The adsorption of large organic molecules on surfaces is important in the emerging field of nanotechnology . Molecular ordering is in general controlled by a delicate balance between intermolecular binding forces and molecule-substrate interactions. In this talk I will show how the unique resolving power of Scanning Tunneling Microscopy, together with its ability to manipulate individual atoms and molecules, can provide important new information on molecular diffusion and assembly.
I will begin by addressing the issue of surface diffusion. The motion of atomic and molecular adsorbates across surfaces can be followed directly by time-resolved STM movies. In the simplest picture of surface diffusion, the adsorbate jumps between nearest neighbour sites. Surprisingly, by studying the diffusion of two related aromatic molecules, DC (C36H18) and HtBDC (C60H66) on Cu(110), we find that their diffusion is dominated by so-called long jumps . The HtBDC molecule has a core part identical to DC, and six additional spacer legs, which increase its diffusion coefficient by four orders of magnitude with respect to DC. These results demonstrate how molecules can be custom designed to engineer their diffusion properties.
Second, I will describe the adsorption of Lander molecules  (C90H98) on Cu(110) in the temperature range 100 300 K. The Lander is a prototype of a molecular wire. It is composed of a conducting backbone, and four spacer legs for isolation from the substrate. Manipulation experiments with the STM at low temperatures on isolated molecules adsorbed on step edges reveal that this molecule acts as a nanoscale template , capable of reshaping metal step edges into characteristic nanostructures. This process shows that organic molecules can be custom designed to assemble predefined structures on metal surfaces.
 C. Joachim, J.K. Gimzewski and A. Aviram, Nature 408, 541 (2000).
 M. Schunack, T.R. Linderoth, F. Rosei et al., Phys. Rev. Lett. 88, 156102 (2002).
 F. Rosei et al., Organic molecules acting as templates on Metal Surfaces, Science 296, 328 (2002).
The speaker will give a general overview of the field suitable for undergraduates and other non-specialists. This will include introductory material on Nanoscience in general and Scanning Tunneling Microscopy in particular.