N2 Discharge Research Articles

Integral cross sections for electronimpact excitation of electronic states of N2

We report integral cross sections (ICSs) for electron impactexcitation of the A 3Σ+u, B 3Πg,W 3Δu, B' 3Σ-u,a' 1Σ-u, a 1Πg,ω1Δu, C 3Πu,E 3Σ+g and a'' 1Σ+g electronic states of N2. The present data, for eachstate, were derived at five incident electron energies in therange 15-50 eV, from the earlier crossed-beam differentialcross section (DCS) measurements of our group. This wasfacilitated by using a molecular phase shift analysis techniqueto extrapolate the measured DCSs to 0° and 180°,before performing the integration. A comprehensive comparison ofthe present ICSs with the results of earlier experimentalstudies, both crossed beam and electron swarm, and theoreticalcalculations is provided. This comparison clearly indicates thatsome of the previous estimates for these excitedelectronic-state cross sections need to be reassessed. Inaddition, we have used the present ICSs in a Monte Carlosimulation for modelling the behaviour of an electron swarm inthe bulk of a low current N2 discharge. The macroscopictransport parameters determined from this simulation arecompared against those measured from independent swarm-basedexperiments and the self-consistency of our ICSs evaluated.

Synthesis of oxygen-free nanosized InN by pulse discharge

AbstractOxygen-free nanosized InN was synthesized by pulse discharge. NH3/N2 mixture and bulk indium were used as nitrogen source and discharge cathode, respectively. Optical emission spectra show that N2 and NH3 were highly dissociated in the discharge and oxygen could be eliminated effectively. A comparison was made among samples produced in the discharge of N2, NH3 and N2/NH3, respectively. The XPS was used to determine the composition of the synthesized materials. Only In-N was produced when N2/NH3 was used as the discharge gas, whereas indium oxide was found in the case using N2 or NH3 as the discharge gas. The size of the produced InN was between 5 and 200 nm. A broad band with a blue shift of 150 nm from that of bulk InN was detected in the photoluminescence of the produced nanosized InN.

Kinetic Characteristics of Production and Loss of Nitrogen Atoms in N2Plasma

The method of electron paramagnetic resonance (EPR) is used to measure the rates of production and concentration of nitrogen atoms, the rate constants of their heterogeneous loss, and some electrophysical characteristics of plasma at gas pressures of 60–533 Pa and discharge currents of 10–80 mA in the positive column of a d.c. discharge in N2. Analysis of the dissociation processes revealed that, in addition to the decay of electron states excited from N2(X1Σg) by electron impact, reactions involving excited nitrogen molecules may play an important role in the formation of N atoms.

Sterilization of medical productsin low-pressure glow discharges

Results are presented from experimental and theoretical studies of the sterilization of medical products by the plasmas of dc glow discharges in different gas media. The sterilization efficiency is obtained as a function of discharge parameters. The plasma composition in discharges in N2 and O2 is investigated under the operating conditions of a plasma sterilizer. It is shown that free surfaces of medical products are sterilized primarily by UV radiation from the discharge plasma, while an important role in sterilization of products with complicated shapes is played by such chemically active particles as oxygen atoms and electronically excited O2 molecules.

Diagnosis of positive ions from the near-cathode region in a high-voltage pulsed corona discharge N2 plasma

Positive ions from the near-cathode region in a wire-plate high-voltage pulsed corona discharge nitrogen plasma were characterized using a molecular beam mass spectrometer under severe electromagnetic interference. The N+ current is 2–8 times greater than that of N2+ at N2 pressure of 5–25 Torr, peak voltage of 4–10 kV, and repetition rate of 10–70 Hz. The nitrogen ion signals rise with increasing peak voltage and repetition rate of pulsed discharge, but exhibit a clear peak over the N2 pressure range studied. The kinetics of the physicochemical processes involved in the earlier N2 plasma has been studied. Nitrogen ion generation near the corona wire area and migration path to the cathode plate are the key areas in the understanding the phenomenon and mechanisms that are involved.

Effect of N2 discharge treatment on AlGaN/GaN high electron mobility transistor ohmic contacts using inductively coupled plasma

The contact resistance of Ti/Al/Pt/Au metallization on AlGaN/GaN high electron mobility transistors was measured as a function of plasma exposure conditions prior to metal deposition. Inductively coupled plasma N2 discharges were used to create nitrogen-deficient near-surface regions in the AlGaN/GaN structures. At modest ion fluxes (∼4×1016 cm2 s−1) and low ion energies (125 eV), there was no detectable surface roughening of the AlGaN. Under optimized conditions, the plasma treatment reduces the ohmic contact resistance by a factor of approximately 3.

Epitaxial TiN(001) Grown and Analyzed In situ by XPS and UPS. I. Analysis of As-deposited Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited epitaxial TiN(001) layers grown in situ. The films were deposited by ultrahigh vacuum reactive magnetron sputtering on MgO(001) at 850 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa). Mg Kα and monochromatic Al Kα x-ray sources were used to obtain the XPS spectra, while the UPS data was generated by He I and He II UV radiation. The spectra show that the TiN(001) surfaces are free of O and C. The films were found to be stoichiometric in agreement with Rutherford backscattering spectroscopy (RBS) results, yielding a N/Ti ratio of 1.02 ± 0.02.

Epitaxial ScN(001) Grown and Analyzed In situ by XPS and UPS. I. Analysis of As-deposited Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited ScN(001) layers grown in situ. The films were deposited by ultrahigh vacuum reactive magnetron sputtering on MgO(001) at 800 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa). Mg Kα and monochromatic Al Kα x-ray sources were used to obtain the XPS spectra, while the UPS data were generated by He I and He II UV radiation. The spectra show that the ScN(001) surfaces are free of O and C. The films were found to have a slight excess of nitrogen, in agreement with Rutherford backscattering spectroscopy (RBS) results, yielding a N/Sc ratio of 1.11 ± 0.03.

Epitaxial VN(001) Grown and Analyzed In situ by XPS and UPS. I. Analysis of As-deposited Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited epitaxial VN(001) layers grown in situ. The films were deposited on MgO(001) at 650 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa). Mg Kα and monochromatic Al Kα x-ray sources were used to generate the XPS spectra, while the UPS data were generated by He I and He II UV radiation. Analysis of the results show that the VN(001) surfaces are free of O and C. The films were found to be stoichiometric in agreement with Rutherford backscattering spectroscopy (RBS) results, yielding a N/V ratio of 1.06±0.02.

Epitaxial VN(001) Grown and Analyzed In situ by XPS and UPS. II. Analysis of Ar+ Sputter Etched Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to study epitaxial VN(001) layers grown in situ which were Ar+ sputter etched. The films were deposited on MgO(001) at 650 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa) and shown to have a N/V ratio of 1.06 ± 0.02 by Rutherford backscattering (RBS). The films were sputter etched with 3 keV Ar+ at an angle of 40° to a constant nitrogen-to-vanadium ratio. A Mg Kα x-ray source was used to obtain the XPS data, while the UPS data was generated by He I and He II UV radiation. The sputter etched films were found to have a N/V ratio of 0.46, indicating a preferential removal of nitrogen.

Epitaxial CrN(001) Grown and Analyzed In situ by XPS and UPS. II. Analysis of Ar+ Sputter Etched Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to study epitaxial CrN(001) grown in situ which were Ar+ sputter etched. The films were deposited on MgO(001) at 650 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67) and shown to have a N/Cr ratio of 1.04 ± 0.02 by Rutherford backscattering (RBS). The films were sputter etched with 3 keV Ar+ at an angle of 40° to a constant nitrogen-to-chromium ratio. A Mg Kα x-ray source was used to obtain the XPS data, while the UPS data was generated by He I and He II UV radiation. The sputter etched films were found to have a N/Cr ratio, as determined by XPS, of 0.63, a decrease of 29% of that determined from the as-deposited surface. This indicates a preferential removal of nitrogen from the sputtered layers.

Epitaxial ScN(001) Grown and Analyzed In situ by XPS and UPS. II. Analysis of Ar+ Sputter Etched Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited epitaxial ScN(001) layers grown in situ which were Ar+ sputter etched. The films were deposited by ultrahigh vacuum reactive magnetron sputter deposition on MgO(001) at 800 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa) and shown to have a N/Sc ratio of 1.11 ± 0.03 by Rutherford backscattering spectroscopy (RBS). The films were sputter etched with 3 keV Ar+ at an angle of 40° until a constant nitrogen-to-scandium ratio was established. A Mg Kα x-ray source was used to obtain the XPS data, while the UPS data was generated by He I and He II UV radiation. The sputter etched films have a N/Sc ratio of 0.99 indicating a preferential removal of nitrogen.

Influence of plasma parameters on the growth and properties of magnetron sputtered CNx thin films

Carbon nitride CNx thin films were grown by unbalanced dc magnetron sputtering from a graphite target in a pure N2 discharge, and with the substrate temperature Ts kept between 100 and 550 °C. A solenoid coil positioned in the vicinity of the substrate was used to support the magnetic field of the magnetron, so that the plasma could be increased near the substrate. By varying the coil current and gas pressure, the energy distribution and fluxes of N2+ ions and C neutrals could be varied independently of each other over a wide range. An array of Langmuir probes in the substrate position was used to monitor the radial ion flux distribution over the 75-mm-diam substrate, while the flux and energy distribution of neutrals was estimated through Monte Carlo simulations. The structure, surface roughness, and mechanical response of the films are found to be strongly dependent on the substrate temperature, and the fluxes and energies of the deposited particles. By controlling the process parameters, the film structure can thus be selected to be amorphous, graphite-like or fullerene-like. When depositing at 3 mTorr N2 pressure, with Ts>200 °C, a transition from a disordered graphite-like to a hard and elastic fullerene-like structure occurred when the ion flux was increased above ∼0.5–1.0 mA/cm2. The nitrogen-to-carbon concentration ratio in the films ranged from ∼0.1 to 0.65, depending on substrate temperature and gas pressure. The nitrogen film concentration did, however, not change when varying the nitrogen ion-to-carbon atom flux ratios from ∼1 to 20.

Epitaxial CrN(001) Grown and Analyzed In situ by XPS and UPS. I. Analysis of As-deposited Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited epitaxial CrN(001) layers grown in situ. The films were deposited on MgO(001) at 650 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa). Mg Kα and monochromatic Al Kα sources were used to obtain the XPS spectra, while the UPS data was generated by He I and He II UV radiation. Analysis of the results show that the CrN(001) surfaces are free of O and C. A distinct splitting of the Cr 2p3/2 line is also observed. The films were found to be stoichiometric with Rutherford backscattering spectroscopy (RBS) results, yielding a N/Cr ratio of 1.04 ± 0.02. However, composition determined by XPS (N/Cr=0.73) show an excess of chromium.

Epitaxial TiN(001) Grown and Analyzed In situ by XPS and UPS. II. Analysis of Ar+ Sputter Etched Layers

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to study epitaxial TiN(001) layers grown in situ which were Ar+ sputter etched. The films were deposited on MgO(001) at 850 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa) and shown to have a N/Ti ratio of 1.02 ± 0.02 by Rutherford backscattering spectroscopy (RBS). The films were sputter etched with 3 keV Ar+ at an angle of 40° to a constant nitrogen-to-titanium ratio. A Mg Kα x-ray source was used to obtain the XPS data, while the UPS data was generated by He I and He II radiation. The sputter etched films were found to have a N/Ti ratio of 0.73, indicating a preferential removal of nitrogen.

Surface and volume loss of atomic nitrogen in a parallelplate rf discharge reactor

The loss of atomic nitrogen due to surface and volume reactions in aparallel plate rf reactor was investigated using a pulsed N2 discharge andtwo-photon laser induced fluorescence detection of ground-state atomicnitrogen. Stainless-steel and aluminium electrode surfaces as well as siliconand boron nitride substrates were investigated for their reactivity withatomic nitrogen within the pulsed discharge environment at 1-5 Torr N2.Aluminium was found to have a surface loss rate of three to five times lessthan that of stainless-steel, while boron nitride had the lowest N atomrecombination rate of the materials studied. The N atom recombinationprobability coefficient was found to have an inverse pressure dependence foreach of the materials, with values ranging from 0.5 to 0.02%. The volume lossrate of N atoms was also quantified due to minute O2 impurities introducedinto the pulsed rf N2 discharge.

Mass-resolved ion energy distributions in continuous dual mode microwave/radio frequency plasmas in argon and nitrogen

The control of plasma-surface interactions in terms of synergistic effects of ions, photons, and chemically active species is important for the optimization of plasma enhanced chemical vapor deposition of thin films and for plasma-induced surface modification. In the present work, we use a dual-mode microwave/radio frequency (MW/rf) plasma system, in which we investigate the effect of plasma parameters (gas type and pressure, self-bias voltage, for example) on the energy and flux of ionic species arriving at the specimen surface. We determine the ion energy distribution functions (IEDFs) using a mass spectrometer/energy analyzer, in Ar and N2 discharges, excited at different frequencies. The results for Ar+, N2+, and N+ ions show structured IEDFs at the rf-powered electrode in the single- and dual-frequency modes, while a single peak is observed in the continuous MW plasma. The MW/rf plasma presents substantially higher ion flux and plasma density, and a much thinner sheath than the rf case. Changes in plasma impedance, measured by a rf current–voltage probe, support the results on plasma density and sheath thickness, determined from the IEDFs. The MW/rf discharge impedance displays a resistive behavior in contrast to rf plasma, where the impedance is capacitive.

Evaluation of the rotational temperature in N2 discharges using low-resolution spectroscopy

An improvement of methods for estimating the rotational temperature from the partially resolved 391.44 nm emission band of N2+ (B 2u+ - X 2g+) has been developed by numerically studying this band as a function both of the temperature and of the instrumental function of the detection system. We give a simple tabulation for which one can obtain, without calculation, the rotational temperature in the range 300-900 K from measurements of the band profile considered and the experimental function. The accuracy of the temperature evaluation is better than to within 10%. The approach is validated in the range 340 - 410 K, using measurements of the 391.44 nm band in a pure N2 dc magnetron discharge.

Electrical and optical diagnostics of dielectric barrier discharges (DBD) in He and N2 for polymer treatment

Synchronous, real-time optical and electrical diagnostics have been carried out on dielectric barrier discharges in flowing gases (air, He, N2) at atmospheric pressure. A true “Atmospheric Pressure Glow Discharge” (APGD) is observed in N2 when O2 and H2 concentrations are below ≈500 ppm and 2500 ppm,respectively, and the APGD regime can be beneficially modified by suitably chosen dielectric coatings. X-ray photoelectron spectroscopy (XPS) analyses of some APGD-treated polymer surfaces are presented.

Reduction and activation of phosphate on the primitive earth.

Electrical discharges in water-saturated N2 containing 1-10% CH4 were shown earlier to reduce phosphate to phosphite. This mechanism was suggested as a possible source of water-soluble phosphorus-containing compounds in volcanic environments on the prebiotic Earth. We have now extended our investigations to gas mixtures in which CO2 and N2 are the main components, and studied the effect of introducing small amounts of H2 and CO. We show that surprisingly high conversions to phosphite occur in reducing mixtures and that several percent reduction of apatite occurs even in the presence of as little as 1% each of H2 and CO. We were also able to confirm a previous report of polyphosphate production as a result of heating the mineral apatite in the presence of other minerals.