Photoemission spectroscopy and microscopy for Ta@Si superatoms and their assembled layers.

Superatoms (SAs) with specific compositions have the potential to significantly advance the field of nanomaterials science, leading to next-generation nanoscale functionalities. In this study, we fabricated assembled layers with tantalum metal-atom encapsulating silicon cage (Ta@Si) SAs on an organic C substrate through deposition, and we characterized their electronic and optical properties by photoelectron spectroscopy and microscopy. The alkaline nature of Ta@Si SAs reveals their electronic behaviors, such as charge transfer and electromagnetic near-field sensing, through two-photon photoemission (2PPE) spectroscopy and microscopy with a femtosecond laser.

Alkaline Earth Metal Superatom of W@Si: Characterization of Group 6 Metal Encapsulating Si Cage on Organic Substrates.

Transition metal atom (M)-encapsulating silicon cage nanoclusters (M@Si) exhibit a superatomic nature, depending on the central M atom owing to the number of valence electrons and charge state on organic substrates. Since M@Si superatom featuring group 4 and 5 transition metal atoms exhibit rare-gas-like and alkali-like characteristics, respectively, group 6 transition metal atoms are expected to show alkaline earth-like behavior. In this study, M@Si, comprising a central atom from group 6 (M = Cr, Mo, and W) were deposited on C substrates, and their electronic and chemical stabilities were investigated in terms of their charge state and chemical reactivity against oxygen exposures.

Nitric oxide oxidation of a Ta encapsulating Si cage nanocluster superatom (Ta@Si) deposited on an organic substrate; a Si cage collapse indicator.

The chemical reaction kinetics of an alkali-like superatom comprising a tantalum encapsulating Si cage nanocluster (Ta@Si) deposited on an n-type organic substrate composed of overlayered C fullerene upon exposure to nitric oxide (NO) as a reactive gas are investigated. Core level X-ray photoelectron spectroscopy reveals that Ta@Si oxidation with NO proceeds stepwise from the outer Si cage to the central Ta atom; during the initial stage, NO is dissociatively chemisorbed by the cage surface of Ta@Si without penetrating the cage, while under extreme reaction conditions, the collapse of the Si cage leads to NO oxidation of the central Ta atom. In particular, molecular NO adsorption is associated with Ta oxidation only after the collapse of the Si cage of Ta@Si.