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 \textbf{a}$_{1}$ and \textbf{b}$_{1 }$are 16.2 {\AA} each with the angle of 80\r{ } between the lattice vectors. The FePc overlayer lattice is commensurate to the substrate lattice with the relationship of \textbf{a}$_{1}$ = 6\textbf{a} - \textbf{b} and \textbf{b}$_{1}$ = -\textbf{a} + 6\textbf{b}, with \textbf{a} and \textbf{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.