Directional ultrafast charge transfer in a WSe2/MoSe2 heterostructure selectively probed by time-resolved SHG imaging microscopy
J.E. Zimmermann, Y.D. Kim, J.C. Hone, U. Höfer, G. Mette
Nanoscale Horizons 5 (2020) 1603
Time-resolved SHG imaging microscopy is used as a new experimental method for investigating ultrafast charge-transfer processes in heterostructures of transition metal dichalcogenides.
Heterostructures of transition metal dichalcogenides (TMD) feature a type-II band alignment which can separate photoexcited electrons and holes into different layers through ultrafast charge transfer. While this charge transfer is essential for potential applications, the underlying mechanisms still remain elusive. Main drawbacks of previous experiments are insufficient time-resolution of the employed microscopy setups and deficiencies of linear optical spectroscopies to address individual layers of the heterostructure selectively.In their new approach, Zimmermann and coworkers have combined the advantages of time-resolved optical second-harmonic generation (SHG) with an optical microscopy setup. On the one hand, their method allows for pump-probe experiments in µm small structures with a superior time-resolution. On the other hand, the tensorial nature of the second-order nonlinear susceptibility allows them to distinguish the response from differently oriented layers to elucidate directional interlayer charge transfer as demonstrated for a rotationally mismatched WSe2/MoSe2 heterostructure. As their results show, the new approach is particularly suited to perform systematic investigations of the charge transfer in dependence of the rotational layer mismatch in TMD heterostructures.