Tuning and Tracking of Coherent Shear Waves in Molecular Films
Lemke, Henrik Till; Breiby, Dag Werner; Ejdrup, Tine; Hammershøj, Peter; Cammarata, Marco; Khakhulin, Dmitry; Rusteika, Nerijus; Adachi, Shin-Ichi; Koshihara, Shinya; Kuhlman, Thomas Scheby; Mariager, Simon Oddsson; Nielsen, Thomas Nørskov; Wulff, Michael; Sølling, Theis Ivan; Harrit, Niels; Feidenhans'l, Robert; Nielsen, Martin Meedom
Journal article, Peer reviewed
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Original versionACS Omega. 2018, 3 (8), 9929-9933. 10.1021/acsomega.8b01400
in ﬁlms as response to femtosecond and picosecond laser pulse heating by timeresolved X-ray diﬀraction. This method allows a direct absolute determination of the molecular displacements induced by electron−phonon interactions, which are crucial for, for example, charge transport in organic electronic devices. We demonstrate that two diﬀerent modes of coherent shear motion can be photoexcited in a thin ﬁlm of organic molecules by careful tuning of the laser penetration depth relative to the thickness of the ﬁlm. The measured response of the organic ﬁlm to impulse heating is explained by a thermoelastic model and reveals the spatially resolved displacement in the ﬁlm. Thereby, information about the proﬁle of the energy deposition in the ﬁlm as well as about the mechanical interaction with the substrate material is obtained.