Twist-Angle-Dependent Ultrafast Charge Transfer in MoS₂-Graphene van der Waals Heterostructures

Abstract

Vertically stacked transition metal dichalcogenide-graphene heterostructures provide a platform for novel optoelectronic applications with high photoresponse speeds. Photoinduced nonequilibrium carrier and lattice dynamics in such heterostructures underlie these applications but have not been understood. In particular, the dependence of these photoresponses on the twist angle, a key tuning parameter, remains elusive. Here, using ultrafast electron diffraction, we report the simultaneous visualization of charge transfer and electron−phonon coupling in MoS 2 -graphene heterostructures with different stacking configurations. We find that the charge transfer timescale from MoS 2 to graphene varies strongly with twist angle, becoming faster for smaller twist angles, and show that the relaxation timescale is significantly shorter in a heterostructure as compared to a monolayer. These findings illustrate that twist angle constitutes an additional tuning knob for interlayer charge transfer in heterobilayers and deepen our understanding of fundamental photophysical processes in heterostructures, of importance for future applications in optoelectronics and light harvesting.

Direct view of phonon dynamics in atomically thin MoS$_{2}$

“…the observed Debye-Waller decay of Bragg peak intensities) in the case of 1L-MoS 2 on sapphire is slower than reported here, 37,38 while the opposite is true for 1L-MoS 2 on SiO 2 . 39 This is as expected based on the dielectric constants of these substrate materials, providing additional evidence in support of our conclusions regarding dielectric screening of the electron-phonon interaction in 1L-MoS 2 .…”

“…[29][30][31][32][33] To date, experimental investigations of EPC effects and nonequilibrium phonon dynamics in monolayer and few-layer TMDs have been limited to what can be learned about zone-centered optical phonons via conventional and time-resolved Raman spectroscopy [34][35][36] or averaged atomic meansquared displacements via UED. [37][38][39] The momentum selectivity of phonon emission and the time-dependent anisotropic phonon populations, expected throughout the Brillouin zone (BZ) of TMDs, 21,26 is hidden from view with these techniques. By contrast, UEDS provides momentum-resolved information on EPC and its modification due to (i) the dielectric environment, (ii) nonequilibrium phonon relaxation in 1L-MoS 2 (including anharmonic decay within the monolayer), and (iii) phonon transport to the underlying substrate as we show here.…”

Atomic‐Level Design of Active Site on Two‐Dimensional MoS2 toward Efficient Hydrogen Evolution: Experiment, Theory, and Artificial Intelligence Modelling

“…As for moiré superlattice, the twist angles and interlayer spacing are two key parameters that determined the physicochemical properties. [233] It is urgently needed to systematically discuss the interaction between two layers to find out the potential relation and properties evolution trend that is of great significance to develop the application of moiré superlattice in catalysis. Liu et al have discussed the interlayer coupling evolution in twisted MoS 2 bilayers which may be instructive to further relevant research in moiré superlattice.…”

Ultrafast Electron Diffraction: Visualizing Dynamic States of Matter

“…The changes in lattice and charge order that is associated with the transformation can now be followed in remarkable detail with UED, as is illustrated by the example below. Thanks to the strong interaction of electrons with the lattice even monolayer (He et al, 2020;Mannebach et al, 2015) and few-layer heterostructures (Luo et al, 2021) are accessible.…”