Unconventional post-deposition chemical treatment on ultra-thin H2TPP film grown on graphite

Free-base H2TPP porphyrin layers have been grown on highly oriented pirolitic graphite by organic molecular beam epitaxy. The growth follows a Stranski-Krastanov (SK) mode, as observed by atomic force microscopy (AFM), showing 3D porphyrin structures above a single flat porphyrin layer, which can be considered as an organic wetting layer. The 3D phase precludes a priori the possibility of studying and exploiting the physical-chemical properties of the pure 2D phase. Here we describe a promising post growth strategy to overcome the limitations imposed by the SK film evolution. We are able to reduce the number of 3D structures on the surface without perturbing the porphyrin wetting layer, as experimentally observed by AFM and optical spectroscopy. The strategy described in this work is fully generalizable and, in principle, could be extended to other free-base porphyrinic compounds.