Scanning Tunneling Microscopy Investigation of Ordered Iron Phthalocyanine Molecules on Ag(111)

A well-ordered, molecular thin films (about 0.5 monolayers) of iron phthalocyanine (FePc) on Ag(111) has been investigated using a scanning tunneling microscopy. The room temperature deposition, followed by 30 minutes of annealing up to 475 K results in well-ordered islands of FePc molecules which form a two-dimensional, oblique lattice. The overlayer lattice vectors a₁ and b₁ are 16.2 å each with the angle of 80 between the lattice vectors. The FePc overlayer lattice is commensurate to the substrate lattice with the relationship of a₁ = 6a - b and b₁ = -a + 6b, with a and b are the Ag(111) lattice vectors. Furthermore, FePc molecules at the opposite corners within the unit cell align their isoindole rings at each other, significantly increasing the nearest and the next-nearest neighbor distances in the overlayer. The commensurate overlayer lattice structure and the distinct molecular orientation within the unit cell are attributed to the molecule-surface interaction via the Fe 3d_xz,yz and Ag 4d_xz,yz orbitals.