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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:13 Percentile:57.42(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

Observation of the laser-induced surface dynamics using the single-shot soft X-ray laser probe

Hasegawa, Noboru; Ochi, Yoshihiro; Kawachi, Tetsuya; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kaihori, Takeshi; Morita, Toshimasa; Sasaki, Akira; Terakawa, Kota*; et al.

X-Ray Lasers 2012; Springer Proceedings in Physics, Vol.147, p.117 - 120, 2014/00

 Times Cited Count:0 Percentile:0

We have developed the femto-second laser pump and soft X-ray laser probe system in order to observe the dynamical processes of the femto-second laser ablation. By using this system, we succeed to obtain the temporal evolution of the soft X-ray reflectivity from the laser induced Pt surface. The results lead that the rate of decrease in the reflectivity of the probe beam has a non-linear relation with the pump laser fluence.

Journal Articles

Measurement of femtosecond laser ablation by soft X-ray laser interferometory and reflective imaging

Nishikino, Masaharu; Hasegawa, Noboru; Ishino, Masahiko; Yamagiwa, Mitsuru; Kawachi, Tetsuya; Minami, Yasuo*; Terakawa, Kota*; Takei, Ryota*; Baba, Motoyoshi*; Suemoto, Toru; et al.

JAEA-Conf 2013-001, p.16 - 19, 2013/09

The dynamics of the femtosecond laser ablation is still not clear at the early stage. Several studies on the time-resolved imaging of femtosecond laser ablation process have been performed on various materials. In this study, we have demonstrated a pump and probe imaging of the metal surface morphology during the femtosecond laser ablation by using the laser-driven plasma induced soft X-ray laser (SXRL) as a probe beam. The pumping laser used for ablation was a Ti:Sapphire laser system based on chirped pulse amplification. The pump beam had a Gaussian profile and the focal spot size on the metal surface was about 70 micron at FWHM. The dependence for the pump laser fluence of the ablation surface expansion and the surface condition (roughness and density gradient) were observed from the soft X-ray interferogram and reflective image, respectively.

Journal Articles

Experimental verification of femtosecond laser ablation schemes by time-resolved soft X-ray reflective imaging

Tomita, Takuro*; Yamamoto, Minoru*; Hasegawa, Noboru; Terakawa, Kota*; Minami, Yasuo*; Nishikino, Masaharu; Ishino, Masahiko; Kaihori, Takeshi*; Ochi, Yoshihiro; Kawachi, Tetsuya; et al.

Optics Express (Internet), 20(28), p.29329 - 29337, 2012/12

 Times Cited Count:18 Percentile:69.28(Optics)

Pump and probe reflective imaging using a soft X-ray laser probe was applied to the observation of the early stage of femtosecond laser ablation process on platinum. In strongly excited area, drastic and fast reflectivity drop was observed. In moderately excited area, the decay of the reflectivity is slower than that in the strongly excited area, and the reflectivity reaches its minimum at t = 160 ps. In weakly excited area, laser-induced reflectivity change was not observed. These results give the critical information about the femtosecond laser ablation.

Journal Articles

Development of the X-ray interferometer and the method of temporal synchronization of X-ray and optical pulse

Hasegawa, Noboru; Yamamoto, Minoru*; Terakawa, Kota*; Nishikino, Masaharu; Ochi, Yoshihiro; Minami, Yasuo*; Tomita, Takuro*; Kawachi, Tetsuya; Suemoto, Toru

AIP Conference Proceedings 1465, p.23 - 27, 2012/07

 Times Cited Count:0 Percentile:0.13

We have developed a soft X-ray laser (SXRL) interferometer capable of the single-shot imaging of nano-scaled structure dynamics. The depth and lateral resolutions of the interferometer were about 1 nm and 1.8 micron, respectively. We observed the initial stage ($$sim$$50 ps) of the ablation process of the Pt surface pumped by a 70 fs Ti:Sapphire laser pulse. The expansion speed of the Pt surface (34 nm/50 ps) indicated that the nano-bubble structures were formed in the initial stage of the ablation. In order to observe the detailed dynamics, the precision of temporal synchronization between the pump and probe pulses was improved to be 3 ps by adopting a portion of the SXRL and pump beams as the time fiducials.

Journal Articles

Picosecond soft-X-ray laser interferometer for probing nanometer surface structure

Ochi, Yoshihiro; Terakawa, Kota*; Hasegawa, Noboru; Yamamoto, Minoru*; Tomita, Takuro*; Kawachi, Tetsuya; Minami, Yasuo*; Nishikino, Masaharu; Imazono, Takashi; Ishino, Masahiko; et al.

Japanese Journal of Applied Physics, 51(1), p.016601_1 - 016601_3, 2012/01

 Times Cited Count:10 Percentile:44.63(Physics, Applied)

We have developed a soft X-ray laser interferometer based on the double Lloyd's mirror and obtained a single shot interferogram by a 7-ps pulse at the wavelength of 13.9 nm. Micrometer grooves with 5-nm depth were successfully reconstructed from the interferogram. The lateral and depth resolutions were estimated to be 1.5 $$mu$$m and better than 1 nm, respectively. This interferometer will be an attractive diagnostic device for observing transiently changing nano-scale deviations on solid surfaces.

Journal Articles

Phosphorus and boron codoping of silicon nanocrystals by ion implantation; Photoluminescence properties

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

Physical Review B, 85(4), p.045441_1 - 045441_7, 2012/01

 Times Cited Count:24 Percentile:72.65(Materials Science, Multidisciplinary)

Silicon nanocrystals (Si-nc's) such as nanometer-sized Si dots embedded in a SiO$$_{2}$$ matrix and porous Si have been intensively investigated because of their interesting photoluminescence (PL) properties. Si-nc's exhibit strong and visible emission at room temperature. Because of their compatibility with Si-based technology, light-emitting Si-nc's are an attractive candidate for materials used in various optoelectronic device applications. In this study, the PL properties of n- and p-type dopants phosphorus (P) and boron (B) co-doped Si-nc's prepared by the ion implantation were studied. For (P, B) co-doped Si-nc's, the donor-acceptor (D-A)-pair recombination emission was clearly observed on the long-wavelength side of the intrinsic Si-nc emission. The D-A-pair recombination energy is found to be smaller than the band-gap energy of bulk Si and is strongly dependent on the number of P and B impurities doped in a Si-nc's.

Journal Articles

Source development and novel applications of laser-driven plasma X-ray lasers in JAEA

Kawachi, Tetsuya; Hasegawa, Noboru; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Oba, Toshiyuki; Kaihori, Takeshi; Kishimoto, Maki; Ochi, Yoshihiro; Tanaka, Momoko; et al.

X-Ray Lasers 2010; Springer Proceedings in Physics, Vol.136, p.15 - 24, 2011/12

This paper reviews recent improvement in the source development of laser-driven X-ray lasers and the applications in the research fields of material science, laser processing, X-ray imaging, and radiation damage in biological cells. In the application for material science, we have firstly observed temporal correlation between the domain structures of ferro-electric substance under the Curie temperature. In the laser processing, new X-ray laser interferometer reveals us the nano-scale surface distortion of substance pumped by a femto-second optical pulse. In the X-ray diffraction image, we have taken several static images of micro-structure of samples: now we are trying to extend the objective to nano-scale dynamics using pump and probe method. In the radiation damage of biological cells, we observed double strand break in DNA using X-ray laser exposure; this results are compared with the case using incoherent several KeV X-ray exposure.

Journal Articles

Development of the X-ray interferometer and the method of spatial and temporal synchronization of XRL and optical pulse

Hasegawa, Noboru; Ochi, Yoshihiro; Kawachi, Tetsuya; Terakawa, Kota*; Tomita, Takuro*; Yamamoto, Minoru; Nishikino, Masaharu; Oba, Toshiyuki; Kaihori, Takeshi; Imazono, Takashi; et al.

X-Ray Lasers 2010; Springer Proceedings in Physics, Vol.136, p.353 - 358, 2011/12

The understanding of the dynamics of the initial process is important for the micro processing and welding by the ultra-short laser pulse. The X-ray laser is suitable for probing this initial process because it has short wavelength (Ni-like Ag, 13.9 nm) and short duration (7 ps). For this investigation, the origin of time of the pumping pulse is quite important. In this study, we used the scintillation plate and the plasma gate technique to realize the spatial and temporal synchronization of the pump and probe pulses. For the spatial alignment, a CsI scintillation plate that was set at the sample position was illuminated by both the X-ray laser pulse, and the fluorescence light were detected by the CCD camera. For the temporal synchronization, we set a thin foil at the sample position. We measured the transmission of the X-ray laser while changing a temporal delay of the pumping laser with respect to the time of X-ray laser pulse to obtain the origin of the irradiation time.

Journal Articles

Observation of the laser-induced surface dynamics by the single-shot X-ray laser interferometer

Hasegawa, Noboru; Ochi, Yoshihiro; Kawachi, Tetsuya; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kaihori, Takeshi; Sasaki, Akira; Terakawa, Kota*; Minami, Yasuo*; et al.

Proceedings of SPIE, Vol.8140, p.81400G_1 - 81400G_8, 2011/10

 Times Cited Count:3 Percentile:84.58

We have developed a soft X-ray laser (SXRL) interferometer capable of the single-shot imaging of nano-scaled structure dynamics. The interferometer consisted of the reflection optics including double Lloyd's mirrors and focusing optics, and the interference fringes are produced on the detector surface. By using this interferometer, the initial stage ($$sim$$50 ps) of the ablation process of the Pt surface pumped by a 70 fs Ti:Sapphire laser pulse was observed. The expansion speed of the surface estimated from the result (34 nm/50 ps) indicated that the nano-bubble structures were formed in the initial stage of the ablation. In order to observe the detailed dynamics, the temporal synchronization between the pump and probe pulses was improved to be 3 ps by adopting a portion of the SXRL and pump beams as the time fiducials, to which the pump and probe timing was adjusted by using the X-ray streak camera.

Journal Articles

Observation of femtosecond laser ablation process by using the soft X-ray laser interferometer

Yamamoto, Minoru; Hasegawa, Noboru; Terakawa, Kota*; Umeda, Yoshifumi*; Tomita, Takuro*; Ochi, Yoshihiro; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kaihori, Takeshi; et al.

Proceedings of 12th International Symposium on Laser Precision Microfabrication (LPM 2011) (Internet), 4 Pages, 2011/06

Femtosecond lasers have been used for material processing. However, the physical processes responsible for femtosecond laser ablation have not been understood completely. These processes involve melting, vaporization, re-solidification or ablation, which occur in a very short time from pico- to nano-seconds. To understand the physical processes, it is essential to reveal the dynamics of ultrafast surface morphological change after laser irradiation. At JAEA, the laser-driven plasma soft X-ray laser (SXRL) that has extremely high spatial and spectral purity was constructed. It delivers soft X-ray photons at 89.2 eV (13.9 nm) with a photon number of exceeding $$10^{10}$$, which is sufficient to obtain a single shot interferogram. By using this system, the soft X-ray laser interferometer with the lateral resolution of 1.8 $$mu$$m and a depth resolution of 1 nm was developed. We report on demonstration of time-resolved measurement of femtosecond-laser ablation dynamics by using the soft X-ray laser interferometer.

Journal Articles

Enhancement of local electrical conductivities in SiC by femtosecond laser modification

Deki, Manato; Ito, Takuto*; Yamamoto, Minoru*; Tomita, Takuro*; Matsuo, Shigeki*; Hashimoto, Shuichi*; Kitada, Takahiro*; Isu, Toshiro*; Onoda, Shinobu; Oshima, Takeshi

Applied Physics Letters, 98(13), p.133104_1 - 133104_3, 2011/03

 Times Cited Count:13 Percentile:52.83(Physics, Applied)

Journal Articles

A Study on groundwater infiltration in the Horonobe area, northern Hokkaido, Japan

Yokota, Hideharu; Yamamoto, Yoichi; Maekawa, Keisuke; Hara, Minoru*

Proceedings of 13th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM 2010) (CD-ROM), p.81 - 86, 2010/10

It is important for assessing the safety of geological disposal of high-level radioactive waste to understand groundwater flow as the driving force of mass transport. In the groundwater-flow simulation, hydraulic boundary conditions are required, including groundwater recharge rates. However, infiltration of water from the surface is difficult to clarify in detail because water near the surface is sensitive to external influence such as climatic variations. In the Horonobe area of northern Hokkaido, the Japan Atomic Energy Agency has been carrying out various hydrological observations to estimate the recharge rate. In the Horonobe area, subsurface temperature and soil moisture content have been observed at HGW-1 site and Hokushin Meteorological Station. These results have revealed the groundwater infiltration and recharge occurring throughout year, the shallow groundwater-infiltration velocity depending on the depth, and the position of Zero Flux Plane. In the future, it is necessary to quantitatively assess the shallow groundwater infiltration and recharge rate, the intermediate runoff, and the evapotranspiration based on the observed data of the weighing lysimeter, the tensiometer, and so on.

Journal Articles

Single-shot picosecond interferometry with one-nanometer resolution for dynamical surface morphology using a soft X-ray laser

Suemoto, Toru; Terakawa, Kota*; Ochi, Yoshihiro; Tomita, Takuro*; Yamamoto, Minoru; Hasegawa, Noboru; Deki, Manato*; Minami, Yasuo*; Kawachi, Tetsuya

Optics Express (Internet), 18(13), p.14114 - 14122, 2010/06

 Times Cited Count:33 Percentile:82.72(Optics)

Using highly coherent radiation at a wavelength of 13.9 nm from a Ag-plasma soft X-ray laser, we constructed a pump-and-probe interferometer based on a double Lloyd's mirror system. The spatial resolutions are evaluated with a test pattern, showing 1.8 micrometers lateral resolution, and 1-nm depth sensitivity. This instrument enables a single-shot observation of the surface morphology with a 7-ps time-resolution. We succeeded in observing a nanometer scale surface dilation of Pt films at the early stage of the ablation process initiated by a 70 fs near infrared pump pulse.

Journal Articles

Electronic properties of femtosecond laser induced modified spots on single crystal silicon carbide

Tomita, Takuro*; Iwami, Masahiro*; Yamamoto, Minoru*; Deki, Manato*; Matsuo, Shigeki*; Hashimoto, Shuichi*; Nakagawa, Yoshinori*; Kitada, Takahiro*; Isu, Toshiro*; Saito, Shingo*; et al.

Materials Science Forum, 645-648, p.239 - 242, 2010/04

no abstracts in English

JAEA Reports

Plan and reports of coupled irradiation (JRR-3 and JOYO of research reactors) and hot facilities work (WASTEF, JMTR-HL, MMF and FMF); R&D project on irradiation damage management technology for structural materials of long-life nuclear plant

Matsui, Yoshinori; Takahashi, Hiroyuki; Yamamoto, Masaya; Nakata, Masahito; Yoshitake, Tsunemitsu; Abe, Kazuyuki; Yoshikawa, Katsunori; Iwamatsu, Shigemi; Ishikawa, Kazuyoshi; Kikuchi, Taiji; et al.

JAEA-Technology 2009-072, 144 Pages, 2010/03


"R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant" was carried out from FY2006 in a fund of a trust enterprise of the Ministry of Education, Culture, Sports, Science and Technology. The coupled irradiations or single irradiation by JOYO fast reactor and JRR-3 thermal reactor were performed for about two years. The irradiation specimens are very important materials to establish of "Evaluation of Irradiation Damage Indicator" in this research. For the acquisition of the examination specimens irradiated by the JOYO and JRR-3, we summarized about the overall plan, the work process and the results for the study to utilize these reactors and some facilities of hot laboratory (WASTEF, JMTR-HL, MMF and FMF) of the Oarai Research-and-Development Center and the Nuclear Science Research Institute in the Japan Atomic Energy Agency.

Journal Articles

Celebration of 30th anniversary of the experimental fast reactor Joyo

Nakai, Satoru; Aoyama, Takafumi; Ito, Chikara; Yamamoto, Masaya; Iijima, Minoru; Nagaoki, Yoshihiro; Kobayashi, Atsuko; Onoda, Yuichi; Ohgama, Kazuya; Uwaba, Tomoyuki; et al.

Kosoku Jikkenro "Joyo" Rinkai 30-Shunen Kinen Hokokukai Oyobi Gijutsu Koenkai, 154 Pages, 2008/06

no abstracts in English

Journal Articles

Simulation of the atmospheric dispersion of $$^{85}$$Kr from a reprocessing plant over a coastal area; Performance examination of an emergency environmental radiation dose evaluation code system "SIERRA-II"

Takeyasu, Masanori; Iida, Takao*; Watanabe, Hitoshi; Takeishi, Minoru; Yamamoto, Asao*

Journal of Radioanalytical and Nuclear Chemistry, 275(1), p.43 - 54, 2008/01

 Times Cited Count:1 Percentile:10.92(Chemistry, Analytical)

The performance of the computer code system "SIERRA-II" for calculating the environmental radiation dose due to an accident was assessed using the environmental monitoring data around the coastally located Tokai Reprocessing Plant (TRP) when $$^{85}$$Kr was discharged during its operation. The agreement within a factor of 5 between the calculated and observed air concentrations of $$^{85}$$Kr in areas of a few km from the TRP was achieved in 57% of the comparison data, and the agreement within a factor of 2 was obtained in 29%, disregarding the internal boundary layer. According to the vertical profile of atmospheric temperatures, the internal boundary layer was modeled in the SIERRA-II and the agreement became better than when the internal boundary layer was not considered.

JAEA Reports

Analysis of ground water from boreholes, river water and precipitation in the Underground Research Laboratory Project

Kunimaru, Takanori; Shibano, Kazunori; Kurikami, Hiroshi; Tomura, Goji; Hara, Minoru; Yamamoto, Hajime*

JAEA-Data/Code 2007-015, 113 Pages, 2007/11


In the Horonobe Underground Research Laboratory (URL) Project, ground water from boreholes, river water and precipitation have been preiodically analyzed for the environmental monitoring since the fiscal year 2001. This report shows the data set of water chemistry since the fiscal year 2001 to the fiscal year 2006.

JAEA Reports

Improvement in oil seal performance of Gas Compressor in HTTR

Oyama, Sunao*; Hamamoto, Shimpei; Kaneshiro, Noriyuki*; Nemoto, Takahiro; Sekita, Kenji; Isozaki, Minoru; Emori, Koichi; Ito, Yoshiteru*; Yamamoto, Hideo*; Ota, Yukimaru; et al.

JAEA-Technology 2007-047, 40 Pages, 2007/08


High-Temperature engineering Test Reactor (HTTR) built by Japan Atomic Energy Agency (JAEA) has commonly used reciprocating compressor to extract helium gas and discharge helium gas into primary/secondary coolant helium loop from helium purification system. Rod-seal structure of the compressor is complicated from a prevention coolant leak standpoint. Because of frequently leakage of seal oil in operation, Rod seal structure isn't as reliable as it should be sustainable in the stable condition during long term operation. As a result of investigations, leakage's root is found in that seal were used in a range beyond limit sliding properties of seal material. Therefore a lip of the seal was worn and transformed itself and was not able to sustain a seal function. Endurance test using materials testing facility and verification test using a actual equipment on candidate materials suggest that a seal of fluorine contained resin mixed graphite is potentially feasible material of seal.

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