Gas Flow Ratio Research Articles

Catalyst-Less and Transfer-Less Synthesis of Graphene on Si(100) Using Direct Microwave Plasma Enhanced Chemical Vapor Deposition and Protective Enclosures.

In this study, graphene was synthesized on the Si(100) substrates via the use of direct microwave plasma-enhanced chemical vapor deposition (PECVD). Protective enclosures were applied to prevent excessive plasma etching of the growing graphene. The properties of synthesized graphene were investigated using Raman scattering spectroscopy and atomic force microscopy. Synthesis time, methane and hydrogen gas flow ratio, temperature, and plasma power effects were considered. The synthesized graphene exhibited n-type self-doping due to the charge transfer from Si(100). The presence of compressive stress was revealed in the synthesized graphene. It was presumed that induction of thermal stress took place during the synthesis process due to the large lattice mismatch between the growing graphene and the substrate. Importantly, it was demonstrated that continuous horizontal graphene layers can be directly grown on the Si(100) substrates if appropriate configuration of the protective enclosure is used in the microwave PECVD process.

Modelling of autonomous power source for gas distribution station using ASPEN HYSYS

The article is devoted to the study of energy conservation issues in gas transmission and gas distribution systems. In the Aspen HYSYS software package, the authors developed a model of an autonomous power source for gas distribution station (GDS). A brief simulation sequence is described. The dependence of the electric power of the expander-generator unit on the natural gas flow ratio is determined.

Preparation of CrCN Super-Hard Coating

The cutting tool is prone to wear and failure during turning process, which affects the quality of the machined surface. In order to increase the hardness, wear resistance, and extend lifespan of the cutting tool, this work proposed a CrCN super-hard coating and optimized its parameters of preparation process. The CrCN super-hard coating was deposited on cemented carbides by radio frequency reactive magnetron sputtering. Cr3C2 (99.9%) was selected as the target, N2 and Ar as the reaction gas. The effects of power, N2/Ar flow ratio, deposition temperature, and deposition pressure on the properties of deposited CrCN super-hard coatings were investigated. The deposition rate, Vickers hardness, crystal degree, and surface morphology of the coating were comprehensive analyzed, and then, the optimal parameters for preparing CrCN super-hard coating were obtained: sputtering power of 300 W, N2/Ar gas flow ratio of 4/46 sccm, deposition temperature of 200 °C, and deposition pressure of 0.8 Pa. After measurement, the physical and mechanical properties of the CrCN super-hard coating were: the thickness of 1.8 μm, the hardness of 2700 HV, and the bonding force of 52 N.

Effect of SF6 flow ratio on microstructure and properties of MgF2 thin films prepared by magnetron sputtering

In order to suppress F- deficiency of MgF2 film prepared with magnetron sputtering, the effects of SF6: Ar gas flow ratio on the structure and properties of the film were investigated. F: Mg ratio increased rapidly first then decreased with the increase of SF6 flow ratio, got 2.13 at 7%, closest to the stoichiometric ratio 2:1; while the film's refractive index first decreased and then increased, got a minimum at 550 nm 1.409 at 7%. MgF2 film increased the glass substrate transmittance within 300–1100 nm to 94.24% from 93.2%, and improved photoelectric conversion efficiency of GaAs solar cell by 2.1%.

Low-resistivity SrRuO3 thin films formed on SiO2 substrates without buffer layer by RF magnetron sputtering

Thin films of SrRuO3, which is a conductive oxide, have the potential for use as electrode layers in versatile electronic applications, particularly with perovskite structured dielectric and ferroelectric oxide thin films. Moreover, for practical device applications, it is important to develop the deposition process of low-resistivity SrRuO3 thin films on SiO2 substrates. Therefore, in this study, the growth and characteristics of SrRuO3 thin films deposited by radiofrequency magnetron sputtering on SiO2 substrates without a buffer layer were investigated. It was found that the oxygen flow ratio in the growth ambient, post-deposition annealing temperature, and post-deposition annealing time are key parameters in realizing high-quality SrRuO3 thin films. When SrRuO3 thin films were deposited with a gas flow ratio of Ar:O2 = 1:1.5 and subjected to post-deposition annealing in an oxygen ambient at 750 °C for 3 min, they exhibited an excellent resistivity of 148 μΩ-cm. This value is comparable to that of SrRuO3 thin films epitaxially grown on single-crystal SrTiO3 or LaAlO3 substrates.

Electrochromic tungsten oxide films prepared by sputtering: Optimizing cycling durability by judicious choice of deposition parameters

Thin films of W oxide were prepared by reactive DC magnetron sputtering (5 cm-diameter W target), and their electrochromic (EC) properties were investigated in an electrolyte of LiClO4 in propylene carbonate. The purpose of the study was to elucidate the role of critical deposition parameters—oxygen/argon gas flow ratio for the sputter plasma Γ, total pressure in the sputter plasma ptot, and sputtering power Ps—on the EC performance with foci on electrochemical cycling durability and optical modulation range ΔT. Specifically, we used 0.15 ≤ Γ ≤ 0.90, 5 ≤ ptot ≤ 30 mTorr, and 200 ≤ Ps ≤ 400 W and studied cycling durability for up to 500 voltammetric cycles in the range 2.0–4.0 V vs. Li/Li+ together with optical properties at a wavelength of 528 nm. Most significantly, we discovered that a judicious choice of deposition parameters could yield films with superior cycling durability. Thus a ~300 nm-thick film prepared at Γ = 0.90, ptot = 10 mTorr, and Ps = 200 W showed ΔT ≈ 65% after an initial “training” during ~100 voltammetric cycles; higher values of ptot, on the other hand, yielded films whose ΔTs degraded by ~10% during the cycling, and a lower value of ptot led to dark films with only marginal electrochromism. Hence our work delineates a pathway towards W oxide films with excellent durability of the EC properties.

Behaviors of supersonic double-parameter jets and their impingement onto molten bath in BOF steelmaking

The dynamic characteristics of supersonic double-parameter jets and their interaction with the molten pool were experimentally studied. The effects of jet inclination angles and gas flow ratios on gas intensity, coalescence characteristics, and dynamic parameter distributions were discussed. The characteristics of the cavity formed by the interaction of the jet and molten pool were revealed. The results show that the jet inclination angle has more influence on the jet coalescence compared with the gas flow rate. However, the gas flow ratio plays a decisive role in the velocity distribution along the jet centerline compared with the jet inclination angle. The velocity peaks of the double-parameter jets were obviously different at fixed axial distances. Compared with other variables, the small-nozzle inclination has a greater impact on the cavity diameter, while the large-nozzle flow ratio has a greater impact on the cavity depth. The depth and width of the cavity formed by the double-parameter jets are more advantageous than that formed by the single-parameter jets. Furthermore, the double-parameter jets were applied to the actual smelting of a 260t converter.

Preparation of Copper Nitride Films with Superior Photocatalytic Activity through Magnetron Sputtering.

TiO2 possesses a wide forbidden band of about 3.2 eV, which severely limits its visible light absorption efficiency. In this work, copper nitride (Cu3N) films were prepared by magnetron sputtering at different gas flow ratios. The structure of the films was tested by scanning electron microscope, X-ray diffractometer, and X-ray photoelectron spectroscope. Optical properties were investigated by UV-vis spectrophotometer and fluorescence spectrometer. Results show that the Cu3N crystal possesses a typical anti-ReO3 crystal structure, and the ratio of nitrogen and Cu atoms of the Cu3N films was adjusted by changing the gas flow ratio. The Cu3N films possess an optical band gap of about 2.0 eV and energy gap of about 2.5 eV and exhibit excellent photocatalytic activity for degrading methyl orange (degradation ratio of 99.5% in 30 min). The photocatalytic activity of Cu3N mainly originates from vacancies in the crystal and Cu self-doping. This work provides a route to broaden the forbidden band width of photocatalytic materials and increase their photoresponse range.

The Forming Control Method of Multi-Track Laser Cladding on Curved Surface

This paper investigated the correlation between the processing parameters and the properties of clad deposited by laser cladding on a curved surface. Mathematical models relating the processing parameters (laser power, scanning speed, gas flow, and overlap ratio) and clad properties (flatness ratio and pore area) were established by central composite design. Analysis of variance and experimental validation confirmed the validity of the models. The results indicated that the flatness ratio was negatively influenced by the larger scanning speed, gas flow, and overlap ratio, while the pore area was enlarged by the increasing of scanning speed, and increasing the overlap ratio lead to the pore area reducing at first and then increasing. Optimized processing parameters were obtained under the target of maximizing the flatness ratio and minimizing the pore area. The developed mathematical models enabled predicting the flatness ratio and pore area with optimized processing parameters. The validation experimental result verified the prediction accuracy of the models and displayed target improvement compared with the original central composite design. The results provide theoretical guidance in multi-track laser cladding on a curved surface for the prediction and control of the geometric characteristics of the coating and the optimization of the processing parameters. This research outcome provides guidance for the coating deposition application in crankshaft surface coating or surface restoration, rotary parts coating deposition, or complex shape tool manufacturing. It also forms the fundamental basis for the extensive application of multi-track laser cladding on curved substrates in the additive manufacturing industry.

P‐45: Effect of Ar / O2 Flow Ratio during Sputtering of InZnO Active Layer on Photocurrent and Responsivity Characteristics of Amorphous InZnO Thin Film Transistors

The photocurrent and responsivity characteristics of amorphous InZnO (a‐IZO) thin film transistors (TFTs) under different Ar:O2 gas flow ratio when growing the IZO active layer by sputtering are investigated. As the Ar:O2 gas flow ratio increases, the photocurrent and responsivity increase by nearly two orders of magnitude, under the same light power density at a wavelength of 400 nm to 475 nm light illumination.

Sensitivity of germanium content on growth conditions of silicon-germanium nanoparticles prepared in nonthermal capacitively-coupled plasmas

We report on the synthesis of Si1−x Ge x alloy nanocrystals by very-high-frequency plasma-enhanced chemical vapor deposition (VHF PECVD) technique at different silane to germane gas flow ratio (R) in a mixture of (H2+Ar) dilution gas and H2 dilution gas alone. TEM, SAED, EDS studies and HAADF-STEM mapping of the samples were done to investigate the NCs' size, crystallinity and distribution of Si and Ge in the Si1−x Ge x alloy NCs. The average estimated size of the NCs in all the samples are in the order of exciton Bohr radius of Ge (24.3 nm), thereby indicating the probability of good quantum confinement. The alloy nature of NCs was confirmed in Raman study. The content of Ge in SiGe NCs was evaluated from Raman spectra which show a direct correlation with the fraction of hydrogen flow in the dilution gas mixture.

Optimization of passivation in AlGaN/GaN heterostructure microwave transistor fabrication by ICP CVD

We have studied the effect of silicon nitride (SiN) dielectric passivating film deposition by inductively coupled plasma chemical vapor deposition (ICP CVD) on the parameters of AlGaN/GaN heterostructure high electron mobility transistors (HEMT). Study of the parameters of the dielectric layers has allowed us to determine the effect of RF and ICP power and working gas flow ratio on film growth rate and structural perfection, and on the current vs voltage curves of the passivated HEMT. The deposition rate changes but slightly with an increase in RF power but increases with an increase in ICP power. Transistor slope declines considerably with an increase in RF power: it is the greatest at minimum power RF = 1 W. In the beginning of growth even at a low RF power (3 W) the transistor structure becomes completely inoperable. Dielectric deposition for HEMT passivation should be started at minimum RF power. We have developed an AlGaN/GaN microwave HEMT passivation process providing for conformal films and low closed transistor drain–source currents without compromise in open state transistor performance: within 15 and 100 mA, respectively, for a 1.25 and 5 mm common T-gate (Ug = –8 V and Ud-s = 50 V).

INFLUENCIA DE LAS CONDICIONES DE OPERACIÓN EN EL REFINO DE BIOGAS PARA PRODUCIR BIOMETANO MEDIANTE CONTACTORES DE MEMBRANA

In this paper, the behavior of micro-porous hollow fiber membrane contactors has been studied for biogas upgrading under different operational conditions. Physical solvents, as deionized water and sodium chloride solution, were initially used. In these cases, carbon dioxide absorption was dependent upon liquid phase flow. Sodium hydroxide was subsequently used as a comparative chemical absorption solvent. In this case, CO2 mass transfer increased by increasing gas velocity which was attributed to the excess of reactive hydroxide ions present in the solvent. Under optimum conditions, with two membrane contactors operating in series, it was possible to obtain a gas stream with more than 99% of pure methane using deionized water as solvent. The same yields were obtain with NaOH as solvent, but in this case working with just one membrane module, that is, reducing by half the available surface area for molecules diffusion. At constant liquid to gas flow ratios, better separation behavior was targeted at pressures higher than 2.0 barg. When dealing with solvent reuse without regeneration, NaOH is the only adsorbent allowing a high number of solvent recirculation cycles. This aspect could be very interesting for the economy of the process. Keywords: biogas, biomethane, gas-liquid absorption, membrane contactors, biogas upgrading, natural gas substitute

Experimental and CFD-DEM numerical evaluation of flow and heat transfer characteristics in mixed pulsed fluidized beds

Pulsed fluidized beds can make gas-solid mix and contact more uniform, therefore obviously improving heat transfer efficiency. The mixed pulsed fluidized bed, whose total gas flow is composed of stable gas flow and pulsed gas flow, is proposed in this research. Firstly, the experimental device for drying particles in a mixed pulsed fluidized bed is established. Pressure signals with different frequencies and gas flow ratios are collected, and flow pattern diagrams are obtained through a high-speed camera. Secondly, the CFD-DEM parallel numerical simulation method is constructed to research the mixed pulsed fluidized bed performance. Particle mixing, motion and heat transfer characteristics under different pulse frequencies and flow ratios are studied. Results show that particles in the mixed pulsed fluidized bed exhibit regular periodic motion, thereby promoting the mixing effect of particles. Moreover the bubble nucleation point moves to the bottom of the bed with the increasing pulse frequency. When the total gas velocity is relatively low, particle mixing effect can be enhanced by increasing the proportion of pulsed gas. However, when the velocity is relatively high,particle mixing effect will be enhanced by decreasing the proportion.

Reactively sputtered Zn(O,S) buffer layers for controlling band alignment of Cu(In,Ga)Se2 thin-film solar cell interface

Abstract Buffer layers in Cu(In,Ga)Se2 (CIGS) solar cells are highly preferable to be vacuum-compatible and use non-toxic materials not only for the film but also for the manufacturing process. Moreover, high controllability for the energy levels of buffer layers is greatly desirable for achieving higher solar cell efficiency because the buffer layer is formed directly onto the absorber layer which generates carriers. In this study, the S/(O + S) composition ratio of the Zn(O,S) thin films was finely controlled by varying O2/(Ar + O2) gas flow ratio using a reactive sputtering method including an Ar/O2 mixture gas and a single ZnS sputter target. The structural, electrical, and photovoltaic performance properties of the Zn(O,S) thin films and their CIGS solar cells were investigated at varied S/(O + S) composition ratios. As the S/(O + S) composition ratio of the Zn(O,S) films increased, bandgap bowing occurred with the increase of the conduction band and valence band energy levels. The photovoltaic performance was greatly influenced by the difference of the conduction band energies between the Zn(O,S) buffer and the CIGS absorber. When the conduction band energy of the Zn(O,S) was too high or too low compared to that of the CIGS, it increased the carrier recombinations or series resistance, respectively, which induced losses of the open-circuit voltage and the fill factor. The controlling and optimizing the energy levels at the Zn(O,S)/CIGS interface were crucial for improved solar cell performances.

Gate leakage current reduction and improved reliability with an ultra-thin Ti layer for low-power applications

This study analyzed the physical and electrical characteristics of the interface reactions between hafnium-based high-k gate dielectrics and a TiN-based metal gate. Decreasing the N2 gas flow ratio (RN2 = N2/Ar+N2) from the physical-vapor-deposited TiN decreased the gate leakage current (JG) and the effective work function (EWF) of the metal gate. X-ray photoelectron spectroscopy analysis confirmed that TiN deposited with a lower RN2 condition can be easily oxidized to form TiOx at the gate oxide and metal gate interface after annealing at 1050 °C. This newly created oxide layer can prevent oxygen diffusion from the gate oxide through TiN to the TiN/poly-silicon interface, resulting in improved gate oxide quality. Inserting a thin Ti layer (< 1 nm) on the gate oxide formed a TiOx layer without a change in EWF, indicating that TiN composition variation followed the same trend as capacitance equivalent thickness (CET) versus JG. Therefore, an oxygen-blocking layer can have the same effect as gate oxide quality improvement for both scenarios—low RN2 of TiN and the thin Ti insertion—due to decreased oxide charge density. The Ti insertion process was associated with improved gate oxide leakage, negligible CET increase (0.2 Å), and gate oxide reliability, including time-dependent dielectric breakdown characteristics due to the blockage of oxygen up-diffusion.

Innovative scrubber technology model for domestic boiler application

Many treatment technologies exist for particulate matter capture from the flue gas. Heat recovery from flue gases is a significant advantage of scrubber technology, which promotes energy efficiency increase of the combustion unit. The amount of recovered heat depends on heat and mass transfer in the scrubber. This paper presents the investigation of innovative small-scale flue gas treatment technology—fog unit. Households produce significant share of particulate matter in Europe. Therefore, there is a need to provide flue gas treatment technologies for domestic boilers in agreement with EU directive 2009/125/EC. Experimental research was done to identify the performance of proposed technology depending on inlet water flow rate, gas flow rate, water temperature, droplets diameter and water–gas flow ratio. The regression equations were developed based on performed data analysis. Equations can be used to predict the capacity of fog unit, outlet water temperature and outlet gas temperature.

Investigation into Micro-Hardness and Wear Resistance of 316L/SiC Composite Coating in Laser Cladding

In order to improve the performance of the cladding layer, this study used the Taguchi orthogonal design to investigate the influence of laser power, scanning speed, gas flow, and SiC powder ratio on the micro-hardness and wear volume of the cladding layer. The results indicate that the SiC powder ratio was the major factor that had the main impact on the micro-hardness and wear volume of the cladding layer. The contribution of SiC powder ratio on the micro-hardness and wear volume are 92.08% and 79.39%, respectively. Through signal to noise ratio conversion and combining grey relational analysis, the multiple objectives optimization was attained. With the target of maximizing the micro-hardness and minimizing the wear volume simultaneously, grey relational analysis was applied to obtain the optimal processing parameters set and predict the corresponding grey relational grade. The error rate was 5.3% between the prediction and experimental validation. This study provides the guidance for optimizing multiple goals at the same time using grey relational analysis about the coating properties deposited by laser cladding in actual industrial applications. It provided theoretical basis for the processing parameters optimization with targeting the micro-hardness and wear resistance.

Structural, Compositional, and Plasmonic Characteristics of Ti-Zr Ternary Nitride Thin Films Tuned by the Nitrogen Flow Ratio in Magnetron Sputtering.

Ternary nitride gives high diversity and tunability of the plasmonic materials. In this work, highly crystallized ternary (Ti, Zr)N films were prepared by magnetron co-sputtering with different nitrogen gas flow ratio . The structural and plasmonic properties of the films tuned by were investigated. All the films are solid solutions of TiN and ZrN with a rocksalt structure and (111) preferred orientation. The films are nitrogen-overstoichiometric and the main defects are cation vacancies. Increased reduces the zirconium content, and therefore leads to the reduction of lattice constant and enhancement of the crystallinity. As increases, the screened plasma frequency decreases for the reduction of free electron density. The maximum of the energy loss spectra of (Ti, Zr)N films shifts to long-wavelength with increasing. The calculated electronic structure shows that increased nitrogen content enhances the electronic density of states of nitrogen and reduces that of metal, and therefore elevates the energy level at which interband transition is exited. The results show that (Ti, Zr)N films give a relatively high plasmonic quality in the visible and near-infrared region, and the film properties can be significantly tuned by the nitrogen content.

Effect of the boron-to-nitrogen ratio on leakage current characteristics of boron nitride films prepared by surface-wave plasma enhanced chemical vapor deposition

Sp2-bonded boron nitride (BN) films with different B-to-N ratios are deposited on Si and Ni substrates at an ion impact energy of around 50 eV by surface-wave plasma enhanced chemical vapor deposition. The overall crystallinity and order of sp2 bonding structure are almost retained with increasing BF3/N2 gas flow ratio in the plasma, while the B-to-N ratio in the film is varied from 0.89 to 0.96. The electrical resistivity of the films measured at room temperature for Ni-BN-Ni structures shows a large increase up to the order of 1010 Ω cm when the B-to-N ratio in the film is increased closer to the stoichiometry due to a lower density of defect states related to the boron vacancy. The characteristics of leakage current vs. applied bias voltage show Ohmic behavior at low fields and non-Ohmic behavior governed by the thermionic emission mechanism at high fields for any B-to-N ratio.