Pressure In Deposition Chamber Research Articles

Measurement of velocities of copper nanoparticles exiting a gas aggregation source

Gas aggregation sources have become a valuable tool for the effective production of nanoparticles and nanoparticle films. In some cases (e.g. during in-flight coating of nanoparticles or interaction between nanoparticles and substrate), the critical parameter that influences the applicability of these sources and properties of fabricated nanomaterials is the velocity of produced nanoparticles. Naturally, to control the speed of nanoparticles, it is crucial to determine how it is influenced by process parameters. A mechanical time-of-flight filter has been used to measure the velocities of nanoparticles exiting a magnetron-based gas aggregation source. Nanoparticle velocities have been investigated for various deposition conditions, including aggregation chamber pressure from 20 to 100 Pa, magnetron current from 100 to 500 mA and deposition chamber pressure from 0.015 to 2.5 Pa. Nanoparticles may be accelerated in the area around the exit orifice and decelerated by the background gas in the deposition chamber. This allows tailoring the nanoparticle velocity in the range from 10 m s−1 up to over 100 m s−1. Furthermore, the dependence of the velocity of nanoparticles on their size was found to obey a simple power law. Therefore, the filter may be used not only as a velocity filter but also as a mass filter.

Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions

Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decreased rapidly with an increase in the arc net power and the width of this region decreased with an increase in the deposition chamber pressure. Based on the results of the study, the local Knudsen number was introduced for detecting conditions where the continuum approach is valid under PS-PVD conditions for the first time and the CFD simulations could be reasonably used to determine a process parameter window under the conditions of this study.

Quantitative analysis of ionization rates of depositing particles in reactive plasma deposition using mass-energy analyzer and Langmuir probe

The ionization rates of depositing particles in reactive plasma deposition (RPD) were quantitatively investigated using a measurement system composed of a mass-energy analyzer and a Langmuir probe in order to clarify the formation mechanisms of high-quality transparent conductive oxide films. The detection efficiencies of neutral particles and ions in the mass-energy analyzer were calibrated by the Langmuir probe. The species ionization rates were measured during indium tin oxide (ITO) deposition. The ionization rates associated with changes in the deposition chamber pressure were also measured. During ITO deposition, the lower limits of the following ionization rates were determined: indium ionized at a rate of 74–87%, oxygen atoms at 0.5–0.6%, and oxygen molecules at 0.01–0.02%. These rates may increase depending on the pressure in the deposition chamber. This method would also be applicable for measuring general plasma processes.

Enhancing charge transport in copper phthalocyanine thin film by elevating pressure of deposition chamber

Copper phthalocyanine (CuPc)-based thin film transistors were fabricated using CuPc films grown under different deposition pressure (Pdep) (ranging from 1.8×10−4Pa to 1.0×10−1Pa). The transistor performance highly depended on Pdep. A field-effect mobility of 2.1×10−2cm2/(Vs) was achieved under 1.0×10−1Pa. Detailed investigations revealed that Pdep modulates the molecular packing and orientation of the organic films grown on a SiO2/Si substrate and influences the charge transport. Furthermore, from a device physics point of view, contact resistance of the fabricated transistors decreased when Pdep increased, which was beneficial in reducing energy consumption.

Pulse laser deposited nanostructured ZnO thin films: a review.

This review summarizes the work principles of pulse laser deposition (PLD) apparatus, physical processes like ablation, and plasma plume formation accompanying the deposition of un-doped ZnO from target to substrate material. Various modes of deposition and factors influencing the properties of thin films such as substrate temperature, background gas pressure, laser energy density (laser fluence), target to substrate distance, repetition rate, oxygen partial pressure in deposition chamber, deposition time and post growth annealing which control deposition parameters such as adsorption, desorption, surface diffusion, nucleation, and crystallization/re-crystallization are also discussed in this review. Moreover, various film properties such as morphology, roughness of the film surface, film thickness, grain size, optical transmittance, sensitivity, electrical conductivity, uniformity and electrical resistivity of the deposited ZnO thin films have also been enumerated in the present review.

Cobalt/cobalt oxide nanoparticles-assembled coatings with various morphology and composition synthesized by pulsed laser deposition

Nano-particle (NP) catalysts are under intense investigation in the nanotechnology community because of their large surface-to-volume atomic ratio, size- and shape-dependent properties, and high concentration of low-coordinated active surface sites. However, there is no general strategy to synthesize NPs, possibly in one step, of various materials with tailored properties and desired morphologies. In this work, cobalt oxide NPs assembled coatings have been prepared by reactive pulsed laser deposition of Co in O2 atmosphere. Three different deposition parameters have been varied to investigate their relevance in tailoring composition and structure of the synthesized NPs: 1) the target–substrate distance, 2) the oxygen pressure in deposition chamber, and 3) post oxidation of NPs deposited in vacuum condition. It is proved that by appropriate selection of the deposition parameters, several NP types may be obtained in one single step, namely: Co3O4 or CoO NPs, Co–Co3O4 or Co–CoO core shell NPs, with size ranging from a few nm to several tens of nm. Transmission and Scanning Electron Microscopy as well as Raman Spectroscopy have been utilized to carefully investigate the compositional and structural features of the NPs. A correlation is made between final NP properties and laser-induced processes mainly related to phase explosion generating liquid droplets that cool during flight or on the substrate. Photocatalytic properties of this heterogeneous Co3O4 NPs-assembled coating catalyst for degradation of methylene blue solution under light irradiation are assessed and compared to that of homogenous catalyst producing Co2+ ions in methylene blue solution.

Thermal barrier coating deposition by rarefied gas jet assisted processes: Simulations of deposition on a stationary airfoil

The uniform coating of a complex shaped substrate, such as a gas turbine airfoil, by collisionless physical vapor deposition processes requires rotation/translation of the substrate or sources and is inconceivable for regions on the substrate that are never in the line-of-sight of the vapor source. Recently developed directed vapor deposition processes use electron beam evaporation and inert gas jets to entrain, transport, and deposit metal oxide vapor in an environment where many vapor atom collisions occur prior to deposition. Direct simulation Monte Carlo simulations and experimental depositions of a rare earth modified thermal barrier coating are used to investigate fundamental aspects of the deposition process, including coating thickness and column orientation, over the surface of a nonrotated model airfoil substrate with substantial non-line-of-sight regions. The coating thickness uniformity was found to depend on the deposition chamber pressure and the pressure ratio between the low-pressure deposition chamber and high-pressure reservoir upstream of the gas jet forming nozzle. Under slow flow conditions, significant coating of the non-line-of-sight regions was possible. The growth column orientation is found to also vary over the substrate surface due to changes in the local incidence angle distribution of depositing vapor atoms. The variation in growth column orientation is not predictable by the Tangent rule widely used for predicting columnar growth orientation in physical vapor deposition processes.

The effect of Oxygen partial pressure during deposition in the magnetic properties of ZnO thin film

ABSTRACTWe have studied the magnetic properties of 100 nm thick ZnO thin films prepared by magnetron sputtering in different oxygen partial pressures (ratio of oxygen pressure to total pressure in deposition chamber, POxy). Only the films fabricated at POxy below ~ 0.5 show room temperature ferromagnetism. The saturation magnetization at room temperature is initially found to increase as POxy increases and reaches maximum value of ~ 5 emu/gm at POxy ~ 0.3 and then starts to decrease and becomes diamagnetic for POxy > 0.5. From small angle XRD study of structural properties of the films, we find that the lattice stress developed in the film along c-axis also exhibits a similar behavior with the variation of POxy. Thus, both the room temperature ferromagnetism and lattice stress appear to originate from the intrinsic defects present in the sample.

Effect of Microstructure on the Electrical Properties of Nano-Structured TiN Coatings Deposited by Vacuum Cold Spray

TiN coatings on Al2O3 substrates were fabricated by vacuum cold spray (VCS) process using ultrafine starting ceramic powders of 20 nm in size at room temperature (RT). Microstructure analysis of the samples was carried out by scanning electron microscopy, transmission electron microscopy, and x-ray diffraction. Sheet resistance of the VCS TiN coatings was measured with a four-point probe. The effects of microstructure on the electrical properties of the coatings were investigated. It was found that the sheet resistance and electrical resistivity of TiN coatings were significantly associating with the spray distance, nozzle traversal speed, and deposition chamber pressure. A minimum sheet resistance of 127 Ω was achieved. The microstructural changes can be correlated to the electrical resistivity of TiN coatings.

Control of Thermal Spray Process through Observation on Individual Splat Behavior

In plasma spray process, the individual droplet behavior at impact is the fundamental element to understand the resulting coating microstructure and corresponding coating properties. In this study, the flattening behavior of the sprayed individual particle was systematically investigated by changing the substrate preheating temperature and ambient pressure in deposition chamber. The splat shape change transitionally from a splash shape to a disk shape by substrate preheating or ambient pressure reduction. A transition temperature, Tt, and transition pressure, Pt, were defined and introduced, respectively. Furthermore, the wetting behavior of water droplet and flattening behavior of thermal sprayed particles were studied on the substrate with different elapsed time in an air atmosphere after preheating. It is clearly found that the contact angle increase gradually with an increase of the elapsed time. More splash splats were observed on the substrate with increase of the elapsed time, which agreed with the contact angle measurement results well. Experiment results indicate that wetting of substrate by molten droplet may dominate the flattening behavior of the thermal sprayed particles. Good wetting may be generated by removing the adsorbed gas/condensation through substrate preheating or ambient pressure reduction. Based on the study above, a three-dimensional transition map was proposed as a controlling principle of the thermal spray process.

Hardness and structure characterization of [formula omitted] films produced by reactive magnetron sputtering on a conventional austenitic stainless steel

Ti6Al4V thin films were grown by magnetron sputtering on a conventional austenitic stainless steel. Five deposition conditions varying both the deposition chamber pressure and the plasma power were studied. Highly textured thin films were obtained, their crystallite size being around 10–30nm and their hardness being around 10GPa.

Influence of deposition chamber pressure and substrate temperature on the properties of fluorescent blue and phosphorescent red OLED deposited by OVPD

ABSTRACTOrganic light-emitting diodes (OLED) offer the potential to replace conventional light sources such as incandescent bulbs and fluorescent tubes. The question which thin-film technology is most favorable to produce OLED on an industrial scale is still unanswered. The most established technology for the deposition of small-molecule organic layers is vacuum thermal evaporation. A comparably novel technology is organic vapor phase deposition (OVPD), which offers some unique features in terms of adjustable process parameters such as deposition chamber pressure (P) and substrate temperature (TS). The impact of these parameters on the morphology of organic single layers as well as on the performance of OLED is mostly unknown. In this work, phosphorescent red OLED were produced with different TS and a strong influence on the device efficiency was found. Atomic force microscopy measurements were conducted to investigate the morphology of the hole injection and hole transport layers of the devices deposited at different TS. In addition to this, the influence of TS and P on the performance of fluorescent blue OLED and the morphology of organic single layers was tested. By varying TS and P for the emission layer only, current efficiencies in the range from 4.3 to 6.8 cd/A were found despite the fact that all devices had the same structure. Atomic force microscopy measurements conducted on organic single layers which were deposited at the same process conditions showed rms values ranging from 1.4 to 57 nm.

Hardness of bioactive glass film deposited on titanium alloy by pulsed laser ablation

Certain glasses which contain specific amounts of SiO2, Na2O, CaO and P2O5 (bioglasses) are of a limited number of materials forming strong chemical bonds with bone in vivo, while remaining stable under the harsh conditions encountered in the human body [1–7]. These glasses contain usually less than 60 mol% SiO2, and are of a high Na2O content and a high CaO/P2O5 ratio [5]. Such a composition produces a surface that becomes highly reactive when exposed to a water-containing environment, e.g. of the human body fluids [5]. Monolithic bioglasses are too brittle to be used in structural applications, e.g. as dental root implants. Poor fracture toughness and strength limited the use of these bulk materials to non-load-bearing implants. One way to overcome this problem is to coat a metallic implant with bioglass. The coating provides the bone bonding capacity while the metal substrate provides the structural support. For this reason, various methods were tested to coat metallic implants with glass. The success achieved by these methods is variable. The most commonly used techniques are enameling, electrophoresis, sol-gel, and plasma spraying. The main disadvantage of these methods is poor adhesion strength of the coating to substrate. Besides, electrophoresis and sol-gel methods are substrate specific. Pulsed laser technique has recently been used for fabrication of numerous organic and inorganic films and coatings, as well as for their surface modification [8–11]. Over the last decade laser-induced processes were effectively introduced into advanced biomaterials research and development. The advantage of pulsed laser ablation deposition (PLAD) results from the following. Through the use of a laser radiation on a target, it is possible to vaporize a high refractory material altering the solid only at the zone of the laser spot. The ablated material forms dense plasma. Plasma plume spreads out transporting atoms, ions, clusters and particles to the substrate to form a thin coating. High temperature reached on the target, strongly contributes to maintain the starting materials stoichiometry even for multi-component systems with species of very different vapor pressures. PLAD allows to optimize physical properties of the coating which can be monitored by simply tuning the various deposition parameters: laser irradiation wavelength, energy of the laser pulse, pulse duration, gas composition and pressure in deposition chamber, type of the target and temperature of substrate. PLAD provides strong bonding of the coating with substrate, low residual stress imposed on the coating, and controlled roughness of the surface. Strong bonding of the coating to the substrate is due to the high energy of impacted species. Moreover, PLAD is a versatile technique and can be applied effectively for deposition of multilayered coatings. At the same time, PLAD is well matched with other coating methods, such as plasma spray and biomimetics. This allows to optimize the coatings parameters for different kinds of implants. The structural functions, which an implant should perform in service, are dependent on mechanical properties of the coating, the hardness being one of the most important characteristics. Due to the high reactivity of bioglass with respect to the humid environment, the hardness can be varying along the coating thickness. This may particularly allow to evaluate the hydration depth of the bioglass. In this letter, a study of the PLAD of a commercial Bioglass® on Ti-6A1-4V alloy substrate and hardness of the coating is reported. The original Bioglass® 45S5 has a nominal composition (at.%): Na 38.31, Ca 21.21, Si 36.37, P 4.11, by excluding the oxygen content to permit a comparison with energy dispersive X-ray (EDS) analysis. Before starting the PLAD process, EDS revealed the bioglass target compositions is as follows (at.%): Na 30.3, Ca 23.2, Si 43.8, P 2.8. The compositions difference could probably be due to hydratation and/or losses of volatile compounds. Further, by analyzing small areas at high magnification, small inhomogeneities in the elemental composition were found, but the discrepancy does not exceed 3%. The substrate material for the PLAD coating was a commercial Ti-6A1-4V alloy. Surface of

Growth conditions and microstructure of Y 2O 3 buffer layers on cube-textured Ni

Y 2O 3 films were deposited on cube-textured Ni substrates by electron-beam evaporation as part of a buffer layer study for YBa 2Cu 3O 7− δ (YBCO) coated conductors. Their microstructure was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their crystallographic texture and surface roughness evaluated by X-ray diffraction (XRD) and atomic force microscopy (AFM). Previous studies showed the Y 2O 3 surface normal changed from {100} to {111} on decreasing the deposition chamber pressure from 10 −5 to 10 −6 Torr. In this work, 300 nm thick Y 2O 3 buffer layers were deposited at two different deposition chamber pressures, ∼5×10 −4 Torr N 2 and ∼2×10 −5 Torr air, so as to make the {100} orientation dominant. However, the morphology of the Y 2O 3 buffer layers was significantly affected by changing the deposition chamber pressure, the lower pressure buffer layer being denser and smoother than that made at the higher pressure. The Y 2O 3 grains in a 600 nm thick Y 2O 3 buffer layer grown under 2×10 −5 Torr air became larger and more uniformly square as the film grew thicker. The Y 2O 3 grown on thermally grooved Ni deposited at 2×10 −5 Torr air, showed 〈111〉-oriented grains near the grooves. This local imperfection in the texture could lead to significant barriers to supercurrent flow in the YBCO overlayer.

Novel Parylene-N films deposited at liquid nitrogen temperatures

Vapor deposition polymerization of Parylene-N films at −196°C produces optically opaque, highly porous films. Film density averaged 0.195 g/cm 3, more than five times less than that of conventional non-porous Parylene-N films deposited near room temperature, which have densities of 1.11 g/cm 3. Deposition rates, measured as the change in film thickness per unit time, averaged 8.3 μm/min. This rate is more than two orders of magnitude greater than the deposition rates of nonporous films near room temperature, at otherwise fixed conditions of monomer delivery rate and deposition chamber pressure. On a mass deposition rate basis, the new low temperature film deposition rate is more than an order of magnitude faster than the corresponding rate at room temperature.

Wave Polymerization During Vapor Deposition of Porous Parylene-N Dielectric Films

AbstractParylene-N films vapor deposited near liquid nitrogen temperature (77 K) undergo a unique ‘wave’ polymerization process in which a rapidly moving reaction front is apparent as the film changes from translucent to optically opaque. This moving reaction front produces a highly porous polymer film. The porosity of these films is approximately 80%. By capturing the wave process on video we have quantified the moving ‘wave’ velocity, which averages 11 cm/s. Timeaveraged deposition rates of the resulting opaque, porous films are more than 8 μm/min. This rate is more than two orders of magnitude greater than the measured deposition rates of nonporous films that are deposited at higher temperatures, at otherwise fixed conditions of monomer delivery rate and deposition chamber pressure.

Effect of coupling of radio-frequency plasma on the growth of diamond films in a hot filament reactor

Diamond films have been deposited using a chemical vapour deposition (CVD) technique involving a hybridization of the hot filament and the capacitively coupled radio-frequency (RF) plasma. The changes produced in the surface morphology and Raman spectra of these films are investigated as a function of the magnitude of RF power and deposition chamber pressure. The coupling of low levels of RF power with the hot filament CVD is observed to improve the growth rate as well as quality of the diamond films while higher levels of RF power decreased the growth rate and produced porous films containing needle-shaped microcrystals. These changes are attributed to the ion bombardment of the growing film due to the self-biasing effect of the RF plasma.

Functionally graded materials synthesis via low vacuum directed vapor deposition

The spatially distributed microstructures needed to implement many functionally graded material (FGM) designs are difficult to realize affordably with today's materials synthesis/processing technologies. To address this need, a new directed vapor deposition (DVD) technique has been developed and explored as a potential FGM synthesis tool. The technique exploits supersonic helium jets in combination with electron beam/resistive evaporation under low vacuum (10 −3 -10 Torr) conditions to atomistically spray deposit a wide variety of monolithic and composite materials. Two of the most important processing parameters (the carrier gas velocity and the deposition chamber pressure) that control deposition are identified, and their effect upon deposition efficiency for flat and fiber substrates is explored systematically. Under certain conditions, the DVD approach is found to deposit vapor onto fibers with a significantly higher efficiency than traditional high vacuum line-of-sight vapor deposition techniques. It can even deposit material onto surfaces that are not in the line-of-sight of the source. A computational fluid dynamics model has been used to interpret the experimental observations and to identify the role of carrier gas dynamics in controlling deposition efficiency and spatial distribution.

Techniques for the growth of superconducting oxide thin films using pure ozone vapor

A simple, inexpensive apparatus for the production of pure ozone vapor for use in the in situ growth of superconducting oxide thin films is described. Pure condensed ozone is distilled at 77 K from a dilute mixture of ozone in oxygen gas. The condensed ozone is subsequently heated, raising its vapor pressure to provide an adequate flow of ozone gas into the thin film growth chamber. Thin films of YBa2 Cu3 O7−x with zero resistance at temperatures as high as 85 K have been grown with a deposition chamber pressure of only 2×10−7 Torr and without a post-deposition anneal processing step. Unlike most other commonly used forms of highly reactive oxygen, ozone can be made and stored in very pure form. This makes it very useful when a well-characterized oxidizing gas is needed for systematic studies of the growth kinetics and oxidation of the films. Safety aspects of the ozone-production process are discussed.