CRC 1772/1: Linking structure and collective excitations of mol2Dmat heterostructures by fast electrons (SP A05)

Molecules on 2D systems are typically not as homogeneous, as depicted in the cartoons that illustrate them. For understanding the fundamental materials properties of these heterostructures it is thus essential that one is able to correlate the structure of the system from the atomic to the μmscale with the local electrostatic, electronic, vibrational, and plasmonic properties and the response to optical excitations on one and the same location of the sample with high spatial selectivity. Aberration-corrected momentum-resolved electron microscopy in combination with highly monochromated electron energy-loss spectroscopy (EELS) make this possible. Elastic and inelastic interaction of fast electrons with materials are highly local and very effective probes of the local atomic and electronic structure, as well as electric fields and can also be used to probe the local response to electromagnetic, thermal, mechanical, and chemical stimulation. However, inelastic interaction of electrons with the probed volume may also induce damage, especially in organic materials, which we will therefore minimize with elaborate novel schemes as outlined below.
Key objective of this project is to provide this correlative information for a number of systems studied within the CRC: Polyhalides and dyes intercalated in graphene and nanotubes, strongly doped graphene by means of molecular charge transfer, superradiant systems such as MePTCDI on hBN, or graphene and others. One challenge will be to obtain this information at high spatial resolution while ensuring that the material is not altered by the electron beam. For this purpose, dose efficient approaches will be implemented for mapping electrostatic charges by electron ptychography, for mapping vibrational, electronic, and plasmonic excitations by EELS, and for mapping the response
to optical excitations by electron energy-gain spectroscopy (EEGS). Ptychography is a computational imaging technique using diffraction patterns from overlapping regions to recover phase information. Building on methodical know-how developed within the group, we will further develop and apply electron-beam-based techniques to gently probe and correlate the atomic structure, local electrostatic fields, vibrational resonances, and the response to optical excitations of organic/2D material heterostructures. We will compare the results to theoretical predictions and
complementary experimental techniques applied within the CRC.