Core-shell nanoparticles have been the subject of extensive research due to their potential application in many areas such as microelectronics, optoelectronics, catalysis, and optical devices. In 2005, Yong Lei and Wai-Kin Chim reported the fabrication of highly ordered indium oxide coated indium highly ordered indium oxide coated indium on Si substrates using a three-step oxidation process. First is the preparation of an AAO on the surface of the substrate (Fig. 1a). After the deposition of In (Fig. 1b), the AAO is removed, leaving a highly ordered In nanoparticle array on the substrate. Then, the transformation of In nanoparticles to In/In₂O₃ Core-shell nanoparticles and In₂O₃ nanoparticles was realized by a three-step oxidation process (Fig. 1c,d).