Dresden 2026 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 58: Organic molecules on inorganic substrates: Adsorption and growth III

O 58.6: Vortrag

Mittwoch, 11. März 2026, 11:45–12:00, TRE/PHYS

Mirror domains and adsorption induced dipoles in organic semiconductor films revealed by LEEM and µLEED — •Franz Niklas Knoop, Klaus Stallberg, and Winfried Daum — Institute of Energy Research and Physical Technologies, TU Clausthal, Germany

We apply low-energy electron microscopy (LEEM) and microspot low-energy electron diffraction (µLEED) to study the film growth of nonpolar para-sexiphenyl (p-6P) molecules on natively oxidized silicon. In their second monolayer, the molecules form µm-sized, 2D-crystals with a bulk-like unit cell. LEEM reveals dark lines that split individual islands along their long axis into two domains of roughly equal size. The corresponding diffraction patterns are laterally shifted relative to each other, allowing for dark-field imaging of each domain. We attribute this apparent shift in k-space to the presence of lateral electric fields pointing in opposite directions on either side of an island. Given p-6P’s large polarizability, we ascribe these fields to induced electric dipole moments in the tilted molecules. Thus, the observed dark lines represent boundaries between adjacent domains of mirrored tilt. Since the shift in k-space is independent of the LEEM extractor field, the dipoles must be inherent to the adsorbed molecules on the Si substrate. We observe an increased work function for the second-layer islands compared to the substrate. This and temperature-dependent measurements support our conclusion that adsorption-induced charge transfer causes the polarization of the molecules.

Keywords: LEEM; LEED; organic semiconductor