A role of metal d-band in the interfacial electronic structure at organic/metal interface: PTCDA on Au, Ag and Cu

We analyzed the vacuum level shift (A) induced by the dipole layer at the interfaces between perylene-3,4.9,10-tetracarboxylic dianhydride (PTCDA) and noble metals (Au, Ag and Cu). The variation of Delta observed by ultraviolet photoelectron spectroscopy does not show a simple dependence on the metal work function, which contradicts the prediction by the induced density of interface states (IDIS) model proposed by Vazquez et al. [H. Vazquez, F. Flores, R. Oszwaldowski, J. Ortega, R. Perez and A. Kahn, Appl. Surf. Sci 234 (2004) 107]. We found that two factors, (1) the energy separation between the lowest unoccupied molecular orbital (LUMO) of PTCDA and the metal cl-band states. which results in the attractive effect due to the orbital hybridization, and (2) the coupling matrix element between the adsorbate states and the metal d-band states, which result in the repulsive effect due to the orbital orthogonalization between the adsorbate states and the metal cl-band states, have a clear correlation with the J formation. Our results indicate that the interactions between the molecular orbitals of PTCDA and the metal cl-band states play an important role in determining the interfacial electronic structure, which has not been taken into account within the framework of the IDIS model. (C) 2008 Elsevier B.V. All rights reserved.