This work represents the investigation of the dependence of the breakdown voltage on the gas pressure and on the frequency in radio-frequency argon discharges. Calculations were performed by using a one-dimensional particle-in-cell/Monte Carlo code with three velocity components with a new secondary emission model. The obtained results show that the multivalued nature of the left-hand branch of the breakdown curve can be achieved only by taking into account energy dependence of the yield per ion. The multivalued nature of the left-hand branch of the breakdown curve is attributed to the influence of the secondary emission characteristics of the electrodes on the breakdown voltage. Simulation results show a good agreement with the available experimental data. Disagreements between simulation results and theoretical predictions based on the phenomenological method indicate that a more accurate determination of molecular constants is needed. As a result of the satisfactory agreement between simulation and experimental data for dependence of the breakdown voltage on the frequency, a frequency scaling law is proposed.

In low-pressure dual-frequency capacitive discharges, the effect of the low-frequency current on the electron distribution function (EDF) was investigated through the particle-in-cell simulation with Monte Carlo collision model. As the low-frequency (2MHz) current increases for the fixed high-frequency (27MHz) current, the EDF changes from Druyvesteyn to bi-Maxwellian (in the absence of secondary electron emission) or Maxwellian type (in case with secondary electron emission), along with the significant drop in the effective electron temperature. When the role of secondary electron emission is negligible, the EDF transition is attributed to the transition from collisional to collisionless property (but not stochastic heating) of the low-energy electrons. The Ramsauer minimum which makes low-energy electrons less collisional plays an important role in making this transition as well as in determining the spatial electric field structure. When the role of secondary electron emission is significant, the transition is attributed to the α-γ transition.