Abstract
It is crucial to control the reactivity of surface silicon atoms for applications in miniaturized silicon-based nanodevices. Here we demonstrate that reactive silicon atoms are made unreactive by forming a Si16 cage that encapsulates a metal atom. Specifically, group 5 metal-encapsulating Si16 nanoclusters (M@Si16: M = V, Nb, and Ta) exhibit alkali-like superatomic behavior on n-type C60 substrates, where charge transfer between M@Si16 and C60 satisfies the 68-electron shell closure as M@Si16+. The oxidation properties of M@Si16+ are investigated by X-ray photoelectron spectroscopy, revealing that the chemical stability of the caged silicon surface towards oxygen is enhanced by a factor of 104 compared to a crystalline silicon surface, and that M@Si16 are oxidized stepwise from the outer Si16 cage to the central metal atom. While the nanoclusters share a common Si16 cage, their chemical robustness depends on a superatomic “periodicity” (Ta@Si16 > V@Si16 > Nb@Si16) which is explained by the electron density distributions of M@Si16 investigated by DFT calculations.
Highlights
It is crucial to control the reactivity of surface silicon atoms for applications in miniaturized silicon-based nanodevices
Since miniaturization of functional units with conventional patterning methods like photolithography has almost reached its limit[3], it is urgent that we discover methods to construct Si-based low-dimensional functional nanomaterials that are fabricated with bottom-up technologies utilizing fine synthesis methods in the gas and liquid phases[4,5,6,7,8,9], where each silicon nanomaterial is regarded as a building block of functionality
We previously reported the chemical characterization of Ta@Si16 deposited on a graphite substrate as a demonstration of the use of X-ray photoelectron spectroscopy (XPS) to elementspecifically clarify the local electronic structure of the caged Si atoms[39], the analysis of the chemical reactivity was qualitative and the species were limited to Ta@Si16 in an alkalilike superatomic family
Summary
It is crucial to control the reactivity of surface silicon atoms for applications in miniaturized silicon-based nanodevices. To make a stable Si compound with “zero dimensional” nanostructure, by analogy with C60 fullerene, one can assume that a rounded silicene will have stable caged surface From this viewpoint, much experimental and theoretical research on the simplest Si caged materials have been conducted, including Si6014–17. Transition metal-encapsulating Si16 nanocluster superatoms (M@Si16) can be synthesized in the gas phase, exhibiting a magic number behavior like a C60 fullerene[23,27]. Since their chemical properties can be tuned by choosing a different metal atom in the center of the geometrically close-packed M@Si16, the assembly of a series of M@Si16 could be a pathway to building Si-based nanomaterials. We previously reported the chemical characterization of Ta@Si16 deposited on a graphite substrate as a demonstration of the use of X-ray photoelectron spectroscopy (XPS) to elementspecifically clarify the local electronic structure of the caged Si atoms[39], the analysis of the chemical reactivity was qualitative and the species were limited to Ta@Si16 in an alkalilike superatomic family
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