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Journal Articles

Tolerance of spin-Seebeck thermoelectricity against irradiation by swift heavy ions

Okayasu, Satoru; Harii, Kazuya*; Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Ishida, Masahiko*; Ieda, Junichi; Saito, Eiji

Journal of Applied Physics, 128(8), p.083902_1 - 083902_7, 2020/08

Journal Articles

Swift heavy ion irradiation effects in nanocrystalline gold

Chimi, Yasuhiro; Iwase, Akihiro*; Ishikawa, Norito; Kobiyama, Mamoru*; Inami, Takashi*; Kambara, Tadashi*; Okuda, Shigeo*

Nuclear Instruments and Methods in Physics Research B, 245(1), p.171 - 175, 2006/04

 Times Cited Count:13 Percentile:30.44(Instruments & Instrumentation)

We have studied effects of irradiation with energetic particles on defect accumulation in nanocrystalline gold (nano-Au). The specimens of nano-Au foil (3-5 $$mu$$m thickness) with various grain sizes (23-156 nm) are prepared by the gas deposition method and subsequent thermal annealings. Irradiations of the specimens with 60-MeV $$^{12}$$C ions, 3.54-GeV $$^{136}$$Xe ions or 2.0-MeV electrons are performed at low temperature. The defect accumulation behavior is observed by measuring the electrical resistivity change during irradiation. Through an analysis of defect accumulation behavior, cross-sections for defect production, $$sigma$$$$_{d}$$, and annihilation, $$sigma$$$$_{r}$$, in nano-Au increase monotonically as the grain size decreases. These results are considered to be caused by the existence of a large volume fraction of the regions near grain boundaries in nano-Au where the threshold energy for atomic displacements, E$$_{d}$$, becomes lower than in polycrystalline gold. The possibility of electronic excitation effects in nano-Au is also discussed.

Journal Articles

Effects of swift heavy ion irradiation on magnetic properties of Fe-Rh alloy

Fukuzumi, Masafumi*; Chimi, Yasuhiro; Ishikawa, Norito; Suzuki, Motohiro*; Takagaki, Masafumi*; Mizuki, Junichiro; Ono, Fumihisa*; Neumann, R.*; Iwase, Akihiro*

Nuclear Instruments and Methods in Physics Research B, 245(1), p.161 - 165, 2006/04

 Times Cited Count:17 Percentile:22.34(Instruments & Instrumentation)

We have performed swift heavy ion irradiations in Fe-50at.%Rh alloys at room temperature. Before and after the irradiations, the magnetic properties and the lattice structure are measured using Superconducting QUantum Interference Device (SQUID) and X-Ray Diffractometer (XRD), respectively. We have also performed X-ray Magnetic Circular Dichroism (XMCD) measurement near the Fe K-edge at the synchrotron radiation facility, SPring-8, to examine the irradiation-induced ferromagnetic state near the specimen surface. We have found that the swift heavy ion irradiations induce the ferromagnetic state in Fe-50at.%Rh alloy below the antiferromagnetism-ferromagnetism transition temperature of the unirradiated alloy and the lattice expasion by 0.3%. For the specimens irradiated with swift heavy ions, we observe the XMCD spectra correponding to ferromagnetisim, which depend on the mass of irradiating ions and/or irradiation fluence. Effects of energy loss through electronic excitation and elastic collisions on lattice and magnetic structures of Fe-Rh alloy are discussed.

Journal Articles

Microstructure and atomic disordering of magnesium aluminate spinel irradiated with swift heavy ions

Yamamoto, Tomokazu*; Shimada, Mikio*; Yasuda, Kazuhiro*; Matsumura, Sho*; Chimi, Yasuhiro; Ishikawa, Norito

Nuclear Instruments and Methods in Physics Research B, 245(1), p.235 - 238, 2006/04

 Times Cited Count:11 Percentile:35.92(Instruments & Instrumentation)

We have investigated the microstructure change and atomic disordering process in magnesium aluminate spinel, MgO ${it n}$Al$$_{2}$$O$$_{3}$$ with ${it n}$=1.1 and 2.4, irradiated with swift heavy ions of 200-MeV Xe$$^{14+}$$ and 350-MeV Au$$^{28+}$$. Transmission electron microscopy techniques of bright-field (BF) and high-resolution (HR) imaging, as well as high angular resolution electron channeling X-ray spectroscopy (HARECXS) are employed in quantitative analysis of irradiation-induced structural change. Ion tracks show columnar dark contrast of 4-7 nm in diameter at the incident surface in BF images. Strong strain contrast often arises among plural ion tracks formed closely. Clear lattice fringes are observed in HR images even inside the ion tracks. It indicates that the spinel crystals are not amorphized but partially disordered along the ion tracks. Quantitative HARECXS analysis shows that cation disordering progresses with ion fluence. It is revealed that the disordered regions are extended over 12$$pm$$2 nm in diameter along the ion tracks.

Oral presentation

Material modification and nanostructuring by swift heavy ions

Ishikawa, Norito

no journal, , 

Radiation damage due to irradiation with swift heavy ions (SHI) with the energy above 1 MeV/u has many different features compared to that due to irradiation with electrons and neutrons. One of the well-known phenomena related to SHI irradiation is formation of ion tracks. An ion track is a cylindrical region where the material near ion-path is locally modified in nanometric scale. Ion tracks are of great interest in a wide variety of research fields including nuclear materials science, physics of ion-solid interaction, nanotechnology, archaeology and so on. Mechanism of ion track formation in inorganic materials has always been one of the central and intriguing subjects in the SHI research community. It is still challenging to untangle the related problems. In this plenary talk, I would like to concentrate on the vital part of the recent advancement so that the audience can understand the logical pathway of the latest research works.

Oral presentation

FE-SEM observation of dotted hillocks formed by irradiation at grazing incidence of swift heavy ions

Kitamura, Akane; Ishikawa, Norito; Kondo, Keietsu; Fujimura, Yuki; Yamamoto, Shunya*

no journal, , 

Swift heavy ions can create nanosized hillocks on the surfaces of various ceramics. When these materials are irradiated with swift heavy ions at normal incidence, each ion impact results in the formation of a single hillock on the surfaces. In contrast, irradiation at grazing incidence forms chains of multiple hillocks on the surface such as strontium titanate (SrTiO$$_{3}$$). So far, chains of multiple hillocks have been investigated using atomic force microscopy (AFM). It should be noted that AFM measurements involve systematic errors of several nanometers due to the finite size of the probe tip. Consequently, it is possible that the image of one hillock may merge with that of a neighboring hillock even if the two hillocks are well separated. In contrast to AFM, field-emission scanning electron microscopy (FE-SEM) is a useful technique for obtaining higher-resolution images. In this study, we observed multiple nanohillocks on the surfaces of SrTiO$$_{3}$$ using FE-SEM. Crystals of SrTiO$$_{3}$$(100) and 0.5 wt% Nb-doped SrTiO$$_{3}$$(100) were irradiated with 200 MeV Xe ions, respectively. The irradiated angle between the sample surface and the beam was less than 2$$^{circ}$$. On the SrTiO$$_{3}$$ surface, a chain of periodic nanohillocks is created along the ion path. In contrast, black lines accompanied by hillocks are observed on the Nb-doped SrTiO$$_{3}$$ surface. As a result, we proposed a new model of formation process for the hillock chains in the framework of Rayleigh instability.

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