisomerization of the azo groups present in them. The fluorescence of TAFPs are quenched in the presence of C60, which supports their strong affinity for each other. Since both TAFP1 and TAFP2 form stable thin films of uniform thickness over large area coupled with their interaction with C60, these polymers may find potential applications in the development of optoelectronic devices or as molecular sensors in supramolecular chemistry.

Towards Scalable Large-Area Pulsed Laser Deposition.

One of the significant limitations of the pulsed laser deposition method in the mass-production-technologies of micro- and nanoelectronic and molecular device electronic fabrication is the issue of ensuring deposition of films with uniform thickness on substrates with large diameter (more than 100 mm) since the area of the laser spot (1–5 mm2) on the surface of the ablated target is incommensurably smaller than the substrate area. This paper reports the methodology that allows to calculate the distribution profile of the film thickness over the surface substrate with a large diameter, taking into account the construction and technological parameters of the pulsed laser deposition equipment. Experimental verification of the proposed methodology showed that the discrepancy with the experiment does not exceed 8%. The modeling of various technological parameters influence on the thickness uniformity has been carried out. Based on the modeling results, recommendations and parameters are proposed for manufacturing uniform thickness films. The results allow for increasing the film thickness uniformity with the thickness distribution < 5% accounts for ~ 31% of 300 mm diameter substrate.

Al-Ti-W alloys deposited by magnetron sputtering: Effective barrier to prevent steel hydrogen embrittlement

Thin film represents a promising alternative for the protection of metallic structures against hydrogen embrittlement and corrosion degradation. Al-Ti-W coatings were deposited by magnetron sputtering technique using three pure metallic targets. Tungsten was incorporated in Al-Ti amorphous coating with different contents ranging from 0 to 17 at% by keeping a constant Ti/Al ratio at an average of 0.8. The deposition rate was calculated in order to obtain 4 µm as an uniform film thickness. XRD, DSC and TEM analyses were performed to confirm the amorphous state of the coatings and to determine the glass transition temperature (Tg) and crystallization temperature peak (Tp). These temperatures were increased respectively from 423 °C and 595 °C to 490 °C and 665 °C with the increase of W concentration up to 17 at%. Corrosion resistance in a saline solution decreased with the increase of W content.The incorporation of W element induced an increase of the thin film hardness (H) and Young’s modulus (Er) from 9 GPa to 9.35 GPa and from 117 GPa to 131,79 GPa, respectively. The surface roughness varied with the incorporation of W that strongly influenced the coatings’ corrosion behavior. Chemical and electrochemical hydrogen charging techniques were performed to expose coated steels to hydrogen sources. W addition in the binary Al-Ti coatings strongly enhanced their resistance to hydrogen absorption. The estimated total hydrogen content trapped in the coated steel during a cathodic polarization decreased with the incorporation of W.

Computational Simulation of a Hot Filament Chemical Vapor Deposition Process for Depositing SRO Films

In the present report, a two dimensional (2D) model was developed to describe the fluid dynamics, heat and mass transfer of a Chemical Vapor Deposition activated by a Hot Filament (HFCVD) reactor, as well as the chemical generation of the precursor species which are present in the growth of non-stoichiometric silicon rich oxide (SRO) films. The SRO is known for have excellent photo luminescent properties which are useful in optoelectronic applications. This material can be obtained by the HFCVD technique which offers important advantages such as the easily to obtain thin films with diverse structural, compositional and optical characteristics. During deposition is a priority to control key parameters as inlet flow, substrate temperature and pressure so it compels to know previous theoretical information about these parameters which can be obtained by computational simulation. Therefore, by means of commercial Computational Fluid Dynamics (CFD) were solved the continuity, momentum and energy equations in steady state. Also, a thermodynamic equilibrium study of the SiO2(s) + H2 (g) reaction was carried out with the Factsage software. The thermodynamic equilibrium results provide the main chemical species which are present during the deposit process of the SRO films. The 2D model was used to simulate the temperature and velocity distribution of the hydrogen in the deposit process. The theoretical calculated temperatures were compared with those obtained experimentally by thermocouple measurements. From the simulation results, the temperature and gas velocity profiles were obtained at different hydrogen flow levels (50, 75, 100 sccm) and temperature source-substrate distances (5, 6 and 7mm) for a 50 sccm level. SEM micrographs and profilometry measurements disclose that the outlet configuration affects substantially both the thickness and surface uniformity of the SRO films. This parameter was modified to obtain a better quality (thickness and uniformity) and a large deposit area.

Effect of current density on electrodeposited cobalt ferrous tungsten magnetic thin films

Co-Fe-W electrodeposited magnetic thin film properties were studied to identify the possible applications in different area. The film was prepared using the electrodeposition method with different current densities, in order to get the uniform deposition with different thickness. A vibrating sample magnetometer studies provide the value of magnetic saturation (Ms=0.112emu), retentivity (Mr=0.020emu) and coercivity (Hc=88.95Oe). The prepared film is (45min, thickness is 3.10μm) more suitable to develop tiny integrated memory devices. X-ray diffraction studies (XRD) confirm the cubic crystalline nature of the prepared thin films. Surface morphology analysis clearly shows the uniform thickness (0.2 μm) of the thin film [scanning electron microscope (SEM)]. The highest percentage of Co, Fe and W composition in the thin films were obtained by using energy dispersive X-ray analysis. The maximum hardness value is 212/7.5 mAcm2 for 45min and best adhesion with desirable magnetic properties have been reported in the present communication.

Atomic Layer Deposition of Ternary Indium/Tin/Aluminum Oxide Thin Films, Their Characterization and Transistor Performance under Illumination.

Multilayered heterostructures comprising of In2O3, SnO2, and Al2O3 were studied for their application in thin‐film transistors (TFT). The compositional influence of tin oxide on the properties of the thin‐film, as well as on the TFT characteristics is investigated. The heterostructures are fabricated by atomic layer deposition (ALD) at 200 °C, employing trimethylindium (TMI), tetrakis(dimethylamino)tin (TDMASn), trimethylaluminum (TMA), and water as precursors. After post‐deposition annealing at 400 °C the thin‐films are found to be amorphous, however, they show a discrete layer structure of the individual oxides of uniform film thickness and high optical transparency in the visible region. Incorporation of only two monolayers of Al2O3 in the active semiconducting layer the formation of oxygen vacancies can be effectively suppressed, resulting in an improved semiconducting and switching behavior. The heterostacks comprising of In2O3/SnO2/Al2O3 are incorporated into TFT devices, exhibiting a saturation field‐effect mobility (μsat) of 2.0 cm2 ⋅ V−1 s−1, a threshold‐voltage (Vth) of 8.6 V, a high current on/off ratio (IOn/IOff) of 1.0×107, and a subthreshold swing (SS) of 485 mV ⋅ dec−1. The stability of the TFT under illumination is also altered to a significant extent. A change in the transfer characteristic towards conductive behavior is evident when illuminated with light of an energy of 3.1 eV (400 nm).

Tunable thickness and uniform drop deposition of graphene oxide on porous anodic aluminum oxide and a reliable thickness measurement technique

The pinned contact line of sessile droplets containing micro/nanoparticles on a substrate results in nonuniform depositions with noncontrollable thicknesses, thereby producing the coffee-ring effect. In this study, we demonstrated that the thickness of graphene oxide (GO) films can be engineered using porous anodic aluminum oxide (AAO) substrates to fabricate uniform GO films. The outstanding thickness controllability and uniformity of GO films were obtained via tailorable hydrodynamic flow in a sessile droplet due to the pores of the AAO substrate. Furthermore, we developed a novel approach for measuring the micro/nanoscale thicknesses of GO films using an optical microscope. The thicknesses of the deposited GO film, measured via optical microscopy, demonstrated good agreement with those obtained via atomic force microscopy. These findings are beneficial for GO film applications, such as in wearable sensors, filtration, inkjet printing.

Evolution of a facile and novel general strategy for fabricating single and mixed 3d-block transition metal hydroxide/oxide films for innumerable applications

A single-step, unique, less arduous, and economical strategy has been employed to fabricate floating Co0.33Ni0.67(OH)2 (~536 nm thick) film of predominantly uniform thickness on the surface of a precursor solution via homogeneous nucleation by purging NH3 vapors over it. Subsequently, transferring 1 sq. inch part of as-fabricated films onto the glass substrate, they were transformed into the films of CoNi2O4 by calcining them at a temperature of 300 °C. The transferability of as-formed films on the glass substrate and the robust mechanism to control their thickness assign splendid features to this synthesis technique. A comprehensive study based on the firm footing of experimental observations and findings, pertaining to unfold the inherent mysteries of primary film formation mechanism associated with the employed strategy, has been pursued in this work. In addition to this, due to multitudinous innovative and potential applications in different fields, the promising single and mixed 3d-block transition metal hydroxide/oxide (TMH/TMO) films have triggered an immense enthusiasm amongst the researchers globally for investigating them for the benefit of humanity. Thus, due to this exigency, a trivial novel synthesis strategy is also required for fabricating them. Conceiving an idea from the film formation strategy employed in our previous as well as the current study, this employed strategy has also been generalized for the fabrication of single/mixed 3d-block TMH/TMO films. Uniformity of film thickness, transferability on a desired substrate and reliable mechanism to control the film thickness assign advantageous features to this strategy over the prevailing solution processable film deposition methods and make it more suitable for depositing TMH/TMO films for their versatile applications in the fields of electronics, energy storage and optoelectronics etc.