Attractive mode manipulation of covalently bound molecules

We have investigated the manipulation of C60 molecules on Si(1 0 0)-2×1 using the tip of a scanning tunnelling microscope. An attractive mode of manipulation has been identified in which molecules hop across the Si(1 0 0)-2×1 surface in steps of two lattice constants. An abrupt transition to repulsive manipulation occurs as the tip is lowered towards the surface. The attractive interaction is attributed to chemical forces between the tip and molecule.