Berlin 2008 – scientific programme

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 2: Organic Interface Structure and Growth

SYSA 2.3: Talk

Tuesday, February 26, 2008, 11:30–11:45, H 0105

Growth and Electronic Structure of Pentacene on Pd & Pt Surfaces — •Daniel Käfer and Gregor Witte — Physikalische Chemie I, Ruhr-Universität Bochum, Germany

Due to its high charge carrier mobility pentacene is a promising molecular semiconductor for the fabrication of organic field effect transistors (OFETs). While gold has been commonly used as electrode material in pentacene based thin film transistors recent studies have shown improved device characteristics for Pd electrodes.

In this study the growth and structures of pentacene films on single-crystalline and polycrystalline Pd and Pt surfaces has been investigated by means of SEM and NEXAFS spectroscopy. Significant differences were found for the molecular orientation in multilayer films grown on both substrates, which is important for the realization of OFETs in view of the large anisotropy of charge carrier mobility in crystalline pentacene. In addition a rather different film morphology was observed for the various substrates ranging from a quasi layer-by-layer fashion to extreme dewetting. The interaction strength of pentacene with both metal surfaces was further characterized by TDS measurements. Moreover, by using UPS the electronic structure of pentacene thin films on Pd and Pt has been analyzed in detail. These results reveal a different electronic coupling between the metal substrate and the first monolayer on the one hand, and between the first layer and pentacene multilayers on the other hand, which has to be taken into consideration for an understanding and optimization of charge injection in such devices.