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Influences of H ion implantation on Ti:O,H,D films prepared by rf sputtering
Nuclear Instruments and Methods in Physics Research B 169 (2000) 156±160
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In¯uences of H ion implantation on Ti:O,H,D ®lms prepared by rf sputtering Setsuo Nakao *, Soji Miyagawa, Yoshiko Miyagawa, Ping Jin, Takeshi Mizota, Hiroaki Niwa, Kazuo Saitoh National Industrial Research Institute of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya 462-8510, Japan
Abstract A 30 keV H ion implantation on Ti:O,H,D ®lms which were composed of titanium oxide, hydride and deuteride phase was carried out, and the changes in the microstructure and H concentration were examined by X-ray diraction (XRD) measurements, atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analysis. It was found that the crystallinity of the d-phase Ti:H,D was decreased and c-phase Ti:H,D was observed after H ion implantation. The surface morphology was also changed and the surface roughness was reduced after implantation. The distribution of H atoms was spread out toward the substrate as H ion dose was increased. The total amount of H estimated from ERD spectra was slightly increased, but the D concentration was decreased after H ion implantation. Ó 2000 Elsevier Science B.V. All rights reserved. Keywords: Ti:O,H,D ®lms; H ion implantation; rf Sputtering; X-ray diraction; ERD spectra; RBS spectra; AFM observation
1. Introduction Titanium hydride (Ti:H) ®lms have attracted much attention because of their potential applications as neutron mirror, H storage layer and standard for H quantitative analysis. Moreover, titanium deuteride (Ti:D) ®lms are useful as a conventional neutron source in ion beam technology. However, Ti:H is a non-stoichiometric compound and the H content is largely changed
*
Corresponding author. Tel.: +81-52-911-2111; fax: +81-52911-2141. E-mail address: [email protected] (S. Nakao).
[1,2]. In addition, the titanium oxide (Ti:O) phase is usually grown together with the hydride (or deuteride) phase in the preparation of ®lms. The presence of Ti:O phase causes the reduction of the H (or D) content in the ®lms. In a previous study [3,4], we attempted to prepare Ti:D ®lms by rf reactive sputtering, but the ®lms included a lot of unexpected elements of O and H. These ®lms were referred to as Ti:O,H,D ®lms and were used as a neutron source using D±D nuclear reaction in the experiments of neutron elastic recoil detection (NERD) analysis [5]. However, the NERD measurement required a relatively long time period because of low neutron production. It is desirable that the target ®lms of neutron source are desirable
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 0 3 2 - X
S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
to contain a large amount of D since increasing D concentration in the ®lm causes increasing neutron production. On the other hand, if ion implantation is an eective method for incorporation of additional element into target materials, then, it seems to increase D concentration in the ®lms by D ion implantation. Jackman et al. [6] described the test of hydride formation in Zr and Ti as a result of low-energy H ion implantation. Trocellier [7] also demonstrated the D incorporation in SiO2 target during D microbeam irradiation. However, the details were not mentioned and there also still remains the question, whether it is possible to increase H or D concentration in the ®lms by using ion implantation technique. Moreover, structural changes of the ®lms are also not clear under ion beam irradiation. The aim of our study is to clarify the structural changes of Ti:O,H,D ®lms against ion beam irradiation and the possibility of the incorporation of additional H and/or D in the ®lms by ion beam implantation. In this paper, for the ®rst attempt, the in¯uences of H ion implantation on the microstructure and H concentration of the Ti:O,H,D ®lms were examined. 2. Experimental Ti:O,H,D ®lms were deposited on Si(1 0 0) wafers by rf reactive sputtering. Pure Ti metal was used as a sputter target and Ar and D2 gases were used. Si substrates were attached to a substrate holder cooled by water. The substrate temperature was measured by a chromel±alumel thermocouple in contact with the surface of the substrate holder. The substrate temperature during sputtering was less than 80°C. The total gas pressure during deposition was about 2 Pa. The thickness of the ®lms was about 400 nm. Details of preparation conditions are described elsewhere [3,4]. A 30 keV H ion implantation was carried out by using 200 kV ion accelerator. Typical conditions for H ion implantation are summarized in Table 1. The crystal structure of the ®lms was examined by X-ray diraction (XRD) measurements at a
157
Table 1 Typical conditions for hydrogen ion implantation Ion species Acceleration voltage Ion current intensity Dose Temperature Shape Area
H 2 60 kV 13.4 lA/cm2 0:1±1 1018 H/cm2 RT 8 mm£ ca. 0.5 cm2
glancing angle of 3°. The surfaces of the ®lms were observed by atomic force microscopy (AFM). The composition of the ®lms was analyzed by Rutherford backscattering spectrometry (RBS) using a 1.8 MeV He beam and elastic recoil detection (ERD) analysis using a 2.8 MeV He beam with a 1.7 MV tandem-type ion accelerator of NIRIN [8]. The programs of RUMP [9] and RBX [10] were used in order to analyze RBS and ERD spectra, respectively.
3. Results and discussion Fig. 1 shows the XRD patterns of the ®lms: (a) before and after 30 keV H ion implantation at doses of (b) 1 1017 H/cm2 and (c) 1 1018 H/ cm2 . For the ®lm (a), a clear peak is observed at about 35°. This peak is in agreement with the diraction peak from d-phase Ti:D(1 1 1) or Ti:H (1 1 1) plane. If the diraction peak of d-Ti:H(1 1 1) is very close to that of d-Ti:D(1 1 1), then it is denoted by Ti:D,H(1 1 1) in Fig. 1. After H ion implantation, this peak decreased in intensity and shifts to about 35.5°. In the ®lm (c), a small shoulder at about 36° and a small bump at about 43.5° appear. These peaks are in agreement with the diraction peaks from c-phase Ti:D,H(1 1 1) and Ti:D,H(2 0 0) planes. Fig. 2 shows the AFM images of the surface of the ®lms before and after H ion implantation. The samples (a)±(c) correspond to those of Fig. 1. For the sample (a), it is observed that many grains about 0.2 lm in diameter having sharp edges are scattered on the surface of the ®lm. After H ion implantation, however, these grains are decreased in density and the surface appears to be composed of ¯at grains about 0.5 lm in size, as shown in the
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S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
Fig. 1. XRD patterns of the ®lms deposited on Si substrates (a) before and after 30 keV H ion implantation at doses of (b) 1 1017 and (c) 1 1018 H/cm2 .
Fig. 2. AFM images of the surfaces of the ®lms before and after H ion implantation. The samples (a)±(c) correspond to those of Fig. 1.
samples (b) and (c). This result indicates that the surface roughness is reduced by H ion implantation. Fig. 3 shows the (a) RBS and (b) ERD spectra of the samples before and after H ion implanta-
tion. In Fig. 3(a), the yields from Ti and O atoms in the ®lms and from Si of the substrates are observed. Although the small deviation of the Ti and O yields is observed, there is no signi®cant dierence among the samples. In Fig. 3(b), the yields
S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
159
Fig. 3. (a) RBS and (b) ERDA spectra of the samples before and after H ion implantation.
from D and H atoms in the ®lms are observed. In contrast to RBS spectra, ERD spectra are changed with H ion dose. The yields of D are decreased with increasing H ion dose, while the yields of H are spread out toward low channel number. The results clearly show that the amount of D is decreased and H diuses into Si substrate after H ion implantation. The peak at about 125 channel is also decreased with ion dose, which is caused by overlapping of the yields from H and D atoms. Fig. 4 shows the concentration of Ti, O, H and D in the samples before and after H ion implantation. H0, H17 and H18 in Fig. 4 denote the samples unimplanted, after implanted at doses of 1 1017 and 1 1018 H/cm2 , respectively. The concentration of Ti and O was estimated by analyzing RBS spectra using the RUMP program. On the other
hand, the concentration of H and O was estimated by analyzing ERD spectra using the RBX program. The concentrations of Ti and O are not changed by H ion implantation. The total concentration of H is slightly increased. However, the increment of H is very small as compared with the maximum ion dose of 1 1018 H/cm2 . This means that the implanted H almost diused out of the sample. The concentration of D is decreased to about one-half of unimplanted sample by H ion implantation. Total amount of H D does not seem to be aected by H ion implantation as shown in Fig. 4. However, it is noted that H atoms diuse into Si substrate as shown in Fig. 3(b). The amount of H in Si substrate was roughly estimated as about 6:6 1016 H/cm2 in the sample after implantation at the dose of 1 1018 H/cm2 . Therefore, the
Fig. 4. The concentration of Ti, O, H and D atoms of the samples before and after H ion implantation. H0, H17 and H18 represent the samples unimplanted, after implanted at doses of 1 1017 and 1 1018 H/cm2 , respectively.
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S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
amount of H in the ®lms was estimated as about 1:2 1017 H/cm2 . This value is similar to the unimplanted sample. These ®lms included a lot of O atoms, as shown in Figs. 3(a) and 4. However, there is no signi®cant diraction peak caused by Ti:O crystal structure in Fig. 1. The results suggested that the Ti:O is presented as an amorphous structure in the ®lms. The results of the XRD measurements, as shown in Fig. 1, show that the peak of dTi:D,H(1 1 1) was decreased and shifted to a larger angle after H ion implantation. In addition, the small peak of c-phase Ti:D,H was observed after H ion implantation. These results indicate that the crystallinity of d-Ti:D,H crystal was decreased and the lattice constant was also reduced by H ion implantation, suggesting that the contents of D and H in the ®lms are decreased. It is known that the lattice constant of d-Ti:H or Ti:D crystal is varied with H or D content and phase transformation from d to c occurs as the H or D content is decreased [1,2]. Therefore, it is considered that the concentration of D and H was reduced in the ®lms and the phase transformation from d to c occurred by H ion implantation. Regrettably, the expected results show that increased H concentrations in the ®lms with increasing H ion dose were not obtained in this experiment. However, it is believed that the opportunity to explore optimum implantation condition remains. In order to reduce the diusion of implanted hydrogen, low temperature during implantation may be required. Further investigation is underway. 4. Summary The in¯uences of 30 keV H ion implantation on Ti:O,H,D ®lms prepared by rf reactive sputtering
on the microstructure and H concentration were examined. Our ®ndings are as follows: 1. The crystallinity of d-phase Ti:D,H (fcc CaF2 structure) was decreased and c-phase Ti:D,H was grown by H ion implantation. 2. The surface roughness of the ®lms was reduced by decreasing the small grains with sharp edge after H ion implantation. 3. The concentrations of Ti and O atoms were not aected by H ion implantation. 4. The total amount of H atoms was slightly increased as H ion dose was increased, although a part of H diused into the Si substrate and the concentration of D atoms was decreased by H ion implantation.
References [1] H. Numakura, Nippon Kinzoku Gakkai kaihou 31 (1992) 525. [2] D.V. Schur, S.Yu. Zaginaichenko, V.M. Adejev, V.B. Voitovich, A.A. Lyashenko, V.I. Tre®lov, Int. J. Hydrogen Energy 21 (1996) 1121. [3] S. Nakao, M. Tazawa, P. Jin, T. Hirahara, K. Saitoh, in: Conference Digest of 23rd International Conference on Infrared and Millimeter Waves, 1998, p. 266. [4] S. Nakao, K. Saitoh, T. Hirahara, M. Ikeyama, M. Tazawa, P. Jin, H. Niwa, S. Tanemura, Y. Miyagawa, S. Miyagawa, K. Yasuda, Thin Solid Films 343±344 (1999) 195. [5] K. Saitoh, S. Nakao, H. Matsuda, H. Niwa, Y. Saitoh, Y. Nakajima, S. Tajima, H. Naramoto, TIARA Annual Report, 1997, 1998, p. 190. [6] J.A. Jackman, G.J.C. Carpenter, J. McCrey, Nucl. Instr. and Meth. B 80/81 (1993) 472. [7] P. Trocellier, Nucl. Instr. and Meth. B 104 (1995) 571. [8] K. Saitoh, H. Niwa, M. Kobayakawa, S. Tanemura, M. Ikeyama, M. Takeda, H. Masuda, Y. Miyagawa, S. Nakamura, S. Miyagawa, K. Yasuda, Rep. Gov. Ind. Res. Nagoya 9 (1990) 259. [9] L.R. Doolittle, Nucl. Instr. and Meth. B 15 (1986) 227. [10] E. Kotai, Nucl. Instr. and Meth. B 85 (1994) 588.
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In¯uences of H ion implantation on Ti:O,H,D ®lms prepared by rf sputtering Setsuo Nakao *, Soji Miyagawa, Yoshiko Miyagawa, Ping Jin, Takeshi Mizota, Hiroaki Niwa, Kazuo Saitoh National Industrial Research Institute of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya 462-8510, Japan
Abstract A 30 keV H ion implantation on Ti:O,H,D ®lms which were composed of titanium oxide, hydride and deuteride phase was carried out, and the changes in the microstructure and H concentration were examined by X-ray diraction (XRD) measurements, atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analysis. It was found that the crystallinity of the d-phase Ti:H,D was decreased and c-phase Ti:H,D was observed after H ion implantation. The surface morphology was also changed and the surface roughness was reduced after implantation. The distribution of H atoms was spread out toward the substrate as H ion dose was increased. The total amount of H estimated from ERD spectra was slightly increased, but the D concentration was decreased after H ion implantation. Ó 2000 Elsevier Science B.V. All rights reserved. Keywords: Ti:O,H,D ®lms; H ion implantation; rf Sputtering; X-ray diraction; ERD spectra; RBS spectra; AFM observation
1. Introduction Titanium hydride (Ti:H) ®lms have attracted much attention because of their potential applications as neutron mirror, H storage layer and standard for H quantitative analysis. Moreover, titanium deuteride (Ti:D) ®lms are useful as a conventional neutron source in ion beam technology. However, Ti:H is a non-stoichiometric compound and the H content is largely changed
*
Corresponding author. Tel.: +81-52-911-2111; fax: +81-52911-2141. E-mail address: [email protected] (S. Nakao).
[1,2]. In addition, the titanium oxide (Ti:O) phase is usually grown together with the hydride (or deuteride) phase in the preparation of ®lms. The presence of Ti:O phase causes the reduction of the H (or D) content in the ®lms. In a previous study [3,4], we attempted to prepare Ti:D ®lms by rf reactive sputtering, but the ®lms included a lot of unexpected elements of O and H. These ®lms were referred to as Ti:O,H,D ®lms and were used as a neutron source using D±D nuclear reaction in the experiments of neutron elastic recoil detection (NERD) analysis [5]. However, the NERD measurement required a relatively long time period because of low neutron production. It is desirable that the target ®lms of neutron source are desirable
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 0 3 2 - X
S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
to contain a large amount of D since increasing D concentration in the ®lm causes increasing neutron production. On the other hand, if ion implantation is an eective method for incorporation of additional element into target materials, then, it seems to increase D concentration in the ®lms by D ion implantation. Jackman et al. [6] described the test of hydride formation in Zr and Ti as a result of low-energy H ion implantation. Trocellier [7] also demonstrated the D incorporation in SiO2 target during D microbeam irradiation. However, the details were not mentioned and there also still remains the question, whether it is possible to increase H or D concentration in the ®lms by using ion implantation technique. Moreover, structural changes of the ®lms are also not clear under ion beam irradiation. The aim of our study is to clarify the structural changes of Ti:O,H,D ®lms against ion beam irradiation and the possibility of the incorporation of additional H and/or D in the ®lms by ion beam implantation. In this paper, for the ®rst attempt, the in¯uences of H ion implantation on the microstructure and H concentration of the Ti:O,H,D ®lms were examined. 2. Experimental Ti:O,H,D ®lms were deposited on Si(1 0 0) wafers by rf reactive sputtering. Pure Ti metal was used as a sputter target and Ar and D2 gases were used. Si substrates were attached to a substrate holder cooled by water. The substrate temperature was measured by a chromel±alumel thermocouple in contact with the surface of the substrate holder. The substrate temperature during sputtering was less than 80°C. The total gas pressure during deposition was about 2 Pa. The thickness of the ®lms was about 400 nm. Details of preparation conditions are described elsewhere [3,4]. A 30 keV H ion implantation was carried out by using 200 kV ion accelerator. Typical conditions for H ion implantation are summarized in Table 1. The crystal structure of the ®lms was examined by X-ray diraction (XRD) measurements at a
157
Table 1 Typical conditions for hydrogen ion implantation Ion species Acceleration voltage Ion current intensity Dose Temperature Shape Area
H 2 60 kV 13.4 lA/cm2 0:1±1 1018 H/cm2 RT 8 mm£ ca. 0.5 cm2
glancing angle of 3°. The surfaces of the ®lms were observed by atomic force microscopy (AFM). The composition of the ®lms was analyzed by Rutherford backscattering spectrometry (RBS) using a 1.8 MeV He beam and elastic recoil detection (ERD) analysis using a 2.8 MeV He beam with a 1.7 MV tandem-type ion accelerator of NIRIN [8]. The programs of RUMP [9] and RBX [10] were used in order to analyze RBS and ERD spectra, respectively.
3. Results and discussion Fig. 1 shows the XRD patterns of the ®lms: (a) before and after 30 keV H ion implantation at doses of (b) 1 1017 H/cm2 and (c) 1 1018 H/ cm2 . For the ®lm (a), a clear peak is observed at about 35°. This peak is in agreement with the diraction peak from d-phase Ti:D(1 1 1) or Ti:H (1 1 1) plane. If the diraction peak of d-Ti:H(1 1 1) is very close to that of d-Ti:D(1 1 1), then it is denoted by Ti:D,H(1 1 1) in Fig. 1. After H ion implantation, this peak decreased in intensity and shifts to about 35.5°. In the ®lm (c), a small shoulder at about 36° and a small bump at about 43.5° appear. These peaks are in agreement with the diraction peaks from c-phase Ti:D,H(1 1 1) and Ti:D,H(2 0 0) planes. Fig. 2 shows the AFM images of the surface of the ®lms before and after H ion implantation. The samples (a)±(c) correspond to those of Fig. 1. For the sample (a), it is observed that many grains about 0.2 lm in diameter having sharp edges are scattered on the surface of the ®lm. After H ion implantation, however, these grains are decreased in density and the surface appears to be composed of ¯at grains about 0.5 lm in size, as shown in the
158
S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
Fig. 1. XRD patterns of the ®lms deposited on Si substrates (a) before and after 30 keV H ion implantation at doses of (b) 1 1017 and (c) 1 1018 H/cm2 .
Fig. 2. AFM images of the surfaces of the ®lms before and after H ion implantation. The samples (a)±(c) correspond to those of Fig. 1.
samples (b) and (c). This result indicates that the surface roughness is reduced by H ion implantation. Fig. 3 shows the (a) RBS and (b) ERD spectra of the samples before and after H ion implanta-
tion. In Fig. 3(a), the yields from Ti and O atoms in the ®lms and from Si of the substrates are observed. Although the small deviation of the Ti and O yields is observed, there is no signi®cant dierence among the samples. In Fig. 3(b), the yields
S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
159
Fig. 3. (a) RBS and (b) ERDA spectra of the samples before and after H ion implantation.
from D and H atoms in the ®lms are observed. In contrast to RBS spectra, ERD spectra are changed with H ion dose. The yields of D are decreased with increasing H ion dose, while the yields of H are spread out toward low channel number. The results clearly show that the amount of D is decreased and H diuses into Si substrate after H ion implantation. The peak at about 125 channel is also decreased with ion dose, which is caused by overlapping of the yields from H and D atoms. Fig. 4 shows the concentration of Ti, O, H and D in the samples before and after H ion implantation. H0, H17 and H18 in Fig. 4 denote the samples unimplanted, after implanted at doses of 1 1017 and 1 1018 H/cm2 , respectively. The concentration of Ti and O was estimated by analyzing RBS spectra using the RUMP program. On the other
hand, the concentration of H and O was estimated by analyzing ERD spectra using the RBX program. The concentrations of Ti and O are not changed by H ion implantation. The total concentration of H is slightly increased. However, the increment of H is very small as compared with the maximum ion dose of 1 1018 H/cm2 . This means that the implanted H almost diused out of the sample. The concentration of D is decreased to about one-half of unimplanted sample by H ion implantation. Total amount of H D does not seem to be aected by H ion implantation as shown in Fig. 4. However, it is noted that H atoms diuse into Si substrate as shown in Fig. 3(b). The amount of H in Si substrate was roughly estimated as about 6:6 1016 H/cm2 in the sample after implantation at the dose of 1 1018 H/cm2 . Therefore, the
Fig. 4. The concentration of Ti, O, H and D atoms of the samples before and after H ion implantation. H0, H17 and H18 represent the samples unimplanted, after implanted at doses of 1 1017 and 1 1018 H/cm2 , respectively.
160
S. Nakao et al. / Nucl. Instr. and Meth. in Phys. Res. B 169 (2000) 156±160
amount of H in the ®lms was estimated as about 1:2 1017 H/cm2 . This value is similar to the unimplanted sample. These ®lms included a lot of O atoms, as shown in Figs. 3(a) and 4. However, there is no signi®cant diraction peak caused by Ti:O crystal structure in Fig. 1. The results suggested that the Ti:O is presented as an amorphous structure in the ®lms. The results of the XRD measurements, as shown in Fig. 1, show that the peak of dTi:D,H(1 1 1) was decreased and shifted to a larger angle after H ion implantation. In addition, the small peak of c-phase Ti:D,H was observed after H ion implantation. These results indicate that the crystallinity of d-Ti:D,H crystal was decreased and the lattice constant was also reduced by H ion implantation, suggesting that the contents of D and H in the ®lms are decreased. It is known that the lattice constant of d-Ti:H or Ti:D crystal is varied with H or D content and phase transformation from d to c occurs as the H or D content is decreased [1,2]. Therefore, it is considered that the concentration of D and H was reduced in the ®lms and the phase transformation from d to c occurred by H ion implantation. Regrettably, the expected results show that increased H concentrations in the ®lms with increasing H ion dose were not obtained in this experiment. However, it is believed that the opportunity to explore optimum implantation condition remains. In order to reduce the diusion of implanted hydrogen, low temperature during implantation may be required. Further investigation is underway. 4. Summary The in¯uences of 30 keV H ion implantation on Ti:O,H,D ®lms prepared by rf reactive sputtering
on the microstructure and H concentration were examined. Our ®ndings are as follows: 1. The crystallinity of d-phase Ti:D,H (fcc CaF2 structure) was decreased and c-phase Ti:D,H was grown by H ion implantation. 2. The surface roughness of the ®lms was reduced by decreasing the small grains with sharp edge after H ion implantation. 3. The concentrations of Ti and O atoms were not aected by H ion implantation. 4. The total amount of H atoms was slightly increased as H ion dose was increased, although a part of H diused into the Si substrate and the concentration of D atoms was decreased by H ion implantation.
References [1] H. Numakura, Nippon Kinzoku Gakkai kaihou 31 (1992) 525. [2] D.V. Schur, S.Yu. Zaginaichenko, V.M. Adejev, V.B. Voitovich, A.A. Lyashenko, V.I. Tre®lov, Int. J. Hydrogen Energy 21 (1996) 1121. [3] S. Nakao, M. Tazawa, P. Jin, T. Hirahara, K. Saitoh, in: Conference Digest of 23rd International Conference on Infrared and Millimeter Waves, 1998, p. 266. [4] S. Nakao, K. Saitoh, T. Hirahara, M. Ikeyama, M. Tazawa, P. Jin, H. Niwa, S. Tanemura, Y. Miyagawa, S. Miyagawa, K. Yasuda, Thin Solid Films 343±344 (1999) 195. [5] K. Saitoh, S. Nakao, H. Matsuda, H. Niwa, Y. Saitoh, Y. Nakajima, S. Tajima, H. Naramoto, TIARA Annual Report, 1997, 1998, p. 190. [6] J.A. Jackman, G.J.C. Carpenter, J. McCrey, Nucl. Instr. and Meth. B 80/81 (1993) 472. [7] P. Trocellier, Nucl. Instr. and Meth. B 104 (1995) 571. [8] K. Saitoh, H. Niwa, M. Kobayakawa, S. Tanemura, M. Ikeyama, M. Takeda, H. Masuda, Y. Miyagawa, S. Nakamura, S. Miyagawa, K. Yasuda, Rep. Gov. Ind. Res. Nagoya 9 (1990) 259. [9] L.R. Doolittle, Nucl. Instr. and Meth. B 15 (1986) 227. [10] E. Kotai, Nucl. Instr. and Meth. B 85 (1994) 588.