Structure and Phonons of Heteroepitaxial Stacks of Weakly Interacting 2D Materials and Molecular Layers

Summary

The normal incidence x-ray standing wave technique can measure the absolute vertical positions of atoms and molecules at single crystalline surfaces with unrivalled accuracy (typical error 0.05 Å). The method does not require lateral ordering. It yields vertical “adsorption” heights with chemical sensitivity. This allows the determination of structural distortions, and thus conclusion regarding the chemical bonding at the interface can be reached. As an example, the vertical distance allows a clear-cut distinction between pure van der Waals and chemical bonding at the interface, and moreover even the strength of the van der Waals bonding can be gauged. This capability will be exploited to investigate heteroepitaxial stacks of weakly interacting 2D materials, consisting e.g. of graphene, hexagonal BN, and transition metal dichalcogenides, and molecular adsorbates on them. In addition, we will employ high-resolution electron energy loss spectroscopy to investigate the vibrational properties of these stacks. In particular, a new spectrometer, developed in our institute, allows the efficient measurement of the full phonon dispersion with high resolution both in energy and k-space for these interface-determined materials.

Project-related publications

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