Organic/Inorganic Molecular Beam Epitaxy: Formation of an Ordered Phthalocyanine/SnS₂ Heterojunction

We report the growth of thin films of the metal dichalcogenide, SnS₂, on cleaved mica surfaces, followed by the deposition of monolayers and multilayers of chloroindium phthalocyanine, InPc–Cl. Reflection high-energy electron diffraction(RHEED) was used to show that the SnS₂ thin films grew with a principal axis oriented along a principal axis of the mica substrate, even at submonolayer coverages of SnS₂. X-ray photoelectron spectroscopy(XPS), reflection electron energy loss spectroscopies(REELS), and optical spectroscopies were used to confirm that the stoichiometry and electronic properties of these SnS₂ thin films were those of 2H-SnS₂. As with the deposition of InPc–Cl on melt-grown, bulk SnS₂, the first monolayer of InPc–Cl on SnS₂/mica gave RHEED patterns consistent with the formation of a closest packed monolayer, with the Pc’s lying flat on the surface. On the MBE-grown SnS₂, InPc–Cl multilayer films were grown that gave the same RHEED patterns as seen for the monolayer deposits. These diffraction data are consistent with the buildup of each Pc monolayer in registry with the initial monolayer. Transmission optical spectra of these Pc thin films show a strong, narrow absorption spectrum, in sharp contrast to those seen for polycrystalline InPc–Cl deposits, suggesting that the Pc chromophores sit in essentially equivalent environments.