Driving frequency effect on electron heating mode transition in capacitive discharge

A study was conducted on the dependence of the electron heating mode transition upon driving frequency in capacitive discharge. The evolution of the electron energy distribution functions (EEDFs) over a wide range of gas pressures was investigated at different driving frequencies. Regardless of the driving frequency, the measured EEDFs exhibited a typical evolution of EEDF from bi-Maxwellian distribution to Druyvesteyn-like distribution with gas pressure, signifying the electron heating mode transition from collisionless to collisional heating. However, the gas pressure, which the heating mode transition takes place, significantly decreased as the driving frequency increased. This result is ascribed to the fact that the collisionless stochastic heating becomes inefficient at high frequency compared with collisional heating.