NH3 Pressure Research Articles

Constructive versus destructive effects of electron beam irradiation: an application to plasma nitridation of SiO2 thin films

Low energy (3–100 eV) electrons are shown to be efficient promoters of the superficial nitridation of thin (15 nm) SiO2 films using low pure NH3 pressures (⩽2 × 10−4 mbar) at ambient temperature. The ultrahigh vacuum experimental set-up permits us to uncouple two important effects both present in a thermally-assisted (700–950 °C) r.f. NH3 plasma nitridation process: the role played by low energy (3–5 eV) electrons and the temperature. It is found that the existence of charged particles near the sample surface must be taken into account in the plasma reaction process and that the main effect of thermal activation is to enhance the reaction and the diffusion of nitrogen species through the SiO2 layer down to the SiO2/Si interface.Auger sputter depth profiles of the plasma nitrided SiO2 films have been measured before and after bombardment with energetic electrons (1, 3, or 5 keV). Electron irradiation of the film induced a nitrogen depletion at the vacuum/dielectric interface and a nitrogen pile-up at the dielectric/silicon interface. Our results indicate that this phenomenon is a maximum for the lowest primary electron energy. This behavior can be understood on the basis of an electron-stimulated Si—N bond decomposition and the creation of positive nitrogen ions. The released nitrogen ions were found to either escape in vacuum or migrate through the dielectric layer and pile-up at the dielectric/silicon interface because of the existence inside the layer of a non-uniform electric field, in agreement with recent theoretical predictions.

Structural and magnetic properties of rf-sputtered iron nitrides using NH3 (abstract)

Thin films of iron nitrides have attracted much attention due to their superior magnetic properties. Conventional rf reactive sputtering using N2 gas encounters a number of difficulties, including mixed phases, which are alleviated by the use of NH3 gas. By controlling the partial pressure of NH3, we have been able to fabricate all stable Fe nitrides of ζ-Fe2N, ε-Fe2–3N, and γ′-Fe4N in single-phase films. The structure has been determined using an x-ray diffractometer. The magnetic properties have been investigated using VSM, SQUID magnetometers, and Mössbauer spectroscopy. All nitrides except Fe2N have high saturation moments with a large in-plane anisotropy. The saturation moment decreases with increasing nitrogen concentration. The Mössbauer results, in excellent agreement with those from bulk samples, are consistent with structural results and magnetization measurements.

Spectral characteristic study of Raman transition interaction in optically pumped FIR laser

The spectral characteristic of an optically pumped NH3 molecules FIR laser has been studied by a F-P interferometer and a Michelson interferometer. It was verified that when NH3 molecules were pumped by CO2-9R(16) line, a emission by Raman transitions of two photons was produced. When the gas pressure of NH3 increased, the interaction of the Raman transitions rose, then the emission was enhanced and the width of spectral lines were broadened. The experimental results are in good agreement with the theoretical calculations.

Low Temperature CVD of TiN from Ti(NR2)4 and NH3: FTIR Studies of the Gas-Phase Chemical Reactions

AbstractThe gas-phase chemical reaction between Ti(NMe2)4 and NH3 is a critical step in the Metallorganic Chemical Vapor Deposition (MOCVD) of TiN at low temperatures. We have examined this reaction using a flow-tube reactor coupled to an FTIR spectrometer. A sliding injector provides control over the reaction time and the kinetics of reactive species can be measured as a function of the partial pressure of an added reagent. The disappearance of Ti(NMe2)4 was measured as a function of reaction time and NH3 pressure at 26°C. The resulting bimolecular rate constant is (1.1±0. 1) x 10-16 cm3molecules−1s−1 Dimethylamine is observed as a direct product from this reaction consistent with other studies. We have also measured the rate constant using ND3 and find a substantial isotope effect, kh/kd ≈2.4± 0.4. This indicates that H-atom transfer is involved in the rate limiting step. We show that these results can be explained by a mechanism comprised of transamination reactions with NH3.

MA法による窒化鉄合成に及ぼす鉄粉末中の酸素およびNH<SUB>3</SUB>圧力の影響

Mechanical alloying (MA) in NH3 has been applied to prepare Fe16N2 powder where two different kinds of iron powders, i.e., elctrolytic Fe powder and carbonyl Fe powder were used as the starting materials.Nitriding has proceeded better in the electrolytic Fe powder than in the carbonyl Fe powder. On the other hand, oxidation has proceeded further in the latter than in the former. For example, after mechanical alloying in NH3 for 160 h 12 at%N and 2.0 at%O were contained in the specimen of the electrolytic Fe iron powder, and 11.5 at%N and 2.7 at%O in the specimen of the carbonyl Fe powder. The MA process under higher pressure of NH3 has an effect on preventing oxidation.The specimen obtained by the MA process showed a super-saturated bcc structure below 14-15 at%N, and Fe3N structure above 18-19 at%N. Fe16N2 could not be obtained by the MG process for the 11.1 at%N and Fe-13.3 at%N specimens prepared by the MA process.

Ammonia and ammonium fluxes between photolithotrophs and the environment in relation to the global nitrogen cycle

summaryAmmonium (used here to signify NH4+ plus NH3) is the immediate inorganic precursor of organic nitrogen in photolithotrophs. In marine habitats ammonium is also the major exogenous nitrogen source, and the same is probably true of terrestrial habitats. In addition to this major role of ammonium as exogenous nitrogen source, it is also quantitatively very important as an endogenous nitrogen source with nitrate or N2 as exogenous nitrogen source, and as a recycled nitrogen compound in photorespiration and in phenylpropanoid synthesis. The shoots of terrestrial plants have higher NH3 compensation partial pressures than most natural soils, and especially higher than that of the sea. However, long‐distance transport of gaseous NH3 (e.g. from continents to oceans) is a negligible component of the ‘natural’ global nitrogen cycle. Current concepts of evolution of the atmosphere and biosphere do not involve high partial pressure of NH3 in the atmosphere: any ammonium produced in inorganic or biological processes is removed from the atmosphere by rain‐out, or, over larger time‐scales, by the action of ultraviolet radiation (especially before the ozone screen came into being) and of hydroxyl radicals (especially after oxygenation of the atmosphere). In addition to posing problems for the origin of life and arguing for an early rather than a late evolution of diazotrophy, a low NH3 partial pressure renders implausible arguments that phenylpropanoid synthesis was restricted early in evolution by the effect of high ammonia in reversing phenylalanine ammonia‐lyase.

Adsorbate–metal interactions: An optical second harmonic generation study

The interaction of ammonia with clean and CO‐covered Re(0001) surface was investigated, utilizing optical second harmonic generation (SHG), temperature programmed desorption (TPD), and work function change (Δφ) techniques. The surface coverage of ammonia was continuously monitored during both isothermal desorption and equilibrium measurements as a function of crystal temperature and ambient NH3 pressure. A fast decrease of the activation energy for desorption from 21±1 to 9±1 kcal/mol as coverage increases from 0.2 to 0.9 of the saturation coverage was found. This indicates the existence of very strong repulsive interactions among adsorbed ammonia molecules. The pre‐exponent factor was also determined as a function of coverage, for the first time for any ammonia–metal system. Its fast decrease with increasing coverage, reveals an example for a compensation effect in desorption. The coadsorption system of CO and NH3 was also studied. It was found that while ammonia effectively blocks the adsorption of CO on Re(0001) when it is preadsorbed, the opposite order of adsorption, namely preadsorption of CO, hardly affects the adsorption–desorption kinetics of NH3. It was also found that decrease of work function caused by ammonia of 2.4 eV at saturation coverage, shifts upward exactly by the increase of Δφ by CO on the clean surface if the latter is preadsorbed. These minor effects of CO if preadsorbed, are in sharp contrast to the dramatic decrease of the second harmonic (SH) response due to ammonia on Re(0001), if only small amounts of CO are present on the surface. It is suggested that submonolayer coverage of CO are enough to remove any electronic interaction which otherwise leads to a strong SH response. A large SHG quenching cross section of CO is introduced, implying a nonlocal effect of CO on the adsorbed NH3 on Re(0001). If ammonia is preadsorbed, much of the quenching effect due to the coadsorbed CO is removed. This is discussed in terms of NH3 islands formation.

Nitrogen-15 balance in transplanted and direct-seeded flooded rice as affected by different methods of urea application

Alternative N-fertilizer management practices are needed to increase productivity and the N-use efficiency of flooded rice (Oryza sativa L.). In the 1987 dry season, a field study using 15N-labeled urea evaluated the effect of the time and method of fertilizer-N application on grain yield and N-use efficiency in transplanted and direct-seeded flooded rice. Conventional fertilizer application (broadcasting and incorporation) was compared with band placement of liquid urea and point placement of urea supergranules. With band or point placement, the grain yields were significantly greater, and the partial pressure of NH3 (pNH3) in the floodwater was significantly reduced. In the transplanted rice, conventional fertilizer-N application gave a 64% total 15N recovery and 38% crop (grain and straw) recovery. Band placement of liquid urea N resulted in 92% total and 73% crop recovery. In the direct-seeded flooded rice, a conventional N application gave 72% total and 42% crop recovery; band placement, 98% total and 73% crop recovery; and urea supergranule point placement, 97% total and 75% crop recovery.

ChemInform Abstract: Ammonothermal Synthesis of Copper Nitride, Cu3N.

AbstractThe title nitride is synthesized by comproportionation of the ammine complex (I) with Cu at 20 °C in liquid NH3 and subsequent decomposition of the resulting copper(I) ammine complex (III) at higher temp. and NH3 pressure.

Vapor Pressure Isotope Effects in Liquidand Solid Ammonia

The H/D and 14N/15N vapor pressure isotope effects in liquid and solid ammonia have been measured at temperatures between 163 K and 243 K. The isotopic vapor pressure data have been fitted to T ln (P′P) = A/T- B for the liquid/liquid, liquid/solid and solid/solid ranges of temperature. The triple points are; 195.41 K (45.49 torr) for 14NH3, 198.96 K (48.35 torr) for 14ND3, and 195.58 K (48.83 torr) for 15NH3. The isotopic difference in the vapor pressures of NH3 and ND3 at temperatures between 195.41 K and 198.96 K is nearly independent of temperature within the present experimental uncertainty. The phase ratios of the reduced partition function ratios, fliq/fgas and fsol/fgas, deduced from these results are well represented by Tin (fc/fg) = A/T-B. Molecular forces in the liquid and solid ammonias are discussed using a simple cell and a 4-molecular unit cell model, respectively. The librational motions in the liquid are almost as highly hindered as they are in the solid, but the directionality of the external forces on nitrogen atoms in liquid ammonia is not as well defined as in the solid.

Nitrogen use efficiency, floodwater properties, and nitrogen-15 balance in transplanted lowland rice as affected by liquid urea band placement

Alternative N fertilizer management practices are needed to increase productivity and N use efficiency in lowland rice (Oryza sativa L.). In 1986 dry season, a field study using15N-labeled urea evaluated the effect of time and method of fertilizer N application on grain yield and N use efficiency. Conventional fertilizer application was compared with band placement of liquid urea and point placement of urea supergranules (USG). Grain yields were significantly higher with either band or point placement than with broadcast and incorporation or surface application. Partial pressure of NH3 (ϱNH3) was significantly reduced when N was deep-placed.15N balance data show that fertilizer N applied basally and incorporated gave a total15N recovery of 52% and crop (grain + straw) recovery of 30%. Band placement of liquid urea N resulted in 82–90% total and 57–65% crop15N recovery. USG point placement gave 94% total and 70% crop15N recovery. Deep placement of second N application gave only slightly higher (98%)15N recovery compared with broadcast application (89%).

Effect of Meteorological Parameters on Ammonia Loss from Manure in the Field

AbstractA micrometeorological flux measuring technique was used to determine ammonia (NH3) volatilization from surface‐applied swine (Sus scrofa) and dairy (Bos taurus) manure under precipitation‐free June to October weather conditions. An attempt to correlate observed volatilization rates of NH3 to single meteorological parameters such as windspeed, temperature, net radiation, etc. was inconclusive insofar as these variables are not independent under field conditions; correlations with windspeed and net radiation appeared generally high. An approximate linear relationship was obtained, however, between applied total N or ammoniacal‐N and NH3 flux within the meteorological conditions encountered during the experiments. This is consistent with the assumption that volatilization from liquid manure is primarily determined by the drying rate of the manure insofar as partial pressure of NH3 is the primary parameter determining volatilization. A derived meteorological variable such as the hay drying index already used in some network agrometeorological forecasts may thus be the most suitable single indicator of high‐volatilization weather conditions.

Kinetic and X-ray Photoelectron Spectroscopic Studies of the Thermal Nitridation of Si(100)

ABSTRACTThe thermal nitridation of Si(100) by NH3 and N2H4 has been studied by X-ray photoelectron (XPS) and Auger electron (AES) spectroscopies. The pressure dependence of the rates as a function of reaction time has been measured. It has been found that the growth of the first monolayer (ML) of nitride is mediated by a surface reaction step. For subsequent growth, diffusion of one or more of the reacting species becomes an important process in determining the rate of reaction. Such species may be substrate Si diffusing to the vacuum/Si3N4 interface, or possibly network nitrogen diffusing into the Si substrate. The independence of the reaction rate on NH3 or N2H4 pressure at long reaction times rules out a mechanism involving molecular diffusion of the nitriding gas to the Si3N4/Si interface in a manner similar to the oxidation of Si by O2 or H2O. Careful analysis of the Si(2p) XPS spectra reveals the presence of a unique Si species with a Si(2p) binding energy intermediate between elemental Si and Si in Si3N4. Further, the relative intensity of the Si(2p) features due to this species, and the angular dependence of the XPS peaks indicate that they result from a ML of Si at the outermost surface layer, on top of the growing Si3N4 film.

ChemInform Abstract: The Steady‐State Decomposition of Ammonia on the Ru(001) Surface

Abstracthas been investigated at pressures of 1·10‐6 and 2·10‐6 torr and temp. between 500 and 1250 K. Above 750 K, the reaction rate of the catalytic NH3 decomposition approaches first order in NH3 pressure and the apparent activation energy is 5.0 kcal mol‐1. A kinetic isotope effect is observed at these high temp. and the activation energy for ND3 is determined to be 6.6 kcal mol‐1. The apparent activation energy is associated with the difference in activation energies between that of the cleavage of a N‐H (N‐D) bond in chemisorbed NH3 and that of the desorption of molecularly chemisorbed NH3.

Effect of Water Depth on Nitrogen Use Efficiency and Nitrogen‐15 Balance in Lowland Rice1

AbstractBasic studies to understand and delineate N loss mechanisms and to develop management practices to minimize N losses are vital to increasing rice (Oryza sativa L.) productivity and N use efficiency in lowland rice. In 1984, two field studies in lowland rice evaluated the effect of water depth on potential N loss and N use efficiency on Maahas clay (Andaqueptic Haplaquoll) and 15N balance on Maligaya clay (Vertic Tropaquept). In the first experiment on Maahas clay, the partial pressure of NH3 (ρNH3) in the floodwater was lower when fertilizer was incorporated without standing water than when incorporated with 50 mm water. However, when fertilizer was topdressed 10 days after transplanting (DT), ρNH3 was lower with 100 and 150 cm standing water than with 50 mm water due to dilution and lower floodwater pH and temperature. In the second experiment conducted on Maligaya clay, grain yield from urea applied basally and incorporated without and with 25 mm standing water was similar to that from point‐placed urea supergranules. Yields from fertilizer topdressed 10 DT with 0, 50, and 100 mm standing water were similar but significantly lower than when fertilizer was applied basally and incorporated at all water depths. Nitrogen‐15 balance data show that fertilizer applied basally and incorporated without standing water gave a total 15N recovery of 66% and crop (grain + straw) recovery of 39%. Standing water at depths of 25 and 50 mm during incorporation decreased total 15N recovery by 5 to 7%. Topdressing fertilizer 10 DT without standing water resulted in 59% total N recovery and 38% plant recovery.

Slow-release urea fertilizers ? effect on floodwater chemistry, ammonia volatilization and rice growth in an alkali soil

In experiments with transplanted rice (Oryza sativa L.) at the Central Soil Salinity Research Institute, Karnal, India, two methods of application of granular urea, wholly as basal dose U(W) or in splits U(S) were compared with deep, point placement (8 cm) of urea supergranules and broadcast application of two slow-release sources, sulphur-coated urea (SCU) and lac-coated urea (LCU). Comparisons were made in wet season 1984 and 1985 on the basis of ammoniacal N concentration and pH of floodwater, ammonia volatilization, rice yield and N uptake. In 1984 the highest peak concentrations of ammoniacal N (AN) in the floodwater, > 12g m−3, and ammonia volatilization losses ≈ 54% of applied N were produced in U(W). Application of N in splits U(S) reduced peak AN levels ≈ 5g m−3 and losses to 45.1%. LCU was ineffective in reducing peak AN levels (≈ 7.5g m−3) or losses (43.6%). However SCU and USG were effective in reducing peak AN levels to < 2g m−3 and N losses to 16.9 and 3.4% respectively. Total ammonia volatilization losses as well as the initial rate of loss correlated very well with the peak levels (second day) of AN, NH3 (aq.) as well as equilibrium vapour pressure of NH3. Floodwater pH was between 9.5 and 10.0. Split application of granular urea was generally more efficient in terms of yield and N recovery (41.4%, average of two years) as compared to whole application (29.5%). LCU was ineffective in improving grain yields or N recovery (30.9%). SCU was ineffective in improving grain yields but improved N recovery to 57.9%., USG increased grain yields only in first year by 19% over U(S) and improved N uptake to 60.5%. A negative linear relationship was established between N uptake by rice at harvest and AN levels in floodwater two days after fertilization which can be used as an index to evaluate fertilizers.

Amplification of tunable infrared diode laser using optically pumped NH3 under high-pressures.

Gain characteristics of highly pressurized NH3 gas have been studied in detail for amplification of tunable radiation from a Pb1-x Te diode laser. The gain of optically pumped media was measured as a function of pressures of NH3 and buffer gases up to 10 atm. The amplification factor obtained through a cell was found to be more than ten times. A continuously extended width of the gain profile was approximately 30 GHz. Comparison between N2 and He as a buffer gas has also been made.

An Organic Semiconductor as Gas Detector

Abstract The objective was to investigate the application of copper phthalocyanine (CuPc) films to the detection of air-borne NH3. The phenomenon of gas adsorption on the available surface area of an organic semiconductor was studied. Repeatable results can be obtained relatively quickly provided that a certain state of the semiconductor (which may be adopted as a reference system) will be re-established prior to each measurement of air-borne NH3. The development of an appropriate method for the regeneration of the CuPc film following completion of the detection procedure is described. A linear relation between minimum current intensity and partial pressure (concentration) of NH3 in the gas sample is obtained. The method proposed in this study for the measurement of atmospheric NH3 has analytical potential.

Ammonia Volatilization from Nitrogen Sources Applied to Rice Fields: II. Floodwater Properties and Submerged Photosynthetic Biomass

AbstractThe effects of (NH4)2SO4, urea, and urea amended with the urease inhibitor, phenyl phosphorodiamidate (PPD), on floodwater properties were studied concurrently as part of a field NH3 volatilization study. In the (NH4)2SO4 treatment the maximum concentration of ammoniacal‐N in the floodwater (≃ 50 g N m−3) occurred immediately after its application to the floodwater. Thereafter, floodwater ammoniacal‐N concentrations declined rapidly and were negligible 6 d after the application of (NH4)2SO4. Ammoniacal‐N concentrations in the urea treatment reached maxima of ≃ 12 g N m−3, 3 to 5 d after urea was applied and then declined steadily to negligible concentrations in 7 d. Application of PPD (1% wt/wt) along with urea delayed the buildup of ammoniacal‐N in floodwater until 5 to 7 d after N was applied although the maximum ammoniacal‐N concentration in the floodwater was comparable to that obtained in the urea treatment. Floodwater pH displayed a marked diurnal pattern throughout the experiment in the urea‐amended and background fields. In contrast, pH in the floodwater in the (NH4)2SO4‐amended field was buffered at ≃ 8.00 for the first 2 d, probably because high concentrations of NH4HCO3 formed in floodwater. Diurnal fluctuations in pH prevailed after 3 d when ammoniacal‐N concentrations had declined substantially. The partial pressures of NH3 (pNH3) in the floodwater in all treatments were synchronized with diurnal temperature and pH changes in the floodwater. The maximum pNH3 in floodwater was similar in both the (NH4)2SO4‐ and urea‐amended fields even though ammoniacal‐N concentrations were initially significantly higher in the former. Total titratable alkalinity in floodwater increased after urea and urea/PPD were applied but declined following the application of (NH4)2SO4. The initial levels of alkalinity in floodwater were double the content of alkalinity in irrigation water, and it is surmised that evaporation and/or respiration contributed significantly to alkalinity in the floodwater. Enumerations of algae present in the flooded soil showed the biomass to be small and dominated by non‐N2‐fixing blue‐green algae (Syanophyceae). This biomass, however, was associated with marked diurnal fluctuations in floodwater pH, which coupled with the accumulated alkalinity, were the major factors contributing to the rapid NH3 loss following the application of (NH4)2SO4 and urea to the floodwater.

Kinetics of the formation of N2O in the catalytic oxidation of NH3 on Pt-Rh filament

The kinetics of the reactions involving the formation of N2O in the catalytic oxidation of NH_3 have been studied over polyerystalline Pt-10% Rh filament in a static system, using a Fourier transform infrared spectrometer to monitor the partial pressures of NH_3 and N_2O. The formation of N_2O proceeds only over the filament temperatures range of 250～350℃. The reaction rate is of first order in NH_3 pressure and half order in O_3 pressure, and the rate equation can be written as v=k_(app)P_(NH_3)·P_(O_2)~(1/2). The apparent activation energy of the N_2O formation reaction from the temperature coefficient of the rate constants is found to be 25kcal/mol. The interpretation of these results in terms of Eley-Rideal type mechanism has been presented. The rate-controlling step might be the reaction between gaseous ammonia moleoules and the chemisorped oxygen atoms on the surface.