**3. Results and Discussions**

versity.

#### **3. Results and Discussions**  *3.1. Ion Dose and Energy Dependance of Thermal Desorption Behavior 3.1. Ion Dose and Energy Dependance of Thermal Desorption Behavior*

Figure 4 shows the dose dependance of the thermal desorption spectrum after 5.0 keV D2+ ion irradiation at room temperature. Figure 4a–c show the cases of unirradiated samples, samples radiated with 3.0 × 1021 ions/m2, and samples irradiated with 10 × 1021 ions/m2, respectively. As shown in Figure 4a, the desorption stages of HD (mass = 3) and D2 (mass = 4) were not detected prior to irradiation, but, after the D2+ ion irradiation, two major peaks at approximately 600 °C (mass = 3) and 800 °C (mass = 4) were detected. As demonstrated, the desorption stages were designated Peak A and Peak B on the lower temperature side. By increasing the irradiation dose from 3.0 to 10 × 1021 ions/m2, the total desorption of HD and D2 increased from 1.8 to 5.5 × 1019 ions/m2, and from 2.5 to 6.6 × 1018 Figure 4 shows the dose dependance of the thermal desorption spectrum after 5.0 keV D<sup>2</sup> + ion irradiation at room temperature. Figure 4a–c show the cases of unirradiated samples, samples radiated with 3.0 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> , and samples irradiated with <sup>10</sup> <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> , respectively. As shown in Figure 4a, the desorption stages of HD (mass = 3) and D<sup>2</sup> (mass = 4) were not detected prior to irradiation, but, after the D<sup>2</sup> + ion irradiation, two major peaks at approximately 600 ◦C (mass = 3) and 800 ◦C (mass = 4) were detected. As demonstrated, the desorption stages were designated Peak A and Peak B on the lower temperature side. By increasing the irradiation dose from 3.0 to 10 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> , the total desorption of HD and D<sup>2</sup> increased from 1.8 to 5.5 <sup>×</sup> <sup>10</sup><sup>19</sup> ions/m<sup>2</sup> , and from 2.5 to 6.6 <sup>×</sup> <sup>10</sup><sup>18</sup> ions/m<sup>2</sup> , respectively. The increasing rate was 3.1 for HD and 3.8 for D2. These values were nearly consistent with the increasing dose level values, particularly 3.3. *Quantum Beam Sci.* **2021**, *5*, x FOR PEER REVIEW 4 of 10 ions/m2, respectively. The increasing rate was 3.1 for HD and 3.8 for D2. These values were nearly consistent with the increasing dose level values, particularly 3.3.

**Figure 4.** The dose dependance of the thermal desorption spectrum after 5.0 keV D2+ ion irradiation at room temperature: (**a**) before irradiation, (**b**) 3.0 × 10 21 ions/m2, and (**c**) 10 × 1021 ions/m2. **Figure 4.** The dose dependance of the thermal desorption spectrum after 5.0 keV D<sup>2</sup> + ion irradiation at room temperature: (**a**) before irradiation, (**b**) 3.0 <sup>×</sup> <sup>10</sup> <sup>21</sup> ions/m<sup>2</sup> , and (**c**) 10 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> .

ions/m2, respectively. Figure 5b, shows that Peak B became prominent when the ion energy increased to 30 keV. In this figure, the total desorption of deuterium after 30 keV ion irradiation was much higher than that of the sample after 5.0 keV. Since the implanted deuterium atoms do not stay at the same position which is calculated in Figure 2, they diffuse to the thick region of the sample during irradiation and hydrides are formed. In the case of 5.0 keV irradiation, more deuterium atoms were released from the specimen surface than at 30 keV. Detailed estimation of deuterium atom diffusion during irradiation

Figure 6a,b shows the microstructures of these samples. Hydrides were observed in the specimen's edge region following irradiation at 5.0 keV (Figure 6a). However, hydride formation was only detected in the thick region of the C-TEM samples following irradia-

**Figure 5.** The energy dependance of the thermal desorption spectrum after the ion irradiation with

a dose of 3.0 × 1021 ions/m2 at room temperature: (**a**) 5.0 keV and (**b**) 30 keV.

and desorption is needed.

tion at 30 keV (Figure 6b).

Figure 5a,b shows the ion energy dependance of the thermal desorption spectrum after the administration of 5.0 keV D<sup>2</sup> + ions and 30 keV D<sup>2</sup> + ions with a dose of 3.0 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> , respectively. Figure 5b, shows that Peak B became prominent when the ion energy increased to 30 keV. In this figure, the total desorption of deuterium after 30 keV ion irradiation was much higher than that of the sample after 5.0 keV. Since the implanted deuterium atoms do not stay at the same position which is calculated in Figure 2, they diffuse to the thick region of the sample during irradiation and hydrides are formed. In the case of 5.0 keV irradiation, more deuterium atoms were released from the specimen surface than at 30 keV. Detailed estimation of deuterium atom diffusion during irradiation and desorption is needed. ergy increased to 30 keV. In this figure, the total desorption of deuterium after 30 keV ion irradiation was much higher than that of the sample after 5.0 keV. Since the implanted deuterium atoms do not stay at the same position which is calculated in Figure 2, they diffuse to the thick region of the sample during irradiation and hydrides are formed. In the case of 5.0 keV irradiation, more deuterium atoms were released from the specimen surface than at 30 keV. Detailed estimation of deuterium atom diffusion during irradiation and desorption is needed. Figure 6a,b shows the microstructures of these samples. Hydrides were observed in the specimen's edge region following irradiation at 5.0 keV (Figure 6a). However, hydride formation was only detected in the thick region of the C-TEM samples following irradiation at 30 keV (Figure 6b).

Figure 5a,b shows the ion energy dependance of the thermal desorption spectrum after the administration of 5.0 keV D2+ ions and 30 keV D2+ ions with a dose of 3.0 × 1021 ions/m2, respectively. Figure 5b, shows that Peak B became prominent when the ion en-

*Quantum Beam Sci.* **2021**, *5*, x FOR PEER REVIEW 4 of 10

**Figure 4.** The dose dependance of the thermal desorption spectrum after 5.0 keV D2+ ion irradiation at room temperature:

(**a**) before irradiation, (**b**) 3.0 × 10 21 ions/m2, and (**c**) 10 × 1021 ions/m2.

nearly consistent with the increasing dose level values, particularly 3.3.

ions/m2, respectively. The increasing rate was 3.1 for HD and 3.8 for D2. These values were

**Figure 5.** The energy dependance of the thermal desorption spectrum after the ion irradiation with a dose of 3.0 × 1021 ions/m2 at room temperature: (**a**) 5.0 keV and (**b**) 30 keV. **Figure 5.** The energy dependance of the thermal desorption spectrum after the ion irradiation with a dose of 3.0 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> at room temperature: (**a**) 5.0 keV and (**b**) 30 keV.

Figure 6a,b shows the microstructures of these samples. Hydrides were observed in the specimen's edge region following irradiation at 5.0 keV (Figure 6a). However, hydride formation was only detected in the thick region of the C-TEM samples following irradiation at 30 keV (Figure 6b). *Quantum Beam Sci.* **2021**, *5*, x FOR PEER REVIEW 5 of 10

**Figure 6.** The energy dependance of the microstructure after the ion irradiation with a dose of 3.0 × 1021 ions/m2 at room temperature: (**a**) 5.0 keV and (**b**) 30 keV (the arrows show the hydrides formed by irradiation). 1021 ions/m2 at room temperature). The hydrides (shown by arrows) disappeared at 400 °C. **Figure 6.** The energy dependance of the microstructure after the ion irradiation with a dose of 3.0 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> at room temperature: (**a**) 5.0 keV and (**b**) 30 keV (the arrows show the hydrides formed by irradiation).

In our previous study of Zircaloy-2 [19], it was concluded that hydrides formed by

large hydrides were formed in the thick region of the samples. However, as Figure 6a shows, small hydrides formed in the specimen surface region by 5.0 keV D2+ ions irradiation were not stable in a higher temperature region (Peak B in Figure 5b). To investigate the thermal stability of these small hydrides in the surface region of the samples, the TEM samples was annealed at each temperature for 30 min, and the observation was conducted using a heating TEM holder. Figure 7 shows the thermal stability of these small hydrides,

**Figure 7.** The thermal stability of the small hydrides formed in the surface region (30 keV, 3.0 ×

and they disappeared around 400 °C (in Peak A).

In our previous study of Zircaloy-2 [19], it was concluded that hydrides formed by annealing were stable up to 700 ◦C. The cross-sectional view of the sample showed that large hydrides were formed in the thick region of the samples. However, as Figure 6a shows, small hydrides formed in the specimen surface region by 5.0 keV D<sup>2</sup> + ions irradiation were not stable in a higher temperature region (Peak B in Figure 5b). To investigate the thermal stability of these small hydrides in the surface region of the samples, the TEM samples was annealed at each temperature for 30 min, and the observation was conducted using a heating TEM holder. Figure 7 shows the thermal stability of these small hydrides, and they disappeared around 400 ◦C (in Peak A). In our previous study of Zircaloy-2 [19], it was concluded that hydrides formed by annealing were stable up to 700 °C. The cross-sectional view of the sample showed that large hydrides were formed in the thick region of the samples. However, as Figure 6a shows, small hydrides formed in the specimen surface region by 5.0 keV D2+ ions irradiation were not stable in a higher temperature region (Peak B in Figure 5b). To investigate the thermal stability of these small hydrides in the surface region of the samples, the TEM samples was annealed at each temperature for 30 min, and the observation was conducted using a heating TEM holder. Figure 7 shows the thermal stability of these small hydrides, and they disappeared around 400 °C (in Peak A).

**Figure 6.** The energy dependance of the microstructure after the ion irradiation with a dose of 3.0 × 1021 ions/m2 at room temperature: (**a**) 5.0 keV and (**b**) 30 keV (the arrows show the hydrides

*Quantum Beam Sci.* **2021**, *5*, x FOR PEER REVIEW 5 of 10

**Figure 7.** The thermal stability of the small hydrides formed in the surface region (30 keV, 3.0 × 1021 ions/m2 at room temperature). The hydrides (shown by arrows) disappeared at 400 °C. **Figure 7.** The thermal stability of the small hydrides formed in the surface region (30 keV, 3.0 <sup>×</sup> <sup>10</sup><sup>21</sup> ions/m<sup>2</sup> at room temperature). The hydrides (shown by arrows) disappeared at 400 ◦C.
