Characteristics of Vertical Spatial Distribution of Dust Particles in Radio Frequency-Plasma Sheath

The vertical spatial distribution of dust particles in radio frequency (RF) discharge plasma sheath is studied. The dust particles are levitated above the powered electrode in the discharge. From the distribution of the dust particles of different sizes generated by mixing of suitable gases, the effect of changing the RF power on the dust cloud behavior is studied. It is found that the distribution of the different sized dust particles in the sheath with variable bias differs significantly from that of single sized dust particles with fixed bias. As the RF power increases, the distribution range as well as the levitation height of the dust cloud above the powered electrode decrease. A theory for the observed results is also given. Based on the experimental and numerical results, we attribute the observed dependence to a combination of the enhanced sheath electric field and the ion drag force, but the decrease of the sheath thickness with increase of the discharge power has only minor contribution.