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

Abstract

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-perihexabenzocoronene (HB-HBC, C 66 H 66 ), and the electronic states of M@Si 16 on the organic substrates are characterized by Xray 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.

Bridging the gas and condensed phases for metal-atom encapsulating silicon- and germanium-cage superatoms: electrical properties of assembled superatoms

“…In fact, the chemical reactivity of halogen-like Lu@Si 16 against molecular oxygen is suppressed when it is deposited on HB-HBC to form Lu@Si 16 − HB-HBC + with satisfying 68 electron closure. 30 For the characterization of the behavior of M@Si 16 BCSAs on different kinds of substrate, Ta@Si 16 was deposited on strontium titanate (STO) as a representative of oxide substrate with step-by-step deposition. XPS measurement revealed that a layered film was formed.…”

“…110 The CT complex formed between Ta@Si 16 and the C 60 molecular layer can be explained by considering the energetics for CT complexation. 30 Endothermic dissociation limits (DE) of Ta@Si 16 + C 60 À and Ta@Si 16 À C 60 + against the neutrals of M@Si 16 and C 60 can be calculated by the ionization energy and electron affinity of Ta@Si 16 and C 60 . The value of DE is smaller for Ta@Si 16 + C 60 À compared to Ta@Si 16 À C 60 + , which is consistent with the XPS results.…”

“…In fact, the chemical reactivity of halogen-like Lu@Si 16 against molecular oxygen is suppressed when it is deposited on HB-HBC to form Lu@Si 16 − HB-HBC + with satisfying 68 electron closure. 30…”

“…20,21 The NC source enables us to fabricate NC-deposited substrates applicable as catalysts, [22][23][24][25] plasmonic sensitizer, 26 and optoelectronic materials 27 and have a deep understanding of cluster-surface interaction with organic substrates. [28][29][30] In addition, the NC source can be modified to obtain NC solutions 31 and NC-deposited powders. 32 The methods are called direct liquid/powder embedded trapping (DiLET/DiPET), 31,30 opening an opportunity to investigate the properties of bare NCs under various environments.…”

“…[28][29][30] In addition, the NC source can be modified to obtain NC solutions 31 and NC-deposited powders. 32 The methods are called direct liquid/powder embedded trapping (DiLET/DiPET), 31,30 opening an opportunity to investigate the properties of bare NCs under various environments. What is more is the fabrication of assembled films and characterization of macroscopic properties such as electrical conduction.…”