In a new publication in ACS Nano, Zimmermann and coworkers investigate ultrafast charge-transfer processes in twisted heterostructures of transition metal dichalcogenides by means of time-resolved SHG imaging microscopy.
Two-dimensional heterostructures of transition metal dichalcogenides (TMDC) represent very well-defined and at the same time highly versatile model systems of van-der-Waals interfaces. Many material combinations feature a type-II band alignment, which can separate photoexcited electrons and holes into different layers through ultrafast charge transfer leading to the formation of so-called interlayer excitons. Since the coupling within these structures depends considerably on the layer stacking, a strong influence of the interlayer twist on the ultrafast charge-transfer, recombination and other properties of the interlayer excitons has been expected.
In their study, Zimmermann and coworkers have employed time- and polarization-resolved second-harmonic imaging microscopy to investigate the ultrafast charge-carrier dynamics across the MoS2/WSe2 heterostructure interface for different stacking configurations. The excellent time resolution made it possible to identify stacking-dependent differences in the ultrafast charge transfer that were not accessible in previous approaches. For lower excitation energies of 1.70 eV, ultrafast electron transfer from WSe2 to MoS2 is found to depend considerably on the stacking angle and the transfer time is reduced by a factor of seven when going from a larger rotational mismatch towards 2H-stacking. At higher excitation energies, hole transfer processes from MoS2 to hybridized states at the Γ-point and to the K-points of WSe2 have to be considered in addition. The respective decay dynamics, however, does not show a significant dependence on the stacking angle indicating that radiative recombination of indirect Γ-K excitons becomes the dominant decay route for all samples.
J.E. Zimmermann, M. Axt, F. Mooshammer, P. Nagler, C. Schüller, T. Korn, U. Höfer, G. Mette
Ultrafast Charge-Transfer Dynamics in Twisted MoS2/WSe2 Heterostructures
ACS Nano (2021) DOI:10.1021/acsnano.1c04549
Dr. Gerson Mette
SFB 1083 subproject B5
Tel.: 06421 28-24123