A very-high-frequency (VHF) plasma at 100 MHz is experimentally investigated in parallel-plate configuration in H2 using spatiotemporal optical emission spectroscopy and current-voltage-power waveforms. The observed optical emission intensity and net excitation rate profiles have strong temporal and spatial variations. The VHF plasma is still capacitive, and is maintained by reflected electrons in the oscillating sheath next to the instantaneous cathode. The characteristics of VHF plasmas, that the excitation rate increases in proportion to the square of driving frequency, and that the minimum sustaining voltage and pressure decrease with increasing frequency, are experimentally confirmed at pressures, ranging from 0.01 to 2 Torr and at the frequency of 100 MHz.
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