AVS 52nd International Symposium
    Electronic Materials and Processing Wednesday Sessions
       Session EM+SS-WeM

Paper EM+SS-WeM10
Observation of Interface Gap-State between Pentacene Molecules and Gold Metal by Scanning Tunneling Spectroscopy

Wednesday, November 2, 2005, 11:20 am, Room 309

Session: Contacts to Organic and Molecular Devices
Presenter: Y.J. Song, Seoul National University, Korea
Authors: Y.J. Song, Seoul National University, Korea
S.H. Kim, Seoul National University, Korea
Y. Kuk, Seoul National University, Korea
K. Lee, Seoul National University, Korea
J. Yu, Seoul National University, Korea
Correspondent: Click to Email
Pentacene has been studied widely as a candidate for an organic thin film transistor (OTFT) because of its high mobility, and easy processing on various substrates. It has been pointed out that interface states work as scattering centers and results in poorly reproduced potential barriers for various metal contacts in the transport measurement. In this work, we investigated the electronic structure of a single pentacene molecule adsorbed on Au(100) surface with one dimensional spatially-resolved scanning tunneling spectroscopy (1D SR-STS) to map position-dependent local density of states (LDOS).@footnote 1@ In the geometry of metal-pentacene-metal transport measurement with a single crystal or a thin film pentacene, the molecule is positioned as if it flat on the contact metal. This geometry can be achieved by adsorbing the molecule on a metal substrate. Au(100) surface was chosen since it offers both near-hexagonal and square symmetry, depending on a location of the (5x20) reconstruction. We measured SR-STS at various sites on the Au(100)-(5x20) surface. Unlike previously observed spectroscopy results on an insulator surface,@footnote 2@ two dominant features are clearly resolved in the HOMO-LUMO gap of the spectroscopy: 1) Au surface state peaks of which energy level is position independent, and 2) a HOMO derived gap state which depend on the registry of the pentacene molecule on the substrate. We expect that these gap states work as a scattering center and change the barrier height between metal contact and organics in the transport measurement. A density functional theory (DFT) calculation confirms our observation. @FootnoteText@ @footnote 1@ Jhinhwan Lee, H. Kim, S.-J. Kahng, G. Kim, Y.-W. Son, J. Ihm, H. Kato, Z. W. Wang, T. Okazaki, H. Shinohara and Young Kuk, Nature (London) 415, 1005 (2002)@footnote 2@ Jascha Repp, Gerhard Meyer, Sladjana M. Stojkovic´, Andre´ Gourdon and Christian Joachim, Phys. Rev. Lett. 94, 026803 (2005)