Interfacial oxidation of TA-encapsulating Si₁₆ cage superatoms (Ta@Si₁₆) on strontium titanate substrates

Nanocluster immobilization on an oxide surface is fundamentally important for forming nanocluster-assembled layered materials. We fabricated multilayered superatom films made of tantalum-encapsulating Si₁₆ cage nanocluster (Ta@Si₁₆) on a strontium titanate substrate (SrTiO₃; STO) by the soft landing of size-selective Ta@Si₁₆. X-ray photoelectron spectroscopy (XPS) revealed that Ta@Si₁₆ survived at the interfacial oxide layer without oxidizing the central Ta atom, and pure Ta@ Si₁₆ layers were formed successively on the modified Ta@Si₁₆/STO interfacial layer. The Ta@Si₁₆ superatoms in the multilayered Ta@Si₁₆ showed high chemical robustness against O₂ exposure, although the topmost Ta@Si₁₆ surface layer, including the central Ta atom, completely oxidized in ambient O₂ over several days. XPS depth analysis showed that Ta@Si₁₆ oxide formation was limited only at the topmost single layer, revealing that the middle Ta@Si₁₆ layers sandwiched between the top and bottom were protected by the formation of interfacial oxides.