Ion-energy-distribution functions (IEDFs) are numerically investigated in capacitively coupled (cc) radio frequency (rf) Ar/CF(4)/N(2) discharges by a one-dimensional particle-in-cell/Monte Carlo model. The simulation considers electron-neutral collisions, various kinds of collisions of ions (Ar+, CF+3, N+2, F-, and CF-3) with neutral, positive-negative ion, and electron-ion recombination. The influence of pressure, applied voltage amplitude, and applied frequency on the Ar+, CF+3, and N+2 IEDFs is presented. The dependence on the frequency regime is investigated by simulations of the Ar/CF(4)/N(2) mixture in single (13.56 MHz) and dual frequency (2+27 MHz or 1+27 MHz) cc reactors. A comparison of the simulation results with analytical calculations in a collisionless rf sheath is discussed. The results show that the IEDFs shift toward the low energies with increasing pressure or decreasing applied voltage amplitude. The Ar+ and N+2 IEDFs exhibit secondary maxima due to the charge transfer collisions. The CF+3 IEDF has a peak at high energies in consistency with the average sheath potential drop. The IEDFs in the dual frequency regime are broad and bimodal.

A one-dimensional particle-in-cell/Monte Carlo model is developed to study a capacitively coupled radio frequency discharge in a gas mixture of argon and CF 4 . The simulation takes into account the following charged particles: electrons, two kinds of positive ions (Ar ϩ , CF 3 ϩ ), and two kinds of negative ions (F Ϫ , CF 3 Ϫ ). The model considers electron-Ar collisions, electronϪCF 4 collisions, various kinds of collisions of CF 3 ϩ , F Ϫ , CF 3 Ϫ , or Ar ϩ with Ar or CF 4 , and positive-negative ion recombination. The probability for the positive-negative ion recombination is determined from a recombination rate constant. The ion-neutral elastic and reactive collisions are simulated by an ion-molecule collision model for endothermic reactions. The typical results of this model are electron and ion densities, fluxes and energy distributions, collision rates, and electric field and potential distributions. The simulation is performed for 0.1/0.9, 0.5/0.5, and 0.9/0.1 ratios of a Ar/CF 4 mixture, as well as for pure Ar and pure CF 4 discharges at a pressure of 200 mTorr. It is observed that at high CF 4 concentration the discharge behaves as a typical electronegative discharge and that CF 3 ϩ is the major positive ion. At low CF 4 concentration, keeping the other operating parameters the same, the double layer structure and the electron density maxima at the bulk-sheath interface, which are representative for an electronegative discharge, disappear and the Ar ϩ density exceeds the CF 3 ϩ density by more than 1 order of magnitude. The results show that the F Ϫ ions are the dominant negatively charged species for all Ar/CF 4 ratios investigated.

No abstract

A one-dimensional particle-in-cell/Monte Carlo model is developed to study capacitively coupled ͑cc͒ radio-frequency discharges in a gas mixture of Ar, CF 4 , and N 2. The charged species, which are followed in the model, are: Electrons and Ar ϩ , CF 3 ϩ , N 2 ϩ , F Ϫ , and CF 3 Ϫ ions. The simulation considers electron-neutral ͑Ar, CF 4 , and N 2) collisions, various kinds of collisions of ions with neutrals, positive-negative ion recombination, and electron-ion recombination. The model yields results for electron and ion densities, fluxes and energy distributions, collision rates and electric field, and potential distributions. The simulations are performed for a 0.8/0.1/0.1 ratio of Ar/CF 4 /N 2 mixture at a pressure of 30 mTorr in single ͑13.56 MHz͒ and dual frequency (2ϩ27 MHz) cc reactors and a comparison between the two frequency regimes is made. Results show that the structure of the discharges is electronegative in both cases. F Ϫ and CF 3 Ϫ ions are the main negative charge carriers in the single and dual frequency regime, respectively. In the presence of low-frequency ͑2 MHz͒ and a strong electric field, the light F Ϫ ions are no longer confined in the bulk plasma and they partially respond to the instantaneous electric field. The calculated electron energy probability function profiles can be approximated to a Druyvesteyn and bi-Maxwellian distribution with high-energy tails in the single-and dual-frequency regime, respectively. The ion energy distribution is narrow with one outstanding peak in the single-frequency scheme, whereas it is wide and bimodal in the dual-frequency scheme.

A one-dimensional particle-in-cell/Monte Carlo model is used to investigate Ar/ CF 4 /N 2 discharges sustained in capacitively coupled dual frequency reactors, with special emphasis on the influence of the reactor parameters such as applied voltage amplitudes and frequencies of the two voltage sources. The presented calculation results include plasma density, ion current, average sheath potential and width, electron and ion average energies and energy distributions, and ionization rates. The simulations were carried out for high frequencies ͑HFs͒ of 27, 40, 60, and 100 MHz and a low frequency ͑LF͒ of 1 or 2 MHz, varying the LF voltage and keeping the HF voltage constant and vice versa. It is observed that the decoupling of the two sources is possible by increasing the applied HF to very high values ͑above 60 MHz͒ and it is not defined by the frequency ratio. Both voltage sources have influence on the plasma characteristics at a HF of 27 MHz and to some extent at 40 MHz. At HFs of 60 and 100 MHz, the plasma density and ion flux are determined only by the HF voltage source. The ion energy increases and the ion energy distribution function ͑IEDF͒ becomes broader with HF or LF voltage amplitude, when the other voltage is kept constant. The IEDF is broader with the increase of HF or the decrease of LF.

Using a molecular dynamics model the crystallinity of Mg x Al y O z thin films with a variation in the stoichiometry of the thin film is studied at operating conditions similar to the experimental operating conditions of a dual magnetron sputter deposition system. The films are deposited on a crystalline or amorphous substrate. The Mg metal content in the film ranged from 100% (i.e. MgO film) to 0% (i.e. Al 2 O 3 film). The radial distribution function and density of the films are calculated. The results are compared with x-ray diffraction and transmission electron microscopy analyses of experimentally deposited thin films by the dual magnetron reactive sputtering process. Both simulation and experimental results show that the structure of the Mg-Al-O film varies from crystalline to amorphous when the Mg concentration decreases. It seems that the crystalline Mg-Al-O films have a MgO structure with Al atoms in between.

An overview of the recent progress on plasma-assisted CO2 conversion in microwave discharges is given. Special attention is devoted to the results obtained using plasma catalysis, which are compared to the plasma-only CO2 decomposition cases. The effects of plasma operating conditions, catalyst preparation methods, nature of plasma activation gas, gas mixture, as well as the NiO content on the TiO2 surface on CO2 conversion and its energy efficiency are discussed. A significant improvement in CO2 conversion is obtained with a NiO/TiO2 catalyst activated in Ar plasma, when the NiO content is about 10 wt.%. The catalyst characterization data show that Ar plasma treatment results in a higher density of oxygen vacancies and a comparatively more uniform distribution of NiO on the TiO2 surface, which strongly influence CO2 conversion and its energy efficiency. The dissociative electron attachment of CO2 at the catalyst surface enhanced by the oxygen vacancies and by plasma electrons may also explain the increase in conversion and energy efficiencies. A mechanism for the plasma-catalytic CO2 conversion at the surface of an Ar plasma-threated catalyst is proposed.

No abstract