Speaker
Description
Van der Waals crystals enable the construction of arbitrary, atomically precise heterostructures through straightforward layering of different monolayers without requiring covalent bonds or epitaxial matching. Understanding charge and energy transfer mechanisms in these atomically thin, two-dimensional (2D) material interfaces is fundamental to their electronic and electrochemical applications. Earlier research has demonstrated that extremely rapid charge transfer at energetically staggered or type II heterojunctions between 2D semiconductors occurs within tens of femtoseconds after photoexcitation. However, energy dissipation during charge transfer and the interaction of charge carriers with lattice vibrational modes remain inadequately characterized.
In this work, we utilize ultrafast electron diffraction to directly observe lattice behavior within individual monolayers of van der Waals heterojunctions and uncover how layer-hybridized electronic states influence energy and charge transport across atomically sharp interfaces. Through examination of Bragg peak intensity changes following photoexcitation, we monitor interlayer energy transfer, while phonon dynamics are analyzed via diffuse scattering measurements. Supported by first-principles theoretical calculations, our results elucidate how lattice dynamics and electronic state hybridization contribute to ultrafast electronic phenomena at 2D van der Waals heterojunctions.
Reference:
A. Sood, J. Haber, A. Raja et al. "Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer," Nature Nanotechnology 18 (1), 29-35 (2023).
