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Damage evolution in TiC crystals during hydrogen and helium dual-ion beam irradiation
Nuclear Instruments and Methods in Physics Research B 148 (1999) 720±725
Damage evolution in TiC crystals during hydrogen and helium dual-ion beam irradiation K. Hojou a
a,*
, H. Otsu a, S. Furuno a, K.N. Kushita a, N. Sasajima b, K. Izui
a
Japan Atomic Energy Research Institute, Department of Material Science and Engineering, Tokai-mura, Ibaraki-ken 319-1195, Japan b Department of Quantum Engineering, Nagoya University, Chikusa-ku, Nagoya 464, Japan
Abstract The eect of He ion irradiation after H 2 ion pre-injection and of simultaneous 25 keV H2 and 20 keV He ion irradiation at RT to 1423 K on the formation of bubbles in TiC crystals were examined. No amorphization occurred under these irradiation conditions. The formation and growth of bubbles produced by He ion irradiation is not enhanced by pre-injection of hydrogen atoms at RT. Bubbles are formed but do not grow appreciably by He ion, H 2 pre-injection and H 2 He dual-ion irradiation at room temperature. Remarkable growth and coalescence occurred during irradiation at high temperature of 1423 K. Ó 1999 Elsevier Science B.V. All rights reserved.
Keywords: In-situ observation; Dual-ion beam irradiation; TiC crystal; Bubble formation
1. Introduction TiC is one of the candidate materials for the ®rst wall of a fusion reactor because of its low induced radioactivity, high resistance for radiation damage, high thermal conductivity and low sputtering by the bombardment of energetic particles. Many researchers have studied the eects of electron-, ion- and neutron-irradiation on TiC [1,2]. We have observed the dynamic behavior of the damage process in TiC crystal during hydrogen-, deuterium- and helium-ion irradiation at various temperatures [3±5]. It was found that TiC did not become amorphous at 20 keV He ion
* Corresponding author. Tel.: +81 29 282 5465; fax: +81 29 282 6716; e-mail: [email protected]
irradiation at temperature from 12 to 1473 K [3]. On the other hand, an amorphization was found to occur in TiC irradiated with hydrogen and deuterium ions at low temperature, although the ¯uences necessary for causing amorphization is dierent between hydrogen and deuterium ion irradiation. This dierence is considered to be due to the isotope eect between hydrogen and deuterium [4,5]. These experiments, however, were conducted with single species of irradiation particles. In a simulation experiment for the fusion environment, it is desirable to employ multiple-beam irradiation because several dierent species will simultaneously impinge on the ®rst wall and blanket component materials. We have developed a system which allows an in-situ observation and chemical analysis during single and/or dual-ion irradiation [6]. We have
0168-583X/98/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 8 5 0 - 7
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
reported previously as to hydrogen and helium dual-ion irradiation on SiC crystals under the various conditions and found that the formation and growth of bubbles in SiC crystals by helium ion irradiation after a hydrogen-ion pre-irradiation are enhanced in comparison with the case of helium single ion irradiation and also found that in the case of simultaneous dual-ion irradiation the bubble formation and growth feature is similar to the case of a helium single ion irradiation [7,8]. In the present experiments, eects of simulta neous H 2 and He ion irradiation were examined and the results were compared with those obtained by He ion irradiation after H 2 ion per-irradiation at room temperature and 1423 K. 2. Experimental procedures The specimens used in the present work were TiC sintered polycrystals. They were supplied by Furuuchi kagaku Co. The structure of TiC was of NaCl type. Disks with about 3 mm diameter were
721
cut out from a plate by ultrasonic machining and the center part of the disk was polished to a thickness of 10±20 lm with a dimple grinder to form a concave surface. Thin ®lms suitable for electron microscopy were then made by 2.5 keV Ar ion milling with an etching angle of 20° to the sample surface at room temperature. The analytical electron microscope used in this study consisted of 400 keV TEM (JEOL-4000FX) equipped with a parallel-EELS (GATAN-666) and two sets of ion accelerators [6]. The energies of H 2 and He ions were taken to be 25 and 20 keV, respectively so that the average penetration depth of each ion has the same value, about 240 nm, on the basis of TRIM-cord calculation. One half of the energy of the two-atom molecule (25 keV H 2 ion) is shared by two individual atoms (12.5 keV H ion). Therefore, almost all implanted atoms were considered to stop within the specimen. To examine the eect of hydrogen atom injection on bubble formation in He ion irradiation TiC crystals, the following three experiments were performed:
Fig. 1. Evolution of bubbles in TiC crystals during 20 keV He ion irradiation at 1423 K with the ¯ux of 2.5 ´ 1014 (He)/cm2 /s. Helium ¯uence: (a) 1.5 ´ 1017 (He)/cm2 , (b) 3 ´ 1017 (He)/cm2 , (c) 4.5 ´ 1017 (He)/cm2 , (d) 9 ´ 1017 (He)/cm2 .
722
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
1. 25 keV H 2 ion irradiation with a ¯ux of 2.5 ´ 1014 (H2 )/cm2 s. 2. He ion irradiation with a ¯ux of 2.5 ´ 1014 (He)/cm2 s after a pre-irradiation at a ¯uence of 9 ´ 1017 (H)/cm2 . 3. Simultaneous irradiation of H 2 and He ions at 14 2 a ¯ux of 2.5 ´ 10 (He)/cm s for both ions with the atomic ratio of H:He 1:1. The ion irradiation was carried out at room temperature (RT) and high temperature (1423 K). 3. Experimental results and discussion 3.1. Eect of helium ion irradiation Fig. 1 shows a series of photographs of bubbles formation in TiC crystals irradiated with 20 keV He ions of the ¯ux of 2.5 ´ 1014 (He)/cm2 s at 1423 K. Bubbles are typically observed as with particles with diameter of 2 nm in Fig. 1(b) and (c). Small bubbles were formed at ¯uence near 2.5 ´ 1016 (He)/cm2 . As the irradiation proceeded, these
bubbles continued to increase in number density and size up to the ¯uence of about 1.5 ´ 1017 (He)/ cm2 . Beyond this ¯uence some bubbles grew by coalescence with each other. Also, the bubble size showed a bimodal distribution. Bubble size as a function of ¯uence was shown at RT and 1423 K in Fig. 5. In the case of irradiation at RT, small bubbles were formed at ¯uence near 5 ´ 1016 (He)/cm2 . As the irradiation proceeded, the density of bubbles increased but the size of bubbles was not observed to grow remarkably. Bubbles seemed to keep their size in the value of 1±2 nm to the end of irradiation. No amorphization occurred under the condition of the 20 keV He ion irradiation at RT. 3.2. Eect of H2 -ion pre-injection on He -ion irradiation Fig. 2 shows a series of bubbles in TiC crystals during 20 keV He ion irradiation with the ¯ux of 2.5 ´ 1014 (He)/cm2 s (Fig. 2(c)±(e)) after 25 keV H 2
Fig. 2. Evolution of bubbles in TiC crystals during 20 keV He ion irradiation with the ¯ux of 2.5 ´ 1014 (He)/cm2 /s after 25 keV H 2 ion pre-injection with the ¯ux of 2.5 ´ 1014 (H)/cm2 /s at RT. Hydrogen ¯uence: (a) 4.5 ´ 1017 (H)/cm2 , (b) 9 ´ 10 17 (H)/cm2 . Helium ¯uence 17 (H)/cm2 : (c) 3 ´ 1016 (He)/cm2 , (d) 2.2 ´ 1017 (He)/cm2 , (e) 3 ´ 1016 (He)/cm2 . after (b) H 2 ion pre-injection with the ¯uence of 9 ´ 10
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
ion pre-injection at RT with the ¯uence up to 9 ´ 1017 (H)/cm2 (Fig. 2(b)). Very small bubbles less than 1 nm were formed at ¯uence near 9 ´ 10 17 (H)/cm2 during H 2 pre-irradiation and then the bubbles stopped growing and seemed to keep their size in the value of 1±2 nm to the end of helium irradiation after 25 keV H 2 ion pre-injection, as shown Fig. 2(e). The eect of H 2 ion pre-injection on the formation of helium bubbles in TiC crystals was not clear, in comparison with the case of the formation and growth of helium bubble in SiC crystals enhanced by pre-irradiation of hydrogen [7]. The bubble size as a function of ¯uence was shown in Fig. 5. Furthermore, no amorphization occurred also by He -ion irradiation after H 2 -ion
723
pre-injection, which is the same as the result of the helium ion irradiation at RT. 3.3. Eect of simultaneous He - and H2 -ion irradiations Fig. 3 shows the results of in-situ observation of the process of bubbles formation and growth in TiC irradiated simultaneously with 25 keV H 2 and 20 keV He ions at RT. Under the condition of simultaneous H 2 - and He -irradiations at RT, amorphization did not occur after a ¯uence of 1.8 ´ 1018 (H + He )/cm2 and a number of defect clusters were formed after a ¯uence of 3 ´ 1016 (H + He )/cm2 and then the bubbles seemed to
Fig. 3. Evolution of bubbles in TiC crystals during 20 keV He and 25 keV H 2 ions simultaneous dual ion irradiation at RT. Hydrogen atomic ¯ux and helium atomic ¯ux is 2.5 ´ 1014 (H, He)/cm2 /s. Fluence: (a) 2.25 ´ 1017 (H)/cm2 + 2.25 ´ 1017 (He)/cm2 , (b) 4.5 ´ 1017 (H)/cm2 + 4.5 ´ 1016 (He)/cm2 , (c) 9 ´ 1017 (H)/cm2 + 9 ´ 1017 (He)/cm2 .
724
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
Fig. 4. Evolution of bubbles in TiC crystals during 20 keV He and 25 keV H 2 ions simultaneous dual ion irradiation at 1423 K. Hydrogen atomic ¯ux and helium atomic ¯ux is 2.5 ´ 1014 (H, He)/cm2 /s. Fluence: (a) 7.5 ´ 1016 (H)/cm2 + 7.5 ´ 1016 (He)/cm2 , (b) 1.5 ´ 1017 (H)/cm2 + 1.5 ´ 1017 (He)/cm2 , (c) 4.5 ´ 1017 (H)/cm2 + 4.5 ´ 1017 (He)/cm2 , (d) 6.75 ´ 1017 (H)/cm2 + 6.75 ´ 1017 (He)/cm2 , (e) 9 ´ 1017 (H)/cm2 + 9 ´ 1017 (He)/cm2 .
keep their size in the value of 1±2 nm. Fig. 4 shows the results of in-situ observation of the process of bubbles formation and growth in TiC irradiated simultaneously with H 2 and He ions at 1423 K. Small bubbles can be seen at 1.5 ´ 1017 (H + He )/ cm2 , as shown in Fig. 4(a). Beyond a ¯uence of 3 ´ 1017 (H + He )/cm2 , some bubbles grew by coalescence with each other, as shown in Fig. 4(b)± (e). This size of bubble in TiC irradiated simulta neously with H 2 and He ions at RT and 1423 K was shown in Fig. 5. The results obtained in the present irradiation experiments are that no amorphization occurs in TiC under the three kinds of irradiations, 20 keV He ion, 20 keV He ion after a pre-irradiation of 25 keV H 2 ion and simultaneous 25 keV H2 and 20 keV He ion at RT to 1423 K. This fact indicates that irradiation-induced interstitials are mobile and easy to recombine with vacancies by short range migration, thus resulting in keeping the crystalline structure after high ¯uence irradiation. It is considered that this situation is very similar to the case of metals [9].
4. Conclusions The results obtained in the present experiments are summarized as follows:
Fig. 5. Bubble size as function of ¯uence for various irradiation temperature.
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
1. No amorphization occurred in TiC by the three kinds of irradiations, H 2 ion, He ion after H2 ion pre-injection and successive H2 + He dualion irradiation at room temperature and 1423 K, respectively. 2. The formation and growth of bubbles in TiC produced by He ion irradiation is not enhanced by pre-injection of hydrogen atoms at room temperature. This result is quite dierent from the helium bubble formation and growth in SiC, which is enhanced by pre-injection of hydrogen atoms [7]. 3. Bubbles are formed but do not grow appreciably by the two kinds of irradiations, He ion af dual-ion ter H 2 pre-injection and H2 + He irradiation at room temperature. 4. The bubbles grow rapidly during He ion irradiation and dual-ion irradiation at 1423 K.
725
References [1] M. Iseki, Z. Kabeya, J. Nucl. Mater. 133/134 (1985) 722. [2] D. Fournier, M.O. Ruault, R.G. Saint-Jacques, Nucl. Instr. and Meth. B 19/20 (1987) 559. [3] K. Hojou, H. Otsu, S. Furuno, K. Izui, T. Tsukamoto, J. Nucl. Mater. 212±215 (1994) 281. [4] K. Hojou, H. Otsu, S. Furuno, K. Izui, J. Nucl. Mater. 239 (1996) 279. [5] K. Hojou, H. Otsu, S. Furuno, N. Sasajima, K. Izui, Nucl. Instr. and Meth. B 127/128 (1997) 203. [6] S. Furuno, K. Hojou, H. Otsu, T.A. Sasaki, K. Izui, T. Tsukamoto, T. Hata, J. Electron Microsc. 41 (1992) 273. [7] K. Hojou, S. Furuno, K.N. Kushita, H. Otsu, K. Izui, J. Nucl. Mater. 191±194 (1992) 583. [8] K. Hojou, S. Furuno, K.N. Kushita, H. Otsu, K. Izui, Nucl. Instr. and Meth. B 91 (1994) 534. [9] S. Furuno, K. Hojou, H. Otsu, N. Kamigaki, T. Kino, J. Nucl. Mater. 179±181 (1991) 1011.
Damage evolution in TiC crystals during hydrogen and helium dual-ion beam irradiation K. Hojou a
a,*
, H. Otsu a, S. Furuno a, K.N. Kushita a, N. Sasajima b, K. Izui
a
Japan Atomic Energy Research Institute, Department of Material Science and Engineering, Tokai-mura, Ibaraki-ken 319-1195, Japan b Department of Quantum Engineering, Nagoya University, Chikusa-ku, Nagoya 464, Japan
Abstract The eect of He ion irradiation after H 2 ion pre-injection and of simultaneous 25 keV H2 and 20 keV He ion irradiation at RT to 1423 K on the formation of bubbles in TiC crystals were examined. No amorphization occurred under these irradiation conditions. The formation and growth of bubbles produced by He ion irradiation is not enhanced by pre-injection of hydrogen atoms at RT. Bubbles are formed but do not grow appreciably by He ion, H 2 pre-injection and H 2 He dual-ion irradiation at room temperature. Remarkable growth and coalescence occurred during irradiation at high temperature of 1423 K. Ó 1999 Elsevier Science B.V. All rights reserved.
Keywords: In-situ observation; Dual-ion beam irradiation; TiC crystal; Bubble formation
1. Introduction TiC is one of the candidate materials for the ®rst wall of a fusion reactor because of its low induced radioactivity, high resistance for radiation damage, high thermal conductivity and low sputtering by the bombardment of energetic particles. Many researchers have studied the eects of electron-, ion- and neutron-irradiation on TiC [1,2]. We have observed the dynamic behavior of the damage process in TiC crystal during hydrogen-, deuterium- and helium-ion irradiation at various temperatures [3±5]. It was found that TiC did not become amorphous at 20 keV He ion
* Corresponding author. Tel.: +81 29 282 5465; fax: +81 29 282 6716; e-mail: [email protected]
irradiation at temperature from 12 to 1473 K [3]. On the other hand, an amorphization was found to occur in TiC irradiated with hydrogen and deuterium ions at low temperature, although the ¯uences necessary for causing amorphization is dierent between hydrogen and deuterium ion irradiation. This dierence is considered to be due to the isotope eect between hydrogen and deuterium [4,5]. These experiments, however, were conducted with single species of irradiation particles. In a simulation experiment for the fusion environment, it is desirable to employ multiple-beam irradiation because several dierent species will simultaneously impinge on the ®rst wall and blanket component materials. We have developed a system which allows an in-situ observation and chemical analysis during single and/or dual-ion irradiation [6]. We have
0168-583X/98/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 8 5 0 - 7
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
reported previously as to hydrogen and helium dual-ion irradiation on SiC crystals under the various conditions and found that the formation and growth of bubbles in SiC crystals by helium ion irradiation after a hydrogen-ion pre-irradiation are enhanced in comparison with the case of helium single ion irradiation and also found that in the case of simultaneous dual-ion irradiation the bubble formation and growth feature is similar to the case of a helium single ion irradiation [7,8]. In the present experiments, eects of simulta neous H 2 and He ion irradiation were examined and the results were compared with those obtained by He ion irradiation after H 2 ion per-irradiation at room temperature and 1423 K. 2. Experimental procedures The specimens used in the present work were TiC sintered polycrystals. They were supplied by Furuuchi kagaku Co. The structure of TiC was of NaCl type. Disks with about 3 mm diameter were
721
cut out from a plate by ultrasonic machining and the center part of the disk was polished to a thickness of 10±20 lm with a dimple grinder to form a concave surface. Thin ®lms suitable for electron microscopy were then made by 2.5 keV Ar ion milling with an etching angle of 20° to the sample surface at room temperature. The analytical electron microscope used in this study consisted of 400 keV TEM (JEOL-4000FX) equipped with a parallel-EELS (GATAN-666) and two sets of ion accelerators [6]. The energies of H 2 and He ions were taken to be 25 and 20 keV, respectively so that the average penetration depth of each ion has the same value, about 240 nm, on the basis of TRIM-cord calculation. One half of the energy of the two-atom molecule (25 keV H 2 ion) is shared by two individual atoms (12.5 keV H ion). Therefore, almost all implanted atoms were considered to stop within the specimen. To examine the eect of hydrogen atom injection on bubble formation in He ion irradiation TiC crystals, the following three experiments were performed:
Fig. 1. Evolution of bubbles in TiC crystals during 20 keV He ion irradiation at 1423 K with the ¯ux of 2.5 ´ 1014 (He)/cm2 /s. Helium ¯uence: (a) 1.5 ´ 1017 (He)/cm2 , (b) 3 ´ 1017 (He)/cm2 , (c) 4.5 ´ 1017 (He)/cm2 , (d) 9 ´ 1017 (He)/cm2 .
722
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
1. 25 keV H 2 ion irradiation with a ¯ux of 2.5 ´ 1014 (H2 )/cm2 s. 2. He ion irradiation with a ¯ux of 2.5 ´ 1014 (He)/cm2 s after a pre-irradiation at a ¯uence of 9 ´ 1017 (H)/cm2 . 3. Simultaneous irradiation of H 2 and He ions at 14 2 a ¯ux of 2.5 ´ 10 (He)/cm s for both ions with the atomic ratio of H:He 1:1. The ion irradiation was carried out at room temperature (RT) and high temperature (1423 K). 3. Experimental results and discussion 3.1. Eect of helium ion irradiation Fig. 1 shows a series of photographs of bubbles formation in TiC crystals irradiated with 20 keV He ions of the ¯ux of 2.5 ´ 1014 (He)/cm2 s at 1423 K. Bubbles are typically observed as with particles with diameter of 2 nm in Fig. 1(b) and (c). Small bubbles were formed at ¯uence near 2.5 ´ 1016 (He)/cm2 . As the irradiation proceeded, these
bubbles continued to increase in number density and size up to the ¯uence of about 1.5 ´ 1017 (He)/ cm2 . Beyond this ¯uence some bubbles grew by coalescence with each other. Also, the bubble size showed a bimodal distribution. Bubble size as a function of ¯uence was shown at RT and 1423 K in Fig. 5. In the case of irradiation at RT, small bubbles were formed at ¯uence near 5 ´ 1016 (He)/cm2 . As the irradiation proceeded, the density of bubbles increased but the size of bubbles was not observed to grow remarkably. Bubbles seemed to keep their size in the value of 1±2 nm to the end of irradiation. No amorphization occurred under the condition of the 20 keV He ion irradiation at RT. 3.2. Eect of H2 -ion pre-injection on He -ion irradiation Fig. 2 shows a series of bubbles in TiC crystals during 20 keV He ion irradiation with the ¯ux of 2.5 ´ 1014 (He)/cm2 s (Fig. 2(c)±(e)) after 25 keV H 2
Fig. 2. Evolution of bubbles in TiC crystals during 20 keV He ion irradiation with the ¯ux of 2.5 ´ 1014 (He)/cm2 /s after 25 keV H 2 ion pre-injection with the ¯ux of 2.5 ´ 1014 (H)/cm2 /s at RT. Hydrogen ¯uence: (a) 4.5 ´ 1017 (H)/cm2 , (b) 9 ´ 10 17 (H)/cm2 . Helium ¯uence 17 (H)/cm2 : (c) 3 ´ 1016 (He)/cm2 , (d) 2.2 ´ 1017 (He)/cm2 , (e) 3 ´ 1016 (He)/cm2 . after (b) H 2 ion pre-injection with the ¯uence of 9 ´ 10
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
ion pre-injection at RT with the ¯uence up to 9 ´ 1017 (H)/cm2 (Fig. 2(b)). Very small bubbles less than 1 nm were formed at ¯uence near 9 ´ 10 17 (H)/cm2 during H 2 pre-irradiation and then the bubbles stopped growing and seemed to keep their size in the value of 1±2 nm to the end of helium irradiation after 25 keV H 2 ion pre-injection, as shown Fig. 2(e). The eect of H 2 ion pre-injection on the formation of helium bubbles in TiC crystals was not clear, in comparison with the case of the formation and growth of helium bubble in SiC crystals enhanced by pre-irradiation of hydrogen [7]. The bubble size as a function of ¯uence was shown in Fig. 5. Furthermore, no amorphization occurred also by He -ion irradiation after H 2 -ion
723
pre-injection, which is the same as the result of the helium ion irradiation at RT. 3.3. Eect of simultaneous He - and H2 -ion irradiations Fig. 3 shows the results of in-situ observation of the process of bubbles formation and growth in TiC irradiated simultaneously with 25 keV H 2 and 20 keV He ions at RT. Under the condition of simultaneous H 2 - and He -irradiations at RT, amorphization did not occur after a ¯uence of 1.8 ´ 1018 (H + He )/cm2 and a number of defect clusters were formed after a ¯uence of 3 ´ 1016 (H + He )/cm2 and then the bubbles seemed to
Fig. 3. Evolution of bubbles in TiC crystals during 20 keV He and 25 keV H 2 ions simultaneous dual ion irradiation at RT. Hydrogen atomic ¯ux and helium atomic ¯ux is 2.5 ´ 1014 (H, He)/cm2 /s. Fluence: (a) 2.25 ´ 1017 (H)/cm2 + 2.25 ´ 1017 (He)/cm2 , (b) 4.5 ´ 1017 (H)/cm2 + 4.5 ´ 1016 (He)/cm2 , (c) 9 ´ 1017 (H)/cm2 + 9 ´ 1017 (He)/cm2 .
724
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
Fig. 4. Evolution of bubbles in TiC crystals during 20 keV He and 25 keV H 2 ions simultaneous dual ion irradiation at 1423 K. Hydrogen atomic ¯ux and helium atomic ¯ux is 2.5 ´ 1014 (H, He)/cm2 /s. Fluence: (a) 7.5 ´ 1016 (H)/cm2 + 7.5 ´ 1016 (He)/cm2 , (b) 1.5 ´ 1017 (H)/cm2 + 1.5 ´ 1017 (He)/cm2 , (c) 4.5 ´ 1017 (H)/cm2 + 4.5 ´ 1017 (He)/cm2 , (d) 6.75 ´ 1017 (H)/cm2 + 6.75 ´ 1017 (He)/cm2 , (e) 9 ´ 1017 (H)/cm2 + 9 ´ 1017 (He)/cm2 .
keep their size in the value of 1±2 nm. Fig. 4 shows the results of in-situ observation of the process of bubbles formation and growth in TiC irradiated simultaneously with H 2 and He ions at 1423 K. Small bubbles can be seen at 1.5 ´ 1017 (H + He )/ cm2 , as shown in Fig. 4(a). Beyond a ¯uence of 3 ´ 1017 (H + He )/cm2 , some bubbles grew by coalescence with each other, as shown in Fig. 4(b)± (e). This size of bubble in TiC irradiated simulta neously with H 2 and He ions at RT and 1423 K was shown in Fig. 5. The results obtained in the present irradiation experiments are that no amorphization occurs in TiC under the three kinds of irradiations, 20 keV He ion, 20 keV He ion after a pre-irradiation of 25 keV H 2 ion and simultaneous 25 keV H2 and 20 keV He ion at RT to 1423 K. This fact indicates that irradiation-induced interstitials are mobile and easy to recombine with vacancies by short range migration, thus resulting in keeping the crystalline structure after high ¯uence irradiation. It is considered that this situation is very similar to the case of metals [9].
4. Conclusions The results obtained in the present experiments are summarized as follows:
Fig. 5. Bubble size as function of ¯uence for various irradiation temperature.
K. Hojou et al. / Nucl. Instr. and Meth. in Phys. Res. B 148 (1999) 720±725
1. No amorphization occurred in TiC by the three kinds of irradiations, H 2 ion, He ion after H2 ion pre-injection and successive H2 + He dualion irradiation at room temperature and 1423 K, respectively. 2. The formation and growth of bubbles in TiC produced by He ion irradiation is not enhanced by pre-injection of hydrogen atoms at room temperature. This result is quite dierent from the helium bubble formation and growth in SiC, which is enhanced by pre-injection of hydrogen atoms [7]. 3. Bubbles are formed but do not grow appreciably by the two kinds of irradiations, He ion af dual-ion ter H 2 pre-injection and H2 + He irradiation at room temperature. 4. The bubbles grow rapidly during He ion irradiation and dual-ion irradiation at 1423 K.
725
References [1] M. Iseki, Z. Kabeya, J. Nucl. Mater. 133/134 (1985) 722. [2] D. Fournier, M.O. Ruault, R.G. Saint-Jacques, Nucl. Instr. and Meth. B 19/20 (1987) 559. [3] K. Hojou, H. Otsu, S. Furuno, K. Izui, T. Tsukamoto, J. Nucl. Mater. 212±215 (1994) 281. [4] K. Hojou, H. Otsu, S. Furuno, K. Izui, J. Nucl. Mater. 239 (1996) 279. [5] K. Hojou, H. Otsu, S. Furuno, N. Sasajima, K. Izui, Nucl. Instr. and Meth. B 127/128 (1997) 203. [6] S. Furuno, K. Hojou, H. Otsu, T.A. Sasaki, K. Izui, T. Tsukamoto, T. Hata, J. Electron Microsc. 41 (1992) 273. [7] K. Hojou, S. Furuno, K.N. Kushita, H. Otsu, K. Izui, J. Nucl. Mater. 191±194 (1992) 583. [8] K. Hojou, S. Furuno, K.N. Kushita, H. Otsu, K. Izui, Nucl. Instr. and Meth. B 91 (1994) 534. [9] S. Furuno, K. Hojou, H. Otsu, N. Kamigaki, T. Kino, J. Nucl. Mater. 179±181 (1991) 1011.