CPM Seminar

Organic Molecules on a Metal Surface: Fundamentals and Applications

Federico Rosei

INRS-EMT Energie
Université du Québec

In terms of surface diffusion, the motion of atomic and molecular adsorbates across surfaces can be followed directly by acquiring time-resolved `STM movies'. In the simplest picture, the adsorbate jumps between nearest neighbor sites. Our results suggest this is not necessarily true for complex organic molecules. By comparing the diffusion behavior 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, spanning multiple lattice spacings [2]. Since HtBDC and DC have very similar chemical structures, this ultimately demonstrates how molecules can be custom designed to engineer their diffusion properties.

Second, I will describe the adsorption of the Lander molecule [3] (C₉₀H₉₈) on Cu(110) by STM in the temperature range 100 - 300 K. The Lander has a central polyaromatic molecular wire (conducting backbone), and four `spacer legs' (3,5-di-tert-buthylphenyl), designed to isolate the wire part from the substrate. Manipulation experiments with the STM at low temperatures on isolated Lander molecules adsorbed on step edges reveal a restructuring of Cu steps [3]: when removed from a step, a characteristic nanostructure appears. The structure's width is two atomic rows, matching the distance between the spacer legs within the molecule. The restructuring process is thermally activated: repeating the same manipulation experiments on molecules adsorbed at low temperatures (150 K), no restructuring of Cu step edges is found. This ultimately shows that molecules can be designed from first principle to induce predefined reconstructions on a metal surface.

[1] C. Joachim, J.K. Gimzewski and A. Aviram, Nature 408, 541 (2000).
[2] M. Schunack, T.R. Linderoth, F. Rosei et al., Phys. Rev. Lett. 88, 156102 (2002).
[3] F. Rosei et al., Science 296, 328 (2002).