AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM1
Long Jumps in the Surface Diffusion of Large Molecules

Tuesday, November 5, 2002, 8:20 am, Room C-110

Session: Diffusion & Growth on Metal Surfaces
Presenter: T.R. Linderoth, University of Aarhus, Denmark
Authors: M. Schunack, University of Aarhus, Denmark
T.R. Linderoth, University of Aarhus, Denmark
F. Rosei, University of Aarhus, Denmark
E. Laegsgaard, University of Aarhus, Denmark
I. Stensgaard, University of Aarhus, Denmark
F. Besenbacher, University of Aarhus, Denmark
Correspondent: Click to Email
While the surface mobility of atomic adsorbates has been studied extensively, similar investigations of large organic molecules are very scarce. Here, we report a detailed variable-temperature Scanning Tunneling Microscopy investigation of the one-dimensional diffusion of two largish molecules, decacyclene (DC) and hexa-tert-butyl-decacyclene (HtBDC), on a Cu(110) surface. The molecular diffusion was studied by acquiring series of STM-images at substrate temperatures of 172-200 K and 218-251 K for HtBDC/DC, respectively. Surprisingly, we find that long jumps, i.e. adsorbate transitions spanning multiple lattice sites, play a dominating role for the diffusion of DC and HtBDC. The root mean-squared (RMS) jump lengths are as large as 3.9 and 6.8 Cu lattice spacings, respectively. The presence of long jumps is revealed by a new and simple method of analysis, which we have tested quantitatively by kinetic Monte Carlo simulations. The dominating role played by long jumps is in strong contrast to previously investigated adsorbate systems where diffusion typically occurs by jumps between nearest neighbor sites. Our results furthermore demonstrate the possibility of tailoring molecular diffusion properties: DC and HtBDC both have the same aromatic plane, which interacts strongly with the surface. In the case of HtBDC, however, the plane is raised away from the surface by spacer groups, resulting in an approximately four orders of magnitude higher diffusion constant compared to DC. The higher diffusivity results both from the larger RMS jump length and from a reduction of the activation barrier for diffusion from 0.73 to 0.59 eV.