Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 101: Focus Session: Structural Dynamics in Nanoscale Materials, Probed by Ultrafast Electron Pulses II

O 101.5: Vortrag

Donnerstag, 15. März 2018, 16:45–17:00, HE 101

Ultrafast structural dynamics of transition metal dichalcogenide heterostructures — •Daniela Zahn, Thomas Vasileiadis, Lutz Waldecker, and Ralph Ernstorfer — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany

Vertical heterostructures of two-dimensional crystals offer intriguing new perspectives for the fabrication of novel nanodevices [1]. Since all devices are operated in non-equilibrium conditions, interactions between the different degrees of freedom play an important role in their functionality. These interactions can be studied using femtosecond pump-probe techniques. In particular, femtosecond electron diffraction allows to directly observe the structural response to photoexcitation [2]. Electron-phonon and phonon-phonon coupling as well as electronic and vibrational coupling across interfaces can be studied.

We focus on heterostructures with staggered (=type II) band alignment. This particular band alignment leads to photo-induced charge separation across the interface and is therefore interesting for many applications, e.g. photovoltaic devices. We present a study on multilayer WSe2/WS2 heterostructures using two different excitation wavelengths. Different dynamics are observed, suggesting that the interfacial carrier transfer depends on the initial hot carrier distribution in k-space.

[1] A. Geim, I.V. Grigorieva, Nature 499, 419-425 (2013).

[2] L. Waldecker, R. Bertoni, R. Ernstorfer, JAP 117, 044903 (2015).

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