EFFECT OF DIRECTED (RADIAL) GAS-FLOW ON SPUTTERING AND EMISSION CHARACTERISTICS IN RADIO-FREQUENCY POWERED GLOW-DISCHARGE DEVICES

An assembly has been constructed for the radial introduction of Ar support gas toward the cathode surface of a radio frequency glow discharge atomic emission device. Studies of directed gas flow suggest two counteracting processes. At lower flow rates (<300 ml/min), the gas has a sweeping effect to remove sputtered material from the region directly above the cathode surface, presumably inhibiting the redeposition process. At higher flow rates, a localized high-pressure region is established with a consequent lowering of the dc bias potential and resultant decrease in sputtering rates. Use of directed gas flow is found to increase the extent of self-absorption for low-lying atomic transitions, while ionic emission is found to be enhanced. The use of continuous, radial gas introduction allows for retention of desired sputter crater shapes.