N2 Flux Research Articles

Impact of pyrolysis heating methods on biochars with enhanced CO2/N2 separation and their incorporation in 3D-printed composites

N-doped biochars, derived from chitosan sourced from waste crustaceous shells, were produced via microwave-assisted pyrolysis at temperatures ranging from 400 to 800 °C to enhance CO2 and N2 separation. Their performance was compared with biochars from conventional pyrolysis. Microwave-derived biochars exhibited superior CO2 adsorption capacity at 25 °C and 100 kPa (0.78 – 1.56 mmol g−1) compared to conventionally produced ones (0.55 – 1.43 mmol g−1). Increasing the pyrolysis temperature up to 600 °C significantly improved biochar properties, including surface area, pore volume, and CO2 adsorption capacity. Microwave-derived biochar featured enhanced surface area, larger pore volumes, and unique morphologies, requiring, on average, 61 % less preparation time. The higher ultramicroporosity and N-species concentration correlated with superior performance in the biochar produced at 600 °C. In gas mixture experiments (20 % CO2 and 80 % N2) under flow conditions, these biochars showed rapid adsorption/desorption rates due to enhanced macroporosity at samples produced at 600 and 800 °C, facilitating gas diffusion along the ultramicropores. Adsorption heat analysis indicated that the CO2 adsorption is predominantly driven by physisorption, supported by complete sample regeneration when applying N2 flux or increasing the temperature during desorption. The study also explores the feasibility of 3D-printing a composite using the most effective biochar and inorganic polymers sourced from waste, presenting potential benefits for industrial applications.

Subtropical stormwater ponds are more frequently net nitrogen fixing compared to natural ponds

Urban stormwater ponds (SWPs) are engineered ecosystems designed to prevent flooding and protect downstream ecosystems by retaining nutrients associated with stormwater runoff, including nitrogen (N). Despite these expectations, multiple studies have found that SWPs have low N removal efficiencies and can be sources of N to downstream ecosystems. To understand mechanisms controlling the fate of N in SWPs, we quantified dinitrogen (N2) gas saturation to characterize net N2 exchange as either net denitrification or net N-fixation. We assessed temporal and spatial patterns of N2 dynamics in fifteen SWPs and six naturally occurring ponds in undisturbed watersheds (Florida, USA) by sampling in two seasons (dry and wet) and from multiple depths of the water column. Samples from SWPs were equally likely to exhibit N2 supersaturation (net denitrification; 50%) or undersaturation (net N-fixation; 50%). In contrast, the majority (82%) of samples from natural ponds were supersaturated with N2, indicating net denitrification. The mean SWP air–water N2 flux was − 1.7 μg N2-N m−2 h−1 (range − 500 to 433 μg N2-N m−2 h−1), which was lower than clear (40 μg N2-N m−2 h−1; range − 68 to 74 μg N2-N m−2 h−1) and humic (202 μg N2-N m−2 h−1; range 41 to 407 μg N2-N m−2 h−1) natural ponds despite considerably higher variation in SWPs. These results indicate that SWPs may have low N removal efficiencies in part due to N-fixation adding new N to the system. Overall, this study shows that SWPs are less effective than natural ponds at removing reactive N from the environment, potentially impacting downstream water quality.

Density‐dependent influence of ribbed mussels on salt marsh nitrogen pools and processes

Abstract Bivalves are becoming an increasingly popular tool to counteract eutrophication, particularly in vegetated coastal ecosystems where synergistic interactions between bivalves and plants can govern important N sequestration pathways. In turn, new calls to evaluate how bivalve densities modify N pools and processes across multiple scales have surfaced. Ribbed mussels, Geukensia demissa, and their relationship with smooth cordgrass present a classic demonstration of positive bivalve‐plant interactions and offer a useful model for assessing density dependence. We measure porewater ammonium concentrations, N stable isotope signatures in cordgrass tissue, and sediment N fluxes in mussel aggregations and in cordgrass‐only plots across a southeastern U.S. salt marsh. In addition to measuring the effect of mussel presence, we evaluate mussel density dependence through a multiscale approach. At the patch scale, we quantify mussel density effects within their aggregations (individuals m−2) while at a larger landscape scale, we quantify mussel density effects on the cordgrass‐only areas they neighbour (individuals ~30 m−2). Porewater ammonium concentrations were halved in mussel biodeposits relative to sediments in cordgrass‐only areas and negatively related to mussel density within aggregations. Leaf clip ẟ15N signatures were nearly 2‰ higher in cordgrass growing among mussel aggregations and increased with increasing patch mussel density. Microcosm incubations showed that mussels enhanced N2 flux (i.e., nitrogen removal) and DIN flux (i.e., N regeneration) into the water column, where only nitrogen removal increased with increasing patch‐scale mussel density. Across the marsh landscape, mussel coverage drove ammonium accumulation and N2 flux in sediments. Synthesis. Our results suggest that, at the patch scale, mussels stimulate the microbial metabolism of N, the assimilation of this bioavailable N by cordgrass, and nitrogen removal in a positive, density‐dependent manner. Tidal currents redistribute mussel biodeposits from mussel aggregations to surrounding areas, influencing biogeochemical transformations at scales beyond their physical footprint. We emphasize that the N regeneration potential of bivalve populations is a significant metric contributing to their mitigation potential and that bivalve density effects may be non‐linear, vary across patch to ecosystem scales, and have differing implications for the plants with which they interact.

Divergent drivers of the spatial variation in greenhouse gas concentrations and fluxes along the Rhine River and the Mittelland Canal in Germany

Lotic ecosystems are sources of greenhouse gases (GHGs) to the atmosphere, but their emissions are uncertain due to longitudinal GHG heterogeneities associated with point source pollution from anthropogenic activities. In this study, we quantified summer concentrations and fluxes of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and dinitrogen (N2), as well as several water quality parameters along the Rhine River and the Mittelland Canal, two critical inland waterways in Germany. Our main objectives were to compare GHG concentrations and fluxes along the two ecosystems and to determine the main driving factors responsible for their longitudinal GHG heterogeneities. The results indicated that the two ecosystems were sources of GHG fluxes to the atmosphere, with the Mittelland Canal being a hotspot for CH4 and N2O fluxes. We also found significant longitudinal GHG flux discontinuities along the mainstems of both ecosystems, which were mainly driven by divergent drivers. Along the Mittelland Canal, peak CO2 and CH4 fluxes coincided with point pollution sources such as a joining river tributary or the presence of harbors, while harbors and in-situ biogeochemical processes such as methanogenesis and respiration mainly explained CH4 and CO2 hotspots along the Rhine River. In contrast to CO2 and CH4 fluxes, N2O longitudinal trends along the two lotic ecosystems were better predicted by in-situ parameters such as chlorophyll-a concentrations and N2 fluxes. Based on a positive relationship with N2 fluxes, we hypothesized that in-situ denitrification was driving N2O hotspots in the Canal, while a negative relationship with N2 in the Rhine River suggested that coupled biological N2 fixation and nitrification accounted for N2O hotspots. These findings stress the need to include N2 flux estimates in GHG studies, as it can potentially improve our understanding of whether nitrogen is fixed through N2 fixation or lost through denitrification.

Structural analysis of NbN thin films grown through rf magnetron sputtering

In this work NbN thin films have been grown through rf magnetron sputtering technique from an 8-NbN (99.99%) target. In particular, we have studied the influence of the additional N2 flux in the preparation chamber on crystallization and microstructure of the deposited films. The films have been characterized by X-Ray diffraction (XRD) in 0-20 configuration and at a grazing angle, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD results show that the films grown at different fluxes of N2 have high textured coefficients along the [200] direction. SEM results indicate the films have columnar growth with high homogeneity and an average thickness of 0.7 μm. TEM results reveal that the films have grown from crystalline nanoparticles of NbN with high texture along the (200) plane.

Short-term effect of liquid organic fertilisation and application methods on N2, N2O and CO2 fluxes from a silt loam arable soil

AbstractThe absence of N2 flux measurements in liquid manure-amended soils has resulted in a poor understanding of the effect of manure application on gaseous N losses. The aim of this study was to quantify N2, N2O, CO2, N2O reduction to N2, depth distribution of moisture, water-extractable organic C, NO3−, NH4+, pH, and diffusivity in a laboratory incubation experiment with an arable silt-loam soil. To quantify N processes and gaseous fluxes, 15N tracing was applied. An artificial livestock slurry-mixture was added to the soil in various treatments (control, surface or injected application; slurry-application rate: 42.9 kg N ha− 1; soil water content of either 40% or 60% water-filled pore space (WFPS)). The soil was incubated for 10 days. The depth distribution of the control parameters was measured twice during the experiment on days 5 and 10. The average increase in N2 and N2O fluxes from denitrification was about 900% in slurry-amended soils. The highest N2 and N2O fluxes from denitrification were measured in the slurry injection, 60% WFPS treatment (7.83 ± 3.50 and 11.22 ± 7.60 mg N m− 2 d− 1, respectively). The hypothesis that injected slurry at a higher water content enhances denitrification was confirmed. This study provides important insights into the formation, spatial and temporal variation of the manure-soil hotspot and its impact on the denitrification process. The results will form part of a dataset to develop, improve and test manure application submodules of biogeochemical models and will help to understand in detail the effect of hotspots on N-cycling in manure-treated soils.

Towards enhanced sensitivity of the 15N gas flux method for quantifying denitrification in soil

Denitrification is the least studied process of the global N cycle mainly due to the sensitivity required to discriminate small fluxes of soil emitted N2 against the high atmospheric N2 background. We aimed to enhance the sensitivity of the 15N Gas Flux method to measure in situ denitrification rates by optimising the quantity of 15N–NO3 tracer applied and by using an artificial atmosphere (containing 5 % N2, 20 % O2, 75 % He and 0.11 ppm of N2O) during field incubation. We first conducted a dose-response laboratory study to assess the stimulation effect of nitrate tracer addition. Subsequently, we developed two novel approaches to measure in situ denitrification rates, using either modified static chambers or intact soil cores inside plastic liners; where in both cases the entire headspace was replaced by the artificial atmosphere prior to incubation. Furthermore, we compared the two models of calculations of the 15N Gas Flux method (the “Mulvaney & Boast” and “Arah” models) as well as the calculated 15N enrichment of the soil denitrifying pool based on either N2 or N2O isotopologue distribution data. The results showed that doubling the amount of ambient nitrate did not lead to a significant stimulation of denitrification activity in our case. However, excessive amendment of nitrate (e.g. 20 times the ambient levels) increased the denitrification product ratio by stimulating nitrous oxide emission. Our two novel field techniques were successful in measuring in situ denitrification rates, however, the liner method was preferred due to a higher success rate of N2 flux detection (up to 90 %), a higher throughput (up to 24 cores at a time) and improved spatial resolution. Under high-resolution instruments, our N2 limit of detection was 160 ppb, which is 5-fold better than the original method. The Mulvaney & Boast model performed better than the Arah one and consistently yielded higher fluxes (17 % at maximum), especially for low 15N enrichments of the soil denitrifying pool and short times of incubation. The 15N enrichments calculated with either N2 or N2O data differed statistically, but the magnitude of difference was small (4.6 % at maximum). Measuring in situ denitrification is imperative to quantify realistic fluxes and the liner method presented here is an inexpensive, reproducible and high-resolution candidate. For increased sensitivity, we recommend using the method of Mulvaney & Boast for N2O emissions and the resulting 15N enrichment in combination with 29N2 data (only) to determine N2 emissions.

UV photo-degradation of the secondary lichen substance parietin: A multi-spectroscopic analysis in astrobiology perspective

The cortical anthraquinone yellow-orange pigment parietin is a secondary lichen substance providing UV-shielding properties that is produced by several lichen species. In our work, the secondary metabolite has been extracted from air-dried thalli of Xanthoria parietina. The aims of this study were to characterize parietin absorbance through UV–VIS spectrophotometry and with IR spectroscopy and to evaluate its photodegradability under UV radiation through in situ reflectance IR spectroscopy to understand to what extent the substance may have a photoprotective role. This allows us to relate parietin photo-degradability to the lichen UV tolerance in its natural terrestrial habitat and in extreme environments relevant for astrobiology such as Mars. Extracted crystals were UV irradiated for 5.59 h under N2 flux. After the UV irradiation, we assessed relevant degradations in the 1614, 1227, 1202, 1160 and 755 cm−1 bands. However, in light of Xanthoria parietina survivability in extreme conditions such as space- and Mars-simulated ones, we highlight parietin UV photo-resistance and its relevance for astrobiology as photo-protective substance and possible bio-hint.

Biofilms on plastic litter in an urban river: Community composition and activity vary by substrate type.

In aquatic ecosystems, plastic litter is a substrate for biofilms. Biofilms on plastic and natural surfaces share similar composition and activity, with some differences due to factors such as porosity. In freshwaters, most studies have examined biofilms on benthic substrates, while little research has compared the activity and composition of biofilms on buoyant plastic and natural surfaces. Additionally, the influence of substrate size and successional stage on biofilm composition has not been commonly assessed. We incubated three plastics of distinct textures that are buoyant in rivers, low-density polyethylene (rigid; 1.7 mm thick), low-density polyethylene film (flexible; 0.0254 mm thick), and foamed polystyrene (brittle; 6.5 mm thick), as well as wood substrates (untreated oak veneer; 0.6 mm thick) in the Chicago River. Each material was incubated at three sizes (1, 7.5, and 15 cm2 ). Substrates were incubated at 2-10 cm depths and removed weekly for 6 weeks. On each substrate we measured chlorophyll concentration, biofilm biomass, respiration, and flux of nitrogen gas. We sequenced 16S and 23S rRNA genes at Weeks 1, 3, and 6 to capture biofilm community composition across successional stages. Chlorophyll, biomass, and N2 flux were similar across substrates, but respiration was greater on wood than plastics. Bacterial and algal richness and diversity were highest on foam and wood compared to polyethylene substrates. Bacterial biofilm community composition was distinct between wood and plastic substrates, while the algal community was distinct on wood and foam, which were different from each other and polyethylene substrates. These results indicate that polymer properties influence biofilm alpha and beta diversity, which may affect transport and distribution of plastic pollution and associated microbes, as well as biogeochemical processes in urban rivers. This study provides valuable insights into the effects of substrate on biofilm characteristics, and the ecological impacts of plastic pollution on urban rivers. PRACTITIONER POINTS: Plastic physical and chemical properties act as forces of selection for biofilm. Biofilm activity was similar among three different types of plastic. Community composition between plastic and wood was different.

Ditch level-dependent N removal capacity of denitrification and anammox in the drainage system of the Ningxia Yellow River irrigation district

Drainage networks, consisting of different levels of ditches, play a positive role in removing reactive nitrogen (N) via self-purification before drainage water returns to natural water bodies. However, relatively little is known about the N removal capacity of irrigation agricultural systems with different drainage ditch levels. In this study, we employed soil core incubation and soil slurry 15N paired tracer techniques to investigate the N removal rate (i.e., N2 flux), denitrification, anaerobic ammonium oxidation (anammox), and dissimilatory nitrate reduction to ammonium (DNRA) rates in the Ningxia Yellow River irrigation district at various ditch levels, including field ditches (FD), paddy field ditches (PFD), lateral ditches (LD1 and LD2), branch ditches (BD1, BD2, BD3), and trunk ditches (TD). The results indicated that the N removal rate ranged from 44.7 to 165.22 nmol N g−1 h−1 in the ditches, in the following decreasing order: trunk ditches > branch ditches > paddy field ditches > lateral ditches > field ditches. This result suggested that the N removal rate in drainage ditches is determined by the ditch level. In addition, denitrification and anammox were the primary pathways for N removal in the ditches, contributing 68.40–76.64 % and 21.55–30.29 %, respectively, to the total N removal. In contrast, DNRA contributed only 0.82–2.15 % to the total nitrate reduction. The N removal rates were negatively correlated with soil EC and pH and were also constrained by the abundances of denitrification functional genes. Overall, our findings suggest that the ditch level should be considered when evaluating the N removal capacity of agricultural ditch systems.

Poly(4-methyl-1-pentene) hollow-fiber membranes with high plasma-leakage resistance prepared via thermally induced phase separation method

Poly (4-methyl-1-pentene) (PMP) hollow-fiber membranes (HFMs) with bi-continuous structure and high plasma-leakage resistance were successfully prepared via thermally induced phase separation using binary diluents of nontoxic paraffin oil (PO) and oleic acid (OA) for oxygenation. The phase separation mechanism of the PMP HFM with 30–40 wt% PMP shifted from solid–liquid to liquid–liquid as the PO/OA mass ratio was increased, changing its flaky crystal structure to a bi-continuous or cellular structure. The effects of the air-gap distance, take-up speed, and PMP concentration on the HFM structure and performance were also investigated. The results showed that a shorter air-gap distance and higher take-up speed reduced the pore size and gas permeability of the membranes. Under the optimal conditions (PMP concentration: 40 wt%, PO/OA mass ratio: 49/11, take-up speed: 60 rpm air-gap distance: 10 mm), PMP HFM exhibited excellent gas permeability (N2 flux: 2.4 mL/(bar·cm2·min) or 533 GPU), mechanical properties (tensile strength: 10.4 MPa; elongation at break: 150.6 %), and plasma-leakage resistance (leakage time: >5900 at an external liquid and internal gas pressures of 0.1 and 0.08 MPa, respectively). Therefore, this study has significant implications for the large-scale production of PMP HFMs.

An In situ Proton Filter Covalent Organic Framework Catalyst for Highly Efficient Aqueous Electrochemical Ammonia Production

AbstractThe electrocatalytic nitrogen reduction reaction (NRR) driven by renewable electricity provides a green synthesis route for ammonia (NH3) production under ambient conditions but suffers from a low conversion yield and poor Faradaic efficiency (F.E.) because of strong competition from hydrogen evolution reaction (HER) and the poor solubility of N2 in aqueous systems. Herein, an in situ proton filter covalent organic framework catalyst (Ru‐Tta‐Dfp) is reported with inherent Ruthenium (Ru) sites where the framework controls reactant diffusion by suppressing proton supply and enhancing N2 flux, causing highly selective and efficient catalysis. The smart catalyst design results in a remarkable ammonia production yield rate of 2.03 mg h−1 mgcat−1 with an excellent F.E. of ≈52.9%. The findings are further endorsed with the help of molecular dynamics simulations and control COF systems without in situ proton filter feasibility. The results point to a paradigm shift in engineering high‐performance NRR electrocatalysts for more feasible green NH3 production.

Advanced approach of bulk (111) 3C-SiC epitaxial growth

3C-SiC films grown on (111) Si substrates exhibit poor crystal quality and experience wafer cracks and bowing preventing access to bulk growth. This work reports innovative Chemical Vapor Deposition (CVD) growth methodology on 4 in. Si substrates which allowed the growth of 230 mm thick layer of (111) 3C-SiC through the melting of the Si substrate in the CVD chamber and the adoption of the resulting free standing 3C-SiC for the growth of bulk (111) 3C-SiC layer under high N fluxes. From the molten KOH etching and subsequent SEM investigation it has been ascertained that with a N2 flux of 1600 sccm there is a significant reduction in the concentration of stacking faults (SFs) from (7.16 ± 0.04) × 103 cm−1 to (0.4 ± 0.3) × 103 cm−1. This reduction is consistent with the cross section m-PL response displaying steep and uniform increase in the intensity of the band-edge signal a factor 10 higher on the surface with respect to the equal (100) 3C-SiC grown thickness. Furthermore, the emission attributed to point defects is considerably lower in (111) 3C-SiC. From Scanning Transmission Electron Microscopy (STEM) investigation it appears evident how the typical mechanism valid in (100) growths consisting in the mutual closure of SFs coming from opposing {111} planes that give rise to Lomer and l-shaped dislocations is replaced by a different panorama of evolution. Indeed, it is shown how the SFs shred but do not interrupt each other during growth. Furthermore, dropping in the number of atomic planes composing SFs layers appears to be a key phenomenon leading to both the shrinkage of the number of SF atomic layers as well as to the SF self-closure. High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) attested how the crystal tends to smooth out the lattice mismatch until the SF is suppressed. Because of the foregoing, the mechanisms of evolution of the defects in (111) 3C-SiC revealed in this study, demonstrates how the growth parameters must be matched with the kinetics of the defects in order to endorse (111) 3C-SiC adoption in high performing devices.

CO2 capture performance of ceramic membrane with superhydrophobic modification based on deposited SiO2 particles

Membrane absorption is a promising CO2 capture technology, which is limited by the high cost of membrane materials. Coal fly ash (CFA)-based ceramic membrane as an alternative material for membrane modules can effectively reduce the preparation cost. In this study, CFA-based ceramic membrane with superhydrophobic properties is prepared by depositing SiO2 nanoparticles and grafting 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS). Characters including pore size distribution, porosity and N2 flux of superhydrophobic membrane are performed. The superhydrophobic modified ceramic membrane is applied to CO2 capture experiments using ethanolamine (MEA) solution as the absorbent. The result shows that the contact angle of the modified ceramic membrane reaches 155.0°, which significantly improves the anti-wetting properties of the membrane surface. The CO2 capture experiment demonstrates a maximum capture efficiency of 97.45% and a mass transfer rate of 21.17 mol/(m2·h). In addition, the superhydrophobic modified ceramic membrane exhibits excellent thermal and chemical stability, sustaining high performance even after 8 h of continuous operation. This study provides the theoretical and empirical foundation for the application of CFA-based superhydrophobic ceramic membranes in CO2 capture.

Improved electrochemical detection of copper ions in nitrogen doped ta-C films for marine corrosive monitoring

The corrosion of copper-based alloy in the harsh marine environment threatens the reliable operation and service life of marine engineering equipment. In this work, the nitrogen modified tetrahedral amorphous carbon (ta-C:N) film electrodes were prepared for marine-oriented copper ions detection. The relationship between structural evolution and electrochemical performance of ta-C:N film electrode tailored by N2 flux was evaluated. The sp2 cluster and the content of sp2-bonded carbon in ta-C:N film were promoted with the increase of N2 flux. XPS results indicated that the variation of N2 flux modified the nitrogen-containing groups of the ta-C:N film electrodes. The optimized ta-C:N film electrode deposited at N2 flux of 3 sccm showed a quasi-reversible electrode behaviors. Moreover, the ta-C:N film electrode exhibited a linear range from 8 × 10−3 mM to 5 mΜ, a detection limit of 8 × 10−3 mM, and good repeatability and reproducibility for Cu2+ detection in 3.5 wt% NaCl solution. The improved Cu2+ sensing properties were ascribed to the enhanced sp2 cluster and the introduction of multiple nitrogen-containing functional groups, especially the pyrrolic nitrogen and graphitic nitrogen. DFT computation and wavefunction analysis revealed that the pyrrolic nitrogen possessed the strongest interaction for copper ions among different nitrogen configurations.

Small ponds have stronger potential for net nitrogen removal: Insight from direct dissolved N2 measurement

Growing demands for watershed nitrogen (N) removal have called attention to abundant small bodies of water such as ponds, which have long been heralded as efficient storage and processing systems. Although pond conservation, restoration, and creation have been widely implemented to mitigate N pollution, information is limited regarding the impact of size—that is, whether N removal potential and efficiency are dependent upon pond size. We investigated the dynamics of N removal rates in 56 ponds from a hilly watershed by studying their bimonthly N2 concentrations and fluxes. Our results showed that smaller ponds performed better in net N removal. This can be discerned from the areal N2 fluxes, which were the highest in small ponds (< 4, 000 m2). The corresponding N2 fluxes (4.73 ± 4.53 mmol N2 m−2 d−1) were 2 to 14 times greater than those observed in larger ponds. The N removal efficiency, a metric used to describe the portions of the substrates released as N2, was also significantly higher in the small ponds (∼8.7 %) than in the larger ponds (∼5.0 %). Further regression analysis showed that both areal N2 flux and N removal efficiency were negatively correlated with pond area. The underlying mechanisms behind the size effects of N removal could be attributed to small ponds having larger sediment contact area to water volume ratios. Thus, smaller ponds allow more opportunities for N to interact with bioactive sediments than larger ponds. Overall, our findings contribute to the understanding of the distal role of pond size in affecting N removal. This research also provides a strong rationale for considering the effects of system size when implementing management practices dedicated to maximizing N removal.

Effect of N2 flux on the field emission properties of synthesized ZnO/ZrN core-shell nanostructures

In this paper, the highly oriented ZnO/ZrN nanoneedle emitters with excellent field emission performance were fabricated by sputtering ZrN particles with different N2 flux to modify ZnO nanoneedle arrays. The effects of different N2 flow on the microscopic morphology, structure and field emission properties of ZnO nanoneedles were investigated. The results shows that the ZnO/ZrN nanoneedles (ZnO/ZrN-1.6) emitter prepared when the flow of N2 gas is 1.6 SCCM exhibits the best field emission performance, with the lowest turn-on electric field Eto at 0.81 V/μm, and a field emission current density of 25 mA/cm2 which was 25 times of pure ZnO. In addition to the improvement of band structure, the improvement of field emission performance can also be attributed to the tunneling effect of electrons through heterostructure. This well-aligned ZnO/ZrN core-shell cathode with excellent emission characteristics grown on carbon cloth substrate has the potential applications in future flexible light source devices.

Effect of Growth Conditions on the Surface Morphology and Defect Density of CS‐PVT‐Grown 3C‐SiC

AbstractA systematic approach to determine the most crucial growth parameters and their effect on the surface morphology and defect density of sublimation grown (001) cubic silicon carbide (3C‐SiC) is conducted. Close space physical vapor transport (CS‐PVT) growth on 3C‐SiC and 4° off oriented homoepitaxial chemical vapor deposition (CVD) grown seeding layers is performed. For each growth run, one growth parameter, e.g., temperature, pressure, or N2 flux is varied, while the other parameters are kept constant. Raman spectroscopy, potassium hydroxide (KOH) etching, as well as optical microscopy and atomic force microscopy (AFM) are used for the sample characterization. Step‐flow‐controlled growth is observed on all grown samples, while the stacking fault density is generally reduced with respect to the seeding layers. Increased temperature as well as increased pressure leads to roughening of the growth surface attributed to step bunching, while their effect on the stacking fault density seems to be only minor in the analyzed parameter range. Areas of strongly enhanced step bunching are present on all samples, and this effect is more pronounced at higher temperature and pressure. Increased nitrogen doping leads to a decreased stacking fault density but also increases the length of remaining stacking faults. The surface morphology is influenced by N2 on a macroscopic level rather than on microscopic scale.

Effects of nitrogen flux and RF sputtering power on the preparation of crystalline a-plane AlN films on r-plane sapphire substrates

A-plane aluminum nitride (AlN) with high quality is crucial to fabricate high-performance non-polar deep-ultraviolet optoelectronic devices. In this work, we prepared crystalline a-plane AlN films on r-plane sapphire substrates by combining reactive magnetron sputtering and high temperature annealing (HTA). The effects of N2 flux and radio frequency (RF) sputtering power on the crystal quality, the surface morphology and the in-plane stress state of a-plane AlN films were comprehensively investigated. The results suggest that the properties of high temperature annealed a-plane AlN (HTA-AlN) films positively depend on the initial states of the sputtered AlN (SP-AlN) films. Increasing the N2 flux or the RF sputtering power can improve the crystalline quality of SP-AlN films by reducing the kinetic energy of deposited particles, which facilitates a-plane AlN deposition. A higher N2 flux smoothens the surface morphology due to the relieved bombardment effect, which is confirmed by the enlarged in-plane tensile stress state. However, a higher sputtering power leads to a rougher surface because of the accelerated deposition rate. With optimized sputtering parameters, a high-quality a-plane HTA-AlN template was obtained with full width at half maximum values of (11–20) plane x-ray rocking curves as low as 1188 and 1224 arcsec along [0001] and [1–100] directions, respectively. The surface presents an ordered stripe-like morphology with a root-mean-square value of 0.79 nm. Our work provides a convenient and effective strategy to prepare high quality a-plane AlN templates and accelerate the versatile application of non-polar deep-ultraviolet light-emitting diode devices.

Modelling of the kinetics adsorption of gold (I) cyanide complex ion by active carbons prepared from Parinari macrophylla shells

Nowadays, one of the sectors to valorization of waste is their transformation in nobler materials rather than in energy. This study is about the valorization of agricultural waste (Parinari Macrophylla shells) for the development of active carbons, the characterization of porous materials gotten and the kinetic study for adsorption of gold (I) cyanide complex ion. The development is made by impregnation in KOH followed of a pyrolysis under flux of N2 or CO2. The characteristics determined for adsorption are iodine index, methylene blue index, pH to point of zero charge (pHPZC) as well as the textures characteristics gotten by adsorption of nitrogen at 77 K. For adsorption of gold (I) cyanide complex ion , the kinetics model’s pseudo-order 1, pseudo-order 2, the model of Elovich and those diffusions of Boyd and Weber-Morris are studied. The results of the characterization showed that samples are basic (pHPZC &gt; 7), present the specific surfaces of 1008 m2/g and 1063 m2/g with percentages in microporous surface more than 78% and for microporous volume more than 71%. The kinetics of adsorption of gold (I) cyanide complex ion (Au(CN)2-) obeys more to pseudo-order 2 model and a multi-linearity of the models of Elovich and diffusions during adsorption.