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High Hole-Mobility Molecular Layer Made from Strong Electron Acceptor Molecules with Metal Adatoms

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journal contribution
posted on 18.10.2017, 00:00 by Hiroyuki Yamane, Nobuhiro Kosugi
The electronic structure of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-TCNQ (F4TCNQ) monolayers on Au(111) has been investigated by means of angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. In contrast to the physisorbed TCNQ/Au(111) interface, the high-resolution core-level photoemission spectra and the low-energy electron diffraction at the F4TCNQ/Au­(111) interface show evidence for the strong charge transfer (CT) from Au to F4TCNQ and for the Au atom segregation from the underlying Au(111) surface, suggesting a possible origin of the spontaneous formation of the two-dimensional F4TCNQ-Au network. The ARPES experiment reveals a low hole-injection barrier and large band dispersion in the CT-induced topmost valence level of the F4TCNQ-Au network with 260 meV bandwidth due to the adatom-mediated intermolecular interaction. These results indicate that strong electron acceptor molecules with metal adatoms can form high hole-mobility molecular layers by controlling the molecule–metal ordered structure and their CT interaction.