AVS 53rd International Symposium
    Surface Science Wednesday Sessions
       Session SS2+EM-WeA

Paper SS2+EM-WeA7
Epitaxial Nanolayers of Organic Small Band Gap Semiconductors: Growth and Electronic Properties of Quaterrylenes on Au

Wednesday, November 15, 2006, 4:00 pm, Room 2004

Session: Organic Film Growth and Characterization
Presenter: R. Franke, TU Dresden, Germany
Authors: R. Franke, TU Dresden, Germany
C. Wagner, TU Dresden, Germany
S. Franke, TU Dresden, Germany
S.C.B. Mannsfeld, Stanford University
F. Fritz, TU Dresden, Germany
Correspondent: Click to Email
The understanding of the physical properties of organic thin films is of importance for their application in novel devices. Thin films grown by the Organic Molecular Beam Epitaxy technique often exhibit highly ordered layer structures. Their physical structure is usually governed by a fine balance between weak molecule-molecule interactions and a small lateral variation of the molecule-substrate interaction potential. In order to investigate the energetics of such a heteroepitaxial layer system, one has to consider large molecular domains.@footnote 1,2@ Here we report on films of large molecules, namely quaterrylene (QT) and quaterrylenetetracarboxylic-dianhydride-diimide (QTCDI), on Au(111) in UHV. These materials are especially interesting due to their long-wavelength absorption in the NIR. In our combined LEED and STM study we found a point-on-line coincident growth with flat lying molecules for the first monolayer (ML) of QT, while we observe alternating upstanding and flat lying molecules in the second ML.@footnote 3@ In contrast, the arrangement of the QTCDI molecules in the first ML differs strongly, due to the presence of the substituents. We will also show that our experimental results correspond nicely to potential energy calculations on large ordered QT and QTCDI domains. The electronic properties of these ultrathin films were investigated by Scanning Tunneling Spectroscopy. In case of QTCDI we found a HOMO-LUMO gap of 2.1 eV, while we obtained 2.5 eV for the smaller QT. The comparison to absorbance measurements on mica allows us to estimate the exciton binding energies. @FootnoteText@ @footnote 1@ S.C.B. Mannsfeld and T. Fritz, PRB 93 (2004) 075416.@footnote 2@ S.C.B. Mannsfeld, K. Leo, and T. Fritz, PRL 94 (2005) 056104.@footnote 3@ R. Franke, S. Franke, S.C.B. Mannsfeld, C. Wagner, T. Dienel, and T. Fritz, APL 88, (2006) 161907.