Dipole formation at metal/PTCDA interfaces: Role of the Charge Neutrality LevelH. Vázquez1, R. Oszwaldowski1, P. Pou1, J. Ortega1, R. Pérez1, F. Flores1 and A. Kahn2
1 Departamento de Física Teórica de la Materia Condensada Universidad Autónoma de Madrid - E-28049 Madrid, Spain
2 Department of Electrical Engineering, Princeton University Princeton, NJ 08544, USA
(Received 10 June 2003; accepted in final form 22 January 2004)
The formation of a metal/PTCDA (3, 4, 9, 10-perylenetetracarboxylic dianhydride) interface barrier is analyzed using weak-chemisorption theory. The electronic structure of the uncoupled PTCDA molecule and of the metal surface is calculated. Then, the induced density of interface states is obtained as a function of these two electronic structures and the interaction between both systems. This induced density of states is found to be large enough (even if the metal/PTCDA interaction is weak) for the definition of a Charge Neutrality Level for PTCDA, located 2.45 above the highest occupied molecular orbital. We conclude that the metal/PTCDA interface molecular level alignment is due to the electrostatic dipole created by the charge transfer between the two solids.
71.20.Rv - Polymers and organic compounds.
68.43.Bc - Ab initio calculations of adsorbate structure and reactions.
73.30.+y - Surface double layers, Schottky barriers, and work functions.
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