論文 - 中嶋　敦

Chemical Reaction Dynamics by Electron and Atom Impact in Molecular Beam Studied by Laser Induced Fluorescence

Atsushi Nakajima

博士学位論文（東京大学） 1989年03月

学位論文（博士）, 単著, 筆頭著者, 最終著者, 責任著者, 査読有り

Clarifying photodetachment in Al13− anions and photoionization in Al13 neutrals using diffusion Monte Carlo

Meliton R. Chiong III, Atsushi Nakajima, and Yoshitada Morikawa∗

Journal of Physical Chemistry A （American Chemical Society (ACS)）  130 （ 9 ） 1851 - 1860 2026年02月

研究論文（学術雑誌）, 共著, 査読有り

From Si₁₆ to Ge₁₆: Geometric Origins of Robustness in Binary Cage Superatoms on Organic Substrates

Yugo Osada, Ryoichi Sato, Takashi Nishikawa, Miwa Tokita, Toshiaki Kamoshida, Masahiro Shibuta, Tsugunosuke Masubuchi, Miho Hatanaka, Atsushi Nakajima*

Journal of Physical Chemistry C （American Chemical Society (ACS)）  130 （ 9 ） 3518 - 3525 2026年02月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

Competitive Stability of W@Si₁₅ and W@Si₁₆ Superatoms: Oxidative Reactivity and Electrical Conductivity

Takaho Yokoyama, Kanata Nakamura, Kazuya Terasaka, Takumi Ichikawa, Atsushi Nakajima

J. Phys. Chem. Letters （American Chemical Society (ACS)）  17 （ 6 ） 1862 - 1869 2026年02月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

Interpretable Deep Learning for Atomicity Classification of Platinum Nanoclusters in STEM Images

Keizo Tsukamoto,* Naoyuki Hirata, Masahide Tona,* and Atsushi Nakajima*

npj Computational Materials （Springer Nature）  in press 2026年02月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

Evaluating Atomic Counts in Metal Nanoclusters via Transmission Electron Microscopy

K. Tsukamoto, N. Hirata, M. Tona, Y. Nemoto, A. Nakajima

Ultramicroscopy （Elsevier Science BV）  278   114242 2025年09月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

Size-selected platinum subnanocluster catalysts alloyed with nickel (Pt_nNi_m, n = 3 – 7, m = 1 – 3) or cobalt (Pt_nCo_m, n = 4 – 8, m = 1 – 2) for the oxygen reduction reaction

A. Ohnuma, P. Zhao, K. Matsunaga, K. Takahashi, T. Masubuchi, T. Inoue, Y. Wang, M. Ehara, N. Ichikuni, A. Nakajima

ACS Applied Nano Materials （American Chemical Society）  8 （ 34 ） 16748 - 16758 2025年08月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

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Charge State and Chemical Reactivity of Single-Sized Silver Nanoclusters Supported on Organic Substrates

T. Nishikawa, K. Shinomiya, K. Mizoguchi, T. Ichikawa, T. Inoue, A. Nakajima

The Journal of Physical Chemistry C （American Chemical Society）  129 （ 33 ） 14720 - 14728 2025年08月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

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Localized Surface Plasmon Resonances of Size-Selected Gold and Copper Nanoclusters Soft-Landed on a C₆₀ Organic Substrate

M. Tokita, T. Inoue, A. Nakajima

ACS Photonics （American Chemical Society）  12 （ 8 ） 4243 - 4250 2025年06月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

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Tailoring Superatomic Stability with Transition Metals in Silicon Cages: Shrinking to M@Si₁₅ (M = Re, Os, Ir)

T. Ichikawa, K. Terasaka, A. Sasaki, A. Nakajima

Journal of Physical Chemistry Letters （American Chemical Society）  15 （ 46 ） 11678 - 11686 2024年11月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り

　概要を見る

The design of materials with intriguing electronic properties is crucial for advancing nanoscale technologies, where precise control over atomic structure and electronic behavior is essential. Metal-encapsulating silicon cage superatoms (SAs) provide a new paradigm for molecular-scale material design, allowing fine-tuning of both structure and electronic characteristics. The formation of superatoms mimicking halogens, noble gases, and alkali metals has been well-studied, particularly with M@Si16, where early transition metals from groups 3 to 5 stabilize within a Si16 cage, achieving a 68-electron configuration. For late transition metals with excess electrons, a Si15 cage offers enhanced stability by fulfilling the 68-electron rule with one fewer Si atom. This research synthesizes Si15 cage-SAs with rhenium (Re) from group 7 and iridium (Ir) from group 9 on p-type and n-type organic substrates. The stability of Re@Si15 and Ir@Si15 is evaluated via oxidative reactivity with X-ray photoelectron spectroscopy and theoretical calculations, including osmium (Os) from group 8. Re@Si15-, Os@Si150, and Ir@Si15+ exhibit superatomic behaviors similar to halogens, noble gases, and alkali metals due to the 68-electron shell closure. Among them, Re@Si15- on p-type organic substrates shows superior electronic and geometric properties. These findings advance our understanding of M@Sin systems for transition metals, addressing longstanding questions about their properties at n = 15 and 16.

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Photoemission spectroscopy and microscopy for Ta@Si₁₆ superatoms and their assembled layers

M. Shibuta, T. Ohta, T. Kamoshida, K. Yamagiwa, H. Tsunoyama, T. Inoue, T. Masubuchi, A. Nakajima

Nanoscale （Royal Chemical Society）  16 （ 47 ） 21837 - 21846 2024年10月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  20403364

　概要を見る

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@Si16) SAs on an organic C60 substrate through deposition, and we characterized their electronic and optical properties by photoelectron spectroscopy and microscopy. The alkaline nature of Ta@Si16 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. The evolution of the work function for Ta@Si16 SAs on C60, observed by 2PPE spectroscopy, demonstrates charge transfer complexation between the topmost C60 layer and the first Ta@Si16 layer, consistent with the electron-donating alkaline characteristics of Ta@Si16 SAs. Specifically, a small amount of Ta@Si16 SA deposition leads to a dramatic increase in 2PPE intensity, attributable to electromagnetic near-field enhancements, suggesting applications as sensitizers for nonlinear imaging in photoemission microscopy. For the assembled Ta@Si16 SA layers, a plasmonic response of hνp = 17.9 eV is spectroscopically identified, including their valence and conduction band structures, and the plasmonic energetics are discussed in the context of metal doping in bulk silicon.

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Geometric and Electronic Properties of P Atom-Doped Al Nanoclusters: Alkaline-like Superatom of P@Al₁₂

M. Akutsu, K. Koyasu, K. Miyajima, M. Mitsui, T. Inoue, A. Nakajima

Journal of Physical Chemistry A （American Chemical Society）  128 （ 32 ） 6648 - 6657 2024年08月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  10895639

　概要を見る

The geometric and electronic characteristics of phosphorus-atom doped aluminum nanoclusters, AlnPm (n = 7-17, m = 1 and 2), were investigated through a combination of experiments and theoretical calculations. The size dependences of the ionization energy (Ei) for AlnPm NCs exhibit a local minimum of 5.37 eV at Al12P1, attributed to an endohedral P@Al12 superatom (SA). This SA originates from an excess electron toward the 2P shell closing (40e), coexisting with an exohedral isomer featuring a vertex P atom. The stability of the endohedral P@Al12 is further enhanced in its cationic state compared to the exohedral isomer, when complexed with a fluorine (F) atom, forming an SA salt denoted as P@Al12+F- with an elevated Ei ranging from 6.42 to 7.90 eV. In contrast, for the anionic Al12P1-, the exohedral form is found to be more stable than the endohedral one using anion photoelectron spectroscopy and calculations. The geometric and electronic robustness of neutral P@Al12 SAs against electron donation and acceptance is discussed in comparison to rare-gas-like Si@Al12 SAs.

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Localized surface plasmon resonances of size-selected large silver nanoclusters (n = 70-100) soft-landed on a C₆₀ organic substrate

T. Inoue, K. Mizoguchi, M. Tokita, M. Shibuta, M. Nakaya, T. Eguchi, A. Nakajima

Physical Chemistry Chemical Physics （Royal Chemical Society）  26 （ 23 ） 16597 - 16602 2024年05月

研究論文（学術雑誌）, 最終著者, 責任著者, 査読有り,  ISSN  14639076

　概要を見る

Silver nanoclusters (Agn NCs) exhibit a remarkable optical property known as localized surface plasmon resonance (LSPR) in the visible to ultraviolet wavelengths. In this study, we address the size gap in LSPR responses between small NCs and nano-islands by synthesizing large Agn NCs with a countable number of atoms (n = 70-100) using a magnetron sputtering method, which were precisely size-selected and soft-landed onto substrates. The monodispersed Agn NCs were immobilized on a pre-decorated substrate with fullerene (C60) molecules, and their LSPR behaviors were characterized using two-photon photoemission (2PPE) spectroscopy. Due to the distinct polarization selectivity of incident light associated with LSPR, the intensity ratio between p- and s-polarized lights (Ip/Is) in 2PPE spectroscopy serves as a reliable indicator of LSPR and its structural correlations. From n = 70 to 100, the Ip/Is value gradually decreases as the cluster size increases. This decrease is attributed to the enhancement of s-polarized light (Is), indicating that large Agn NCs on a C60 substrate undergo a deformation from spherical to flattened geometries, particularly above approximately n = 55.

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Imaging of ultrafast photoexcited electron dynamics in pentacene nanocrystals on a graphite substrate

M. Shibuta, A. Nakajima

Nanoscale （Royal Chemical Society）  16 （ 26 ） 12397 - 12405 2024年05月

研究論文（学術雑誌）, 最終著者, 責任著者, 査読有り,  ISSN  20403364

　概要を見る

Understanding molecular film growth on substrates and the ultrafast electron dynamics at their interface is crucial for advancing next-generation organic electronics. We have focused on studying the ultrafast photoexcited electron dynamics in nanoscale organic crystals of an aromatic molecule, pentacene, on a two-dimensional material of graphite substrate. Through the use of time-resolved two-photon photoelectron emission microscopy (2P-PEEM), we have visualized the ultrafast lateral evolution of photoexcited electrons. By resonantly tuning the incident photon to excite pentacene molecules, polarization-dependent 2P-PEEM has revealed that pentacene nanocrystals (sub- to several μm) on the substrate exhibit a preferential orientation, in which a molecular π-orbital contacts the substrate in a “lying flat” orientation, facilitating electron transfer to the substrate. The time-resolved 2P-PEEM captures the motion of excited electrons in a femto- to pico-second timescale, clearly imaging the ultrafast charge transfer and lateral expansion two-dimensionally on the graphite substrate. Moreover, we found that the lying-flat molecular orientation of pentacene nanocrystals is transformable into a “standing-up” one through gentle heating up to 50 °C. These experimental insights using time-resolved 2P-PEEM will be highly valuable in enhancing the photofunctionalities of organic electronic devices by controlled molecular deposition.

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Extended X-ray Absorption Fine Structure (EXAFS) Measurements on Alkali Metal Superatoms of Ta-Atom-Encapsulated Si₁₆ Cage

T. Inoue, T. Ina, H. Masai, N. Kondo, F. Matsui, T. Kinoshita, A. Nakajima

Journal of Physical Chemistry Letters （American Chemical Society）  15 （ 20 ） 5376 - 5381 2024年05月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  1948-7185

　概要を見る

The silicon cage nanoclusters encapsulating a tantalum atom, termed Ta@Si16, exhibit characteristics of alkali metal “superatoms (SAs)”. Despite this conceptual framework, the precise structures of Ta@Si16 and Ta@Si16+ remain unclear in quantum calculations due to three energetically close structural isomers: C3v, Td, and D4d structures. To identify the geometrical structure of Ta@Si16 SAs, structural analysis was conducted using extended X-ray absorption fine structure (EXAFS) with a high-intensity monochromatic X-ray source, keeping anaerobic conditions. Focusing on “superordered” films, which constitute amorphous thin films composed solely of Ta@Si16 SAs, this analysis preserved locally ordered structures. Spectral comparisons between experimental and simulated Ta L3-edge EXAFS unveil that Ta@Si16 SAs on a substrate adopt a C3v-derived structure, while Si K-edge EXAFS introduces spectral ambiguity in structural identifications, attributed to both intracluster and intercluster scatterings. These findings underscore the significance of locally ordered structure analyses in understanding and characterizing novel nanoscale materials.

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Alkaline Earth Metal Superatom of W@Si₁₆: Characterization of Group 6 Metal Encapsulating Si₁₆ Cage on Organic Substrates

K. Terasaka, T. Kamoshida, T. Ichikawa, T. Yokoyama, M. Shibuta, M. Hatanaka, A. Nakajima

Journal of the American Chemical Society （American Chemical Society）  146 （ 14 ） 9605 - 9613 2024年03月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  00027863

　概要を見る

Transition metal atom (M)-encapsulating silicon cage nanoclusters (M@Si16) 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@Si16 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@Si16, comprising a central atom from group 6 (MVI = Cr, Mo, and W) were deposited on C60 substrates, and their electronic and chemical stabilities were investigated in terms of their charge state and chemical reactivity against oxygen exposures. In comparison to alkali-like Ta@Si16, the extent of charge transfer to the C60 substrate is approximately doubled, while the oxidative reactivity is subdued for MVI@Si16 on C60, especially for W@Si16. The results show that a divalent state of MVI@Si162+ appears on the C60 substrate, which is consistently calculated to be a symmetrical cage structure of W@Si162+ in C3v, revealing insights into the “periodic law” of M@Si16 superatoms pertaining to the characteristics of alkaline earth metals.

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Oxidative Activation of Small Aluminum Nanoclusters with Boron Atom Substitution prior to Completing the Endohedral B@Al₁₂^- Superatom

T. Inoue, M. Hatanaka, A. Nakajima

Journal of the American Chemical Society （American Chemical Society）  145 （ 42 ） 23088 - 23097 2023年10月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  00027863

　概要を見る

Elemental substitution and doping validate the optimization of chemical and physical properties of functional materials, and the composition ratio of the substituting atoms generally determines their properties by changing their geometric and electronic structures. For atomically precise nanoclusters (NCs) consisting of countable atom aggregates, the composition can be controlled accurately to provide an ideal model to study the heteroatom substitution effects. Since aluminum (Al) and boron (B) both belong to group 13 in the periodic table, the effect of B atom substitution on Aln NCs can be investigated while maintaining the total number of valence electrons in AlnBm NCs. In this study, oxidative reactivities of small Al NCs with B atom substitution are studied for AlnBm NCs (m = 1, n = 6-14 and m = 2, n = 11) supported on organic surfaces by using X-ray photoelectron spectroscopy and oxygen molecule (O2) exposure measurements. Before completing the endohedral B@Al12- superatomic NC, one B atom substitution in Al NCs (AlnB) enhances oxidative reactivities 3-20 times compared to those of Aln+1, particularly for n ≤ 11. When one Al atom of Al12B is further substituted by a B atom to form Al11B2, the reactivity drastically increases (6.6 × 102 times), showing that the B atom substitution makes the NC chemically active or inactive geometrically depending on the exohedral or endohedral site for the B atom in the Al NC. In addition, density functional theory calculations show that the electronegative B atom contributes to forming a locally positive Al site to facilitate O2 adsorption except in Al12B, in which the B atom is geometrically shielded by the surface of the Al12 cage in B@Al12

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Two-Photon Photoemission Spectroscopy and Microscopy for Electronic and Plasmonic Characterizations of Molecularly Designed Organic Surfaces

M. Shibuta, A. Nakajima

Journal of Physical Chemistry Letters （American Chemical Society）  14 （ 13 ） 3285 - 3295 2023年03月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  1948-7185

　概要を見る

Functional surfaces decorated with organic molecules and/or nanoclusters (NCs) composed of several tens of atoms are promising for use in future photoelectronic substrates, whose functionalities are governed by molecular local electronic/plasmonic excitations at the interfaces. Here, we combine two-photon photoemission spectroscopy (2P-PES) and microscopy (2P-PEEM) to investigate the local excited-state dynamics at organic surfaces functionalized with NCs. The 2P-PES and 2P-PEEM for organic fullerene (C60) layers on graphite and Au substrates demonstrated photophysical characterization of electronic and plasmonic properties, including propagating surface plasmon polaritons (SPPs). The SPP propagation at the Au interface buried by overlayered C60 can be visualized by Agn NC deposition, which enhances plasmon-induced hot electrons, where the threshold number of Ag atoms (n ≥ 9) for the plasmonic response is revealed by the size dependence of 2P-PES for Agn NCs on C60 layers.

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Bridging the gas and condensed phases for metal-atom encapsulating silicon- and germanium-cage superatoms: electrical properties of assembled superatoms

T. Yokoyama, A. Nakajima

Physical Chemistry Chemical Physics （Royal Chemical Society）  25 （ 14 ） 9738 - 9752 2023年03月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  14639076

　概要を見る

With the development of nanocluster (NC) synthesis methods in the gas phase, atomically precise NCs composed of a finite number of metal and semiconductor atoms have emerged. NCs are expected to be the smallest units for nanomaterials with various functions, such as catalysts, optoelectronic materials, and electromagnetic devices. The exploration of a stable NC called a magic number NC has revealed a couple of important factors, such as a highly symmetric geometric structure and an electronic shell closure, and a magic number behavior is often enhanced by mixing additional elements. A synergetic effect between geometric and electronic structures leads to the formation of chemically robust NC units called superatoms (SAs), which act as individual units assembled as thin films. The agglomeration of non-ligated bare SAs is desirable in fabricating the assembled SAs associated with intrinsic SA nature. The recent development of an intensive pulsed magnetron sputtering method opens up the scalable synthesis of SAs in the gas phase, enabling the fabrication of SA assembly coupled with the non-destructive deposition of a soft-landing technique. This perspective describes our recent progress in the investigation of the formation of binary cage SA (BCSA) assembled thin films composed of metal-atom encapsulating silicon-cage SAs (M@Si16) and germanium-cage SAs (M@Ge16), with a focus on their electrical properties associated with a conduction mechanism toward the development of new functional nanoscale materials.

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Superatom Generation and Deposition of Alkali-like Ta@Si₁₆ and Halogen-like Al₁₃ via Atomic Aggregation

T. Inoue, T. Ichikawa, K. Matsunaga, R. Birumachi, K. Nakamura, A. Nakajima

Journal of the Electrochemical Society （Electrochemical Society）  169 （ 10 ） 102511 2022年10月

研究論文（学術雑誌）, 共著, 最終著者, 責任著者, 査読有り,  ISSN  00134651

　概要を見る

Surface modification with uniform nanostructures is a promising way to fabricate functionalized surface, and the synthetic electrode functionalization can be performed by depositing atomically precise nanoclusters with a specific number of atoms and compositions. During atomic nucleation and growth in gas phase, atomic aggregates exhibit novel electronic properties, mimicking atoms at a specific number of atoms and composition, which is called superatom (SA). Tantalum-encapsulating Si16 cage nanoclusters (Ta@Si16) and aluminum 13-mer (Al13) are promising SAs for designing their assembled materials with tunable properties, where one-electron-excessive Ta@Si16 and one-electron-deficient Al13 exhibit alkali- and halogen-like characteristics, respectively, owing to the electron shell closing. In this study, with an intense nanocluster ion source, Ta@Si16+ and Al13− were generated during the formation of TaSin + cations and Aln − anions, where Ta@Si16+ was remarkably generated compared with the neighboring species. SA deposition provided uniformly decorated surfaces exhibiting nanofunctional properties superior to those obtained by conventional atom deposition. With mass spectrometry, Ta@Si16+ and Al13− SAs were size-selectively soft-landed on the substrate surfaces predeposited with n-type fullerene (C60) and p-type hexa-tert-butyl-hexa-peri-hexabenzocoronene (HB-HBC, C66H66). The electronic states of Ta@Si16 and Al13 SAs immobilized on the organic substrates were characterized by X-ray photoelectron spectroscopy and oxidative reactivities under O2 exposure.

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