AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS1-TuA

Paper PS1-TuA3
Hollow Cathode Sustained Atmospheric Plasma Microjets

Tuesday, November 5, 2002, 2:40 pm, Room C-103

Session: Microdischarges
Presenter: R.M. Sankaran, California Institute of Technology
Authors: R.M. Sankaran, California Institute of Technology
K.P. Giapis, California Institute of Technology
Correspondent: Click to Email
Microhollow cathode discharges (MHCDs) or microdischarges have gained recent attention for their high-pressure operation and intense UV radiation. They are normally formed between two metal foils, a cathode with a pin-hole (diameter~100 µm) and an anode of arbitrary shape. To more easily incorporate these discharges in materials processing, we have recently extended their operation to a tube geometry where gas flow can be directly coupled to the electrodes. Discharges are formed in the tube hole similar to a static case, but the flow carries the plasma outside the tube to form a microjet. In this talk, we will present features of this novel source and discuss possible applications in thin film growth and effluent gas treatment. Plasma microjets are ignited in direct current mode using a stainless steel capillary tube with a 178 µm diameter hole as the cathode and a metal grid or plate as the anode. Optical characterization has confirmed that it is necessary to shrink the hole size to below 200 µm in diameter to operate inert gases at atmospheric pressure in the hollow cathode mode. Argon microjets can be operated in ambient air at 760 Torr with voltages as low as 260 V for cathode-anode gaps of 0.5 mm. Increasing the gap and extending the plasma microjet results in an increase in the plasma voltage. The current-voltage characteristics of the plasma microjet are also influenced by the gas flow rate. For a given interelectrode distance and plasma current, increasing the flow rate reduces the plasma voltage by as much as 200 V. These effects suggest that the diffusion of air into the argon plasma stream is important. Plasma microjets offer a simple tool to perform rapid materials optimization by operating arrays of discharges. As a proof-of-concept, we have demonstrated that CH@sub 4@/H@sub 2@ plasma microjets can be used to grow diamond with fine control of the film properties by changing the gas composition.