Substrate-mediated electron tunneling through molecule-electrode interfaces

Electron tunneling properties at the molecule-electrode interfaces formed by coronene molecules adsorbed on Ag(111) and highly oriented pyrolytic graphite surfaces are investigated by scanning tunneling microscopy and first-principles calculations. Experimentally, the coronene molecules 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 reveals that substrate dependent molecular image contrast is ascribed to the resonant tunneling process mediated by geometrically different substrates. Possible consequences for electron transport are briefly discussed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650248]