  Equilibrating gravitation by electric forces, microparticles can be confined
in the plasma sheath above suitably biased local electrodes.Their position
depends on the detailed structure of the plasma sheath and on the charge that
the particles acquire in the surrounding plasma, that is by the electron and
ion currents towards it. Bias switching experiments reveal how the charge and
equilibrium position of the microparticle change upon altered sheath
conditions. We observe similar particle behaviors also in the afterglow of the
discharge for a persisting bias voltage on the electrode: damped oscillation
into a new equilibrium or (accelerated) fall according to the bias.

Plasma Physics