Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 90: Methods: Scanning Probe Techniques II

O 90.1: Vortrag

Freitag, 29. Februar 2008, 10:15–10:30, MA 042

Multiple distance scanning tunneling spectroscopy of organic layers — •Christian Wagner and Torsten Fritz — Institut für Angewandte Photophysik, TU-Dresden, George Bähr Str. 1, 01069 Dresden

Scanning tunneling spectroscopy (STS) has been proven to be a powerful tool to investigate the energetic position of electronic states of organic molecules adsorbed on conductive surfaces. Since already the front orbitals are typically situated 1 to 2 eV below and above the substrate’s Fermi energy, one inherent problem is the need to apply equivalently high voltages, which might in turn damage the rather sensitive organic layer. One technique which is able to limit the electric field strength is the multiple distance STS, where several I- V spectra are recorded subsequently at a fixed lateral position while increasing the tip sample distance and voltage range from one spectrum to the next [1]. In our contribution we want to discuss the applicability of this method to organic adsorbates on the example of unsubstituted quaterrylene on Au, a molecule which has a large π-system and a comparably small HOMO-LUMO gap. We answer the question whether the multiple distance STS can be combined with a DOS calculation via the 1D WKB model [2]. As this method allows including the tip sample distance directly into the evaluation process, one could calculate an unambiguous sample DOS from the multiple I- V curves.

[1] R. M. Feenstra and J. A. Stroscio, J. Vac. Sci. Technol. B 5, 923 (1987)

[2] C. Wagner et al., Phys. Rev. B 75, 235432 (2007)