Low-temperature Helium Plasma Research Articles

Birch Reduction of Benzene in a Low‐Temperature Plasma

Selective and specific dihydrogenation of benzene and other arenes has been observed in a low-temperature helium plasma. A surface Birch reduction mechanism has been proposed in which benzene molecules adsorbed on the discharge surface capture low-energy surface-adsorbed electrons and subsequently undergo protonation (see picture). Gas-phase oxidation processes accompany the reduction reaction.

Nano Effects of Helium-Plasma Treatment Nano-SiO<sub>2</sub> Coating Vectran

The plasticity treatment of APPJ on microstructure and tensile deformation of Nano SiO2 coating Vectran in the dynamic states was investigated by specialized tensile testing at room temperature. With the addition of low-temperature Helium plasma treatment, Young's modulus and yield stress changed. It was found that micro structural parameter such as the activation volume was important to describe the Nano SiO2 coating Vectran and inter-phase strength between filaments and coating. The results of different APPJ treatments on the Nano SiO2 coating Vectran showed the change of the rate sensitivity of the filaments. The flow stress dependence of the strain rate sensitivity indicated that dynamical recover processes associated with the dislocation-dislocation interactions, which develop in the APPJ treatment Nano SiO2 coating Vectran and Vectran after small amount of deformation, leaded to strain localizations and early failure. Results revealed that APPJ treatment Nano SiO2 coating Vectran and the inter-phase would enhance the ductility of Vecetran at room temperature.

Nano Effects of Helium Plasma Treatment Carbon Nanotubes Coating Basalt Filament

The plasticity of APPJ treatment on microstructure and tensile deformation of carbon nanotube coating basalt fiber in the dynamic states was investigated by specialized tensile testing at room temperature. With the addition of low-temperature helium plasma treatment, Young's modulus and yield stress changed. It was found that micro-structural parameter such as the activation volume was important descriptors for carbon nanotube coating basalt fiber and inter-phase effect on strength. The different APPJ treatments on the carbon nanotube coating basalt fiber showed the change rate sensitivity. Results revealed that APPJ treatment carbon nanotube coating basalt fiber and the inter-phase would enhance the ductility of basalt at room temperature. From the SEM micrographs, an increase in surface roughness has been observed and the degree of fibrillation decreased after helium and oxygen plasma treatment. Contact angle analysis showed taht the treated Basalt filament had lower contact angles than the untreated one. Based on FTIR results, the change of wettability and surface energy depended the amount of polar functional groups on the fiber surface introduced by the treatments.

Comparison between Laser Thomson Scattering and Spectroscopic Measurements in Low Temperature Helium Plasmas in Divertor/Edge Simulator MAP-II

Electron temperature and density measurements of low temperature Helium plasmas are performed in the divertor/edge plasma simulator MAP-II, by means of Laser Thomson Scattering (using a ND:YAG Laser, a double monochromator and an ICCD detector) and optical emission spectroscopy (using a spectrometer and a CCD detector). The recent upgrades of our LTS system (reduction of the level of stray light and reduction of the band width of the notch filter) allowed the measurement of temperatures as low as 0.1 eV and the investigation of Electron Ion Recombination (EIR) processes in He plasma. Spatial profiles of electron temperature and density along the plasma column have been taken moving the plasma recombination front across the measurement point by controlling the gas pressure from 80 to about 145 mTorr. A comparison between LTS results and spectroscopic analysis based on a He I CR model including radiation trapping is shown in order to confirm the consistency of the diagnostics. CR model results, obtained fitting the excited state populations with principal quantum number n = 3,4, are consistent with those from LTS. The discrepancies are found to be attributable to the mixing of the ionization and recombination regimes over the line of sight of the optics.

Measurement of Rotational Populations of CH Radicals in Low-Temperature Plasmas

Rotational population of CH radicals in A2Δ state was measured using a high resolution visible spectrometer in low-temperature helium plasmas with methane injection in materials and plasma (MAP)-II device. The rotational population in the A2Δ state is characterized by bi-Maxwellian distributions with different rotational temperatures, THOT and TCOLD. The rotational temperatures of both components decreased through collisions with background helium. The dependence of emission intensity on plasma parameters suggests that dissociative recombination of methane ions, which are ionized by charge exchange of methane with helium ions should be taken into account in the discussion of the dissociation processes in CH radicals in the pressure regime from 0.24 to 1.2 Pa in this experiment.

Experimental investigations on hydrocarbon-enhanced MAR processes in low temperature plasma in divertor simulator MAP-II

Plasma recombination phenomena were observed in the interactions of hydrogen or hydrocarbon gasses with low temperature helium plasma stream along the longitudinal magnetic field, which simulated the divertor region. The reduction of the ion saturation current implies the existence of molecular activated/assisted recombination (MAR) processes. The recombination efficiency is much stronger in the methane and ethane than in the hydrogen injection case, namely, He≪H 2≪CH 4<C 2H 6. In order to clarify the dominant processes in the hydrocarbon-enhanced MAR phenomena, spectroscopy on the A 2Δ–X 2Π band of CH radical was conducted. In the electron temperature lower than about 6 eV, the dominant dissociation and emission processes of the CH radicals have qualitatively been revealed to be related to their charge exchange with bulk ions, which can be followed by the dissociative recombination with electrons.

Surface modification of poly(ether sulfone) ultrafiltration membranes by low-temperature plasma-induced graft polymerization

Low-temperature helium plasma treatment followed by grafting of N-vinyl-2-pyrrolidone (NVP) onto poly(ether sulfone) (PES) ultrafiltration (UF) membranes was used to modify commercial PES membranes. Helium plasma treatment alone and post-NVP grafting substantially increased the surface hydrophilicity compared with the unmodified virgin PES membranes. The degree of modification was adjusted by plasma treatment time and polymerization conditions (temperature, NVP concentration, and graft density). The NVP-grafted PES surfaces were characterized by Fourier transform infrared attenuated total reflection spectroscopy and electron spectroscopy for chemical analysis. Plasma treatment roughened the membrane as measured by atomic-force microscopy. Also, using a filtration protocol to simulate protein fouling and cleaning potential, the surface modified membranes were notably less susceptible to BSA fouling than the virgin PES membrane or a commercial low-protein binding PES membrane. In addition, the modified membranes were easier to clean and required little caustic to recover permeation flux. The absolute and relative permeation flux values were quite similar for the plasma-treated and NVP-grafted membranes and notably higher than the virgin membrane. The main difference being the expected long-term instability of the plasma treated as compared with the NVP-grafted membranes. These results provide a foundation for using low-temperature plasma-induced grafting on PES with a variety of other molecules, including other hydrophilic monomers besides NVP, charged or hydrophobic molecules, binding domains, and biologically active molecules such as enzymes and ribozymes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1699–1711, 1999

Continuous emission from a low-temperature helium plasma due to radiative charge exchange and radiative ion-atom recombination

Radiative recombination and radiative charge exchange in symmetrical He + + He collisions are considered using a semiclassical adiabatic model of collisions in low-temperature plasmas. The reaction channels are assumed to be uncoupled and the corresponding total and partial spectral coefficients for the spontaneous continuous electromagnetic emission are calculated for helium-plasma temperatures below 3×10 4K. The results are compared with the similar spectral densities for electron-ion and electron-atom scattering. It is found that in a wide range of physical conditions radiative processes involving ion-atom collisions should be taken into account in the analysis of the continuum radiation from helium plasmas.

Electrical properties of Si−SiO 2 structures treated in helium plasma

Experimental data are presented for the influence of helium plasma on the electrical properties of Si−SiO 2 structures with dry thermal oxide (d=16−72 nm). It is found that for strongly damaged structures low temperature helium plasma introduces acceptor-type interface states near the conduction band edge and has an annealing effect on the deep acceptor-type states. It has also shown that the initial characteristics of the Si−SiO 2 structures and the gas used are critical for the plasma-forming of both the interface and inversion channel properties.

On the mechanism of population of He I and He II levels in low-temperature helium plasmas

Abstract A simplified collisional-radiative model of a helium plasma (along with level by level population mechanism) is presented which neglects more than 70% of the atomic processes used in models reported in the recent literature and yet predicts substantially the same population densities obtained from more elaborate models.