Regensburg 2016 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 17: Adsorption on Metal Surfaces
O 17.5: Vortrag
Montag, 7. März 2016, 16:00–16:15, H6
Line shapes of C60 vibrational modes in inelastic electron tunnelling spectroscopy — •Stefan Meierott, Nicolas Néel, and Jörg Kröger — Institut für Physik, Technische Universität Ilmenau, D-98693 Ilmenau, Germany
Tunnelling contacts comprising W tips coated with Pb and terminated by single C60 molecules as well as pristine and C60-covered Pb(111) surfaces were investigated with a low-temperature scanning tunnelling microscope. The junctions exhibited C60 vibrational signatures, which were previously observed [1]. While Pb-coated W tips led to peak-like line shapes of the vibrational modes in inelastic tunnelling spectra [1] C60-terminated tips gave rise to Fano-type profiles. In agreement with previous calculations [2] we assign the Fano-type line shape to the electronic structure of the C60-terminated tip. The lowest unoccupied molecular orbital (LUMO) of C60 at the tip apex covered the range of vibrational energies, which was identified as a prerequisite for observing Fano-type line shapes [2]. To test the proposed scenario, the LUMO energy of C60 attached to the tip was deliberately modified, presumably owing to different adsorption geometries at the tip apex [3]. Upon moving the LUMO energy farther away from the Fermi level and concomitantly avoiding its overlap with vibrational energies, the peak-like structures in the vibrational spectra were recovered. Financial support by the DFG through KR 2912/7-1 is acknowledged.
[1] K. J. Franke et al., J. Phys. Chem. Lett. 1, 500 (2010).
[2] A. Baratoff et al., J. Vac. Sci. Technol. A 6, 331 (1988).
[3] G. Schull et al., New J. Phys. 10, 065012 (2008).