Adsorption of metal-free phthalocyanine on InSb and InAs(001)-4x2/c(8x2) surface

We have studied the adsorption of metal-free phthalocyanine on 4 x 2/c(8 x 2) surface reconstruction of both InSb(001) and InAs(001) surfaces, by means of low-energy electron diffraction and high-resolution electron energy loss spectroscopy. We show that the molecule-surface interaction is stronger in the case of the InAs substrate as compared to the InSb one. Indeed, we observed that at full monolayer coverage, when the molecules are adsorbed on the InAs, and only in that case, there are substantial energy shifts of both the substrate surface plasmon and the first valence exciton of the molecules. These shifts are evidence of charge transfer from the molecules toward the substrate responsible for a strong molecule-substrate interaction such as chemisorption. In spite of the difference between the two substrates, at monolayer completion, H2Pc on InAs and InSb adopts a common (4n x 3) surface arrangement. The same that was already reported for the nonplanar lead and tin phthalocyanines (respectively, PbPc and SnPc) adsorbed on InSb(001).