Charge Transfer Complexation of Ta-Encapsulating Ta@Si₁₆ Superatom with C₆₀

The tantalum-encapsulating Si₁₆ cage nanocluster superatom (Ta@Si₁₆) has been a promising candidate for a building block of nanocluster-based functional materials. Its chemical states of Ta@Si₁₆ deposited on an electron acceptable C₆₀ fullerene film were evaluated by X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS, respectively). XPS results for Si, Ta, and C showed that Ta@Si₁₆ combines with a single C₆₀ molecule to form the superatomic charge transfer (CT) complex, (Ta@Si₁₆)⁺C₆₀^-. The high thermal and chemical robustness of the superatomic CT complex has been revealed by the XPS and UPS measurements conducted before and after heat treatment and oxygen exposure. Even when heated to 720 K or subjected to ambient oxygen, Ta@Si₁₆ retained its original framework, forming oxides of Ta@Si₁₆ superatom.