A scanning tunneling microscopy study on the effect of post-deposition annealing of copper phthalocyanine thin films

Using scanning tunneling microscopy, overlayer lattice structures and thin film morphology of copper phthalocyanine (CuPc) have been investigated while varying posterior, annealing temperatures. The room temperature deposition of CuPc on Ag(1 1 1) resulted in ordered domains, which were three molecular layers high and separated with disordered regions. The ordered surface also exhibited an oblique lattice with the lattice constants of 13.3 Å and 16.4 Å and the angle of 74° between the two. By annealing the thin films systematically to 580 K, the symmetry of overlayer lattice increased from the oblique to the square lattice, commonly observed on various substrates. Further annealing to 780 K desorbed much of the CuPc molecules. However, the remaining molecules reacted and formed dendrite-like chains, in which each CuPc molecule was linked through its isoindole rings. A possible model for the formation of dendritic chains through polymerization is discussed.