Germanium FCC structure from a colloidal crystal template

Here we show a method to fabricate a macroporous structure in which the por es, essentially identical, arrange regularly in a face-centered cubic (FCC) lattice. The result is a network of air spheres in a germanium medium. Thi s structure presents the highest dielectric contrast (epsilon(Ge)/epsilon(a ir) = 16) ever achieved in the optical regime in such periodic structures, which could result in important applications in photonics. We employ solid silica colloidal crystals (opals) as templates within which a cyclic german ium growth process is carried out. Thus, the three-dimensional periodicity of the host is inherited by the guest. Afterward, the silica is removed and a germanium opal replica is obtained.