Superatom Generation and Deposition of Alkali-like Ta@Si₁₆ and Halogen-like Al₁₃ via Atomic Aggregation

Surface modification with uniform nanostructures is a promising way to fabricate functionalized surface, and the synthetic electrode functionalization can be performed by depositing atomically precise nanoclusters with a specific number of atoms and compositions. During atomic nucleation and growth in gas phase, atomic aggregates exhibit novel electronic properties, mimicking atoms at a specific number of atoms and composition, which is called superatom (SA). Tantalum-encapsulating Si₁₆ cage nanoclusters (Ta@Si₁₆) and aluminum 13-mer (Al₁₃) are promising SAs for designing their assembled materials with tunable properties, where one-electron-excessive Ta@Si₁₆ and one-electron-deficient Al₁₃ exhibit alkali- and halogen-like characteristics, respectively, owing to the electron shell closing. In this study, with an intense nanocluster ion source, Ta@Si₁₆⁺ and Al₁₃⁻ were generated during the formation of TaSi_n ⁺ cations and Al_n ⁻ anions, where Ta@Si₁₆⁺ was remarkably generated compared with the neighboring species. SA deposition provided uniformly decorated surfaces exhibiting nanofunctional properties superior to those obtained by conventional atom deposition. With mass spectrometry, Ta@Si₁₆⁺ and Al₁₃⁻ SAs were size-selectively soft-landed on the substrate surfaces predeposited with n-type fullerene (C₆₀) and p-type hexa-tert-butyl-hexa-peri-hexabenzocoronene (HB-HBC, C₆₆H₆₆). The electronic states of Ta@Si₁₆ and Al₁₃ SAs immobilized on the organic substrates were characterized by X-ray photoelectron spectroscopy and oxidative reactivities under O₂ exposure.