(a)

(b)

(c)

(d)

Figure 3: TEM images of the nanoparticles with SiO2 capping. The reaction time of the SiO2 capping: (a) 1 hour and (b) 4 hours. (c) High-magnification TEM image of the SiO2 capped nanoparticles. (d) Electron diffraction pattern of the SiO2-capped nanoparticles.