Zhi-Gang Guo

Influence of operating pressure on surface dielectric barrier discharge plasma aerodynamic actuation characteristics

This letter reports an experimental study of surface dielectric barrier discharge plasma aerodynamic actuation characteristics’ dependence on operating pressure. As the pressure decreases, the N2(CПu3) rotational temperature decreases, while its vibrational temperature decreases initially and then increases. In addition, the discharge mode changes from a filamentary type to a glow type at 45Torr. In the filamentary mode, the electron density decreases with pressure, while the electron temperature remains almost unchanged. In the glow mode, however, both the electron density and the electron temperature increase while the pressure decreases. The induced velocity shows a maximum value at 445Torr.

Polymer coating on the surface of zirconia nanoparticles by inductively coupled plasma polymerization

Polymer coating on the surface of inorganic ceramic nanoparticles is beneficial to decrease agglomeration and improve dispersion in organic solvent in ceramic injection moulding technology. A layer of thin polymer film on zirconia nanoparticles is deposited by inductively coupled ethylene/nitrogen plasma. Transmission electron microscopy photographs indicate the presence of uniform polymer coatings and the thickness of the polymer layer is estimated as several nanometers. The chemical structure of the film is revealed as quasi-polyethylene long hydrocarbon chain by x-ray photoelectron spectroscopy examination.

Electron density and ion energy dependence on driving frequency in capacitively coupled argon plasmas

The dependence of the electron density and the mean ion energy relative to the ground electrode on the driving frequency (13.56?156?MHz) is investigated in capacitively coupled argon plasmas. It is found that at constant rf power, the electron density increases with the driving frequency then starts to level off after reaching some transition frequency. When the driving frequency exceeds this transition frequency, almost all rf power is spent on electron heating and the electron density remains unchanged even when the frequency continues to increase. The measured data is compared with the results from an inhomogeneous plasma model. The variations of the measured electron density and mean ion energy are found to be consistent with the scaling between the electron heating and the ion acceleration power and their dependence on driving frequency, as obtained earlier by Godyak.

A novel method to determine electron density by optical emission spectroscopy in low-pressure nitrogen plasmas

A novel method to determine volume averaged electron density by optical emission spectroscopy is investigated in inductively coupled nitrogen plasma. Using a kinetic model of low-pressure nitrogen discharge, volume averaged electron density can be obtained from experimentally measured vibrational distribution of the excited state C3Πu of the nitrogen molecule. Electron density versus rf power determined by this method and Langmuir probe measurement is compared and found to be in good agreement.

Comparative characterization of high-density plasma reactors using emission spectroscopy from VUV to NIR

Emission spectroscopy is used to investigate the effect of inert gas mixing in nitrogen plasmas generated in inductively coupled plasma (ICP) and electron cyclotron resonance (ECR) plasma sources. Vacuum ultraviolet (VUV) emission of resonance lines is used to determine concentration of atomic nitrogen while electron temperature is obtained from optical emission spectra. It is found that electron temperature can be either raised or reduced effectively by mixing helium or argon in a nitrogen discharge. Electron-electron collisions and superelastic collisions involving metastable species are key factors in electron temperature tuning.

Spatially resolved optical emission spectroscopy investigation of E and H modes in cylindrical inductively coupled plasmas

Spatially resolved optical emission spectroscopy and Langmuir probe measurement are used to investigate the characteristics of a cylindrical inductively coupled plasma in both E and H modes for Ar/N2 discharges. Axial profiles of optical emission intensities are obtained and the results indicate that the electron density becomes non-uniform in the discharge region when the operating mode is changed from the E to the H mode. In the downstream region, electron density in the H mode is lower than that in the E mode, signifying a more lossy nature for the charged species in the E mode than in the H mode. The emission intensities of three argon lines show different behaviours during E to H transition in the downstream region. It is believed that they are due to the difference in contribution to the emission intensity by the metastables in the downstream region in these two modes.

Effect of wall reflection on the determination of electron temperature by the line-ratio method in inductively coupled plasmas

The light collected from inductively coupled CH4∕N2 and N2 plasmas is strongly affected by wall reflection. Since wall reflectivity varies with wavelength, the effect can lead to a significant error in the electron temperature determined by the line-ratio method.

Optical interference induced by deposited wall-film in inductively coupled plasmas

Temporal periodic variation and long-time decrease of optical emission intensity collected by a spectrometer in an inductively coupled CH4/N2 plasma, which deposits a film of growing thickness on the chamber wall, are measured. The periodic variation is interpreted as a result of the interference between the light reflected from the film surface and that which re-emerged from the surface after being reflected by the chamber wall. The re-emerged light is attenuated due to absorption by the film and thus leads to the long-time decrease of the intensity. The periodic variation of the line intensities, however, can be used for in situ film thickness monitoring.

Spatially-resolved oes measurement of inductively-coupled plasmas in E and H modes

Summary form only given. Spatially-resolved OES and single Langmuir probe measurements are used to investigate the discharge characteristics in both E and H modes in inductively coupled pure Ar and Ar-N2 mixture plasmas. Different behaviors of electron density and certain line intensities are observed in the downstream region when the plasma experiences a mode transition. Since mode transition is a localized phenomenon and the distribution of different species in the plasma is affected by both the generation process and diffusion process, the variation of line intensity with axial position in the discharge region during mode transition is interpreted in terms of the transport of metastable species and electron confinement in both modes. Different shape of hysteresis curves for different lines are also observed. This phenomenon is highly relevant to the excitation cross section of the argon metastable atoms

Investigation on a low pressure plasma jet in an inductively coupled plasma

Summary form only given. Tuning of electron temperature or high energy electron population enhancement can greatly influence the yield of active species and hence be quite significant for material processing. In our recent experiment of N/sub 2//Ar and N/sub 2//He discharges, a low pressure plasma jet (LPPJ) is observed out of a rectangular hole on a metallic cylinder which is used to confine an inductively coupled plasma and is placed in a large vacuum chamber. The occurrence of the LPPJ depends on the gas pressure (typically 5/spl sim/30 mTorr) and gas composition. Usually the LPPJ is about several centimeters long and has a regular profile. By using a Langmuir probe, spatially-resolved electron temperature, electron density and electron energy distribution function (EEDF) of the LPPJ are measured. An EEDF with overpopulated high energy electrons is found near the hole. A much stronger VUV radiation intensity and higher atomic nitrogen density in the LPPJ mode suggest that LPPJ can be a good source of active species and can have a profound effect in certain material processing applications.