LOW-ENERGY-ELECTRON TRANSMISSION SPECTROSCOPY OF THIN-FILMS OF CHLOROALUMINUM PHTHALOCYANINE ON MOS2

The growth of chloroaluminum phthalocyanine (CIAIPc) thin films on MoS 2 surfaces was studied by low-energy electron transmission (LEET) spec troscopy. We observed that the as-grown monolayer, prepared by vacuum deposition, consists of islands of CIAIPc multilayers and the molecule s spread over the substrate surface to form a uniform monolayer by hea t treatment. Furthermore, we found that for heat-treated films the vac uum level of the sample system oscillates with increasing the film thi ckness from 0 to 2 monolayers. For the monolayer, the change of the va cuum level with respect to the substrate Delta phi(=phi(film)-phi(subs trate)) was positive, while for the doublelayer it was negative. These results indicate that in the monolayer the molecules lie flat with th e Cl atoms protruding outside the film to form an electric dipole laye r directing to the substrate, and in the doublelayer the molecules in the outer layer are turned over with the Cl atoms protruding inside th e film to compensate the dipole originating from the first monolayer. Furthermore the thickness independent characteristics of LEET spectra above the doublelayer suggest that thicker films consist of a stack of a double layer-like structures.