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Journal Articles

Structure and magnetic properties of Fe nanoparticles in amorphous silica implanted with Fe ions and effect of subsequent energetic heavy ion irradiation

Iwase, Akihiro*; Fukuda, Kengo*; Saito, Yuichi*; Okamoto, Yoshihiro; Semboshi, Satoshi*; Amekura, Hiroshi*; Matsui, Toshiyuki*

Journal of Applied Physics, 132(16), p.163902_1 - 163902_10, 2022/10

 Times Cited Count:0 Percentile:0(Physics, Applied)

Amorphous SiO$$_{2}$$ samples were implanted with 380 keV Fe ions at room temperature. After implantation, some of the samples were irradiated with 16 MeV Au ions. magnetic properties were investigated using a SQUID magnetometer, and the morphology of the Fe-implanted SiO$$_{2}$$ samples was examined using transmission electron microscopy and X-ray absorption spectroscopy (EXAFS and XANES), which showed that the size of Fe nanoparticles was increasing The size of Fe nanoparticles increased with increasing Fe implantation amount; some of the Fe nanoparticles consisted of Fe oxides, and the valence and structure of Fe atoms became closer to that of metallic $$alpha$$-Fe with increasing Fe injection amount. The magnetization-field curve of the sample implanted with a small amount of Fe was reproduced by Langevin's equation, suggesting that the Fe nanoparticles behave in a superparamagnetic manner. In addition, when a large amount of Fe was implanted, the magnetization-magnetic field curve shows a ferromagnetic state. These magnetic property results are consistent with the X-ray absorption results. Subsequent 16 MeV Au irradiation crushed the Fe nanoparticles, resulting in a decrease in magnetization.

Journal Articles

Ion tracks in silicon formed by much lower energy deposition than the track formation threshold

Amekura, Hiroshi*; Toulemonde, M.*; Narumi, Kazumasa*; Li, R.*; Chiba, Atsuya*; Hirano, Yoshimi*; Yamada, Keisuke*; Yamamoto, Shunya*; Ishikawa, Norito; Okubo, Nariaki; et al.

Scientific Reports (Internet), 11(1), p.185_1 - 185_11, 2021/01

 Times Cited Count:10 Percentile:79.44(Multidisciplinary Sciences)

We report the track formation of 10 nm in diameter in silicon irradiated with 6 MeV C$$_{60}$$, i.e., much lower energy than the previously reported energy threshold.

Journal Articles

Irradiation effects of swift heavy ions detected by refractive index depth profiling

Amekura, Hiroshi*; Li, R.*; Okubo, Nariaki; Ishikawa, Norito; Chen, F.*

Quantum Beam Science (Internet), 4(4), p.39_1 - 39_11, 2020/12

Evolution of depth profiles of the refractive index in Y$$_{3}$$Al$$_{5}$$O$$_{12}$$ (YAG) crystals were studied under 200 MeV Xe ion irradiation. The index changes were observed at three different depth regions; (i) a plateau near the surface between 0 and 3 $$mu$$m in depth, which can be ascribed to the electronic stopping Se, (ii) a broad peak at 6 $$mu$$m in depth, and (iii) a sharp dip at 13 $$mu$$m in depth, which is attributed to the nuclear stopping Sn peak.

Journal Articles

Swift heavy ion irradiation to non-amorphizable CaF$$_{2}$$ and amorphizable Y$$_{3}$$Al$$_{5}$$O$$_{12}$$ (YAG) crystals

Amekura, Hiroshi*; Li, R.*; Okubo, Nariaki; Ishikawa, Norito; Chen, F.*

Nuclear Instruments and Methods in Physics Research B, 474, p.78 - 82, 2020/07

 Times Cited Count:5 Percentile:64.77(Instruments & Instrumentation)

Yttrium-aluminum-garnet (YAG) and calcium fluoride (CaF$$_{2}$$) were irradiated with 200 MeV Xe ions. YAG crystal was transformed to an amorphous phase, whereas CaF$$_{2}$$ shows the non-amorphizable nature. In spite of amorphization, YAG maintained its transparency, whereas CaF$$_{2}$$ markedly loses it transparency showing a broad absorption band centered at 550 nm.

Journal Articles

Matrix-material dependence on the elongation of embedded gold nanoparticles induced by 4 MeV C$$_{60}$$ and 200 MeV Xe ion irradiation

Li, R.*; Narumi, Kazumasa*; Chiba, Atsuya*; Hirano, Yu*; Tsuya, Daiju*; Yamamoto, Shunya*; Saito, Yuichi*; Okubo, Nariaki; Ishikawa, Norito; Pang, C.*; et al.

Nanotechnology, 31(26), p.265606_1 - 265606_9, 2020/06

 Times Cited Count:4 Percentile:35.09(Nanoscience & Nanotechnology)

We report the elongation of embedded Au nanoparticles (NPs) in three different matrices under irradiations of 4 MeV C$$_{60}$$ ions and 200 MeV Xe ions. Large elongation of Au NPs was observed for crystalline indium tin oxide (ITO) under both 4 MeV C$$_{60}$$ and 200 MeV Xe irradiation. The ITO layer preserved the crystallinity even after large elongation was induced. This is the first report of the elongation of metal NPs in a crystalline matrix.

Journal Articles

Ag nanoparticles embedded in Nd:YAG crystals irradiated with tilted beam of 200 MeV Xe ions; Optical dichroism correlated to particle reshaping

Li, R.*; Pang, C.*; Amekura, Hiroshi*; Ren, F.*; H$"u$bner, R.*; Zhou, S.*; Ishikawa, Norito; Okubo, Nariaki; Chen, F.*

Nanotechnology, 29(42), p.424001_1 - 424001_8, 2018/10

 Times Cited Count:5 Percentile:28.92(Nanoscience & Nanotechnology)

We report on the fabrication of reshaped Ag nanoparticles (NPs) embedded in a Nd:YAG crystal by combining Ag ion implantation and swift heavy Xe ion irradiation. The localized surface plasmon resonance (LSPR) effect is proved to be efficiently modulated according to the phenomenon of polarization-dependent absorption. The LSPR peak located at 448 nm shows red shift and blue shift at 0 degree and 90 degree polarization, respectively, which is in good agreement with calculation by discrete dipole approximation. Based on the near-field intensity distribution, the interaction between reshaped NPs shows a non-ignorable effect on the optical absorption. Furthermore, the polarization-dependence of the photoluminescence (PL) intensity is analyzed, which is positively related to the modulated LSPR absorption. It demonstrates the potential of the enhancement of PL intensity by embedded plasmonic Ag NPs.

Journal Articles

Vaporlike phase of amorphous SiO$$_{2}$$ is not a prerequisite for the core/shell ion tracks or ion shaping

Amekura, Hiroshi*; Kluth, P.*; Mota-Santiago, P.*; Sahlberg, I.*; Jantunen, V.*; Leino, A. A.*; Vazquez, H.*; Nordlund, K.*; Djurabekova, F.*; Okubo, Nariaki; et al.

Physical Review Materials (Internet), 2(9), p.096001_1 - 096001_10, 2018/09

 Times Cited Count:8 Percentile:35.48(Materials Science, Multidisciplinary)

When a swift heavy ion (SHI) penetrates amorphous SiO$$_{2}$$, a core/shell (C/S) ion track is formed due to vaporization, where the ion track consists of a lower-density core and a higher-density shell. Here we reexamine this hypothesis. The MD simulations indicate that the vaporization is not induced under 50-MeV Si irradiation ($$Se$$ = 3 keV/nm), but the C/S tracks and the ion shaping of nanoparticles are nevertheless induced. Thus, the vaporization is not a prerequisite for the C/S tracks and the ion shaping.

Journal Articles

Shape elongation of embedded Zn nanoparticles induced by swift heavy ion irradiation; A SAXS study

Amekura, Hiroshi*; Kono, Kenichiro*; Okubo, Nariaki; Ishikawa, Norito

Physica Status Solidi (B), 252(1), p.165 - 169, 2015/01

 Times Cited Count:10 Percentile:44.22(Physics, Condensed Matter)

Zinc nanoparticles (NPs) of 10 nm in diameter were irradiated with 200 MeV Xe$$^{14+}$$ ions with various fluences. The shape elongation of the NPs and the mean inter-particle (IP) distance were evaluated by small angle X-ray scattering (SAXS) in the transmission configuration using synchrotron X-ray of 18 keV. The azimuth angle dependence of SAXS signal, which was isotropic for unirradiated state, changed to anisotropic. It indicated that the NPs collectively deformed from spheres to spheroids.

Journal Articles

Thermal stability of embedded metal nanoparticles elongated by swift heavy ion irradiation; Zn nanoparticles in a molten state but preserving elongated shapes

Amekura, Hiroshi*; Sele, M. L.*; Ishikawa, Norito; Okubo, Nariaki

Nanotechnology, 23(9), p.095704_1 - 095704_7, 2012/03

 Times Cited Count:12 Percentile:47.64(Nanoscience & Nanotechnology)

The degree of shape elongation was evaluated at room temperature (RT) by two different optical methods for solid Zn and V nanoparticles. The melting of NPs is not the key factor for the recovery to the spherical shape.

Journal Articles

Asynchronous melting of embedded metal nanoparticles and silica matrix for shape elongation induced by swift heavy ion irradiation

Amekura, Hiroshi*; Ishikawa, Norito; Okubo, Nariaki; Nakayama, Yoshiko*; Mitsuishi, Kazuki*

Nuclear Instruments and Methods in Physics Research B, 269(23), p.2730 - 2733, 2011/12

 Times Cited Count:12 Percentile:68.71(Instruments & Instrumentation)

Although the mechanism of shape-elongation of nanoparticles (NPs) by swift-heavy-ion-irradiation is still under debate, melting and solidification for pico-seconds of NPs by thermal spikes has been proposed as one of the processes involved. Elongation of high melting point (MP) NPs (vanadium, $$T$$$$_{rm MP}^{rm bulk}$$ = 1890 $$^{circ}$$C) and of low MP NPs (zinc, $$T$$$$_{rm MP}^{rm bulk}$$ = 420 $$^{circ}$$C) were compared under irradiation with 200 MeV Xe$$^{14+}$$ ions. Irrespective of the large difference in their MPs, both the V and Zn NPs showed comparable elongation. The insensitivity of elongation to the MP can be explained by the asynchronicity of melting of the silica and the NPs.

Journal Articles

Zn nanoparticles irradiated with swift heavy ions at low fluences; Optically-detected shape elongation induced by nonoverlapping ion tracks

Amekura, Hiroshi*; Ishikawa, Norito; Okubo, Nariaki; Ridgway, M.*; Giulian, R.*; Mitsuishi, Kazuki*; Nakayama, Yoshiko*; Buchal, C.*; Mantl, S.*; Kishimoto, Naoki*

Physical Review B, 83(20), p.205401_1 - 205401_10, 2011/05

 Times Cited Count:34 Percentile:78.85(Materials Science, Multidisciplinary)

Elongation of metal nanoparticles (NPs) embedded in silica induced by swift heavy-ion irradiation, from spheres to spheroids, has been evaluated at low fluences by linearly polarized optical absorption spectroscopy. It is important to clarify whether the high fluences, i.e., track overlaps, are essential for the elongation. Zn NPs embedded in silica were irradiated with 200-MeV Xe ions. The comparison with numerical simulation suggested that the elongation of Zn NPs was induced by nonoverlapping ion tracks.

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