In situ scanning tunneling microscopy studies of zinc(II) octaethylporphyrin arrays self-assembled on graphite and Au(111) surfaces in organic solution

Abstract

We have prepared ordered adlayers of Zn(II) octaethylporphyrin (ZnOEP) molecules on highly oriented pyrolytic graphite (HOPG) and Au(111) surfaces in 1,2-dichlorobenzene solution. Packing structures and even internal structure of the molecules on these two substrates have been investigated in situ by scanning tunneling microscopy with the tip being immersed in the organic solution. The ZnOEP molecules have been found to adsorb on the HOPG surface with two pairs of ethyl groups curling down and the other two pairs curling up. This shape is consistent with the molecular geometry in the ZnOEP crystal. Compared to the HOPG substrate, the ZnOEP molecules adsorbed on the Au(111) substrate exhibit a lower resolution, and the order of the molecular adlayer is not as good as that on the HOPG surface due to the strong molecule-substrate interaction.