Koji Kaya

Ankara Yıldırım Beyazıt University

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Co-Authors

Atsushi Nakajima

Keio University

119

Kiyokazu Fuke

Toyota Physical and Chemical Research Institute

Yuichi Negishi

Tokyo University of Science

Mitsuo Itô

Japan Atomic Energy Agency

Tsuyoshi Kurikawa

Keio University

Reiko Kishi

RIKEN

Satoshi Nagao

Japan Synchrotron Radiation Research Institute

Hiroshi Kawamata

High Energy Accelerator Research Organization

Ken Miyajima

The University of Tokyo

Kuniyoshi Hoshino

Hitachi (Japan)

Cooperative Institutions

Keio University

The University of Tokyo

Tohoku University

Institute for Molecular Science

RIKEN

Kyoto University

Tokyo Institute of Technology

Osaka University

Japan Science and Technology Agency

Tokyo University of Science

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Papers

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Fabrication of ferromagnetic nanocluster rods by magnetic trapping

Journal of Applied Physics (2004)

Seung Hun Huh Atsushi Nakajima Koji Kaya

In a one-pot fabrication at room temperature, both an iron-neodymium-dysprosium-boron permanent magnet (Fe66Nd28Dy4B1) and cobalt (Co) metal have been directly converted into the corresponding ferromagnetic nanometer-scale cluster (nanocluster) rods using pulsed-laser ablation combined with magnetic-field trapping. The morphology of the produced nanomaterials was analyzed by electron microscopy and the composition by electron energy-loss spectroscopy, and it was found that one-dimensional structured soft magnets, up to ∼150 nm in length, consist of magnetic clusters a few nanometers in diameter. The mechanism and driving behind their growth process and their magnetic evolution have been proposed.

Dysprosium

Nanometre

Laser Ablation

10.1063/1.1638885

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Citations (10)

Absolute intensity ratios of Raman lines of benzene and ethylene derivatives with 5145 Å and 3371 Å excitation

Journal of Raman Spectroscopy (1973)

Y. Udagawa N. Mikami Koji Kaya Masafumi Ito

Abstract Absolute Raman intensities of benzene and ethylene derivatives were measured in the vapour phase with 5145 Å and 3371 Å excitation. Intensity increase of benzene 992 cm −1 band, which has been frequently used as an intensity standard, was found to be much smaller than expected. The observed intensity increases of ethylene derivatives nicely agree with the theory by assuming the contributing virtual states are the lowest allowed 1 π, π* state.

Intensity

10.1002/jrs.1250010404

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Citations (28)

Enhanced electrochemical detection of SARS-CoV-2 IgG using magnetic nanocomplexes: evaluation of preparation processes and sensor stability

Journal of Nanoparticle Research (2025)

Nimet Yildirim Ezgi Ayni Koji Kaya

10.1007/s11051-025-06240-2

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Citations (0)

Structures and Properties of Semiconductor Microclusters. Study on Electronic Structures of Silicon Clusters by Hetero-Atom Doping.

Hyomen Kagaku (1997)

Atsushi Nakajima Koji Kaya

Electronic properties of small silicon clusters (n≤11), produced by a laser vaporization method, were investigated by photoelectron spectroscopy of their anions. The doping of F or Na atoms enables us to substract or add an electron from/into the silicon clusters without any serious geometric rearrangement, revealingelectronic structures of the silicon clusters. Both the doped F and Na atoms areattached onto the surface of the silicon clusters, which is in agreement with abinitio theoretical calculation on electronic and geometric structures of the Si-F and Si-Na binary clusters. The cluster size dependence of HOMO-LUMO gaps in the neutral silicon clusters were measured experimentally with the F atom doping, and the electronic structures above the LUMO of the neutral silicon clusters were revealed with the Na atom doping. The doping of C atoms, furthermore, induces some geometric change of the silicon clusters, and the substitution of Si atoms to C atoms results in a phase transition.

HOMO/LUMO

10.1380/jsssj.18.141

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Ionization potentials of cobalt–sodium bimetallic clusters (Co_nNa_m)

The Journal of Chemical Physics (1992)

Kuniyoshi Hoshino Takashi Naganuma Yoshiyuki Yamada Katsura Watanabe Atsushi Nakajima

Cobalt–sodium bimetallic clusters (ConNam, n=3–48) were produced by a two independent laser-vaporization method. Ionization potentials of the ConNam clusters were measured up to m=3 using a tunable ultraviolet laser combined with a time-of-flight (TOF) mass spectrometer. In general, the ionization potentials decrease monotonically with the number of sodium atoms, and the ionization potentials of ConNam+1 decrease by 0.2–0.8 eV compared to those of the corresponding ConNam cluster. However, the amount of IP decrement by the Na doping is relatively large at n≤17 whereas it is small and constant at n≥18. This feature can be explained by a geometric rearrangement; at small n, the Na doping induces a large geometric rearrangement of the cluster, but at large n, the geometric change is small. Reactivity of ConNam cluster toward H2 was also measured and the effect of the Na doping was studied. The reactivity also suggests the geometric change induced by the Na doping. Moreover, we examined the anticorrelation between IP and reactivity of the ConNam clusters, and no anticorrelation between them could be revealed.

Reactivity

Bimetallic strip

Thermal ionization

10.1063/1.462961

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Citations (18)

SAW properties of LiNbO/sub 3/ and LiTaO/sub 3/ films grown by pulsed laser deposition

Proceedings of the IEEE International Frequency Control Symposium (2002)

Yoshihiko Shibata Naohiro Kuze Masahiro Matsui Koji Kaya Masaki Kanai

LiNbO/sub 3/ and LiTaO/sub 3/ films are deposited on sapphire and AlN/sapphire substrates using Ar-F excimer laser ablation. The deposition and structure of the films are investigated systematically. The structure of the films is analyzed by X-ray pole figure, high-resolution X-ray diffraction and transmission electron microscopy. The results of these analysis indicate that deposited films are extremely high-quality epitaxial films. As-grown LiNbO/sub 3/ and LiTaO/sub 3/ films are sufficiently piezoelectric to fabricate SAW devices. The experimental data of SAW velocity (Vs) and electromechanical coupling coefficients (k/sup 2/) almost coincide with the calculated data.

Pulsed Laser Deposition

Laser Ablation

Deposition

10.1109/freq.1996.559835

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Citations (1)

Resonance Raman scattering and the Jahn-Teller effect of oxocarbon ions

Chemical Physics (1978)

Machiko Takahashi Koji Kaya Mitsuo Itô

Jahn–Teller effect

Vibronic coupling

10.1016/s0301-0104(78)85245-8

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Citations (41)

Multiple dumbbell structures of vanadium–C60 clusters

The Journal of Chemical Physics (1997)

Atsushi Nakajima Satoshi Nagao Hiroaki Takeda Tsuyoshi Kurikawa Koji Kaya

Vanadium (V)–C60 mixed clusters were produced by two laser vaporization methods. In the mass spectra of cationic Vn(C60)m+, the abundant clusters were produced at the composition of (n,m)=(1,1), (1,2), (2,3), (3–4,4), and (5,5). This pattern is explicable in terms of a multiple dumbbell structure; V atom and C60 are alternatively piled up. The ionization energy and the reactivity of the dumbbell clusters toward O2 and CO show V1(C60)2 takes a structure of V1(η6−C60)2.

Dumbbell

Laser vaporization

Cationic polymerization

Vanadium Oxide

Vaporization

10.1063/1.474307

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Citations (68)

Ionization energies of aluminum-cesium bimetallic clusters (Al Cs )

Chemical Physics Letters (1994)

Kuniyoshi Hoshino Katsura Watanabe Yuji Konishi T. Taguwa Atsushi Nakajima

Caesium

Bimetallic strip

Ultraviolet

Vaporization

10.1016/0009-2614(94)01287-3

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Citations (43)

Electronic structures of HonC60 clusters (n=1–5): High electron acceptability of C60

The Journal of Chemical Physics (2002)

Satoshi Nagao Yuichi Negishi Akiko Kato Yoshiaki Nakamura Atsushi Nakajima

The electronic structures of gas-phase exohedral holmium (Ho)–C60 clusters, HonC60 with n=1–5, were studied by photoionization spectroscopy of the neutrals and photoelectron spectroscopy of their anions. Both spectroscopic analyses reveal that each Ho atom donates its three valence electrons to the unoccupied molecular orbitals of C60. The electron filling through the charge transfer allows us to observe the unoccupied levels of C60 due to high electron acceptability.

Electron spectroscopy

Holmium

Valence electron

10.1063/1.1492801

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Citations (3)