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Oka, Toshitaka; Oshima, Akihiro*; Washio, Masakazu*
Radiation Physics and Chemistry, 215, p.111364_1 - 111364_4, 2024/02
Times Cited Count：1 Percentile：30.19(Chemistry, Physical)The polymer electrolyte fuel cell (PEFC) is a promising electrochemical device to produce power through hydrogen and oxygen reaction. It has been expected as a leading future clean power source for a vehicle and a residential power generation. Proton exchange membrane (PEM) is a key material for the performance and the cost of PEFC, development of a high performance and a low-cost PEM is required. Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) was irradiated by an electron beam under oxygen-free atmosphere at 25
C, grafted with styrene in liquid phase at 80, and then sulfonated with a mixture of chlorosulfonic acid in carbon-tetrachloride at 25 for 24 h. The free volume size and the o-Ps annihilation probability were affected by not only the amount of the grafted styrene but also the sulfonic acid group.
Kobayashi, Yoshinori*; Sato, Kiminori*; Yamawaki, Masato*; Michishio, Koji*; Oka, Toshitaka; Washio, Masakazu*
Radiation Physics and Chemistry, 202, p.110590_1 - 110590_6, 2023/01
Times Cited Count：6 Percentile：71.68(Chemistry, Physical)Because of their different charge states, positrons and positronium (Ps) behave quite differently in macromolecules. The behavior of positively charged positrons is strongly influenced by electrostatic interactions. In nonpolar macromolecules such as polyethylene, energetic positrons, if not incorporated into Ps, fall into a delocalized state. These positrons are sensitively trapped by polar groups, if any. On the other hand, charge-neutral Ps is localized in a free volume regardless of the macromolecule's chemical structure. In this study, we discuss the behavior and annihilation characteristics of positrons and Ps in various macromolecules, emphasizing their differences.
Kobayashi, Yoshinori*; Sato, Kiminori*; Yamawaki, Masato*; Michishio, Koji*; Oka, Toshitaka; Washio, Masakazu*
Applied Physics Express, 15(7), p.076001_1 - 076001_4, 2022/07
Times Cited Count：2 Percentile：17.73(Physics, Applied)We discuss the energy dissipation of short-lived 
-positronium (
-Ps) in polymers and silica glass. The 
parameter characterizing the Doppler broadening of -Ps annihilation is determined from the previously reported systematic data of positron annihilation age momentum correlation for various polymers and silica glass. A comparison of the parameter with that expected for thermalized -Ps trapped in a free volume reveals that -Ps is not thermalized and possesses excess energy in fluorinated polymers and silica glass, indicating that it is difficult for Ps to lose energy in substances containing heavy elements such as fluorine and silicon.
Oyama, Tomoko; Nakamura, Hirotaka*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*
Applied Physics Express, 7(3), p.036501_1 - 036501_3, 2014/03
Times Cited Count：7 Percentile：29.34(Physics, Applied)A chlorinated polymer ZEP is a main-chain scission type (positive-tone) high-sensitivity resist. However, we found that ZEP changes to negative-tone with a high dose of electron beam irradiation. The sensitivities to a 100 kV electron beam as a dual-tone are evaluated with various developers. Owing to different solvation strengths, the resist sensitivity varied with different developers in the positive-tone region. On the other hand, it was found that the threshold dose for the positive-negative inversion is independent of the developer. According to an analysis using X-ray photoelectron spectroscopy and NMR spectroscopy, we found that the amount of chlorine atoms and terminal double bonds generated by chain scission determines the threshold of the P-N inversion. This result provides important information for possible ZEP applications such as a dual-tone resist.
Washio, Masakazu*; Oyama, Tomoko
O plus E, 36(3), p.272 - 275, 2014/03
no abstracts in English
Hosaka, Yuji*; Oyama, Tomoko; Oshima, Akihiro*; Enomoto, Satoshi*; Washio, Masakazu*; Tagawa, Seiichi*
Journal of Photopolymer Science and Technology, 26(6), p.745 - 750, 2013/12
Times Cited Count：13 Percentile：38.51(Polymer Science)ZEP520A is one of the most popular positive electron beam (EB) resists used in research and photomask fabrication owing to its excellent properties. Herein, EB-induced initial reactions of ZEP520A were investigated via pulse radiolysis (EB energy: 28 MeV, time resolution: 10 ns). Dissociative electron attachment and formation of a charge transfer complex were definitive contributing factors to the efficient degradation of ZEP520A. Furthermore, products induced by direct ionization of ZEP520A were observed in a highly concentrated ZEP520A solution in tetrahydrofuran, suggesting that initial reactions in the ZEP520A solid film that are induced only by direct ionization could be simulated via pulse radiolysis in specific solutions.
-lactic acid) using focused ion beam direct etchingOyama, Tomoko; Hinata, Toru*; Nagasawa, Naotsugu; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*; Taguchi, Mitsumasa
Applied Physics Letters, 103(16), p.163105_1 - 163105_4, 2013/10
Times Cited Count：11 Percentile：42.62(Physics, Applied)Micro/nanofabrication of biocompatible and biodegradable poly(-lactic acid) (PLLA) was evaluated using focused Ga ion beam direct etching. The fabrication performance was determined with different ion fluences and fluxes. It was found that the etching speed and fabrication accuracy were affected by irradiation-induced heat because the resistance of PLLA to thermal deformation is decreased when above its glass transition temperature (approximately 60C). By controlling the irradiation conditions, controlled micro/nanostructures of PLLA were fabricated, such as holes (
80 nm) and alphabets (width: 100 nm). Moreover, focused ion beam (FIB)-irradiated surfaces were analyzed using micro-area X-ray photoelectron spectroscopy. Owing to reactions such as the physical sputtering of atoms and radiation-induced decomposition, PLLA was gradually carbonized with increasing C=C bonds expected to have good cell attachment properties.
Oyama, Tomoko; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*
Journal of Vacuum Science and Technology B, 31(4), p.041604_1 - 041604_5, 2013/07
Times Cited Count：9 Percentile：44.00(Engineering, Electrical & Electronic)
-lactic acid) using electron beam nanoimprint lithographyOkubo, Satoshi*; Nagasawa, Naotsugu; Kobayashi, Akinobu*; Oyama, Tomoko*; Taguchi, Mitsumasa; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*
Applied Physics Express, 5(2), p.027303_1 - 027303_3, 2012/02
Times Cited Count：4 Percentile：17.51(Physics, Applied)Electron beam nanoimprint lithography was proposed for fabricating the micro-/nanostructures of cross-linked poly(-lactic acid) (RX-PLLA). PLLA with triallyl isocyanurate (TAIC) solutions were dropped on the Si-molds fabricated by the conventional EB lithography technique. PLLA/TAIC on Si-molds were imprinted and cross-linked with doses from 10 to 500 kGy at room temperature under vacuum. The micro-/nanostructures of RX-PLLA were successfully obtained with high accuracy. Hence, it was found that the imprinted structures of RX-PLLA (100 kGy irradiation) show low line edge roughness and high thermal durability at 120 C.
Shiraki, Fumiya*; Yoshikawa, Taeko*; Oshima, Akihiro*; Oshima, Yuji*; Takasawa, Yuya*; Fukutake, Naoyuki*; Oyama, Tomoko*; Urakawa, Tatsuya*; Fujita, Hajime*; Takahashi, Tomohiro*; et al.
Nuclear Instruments and Methods in Physics Research B, 269(15), p.1777 - 1781, 2011/08
Times Cited Count：8 Percentile：51.74(Instruments & Instrumentation)The graded energy deposition of heavy ion beam irradiation to polymeric materials was utilized to synthesize a novel proton exchange membrane (PEM) with the graded density of sulfonic acid groups toward the thickness direction. Stacked Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were irradiated by Xe
ion beam with the energy of 6 MeV/u under a vacuum condition. Irradiated films were grafted with styrene monomer and then sulfonated. The membrane electrode assembly (MEA) fabricated by the function graded PEM showed improved fuel cell performance in terms of voltage stability. It was expected that the function-graded PEM could control the graded concentration of sulfonic acid groups in PEM.
Gowa, Tomoko*; Shiotsu, Tomoyuki*; Urakawa, Tatsuya*; Oka, Toshitaka; Murakami, Takeshi*; Oshima, Akihiro*; Hama, Yoshimasa*; Washio, Masakazu*
Radiation Physics and Chemistry, 80(2), p.264 - 267, 2011/02
Times Cited Count：9 Percentile：55.44(Chemistry, Physical)High linear energy transfer (LET) heavy ion beams were irradiated to poly(tetrafluoroethylene-co-ethylene) (ETFE) under vacuum and in air. The irradiation effects in ETFE as a function of the depth was precisely evaluated by analyzing each one of the films of the irradiation samples which were made of stacked ETFE films. It was indicated that conjugated double bonds would be generated by heavy ion beam irradiation, and their amounts should show the Bragg-curve-like distributions. Also, it was suggested that higher LET beams would induce radical formation in high density and longer conjugated C=C double bonds could be generated by the second-order reactions. Moreover, for irradiation samples in air, C=O was produced correlating to the yield of oxygen molecules diffusing from the sample surface.
Oka, Toshitaka; Oshima, Akihiro*; Motohashi, Ryota*; Seto, Naoto*; Watanabe, Yuji*; Kobayashi, Ryoji*; Saito, Koki*; Kudo, Hisaaki*; Murakami, Takeshi*; Washio, Masakazu*; et al.
Radiation Physics and Chemistry, 80(2), p.278 - 280, 2011/02
Times Cited Count：8 Percentile：51.74(Chemistry, Physical)The chemical structures of various ion-beam irradiated isotactic-polypropylene samples were studied. Results of micro-Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy suggest not only the linear energy transfer, but also the fluence is effective in local transformation of the isotactic-polypropylene.
Okubo, Satoshi*; Takahashi, Tomohiro*; Takasawa, Yuya*; Gowa, Tomoko*; Sasaki, Takashi*; Nagasawa, Naotsugu; Tamada, Masao; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*
Journal of Photopolymer Science and Technology, 23(3), p.393 - 397, 2010/11
Times Cited Count：4 Percentile：13.31(Polymer Science)Microfabrication of biodegradable polymers such as poly(butylene succinate-
-adipate) (PBSA) and poly(
-caprolactone) (PCL) were demonstrated using focused ion beam (FIB) with maskless direct etching. As the result, the micro structures of PBSA and PCL were obtained. The etching depth of both PBSA and PCL were increased with increasing FIB fluence, and the etching rates were estimated to be about 1.3 
10
m/(ions cm
) and 1.2 10 m/(ions cm), respectively. Moreover, very thin films of PBSA and PCL were made by spin-coating method. The thicknesses of the spin-coated samples were about 200 nm, and the surface roughness was less than 10 nm (RMS). The fine structures such as micro-gear of PBSA and PCL were obtained without solid debris. The line width of the fabricated structure was about 250 nm.
Gowa, Tomoko*; Takahashi, Tomohiro*; Oka, Toshitaka; Murakami, Takeshi*; Oshima, Akihiro*; Tagawa, Seiichi*; Washio, Masakazu*
Journal of Photopolymer Science and Technology, 23(3), p.399 - 404, 2010/08
Hirota, Koichi; Sakai, Hiroki*; Washio, Masakazu*; Kojima, Takuji
Industrial & Engineering Chemistry Research, 43(5), p.1185 - 1191, 2004/03
Times Cited Count：49 Percentile：80.06(Engineering, Chemical)Twenty volatile organic compounds (VOCs) were irradiated with electron beams in laboratory scale to obtain an electron-beam energy required for a 90% treatment. The experiments showed that the energy was related with the chemical structure and roughly estimated from rate constants for reactions with OH radicals. The cost analysis revealed that the unification of a self-shielding electron accelerator with a reactor could reduce the capital cost for an electron-beam system. Electron-beam technology is a promising method for the treatment of VOCs.
Sato, Yasunori*; Yamaguchi, Daichi*; Oshima, Akihiro*; Kato, Takanori*; Ikeda, Shigetoshi*; Aoki, Yasushi*; Tanaka, Shigeru; Tabata, Yoneho*; Washio, Masakazu*
JAERI-Conf 2003-001, p.245 - 250, 2003/03
no abstracts in English
; Kotaki, Hideyuki; Nakajima, Kazuhisa*; Kando, Masaki*; Kondo, Shuji; Dewa, Hidenori*; Watanabe, Takahiro*; Ueda, Toru*; Yoshii, Koji*; Kinoshita, Kenichi*; et al.
Proc. of 11th Symp. on Accelerator Sci. and Technol., p.473 - 475, 1997/00
no abstracts in English
Oshima, Akihiro*; Shiraki, Fumiya*; Takasawa, Yuya*; Fujita, Hajime*; Yoshikawa, Taeko*; Tatsumi, Takahiro*; Tsubokura, Hidehiro*; Takahashi, Tomohiro*; Gowa, Tomoko*; Sakaue, Kazuyuki*; et al.
no journal, ,
no abstracts in English
Oyama, Tomoko*; Enomoto, Kazuyuki*; Hosaka, Yuji*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*
no journal, ,
ZEP520A (1:1 copolymer of 
-chloromethacrylate and -methylstyrene, ZEON) is a main-chain scission-type positive-tone resist widely used for electron beam (EB) lithography. ZEP520A has an excellent resolution as high as 10 nm, which is almost comparable to poly(methyl methacrylate) (PMMA), but its sensitivity is about 10 times higher than that of PMMA. In this study, ZEP520A was irradiated using a 100 kV EB, and the decomposition mechanisms were analyzed by gel permeation chromatography, X-ray photoelectron spectroscopy, NMR spectroscopy, and pulse radiolysis. Chlorines were confirmed to easily dissociate as Cl
ions (dissociative electron attachment, DEA). Multiple channels could be considered for the main-chain scission, including DEA and the charge transfer complex between phenyl rings and chlorines.
Oyama, Tomoko*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*
no journal, ,
Potential application of exposure wavelengths shorter than 13.5 nm has recently been discussed for extension of extreme ultraviolet lithography (EUVL), particularly in the 6.x nm range (6.6-6.8 nm). We experimentally investigated the sensitivities of several resists in the EUV/soft X-ray region, including 6.7 nm. Although the sensitivities were strongly influenced by the absorption properties, each resist has a particular required absorption dose regardless of exposure wavelength. Based on these results, we predicted the resist sensitivities and they agreed well with experimentally obtained ones. The prediction method can aid selection and development of resists for 6.x nm EUVL.
