Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 63: Scanning Probe Microscopy and Spin Phenomena

O 63.4: Talk

Wednesday, March 9, 2016, 16:30–16:45, H4

Voltage-dependent rotational motion of Phthalocyanine molecules — •Andreas Krönlein, Jens Kügel, Paolo Sessi, and Matthias Bode — Physikalisches Institut, Experimentelle Physik II, Universität Würzburg, 97074 Würzburg, Germany

Single particle manipulation offers unique possibilities to tune the electronic properties of molecular and atomic assemblies and thereby opens new pathways for future electronic devices. Therefore, the understanding of the underlying physical mechanisms is of significant importance. We have performed STM/STS measurements of single transition metal phthalocyanine (TMPcs) molecules adsorbed on van der Waals surfaces. We find a voltage-dependent rotational movement threshold which coincidence with the energy of the lowest unoccupied molecular orbital (LUMO) [1] of the investigated molecules as determined by STS. Spatially resolved measurements reveal a good match between the spatial distribution of the rotational frequency and the LUMO conductance, indicating its strong involvement. We speculate that the rotational motion is, like in other molecules [2,3], a consequence of vibrational modes excited by the relaxation of electrons tunneling into the LUMO. Besides the acquisition of information correlated to the manipulation of TMPc on van der Waals surfaces this technique provides an additional approach for energetically and spatially mapping the LUMO of rotationally unstable systems.
A. Nickel et al., ACS Nano 7, 191 (2013).
A. J. Mayne et al., Chem. Rev. 106, 4355 (2006).
B. C. Stipe et al., Phys. Rev. Lett. 81, 1263 (1998).