NH3 Flow Rate Research Articles

Influence of NH3 flow rate on the photoelectric properties of high Al content p-AlGaN.

High Al content (60%) p-AlGaN with different NH3 flow rates was grown using metal-organic chemical vapor deposition (MOCVD), and changes in its photoelectric properties were studied using the Hall effect tester (Hall) and cathodoluminescence (CL) spectrometer. The results show that the film resistivity increases from 3.8 Ω·cm to 46.5 Ω·cm with increasing NH3 flow rate. The impurity peak intensity of p-AlGaN grown under high NH3 flow conditions is particularly high, indicating numerous point defects. The results of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) show a large number of Ga interstitial atoms (Gai) at the interface. As Gai acts as a donor, this may be the main reason for the increase in resistivity. And under high NH3 flow conditions, a lattice distortion and a high density of dislocation occur between p-AlGaN and p-GaN, which can lead to enhanced carrier scattering and decreased mobility. Additional validation via LED growth experiments indicates that the luminescence intensity of samples with low ammonia concentration increased by more than 13000 times.

Effect of NH3 flow rate to titanium nitride as etch hard mask in thermal atomic layer deposition

Effect of NH3 flow rate to titanium nitride as etch hard mask in thermal atomic layer deposition

Ru/Attapulgite as an Efficient and Low-Cost Ammonia Decomposition Catalyst

On-site hydrogen generation from ammonia decomposition is a promising technology to address the challenges of direct transportation and storage of hydrogen. The main problems with the existing support materials for ammonia decomposition catalysts are their high cost and time-consuming preparation process. In this work, ammonia decomposition catalysts consisting of in situ-formed nano-Ru particles supported on a naturally abundant mineral fiber, attapulgite (ATP), were proposed and studied. Also, 1 wt.% Ru was uniformly dispersed and anchored onto the surface of ATP fibers via the chemical method. We found that the calcination temperatures of the ATP support before the deposition of Ru resulted in little difference in catalytic performance, while the calcination temperatures of the 1Ru/ATP precursor were found to significantly influence the catalytic performance. The prepared 1 wt.% Ru/ATP catalyst (1Ru/ATP) without calcination achieved an ammonia conversion efficiency of 51% at 500 °C and nearly 100% at 600 °C, with the flow rate of NH3 being 10 sccm (standard cubic centimeter per minute). A 150 h continuous test at 600 °C showed that the 1Ru/ATP catalyst exhibited good stability with a degradation rate of about 0.01% h−1. The 1Ru/ATP catalyst was integrated with proton ceramic fuel cells (PCFCs). We reported that PCFCs at 650 °C offered 433 mW cm−2 under H2 fuel and 398 mW cm−2 under cracked NH3 fuel. The overall results suggest low-level Ru-loaded ATP could be an attractive, low-cost, and efficient ammonia decomposition catalyst for hydrogen production.

Dislocations/Defects analysis in III-V nitrides - a cost effective MOCVD epitaxy solution

In present paper an innovative technique to reproduce the epitaxial growth results through lateral flow metal organic chemical vapor deposition (MOCVD) reactor process at atomistic scale is reported. It includes the equivalent MOCVD reactor geometry architecture of AIXTRON 200/4 RF-S horizontal flow reactor. The gas- and surface phase chemical reaction kinetics and thermodynamics are given due consideration in the present study without use of any continuum or fluid dynamics models. The optimum conditions are extracted by running design of experiments over TNL-EpiGrow simulator to achieve high crystalline quality aluminum nitride (AlN) films over Si (111) substrate. The impact of variation in precursor NH3 flow rates and carrier gas N2 pressure are used to predict the conditions to optimize the improved morphology and quality of the AlN films. The defects densities are characterized in terms of vacancies and dislocation densities. The roughness and lattice parameters are extracted. The growth rates obtained in present studies are compared against reported the similar experiments. The excellent agreement is observed between experimental and simulated results. The dislocation densities in grown samples are also found in good agreement with the similar experimental reported densities in each sample.

Capture of NH3 using air plasmas to form NH4NO3 for N recycling: Impact factors and mechanisms

Ammonia loss results in significant resource waste and environmental pollution. In this study, we proposed and explored the way of using air plasmas to capture NH3 to form NH4NO3 for N recycling under different reaction modes, discharge powers, and gas flow rates. The reaction mechanisms under different modes were also revealed. A needle-needle discharge driven by AC power was used and ammonia gas was utilized to simulate the volatilized ammonia. Notably, white particles were observed during Mode 1 and Mode 2 (these particles gradually disappeared over time in Mode 2), while no particles or significant NOx were detected in Mode 3 throughout the process. The quantitative NH4NO3 yield was significantly influenced by discharge power and NH3 flow rate, reaching its highest value in Mode 1 at 24 W and 20 sccm in this investigation. Directly mixing the air discharge products with NH3 in Mode 1 under the threshold decomposition temperature of NH4NO3 leads to the stable formation of NH4NO3. Discharging in the NH3/air mixture will inhibit the generation of NOx and further restrain the NH4NO3 formation in Mode 2 and 3. Additionally, the temperature rises during discharge and also decomposes NH4NO3, resulting in unstable NH4NO3 formation in Mode 2.

Ammonia/syngas MILD combustion by a novel burner

Ammonia has received increasing attention as one of the most attractive energy carriers because of its carbon-free nature and the established reliable and economic infrastructure for its storage and distribution. However, the low burning velocity and nitrogen-containment of pure NH3 can cause some challenges for its combustion control such as flame instability and large NOx emissions. To overcome these issues, strategies of co-burning NH3 with highly reactive fuels such as CH4 or H2 have been developed and applied. Syngas, which can be produced from biomass pyrolysis, is a promising alternative fuel in the transition from carbon-based fuels to carbon-free fuels. Therefore, comparing to co-firing NH3 with CH4, co-firing NH3 with syngas is a better environmentally friendly option to improve the NH3 combustion property. However, co-firing NH3 with syngas faces severer combustion instability, NOx emissions and NH3 leakage due to the low heating value of syngas. To the best of the authors’ knowledge, the NH3/syngas combustion with low NOx emissions and zero NH3 leakage has not been achieved in a lab-scale combustor. In the present study, NH3/syngas MILD combustion was carried out in a novel burner developed in our previous work. In the novel burner, the high-temperature and diluted air produced by the lean premixed syngas combustion is the key to accomplish the MILD combustion of NH3. The impact of the temperature and O2 mole fraction of the HTDA on the emissions of NO, NO2, N2O, NH3, and CO was experimentally investigated with varying equivalence ratios and NH3 flow rates. The chemical reactor network was employed to analyze the experimental observation from the chemical kinetic aspect.

Properties of SiCN Films Relevant to Dental Implant Applications.

The application of surface coatings is a popular technique to improve the performance of materials used for medical and dental implants. Ternary silicon carbon nitride (SiCN), obtained by introducing nitrogen into SiC, has attracted significant interest due to its potential advantages. This study investigated the properties of SiCN films deposited via PECVD for dental implant coatings. Chemical composition, optical, and tribological properties were analyzed by adjusting the gas flow rates of NH3, CH4, and SiH4. The results indicated that an increase in the NH3 flow rate led to higher deposition rates, scaling from 5.7 nm/min at an NH3 flow rate of 2 sccm to 7 nm/min at an NH3 flow rate of 8 sccm. Concurrently, the formation of N-Si bonds was observed. The films with a higher nitrogen content exhibited lower refractive indices, diminishing from 2.5 to 2.3 as the NH3 flow rate increased from 2 sccm to 8 sccm. The contact angle of SiCN films had minimal differences, while the corrosion rate was dependent on the pH of the environment. These findings contribute to a better understanding of the properties and potential applications of SiCN films for use in dental implants.

Multiple-objective optimization on ammonia decomposition using membrane reactor

Ammonia plays a key role in the renewable hydrogen economy nowadays, thus, the efficiency of ammonia decomposition for hydrogen production becomes an important research topic. In this study, a numerical model was built to study the performance of ammonia decomposition using a membrane reactor and Ru/Al2O3 catalyst under various operating conditions such as feed NH3 temperature and volume flow rate as well as retentate side pressure. The reactor performance was characterized by ammonia conversion, hydrogen recovery, and recovered hydrogen flow rate. Pre-exponential factor and activation energy of ammonia reaction rate were obtained by equilibrium conversion and two-step parametric sweeping. It was found that ammonia conversion can be increased by about 33% compared to a conventional fixed-bed reactor under the same operating conditions. H2 recovery can be enhanced when the reactant inlet temperature and the pressure difference between the retentate and permeate sides increase. The increase in feed NH3 flow rate (gas hourly space velocity, GHSV) decreased the ammonia conversion and H2 recovery. An optimum GHSV that results in a maximum recovered H2 flow rate can be found. Finally, optimum operation conditions for maximizing the hydrogen recovery and recovered hydrogen flow rate were analyzed using the multi-objective Non-dominated sorting genetic algorithm-II (NSGA-II). It was found that maximum H2 recovery with a value of 79.7% can be obtained under the conditions of inlet temperature of 336 °C, GHSV of 900 h−1, and retentate side pressure of 9.9875 bar. The maximum recovered hydrogen flow rate with a value of 9.55×10−14(mol·s−1) can be obtained under the conditions of an inlet temperature of 394 °C, GHSV of 1315 h−1, and retentate side pressure of 9.9879 bar.

SiNx Coating Deposition on CoCr by Plasma-Enhanced Chemical Vapor Deposition

AbstractCobalt chromium alloys (CoCr) are commonly used as total disc replacement components. However, there are concerns about its long-term biological effects. Coating the CoCr with a ceramic could improve the implant’s biocompatibility and wear resistance. Silicon nitride (SiNx) coatings have emerged as a recent alternative to this end. While many have evaluated physical vapour deposition (PVD) techniques to deposit these coatings, plasma-enhanced chemical vapour deposition (PECVD) may provide certain advantages. For example, it may allow for low-temperature depositions as well as more uniform coatings of complex structures. In this study, silicon nitride (SiNx) coatings with different nitrogen-to-silicon (N/Si ratio) compositions (0.65, 1.16 and 1.42) were deposited onto CoCr substrates by PECVD. It was found that the SiNx coating deposited at an NH3 flow rate of 30 sccm (i.e., N/Si ratio of 1.42), had the highest hardness and elastic modulus, 13.19 ± 1.29 GPa and 132.76 ± 9.32 GPa, respectively. While a coating roughness adequate for the application could be measured, further optimization of the coating adhesion is needed to adequately evaluate its wear properties. It was concluded that the PECVD SiNx coating deposited at an NH3 flow rate of 30 sccm showed the highest potential for the intended application.

Study on the Preparation and Morphology Mechanism of Micron‐Sized Hexagonal Flake Basic Zinc Chloride (Zn5(OH)8Cl2·H2O) by Ammonia Precipitation Method

AbstractThe chemical formula of basic zinc chloride is Zn5(OH)8Cl2 · H2O (denoted as ZHC). It is a new type of zinc source additive, widely used in the feed industry. In this article, micron‐sized hexagonal flake ZHC with a diameter of 10–60 µm is directly prepared by ammonia precipitation method using ZnCl2 as raw material. The products are characterized and analyzed by X‐ray diffraction, scanning electron microscopy, and laser particle size analyzer. The effects of reaction temperature, ammonia flow rate, aging time, and reactant concentration on the product morphology are studied. Under the optimum reaction conditions, the ZnCl2 concentration is 2.0 mol L−1, NH3 flow rate is 300 mL min−1, the reaction time is 1 h, the reaction temperature is 80 °C, and the aging time is 5 h. Lastly, the yield reaches 49.06%. The growth habit of ZHC is theoretically analyzed by the Morphology program. The calculation results are in good agreement with the experimental results. The change of (003) crystal plane exposure caused by temperature is an important reason for the non‐ideality of macroscopic morphology.

Adsorption Capacity and Desorption Efficiency of Activated Carbon for Odors from Medical Waste.

Five types of odor-emitting exhaust gases from medical waste were selected, and their adsorption capacity and desorption efficiency were investigated using activated carbon. The selected gases included polar gases (hydrogen sulfide (H2S) and ammonia (NH3)) and non-polar gases (acetaldehyde (AA), methyl mercaptan (MM), and trimethylamine (TMA))). Commercial activated carbon with a specific surface area of 2276 m2/g was used as the adsorbent. For the removal of odor from medical waste, we investigated: (1) the effective adsorption capacity of a single gas (<1 ppm), (2) the effect of the adsorbed NH3 gas concentration and flow rate, and (3) the desorption rate using NH3 gas. The values of the effective adsorption capacity of the single gas were in the following order: H2S < NH3 < AA < MM < TMA, at 0.2, 4.2, 6.3, 6.6, and 35.7 mg/g, respectively. The results indicate that polar gases have a lower effective adsorption capacity than that of non-polar gases, and that the size of the gas molecules and effective adsorption capacity exhibit a proportional relationship. The effective adsorption performance of NH3 gas showed an increasing trend with NH3 concentration. Therefore, securing optimal conditions for adsorption/desorption is imperative for the highly efficient removal of odor from medical waste.

Thermal decomposition of δ-MoN and ε-Fe2N synthesized under concentrated solar radiation in NH3 gas stream

Decomposition temperatures of δ-MoN and ε-Fe2N synthesized with flowing NH3 gas under concentrated solar radiation heating were evaluated by Differential Scanning Calorimetry (DSC) in Argon (Ar) gas environment. The measured decomposition temperature of δ-MoN and ε-Fe2N were dependent on the solar synthesis conditions, particularly either NH3 or N2 gas flow rate at temperature. Sample containing δ-MoN showed two exothermic peaks around 680 and 900 °C, attributed to the reactions of δ-phase into γ-single-phase and (γ+β)-two-phase Mo2N, respectively, attributed to the dissociation reaction of δ-phase into γ-single phase and the dissociation reaction of γ-phase into metallic M saturated with N, respectively. Decomposition of ε-Fe2N took place into γ’-Fe4N in two steps occurring at 606 and 660 °C, respectively. When N2 instead of ammonia (NH3) gas was used, complete dissociation of γ’-Fe4N into Fe took place at around 610 °C. Full decomposition of γ’-Fe4N into metallic α-Fe(N) was corroborated by X-ray diffraction (XRD) analysis.

Quantitative Analysis of Degree of Nitridation of Ta2O5 to TaON Particles and their Photocatalytic Oxygen Evolution Properties

AbstractOxynitride or nitride photocatalysts are typically synthesized by heating oxide precursor particles at high temperatures under NH3 flow. Although there are numerous reports on optimizing the nitridation conditions for different materials, the detailed nitridation mechanism is still unclear. In this study, the nitridation of Ta2O5 to TaON was investigated. The degree of nitridation was quantitatively analyzed using the change in the weight of a powder after nitridation. Three regions were identified in the nitridation process for different nitridation times and NH3 flow rates. Moreover, the initial stage of the nitridation process (linear region) was formulated for the first time. Structural analysis, absorption properties, and oxygen evolution activity were combined with the degree of nitridation to reveal the relationship between the nitridation process and photocatalytic activity. The results of this work are useful for understanding and improving the photocatalytic properties of oxynitrides.

High-quality AlN growth on flat sapphire at relatively low temperature by crystal island shape control method

In this study, we found that the two-step method for heteroepitaxial AlN on sapphire has some limitations. Growing the buffer layer for a too long time will make it challenging to obtain a flat film surface. So, three-step-growth was introduced and an intermediate layer was inserted. In this step, the surface morphology of samples is controlled by NH3 flow rate and the dislocation density is further reduced. Finally, we are able to obtain high-quality AlN samples grown by metalorganic chemical vapor deposition at 1120 ℃, which is a relatively low temperature for the AlN epitaxial layers. The X-ray diffraction ω-scan full width at half maximum values for (002) and (102) reflections are 172 and 145 arcsec, respectively.

A study on MOCVD growth window for high quality N-polar GaN for vertical device applications

Lateral N-polar GaN devices have outperformed Ga-polar GaN counterparts in mm-wave applications. A vertical N-polar GaN device structure with higher breakdown voltage is expected to further improve the output power density. This paper is aimed at understanding the growth conditions for such a vertical N-polar GaN device stack. A vertical device stack requires high-quality n-GaN layer with low unintentional dopant concentration and high electron mobility for better ON resistance–breakdown voltage performance. A systematic study by varying reactor temperature, pressure and NH3 flow rate is performed in the metal organic chemical vapor deposition growth of N-polar GaN for vertical device structure. Structural quality of the sample is increased with increase growth temperature and higher NH3 flow rate, yet an increase in surface roughness is observed for highest temperature used. The N-polar GaN grown at the optimized conditions exhibited a x-ray diffraction rocking curve full width half maximum of symmetric (0002) and skew-symmetric (20 ) scans of 358″ and 569″ respectively with a low oxygen and carbon concentration of 6 × 1016 cm−3 and 5 × 1016 cm−3, respectively. The optimized sample exhibited a low screw dislocation density of 2.5 × 108 cm−2 on sapphire substrate. A gradual increase in the bulk mobility of electrons with decrease in screw dislocation density in N-polar GaN is also reported.

Simplified CVD route to near-zero thickness silicon nitride films

Silicon nitride (SiNx, x ∼ 1) thin films were deposited by chemical vapor deposition on silicon oxide (SiO2) substrates by combining controlled pulses of the precursor 1,3,5-tri(isopropyl)cyclotrisilazane (TICZ, C9H27N3Si3) with a continuous ammonia (NH3) plasma. This plasma-assisted pulsed CVD (PPCVD) process enables the integration of the nanoscale thickness and uniformity control achieved in atomic layer deposition with the efficiency of plasma-enhanced CVD (PE-CVD). TICZ was selected because it is a nonpyrophoric stable liquid with a high vapor pressure (∼133 Pa at 70 °C) and could act as a single source for SiNx with both high Si and N contents. An optimized PPCVD process window was identified consisting of a substrate temperature of 350 °C, a TICZ pulse of ≤0.2 s, and a TICZ purge pulse ≥10 s in a continuous direct NH3 plasma at a NH3 flow rate and a power of 40 SCCM and 3000 W, respectively. The as-deposited films were analyzed by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. XPS analysis confirmed the absence of any C inclusion and demonstrated the existence of the 1:1 Si:N ratio. In situ, real-time ellipsometry measurements indicated that SiNx growth occurred in a typical PE-CVD regime. They also yielded an as-grown SiNx average refractive index of ∼1.75.

A Study of Thin Film Encapsulation on Improving Electrical Characteristics and Reliability for Flexible OLEDs

In this work, we investigated the effect of thin film encapsulation on Vth shift in a-IGZ0 TFTs. The result shows that decreasing the NH3 flow rate of deposited SiON films, the trend of Vth shift under the operation mode can vary from negative to positive direction, which can be attributed to lower amount of hydrogen diffused from SiON to the a-IGZO TFTs. Beside, we designed the TFE with stable inorganic-organic-inorganic stack structure, of which the CVD1 deposited with low NH3 flow rate and the CVD2 with high barrier property, and a 16.9-inch high performance flexible OLED panel with controlled Vth shift and RA lifetime over 475 h was achieved at the condition of 85 °C and 85% RH. This study demonstrates the influence of TFE on a-IGZO TFTs, and offers an optimized TFE structure which promises both electrical characteristics and reliability for flexible OLEDs.

Lateral organic-inorganic hybrid Vis-NIR photodetectors based on GaN nanowires promoting photogenerated carriers transfer

The narrow bandgap of the low-energy near-infrared (NIR) polymer would lead to overlap between adjacent energy levels, which is a major barrier to the preparation of Vis-NIR polymer bulk heterojunction (BHJ) photodetectors with small responsivity and photocurrent. In this study, a high-performance lateral inorganic-organic hybrid photodetector was constructed to eliminate this barrier by combining GaN nanowires (GaN-NWs) with PDPP3T:PC61BM-based BHJ. In stage one, high-quality GaN-NWs were synthesized by the catalyst-free CVD method. The mechanism for controlling GaN-NWs morphology by adjusting the NH3 flow rate was revealed. In stage two, the GaN-NWs with large electron mobility were used to accelerate the transfer of photogenerated carriers in the BHJ layer. Finally, compared with the BHJ device, the BHJ/GaN device demonstrated obvious improvements in responsivity and photocurrent at the wavelength between 400 and 1000 nm. The responsivity and photocurrent increased over 20-fold at the NIR band of 800–900 nm. Besides, owing to the energy level gradient effect, the BHJ/GaN device has a response speed of 7.8/<5.0 ms, which increases over three orders of magnitude than that of the GaN-NWs-based device (tr/tf: 7.1/10.9 s). Therefore, the novel device structure proposed in this work holds great potential for preparing high-performance Vis-NIR photodetectors.

An enhanced anaerobic digestion BioModel calibrated by parameters optimization based on measured biogas plant data

In this paper an enhanced BioModel was developed to simulate biogas production in the anaerobic digestion process of organic waste. The proposed model considers biochemical and three–phase (gas–liquid–solid) physicochemical processes, where the degradation of carbohydrates, proteins, and lipids leads to the formation of CH4 and many other by-products; the pH value is treated as a state variable. The model contains a large number of feedstock and model parameters, which were calibrated by engaging a special active set optimization procedure. This procedure exploits data from a previously made sensitivity analysis to enable gradual optimization which is started with a rather small set of the most important parameters. This set of active parameters is then gradually increased until all parameters are calibrated. The objective function was defined to minimize the daily differences between simulated and measured rates of biogas, CH4, H2, and H2S, as well as the pH value; the measured data were obtained from an actual operating full-scale biogas plant during an observed time of 365 days. The imposed constraints were related to the values of biogas, CH4, H2, H2S, and NH3 flow rates, initial bacteria concentrations in the complex substrate, and to the pH values during the whole simulation period. The needed limiting values were defined on the basis of the measured output data of the biogas plant. The results obtained confirm the accuracy of the enhanced BioModel and the usefulness of the proposed procedure for model calibration, both, in terms of numerical stability and computational efficiency.

Experimental study and mechanism analysis of the NOx emissions in the NH3 MILD combustion by a novel burner

NH3 can be used as an H2 energy carrier or an alternative carbon-free fuel because of its high volumetric energy density and easy liquefaction, which leads to convenient and economic transportation and storage within the global energy network. However, the combustion of NH3 is associated with some practical challenges, such as weak reactivity and high NOx emission. In this study, Moderate & Intense Low Oxygen Dilution (MILD) combustion of NH3 was conducted experimentally in a novel burner. The heated and diluted air was produced by burning a premixed lean CH4 mixture using a metal fiber burner installed at the bottom of the combustion chamber and NH3 was injected into the furnace by 20 nozzles oppositely installed on the sidewalls of the combustion chamber at 40 mm above its bottom. A total of 20 cases were investigated in the present work, including premixed combustion of CH4 and CH4/NH3, and MILD combustion of NH3, under various conditions. The Chemical reactor network (CRN) in the ANSYS Chemkin 17.0 and the HUST mechanism were used to simulate and analyze the NO formation mechanism under several experimental conditions. The experimental results showed that the NH3 MILD combustion significantly reduces the NOx emissions. The NOx reduction kinetics and the impact of NH3 flow rate and the equivalence ratio on NO emission in NH3 MILD combustion were analyzed in detail.