Fabrication of Core−Shell Structure of M@C (M=Se, Au, Ag₂Se) and Transformation to Yolk−Shell Structure by Electron Beam Irradiation or Vacuum Annealing

Selenium @ carbon core−shell spheres have been synthesized via a simple one-step hydrothermal carbonization process using sucrose and sodium selenite as precursors. Metal selenide or noble metal, e.g. Ag 2 Se or Au, can be easily encapsulated into the carbon shell by using the as-prepared Se@C core−shell samples as site templates. The transformation from core/shell to yolk/shell structure, e.g. Se@C, Au/Se@C and Ag 2 Se@C, can be achieved through thermal evaporation under electron beam irradiation or vacuum annealing to evaporate Se. The optical absorption of the samples can be tuned by varying the structure/compositions of the samples.