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Journal Articles

Reversible elastocaloric effect at ultra-low temperatures in nanocrystalline shape memory alloys

Ahadi, A.*; Kawasaki, Takuro; Harjo, S.; Ko, W.-S.*; Sun, Q. P.*; Tsuchiya, Koichi*

Acta Materialia, 165, p.109 - 117, 2019/02

 Times Cited Count:15 Percentile:7.12(Materials Science, Multidisciplinary)

Journal Articles

Quantum twin spectra in nanocrystalline silicon

Matsumoto, Takahiro*; Ohara, Takashi; Sugimoto, Hidehiko*; Bennington, S. M.*; Ikeda, Susumu*

Physical Review Materials (Internet), 1(5), p.051601_1 - 051601_6, 2017/10

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Size and dopant-concentration dependence of photoluminescence properties of ion-implanted phosphorus- and boron-codoped Si nanocrystals

Nakamura, Toshihiro*; Adachi, Sadao*; Fujii, Minoru*; Sugimoto, Hiroshi*; Miura, Kenta*; Yamamoto, Shunya

Physical Review B, 91(16), p.165424_1 - 165424_8, 2015/04

 Times Cited Count:12 Percentile:42.7(Materials Science, Multidisciplinary)

Semiconductor nanocrystals have unique electrical and optical properties, because of the quantum confinement effect, and the doping of impurities into nanocrystals. In this study, we investigated the photoluminescence (PL) properties of phosphorus- (P) and boron- (B) co-doped Si nanocrystals (Si NCs), which was synthesized using an ion implantation technique. The Si-NC size (average diameter: 3.5, 4.4, 5.2 nm) and the P and B ion doses (0.1-4.5$$times$$10$$^{16}$$ cm$$^{-2}$$)values were systematically varied. We find that the PL peak energy shifts to lower values with increasing the average diameters of Si NCs and PB ion dose. The results of PL measurements indicate that the PL spectra are due to the band-to-band transition at the reduced Si-NC band gap caused by the formation of impurity and the radiative transitions between defect- and/or impurity-related localized states. It was found that the PL properties can be controlled by varying the Si-NC size as well as the dopant concentration.

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

Sputtering of nano-crystalline gold by high energy heavy ions

Matsunami, Noriaki*; Sataka, Masao; Iwase, Akihiro; Inami, Takashi*; Kobiyama, Mamoru*

Journal of Nuclear Materials, 302(2-3), p.206 - 210, 2002/04

 Times Cited Count:8 Percentile:49.66(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Accumulation and recovery of defects in ion-irradiated nanocrystalline gold

Chimi, Yasuhiro; Iwase, Akihiro; Ishikawa, Norito; Kobiyama, Mamoru*; Inami, Takashi*; Okuda, S.*

Journal of Nuclear Materials, 297(3), p.355 - 357, 2001/09

 Times Cited Count:182 Percentile:2.33(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Hillock formation at surface of ceramics irradiated with swift heavy ions

Ishikawa, Norito; Taguchi, Tomitsugu*

no journal, , 

In this study, CeO$$_{2}$$, a surrogate for nuclear fuel ceramics, was irradiated with 200 MeV Au ions at oblique incidence. Observation of as-irradiated samples by transmission electron microscope (TEM) shows that hillocks are created not only at the wide surfaces, but also at the side edge of the thin samples. Since the hillocks created at the side edge can be imaged without overlapping of matrix image, their shape and crystallographic features can be revealed. The present method is also applied for observing hillocks created for CaF$$_{2}$$, which has the same crystal structure with CeO$$_{2}$$. Although hillock-like shape has been reported so far for hillocks of CaF$$_{2}$$, the present study revealed that not only hillock-like shaped but also polyhedron shaped hillocks are created by irradiation with swift heavy ions. The polyhedron shaped hillocks have faceted surfaces reflecting the crystal lattice structure.

Oral presentation

Bridging scale studies of nanocrystalline steels using pulsed neutron diffraction

Harjo, S.; Kawasaki, Takuro; Gong, W.*

no journal, , 

Oral presentation

Barium titanate nanocrystals solid-solutionized with barium zirconate

Saito, Junichi; Kudo, Junki*; Kiba, Kazumasa*; Matsuo, Naoki*; Park, S. K.*; Takesue, Naohisa*

no journal, , 

no abstracts in English

Oral presentation

Barium titanate nanocrystals solid solutionized with barium zirconate and calcium titanate

Saito, Junichi; Matsuo, Naoki*; Kiba, Kazumasa*; Kudo, Junki*; Park, S. K.*; Takesue, Naohisa*

no journal, , 

no abstracts in English

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