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Hirade, Tetsuya; Oka, Toshitaka; Morishita, Norio*; Idesaki, Akira; Shimada, Akihiko
Materials Science Forum, 733, p.151 - 154, 2013/00
Times Cited Count：7 Percentile：93.73(Materials Science, Multidisciplinary)Polyimide polymers such as Kapton show a very good performance at high radiation environment such as in space or in radiation facilities. Positron annihilation lifetime measurement is a widely used method for materials science, and the lifetime of triplet positronium (electron-positron pair) can give important information of free volume of polymers. However, there is no positronium formation in Kapton and hence this method was no applied for polymer studies. Here, we indicated that free positron annihilation lifetime can give information of change of free volume by showing the temperature dependence of the lifetime. We applied this method to study irradiation effects on Kapton and we successfully indicated that the free positron lifetime can be applied for polymer studies.
-Irradiated n-type 4H-SiCBeyer, F. C.*; Hemmingsson, C. G.*; Pedersen, H.*; Henry, A.*; Isoya, Junichi*; Morishita, Norio*; Oshima, Takeshi; Janz
n, E.*
Journal of Physics D; Applied Physics, 45(45), p.455301_1 - 455301_7, 2012/11
Times Cited Count：18 Percentile：57.55(Physics, Applied)
interfacesUmeda, Takahide*; Kosugi, Ryoji*; Fukuda, Kenji*; Morishita, Norio*; Oshima, Takeshi; Ezaki, Kana*; Isoya, Junichi*
Materials Science Forum, 717-720, p.427 - 432, 2012/05
Times Cited Count：7 Percentile：95.12(Materials Science, Multidisciplinary)Metal-Oxide (SiO)-Semiconductor (MOS) structures fabricated on Silicon Carbide (SiC) were studied using Electrically Detected Magnetic Resonance technique (EDMR). The residual Carbons are expected to be near the interface between SiC and SiC-SiOSiO, which is different from Si-SiO interface. By the EDMR measurements at 50K, a defect center related to C dangling bonds which is called P
center and also a center related to C dangling bonds terminated by hydrogens or nitrogens (Ns) which is called P were observed. In addition, a center related to N donor which is called Nh exist near the interface from N-treatment samples. This suggests that carrier concentration increases near the interface due to the introduction of donors, and as a result, the channel conductance increases.
interfaces studied by electrically detected magnetic resonanceUmeda, Takahide*; Ezaki, Kana*; Kosugi, Ryoji*; Fukuda, Kenji*; Oshima, Takeshi; Morishita, Norio*; Isoya, Junichi*
Applied Physics Letters, 99(14), p.142105_1 - 142105_3, 2011/10
Times Cited Count：50 Percentile：85.84(Physics, Applied)
-type 4H-SiCBeyer, F. C.*; Hemmingsson, C.*; Pedersen, H.*; Henry, A.*; Janzn, E.*; Isoya, Junichi*; Morishita, Norio*; Oshima, Takeshi
Journal of Applied Physics, 109(10), p.103703_1 - 103703_6, 2011/05
Times Cited Count：17 Percentile：57.65(Physics, Applied)By low-energy electron (200 keV) irradiation into epitaxial n-type 4H-SiC with a dose of 5
10
/cm
, the bistable M-center is detected in the deep level transient spectroscopy (DLTS) spectrum. The annealing behavior of the M-center is investigated. During the annihilation process of M-center, the bistable EB-centers are detected in the low temperature range of the DLTS spectrum. The value of annealing energy of the M-center is similar to the generation energy of the EB-centers. This suggests that the M-center partially transforms to the EB-centers by annealing. The EB-centers completely disappeared after annealing temperatures higher than 700 
C. Since the threshold energy for moving Si atom in SiC is higher than the applied irradiation energy of electrons, and the annihilation temperatures are relatively low, the M-center and the EB-centers are attributed to defects related to the C atom in SiC.
Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Kudo, Hisaaki*; Katsumura, Yosuke*
Radiation Physics and Chemistry, 80(2), p.149 - 152, 2011/02
Times Cited Count：18 Percentile：77.43(Chemistry, Physical)Carboxymethyl cellulose (CMC), one of polysaccharide derivatives, at highly concentrated aqueous solution undergoes radiation-crosslinking reactions. In this topic, CMC radical, formed by reaction with OH radical attributed to radiation-induced crosslinking reaction, were studied by ESR method to understand the radiation-induced reaction mechanism of CMC aqueous solution. At first, it was succeeded to observe ESR spectra of the CMC radical using photolysis of hydrogen peroxide as the origin of OH radical. Observed ESR spectra were identified as radicals located on the secondary carbon of carboxymethyl groups. Secondly, NO saturated CMC aqueous solution 6 min after electron beam irradiation was measured by ESR method. The spectra were almost same shape as the case of photolysis of hydrogen peroxide, and were assigned as long-lived radicals located on carboxymethyl groups. Next, in the case of N and O saturation, spectra intensity become half or 0. This means that these long-lived radicals are produced by reaction with OH radical.
Hasegawa, Shin; Takahashi, Shuichi*; Iwase, Hiroki*; Koizumi, Satoshi; Morishita, Norio; Sato, Ken*; Narita, Tadashi*; Onuma, Masato*; Maekawa, Yasunari
Polymer, 52(1), p.98 - 106, 2011/01
Times Cited Count：47 Percentile：80.93(Polymer Science)Radiation-induced graft polymerization of sulfo-containing styrene derivatives into poly(ether ether ketone) (PEEK) substrates was carried out to prepare thermally and mechanically stable polymer electrolyte membranes based on an aromatic hydrocarbon polymer. Graft polymerization of ethyl 4-styrenesulfonate into a 32% crystallinity degree PEEK substrate hardly progressed, whereas graft polymerization into 11% PEEK substrate gradually progressed, achieving a grafting degree of more than 50% after 72 h. From Electron Spin Resonance analysis of irradiated PEEK films, it apparent the graft polymerization initiate from the phenoxy radicals. Small-angle X-ray scattering and small-angle neutron scattering observations clearly showed that the graft-type PEEK membranes possessed ion channel domains with the average distance of 13 nm, being larger than that of Nafion. Furthermore, there was a micro-structure in the ion channels with the average distance of 1.8 nm.
calculation study on the EI4 center in 4
- and 6-SiCCarlsson, P.*; Son, N. T.*; Gali, A.*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Magnusson, B.*; Janzn, E.*
Physical Review B, 82(23), p.235203_1 - 235203_11, 2010/12
Times Cited Count：11 Percentile：46.11(Materials Science, Multidisciplinary)Electron Paramagnetic Resonance (EPR) studies of the EI4 center in 4- and 6-Silicon Carbide (SiC) were carried out. The EI4 center was drastically enhanced in electron-irradiated high-purity semi-insulating materials by annealing at 700-750 C. An additional large-splitting 
Si hf structure and 
C hf lines of the EI4 defect were observed. Comparing the data obtained from the hf interactions and the annealing behavior, and also from supercell calculations of different carbon-vacancy-related complexes, we propose a complex between a carbon vacancy-carbon antisite and a carbon vacancy at the third-neighbor site of the antisite in the neutral charge state, (V
-C
V)
, as a new defect model for the EI4 center.
Umeda, Takahide*; Isoya, Junichi*; Oshima, Takeshi; Onoda, Shinobu; Morishita, Norio; Okonogi, Kensuke*; Shiratake, Shigeru*
Applied Physics Letters, 97(4), p.041911_1 - 041911_3, 2010/07
Times Cited Count：5 Percentile：23.5(Physics, Applied)O
catalysts observed by coincidence Doppler broadening techniqueZhang, H. J.*; Chen, Z. Q.*; Wang, S. J.*; Kawasuso, Atsuo; Morishita, Norio
Physical Review B, 82(3), p.035439_1 - 035439_8, 2010/07
Times Cited Count：29 Percentile：72.98(Materials Science, Multidisciplinary)Positronannihilation spectroscopy was used to study the microstructure and surface properties of the pores inside the NiO/AlO catalysts. The positron lifetime spectrum comprises two short and two long lifetime components. The two long lifetime components correspond to ortho-positronium (o-Ps) annihilated in microvoids and large pores, respectively. With increasing NiO content, both the latter lifetime and intensity show continuous decrease. Meanwhile, the para-positronium (p-Ps) intensity, obtained from coincidence Doppler broadening spectra, increases gradually with NiO content. The different variation in o-Ps and p-Ps intensity suggests the ortho-para conversion of Ps in NiO/AlO catalysts. The electron-spin-resonance measurements reveal that the ortho-para conversion of Ps is induced by the unpaired electrons of the paramagnetic centers of NiO.
Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Muroya, Yusa*; Kudo, Hisaaki*; Katsumura, Yosuke*
Radiation Physics and Chemistry, 79(3), p.276 - 278, 2010/03
Times Cited Count：12 Percentile：59.22(Chemistry, Physical)Carboxymethyl chitosan (CMCTS) is one kind of polysaccharide derivatives and has a good water-solubility. At a high concentrated aqueous solution, CMCTS forms gel by ionizing irradiation, though polysaccharide derivatives are generally radiation-degradation type. In general, OH radical, which is one of main water radiolysis products and very oxidative species, is said to induce crosslinking reaction of polymer solution. The purpose of this study is to understand the radiation-crosslinking mechanism of CMCTS at a high concentrated aqueous solution. In this study, identification of CMCTS radical produced by reaction with OH radical was introduced. CMCTS radical in an aqueous solution was observed directly by ESR method using photolysis of hydrogen peroxide. The ESR spectra have a large doublet split and small triplet split like [Triplet Doublet]. However, some species seemed to be overlapped on ESR spectra, because right-and-left triplet spectra are not equiform. Compared with some radicals, which have analogical structure to CMCTS, about hyperfine coupling constant, [Triplet Doublet], assigned as radical on carboxymethyl group linked to C6, and [Doublet], assigned as radical on carboxymethyl group linked to C2 or C3, were isolated from ESR spectra of experimental results. In conclusion, these spectra were identified as radicals located on secondary carbon of carboxymethyl groups.
Kikuchi, Masahiro; Hussain, M. S.*; Morishita, Norio; Ukai, Mitsuko*; Kobayashi, Yasuhiko; Shimoyama, Yuhei*
Spectrochimica Acta, Part A, 75(1), p.310 - 313, 2010/01
An electron spin resonance (ESR) spectroscopic study of radicals induced in irradiated fresh mangoes was performed. Mangoes in the fresh state were irradiated with 
-rays, lyophilized and then crushed into a powder. The ESR spectrum of the powder showed a strong main peak at 
= 2.004 and a pair of peaks centered at the main peak. The main peak was detected from both flesh and skin specimens. This peak height gradually decreased during storage following irradiation. On the other hand, the side peaks showed a well-defined dose-response relationship even at 9 days post-irradiation. The side peaks therefore provide a useful means to define the irradiation of fresh mangoes.
Son, N. T.*; Carlsson, P.*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Magnusson, B.*; Janzn, E.*
Materials Science Forum, 645-648, p.399 - 402, 2010/00
Defects in high-purity semi-insulating 4H SiC irradiated with 2 MeV electrons at room temperature were studied using Electron paramagnetic resonance (EPR). The EPR signal named EI4 defect increased with annealing temperature up to 750 C. Additional large-splitting Si hyperfine (hf) structures and C hf lines by the interaction with one C nucleus were investigated. Based on the observed hf structures, the C
symmetry as well as the annealing behaviour, the EI4 defects is determined to be the complex between two carbon vacancies and a carbon antisite in the neutral charge state, VVC. The formation of the complex is interpreted in terms of the migration of the silicon vacancy and the formation of the carbon vacancy-carbon antisite pair next to a carbon vacancy.
Beyer, F. C.*; Hemmingsson, C.*; Pedersen, H.*; Henry, A.*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Janzn, E.*
Materials Science Forum, 645-648, p.435 - 438, 2010/00
By low-energy electron irradiation of epitaxial n-type 4H-SiC, the Deep Level Transient Spectroscopy (DLTS) peaks called the defects Z1/2 and EH6/7 were observed, which were also observed in as-grown layer and the commonly found peaks EH1 and EH3 (M-center) also appeared. New defect named the EB-centers increased after annealing out of EH1 and EH3. Since low energy electron irradiation (less than 220 keV) affects mainly the carbon atom in SiC, both the M- and EB-centers might be carbon related defects.
Kikuchi, Masahiro; Hussain, M. S.*; Morishita, Norio; Sakashita, Tetsuya; Funayama, Tomoo; Ukai, Mitsuko*; Shimoyama, Yuhei*; Kobayashi, Yasuhiko
JAEA-Review 2009-041, JAEA Takasaki Annual Report 2008, P. 86, 2009/12
When tropical fruits are imported, quarantine treatments are required for preventing plant pests. The irradiation is a choice of the quarantine treatments for tropical fruits in the world. When the irradiation is utilized as the treatment, detection methods are required to endorse the reliability of labels for consumers. To distinguish the irradiated fresh mangoes from non-irradiated ones, radical detection was carried out using ESR. After freeze-drying mangoes, the ESR main peak was observed but the signal intensity was affected by ripeness and period of storage. We found that the existence of side peaks is an effective indicator to detect fresh mangoes irradiated to dose range of quarantine treatment. Since ESR method is able to measure without complicate preparation, this technique is useful to detect the irradiation treatment against a wide variety of foods.
Hasegawa, Shin; Sato, Ken*; Narita, Tadashi*; Suzuki, Yasuyuki; Takahashi, Shuichi; Morishita, Norio; Maekawa, Yasunari
Journal of Membrane Science, 345(1-2), p.74 - 80, 2009/12
Times Cited Count：33 Percentile：70.33(Engineering, Chemical)Radiation-induced graft polymerization of styrene into poly(ether ether ketone) (PEEK) with 32% crystallinity was investigated with DSC, TGA, XRD, and ESR. Endothermic heats of melting of the original and styrene-grafted PEEK (grafted PEEK) films were similar, indicating the crystallinity was almost completely maintained up to a grafting degree of 51%. Lower glass transition temperature of the grafted PEEK film in the DSC, and the absence of an extra halo originating from amorphous polystyrene grafts in the XRD strongly indicate the grafting of styrene to crystalline PEEK films proceeded in the amorphous region of PEEK. This is probably because polystyrene grafts have hydrocarbon structures similar to a base PEEK polymer, resulting in compatibility to the amorphous phase of the PEEK films. The grafted PEEK films can be converted to PEEK-based electrolyte membranes by subsequent sulfonation, and had conductivity of more than 0.01 S/cm and exhibited higher water content above 100%.
Kikuchi, Masahiro; Hussain, M. S.*; Morishita, Norio; Ukai, Mitsuko*; Shimoyama, Yuhei*; Kobayashi, Yasuhiko
Radioisotopes, 58(12), p.789 - 797, 2009/12
no abstracts in English
Son, N. T.*; Hemmingsson, C. G.*; Paskova, T.*; Evans, K. R.*; Usui, Akira*; Morishita, Norio; Oshima, Takeshi; Isoya, Junichi*; Monemar, B.*; Janzn, E.*
Physical Review B, 80(15), p.153202_1 - 153202_4, 2009/10
Times Cited Count：40 Percentile：79.94(Materials Science, Multidisciplinary)GaN samples were irradiated with electrons of 2 MeV at 110
/cm, and electron spin resonance (ESR) was measured at 77 K. As a result, four defect signals which are labeled D1 to D4 were observed. The D2 signal was identified to be negatively charged gallium vacancy - oxygen pair from the details studies of 
N hf structure.
SiCSon, N. T.*; Janzn, E.*; Isoya, Junichi*; Morishita, Norio; Hanaya, Hiroaki; Takizawa, Haruki; Oshima, Takeshi; Gali, A.*
Physical Review B, 80(12), p.125201_1 - 125201_8, 2009/09
Times Cited Count：10 Percentile：42.43(Materials Science, Multidisciplinary)Defects in electron irradiated 3-SiC were studied by electron paramagnetic resonance EPR. The spectrum labeled LE1 was observed in -type 3 SiC after electron irradiation at low temperatures (
80-100 K). Supercell calculations of different configurations of silicon vacancy-interstitial Frenkel-pairs, V
-Si
, were carried out. Comparing the data obtained from experiments using EPR and supercell calculations, the LE1 center is assigned to the Frenkel-pair between V and a second neighbor Si interstitial along the [100] direction in the 3+ charge state. In addition, a path for the migration of Si
was found in 3 SiC. In samples electron-irradiated at low temperatures, the LE1 Frenkel-pair was found to be the dominating defect whereas EPR signals of single vacancies were not detected. The center disappears after warming up the samples to room temperature.
Kikuchi, Masahiro; Ogawa, Hideyuki*; Morishita, Norio; Ukai, Mitsuko*; Kobayashi, Yasuhiko; Shimoyama, Yuhei*
Shokuhin Shosha, 44(1-2), p.9 - 13, 2009/09
no abstracts in English
