不同压力下电容耦合射频放电鞘层区域的电场反转
Electric field reversals in single and dual-frequency capacitively coupled radio frequencydischarges are investigated in the collisionless (1 Pa) and the collisonal (65 Pa) regimes.Phase resolved optical emission spectroscopy is used to measure the excitation of the neutralbackground gas caused by the field reversal during sheath collapse. The collisionless regime isinvestigated experimentally in asymmetric neon and hydrogen single frequency dischargesoperated at 13.56MHz in a GEC reference cell. The collisional regime is investigatedexperimentally in a symmetric industrial dual-frequency discharge operated at 1.937 and27.118 MHz. The resulting spatio-temporal excitation profiles are compared with the results ofa fluid sheath model in the single frequency case and a particle-in-cell/Monte Carlo simulationin the dual-frequency case. The results show that field reversals occur in both regimes. Ananalytical model gives an insight into the mechanisms causing the reversal of the electric field.In the dual-frequency case a qualitative comparison between the electric fields resulting fromthe PIC simulation and from the analytical model is performed. The field reversal seems to becaused by different mechanisms in the respective regimes. In the collisionless case it is causedby electron inertia, whereas in the collisional regime it is caused by a combination of the lowmobility of electrons due to collisions and electron inertia. Finally, the field reversal during thesheath collapse seems to be a general source for energy gain of electrons in both single anddual-frequency discharges.