Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 34: Metal Substrates: Adsorption of Organic/Bio Molecules II
O 34.7: Vortrag
Dienstag, 26. Februar 2008, 15:15–15:30, MA 043
Molecular Switches at Solid Surfaces: A DFT Study of Azobenzene on Coinage Metals — •Erik McNellis, Abbas Dehghan Baghi, and Karsten Reuter — Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin (Germany)
Following the rapidly advancing miniaturization in microelectronics and sensing, molecules that may be switched between defined conformational states are envisioned as fundamental storage and logic units in a future “molecular nanotechnology”. Considering contacting and defined integration into a larger framework, it is more precisely the molecular function when the molecule is stabilized at a solid surface that is of key interest. A necessary prerequisite for an atomic-scale understanding of this function of the adsorbed switch is a detailed structural and electronic characterization of the stable (or meta-stable, long-lived) molecular states. For this, we use density-functional theory and study the prototypical cis-trans isomer azobenzene (C6H5-N=N-C6H5) at coinage metal surfaces. Treating electronic exchange and correlation (xc) at the generalized gradient approximation (GGA) level, we obtain an essentially zero net binding of both conformational isomers at Ag(111) and Au(111). This is significantly different at Cu(111), where the bonding particularly of the cis isomer is strong enough to even reverse the gas phase energetic order of the two isomers. We are able to rationalize these findings as a competition between the covalent bonding of the central azo (-N=N-) bridge to the substrate on the one side, and the surface interaction of the two closed-shell phenyl (-C6H5) rings on the other side.