Initial states of epitaxial growth of vanadyl- and titanyl-phthalocyanines on MoS2 cleaved surfaces

The initial states of epitaxial growth of vanndyl-phthalocyanine (VOPc) and titanyl-phthalocyanine (TiOPc) on MoS2 cleaved surfaces have been investigated, using atomic force microscopy (AFM) and electron energy loss spectroscopy (EELS). In the case of VOPc, formation of the first layer at room temperature which consists of one molecular layer on a MoS2 surface was observed in thr AFM image. In the case elf TiOPc. in contrast, the first layer consisted of two molecular layers formed at room temperature, and the formation of one molecular layer occurred at the annealing at 420 K. These results indicate that the interaction between the VOPc molecule and the MoS2 surface is stronger than that between TiOPc and MoS2. This suggests that the overlap of orbitals of the transition metals at the center of the phthalocyanines with the orbitals of MoS2 substrate creates a large stabilization energy. The results of EELS measurement indicate that the molecular plane of VOPc is parallel to the MoS2 surface, while the molecular plane of TiOPc is inclined. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.