  Iron phthalocyanine (FePc) molecules were investigated on the topological
insulator surface Bi2Se3 using scanning tunneling microscopy (STM) and
spectroscopy (STS) at 77 K in ultra high vacuum (UHV). Sub-molecular resolution
STM images provide the atomic scale registry of the adsorption site of the
molecules, on-top or bridge, with reference to the top surface Se atoms of the
Bi2Se3 surface. STS data reveal a slight shift in the HOMO and LUMO orbitals of
the FePc molecules with respect to the specific binding site. Close to Fermi
energy the STS measurements show that the Dirac point of Bi2Se3 remains
unchanged after depositing FePc molecules. This is indicative of the protection
of the topological insulator surface state (TISS). We speculate that though the
Fe atom has magnetic properties, the ligands attached to Fe in the Pc ring
influence the magnetic behavior of the molecule upon adsorption on the Bi2Se3
substrate. Our work puts forth an example to advance the strategic platform for
tuning the TISS interfaces with different molecules and for designing surfaces
and interfaces with time reversal symmetry protected magnetic textures.
