Production Of Nitrogen Atoms Research Articles

Use of optical emission intensity to characterize an RF plasma source for MBE growth of GaAsN

With the continued importance of 1.3 μm wavelength fiber optic communication, devices based on GaAsN materials are becoming increasingly important components due to their inherent integration capability and their temperature stability. In this paper, we report on the characterization of a radio frequency (RF) plasma source using a dilute nitrogen (N) in argon gas mix, to understand the production of atomic nitrogen and its effect on GaAsN growth. Optical emission intensity was used to characterize nitrogen production, and was found to predict the percentage of nitrogen in an as-grown GaAsN film over a wide range of gas flow and RF power conditions. The RF plasma source was also characterized for the production of ionic species. We found that the number of ions produced, and their energy, varies significantly depending on the RF power, the gas flow rate, and the source gas used (Ar, dilute N in Ar, pure N 2). This data allows for the optimization of RF conditions, which minimize damage from ionic species independently from nitrogen production.

Photochemistry of Pluto's atmosphere and ionosphere near perihelion

We consider Pluto's photochemistry using a background model for a hydrodynamically escaping atmosphere byKrasnopolsky[1999]. Some adjustments are made in the basic continuity equation and in the boundary conditions to account for hydrodynamic flow in the atmosphere. We model the photochemistry for 44 neutral and 23 ion species. Because of the high methane mixing ratio, Pluto's photochemistry is more similar to that of Titan than that of Triton. Charge exchange between N2+and CH4significantly reduces the production of atomic nitrogen. The most abundant photochemical products are C2H2(3×1017), C4H2(1017), HCN (6×1016), H2(4×1016), C2H4(4×1016), HC3N (3.4×1016), C2H6(2×1016), C3H2(9×1015), and C3H4(8×1015, all in cm−2). In addition to the parent N2, CH4, and CO molecules which absorb photons with λ<145 nm, these products absorb almost completely photons with λ<185 nm, therefore significantly increasing the number of dissociation events. Photochemical losses of the parent species are much smaller than their escape. Precipitation rates are the highest for C2H2, C4H2, HC3N, HCN, C2H6, and C2H4(65, 58, 23, 14, 9, and 6 g cm−2Byr−1, respectively, reduced by a factor of 3 to account for seasonal variations). Escape of photochemical products is highest for H2, H, C2H2, C2H4, HCN, and N (2×1026, 1.4×1026, 6×1024, 3.6×1024, 2.3×1024, and 1.8×1024s−1, respectively). The electron density reaches a maximum of 800 cm−3at 2250 km. The most abundant ions are HCNH+, C3H3+, and C3H5+. Some of the photochemical products might be detected using the technique of UV solar occultation spectroscopy from a spacecraft flyby.

Precise control of atomic nitrogen production in an electron cyclotron resonance plasma using N2/noble gas mixtures

The atomic nitrogen flux and impacting ion kinetic energy are two important parameters which influence the quality of deposited nitride films using reactive growth. In this letter, a method is described to control the flux and kinetic energy of atomic and molecular nitrogen ions using an electron cyclotron resonance plasma with N2/Ar and N2/Ne gas mixtures. The results clearly show that the addition of neon to nitrogen plasma can remarkably enhance the production rate of atomic nitrogen due to Penning ionization involving the metastable state of Ne. In contrast, the addition of argon significantly decreases the rate.

Plasma characteristics and the growth of group III-nitrides by metalorganic molecular beam epitaxy

Improved quality and controllability of growth processes are key issues for the maturation of III-N technologies. One of the most important concerns for the growth of III-N materials in ultra high vacuum is the ability to provide an effective nitrogen flux to the growth surface. This work has sought to correlate radio frequency (rf) plasma parameters and their impact on the growth of GaN by plasma-assisted metalorganic molecular beam epitaxy. Utilizing optical emission spectrometry, the atomic nitrogen production has been optimized as a function of rf power and N2 flow rate. Growth experiments indicate that the abundance of atomic nitrogen alone does not control growth. Increasing energy per molecule in the rf source, with a constant level of atomic nitrogen, dramatically decreases the GaN growth rate. High levels of atomic nitrogen with a low energy per molecule resulted in restoration of the growth rate to ∼0.5 µm/h.

Atomic nitrogen production in a high efficiency microwave plasma source

A high-resolution spectroscopic study of a high efficiency nitrogen atom beam source, which provides dissociation fractions of up to 0.67 and is suitable for the treatment and doping of materials, has been used to identify and study atomic and molecular emissions from the source plasma. The ratio of the intensity of selected atomic and molecular emission lines has been compared with the N/N2 concentrations in the beam measured using a quadrupole mass spectrometer. Our observations show that spectroscopic measurements can be used to determine the N atom content of the beam. This technique is likely to be valuable in applications where nitrogen beams are used for the growth and treatment of materials where other means of characterization are precluded.

Multi-photon induced atomic nitrogen production in a low-temperature nitrogen crystal

The emission from the 2D excited state of nitrogen atoms was observed when a low-temperature nitrogen crystal was irradiated by a focused excimer laser light at 248 nm. The emission intensity was found to increase linearly with the laser irradiation time. The increase rate of the emission was dependent on about the third power of the excitation laser intensity. It is concluded that nitrogen atoms and nitrogen molecules in A 3∑+u state are produced through multi-photon processes. Nitrogen atoms accumulate and are excited repeatedly by energy transfer from the excited nitrogen molecules.

Atomic nitrogen production in nitrogen-plasma sources used for the growth of ZnSe : N and related alloys by molecular-beam epitaxy

A high resolution study of the optical emission from nitrogen-plasmas produced by an Oxford Applied Research radio frequency plasma source is reported. Strong atomic emission lines in the near-infrared spectral region provide unequivocal evidence that the nitrogen-plasma source generates an appreciable flux of nitrogen atoms. Nitrogen atoms, rather than N 2 molecules in the plasma, are the most likely nitrogen-plasma species responsible for the successful p-type doping of ZnSe : N and related alloys. Emission spectra from the radio frequency nitrogen-plasma source are compared with similar emission spectra obtained from an electron cyclotron resonance microwave nitrogen-plasma source.

Atomic-nitrogen production in a radio-frequency plasma source

The first high-resolution study, to our knowledge, of the optical emission from an Oxford Applied Research MPD21 nitrogen-plasma source is reported. The spectroscopic results clearly show that the MPD21 nitrogen-plasma source generates an appreciable flux of nitrogen atoms. This suggests that nitrogen atoms are the plasma species responsible for the successful p-type doping of ZnSe:N and related alloys.

Electron impact excitation and dissociation of N2 via the b1Πu state

Electron impact excitation of the b1Πu state in N2 plays a prominent role in the dissociation of the molecule and thus in the production of atomic nitrogen in planetary atmospheres. Electron impact excitation cross sections combined with electron‐impact‐induced fluorescence measurements can yield the corresponding dissociation cross sections. Serious discrepancies exist among excitation cross sections reported in the literature. To clarify the situation, we measured these cross sections at two impact energies using electron energy loss spectroscopy. The new results are in agreement with recent values deduced from optical measurements and fall midway between previous results which are too high or low by factors of 2.

Active species in microwave postdischarge for steel-surface nitriding

Production of nitrogen atoms has been studied in a 2.45-GHz flowing postdischarge in N/sub 2/ and N/sub 2/-H/sub 2/ gas mixtures with Ar as a buffer gas in the high-pressure regime (5*10/sup 3/ to 6.5*10/sup 4/ Pa). N atom densities have been measured by NO titration in the 10/sup 14/-10/sup 15/ cm/sup 3/ range and monitored by the first positive emission resulting from the N atom recombination. The rate coefficient of the N+N+N/sub 2/ recombination has been found to be /sub k/=6*10/sup -33/ cm/sup 6/ atom/sup -2/ s/sup -1/ at T/sub 0/=300 K, which agrees with previously published data. The N atom production (or degree of N/N/sub 2/ dissociation) in front of an Fe-0.1%C substrate correlates well with the thickness of a gamma ' Fe/sub 4/N layer produced by the postdischarge treatment. The H/sub 2/ gas was first introduced in the initial phase of treatment to remove surface oxidizing and then was cut off to keep high densities of N atoms. It is deduced that N atoms are more active nitriding species than NH-type radicals.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurements of the atomic nitrogen population produced by a microwave electron cyclotron resonance plasma

The atomic nitrogen population produced from a microwave electron cyclotron resonance plasma and a microwave plasma has been measured using the nitric oxide gas titration technique for pressures between 0.005 and 0.5 Torr. For 15 W microwave power the atomic nitrogen production efficiency is observed to reach a maximum of 12% at 0.006 Torr. The pressure dependence of atomic nitrogen production efficiency and concentration are found to fall by one order at the pressure where particle mean free path exceeds apparatus dimensions (0.015 Torr). The shift has been attributed to changing electron temperature.

Effect of solar proton events in 1978 and 1979 on the odd nitrogen abundance in the middle atmosphere

Daily average solar proton flux data for 1978 and 1979 have been used in a proton energy degradation scheme to derive ion pair production rates and, subsequently, atomic nitrogen production rates. These atomic nitrogen production rates are computed in a form suitable for inclusion in an atmospheric two‐dimensional time‐dependent photochemical model. Odd nitrogen (N, NO, NO2, NO3, HNO3, HO2NO2, N2O5, and ClONO2) distributions are computed from the model including the atomic nitrogen production from solar protons and are compared with baseline distributions. Comparisons show that the average effect of the solar protons in 1978 and 1979 was to cause changes in odd nitrogen only above 10 mbar and at latitudes only above about 50° in both hemispheres. The influence of the solar‐proton‐produced odd nitrogen on the local abundance of odd nitrogen depends primarily on the background odd nitrogen abundance as well as the altitude and season. The odd nitrogen change in the atmosphere due to solar protons during the solar proton events (SPEs) in 1978 and 1979 is important for 2–3 months, but it is generally negligible 6 months after the SPE. Inclusion of the SPEs' production of odd nitrogen does not produce a substantial change in the agreement between the model results and the Limb Infrared Monitor of the Stratosphere (LIMS) NO2 and HNO3 data.

Lightnings and nitric oxide on Venus

In an updating of energy characteristics of lightnings on Venus obtained from Venera-9 and -10 optical observations, the flash energy is given as 8 × 10 8 J and the mean energy release of lightnings is 1 erg cm −2 s which is 25 times as high as that on the Earth. Lightnings were observed in the cloud layer. The stroke rate in the near-surface atmosphere is less than 5 s −1 over the entire planet if the light energy of the stroke exceeds 4 × 10 5 J and less than 15 s −1 for (1–4) × 10 5 J. The average NO production due to lightnings equals 5 × 10 8 cm −2 s −1, the atomic nitrogen production is equal to 7 × 10 9 cm −2s −1,the N flux toward the nightside is 3.2 × 10 9 cm −2s −1, the number densities [N] = 3 × 10 7cm −3 and [NO] = 1.8 × 10 6cm −3 at 135 km. Almost all NO molecules in the upper atmosphere vanish interacting with N and the resulting NO flux at 90-80 km equals 5 × 10 5cm −2s −1, which is negligibly small as compared with lightning production. If the predissociation at 80–90 km is regarded as the single sink of NO, its mixing ratio, f NO, is 4 × 10 −8, for the case of a surface sink f NO = 0.8 × 10 −9 at 50 km. Excess amounts, f NO ⋍ 4 × 10 −8 , may exist in the thunderstorm region.

The production of nitrogen atoms on Mars and their escape

Quantitative calculations of the escape rate of nitrogen by photodissociation and photoionization, by photoelectron impact processes, by chemical reactions and by dissociative recombination are reported. It is shown that the predicted present escape rate of 2.0 × 10 5 atoms cm −2 S −1 is consistent with the measured 15N/ 14N isotope ratio. A minimum of 4.0 × 10 22 cm −2 S −1 is obtained for the initial reservoir of N 2. The production rates of N( 4S) and N( 2D) atoms in the atmosphere are obtained and the altitude profile of N( 2D) is calculated.

Odd nitrogen production by meteoroids

The process by which odd nitrogen species (atomic nitrogen and nitric oxide) are formed during atmospheric entry of meteoroids is analyzed theoretically. An ablating meteoroid is assumed to be a point source of mass with a continuum regime evolving in its wake. The amounts of odd nitrogen species, produced by high‐temperature reactions of air in the continuum wake, are calculated by numerical integration of chemical rate equations. Flow properties are assumed to be uniform across the wake, and 29 reactions involving five neutral species and five singly ionized species are considered, as well as vibrational and electron temperature nonequilibrium phenomena. The results, when they are summed over the observed mass, velocity, and entry angle distribution of meteoroids, provide odd nitrogen species annual global production rates as functions of altitude. The peak production of nitric oxide is found to occur at an altitude of about 85 km; atomic nitrogen production peaks at about 95 km. The total annual rate for nitric oxide is 4 × 107 kg; for atomic nitrogen it is 1.7 × 108 kg.

Efficiencies for production of atomic nitrogen and oxygen by relativistic proton impact in air

Relativistic electron and proton impact cross sections are obtained and represented by analytic forms which span the energy range from threshold to 109 eV. For ionization processes, the Massey–Mohr continuum generalized oscillator strength surface is parametrized. Parameters are determined by simultaneous fitting to (1) empirical data, (2) the Bethe sum rule, and (3) doubly differential cross sections for ionization. Branching ratios for dissociation and predissociation from important states of N2 and O2 are determined. The efficiency for the production of atomic nitrogen and oxygen by protons with kinetic energy less than 1 GeV is determined using these branching ratio and cross section assignments.

Eleven-Year Variation in Polar Ozone and Stratospheric-Ion Chemistry

A mechanism for producing an 11-year oscillation in ozone over the polar caps is the modulation of galactic cosmic rays by the solar wind. This mechanism has been shown to give the observed phase in ozone oscillations and the correct qualitative dependence on latitude. However, the production of nitrogen atoms from cosmic-ray collisions seems inadequate to account for the ozone amplitude. Negative ions are also produced as a result of cosmic-ray ionization, and negative-ion chemistry may be of importance in the stratosphere. Specifically, NO(x)(-) may go through a catalytic cycle in much the same fashion as NO(x), but with the important distinction that it does not depend on oxygen atoms to complete the cycle. Estimates of the relevant rates of reaction suggest that negative ions may be especially important over the winter polar cap.

Effect of energetic oxygen atoms on neutral density models

The dissociative recombination of O2+ and NO+ in the F region results in the production of atomic oxygen and atomic nitrogen with substantially greater kinetic energy than the ambient atoms. In the exosphere these energetic atoms have long free paths. They can ascend to altitudes of several thousand kilometers and can travel horizontally to distances of the order of the earth's radius. The distribution of energetic oxygen atoms is derived by means of models of the ion and neutral densities for quiet and disturbed solar conditions. A distribution technique is used to study the motion of the atoms in the collision-dominated region. Ballistic trajectories are calculated in the spherical gravitational field of the earth. The present calculations show that the number densities of energetic oxygen atoms predominate over the ambient atomic oxygen densities above 1000 km under quiet solar conditions and above 1600 km under disturbed solar conditions.

Atmospheric implications of predissociation in N2

The purpose of this Letter is to report some initial results of high-resolution (0.038 A) photoelectric absorption studies on molecular nitrogen, which indicate that most of the N2 absorption bands seen between 800 and 960 A are predissociated. This predissociation could contribute significantly, through absorption of solar radiation in this wavelength interval, to the production of atomic nitrogen in the upper atmosphere. The high-resolution absorption spectra were obtained on a 2.2-meter scanning monochromator using a 1200-line/mm grating and 20/μm entrance and exit slits. The 0.038 A bandwidth was obtained by working in second order using an EMI 9603 open photomultiplier to discriminate against the first-order spectrum. The light source was a conventional helium continuum source.

Dissociation of N2 in Weak rf Discharge

It has been established that the production of nitrogen atoms from molecular nitrogen by a weak rf discharge is due predominantly to dissociation of a metastable state of N2 by electron impact.