M. Fadlallah et al., SHEATH ELECTRIC-FIELD OSCILLATION AND ION KINETICS IN RADIOFREQUENCY DISCHARGES, Journal of applied physics, 79(12), 1996, pp. 8976-8981
Time resolved maps of the electric field magnitude in the sheath of di
scharges in pure H-2 have been determined as a function of pressure (0
.6 and 1 Torr) and excitation frequency (30 kHz, 1, and 2.78 MHz). The
electric field was determined from the Stark splitting of the n = 6 l
evel of atomic hydrogen using 2 + 1 photon laser-induced fluorescence
of ground state hydrogen atoms. The sheath electric field oscillations
throughout the rf cycle were observed for different values of the rf
driving frequency, corresponding to different regimes. We observe a ''
low'' frequency regime at 30 kHz, a ''high'' frequency regime at 2.78
MHz, and an intermediate regime at 1 MHz, depending on whether the ion
density profile is modulated during the rf cycle. This is the first o
bservation of an intermediate regime where the ion transit time across
the sheath is comparable to the rf period. Fluid model simulations we
re carried out and are in good a,agreement with our experimental obser
vations. (C) 1996 American Institute of Physics.