C-60 manipulation and cluster formation using a scanning tunneling microscope

We have used the tip of an ultrahigh vacuum scanning tunneling microscope to induce displacements of C-60 molecules on the Si(111)-7 x 7 surface at room temperature. The manipulation is achieved by using a sweeping procedure we have developed which moves the tip closer to the surface and sweeps it across in a predetermined direction. Feedback control of the tunnel current is maintained throughout and the tip-surface separation is adjusted by changing the sample bias and tunnel current. For a 0.007 monolayer (ML) coverage of C-60, a sweeping area of 60 Angstrom x 60 Angstrom was used to move individual C-60 molecules, while for higher coverages (0.05-0.2 ML) a sweeping area of 216 Angstrom x 216 Angstrom was used to move large groups of C-60 molecules. We show an example at 0.2 ML coverage where we have removed C-60 over an area 110 Angstrom x 370 Angstrom resulting in the formation of a line of C-60 molecules 20-30 Angstrom in width. (C) 1996 American Vacuum Society.