Colloidal building blocks with potential for magnetically configurable photonic crystals

This contribution highlights some recent advances in the synthesis of monodispersed colloidal spheres loaded with superparamagnetic components for external manipulation. We firstly discuss how Fe3O4 nanoparticles can be directly coated with silica to form core–shell particles using a sol–gel approach. We then focus on the demonstration of new materials for such an application, with Pb and amorphous Se as the typical examples of metals and semiconductors, respectively. We also illustrate how colloidal spheres of amorphous Se can be converted into Ag2Se and then MSe (M = Zn2+, Cd2+, and Pb2+) without changing the spherical shape. Combined together, these synthetic methods could enable the synthesis of monodispersed colloidal spheres with controlled size, smooth surface, and superparamagnetic features for fabricating photonic crystals whose band structures can be configured using an external magnetic field.