Abstract: Two surface reconstruction patterns, different from the Au(111) intrinsic herringbone reconstruction, have been observed at the interfaces between Au(111) and the self-assembled monolayer of perylene or iron phthalocyanine by scanning tunneling microscopy (STM). These interfacial structures, elucidated by using the two-dimensional Frenkel-Kontorova (F-K) model and density-functional theory (DFT) calculations, are attributed to the anisotropic surface stress caused by interfacial charge transfer. The length scales of the induced reconstruction periodicities are theoretically estimated, in good agreement with experiments. In the second part electron tunneling properties at the molecule-electrode interfaces formed by coronene molecules adsorbed on Ag(111) and HOPG surfaces are investigated by STM experiments and DFT calculations. The coronene molecules are observed to display significant variation in the electronic density of states at the molecular centers on different substrates. An analysis of the electronic structures for both systems by first-principles calculations based on density functional theory (DFT) reveals that substrate dependent molecular image contrast is ascribed to the resonant tunneling process mediated by geometrically different substrates. Our results are further confirmed by STM simulations as implemented by Bardeen approximation. These findings afford the possibilities of tailoring the contact structures and charge transport properties of molecular electronic devices by molecular and surface engineering.
Location: 606 conference room 
Date and time: July 19^th, 2011    10:30 A.M—11:00 A.M