Intense boundary emission destroys normal radio-frequency plasma sheath.

Area of Science:

• Plasma Physics
• Surface Science
• Electromagnetics

Background:

• Plasma sheaths are crucial for plasma-boundary interactions, typically isolating bulk plasma from surfaces.
• Radio-frequency (RF) sheaths form under applied RF voltage, usually consuming most of the applied bias.
• Understanding RF sheath behavior is vital for controlling plasma properties and their effects on materials.

Purpose of the Study:

• To investigate the impact of intense boundary emission on the structure and behavior of RF sheaths.
• To explore a new regime of RF plasma where the external bias is consumed by the bulk plasma.
• To present a model for this novel RF plasma and its potential applications.

Main Methods:

• Experimental observation of RF sheath dynamics under conditions of intense boundary emission.
• Theoretical modeling to explain the observed plasma behavior and particle/energy balance.
• Analysis of ion confinement, electron obstruction, and RF current generation within the plasma.

Main Results:

• Evidence of RF sheath destruction by intense boundary emission, leading to a different plasma state.
• Demonstration that external bias is consumed by bulk plasma, not the sheath, in this new regime.
• Observation of unobstructed plasma electrons and confined ions, resulting in strong RF currents.

Conclusions:

• A novel RF plasma state is established when intense boundary emission disrupts the normal RF sheath.
• This state offers potential for mitigating ion erosion on plasma-facing components.
• The findings inspire new techniques for controlling reaction rates in plasma processing and wave mode conversion.