Visualizing ultrafast lattice dynamics at 2D van der Waals interfaces using femtosecond electron diffraction
Archana Raja, Lawrence Berkeley National Laboratory
Charge and energy transfer processes at the junction of atomically thin, two dimensional (2D) materials are an area of burgeoning interest because van der Waals crystals allow for the creation of arbitrary, atomically precise heterostructures simply by stacking disparate monolayers without the constraints of covalent bonding or epitaxy. At a type II heterojunction between two 2D semiconductors, ultrafast charge transfer has been previously determined to occur on the order of 10’s of femtoseconds after photoexcitation. However, the coupling between the lattice degrees of freedom of the photoexcited monolayers remains less understood. We use ultrafast electron diffraction to directly visualize lattice dynamics in the individual monolayers of the van der Waals heterojunction. We are able to track the transfer of energy from one layer to another by following the change in intensity of the Bragg peaks after photoexcitation. With the aid of first principles calculations, we are able to shed light on the role of lattice dynamics during ultrafast electronic processes at 2D van der Waals heterojunctions.