Abstract
We have used scanning tunneling microscopy and spectroscopy to study the electronic structure of individual molecules adsorbed onto the Au(111) and Ag(100) surfaces. molecules on Au(111) show an increase in the HOMO-LUMO gap of 0.6 eV compared to on Ag(100). Splitting of the LUMO manifold is suppressed for on Au(111), in contrast to the strong splitting observed for on Ag(100). Our data implies a 0.6 eV increase in intramolecular Coulomb energy for on Au(111) as compared to on Ag(100). Topographs and energy-resolved spectral maps, however, show nearly identical features and indicate a similar influence of the two substrates on molecular-orbital geometry. -substrate bonding and charge transfer is further investigated by calculating charge redistribution using ab initio pseudopotential density-functional theory methods. These calculations indicate that a negligible amount of charge is transferred from Au(111) to adsorbed , while about 0.2 electron is transferred to resting on Ag(100), although the precise amount depends on the definition used. This charge transfer likely changes the electronic screening properties of , providing an explanation for observed spectroscopic differences on these two substrates.
- Received 27 December 2003
DOI:https://doi.org/10.1103/PhysRevB.70.115418
©2004 American Physical Society