title: Adsorption-induced intramolecular dipole: correlating molecular conformation and interface electronic structure.
abstract: The interfaces formed between pentacene (PEN) and perfluoropentacene (PFP) molecules and Cu(111) were studied using photoelectron spectroscopy, X-ray standing wave (XSW), and scanning tunneling microscopy measurements, in conjunction with theoretical modeling. The average carbon bonding distances for PEN and PFP differ strongly, that is, 2.34 A for PEN versus 2.98 A for PFP. An adsorption-induced nonplanar conformation of PFP is suggested by XSW (F atoms 0.1 A above the carbon plane), which causes an intramolecular dipole of approximately 0.5 D. These observations explain why the hole injection barriers at both molecule/metal interfaces are comparable (1.10 eV for PEN and 1.35 eV for PFP) whereas the molecular ionization energies differ significantly (5.00 eV for PEN and 5.85 eV for PFP). Our results show that the hypothesis of charge injection barrier tuning at organic/metal interfaces by adjusting the ionization energy of molecules is not always readily applicable.
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Physik, Newtonstrasse 15, 12489 Berlin, Germany. norbert.koch@physik.hu-berlin.de
authors.forename: Norbert
authors.initials: N
authors.lastname: Koch
authors.forename: Alexander
authors.initials: A
authors.lastname: Gerlach
authors.forename: Steffen
authors.initials: S
authors.lastname: Duhm
authors.forename: Hendrik
authors.initials: H
authors.lastname: Glowatzki
authors.forename: Georg
authors.initials: G
authors.lastname: Heimel
authors.forename: Antje
authors.initials: A
authors.lastname: Vollmer
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Sakamoto
authors.forename: Toshiyasu
authors.initials: T
authors.lastname: Suzuki
authors.forename: Jörg
authors.initials: J
authors.lastname: Zegenhagen
authors.forename: Jürgen P
authors.initials: JP
authors.lastname: Rabe
authors.forename: Frank
authors.initials: F
authors.lastname: Schreiber