Conformally back-filled, non-close-packed inverse-opal photonic crystals

The atomic layer deposition (ALD) process to form back-filled, non-close-packed inverse opal photonic crystals, was analyzed. The used process contains two steps, first, conformally infiltrating heavily sintered silica opals with TiO₂ and etching the spheres with hydrofluoric acid, and second, conformally backfilling the resulting inverse opal. This new process allowed a static tunability to ∼400 nm in the position of the directional bandgap. ALD has the unique ability to fully and uniformly infiltrate porous structures, even within extended nanoscale channels, which is critical to successful infiltration and inversion of the template. The power of a two-stage ALD process to uniquely enable the precise formation and tuning of complex PC structures has been demonstrated.