Imaging Surface Acoustic Wave Dynamics in Semiconducting Polymers by Scanning Ultrafast Electron Microscopy
Understanding the mechanical properties of organic semiconductors is essential to their electronic and photovoltaic applications. Despite a large volume of research directed toward elucidating the chemical, physical and electronic properties of these materials, little attention has been directed toward understanding their thermo-mechanical behavior. Here, we report the ultrafast imaging of surface acoustic waves (SAWs) on the surface of the Poly(3-hexylthiophene-2,5-diyl) (P3HT) thin film at the picosecond and nanosecond timescales. We then use these images to measure the propagation velocity of SAWs, which we then employ to determine the Young's modulus of P3HT. We further validate our experimental observation by performing a semi-empirical transient thermoelastic finite element analysis. Our findings demonstrate the potential of ultrafast electron microscopy to not only probe charge carrier dynamics in materials as previously reported, but also to measure their mechanical properties with great accuracy. This is particularly important when in situ characterization of stiffness for thin devices and nanomaterials is required.
Additional Information© 2017 Elsevier B.V. Received 23 January 2017, Revised 14 August 2017, Accepted 20 August 2017, Available online 24 August 2017. This work was supported by NSF grant DMR-0964886 and Air Force Office of Scientific Research grant FA955011-1-0055 in the Physical Biology Center for Ultrafast Science and Technology at California Institute of Technology, which is supported by the Gordon and Betty Moore Foundation. Author contributions: The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
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