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Claus Ropers

Materials Physics Institute and Courant Research Centre Physics, University of Göttingen

Ultrafast Low-Energy eEectron Diffraction Using Nanotip Emitters

Ultrafast structural dynamics in solids and nanostructures can be investigated by an increasing number of sophisticated electron and x-ray diffraction techniques. Despite successful implementations of ultrafast reflection high-energy electron diffraction, the time-resolved diffractive probing of structural processes at surfaces remains an experimental challenge.

We have recently implemented ultrafast low-energy electron diffraction (ULEED) to study structural changes with high temporal resolution and ultimate surface sensitivity, at electron energies from 100 eV to 500 eV. We utilize nanoscopic needle emitters in an electrostatic lens geometry as high-brightness sources of pulsed electrons. The spatial confinement of the source is realized by the local enhancement of nonlinear photoemission at the tip apex.

In this talk, the benefits of nanoscopic cathodes for ultrafast diffraction studies will be introduced, and first time-resolved data will be presented. Specifically, the ultrafast melting dynamics of ordered adsorbate structures on freestanding graphene is investigated in transmission with a temporal resolution below 5 ps. Finally, future improvements of the approach will be discussed.

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