Transition from Attractive to Repulsive Forces between Dust Molecules in a Plasma Sheath

The electrostatic interaction of a system of two single dust particles in a plasma-sheath environment with flowing ions has been investigated quantitatively. It is shown that attractive net ``binding'' forces between the negatively charged particles exist, leading to the formation of a dust molecule. By laser manipulation of the dust particles, it is demonstrated that the attraction is asymmetric in such a way that it acts only on one of the particles. Moreover, the net forces between the particles can be reversibly changed between attraction and repulsion.