Rotation of particles trapped in the sheath of a radio-frequency capacitively coupled plasma

We report experiments on orbiting of particles in the plasma sheath in a horizontal plane under a monolayer of spherical particles with diameter of 9.8 /spl mu/m. The motion is performed by heavier particles, which we assume to be agglomerates of the injected spherical particles. These particles are nonspherical. The dependence of the rotation on the plasma parameters (pressure, power) is analyzed and some properties of the driving force necessary for this phenomenon are discussed.