Dust void formation above rectangular and circular potential traps in an rf plasma

Void formation in one- and two-dimensional complex (dusty) radio frequency (rf) plasmas has been studied using spherical and cylindrically shaped particles. Threshold values for void formation have been determined for plasma power, pressure and number of particles. A comparison between an electropositive argon and an electronegative oxygen plasma shows that void formation in electronegative plasmas is hindered because of a better radial confinement of the particle cloud. No significant dependence on the particle shape (spherical versus cylindrical) has been observed. Comparing one- and two-dimensional structures shows that collective particle behaviour is not responsible for void formation, but possibly does contribute to cloud confinement