Prof. Atsushi Nakajima has established a high-quality and high-intensity nanocluster generation method and a precision-controlled immobilization technique to realize surface functionalization using nanoclusters. He has elucidated the functionalized surface chemistry of supported nanoclusters, which had not been explored in synthetic research. By creating new functionalized surfaces, such as catalytic activity and plasmonic response using nanoclusters, he has expanded the frontiers of nanocluster science. Below are his key achievements.

1. Development of a Novel Surface Functionalization Strategy Using Nanoclusters
Prof. Nakajima developed a nanocluster generation technique based on high-power pulsed magnetron sputtering, enabling the generation of nanocluster ions at approximately 10 to 100 times the conventional level. This method features its narrow translational energy distribution of nanocluster ions, ensuring superior deposition efficiency and providing a high-quality ion beam source that does not disorder the surface morphology. Through this methodology, he successfully discovered numerous novel nanoclusters known as "superatoms." Specifically, he selectively generated high-order structured nanocluster superatoms, such as metal (M)-encapsulating silicon cage superatoms (M@Si₁₆) and boron-encapsulated aluminum cage superatoms (B@Al₁₂).
Furthermore, he developed a precision-controlled immobilization method for nanoclusters using organic molecule-modified substrates, such as electron-accepting C₆₀ and electron-donating coronene derivatives (HB-HBC). By utilizing organic substrates, he achieved fine-tuned control over the charge states and local intermolecular interactions of supported nanoclusters, optimizing the supported state according to nanocluster properties and significantly enhancing surface functionality through nanocluster-based modifications. Additionally, by directly embedding nanoclusters into liquids and powders, he enabled the fabrication of nanocluster dispersion liquids and powders, greatly expanding the application scope of supported nanoclusters.

2. Physicochemical Characterization of Immobilized Nanoclusters
The M@Si₁₆ superatom consists of a transition metal atom (M) encapsulated within a 16-silicon-atom cage, exhibiting high structural symmetry and chemical stability based on a 68-electron closed-shell configuration. Prof. Nakajima demonstrated the periodic properties of M@Si₁₆ superatoms by supporting various metal-encapsulated M@Si₁₆ structures. By incorporating transition metals from groups 3, 4, 5, and 6, he revealed that each M@Si₁₆ superatom exhibits chemical properties similar to halogens, noble gases, alkali metals, or alkaline earth metals. These findings were confirmed using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and oxidation resistance studies of supported superatoms.

Additionally, extended X-ray absorption fine structure (EXAFS) analysis was used to identify metal-encapsulation structures. By combining suitable organic substrates for different M@Si₁₆ superatoms, he unveiled a periodic trend in immobilized M@Si₁₆ superatoms, governed by the electronic configuration of the encapsulated metal atoms.
Moreover, he synthesized and supported Al₁₃^- superatoms, which consist of 13 aluminum atoms forming a geometrically-packed icosahedral structure with electronic stability from its 40 valence electrons in total-along with the boron-centered B@Al₁₂^- superatom. His research demonstrated that these superatoms undergo oxidation on n-type C₆₀ substrates but were chemically stabilized as charge-transfer complexes on p-type HB-HBC organic substrates. This finding highlights the feasibility of surface functionalization of Al-based superatoms through charge-state control on organic substrates.
Furthermore, he elucidated the origin of the plasmonic optical responses in noble metal nanoclusters. By depositing size-selected silver nanoclusters onto C₆₀ substrates and applying two-photon photoemission spectroscopy (2PPE) using an ultrafast femtosecond laser, he revealed the optical characteristics of localized surface plasmon resonance (LSPR). He demonstrated that silver nanoclusters with nine or more atoms exhibit LSPR responses and revealed that the relaxation dynamics of plasmon-excited electrons have an extremely short lifetime of less than 50 femtoseconds. These findings establish a foundational framework for designing new optical devices utilizing plasmonic responses.

3. Functional Property Chemistry Using Supported Nanoclusters
Prof. Nakajima's research has significantly broadened the scope of surface functionalization by utilizing nanoclusters as functional building blocks. In the development of fuel cell catalysts using platinum nanoclusters, he established a technique for immobilizing high-purity platinum nanoclusters of uniform size onto substrates. This method achieved approximately twice the catalytic activity compared to conventional standard catalysts, offering a pathway toward lower-cost and higher-efficiency fuel cell technologies.
Additionally, he fabricated integrated films with multilayer-supported M@Si₁₆ superatoms, revealing that these films exhibit novel electrical conductivity based on hopping conduction. He further demonstrated that the electrical conductivity of these superatomic films varies depending on the encapsulated metal element, with alkali-metal-like M@Si₁₆ superatoms exhibiting higher electrical conductivity than other M@Si₁₆ superatoms. These findings present a new design strategy for electronic material design utilizing superatomic periodicity.
Furthermore, using photoelectron emission microscopy (PEEM), he clarified the propagation characteristics of surface plasmon polaritons (SPPs) at buried interfaces by utilizing the LSPR response of silver nanoclusters as optical sensitizers. This method demonstrated that silver nanoclusters enable non-invasive observation of SPPs at metal interfaces covered with organic molecular films, establishing an evaluation method for new plasmonic device architectures.

Conclusions
Through these achievements, Prof. Nakajima has pioneered functionalized surface chemistry through nanocluster deposition based on a newly developed nanocluster ion source and a precision-controlled monodisperse immobilization technique using organic substrates. He successfully supported superatoms such as substitution-centered M@Si₁₆ and X@Al₁₂ on substrates and elucidated the periodic properties of supported superatoms. Additionally, he deepened the fundamental understanding of plasmonic optical responses of silver nanoclusters. Furthermore, he demonstrated that precision-controlled immobilized nanoclusters could be developed as functional materials applicable to optical elements and electrode catalysts, paving the way for new avenues in functionalized surface chemistry. These numerous remarkable achievements have been recognized as deserving of the Chemical Society of Japan Award.