Berlin 2008 – wissenschaftliches Programm

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 1: Bandalignment in Organic Materials

SYSA 1.1: Hauptvortrag

Dienstag, 26. Februar 2008, 09:30–10:00, H 0105

Level alignment at metal/organic interfaces — •Fernando Flores — Universidad Autónoma de Madrid, Madrid, Spain

A unified model, embodying the Induced Density of Interface States (IDIS), Pauli repulsion and intrinsic molecular dipoles is presented for describing the level alignment at a metal/organic interface. The IDIS model takes into account how charge is transferred between the metal and the organic material [1]: in particular, charge transfer is determined by the relative position of the metal workfunction and the organic Charge Neutrality Level (CNL), as well as by an interface parameter, S, which measures how this potential difference is screened. The Pauli repulsion dipole originates from the orthogonalization of the metal and organic wavefunctions; this dipole is calculated using a many-body LCAO hamiltonian [2], resulting in an effective reduction of the metal workfunction. Intrinsic molecular dipoles are also introduced in this unified model, in such a way that the level alignment at the metal/organic interface is obtained from a calculation that combines all these effects in a selfconsistent way. As a first example, organic materials with no intrinsic molecular dipole are considered (PTCDA, PTCBI, CBP and CuPc). For these cases it will be shown that the IDIS-dipole represents most of the realignment induced at the metal/organic interface, with the Pauli repulsion dipole yielding minor corrections to the IDIS model. In a second example, the Cu/benzenethiolate/pentacene heterostructure is analyzed including IDIS, Pauli repulsion and intrinsic molecular dipoles [3]. The Cu/benzenethiolate interface realignment can be understood in these terms as a function of the benzenethiolate coverage: this also enables us to determine, using the metal workfunction evolution, the molecule orientation as a function of coverage. An extension of this model to heterostructures allows us to analyze in similar terms the benzenethiolate/pentacene interface.

[1] H.Vazquez et al, Europhys. Lett. 65, 802 (2004) [2] H.Vazquez et al, J. Chem. Phys. 126, 144703 (2007) [3] M.G.Betti et al, Phys. Rev. Lett., in press.