AVS 52nd International Symposium
    Surface Science Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA3
Exclusively Linear Diffusion of 9,10-Dithioanthracene on an Isotropic Cu(111) Surface

Thursday, November 3, 2005, 2:40 pm, Room 202

Session: Transport and Structural Stabilization of Surfaces
Presenter: L. Bartels, University of California at Riverside
Authors: K.-Y. Kwon, University of California at Riverside
K.L. Wong, University of California at Riverside
G. Pawin, University of California at Riverside
L. Bartels, University of California at Riverside
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One-dimensional diffusion of adsorbates is a common feature of anisotropic surfaces such as the (110) and (211) cuts of an fcc crystal. The technologically-relevant lowest energy (111) surfaces of coinage metals have sixfold symmetry in the top layer and, hence, generally allow diffusion of adsorbates along more than one direction. Here, we report on the diffusion of individual 9,10-dithioanthracene (DTA) molecules on Cu(111). DTA adsorbs with the aromatic system lying flat on the substrate. In variable-temperature STM studies, we find that it diffuses exclusively in the direction in which it aromatic moiety happened to adsorb. We neither find rotation of the molecule in the surface plane nor diffusion perpendicular to the aromatic axis of the molecule. We investigated the dynamics of the one-dimensional diffusion of DTA and find an energy barrier of 130mev and an attempt frequency of 4 GHz. Density Functional Theory modeling of the diffusion potential shows, that DTA achieves unidirectional motion by sequential placement of its two substrate linker in a fashion that strikingly resembles bipedal locomotion.