Growth of tetraphenyl-porphyrin thin films on Ag(111)

•The growth of 2H-TPP on Ag(111) follows Stranski-Krastanov mode with a three monolayer (ML) thick wetting layer.•The optical properties of the wetting layer differ substantially from each other and from those of 3D crystals.•Two dimensional J-aggregates are formed in the 2H-TPP wetting layer.•Novel optical properties can be introduced by self assembly of organic molecules on surfaces.

The growth of tetraphenyl-porphyrin (2H-TPP) thin films on Ag(111) has been investigated in situ using differential reflectance spectroscopy (DRS) and low energy electron diffraction (LEED). Based on the evolution of the optical properties during deposition, the growth of 2H-TPP on Ag(111) can be assigned to follow the Stranski-Krastanov mode with a three monolayer (ML) thick wetting layer. The optical properties of the first three monolayers differ substantially from each other and from those of 3D crystallites grown on top of the wetting layer. This observation is assigned to the formation of two dimensional J-aggregates in the 2H-TPP wetting layer. The results illustrate how self assembly of organic molecules on surfaces can introduce novel optical properties.