Measurement of the interaction potential of microspheres in the sheath of a rf discharge

The interaction potential of two microspheres that are levitated in the she ath region of a radio frequency (rf) argon discharge is studied experimenta lly by analyzing their trajectories during head-on collisions. It is shown that the interaction parallel to the sheath boundary can be described by a screened Coulomb potential. Thus, values for an effective charge and a scre ening length can be obtained. The horizontal part of the interaction potent ial has been determined for several plasma conditions. There is no evidence for an attractive part in the potential within the accuracy of the present measurements and the given plasma conditions.