Studies of the adsorption of tetraphenylporphyrin molecules on graphite

Combined scanning tunneling microscopy, reflection electron energy loss spectroscopy and X-ray photoelectron studies have been performed in situ under ultra high vacuum condition, on tetraphenylporphyrin molecules (H2TPP) vacuum sublimated on highly oriented pyrolitic graphite. The experimental studies were performed at room temperature, as a function of the amount of deposited porphyrins.The propensity of H2TPP to self-assembly on the graphite surface could be detected after a threshold of deposited material. In this case tetraphenylporphyrin molecules arranged according to a quasi-hexagonal lattice separated from their nearest neighbours by a minimum distance of about 1 nm. The formation of an additional incomplete layer, at a slightly higher coverage, was also detected where the quasi-hexagonal symmetry is retained. Finally, subsequent tetraphenylporphyrins depositions gave molecular aggregates randomly distributed on the graphite surface with subsequent loss of order.