Diffusion of 1,4-butanedithiol on Au(100)-(1×1) : A DFT-based master-equation approach
Abstract
The functionalization of metal surfaces via thiol-bonded molecules and the assembly of nanodevices on the surfaces should profit from a detailed atomistic understanding of the binding and diffusion properties. These differ substantially from the in-depth investigated situation of single adatoms. We report density-functional calculations for the elementary diffusion steps of 1,4-butanedithiol radicals (BDTRs) adsorbed on a Au(100)-(1×1) surface. The elementary diffusion steps are then combined into a description of the diffusion mechanism on long-time scales by integrating a master equation. The two S-Au bonds cause a multivalley potential-energy surface, which implies a complex diffusion mechanism. We identify the effect of the geometry constraints imposed by the (CH2)4 backbone on binding and diffusion. To this purpose we compare to the diffusion of a single SCH3 radical on the same Au(100)-(1×1) surface. Altogether, the motion of the BDTR is walkinglike with the S-atoms crossing bridge sites of the Au surface one after the other. The lowest density-functional theory-Perdew and Wang 91 energy barrier for translation is 0.35 eV while the energy barrier for rotation comes out larger, 0.43 eV. As a result of this difference there will be correlations between subsequent diffusive displacements of the molecule. The isotropic diffusion constant on long-time scales is computed and the numerical results follow an Arrhenius law.
- Publication:
-
Physical Review B
- Pub Date:
- November 2010
- DOI:
- Bibcode:
- 2010PhRvB..82t5423F
- Keywords:
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- 68.43.Jk;
- 87.15.Vv;
- 64.75.Yz;
- Diffusion of adsorbates kinetics of coarsening and aggregation;
- Diffusion;
- Self-assembly