Orientation and structure of rnonolayer -> multilayer phthalocyanine thin films on layered semiconductor (MoS2 and SnS2 surfaces

Thin films of both chloroindium and copper pthalocyanines have been vacuum deposited onto metal dichalcogenide surfaces such as MoS2 and SnS2, with ordering achieved for these four-fold symmetric molecules ranging from below monolayer to multilayers. Reflection high-energy electron diffraction suggests that square lattice geometries are adopted for low coverages of each phthalocyanine (Pc), but with multiple domains. Low-energy electron diffraction confirms the presence of three square lattice domains, each domain rotated by 60° with respect to the other. Basal plane defects, and especially terrace sites in the metal dichalcogenide surface, are implicated as the nucleation sites for the growth of these square lattice domains. Optical spectroscopies have been used to characterize submonolayer to multilayer deposits of chloroindium phthalocyanine on SnS2 thin films, where the packing geometries of the adjacent Pcs cause perceptible changes in the position and width of the absorbance band in the visible/ near-infrared region. The optical data suggest that aggregation (dimerization) of InPc-Cl occurs at even submonolayer coverages, and that the square lattice domains seen actually consist of bilayers of InPc-Cl, arranged in a staggered square lattice configuration.