ION AND NEUTRAL VELOCITY DISTRIBUTIONS IN MULTI-ION PLASMA SHEATHS

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The proposal is directed at investigating the physics of multi-ion sheaths, the generation of supersonic fluxes of energetic ions in spontaneously forming double layers (sheaths), and the creation of fluxes of energetic neutrals that could be used for plasma-aided etching. Neutral etching avoids the problem of substrate charging that occurs when energetic ions are used to etch wafers in the microelectronics industry. The acceleration of ions through sheaths in multi-ion plasmas is a fundamental plasma physics question with important ramifications for systems ranging from space plasmas to fusion plasmas. There are two primary objectives of this proposal. First is the determination of the effect of additional ion species on double layer formation in expanding helicon plasmas, and second, the measurement of the momentum coupling between ions and neutral atoms in the layer due to charge exchange processes. The essential intellectual merit of the proposed activity will be the first detailed measurement of the flow velocities of two different ion species and a single neutral species in a plasma sheath. Ion acceleration through pre-sheaths and sheaths in multi-ion plasmas is not fully understood and this project will make a significant contribution to this active area of fundamental plasma science research. The broader impact of the work involves the training of graduate students in a research environment that emphasizes the synergy between basic and applied plasma physics; improvement of the percentage of women obtaining advanced degrees in physics; and attracting high quality undergraduates into physics through involvement in cutting-edge research activities. Impact on the field of plasma etching of semiconductors is also likely since production of significant fluxes of energetic neutral atoms through charge exchange neutralization of the double layer accelerated ions would provide a new means of etching features in silicon at scales of less than ten nanometers. Impact on the field of plasma propulsion is also likely given that plasma detachment from plasma-based thrusters is an important and unresolved question.