Dust grains as a diagnostic tool for rf-discharge plasma

The location of the sheath edge in a planar rf-discharge has been determined using test dust grains. The diagnostic technique is based on measurement of the equilibrium position of fine dust grains levitated above the powered electrode in an rf-discharge. Estimates show that for grains with radii less than 500 nm the grain equilibrium position and sheath edge location differ by less than 5 percent, and this difference continues to decrease with grain radius. We use this technique to diagnose the sheath in an argon plasma which was generated at pressures in the range 20 - 100 mTorr. The transient motion technique was used for the radial potential profile measurements. The results obtained was compared to the profile obtained using the rf-compensated single Langmuir probe. The two results show good agreement.