Advanced Materials Research Vol. 227

Abstract: In the surface treatment by plasma, the saturation ion current is the macroscopic parameter which can give us information on the ionic density in plasma. For this, we followed the evolution of the saturation ion current versus the pressure and power. Our experimental setup consists of spherical plasma reactor linked with inductively source argon plasma and probe to measure ionic current. The obtained experimental results enabled us to highlight the effect of pressure and power on saturation ion current. We found in this study that the saturation ion current increases with pressure and presents an optimum depending on the power.

Abstract: In this work, we present an experimental study of the reduction of NO and the creation of NO2 by positive corona discharge in N2/O2 mixture (95% N2, 5%O2), where 200ppm of NO are injected at atmospheric pressure. The corona discharge was generated using a wire- to- cylinder reactor. The applied voltage is 5kV and 7 kV and it was maintained for  50 minutes. Ultraviolet absorption spectroscopy operating in the wavelength range 190-330 nm was used to identify the species and quantify their concentration, According to Beer Lambert law who give concentration from absorbance. The temperature was maintained constant for 300K. The obtained resultant show nitrous oxide NO has been destroyed with the augmenta¬tion of corona current. We note different times to NO removal, 50 minutes at 5 kV and 20 minutes at 7 kV. And we observe the creation of NO2 and the apparition of ozone O3.

Abstract: This work presents an electrical and optical emission diagnostics of radiofrequency (RF) magnetron discharge used for titanium deposition in argon (Ar) and methane (CH4) gas precursor. The plasma was produced in incident power and gas pressure ranges of 20-300W and 15-100mTorr, respectively. We have studied the influence of the system operation parameters (incident power, pressure, proportion of gas precursor) on the self- bias voltage (Vdc) and emission intensity IAr of Ar (750.3nm) line. The results obtained show that the pressure of the optimum operation of the magnetron discharge was around 30 mTorr when the incident power varied from 20 to 300W. The relationship between the intensity of IAr (750.3nm) line and the incident power was established.

Abstract: Amorphous hydrogenated carbon (a-C:H) films have been deposited in Microwave Multipolar plasma reactor (MMP) using pure acetylene as precursor with controlling substrate temperature. Investigations on the optical properties of deposited films according to the substrate temperature have been reported. It has been observed that the optical band gap decreases and the Csp2 concentration increases when cooling down the substrate temperature. On the other hand, it has been revealed elsewhere that cooling down the substrate temperature during the deposition process, leads to the increase of particles trapped density in the deposited films due to a phenomenon of thermophoresis. Therefore, the optical properties evolution is linked to the increases of particles trapped density in the deposited films.

Abstract: A single rf-compensated cylindrical Langmuir probe has been developed in order to characterise a plasma RF discharge. A circuit using radiofrequency filtering and the passive compensation method was employed to minimize the probe curve distortions. The effect of the rfcompensation on the probe measurements was discussed. The latter were performed at power and pressure of 50 W and 510-2–1.2 mbar, respectively. Compensated measurements of the electron energy distribution function (EEDF) and plasma parameters were conducted at powers ranging from 5 to 120 W and pressure of 0.3 mbar. They exhibit a transition between the stochastic electron heating mode operating at low powers and the secondary-electron emission heating mode (γ) operating at high powers. The electronic density increases from 1.5×109 to 3.2×1010 cm-3 while the effective electron temperature decreases from 3.7 to 2.3 eV. The EEDFs were found to be Druyvesteyn-like in the range of 5–80W and then evolve to the Maxwellian beyond 90W.

Abstract: In the blue region of the magnetized hydrogen plasma the population inversion has been observed. Possible reaction responsible for the inversion is molecular ion recombination that gives an overpopulation of states 4, 5 and 6. This inversion can be eliminated by using Nd: YAG laser, λ=1064 nm (1.15 eV) to photo-detach H- (0.75 eV). Approximately 60% of Hα and less than 10% of Hβ have been destroyed.

Abstract: The generation of plasmas and the initiation of electrical breakdown are realized by the phenomenon of electrical discharge which is provoked when we apply a sufficient electric field in a gas. Consequently the free charges are accelerated, new charged particles are created and others are destructed. This can be ranged in four phenomena: elastic collision (recombination), attachment, excitation and ionization. The aim of this paper is to study the basic phenomena in an electrical discharge in the case of Oxygen O₂. Monte Carlo Simulation is used to follow the random trajectory of free charges determining in each path many parameters of the discharge. To determinate electrical and physical parameters, we have used the sampling laws. The spatial distributions of space charges (electrons, positive and negative ions) are also obtained. The determination of electrical field depends on distributions of charged particles obtained by solving the Maxwell equations.