KPFM and DFT as tools to correlate the charge distribution and molecular orientation of dendritic adsorbates on different surfaces

Abstract

The interaction between metals and organic layers is currently a hot topic due to its relevance in future applications based on hybrid organic/inorganic systems at the nanoscale. This work studies the surface modification of HOPG and gold substrates by spontaneous adsorption of aryl-dendrons based on either 3,5-bis(3,5-dinitrobenzoylamino) or 3,5-bis(3,5-diaminobenzoylamino) benzoic acids at fully controlled conditions. KPFM is used to assess the local work function variations upon assembly. A correlation between changes in work function values and spatial ordering of the adsorbates is observed. The aryl-dendrons interact with graphite surfaces through π-π stacking, allowing the formation of ordered layers. Due to depolarization effects, these films cause changes in the local work function values that are smaller on graphite surfaces than on gold substrates. Furthermore, the presence of molecular aggregates driven by intermolecular hydrogen bonding for the case of amino functionalized surfaces has a direct impact on the local work function, which varies depending on whether the areas are partially covered or densely packed. DFT calculations were performed in order to gain a deeper understanding of the correlation between the work function variations and the orientation of the effective molecular dipole moment due to the underlying molecular structures of the adsorbed layer.