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Electrode-less plasma excitation methods include
helicon plasma sources, inductively-coupled plasmas, and
surface-wave-sustained discharges.
Electrode-less high-frequency discharges (HF) have two important
advantages over plasmas using electrodes, like capacitively coupled plasmas that are of great interest for contemporary plasma research and
applications:
Firstly, no sputtering of the electrodes occurs.
However, depending on ion energy, sputtering of the reactor walls or the
substrate may still occur. Under conditions typical for plasma modification
purposes, the ion energy in electrode-less HF discharges is about an order of
magnitude lower than in RF discharges. This way, the contamination of
the gas phase and damage of the substrate surface can be reduced.
Secondly, the surface-wave effect allows to generate spatially extended plasmas with electron densities that exceed the critical density.
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