Study of the electric field and wall voltage in a high pressure ac-PDP cell by laser induced fluorescence spectroscopy

The electric field in a surface discharge type ac-PDP cell with He or He/Xe(0.1%) mixture has been measured over a wide range of pressure (5－50 kPa) using laser induced fluorescence detection. The wall voltage was estimated from the measured electric field. The Stark manifolds of triplet atomic helium Rydberg state (2s^3S) with principal quantum numbers (n=8 and 9) have been used to measure the electric field, as the lifetime of 2s^3S is longer than the single atomic helium Rydberg state (2s^1S) in high pressure discharge. Comparison of the Stark manifolds between the n=9 and n=8 shows that the measurement accuracy of electric field can be increased by 10%. The maximum electric field strength during discharge and the wall voltage at the end of pulse decreases with the increase of pressure. The comparison of He and He/Xe(0.1%) discharge at 13 kPa showed that He/Xe gas mixture discharge can accumulate more wall charge on MgO surface and the electric field was somewhat higher than those of pure helium discharge during pulse off period under the same discharge conditions.     

Photoluminescence of ZnO and Mn-Doped ZnO Polycrystalline Films Prepared by Plasma Enhanced Chemical Vapour Deposition

ZnO and Mn-doped ZnO polycrystalline films are prepared by plasma enhanced chemical vapour deposition at low temperature （220℃）, and room-temperature photoluminescence of the films is systematically investigated. Analysis from x-ray diffraction reveals that a11 the prepared films exhibit the wurtzite structure of ZnO, and Mndoping does not induce the second phase in the films. X-ray photoelectron spectroscopy confirms the existence of Mn^2＋ ions in the films rather than metalic Mn or Mn^4＋ ions. The emission efficiency of the ZnO film is found to be dependent strongly on the post-treatment and to degrade with increasing temperature either in air or in nitrogen ambient. However, the enhancement of near band edge （NBE） emission is observed after hydrogenation in ammonia plasma, companied with more defect-related emission. Furthermore, the position of NBE shifts towards to high-energy legion with increasing Mn-doped concentration due to Mn incorporation into ZnO lattice.     

Influence of ion species ratio on grid-enhanced plasma source ion implantation

Grid-enhanced plasma source ion implantation (GEPSII) is a newly proposed technique to modify the inner-surface properties of a cylindrical bore. In this paper, a two-ion fluid model describing nitrogen molecular ions N_2^+ and atomic ions N^+ is used to investigate the ion sheath dynamics between the grid electrode and the inner surface of a cylindrical bore during the GEPSII process, which is an extension of our previous calculations in which only N_2^+ was considered. Calculations are concentrated on the results of ion dose and impact energy on the target for different ion species ratios in the core plasma. The calculated results show that more atomic ions N^+ in the core plasma can raise the ion impact energy and reduce the ion dose on the target.     

Discharge characteristics in plasma display cell at high frequency

We present the experimental and simulation studies of the glow discharge plasma in a macroscopic AC plasma display panel cell operating at a high frequency. We find that at high frequencies the plasma from the previous pulse has a significant influence on the discharge properties. The xenon excitation efficiency is larger than that at low frequencies.The discharge mode and efficiency at high frequencies have been discussed in this paper.     

Charge State Evolution of Uranium in Electron Beam Ion Trap

We present a calculation scheme with significant modifications and improvements for determining the ionization balance and the ion temperature evolution in an electron beam ion trap (EBIT). The scheme is applied to uranium and nitrogen ions using a specific set of EBIT operating parameters. The calculation results are compared to the experimental data. Rates for the individual atomic processes in EBIT, especially single and multiple charge exchange processes, are discussed. The time evolution of the ion temperatures for uranium and its coolant nitrogen are also given.     

Structural and Dynamical Analysis of a Two—Dimensional Dusty Plasma Lattice

A two-dimensional dusty plasma lattice in an rf discharge was observed.The structural and dynamical porperties were analysed by computing pair correlation function,static structure factor.bond-orientational correlation function and mean square displacement.The bond-orientational correlation function was found to fit into the law of ^-0.25,and the mean square displacement experienced “ballistic“,“subdiffusive“and “diffusive“regimes, both of which together with the other parameters indicate that the two-dimensional dusty plasma stayed at a state between liquid and solid.     

Characterizing uniform discharge in atmospheric helium by numerical modelling

One-dimensional fluid model of dielectric barrier discharge (DBD) in helium at atmospheric pressure was established and the discharge was numerically simulated. It was found that not only the spatial distributions of the internal parameters such as the electric field, the electron density and ion density are similar to those in a low-pressure glow discharge, but also the visually apparent attribute (light emission) is exactly the same as the observable feature of a low-pressure glow discharge. This confirms that the uniform DBD in atmospheric helium is a glow type discharge. The fact that the thickness of the cathode fall layer is about 0.5mm, much longer than that of a normal glow discharge in helium at atmospheric pressure, indicates the discharge being a sub-normal glow discharge close to normal one. The multipulse phenomenon was reproduced in the simulation and a much less complicated explanation for this phenomenon was given.     

Influence of Atomic Motion on a Microlaser in an Optical Standing—Wave Cavity

We study the microlaser in an optical standing-wave cavity injected with two-level atoms.The results have shown the obvious influence of atomic centre-of-mass motion on the microlaser,such as the photon distribution,the linewidth and the frequency shift.It was found that when the momentum of atoms is comparable to that of photons,the influence of atomic motion is dominated and the number of photons in the microlaser can be greatly enhanced,owing to part of the atomic kinetic energy being transferred to the resonator.This work provides a comparison of the related studies on the atomic motion under special assumptions.     

Modelling of a Multi-Temperature Plasma Composition

Knowledge of plasma composition is very important for various plasma applications and prediction of plasma properties. We use the Saha equation and Debye length equation to calculate the non-local thermodynamic-equilibrium plasma composition. It has been shown that the model to 2T with T representing the temperature （electron temperature and heavy-particle temperature） described by Chen and Han [J. Phys. D 32 （1999）1711] can be applied for a mixture of gases, where each atomic species has its own temperature, but the model to 4T is more general because it can be applicable to temperatures distant enough of the heavy particles. This can occur in a plasma composed of big- or macro-molecules. The electron temperature Te varies in the range 8000＊20000K at atmospheric pressure.     

Experiment and Simulation of Atmospheric Pressure Glow Surface Discharge

Atmospheric pressure glow discharge was observed in a surface discharge generator. The frequency of ac power supply is more than 9kHz and the sinusoidal peak-to-peak applied voltage is 9kV. The electric field intensity in a kind of surface discharge generators is calculated with the boundary element method. Then a two-dimensional fluid model was used to simulate the ion trapping and electron trapping in a surface discharge just before the breakdown. The simulation results are in good agreement with our observation.     

氮气/氨气的高压快脉冲放电光谱研究

本文测量了氮气、氨气及其混合气体的快脉冲放电等离子体的光谱,用光谱分析方法研究了等离子体成分及其与气压和配比的关系,并讨论了在制备氮化物时使用氮、氨混合气体的有利之处。     

Adsorption and decomposition of ammonia on W(100); XPS and UPS studies

The adsorption and decomposition of ammonia on a clean and c(2 × 2)-N ordered W(100) surface has been studied by photoemission spectroscopy (XPS and UPS). At 120 K molecularly adsorbed ammonia was identified by N(1s) core level emission at 400.9 eV and the valence emissions at 7.6 and 11.7 eV. By heating the sample stepwise the N(1s) core level shifted to lower binding energy. In the valence region, the corresponding spectral changes were obtained, where the dependence of the peak intensity on photon energy was observed. These observations were interpreted to demonstrate that adsorbed ammonia dissociates its hydrogen successively to form NH_x(a) and finally to atomic nitrogen. On the other hand, ammonia was molecularly adsorbed on a c(2 × 2)-N ordered surface even at temperatures as high as 300 K, although the spectra at 400 K or above were very similar to those under a steady state flow condition, where the tungsten surface was mostly covered by atomic nitrogen. At higher ammonia pressure up to about 100 Pa thicker nitride layers were formed at 700 K, which were characterized by the N(1s) core level at 397.3 eV and a broad emission around 6 eV in the valence level.     

N+2离子在氮直流辉光放电中碰撞离解的作用

采用氮辉光放电等离子体快电子和各种重粒子（N＋２，N＋，Nf）的混合Monte Carlo模型，从不同放电条件的离解碰撞率，快原子态粒子（N+，Nf）在阴极鞘层区的输运过程及轰击阴极的能量及角分布三个方面研究了 N＋２+N２→N+＋N+N2f反应在氮气直流辉光放电中的作用.该过程在电压较高时为阴极鞘层区的重要离解过程， 且主要发生在阴极附近，其碰撞率随电压和气压增加而增加；阴极表面附近的活性粒子（N＋，Nf）主要由该离解过程产生（而不是e--N2离解电离过程），而且这些粒子具有中等的平均能量且小角入射，是 关键词： 氮直流辉光放电 Monte Carlo模拟 N＋２-N２碰撞离解     

Vibrational spectra of ammonia adsorbed on Fe(110)

EELS spectra of ammonia adsorbed on a Fe(110) surface at 120 K reveal three different adsorption states of molecular ammonia. Thermal processing of the ammonia covered Fe(110) surface to 315 K indicates fragmentation of the NH₃ molecules into atomic hydrogen and nitrogen. Formation of an NH₂ intermediate is not observed whereas the existence of NH_ad species cannot be excluded at present.     

First-principles calculations of K-shell x-ray absorption spectra for warm dense ammonia

The x-ray absorption spectroscopy is a powerful tool for the detection of thermodynamic conditions and atomic structures on warm dense matter. Here, we perform first-principles molecular dynamics and x-ray absorption spectrum calculations for warm dense ammonia, which is one of the major constituents of Uranus and Neptune. The nitrogen K-shell x-ray absorption spectrum(XAS) is determined along the Hugoniot curve, and it is found that the XAS is a good indicator of the prevailing thermodynamic conditions. The atomic structures at these conditions are ascertained. Results indicate that the ammonia could dissociate to NH_x(x = 0, 1, or 2) fragments and form nitrogen clusters, and the ratios of these products change with varying conditions. The contributions to the XAS from these products show quite different characteristics,inducing the significant change of XAS along the Hugoniot curve. Further model simulations imply that the distribution of the peak position of atomic XAS is the dominant factor affecting the total XAS.     

Enrichment of the nitrogen atomic component with the <Superscript>15</Superscript>N isotope in a post-discharge zone

Isotope atomic composition in the post-discharge zone of a pulsed discharge in a nitrogen flow was studied by electron paramagnetic resonance. It is shown that, while the atomic concentration in the post-discharge zone decreases, the relative content of the ¹⁵N isotope increases more than 30 times compared to its natural abundance. Such a high isotope enrichment exceeds more than fourfold the corresponding maximal value that is predicted for the nitrogen atoms by the existing theoretical model. Analysis of the experimental results shows that the isotope-selective dissociation of nitrogen molecules proceeds in the post-discharge zone after the most part of atoms created in the discharge zone had recombined at the tube surface. A mechanism that explains that a nitrogen isotope enrichment as high as that is quite possible is proposed.     

Spectroscopic investigations of back-corona discharge on fly-ash layer

Results of spectroscopic investigations of back discharge generated in point-plane electrode geometry in ambient air at atmospheric pressure are presented in the paper. The back discharge was generated for the plate electrode covered with fly ash layer. To characterize the discharge process, the emission spectra were measured for the back discharges and compared with those obtained for corona discharge generated in the same electrode configuration but with dielectric layer removed. The measurements have shown that spectral lines emitted by the back discharge depend on the forms of discharge and the discharge current. From comparison of spectral lines of back and normal discharges an effect of the dust layer on discharge morphology can be determined. In normal conditions, the emission spectra are dominated by atmospheric components (molecular nitrogen, atomic oxygen and nitrogen) but for back-discharges, additional lines due to elements and compounds in fly ash were also identified. The studies of back discharge were undertaken because this type of discharge decreases the collection efficiency in electrostatic precipitators.     

The adsorption of ammonia on an Fe(110) single-crystal surface studied by high-resolution electron energy-loss spectroscopy (eels)

The EELS spectra of ammonia adsorbed on an Fe(110) surface at 110 K reveal four different adsorption states of molecular ammonia with increasing coverage : chemisorption at “on-top” sites, chemisorption at multi-coordinated sites, adsorption in a second layer, and multilayer condensation.Thermal processing of an ammonia-covered sample to 155 K causes desorption of both the condensed phase and the second layer without any fragmentation of ammonia.Further heating of the sample leads to a much weaker desorption of molecular ammonia up to a temperature of 260 K. EELS spectra recorded after heating to 290 K show only small amounts of atomic nitrogen and hydrogen present on the surface, indicating partial decomposition of ammonia.The formation of species such as NH₂ (ads) or NH (ads) during the thermal-processing experiments could not be observed.     

On the Adsorption of Gases on Silicon Carbide: Simple Estimates

Physics of the Solid State - The adsorption of atomic and molecular nitrogen and ammonia on silicon carbide is considered within two physically different (solid-state and quantum-chemical)...     

Pink afterglow in nitrogen-argon mixtures

The nitrogen pink afterglow was studied by optical emission spectroscopy in the DC flowing regime at a total gas pressure of 700 Pa and at the discharge current of 120 mA. The discharge was created in a Pyrex tube of 13 mm i.d. using nitrogen and argon of 99.999% purity with additional purification by Oxiclear columns and liquid nitrogen traps. The area ±3 cm around the observation point had to be cooled down to liquid nitrogen wall temperature in order to allow the study of the reactor wall temperature effect on the post-discharge. The maximum pink afterglow emission in pure nitrogen at ambient wall temperature was observed at a decay time of 6 ms. When the argon percentage in the gas mixture was increased the pink emission maximum was shifted to the later decay times. Simultaneously, the intensity of the pink afterglow decreased and at a 1:1 nitrogen-argon ratio the effect disappeared. Similar effects were also observed when the discharge tube wall around the observation point was cooled down to liquid nitrogen temperature. The argon atomic lines were only observed during the post-discharge at the highest argon concentration at a low wall temperature. The kinetic model showed that the pink afterglow quenching was connected to the decrease of the and pooling processes efficiency.