*6.2. Temperature Rise in Al2O<sup>3</sup> Nanocomplex and W Nanoparticles*

When θ-Al2O<sup>3</sup> was irradiated at a density of 1019–10<sup>20</sup> e/cm<sup>2</sup> s, Al and α-Al2O<sup>3</sup> were formed, as shown in Figures 2 and 16, where the reaction proceeded with a small temperature increase of the order of 10 ◦C, as shown in Section 6.1. On the contrary, the flashing mode of electron irradiation by rapid switching between intensities of 5.5 <sup>×</sup> <sup>10</sup><sup>22</sup> and <sup>5</sup> <sup>×</sup> <sup>10</sup><sup>19</sup> e/cm<sup>2</sup> s was applied to θ- and δ-Al2O<sup>3</sup> to induce Al2O<sup>3</sup> nanoball/nanowire complexes, as shown in Figures 17 and 19 [13]. The higher electron beam intensity increased the temperature by more than 300 ◦C, as calculated through *I*<sup>0</sup> in Equation (1) by maintaining 5.5 <sup>×</sup> <sup>10</sup><sup>22</sup> e/cm<sup>2</sup> s even in a short time of less than 0.1 s. This temperature increase was also predicted by Yokota et al. [22]. Rapid and concentrated heat input at the localised resulted in an Al-O recombined nanoball/nanowire complex with epitaxy at the interface, as shown in Figure 18 [14].

Heavy atoms such as W required a higher irradiation intensity of 4 <sup>×</sup> <sup>10</sup><sup>23</sup> e/cm<sup>2</sup> s to obtain W nanoparticles, as shown in Figure 21 [16]. Although the binding energy of W–O in the starting material WO<sup>3</sup> was smaller than that of Al–O, the W atom is ten times heavier than the Al atom, and required a higher energy for sputtering. A temperature rise was also expected in this irradiation condition, but no melting was observed because of its higher melting point, 3680 K.
