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Development of Atmospheric Plasma Technology, 18-R9612

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Principal Investigator
Ronghua Wei

Inclusive Dates:  05/01/06 – 09/01/07

Background - Atmospheric plasma has many advantages over conventional vacuum-based plasma technologies, and certainly the most prominent advantage is to dispose of the cumbersome vacuum equipment. Without the vacuum equipment, the capital investment for equipment is substantially reduced, but also many large components can be treated in the field with a portable instrument. The industrial interests for these techniques include depositing hard coatings and functionalizing polymeric materials. During this quick-look internal research funding, we have studied two types of plasmas: RF hollow cathode plasma (RFHCP) and pulsed hollow cathode plasma (PHCP). For RFHCP, we were able to increase the pressure from a few millitorr to a few torr. Although the present RFHCP cannot be operated at the atmospheric pressure, running at a few torr still has a wide range of applications. Using this setup, we have demonstrated that metallic coatings or ceramic coatings can be accomplished. For the PHCP, we have successfully operated it at atmospheric pressure using two setups: single nozzle hollow cathode or multi-aperture hollow cathode. Using this technique, we have conducted a number of tests, in which we demonstrated the deposition of a diamond-like carbon film.

Approach - Under the internal research funding, we have studied two types of plasmas: RF hollow cathode plasma (RFHCP) and pulsed HC plasma (PHCP). The RFHCP applies RF power to a hollow tube, from which gases are fed. Under certain pressure and RF power, plasma can be generated. By selecting the gas composition such as acetylene, a diamond-like carbon coating can be deposited. On the other hand, by applying a high power on the tube and using pure Ar, vaporization of the tube can be achieved. As a result, metallic coating with the tube material can be obtained. In addition, if nitrogen gas is used, nitride coating can be achieved. The PHCP is similar to the RFHCP in that it also utilizes a hollow cathode, but the plasma is generated using a high, pulsed voltage. Similar coatings to those obtained from the RFHCP can be obtained.

Accomplishments - Using the RFHCP setup, we were able to operate the system at a pressure up to a few torr and deposited metallic coatings (copper and stainless steel) on steel substrates. For the PHCP, we were able to run the system from a few millitorr all the way up to the atmospheric pressure. Using this system, we demonstrated the deposition of diamond-like carbon films. In addition to the single tube cathode, we also tested a large diameter (15 mm), multiholed system at atmospheric pressure.

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