Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 37: Metal substrates: Adsorption of organic / bio molecules V

O 37.4: Vortrag

Mittwoch, 25. März 2009, 15:45–16:00, SCH A118

Understanding Pd island formation on self assembled 4-mercaptopyridine monolayers on Au(111) — •John Keith and Timo Jacob — Institut für Elektrochemie, Universität Ulm, 89081 Ulm

Self-assembled monolayers (SAMs) on metallic substrates show great potential for applications such as molecular sensors or biological nanodevices. Efforts have been made metallize small, aromatic SAMs such as 4-mercaptopyridine (4MP) on Au(111) through electrochemical deposition methods with Pd. However, these methods have not yet been successful due to formation of 2-dimensional islands exhibiting non-metallic character [1]. Motivated by this study, we investigated Pd adsorption and diffusion on a 4MP-SAM using periodic density functional theory [2]. For different Pd coverages, we calculated potential energy surfaces for adsorption and diffusion across the 4MP-SAM, allowing investigation of diffusion processes that explain how Pd islands form. Our studies clearly show Pd cannot diffuse on the clean 4MP-SAM surface. Rather, Pd atoms aggregate into regions above the Au surface and between 4MP monomers. When Pd diffuses across a surface where Pd is already pre-adsorbed, diffusion barriers are greatly reduced from the presence of small particles of Pd. This suggests diffusion and island formation require pre-deposited Pd on the SAM and that these islands are not strictly 2-dimensional.

[1] H.-G. Boyden, et al., Nature Mater., 5, 394 (2006). [2] J. A. Keith, T. Jacob, Nano Lett., submitted.