Molecularly Designed Cluster–Surface Interaction for Halogen-like and Alkali-like Metal-Encapsulating Silicon Cage Superatoms on n- and p-Type Organic Substrates

Metal-encapsulating Si 16 cage clusters (M@Si 16 ) are promising superatoms (SAs) for designing tunable properties for their assembled materials by changing the central metal atom: halogen-like, rare-gas-like, and alkali-like characteristics appear for the central metal atom of groups 3, 4, and 5, respectively. To fabricate SA assemblies, metal-encapsulating M@Si 16 SAs (M = Lu, Hf, and Ta) must be controllably immobilized on a substrate. Substrates decorated with organic molecules can facilitate optimization of a cluster–surface interaction because the molecular local interactions between SAs and predeposited organic molecules govern the electronic properties through molecular complexation. In this study, M@Si 16 SAs are size-selectively soft-landed on organic substrates deposited with n-type fullerene (C 60 ) and p-type hexa- tert -butyl-hexa- peri -hexabenzocoronene (HB-HBC, C 66 H 66 ), and the electronic states of M@Si 16 on the organic substrates are characterized by X-ray and ultraviolet photoelectron spectroscopy. On the C 60 substrate, all M@Si 16 are fixed to be cationic, forming M@Si 16 + C 60 – via a charge transfer interaction, while on an HB-HBC substrate, M@Si 16 – HB-HBC + (M = Lu and Hf) is formed with anionic M@Si 16 – . Together with density functional theory calculations, the charge preference of the M@Si 16 SA is examined based on its chemical stability against O 2 gas exposure; Lu@Si 16 on HB-HBC is more robust toward O 2 than that on C 60, while Ta@Si 16 on HB-HBC is less robust than that on C 60 . Depending on the SA properties, an appropriate selection of organic molecules for deposition provides a molecular designer concept for forming SA-assembled nanomaterials through the cluster–surface interaction.