N2 RF Research Articles

Sapphire Surface Layer Structure and Transmission in Visible after Sputtering in H2–N2 RF Discharge

Sapphire Surface Layer Structure and Transmission in Visible after Sputtering in H2–N2 RF Discharge

Sapphire surface layer structure and transmission in visible after sputtering in H-=SUB=-2-=/SUB=--N-=SUB=-2-=/SUB=- RF discharge

Leucosapphire (c-LS) structure and transmission in visible after surface treatment in 90%H2-10%N2 RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40-50 nm with a high defect density. The c-LS transmission in the angle of 400-1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H2-10%N2 RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor Keywords: Leucosapphire, RF discharge, hydrogen, nitrogen, AFM, TEM, surface layer structure, visible transmission.

Структура поверхностного слоя и пропускание света сапфиром после распыления в ВЧ разряде в смеси H-=SUB=-2-=/SUB=--N-=SUB=-2-=/SUB=-

Leucosapphire (c-LS) structure and transmission in visible after surface treatment in 90%H2-10%N2 RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40–50 nm with a high defect density. The c-LS transmission in the angle of 400–1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H2-10%N2 RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor.

Plasma-engineered bifunctional cobalt-metal organic framework derivatives for high-performance complete water electrolysis.

Metal-organic framework (MOF) derivatives are among the most promising catalysts for the hydrogen evolution reaction (HER) for clean hydrogen energy production. Herein, we report the in situ synthesized MOF-derived CoPO hollow polyhedron nanostructures by simultaneous high temperature annealing and Ar-N2 radio frequency plasma treatment in the presence of a P precursor and subsequent oxygen incorporation from open air at lower temperature. The optimum Ar-N2 gas flow rates are used to precisely tune the P/O ratio, cut Co bonds within the MOFs and reconnect Co with P. Consequently, both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance are enhanced. Meanwhile, the filling of P elements can effectively change the electronic structure around the catalyst to ensure the uniform distribution of catalytically active sites. The resultant CoPO hollow nanocages with large specific surface areas show excellent bifunctional electrocatalytic activity towards both HER and OER with a low overpotential of 105 and 275 mV and a small Tafel slope of 48 and 52 mV dec-1, respectively. Our results open a new avenue for precise plasma-assisted engineering of MOF-derived hybrid hetero-structured electrocatalysts with rich oxygen vacancies and P dopants to simultaneously boost both half reactions in water electrolysis.

The role of active species in the N2 and N2-H2 RF afterglows on selective surface nitriding of ALD-grown TiO2 films

We find that surface modification characteristics of TiO2 using N2 RF plasma are strongly dependent on the detailed composition of active species in the plasma and the afterglows. The surface nitriding of ALD-grown TiO2 films in pure N2 RF afterglows at room temperature (RT) is found to be more effective in the late afterglows than in the early afterglows. Adding a small fraction of H2 in N2 results in suppression of surface nitriding, suggesting that the change in the composition of the active species in the afterglows by H2 is the origin to the suppressed nitriding performance. Here, we present our analysis on the surface chemical composition after the plasma modification as well as the densities of excited species such as N atoms, N2(A) and N2(X, v) metastable molecules and N2+ ions in the afterglows of RF N2 and N2–H2 (<5%) at different positions along the downstream by emission spectroscopy. The early afterglow of N2 changes from a pink to a late afterglow where the N+N recombination is the dominant process with the introduction of H2. The roles of active species such as N–atoms and N2+ ions on TiO2 surface nitriding are found to oppose to each other. We find that N atoms enhance the surface nitriding, while N2+ ions are likely to deplete the surface-bound N species.

Discharge source-dependent variation in the densities of active species in the flowing afterglows of N2 RF and UHF plasmas

With a potential application to surface modification of oxide materials in mind, active species in RF and microwave (UHF) N2 afterglows were analyzed in our newly designed flowing reactors. For both plasma systems, discharge of N2 was generated in a long quartz tube with a small diameter (dia. 5–6 mm) and then was directly injected into a chamber with a large diameter of 15–20 cm. The discharge condition was set to be similar between the two systems; the gas pressure, flow rate and the applied power were 6 Torr, 0.6 slm and 100 W, respectively. Under this condition, the residence time at the chamber inlet was (1–3) x 10−3 s. The RF and UHF afterglows were formed in the chamber with luminous jets from the end of the discharge tube. However, we found that the densities of active species were quite source-dependent; N and N2(A) densities were higher in UHF than in RF in spite of more O-atoms impurity. The origin of such difference is also attributed to the inherent difference in the nature of excitation between the two plasma sources; RF is more vibrational and is longer than UHF.

Comparison of the Active Species in the RF and Microwave Flowing Discharges of N2 and Ar–20 %N2

We report a detailed comparison between RF and microwave (HF) plasmas of N2 and Ar–20 %N2 as well as in the corresponding afterglows by comparing densities of active species at nearly the same discharge conditions of tube diameter (5–6 mm), gas pressure (6–8 Torr), flow rate (0.6–1.0 slm) and applied power (50–150 W). The analysis reveals an interesting difference between the two cases; the length of the RF plasma (~25 cm) is measured to be much longer than that of HF (6 cm). This ensures a much longer residence time (10−2 s) of the active species in the N2 RF plasma [compared to that (10−3 s) of HF], providing a condition for an efficient vibrational excitation of N2(X, v) by (V–V) climbing-up processes, making the RF plasma more vibrationally excited than the HF one. As a result of high V–V plasma excitation in RF, the densities of the vibrationally excited N2(X, v > 13) molecules are higher in the RF afterglow than in the HF afterglow. Destruction of N2(X, v) due to the tube wall is estimated to be very similar between the two system as can be inferred from the γv destruction probability of N2(X, v > 3–13) on the tube wall (2–3 × 10−3 for both cases) obtained from a comparison between the density of N2(X, v > 3–9) in the plasmas to that of the N2(X, v > 13) in the long afterglows. Interestingly enough, densities of N-atoms and N2(A) metastable molecules in the afterglow regions, however, are measured to be very similar with each other. The measured lower density of N2 + ions than expected in the HF afterglow is rationalized from a high oxygen impurity in our HF setup since N2 + ions are very sensitive to oxygen impurity .

Quantitative evaluation of the densities of active species of N2 in the afterglow of Ar-embedded N2 RF plasma

The N2 and Ar-20%N2 RF plasmas and afterglows have been generated in a quartz tube under a flowing condition maintained at 6–8 Torr and a flow rate of 0.5–0.6 slm. The detailed emission characteristics of active species have been analyzed by emission spectroscopy. Under such conditions, the plasma rotational temperature increases from 400 to 800 K with increasing RF powers from 50 to 130 W, while the characteristic vibrational temperature remains at about 104 K. The densities of active species (N, N2(A), N2(X, v > 13) and N2+) in the afterglow are measured to be in the order of ∼1015, ∼1011, ∼1014 and ∼1010 cm−3, respectively. In addition, the following characteristics of the afterglows are noted: First, the same densities of the active species can be obtained at lower RF powers (20–50 W) for Ar-20%N2 than for pure N2 which requires higher RF powers (50–100 W). Second, the ionization degree of N2+/N2 in the plasma increases readily to a saturation value at a lower RF power of 50 W for Ar-20%N2, whereas in the afterglow, the absolute density of N2+ is further reduced below 109 cm−3.

Densities of active species in N2 and N2–H2 RF pink afterglow

The transverse distribution of N2 radiative states has been analyzed in the early afterglow of RF N2 flowing discharge with the introduction of a few H2 molecules (10−5–10−3) in the discharge. The transverse distributions of N2, 1st (580 nm), 2nd pos (316 nm) and ,1st neg (391.4 nm) band intensities have a sharp profile in pure N2. As more H2 was introduced into N2, a sharper profile for the ,1st neg was observed, and inversely a broader profile for the N2, 1st pos. With the introduction of H2 into N2 the early afterglow was changed from a sharp pink to a broad late afterglow where the N + N recombination is the dominant process. After NO titration of N-atom density in pure N2 late afterglow, the variation of N-atom and N2(A) density in the N2–H2 early afterglow is deduced. The N2(X, v > 13) density is also estimated.

Abstracts of the 17th International Symposium on Bioluminescence and Chemiluminescence ‐ (ISBC 2012)

WARNING : The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!

Calculation of layer thickness on nanotube surfaces from XPS intensity data

Surface modification of nanomaterials is the subject of numerous recent investigations. Quantitative characterisation of such modifications is of great theoretical and practical interest. As a first step, our attention is focussed on carbon nanotubes because of their unique morphology and physicochemical properties, having many potential advantages in nanotechnology, electronics, optics and other fields of material science. Surface modification or coating of the nanotubes is essential in several applications, using them as drug carriers, reinforcing component in polymeric matrices or hi‐tech structural ceramics to create reactive surface groups or protection for efficient processing. Applying the simple planar approach to cylindrical‐shaped samples, as known, leading to overestimated layer thickness values because the effective thickness of the layers (seen from the direction of analyser) varies from point to point along the convex surface of the tubes of essentially cylindrical geometry. In case of nanotubes, and any type of nano‐objects, however, a further significant difference is that they have no ‘bulk‐like’ core material because they are usually thin enough to be transparent by the photoelectrons evolving in the XPS measurements. In a step forward for quantitative characterisation, in this article, a special model was developed to calculate the thickness of the modified layer on nanotubes, taking into account that several rows of the tubes are randomly piled on each other. The applicability of the model was tested for quantitative characterisation on multiwall carbon nanotubes (MWCNT), which were treated in d.c.‐biased RF N2 plasma for covalent attachment of nitrogen to their outer shells. This model will be implemented, and thus the calculations would be conveniently performed in the latest versions (from 7.0) of the XPS MultiQuant program. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Comment on ‘Determination of excitation temperature and vibrational temperature of the N2(C 3Πu, v′) state in Ne–N2 RF discharges’

Several important errors and misinterpretations present in a recent publication by Rehman et al (2008 Plasma Sources Sci. Technol. 17 025005) are pointed out and discussed.

Reply to Comment on ‘Determination of excitation temperature and vibrational temperature of the N2(C 3Πu, ν′) state in Ne–N2 RF discharges’

Reply to Comment on ‘Determination of excitation temperature and vibrational temperature of the N2(C 3Πu, ν′) state in Ne–N2 RF discharges’

Photoluminescence of cubic InN films on MgO (001) substrates

AbstractWe have studied photoluminescence from cubic InN films grown on MgO substrates with a cubic GaN underlayer by RF N2 plasma molecular beam epitaxy. A single PL peak was observed at 0.47 eV. By analyzing the reflectance spectra of cubic InN films, we could derive the refractive index and extinction coefficient, and found the band gap energy of cubic InN is 0.48 eV, indicating that the PL peak observed at 0.47 eV is due to the interband transition of cubic InN. The difference in the PL peak energy between hexagonal and cubic InN is in good agreement with that predicted by ab‐initio calculations. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Determination of excitation temperature and vibrational temperature of the N2(C 3Πu, ν′) state in Ne–N2 RF discharges

Optical emission spectroscopy is used to investigate the effect of neon mixing on the excitation and vibrational temperatures of the second positive system in nitrogen plasma generated by a 13.56 MHz RF generator. The excitation temperature is determined from Ne I line intensities, using Boltzmann's plot. The overpopulation of the levels of the N2 (C 3Πu, ν′) states with neon mixing are monitored by measuring the emission intensities of the second positive system of nitrogen molecules. The vibrational temperature is calculated for the sequence Δν = −2, with the assumption that it follows Boltzmann's distribution. But due to overpopulation of levels, e.g. 1, 4, a linearization process was employed for such distributions allowing us to calculate the vibrational temperature of the N2 (C 3Πu, ν′) state. It is found that the excitation temperature as well as the vibrational temperature of the second positive system can be raised significantly by mixing neon with nitrogen plasma. It is also found that the vibrational temperature increases with power and pressure up to 0.5 mbar.

Determination of the vibrational, rotational and electron temperatures in N2 and Ar–N2 rf discharge

In order to characterize a nonequilibrium molecular plasma from the point of view of translational, vibrational and rotational degrees of freedom and their interaction, the characteristic temperatures of such a plasma were measured in an ICP rf reactor. Both pure nitrogen and argon–nitrogen mixture plasmas were examined for this purpose.The experimental results of rotational (Tr), vibrational (Tv) and electron (Te) temperatures are presented. Vibrational and rotational temperatures were measured as a function of nitrogen content for both E and H modes of ICP discharge using a power range of 45–200 W and pressure range of 2.6–13.3 Pa. Additionally, the pressure dependence of electron temperature in a pure nitrogen discharge was studied. Results show that rotational temperature is ≈370 K for E mode and ≈470 K for H mode and almost does not depend on either the applied rf power or the nitrogen content in the discharge. Vibrational temperature groups in the range 5000–12 000 K increase with applied rf power and constantly decay with an increase of nitrogen content. The measured values and behaviour of electron temperature are comparable with those for the positive column of the dc glow discharge. The results also prove that these three temperatures obey the classical inequality Te > Tv > Tr, as well as clarifying the differences in both vibrational and rotational temperature for different modes of the ICP discharge.

Plasma sterilization of Geobacillus Stearothermophilus by O2:N2RF inductively coupled plasma

The aim of this work is to identify the main process responsible for sterilization of Geobacillus Stearothermophilus spores in O2 :N2 RF inductively coupled plasma. In order to meet this objective the sterilization efficiencies of discharges in mixtures differing in the initial O2 /N2 ratios are compared with plasma properties and with scanning electron microscopy images of treated spores. According to the obtained results it can be concluded that under our experimental conditions the time needed to reach complete sterilization is more related to O atom density than UV radiation intensity, i.e. complete sterilization is not related only to DNA damage as in UV sterilization but more likely to the etching of the spore.

Soft X-ray XANES of N in ZnO:N – Why is doping so difficult?

Soft X-ray absorption near-edge experiments (XANES) were carried out at the N K-edge for both as-grown and rapid thermal annealed epitaxial N-doped ZnO samples grown on both {112¯0} sapphire substrates and the (0001) face of ZnO single crystal substrates. Samples were grown by plasma-assisted MBE at a growth temperature of 450°C using a solid Zn source and high-purity O2 and N2 RF radical sources. Calibrated secondary ion microscopy measurements demonstrated an as-grown N chemical concentration of approximately 1020 cm−3. The location in the ZnO lattice of N was determined in concert with first-principles real-space multiple scattering simulations. For as-grown samples, it was determined that N incorporates substitutionally on oxygen sites. It was found that a short 3min rapid thermal anneal to 800°C resulted in the unambiguous formation of molecular nitrogen underscoring the metastable nature of substitutional nitrogen. High resolution XANES scans clearly matched those of a N2 gas standard. These results strongly suggest that while nitrogen can be incorporated in ZnO using metastable growth processes, the small activation barrier to the formation of molecular nitrogen will make it very difficult for nitrogen to be a dopant in actual device fabrication.

In-Flight Spheroidization of Alumina Powders in Ar?H2 and Ar?N2 Induction Plasmas

In-flight spheroidization of alumina powders in Ar–H2 (H2–7.6%, vol/vol) and Ar–N2 (N2–13.0%, vol/vol) RF induction plasmas was investigated numerically and experimentally. The mathematical model for the plasma flows incorporates the k–ɛ turbulence model, and that for particles is the Particle-Source-in-Cell (PSI-Cell) model. Experimental results demonstrate that spheroidized alumina particles are produced in both Ar–H2 and Ar–N2 RF plasmas, with different particle size distributions and crystal phases. Agreement between the predicted and measured particle size distributions is satisfactory under high particle feed rate conditions, while the results obtained for the Ar–H2 plasma are better than those for the Ar–N2 plasma. The discrepancy occurring in low feed rate conditions suggests that particle evaporation is an important factor affecting the plasma–particle heat transfer.

Amorphous carbon nitride film preparation by plasma-assisted pulsed laser deposition method

Amorphous carbon nitride (aCNx) films were prepared by pulsed laser ablation of graphite in N2 RF plasma. The film property was compared with that prepared in N2 gas. The N2 plasma was generated by a mesh electrode, which was inserted between a graphite target and a Si substrate. The gas pressure pN2 was varied from 10 to 100 mTorr. The film deposition rate exponentially decreased with pN2 for both the plasma and gas environment. X-ray photoelectron spectroscopy analysis showed that the ratio of nitrogen content to the carbon one ([N]/[C]) of the aCNx film surface deposited in the N2 plasma was ∼2 times higher than that obtained in the N2 gas. The film structure was shown by Raman spectroscopy analysis that sp2 clustering was enhanced with increasing the [N]/[C]. The effect of plasma on aCNx film deposition was discussed.