Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 77: Focus Session: Structural Dynamics in Nanoscale Materials Probed by Ultrashort Electron Pulses

O 77.5: Talk

Thursday, March 19, 2015, 12:15–12:30, MA 005

Structural dynamics in 2D semiconductors probe by ultrafast electron diffraction. — •Roman Bertoni, Lutz Waldecker, and Ralph Ernstorfer — Structural & Electronic Surface Dynamics, Fritz-Haber-Institut der MPG, Berlin, Germany

Femtosecond electron diffraction is known to be a powerful tool to study the interaction of lattice and electrons in two-dimensional systems during out-of-equilibrium dynamics. Recently, a new class of materials, transition metal dichalcogenide (TMDC), appears promising in order to build nanoscale devices.

We excite a nanometric thin film of WSe2 in resonance with an excitonic band and probe the resulting structural dynamics with ultrafast electron diffraction. We also use complementary technics implying femtosecond optical spectroscopy. By doing so, we address the impact of excitonic excitations onto the lattice and the electron-phonon coupling. Our results reveal an energy transfer from the electronic system to the lattice on picosecond time scale. In parallel, we observe a coherent structural response via the instantaneous activation of coherent phonon.