Nitrogen Ion Flux Research Articles

The Pulse of the Amazon: Fluxes of Dissolved Organic Carbon, Nutrients, and Ions From the World's Largest River

AbstractThe Amazon River drains a diverse tropical landscape greater than 6 million km2, culminating in the world's largest export of freshwater and dissolved constituents to the ocean. Here, we present dissolved organic carbon (DOC), organic and inorganic nitrogen (DON, DIN), orthophosphate (PO43−), and major and trace ion concentrations and fluxes from the Amazon River using 26 samples collected over three annual hydrographs. Concentrations and fluxes were predominantly controlled by the annual wet season flood pulse. Average DOC, DON, DIN, and PO43− fluxes (±1 s.d.) were 25.5 (±1.0), 1.14 (±0.05), 0.82 (±0.03), and 0.063 (±0.003) Tg yr−1, respectively. Chromophoric dissolved organic matter absorption (at 350 nm) was strongly correlated with DOC concentrations, resulting in a flux of 74.8 × 106 m−2 yr−1. DOC and DON concentrations positively correlated with discharge while nitrate + nitrite concentrations negatively correlated, suggesting mobilization and dilution responses, respectively. Ammonium, PO43−, and silica concentrations displayed chemostatic responses to discharge. Major and trace ion concentrations displayed clockwise hysteresis (except for chloride, sodium, and rubidium) and exhibited either dilution or chemostatic responses. The sources of weathered cations also displayed seasonality, with the highest proportion of carbonate‐ and silicate‐derived cations occurring during peak and baseflow, respectively. Finally, our seasonally resolved weathering model resulted in an average CO2 consumption yield of (3.55 ± 0.11) × 105 mol CO2 km−2 yr−1. These results represent an updated and temporally refined quantification of dissolved fluxes that highlight the strong seasonality of export from the world's largest river and set a robust baseline against which to gauge future change.

Control of Ion Species and Energy in High-Flux Helicon-Wave-Excited Plasma Using Ar/N2 Gas Mixtures

The atomic nitrogen (N) ion flux and impacting ion energy are the two important parameters, which influence the performance of production of plasma nitridation applications such as N-doped graphene. In this paper, a novel method is described to control the flux and ion energy of atomic N ion (N+) and molecular N2 ion (N2+) using a helicon-wave-excited plasma (HWP) with Ar/N2 gas mixtures. It shows that by varying the flow-rate ratio of N2/(N2+Ar) ( $\alpha$ ), the ratio of [N+]/[N2+] ( $\beta$ ) can be controlled obviously, and $\beta $ could be increased up to 1.2 at $\alpha = 0.5$ , which is much higher than that in pure N2 HWP discharge ( $\beta \sim 0.2$ ). The maximum density and flux of atomic N+ are obtained, which are $2.5\times 10^{18}\,\,\text {m}^{-3}$ and $8.6\times 10^{21}\,\,\text {m}^{-2}\text {s}^{-1}$ , respectively. The results show that the addition of Ar into N2 plasma can be employed to remarkably increase the [N+]/[N2+] due to electron-impact ionization involving the metastable state of Ar. The N+ ion beams are formed with a speed near to Mach 3, and the ion-beam energy is increased from 30 to 50 eV with increasing $\alpha $ to 0.75.

Effect of Pulsed Nitrogen Plasma and Nitrogen Ion Fluxes on the Structure and Mechanical Properties of Vanadium

The effect of powerful pulsed fluxes of nitrogen plasma and nitrogen ions generated in the PF-4 Plasma Focus setup (LPI; energy flux density of plasma pulse was 108–1010 W/cm2) on the modification of vanadium surface is studied. Melting and ultrafast solidification result in a fine cellular structure (cell size of 100–200 nm) in a thin surface layer in samples. There are irradiation regimes causing directional crack growth after solidification and cooling of the surface layer and the formation of a block microstructure with a block size of several tens of micrometers. The thickness of the melted layer in the samples is 2–4 μm. Cracks propagate to a depth of 5–20 μm. It is established that irradiation by pulsed nitrogen plasma and high-energy nitrogen ions changes the microhardness of the vanadium surface layers. The microhardness increases by a factor of three with the number of plasma pulses and the distance between a sample and the anode of the Plasma Focus (PF) setup. The increase in the microhardness is in agreement with the refinement of coherent scattering regions, the increase in lattice microstrain e, and the formation of vanadium nitrides. Pulsed fluxes of nitrogen plasma and nitrogen ions decrease the lattice parameter much greater than cold working (rolling) does. The lattice parameter decreases when the total irradiation power is increased (the number of pulses increases or the distance between a sample and the anode of the PF setup decreases). Such changes seem to be caused by the action of the residual macrostresses induced by pulsed plasma irradiation. In addition, X-ray diffraction analysis showed a change in the texture of the surface layer after ion-plasma treatment of coldworked vanadium samples in the PF setup.

Study of the effects of plasma immersion ion implantation on austenitic stainless steel using E × B fields

The effect of magnetic field enhanced plasma immersion ion implantation (PIII) on SS304 austenitic stainless steel samples has been investigated. Application of magnetic field in PIII process leads to the formation of the crossed E×B field configuration, promoting the increase of the plasma density by electron-neutrals collision. As a result, a high nitrogen ion flux on SS304 sample was achieved. In this experiment, a moderate temperature of about 350°C was measured after two hour of treatment, discarding the possibility of the formation of chromium nitride. Measurements performed by Auger electron spectroscopy (AES) showed the formation of a nitrogen implanted layer which was much greater than the one obtained by standard PIII (at the same pulsing conditions). Due to that, new peaks in the characteristic profile of X-ray diffraction were observed as consequence of the formation of a new phase (γN phase). It has caused as twice as high improvement in the surface hardness compared to the conventional PIII. Consequently, a substantial reduction in the wear rate was obtained.

Initial stages of the ion-beam assisted epitaxial GaN film growth on 6H-SiC(0001)

Ultra-thin gallium nitride (GaN) films were deposited using the ion-beam assisted molecular-beam epitaxy technique. The influence of the nitrogen ion to gallium atom flux ratio (I/A ratio) during the early stages of GaN nucleation and thin film growth directly, without a buffer layer on super-polished 6H-SiC(0001) substrates was studied. The deposition process was performed at a constant substrate temperature of 700°C by evaporation of Ga and irradiation with hyperthermal nitrogen ions from a constricted glow-discharge ion source. The hyperthermal nitrogen ion flux was kept constant and the kinetic energy of the ions did not exceed 25eV. The selection of different I/A ratios in the range from 0.8 to 3.2 was done by varying the Ga deposition rate between 5×1013 and 2×1014at.cm−2s−1. The crystalline surface structure during the GaN growth was monitored in situ by reflection high-energy electron diffraction. The surface topography of the films as well as the morphology of separated GaN islands on the substrate surface was examined after film growth using a scanning tunneling microscope without interruption of ultra-high vacuum. The results show, that the I/A ratio has a major impact on the properties of the resulting ultra-thin GaN films. The growth mode, the surface roughness, the degree of GaN coverage of the substrate and the polytype mixture depend notably on the I/A ratio.

Increasing of Hardness of Titanium Using Energetic Nitrogen Ions from Sahand as a Filippov Type Plasma Focus Facility

In this paper a 90 kJ plasma focus facility was used to the bombardment of the titanium substrate using nitrogen ion beams. From x-ray diffraction patterns, we investigated the structure properties of titanium nitride layer has been successfully deposited on the titanium substrate such as grain size microstrain and dislocation density. In this work we observed the growth of in grain size with increasing a number of deposition shots. Decrease in dislocation density and microstrain at higher deposition is the another results we observed in this work. The topography and morphology of TiN samples was studied by scanning electron microscopy (SEM) and optical microscopy images. From SEM micrograph, damage of surface and creation of pits and cracks was reported. The goniometric test indicate increasing in contact angle of water drop for irradiated samples in respect to the unirradiated samples. The Knoop microhardness of the samples is increased about 500%. With increasing of nitrogen ion flux, the microhardness increases.

The influence of the nitrogen-ion flux on structure and ionic conductivity of vapor deposited lithium phosphorus oxynitride films

Thin films of lithium phosphorus oxynitride (Lipon) have been grown using a plasma-assisted, directed vapor deposition (PA-DVD) technique. In this approach, a high voltage electron beam is used to vaporize a Li 3PO 4 source and a supersonic, nitrogen-doped, helium gas jet then transport the vapor towards a substrate. A hollow cathode technique was then used to create an argon plasma just above the substrate. This sufficiently ionized the nitrogen in the gas jet to allow its incorporation into the Li 3PO 4 film reactively forming lithium phosphorus oxynitride. Increasing the nitrogen flux in the gas jet also increased the deposition rate from 113 to 178 nm min −1 for the deposition conditions used here, significantly reduced the pore volume fraction in the films and increased the N/P ratio from 0 to 0.75 as the gas jet nitrogen flux was increased from zero to 4.3 × 10 18 molecules cm −2 s −1. Using substrate rotation, pore and columnar-free dense Lipon films could be grown by this method. The Li-ion conductivity increased from 3.7 × 10 −9 to 5.2 × 10 −7 S cm −1 as the nitrogen concentration was increased from zero to 2.1 × 10 18 molecules cm −2 s −1 and was correlated with an increase in the film's Li/P ratio. An optimum nitrogen flux has been identified. As the nitrogen flux was increased above this value, the Lipon films suffered lithium loss and partial crystallization, resulting in a decrease in their Li-ion conductivity.

Nitriding of austenitic stainless steel by pulsed low energy ion implantation

Low energy ion implantation (LEII) of nitrogen into austenitic stainless steel was carried out using an electronic beam switch for a defined regulation of nitrogen ion flux and an additional external radiation heating for assuring a constant process temperature of 460 °C with the aim to investigate the influence of a varying ion energy and ion flux, respective particle flux on nitrogen diffusion, phase formation and hardness of the nitrided austenitic stainless steel, grade 1.4301, samples. No influence of both process parameter variations on the layer thickness was found as long as identical temperature profiles were maintained. This implies that the nitrogen diffusion is decoupled from nitrogen insertion at constant temperature for sufficiently high nitrogen supply. It was found that the pulsed mode does not influence the expended austenite formation, hardness of the nitrided layers as well as their corrosion resistance compared with a continuous LEII-mode at the same ion source plasma parameters.

Influence of N + ion implantation on the corrosion and nano-structure of Ti samples

Nitrogen ions of 30 keV with different fluxes ranging from 5 × 10 16 to 8 × 10 17 ions/cm 2 were implanted in Ti foil of 1.8 mm thickness. X-ray diffraction (XRD) was used to obtain the structural characteristics, while atomic force microscope (AFM) was employed to obtain the surface morphology of the samples. The potentiodynamic method was employed to obtain corrosion resistance of the samples in NaCl (3.5%) solution. Titanium nitride formation was enhanced with increasing the nitrogen ion flux, while grain size and surface roughness of the samples were also increased. Optimum corrosion resistance was obtained for 5 × 10 16 (N + ions/cm 2).

Can land use changes alter carbon, nitrogen and major ion transport in subtropical brazilian streams?

Several studies in tropical watersheds have evaluated the impact of urbanization and agricultural practices on water quality. In Brazil, savannas (known regionally as Cerrados) represent 23% of the country's surface, representing an important share to the national primary growth product, especially due to intense agriculture. The purpose of this study is to present a comprehensive evaluation, on a yearly basis, of carbon, nitrogen and major ion fluxes in streams crossing areas under different land use (natural vegetation, sugar cane and eucalyptus) in a savanna region of SE Brazil. Eucalyptus and sugar cane alter the transport of the investigated elements in small watersheds. The highest concentration of all parameters (abiotic parameters, ions, dissolved organic carbon DOC - and dissolved inorganic carbon - DIC) were found in Sugar Cane Watersheds (SCW). The observed concentrations of major cations in Eucalyptus Watersheds (EW) (Mg, Ca, K, Na), as well as DIN and DOC, were found frequently to be intermediate values between those of Savanna Watersheds (SW) and SCW, suggesting a moderate impact of eucalyptus plantations on the streamwater. Same trends were found in relation to ion and nutrient fluxes, where the higher values corresponded to SCW. It is suggested that sugar cane plantations might be playing an important role in altering the chemistry of water bodies.

Applications of electron-beam generated plasmas to materials processing

Nonequilibrium (T/sub e//spl Gt/T/sub ion,gas/) plasma processing often allows for greater process control with reduced environmental impact when compared to other materials processing methods, and therefore presents tremendous opportunities in the areas of thin film development and surface modification. The U.S. Naval Research Laboratory's "Large Area Plasma Processing System" (LAPPS) has been developed based on the high-energy (2 keV) electron-beam ionization process, with the goal of maximizing the benefits of plasma processing over large areas (/spl sim/1 m/sup 2/). This system has been shown to be: 1) efficient at producing plasma in any gas composition; 2) capable of producing low-temperature plasma electrons (<0.5 eV) in high densities (10/sup 9/-10/sup 12/ cm/sup -3/); and 3) scalable to large area (square meters). In this paper, the progress of a number of applications using LAPPS is discussed. Nitride growth in stainless steel was investigated, which demonstrated high rates (over 20 /spl mu/m/h/sup 1/2/) at low temperatures (/spl les/462/spl deg/C). Complementary mass spectrometry showed that the nitriding results correlated to the flux of atomic ions delivered to the substrate. LAPPS was also combined with magnetron sputtering sources to form hybrid systems for thin film deposition of nitrides. The simultaneous operation of LAPPS with a titanium magnetron sputter source increased the growth of the <200> orientation in TiN films, due to the increased atomic nitrogen ion flux. Polymer pretreatment studies were also initiated in these systems; polytetrafluoroethylene substrates pretreated with an oxygen LAPPS exposure demonstrated a significant increase in copper and aluminum film adhesion compared to untreated substrates, with the dominant factor believed to be the changed surface morphology. Similarly dramatic fluorination of polyethylene was demonstrated with plasmas generated in Ar/SF/sub 6/ mixtures.

Plasma enhanced surface treatments using electron beam-generated plasmas

NRL has developed a ‘large area plasma processing system’ (LAPPS) utilizing a high energy (∼2 keV) modulated electron beam to drive the plasma ionization. This system has been shown to be (1) efficient at producing plasma in any gas composition, (2) capable of producing low temperature plasma electrons (<0.5 eV) in high densities (10 9–10 12 cm −3) and (3) scalable to large area (square meters). In this work, the progress of a number of applications using LAPPS is discussed. Nitride growth in stainless steel was investigated, which demonstrated high rates (up to 20 μm/h 1/2) at low temperatures (≤462 °C). Complementary mass spectrometry showed that the nitriding results correlated to the flux of atomic ions delivered to the substrate. LAPPS was also combined with magnetron sputtering sources to form hybrid systems for surface pretreatments of polymers for metallization and thin film deposition of nitrides. In these systems, Teflon® substrates pretreated with an oxygen LAPPS exposure demonstrated a significant increase in copper and aluminum film adhesion compared to untreated substrates, with the dominant factor believed to be the changed surface morphology. The simultaneous operation of LAPPS with a titanium magnetron sputter source increased the growth of the 〈200〉 orientation in TiN films, due to the increased atomic nitrogen ion flux. Additional LAPPS systems are also discussed.

Influence of defects in low-energy nitrogen ion beam assisted gallium nitride thin film deposition

Epitaxial GaN thin films were grown by low-energy nitrogen ion beam assisted deposition of gallium on c-plane sapphire. By applying X-ray diffraction and transmission electron microscopy, the influence of the ion irradiation induced defects on the formation of the undesired cubic GaN polytype in the hexagonal films is investigated. The results show that in all films containing the cubic polytype it appears in twinned form. An increase of the ion energy as well as the ratio of nitrogen ion flux and gallium atom flux ( I/ A-ratio) leads to an increase in the amount of cubic polytype in the films. The observations are discussed considering the ion beam induced defect creation.

A comprehensive nitriding study by low energy ion beam implantation on stainless steel

In this paper we report nitriding studies of stainless steel 316 using a broad ion beam source. Experiments performed by changing the ion energy (0.2–1.5 KeV), ion current density (1.4–5.7 mA/cm 2) and implantation times (1 and 8 h) at a temperature around 380°C are reported. The microstructure and morphology are studied by glancing angle X-ray diffraction and scanning electron microscopy. For constant ion energy, higher nitrogen ion flux increases the hardness. At higher ion energies the sputtering process prevents the formation of a thick-nitrated layer, even for longer implantation times. The results are examined in the light of recent studies on physical models for ion implantation.

Development of a UHV compatible hollow cathode arc source for the deposition of hard nitride coatings

An ultrahigh vacuum (UHV) compatible hollow cathode arc source has been developed for the deposition of very pure nitride films (especially c-BN films). The crucial compounds of the plasma source have been numerically investigated to find parameters for optimal functioning. Heat conduction as well as radiation problems have been considered in both discharge electrodes, temperature distributions for different cathode materials have been calculated which show a strong dependence of the maximum temperature on the work function of the cathode. In order to deposit pure films a rather small cathode work function should be used. The source has been characterized experimentally with Langmuir probes and mass spectrometry with special regard to the nitrogen ion fluxes which are important for nitride film deposition - He addition to the working gas seemed to be beneficial in increasing the nitrogen ion fluxes. TiNx films could be deposited in the first experiments with a standard parameter set.

Synthesis of adhesive c-BN films in pure nitrogen radio-frequency plasma

Cubic boron nitride (c-BN) thin films were prepared at 600 °C by radio-frequency (rf) plasma pulsed laser deposition. All c-BN films prepared in Ar-rich plasma have poor adhesion on Si(100) substrates, but those prepared in pure N2 plasma can be maintained for more than 5 months without degradation. However, an increase of ion flux at an ion energy similar to that of pure N2 plasma results in the peeling of c-BN films. Thus, application of pure N2 plasma with suppressed ion flux can improve c-BN film adhesion. Under such conditions, an extended sp2-bonded interlayer is suspected, with the onset of the c-BN phase being delayed. Suppression of radiative damage in reduced nitrogen ion flux on both the c-BN and h-BN/t-BN phases are important for the adhesive of c-BN films.

The growth behavior of GaN film on Si(111) substrate by an ion-beam assisted evaporation process

Highly oriented GaN thin films were grown on Si(111) substrate using an ion beam assisted evaporation method. Nitrogen ions, with a kinetic energy of about 40 eV, was supplied by a Kaufman ion source; and Ga vapor was supplied by thermal evaporation. The surface morphology of the nucleation layer, and the crystalline properties of 200–300 nm thick GaN epi-layer were investigated by atomic force microscopy, transmission electron microscopy, and X-ray diffraction. Film grown under a Ga-rich flux condition produced film growth behavior of large islands of hexagonal configuration. Crystallinity on such film, however, was of poorer quality than other films with smaller islands, grown under high nitrogen ion flux conditions. The full width at half-maximum of (0002) diffraction peak was measured at 52 arcminutes for the GaN epilayer single-stepwise grown at 660°C. Ion-enhanced decomposition occurred, causing no film formation at substrate temperatures above 710°C. Additionally, the effect of predeposition of a buffer layer on GaN crystallinity was investigated for surface roughness. AFM measurement revealed that the GaN buffer layer grown on Si(111) showed smooth surface under the relatively N 2 +-sufficient condition. The introduction of thin GaN buffer layer, grown at 600°C under N 2 +-sufficient condition, worked on reducing the lattice-mismatch stress and in-plane misorientation of grains, and thus enhancing the crystallinity of the two-stepwise grown GaN epi-layer. Characteristic behavior of GaN epi-layers, single or two stepwise grown on Si(111), show a type of granular (columnar) epitaxy.

Relative roles of ion energy, ion flux, and sample temperature in low-energy nitrogen ion implantation of FeCrNi stainless steel

A matrix of nitrogen ion energies (0.4, 0.7 and 1.0 keV) and ion fluxes (1, 2, and 3 mA/cm 2) has been selected to investigate the systematics of ion-beam processing of an austenitic FeCrNi stainless steel (AISI 304) at 400°C for 60 min. In addition, the role of temperature was examined over the range from 280°C to 475°C at fixed processing conditions of 0.7 keV, 2 mA/cm 2, and 60 min. Characterization of the composition, structure, magnetic nature, thickness and strength of the nitrogen-containing layers was made by a combination of Auger electron spectroscopy, X-ray diffraction, backscatter Mössbauer spectroscopy, and microhardness measurements. A high N content layer, which is a magnetic, fcc phase, is predominant for all conditions and its thickness increases linearly with either ion energy at fixed ion flux or with ion flux at fixed ion energy. This behavior is consistent with layer growth that is controlled primarily by the N supply rate into the first few atomic layers rather than by thermal diffusion.

Properties of Nitrogen deep implanted industrial steels

Two types of steels, SKD11 and NAK55, with and without chromium were implanted with 30 keV nitrogen ions to a dose 2 × 1017 cm2 using the new deep implantation process after the preliminary surface treatment by a quasi-neutral intense nitrogen ion flux with the energy 300 eV up to the 1019 cm2. The thickness of the hardened layer significantly increased up to ~ 20 μm by 5 minutes irradiation with 300 eV nitrogen ions at temperatures between 250 and 300°C. The wear resistance of martensitic stee! SKD11 was drastically improved by a factor of 20 after pre-plasma irradiation. Deep implantation also reduces the wear of NAK55 by an order of magnitude, associated with an increase in hardness by a factor of 2.4 at an applied load of 50 gf due to the formation of Fe2.4N and CrN.

Effect of Na2O Addition to Ag2O-Doped Phosphate Glasses on Enhancement of Silver Particle Precipitation by Low-Energy Ion Irradiation

The precipitation of Ag particles in x Na2O– yAg2O– zAl2O3–(1- x- y- z)P2O5 glasses was studied. The volume fraction of quantum-size Ag precipitates was enhanced by nitrogen ion irradiation at room temperature. Ion-irradiation-enhanced precipitation was observed up to a distance of 80 nm from the glass surface. In the absence of Na2O (x=0), Ag was selectively sputtered by the nitrogen ion flux. In glasses containing Na2O, irradiation-induced Ag removal could be suppressed and the amount of precipitates increased. The third-order nonlinear optical susceptibility, χ(3), of the irradiated glasses was estimated to range from 5.5 to 8.8×10-7 esu. The large susceptibilities are consistent with the large amount of Ag precipitates. The irradiation-induced decomposition of Ag2O and Na2O is one possible precipitant-forming mechanism.