Multilevel Spherical Photonic Crystals with Controllable Structures and Structure-Enhanced Functionalities

Spherical photonic crystals (SPCs) with tailorable multiscale structure, versatile surface morphology, and controllable optical properties of both photonic stop band (PSB) and surface plasmon resonance (SPR), have been fabricated using a robust and facile method. The fabricated SPCs consist of well-spaced gold nanocrystals (AuNCs) (3rd-tier) anchored on silica nanopatterns (2nd-tier) confined in microspherical templates (1st-tier). Droplet microfluidics is used to produce microdroplets containing silica nanoparticles (SiO2NPs) which assemble to form two-tier SPCs. Subsequently, three-tier SPCs are obtained by thermal dewetting and evaporation of metal films deposited on the two-tier SPCs, with the 3rd-tier morphology being controlled by the deposited film morphology and programmed thermal annealing. Optical PSB and SPR properties of the prepared SPCs can be on-demand tailored by the 2nd and 3rd-tier morphology and their corresponding constituent materials. It is found that the scattering from AuNC arrays on the SPCs can be amplified by tailoring the PSB properties. The hierarchical SPCs manufactured by this method take advantages of low-cost, high controllability, and further processability. The manufacturing of flexible film encapsulated well-assembled SPCs as anticounterfeiting stamps, which are easy to be identified using the mobile phone with a flash, is demonstrated.