Formation of Superatom Monolayer Using Nanocluster Ion Source Based on High-Power Impulse Magnetron Sputtering

Abstract

The assembled monolayer of superatomic nanocluster ions synthesized in the gas phase is formed with monodispersive immobilization of Ta atom-encapsulated Si16 cage superatom (Ta@Si16) with an intensive ion source based on high-power impulse magnetron sputtering (HiPIMS). Scanning tunneling microscopy and spectroscopy have demonstrated that superatom cations of Ta@Si16+ can be densely immobilized on C60-terminated surfaces while retaining their cage shape by forming charge transfer (CT) complexes ((Ta@Si16)+C60−) on the surfaces. Its chemical states of Ta@Si16 deposited on an electron acceptable C60 fullerene film were evaluated by X-ray photoelectron spectroscopies (XPS). XPS results for Si, Ta, and C elements showed that Ta@Si16 combines with a single C60 molecule to form (Ta@Si16)+C60−. The high thermal and chemical robustness of the superatomic CT complex has been revealed by the XPS measurements conducted before and after heat treatment and oxygen exposure. The formation of robust superatom monolayer with HiPIMS demonstrates that the superatoms including metal-encapsulating silicon cage superatoms have a promising potential to be utilized for building blocks of novel functional nanomaterials.