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O: Fachverband Oberflächenphysik

O 44: Ultrafast Electron Dynamics II (joint session O/MA)

O 44.10: Vortrag

Dienstag, 17. März 2020, 13:15–13:30, WIL B321

Temperature effects on the electron dynamics of metal-organic interface states — •Klaus Stallberg¹, Masahiro Shibuta^1,2, and Ulrich Höfer¹ — ¹Fachbereich Physik, Philipps Universität Marburg, Germany — ²Keio Institute of Pure and Applied Sciences, Keio University, Yokohama, Japan

The presence of electronic interface states (IS) can strongly affect the electron dynamics at organic/metal interfaces. In particular, IS mediated charge transfer has been observed for model systems comprising few layers of π-conjugated organic molecules on single-crystalline metal surfaces. The formation of Shockley derived IS is well understood in the meantime and experimentally observed properties, such as the free-electron-like momentum dispersion as well as the energy onset, are well reproduced by ab initio calculations. In contrast, the IS electron dynamics eludes a consistent theoretical description so far, and systematic experimental studies are still missing.

Here, we systematically investigate temperature effects on the formation and the relaxation dynamics of the IS for the organic/metal systems NTCDA/Ag(111) and PTCDA/Ag(111). Using two-photon photoemission (2PPE), we observe a pronounced decrease of the IS energy for increasing temperatures, which we attribute to an extended molecule-metal binding distance due to phonons in the molecular layer. Moreover, a drastic increase of the IS lifetime with temperature is found. While it can qualitatively be explained with a reduced phase space for electron scattering with metal bulk states, this temperature effect is much stronger than expected from a simple physical model.