Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 10: Metal substrates: Adsorption of organic / bio molecules II

O 10.6: Vortrag

Montag, 14. März 2011, 16:15–16:30, TRE Phy

Scanning tunneling spectroscopy and microscopy of α-sexithiophene films on Au(100) — •Rene Hammer, Anke Höfer, Klaus Duncker, and Wolf Widdra — Martin-Luther-Universität Halle-Wittenberg, Institute of Physics, Halle(Saale), Germany

The electronic and the structural properties of epitaxially grown ultrathin films of α-sexithiophene (6T) on Au(100) have been studied by scanning tunneling spectroscopy (STS) and microscopy (STM) at 80 K. The structure of the well-ordered first monolayer grown at 300 K and then cooled to 80 K is nearly identical to the structure reported at 300 K [1]. Subsequent growth proceeds layer-by-layer with flat-lying 6T molecules forming parallel molecular rows also in the second monolayer. Two rotational domains with an angle of 14^∘ in between are found. The row direction in the second monolayer is parallel to the rows of the first layer underneath. STS spectra of the first and second 6T monolayer allow the determination of the lowest unoccupied molecular orbital (LUMO) at 1.2 eV, the LUMO+1 at 1.8 eV and the LUMO+2 at 2.4-2.5 eV with respect to the Fermi level. Additionally the second monolayer exhibits a strong STS feature at 2.15 eV. The highest occupied molecular orbital (HOMO) is found at -1.0 and -1.5 eV for the first and second monolayer, respectively. Mapping of the differential conductivity gives hints to the electron density within these orbitals which will be compared to calculated wavefunctions.

[1] A. Höfer, K. Duncker, M. Kiel, S. Wedekind, and W. Widdra, Phys. Rev. B (submitted)