Regensburg 2013 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 89: Surface Dynamics II

O 89.6: Vortrag

Freitag, 15. März 2013, 11:45–12:00, H33

Long lived electrons trapped in amorphous ice adsorbed on Cu(111) — •Daniel Wegkamp, Michael Meyer, Clemens Richter, Julia Stähler, and Martin Wolf — Fritz-Haber-Institute of the MPG, Dep. of Physical Chemistry, Berlin

In polar environments excess charges are stabilized by reorientation of the surrounding dipoles. We have studied the trapping of excess electrons and their subsequent dynamics in amorphous solid water (ASW) adsorbed on a Cu(111) surface. The electrons are excited in the metal with ultraviolet (UV) femtosecond laser pulses and injected into 20 to 35 bilayer (BL) thick ASW layers. Their stabilization and relaxation dynamics are probed by time-resolved photoemission spectroscopy. In contrast to previous studies on thin (< 7 BL) ASW layers where subpicosecond lifetimes have been reported [1] we observe 14 orders of magnitude longer lifetimes. These electrons reside in an excited state between 2 and 3 eV above the metal’s Fermi level for tens of seconds. The binding sites of the trapped electrons are located at the ice-vacuum interface, as their spectroscopic signature is affected strongly by a co-adsorbed Xe-overlayer. Furthermore, we have studied the changes of workfunction and occupied electronic structure induced by UV irradiation and discuss possible origins.

[1] J. Stähler et al., Chem. Soc. Rev. 37 (2008) 2180