Phthalocyanines (Pc) are an extensively studied class of molecules due to their chemical and thermal stability and high polarizability. These characteristics make them interesting for potential applications such as molecular electronics (organic light emitting devices, photovoltaic devices, photodetectors) and gas sensing devices. Metal phthalocyanines (MePc) have also been discussed as anode and/or cathode catalysts in fuel cells. Often, these fuel cells are based on a carbon substrate as the support for the catalytically active material.
In order to obtain a better understanding of the possible use of MePc's as catalysts in fuel cells we have studied the adsorption of iron(II) phthalocyanine (FeIIPc) on a model carbon support, namely highly oriented pyrolitic graphite (HOPG). The nature of the adsorbate/substrate and intermolecular interactions and the molecular orientation were studied using x-ray photoelectron spectroscopy (XPS), near edge x-ray absorption fine structure (NEXAFS), and resonant photoemission spectroscopy (RPES). We investigated two types of adsorbate/substrate systems, the monolayer and thick multilayer of FeIIPc deposited on the HOPG substrate. The latter served primarily as a reference system for the former, but the growth of highly ordered organic films, such as seen here, is also of great interest due to the interesting properties of such films.
For the monolayer, our NEXAFS measurements indicate a very weak interaction at the FeIIPc/HOPG interface, in which FePc assumes a flat geometry. Interestingly, this geometry is almost perfectly preserved in the thick film. This circumstance is quite special since substrate-supported organic films typically either grow more disordered with thickness or they assume a different geometry in the multilayer as compared to the monolayer. The notion of a weak interaction is also supported by the RPES results, which exhibit characteristics typical for a weak intermolecular and substrate/adsorbate coupling.
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