Uniformity Of Layer Research Articles

Formation mechanism and control of aluminum layer thickness fluctuation in embedded aluminum–steel composite sheet produced by cold roll bonding process

The influences of rolling reduction and aluminum sheet initial thickness (AIT) on the thickness fluctuation of aluminum layer (TFA) of embedded aluminum–steel composite sheet produced by cold roll bonding were investigated, the formation mechanism of TFA was analyzed and method to improve the thickness uniformity of the aluminum layer was proposed. The results showed that when the reduction increased, TFA increased gradually. When the reduction was lower than 40%, AIT had negligible effect on the TFA, while TFA increased with the decrease of AIT when the reduction was higher than 40%. The non-uniformities of the steel surface deformation and the interfacial bonding extent caused by the work-hardened steel surface layer, were the main reasons for the formation of TFA. Adopting an appropriate surface treatment can help to decrease the hardening extent of the steel surface for improving the deformation uniformity during cold roll bonding process, which effectively improved the aluminum thickness uniformity of the embedded aluminum/steel composite sheets.

Microstructure and Adhesion Properties Post-Annealed Metallic Coating of Fecrbmnsi on Tube and Internal Structure Coal-Fired Boiler

Iron-chrome based metallic coating is generally used to increase the life-time tube and internal structure of coal-fired boiler. The most common method used is thermal spray coating. The advantages of this method are simple in application, repair, and low cost. The post-heat treatment coating on metallic coating applied by the thermal spray method can affect to adhesion properties, the number of porosity and microstructure of coating material. The objective of this study is to analyze the influence of post-annealing on the metallic coating FeCrBMnSi applied by Twin Wire Arc-Spraying (TWAS) method on microstructure and adhesion properties which is applied on tube and internal structure of coal-fired boiler. Post-annealing was performed after coating application in vacuum furnace with variety of temperature at 500 o C, 600 o C and 700 o and holding time about 3 hours. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS) were used to analyze the morphology of microstructure, the uniformity of the deposit layer, and the percentage of porosity. X- Ray Diffraction (XRD) was used to determine phase formation and composition phase. Then, Pull Off Test was performed for adhesion test that is referred to ASTM D4541. The results shows that increasing post-annealed temperature cause microstructure of coating more crystalline, percentage of porosity decreased from 3% As-sprayed to 1,4% at 700 o C post-annealing temperature and it has an effect on the adhesion properties of coating which increase up to 25%.

Self-Organized TiO2 Nanotubes: Influence of the Ti Microstructure on the Nanotube Growth

The synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications. The most established member of this group of materials is nanoporous Al2O3, which has been prepared two decades ago by anodic oxidation of Al into perfectly ordered, honeycomb-like porous structures employing suitable electrochemical conditions [1]. Owing to the flexibility of the pore diameter/length and the relative ease of the Al2O3 dissolution, its porous membranes have been since than widely used as template material of choice for a range of materials [2-4]. Recently, TiO2 has received the highest attention after Al2O3 motivated by its range of applications, including photocatalysis, water splitting, solar cells and biomedical uses. Very significant research efforts have led to reproducible synthesis of self-organized TiO2 nanotube layers by means of anodic oxidation, during which the starting Ti substrate is converted into a highly-ordered nanotubular layer by anodization in suitable electrolytes [5-7]. Although advancements in the anodic synthesis of self-organized TiO2 nanotube layers have been presented over the past years [8], the degree of ordering has not reached so far the level known from porous alumina [1]. Numerous factors influence the ordering and the homogeneity of the TiO2 nanotube layers. In the presentation, we demonstrate significant advancements in the understanding of the influence of Ti substrates on the TiO2 nanotube growth compared to the recent state-of-art. Using SEM, AFM, GDOES and optical measurements we will show how to obtain a high degree of ordering, uniformity and homogeneity in the nanotube structure of TiO2 by tailoring the anodization protocol [9, 10]. Furthermore, based on SEM, EBSD and TEM measurements, we will demonstrate how the Ti grain structure influences the lateral uniformity of the nanotube layers [11].

Influence of CVD Growth Parameters on the Corrosion Resistance of the Resultant Graphene Coating

Graphene coatings have been reported to suppress corrosion of various metal substrates due to their chemical inertness. However, the extent of protection offered depends on the uniformity and defect density of the graphene layers developed on the metallic substrates. Among the various synthesis methods, chemical vapour deposition (CVD) is one of the most promising ones to produce graphene coating on a variety of metal substrates. However, achieving controlled CVD growth of large area, uniform and less defective graphene coating is still challenging. This study investigates the influence of various CVD growth parameters during the graphene synthesis, such as hydrogen flow, carbon precursor flow, growth temperature and cooling rate used on the uniformity of the resultant graphene coating and its corrosion resistance. The barrier properties of graphene-coated Cu substrates were evaluated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl for 1008 h. High graphene growth temperature (1060 ºC) and low hydrocarbon flow rate (1 sccm) in the absence of H2 flow were identified to synthesize a uniform graphene coating, which showed durable barrier performance. During the initial hours of immersion, the graphene coated copper (Cu) specimens showed about one and half order of magnitude improvement in corrosion resistance in 0.1 M NaCl and even after 1008 h, the corrosion resistance provided by the graphene coating was almost five times more than that of bare Cu. The optimized CVD graphene parameters reported here can provide a new direction to achieve long-term durable graphene coating.

The synthesis of hexagonal boron nitride via chemical vapor deposition

Hexagonal boron nitride, a two dimensional wide bandgap insulator material which has a similar structure with graphene, has many excellent physical properties. For instance, hexagonal boron nitride has super mechanical properties, chemical and thermal stabilities, resulting in its wide potential applications in the areas of non-linear optics, ultraviolet laser and protection layers. In addition, due to its atomically smooth surface that is free of trapped charge and dangling bonds, hexagonal boron nitride is a super dielectric material for graphene electrical devices. Moreover, hexagonal boron nitride can be fabricated into planar or vertical hetero-structures with other two dimensional materials, which show unique properties and potential applications in novel electronic devices. How to synthesize large scale and high quality hexagonal boron nitride is currently key scientific issue. Up to now, many strategies, including mechanical exfoliation, deposition by ion beam sputtering, co-segregation, chemical vapor deposition and so on, have been developed for growing this material. Among these methods, chemical vapor deposition provides a versatile platform for modulating the growth and etching process of this material and producing a large scale material with high quality. This review summarizes a series of work regarding the synthesis of hexagonal boron nitride by chemical vapor deposition method, in which most recent work is also presented, and discusses the choices of reaction precursors and substrates in details. The use of solid borane ammonia complex leads to better controls over the properties of hexagonal boron nitride such as layer numbers and uniformity compared with the use of mixed B and N compounds as precursors. On the other hand, the types, surface structures and properties of the supporting substrates are critical for the growth of hexagonal boron nitride. For example, Cu substrate has advantages for growing single layered hexagonal boron nitride crystal or film, while the use of Ni or Fe substrates usually leads to multi-layered materials that are applicable to different applications. This difference largely results from two different growth mechanisms in two typical systems, i.e., surface diffusion and co-segregation mechanism. Moreover, owing to the nature of complex systems of chemical vapor deposition, kinetic controls over the growth and etching of hexagonal boron nitride can result in a more precise controls over size, shape and edge structures of this material, and the related progresses are presented. Finally, the key challenge and future directions are also presented. From the basic scientific research and large-scale application points of view, there are still plenty room for further studies of controllable synthesis of hexagonal boron nitride. How to optimize the growth process, further understand the growth mechanism, and realize the large sized layer number controlled growth of single crystal hexagonal boron nitride are important issues required to be solved in future. Further explorations of a better substrate such as an alloy possibly leads to combined advantages of components in an alloy, overcoming the difficulties associated with uniform production of high quality hexagonal boron nitride crystal or film. In addition, searching better reaction precursors also deserves attention, and working on this may be rewarding.

Direct synthesis of thickness-tunable MoS2 quantum dot thin layers: Optical, structural and electrical properties and their application to hydrogen evolution

We report a layer thickness-tunable direct synthesis growth method for bi- to few-layer crystalline molybdenum disulfide (MoS2) thin layers. For the first time, a facile, cost effective, and mass-scalable direct synthesis approach, based on a chemical bath deposition, is designed for quantum dot(QD)-based MoS2 layers using (NH4)6Mo7O24 and thiourea (CH4N2S) as precursors. Using this process, the uniformity of large area thin layer can be retained, and the applicability to various substrates can provide great opportunities in the fabrication of various atomically thin layered structures. The structural and optical properties of the MoS2 QD layers are systematically investigated. Raman, AFM and TEM analyses confirm the formation of continuous and crystalline bi-, tri- and few-layered MoS2. Their electrical properties are evaluated by bottom-gate FETs, and a field-effect mobility value of ~1.06cm2V−1s−1 and a current on/off ratio in the order of ~ 105 are obtained. Particularly, MoS2 prepared as a thin film consisting QD structures of grains shows novel electrocatalytic property. MoS2 QDs on Au/Si are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by Tafel slope (94mVdecade−1), exchange current density (1.91×10-1mAcm−2) and long-term durability for 20h. Our approach opens new avenues for the design and synthesis of functional MoS2 layers for energy harvesting.

Contact pin-printing of albumin-fungicide conjugate for silicon nitride-based sensors biofunctionalization: Multi-technique surface analysis for optimum immunoassay performance

Mass fabrication of integrated biosensors on silicon chips is facilitated by contact pin-printing, applied for biofunctionalization of individual Si3N4-based transducers at wafer-scale. To optimize the biofunctionalization for immunochemical (competitive) detection of fungicide thiabendazole (TBZ), Si3N4 surfaces are modified with (3-aminopropyl)triethoxysilane and examined after: immobilization of BSA-TBZ conjugate (probe) from solutions with different concentration, blocking with bovine serum albumin (BSA), and immunoreaction with a mouse monoclonal antibody against TBZ. Nanostructure, surface density, probe composition and coverage uniformity of protein layers are evaluated with Atomic Force Microscopy, Spectroscopic Ellipsometry, Time-of-Flight Secondary Ion Mass Spectrometry and X-ray Photoelectron Spectroscopy. Contact pin-printing of overlapping probe spots is compared with hand spotted areas. Contact pin-printing resulted in two-fold increase of immobilized probe surface density as compared to hand spotting. Regarding BSA-TBZ immobilization, an incomplete monolayer develops into a bilayer as the concentration of BSA-TBZ molecules in the printing solution increases from 25 to 100μg/mL. Upon blocking, however, a complete protein monolayer is formed for all the BSA-TBZ concentrations used. Free surface sites are filled with BSA for low surface coverage with BSA-TBZ, whereas loosely bound BSA-TBZ molecules are removed from the BSA-TBZ bilayer. As a consequence immunoreaction efficiency increases with the printing probe concentration.

Effect of Anode Shape on Uniformity of Electrodeposition onto Resistive Substrates

This work is devoted to the theoretical study of the effect of anode shape, insulating shields, the exchange current density and operating conditions on the uniformity of metal layer deposited onto the resistive cathode. Laplace’s equation for the potential in the electrolyte solution, Poisson’s equation for the potential in the resistive cathode, and the equation of metal thickness evolution were used as the mathematical model. The numerical solution was performed using the boundary element and finite element methods. The possibilities for controlling the distribution of deposit thickness over the cathode surface are demonstrated by the example of metal deposition onto an annulus workpiece. The use of the anode of the calculated shape enabled us to obtain a deposit of uniform thickness over almost the entire workpiece surface except for the very edges, where the deposit was thicker. The application of shields designed in the work enabled us to eliminate this drawback.

Conformality of PVD shell layers on vertical arrays of rods with different aspect ratios investigated by Monte Carlo simulations

AbstractApplications such as batteries, fuel cells, solar cells, and sensors, can benefit from high surface-to-volume ratio core/shell arrays of nanorods. The fabrication of the conformal shell layers on nanorod arrays has been a formidable task. In order to assess the deposition conditions for the production of conformal shell coatings by physical vapor deposition (PVD) techniques, we employed Monte Carlo (MC) simulations that involved shell depositions under different flux distributions and angles on arrays of rods. We investigated the conformality of PVD shell layers on nanorod arrays of different aspect ratios, which is defined to be the ratio of rod height to the gaps between nearest-neighbor rods. MC simulated core/shell structures were analyzed for the thickness uniformity of the shell layer across the sidewalls of rods. Our results show that a small angle deposition approach involving a uniform oblique flux (U-SAD) with a small incidence angle ≤ 30o can generate a fairly conformal shell coating around small aspect-ratio rods. However, normal angle deposition with an angular flux distribution (A-NAD) achieves superior conformality both on small and high-aspect-ratio structures compared to U-SAD, conventional uniform normal angle deposition (U-NAD), and SAD with an angular flux distribution (A-SAD). A-NAD can be realized in a PVD system such as by high pressure sputter deposition; while U-SAD can be achieved in thermal evaporation system with a small angle incident flux. In addition, U-NAD and A-SAD can correspond to film growth by normal incidence thermal evaporation and SAD-high pressure sputter deposition, respectively.

Characterization of powder bed generation in electron beam additive manufacturing by discrete element method (DEM)

The dynamic behavior of a collection of powder during raking process was simulated by utilizing discrete element method (DEM), aiming at obtaining powder packing features of powder layer, which are valuable for electron beam additive manufacturing. For a better matching between simulation and real process, the mechanical model of particulate system was modified. The simulation results revealed that powder packing density increased with increasing layer thickness, and the powder with better flowability was favored for higher packing density and uniformity of powder layer. The mixture of powder with large and small mean size can increase packing density in some degree, but it was found to be detrimental to the powder flowability.

NUMERICAL ANALYSIS OF EDGE OVER COATING AND BAFFLE EFFECT ON HOT-DIP GALVANIZING

In hot-dip galvanizing process, air jet wiping control is so crucial to determine the coating thickness and uniformity of the zinc layer on the steel strip. A numerical simulation of gas-jet wiping in hot-dip galvanizing was conducted to minimize the occurrence of edge over coating (EOC). The causes of EOC were identified by contrasting and analyzing the airflow fields on the strip edge with and without a baffle. The factors influencing the airflow field on the strip edge during the change in the gap between the baffle and the strip edge were also analyzed. The effect of the distance between the air knife and the strip was evaluated. Technological parameters with on-site guidance role were obtained by combining them with the actual production to elucidate the role of the baffle in restraining the occurrence of EOC. The uniform distribution of pressure and coating thickness on the strip is achieved when the distance of the baffle from the strip edge is about 0.3 times of the jetting distance.

Acetylene Flow Rate as a Crucial Parameter of Vacuum Carburizing Process of Modern Tool Steels

Abstract Carburizing is one of the most popular and wide used thermo-chemical treatment methods of surface modification of tool steels. It is a process based on carbon diffusive enrichment of the surface material and is applied for elements that are supposed to present higher hardness and wear resistance sustaining core ductility. Typical elements submitted to carburizing process are gears, shafts, pins and bearing elements. In the last years, more and more popular, especially in highly advanced treatment procedures used in the aerospace industry is vacuum carburizing. It is a process based on chemical treatment of the surface in lower pressure, providing much higher uniformity of carburized layer, lower process cost and much lesser negative impact on environment to compare with conventional carburizing methods, as for example gas carburizing in Endo atmosphere. Unfortunately, aerospace industry requires much more detailed description of the phenomena linked to this process method and the literature background shows lack of tests that could confirm fulfilment of all needed requirements and to understand the process itself in much deeper meaning. In the presented paper, authors focused their research on acetylene flow impact on carburized layer characteristic. This is one of the most crucial parameters concerning homogeneity and uniformity of carburized layer properties. That is why, specific process methodology have been planned based on different acetylene flow values, and the surface layer of the steel gears have been investigated in meaning to impact on any possible change in potential properties of the final product.

The effect of material attributes and process parameters on the powder bed uniformity during a low-dose dosator capsule filling process

The objective of this work was to assess the effect of process parameters of a dosator nozzle machine on the powder bed uniformity of inhalation powders with various characteristics during a low-dose dosator capsule filling process. Three grades of lactose excipients were extensively characterized and filled into size 3 capsules using different dosing chamber lengths (2.5, 5mm), nozzle diameters (1.9, 3.4mm), powder bed heights (5, 10mm) and filling speeds (500, 3000capsules/h).The fill weight and the weight variability of Lactohale 100 (large particles, good flowability, low cohesion) remained almost the same, regardless of the process parameters throughout the capsule filling run time. Moreover, for this powder an increase in the fill weight at a higher filling speed was observed in all cases. Fill weight variability was significantly higher for lower dosing chamber volumes at a filling speed of 3000 capsules per hour. Lactohale 220 (small particles, poor flowability, high cohesion) delivered entirely different results. After a certain run time, depending on instrumental settings, a ‘steady-state’ with constant fill weights and low weight variability was achieved. For this highly cohesive powder, a high dosing chamber volume requires a low filling speed in order for the powder to completely fill the dosator nozzle. Moreover, it was established that a dosing chamber length of 2.5mm and a powder bed height of 10mm were required due to the powder’s high fill weight variability over time, while the dosator size had no effect on it.In summary, the layer uniformity, the fill weight and the weight variability strongly depend on the powder characteristics and the instrumental settings. The results indicate that Lactohale 220 requires special attention during low-dose capsule filling. The study presents excellent insights into the effect of material attributes and process parameters on the layer uniformity and the quality of end product.

Fabrication of cellulose nanofiber‐based ultrafiltration membranes by spray coating approach

ABSTRACTUltrafiltration membranes containing a cellulose nanofiber barrier layer were fabricated by the spray coating method, where the thickness and uniformity of the barrier layer were systematically investigated as a function of air pressure, flow rate and concentration of the cellulose nanofiber suspension. In specific, the surface morphology of the barrier layer was studied by scanning electron microscopy and its uniformity was examined by the fluorescence dye imaging method. The ultrafiltration performance of the membranes fabricated by the spray coating method was also compared with that of the membranes made by the knife coating approach using dextran molecules as probe, where the former consistently exhibited significantly higher permeation flux while remaining the same rejection ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44583.

Effects of Zn concentration and heat treatment on the microstructure, mechanical properties and corrosion behavior of as-extruded Mg-Zn alloys produced by powder metallurgy

Magnesium alloys have been regarded as potential degradable biomedical materials due to their suitable mechanical properties and excellent biocompatibility. In this study, Mg-Zn alloys were fabricated by powder metallurgy and then hot extruded. The effects of Zn concentration and heat treatment on their microstructure, mechanical properties and corrosion behavior were investigated. The compression test results showed that their mechanical properties were suitable for bone tissue engineering. The corrosion behavior of Mg-Zn alloys was analyzed by immersion tests and electrochemical tests in Ringer's solution. The results revealed that the increasing Zn concentration reduced the corrosion potential but increased corrosion current because severe micro-galvanic corrosion was caused by more large-size intermetallic phases. Although solid solution treatment could reduce intermetallic phase amounts, it caused micropores on the surface. And these micropores could resulted in the pitting corrosion and reduce the corrosion resistance. Notably, aging treatment could reduce the segregation of Zn and promote the compactness and uniformity of corrosion product layer on the surface, leading to the improvement of corrosion resistance. In addition, the as-extruded Mg-6%Zn alloy (wt.%) aged for 72 h was harmless to L-929 cells in cytotoxicity test. Consequently, the as-extruded Mg-Zn alloys prepared by powder metallurgy are promising to develop to be ideal biodegradable implants for bone tissue engineering.

Development of array-type atmospheric-pressure RF plasma generator with electric on-off control for high-throughput numerically controlled processes.

An array-type atmospheric-pressure radio-frequency (RF) plasma generator is proposed for high-precision and high-throughput numerically controlled (NC) processes. We propose the use of a metal-oxide-semiconductor field-effect transistor (MOSFET) circuit for direct RF switching to achieve plasma on-off control. We confirmed that this type of circuit works correctly using a MOSFET with a small parasitic capacitance between its source and gate. We examined the design method for the distance between adjacent electrodes, which corresponds to the parasitic capacitance between adjacent electrodes and is very important in the individual on-off control of each electrode. We developed a prototype array-type plasma generator apparatus with 19 electrodes and the same number of MOSFET circuits; we then confirmed that each electrode could control its plasma on-off state individually. We also demonstrated that the thickness uniformity of the surface Si layer of a silicon-on-insulator wafer could be processed to less than 1 nm peak to valley by the NC sacrificial oxidation method using the apparatus.

Charged Polymer-Coated Separators by Atmospheric Plasma-Induced Grafting for Lithium-Ion Batteries

A simple and fast method of atmospheric plasma-induced grafting was applied over a polyethylene membrane to enhance its performance as a separator for lithium-ion batteries. The process of grafting has formed a thin, durable, and uniform layer on the surface of the porous membrane. The charges of grafted polymers affected the performance of batteries in many ways besides the change of hydrophilicity. Negative charges in polymers improve the capacity retention of batteries and the uniformity of the SEI layer. On the other hand, the electrostatic attraction between different charges contributed to small increases of thermal stability and mechanical strength of separators. Polyampholyte was grafted by using the mixtures of monomers, and the composition of the grafted layer was optimized. The formation of stable uniform SEI layers and the marked improvement in capacity retention were observed in the full cell tests of the lithium battery with the polyampholyte-grafted separators when the polyampholyte has a negative net charge.

Publisher's Note: Electro- and photoluminescence imaging as fast screening technique of the layer uniformity and device degradation in planar perovskite solar cells [J. Appl. Phys. 120, 035702 (2016)

Publisher's Note: Electro- and photoluminescence imaging as fast screening technique of the layer uniformity and device degradation in planar perovskite solar cells [J. Appl. Phys. <b>120</b>, 035702 (2016)

Self-Organized TiO2 Nanotube Arrays: Towards Improved Ordering

Synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications. The nanoporous Al2O3 – most established member of this group of materials – has been prepared by anodic oxidation of Al under suitable electrochemical conditions two decades ago into perfectly ordered, honeycomb-like porous structures (1). Owing to the flexibility of the pore diameter/length and the relative ease of the Al2O3 dissolution, its porous membranes have been since than widely used as template material of the choice for a range of materials (2-4). It is the TiO2 that has received the highest attention after Al2O3 motivated by its range of applications, including photocatalysis, water splitting, solar cells and biomedical uses. Very significant research efforts have led to reproducible synthesis of self-organized TiO2 nanotube layers by means of anodic oxidation, during which the starting Ti substrate is converted into highly-ordered nanotubular layer by anodization in suitable electrolytes (5-7). Although advancements in the anodic synthesis of self-organized TiO2 nanotube layers have been presented over past years (8), the degree of ordering has not reached so far the level known from porous alumina (1). Numerous factors influence the ordering and the homogeneity of the TiO2nanotube layers. In the presentation, we aim to demonstrate significant advancements in the ordering of anodic TiO2nanotubes compared to known state-of-art. In particular, we will show recent results on the extremely ordered nanotube arrays. In addition, utilizing AFM, SEM and optical measurements, we will show how to obtain via tailored anodization protocols a very decent degree of uniformity and homogeneity of the nanotube layers. Moreover, based on SEM, EBSD and TEM measurements, we will demonstrate how the Ti grain structure influences the lateral uniformity of the nanotube layers (9-11).

Lifetime estimation of SiC MOSFETs under high temperature reverse bias test

Reliability physics of silicon carbide (SiC) metal-oxide semiconductor field-effect transistor (MOSFET) is not sufficiently clear; therefore an accurate estimation method of lifetime has been strongly required. The relationship between the failure time of 4H-SiC double implanted MOSFETs under high temperature reverse bias test and the doping concentration in a drift layer was studied to clarify the failure physics. The failure time of the device showed dependence on the doping concentration in the 150mm wafer. The breakdown occurred at the gate oxide over the threading dislocation in the JFET region. The electric field simulation indicated that the oxide electric field linearly depends on the doping concentration, which means the failure time depends on the oxide electric field. According to these results, the electric field acceleration tests were conducted with the samples in the uniform area of the doping concentration so as to exclude the distribution of the oxide electric field in each sample. The lifetime showed dependence on the oxide electric field varied by the drain bias intentionally. These results revealed the importance of the doping concentration uniformity of the epitaxial layer and we established the method to estimate the lifetime accurately.