Fabrication of woodpile photonic crystals & encoded photonic crystal micro particles with internal woodpile structures via prism holographic lithography

Abstract

In part one, we demonstrate the use of (4+1)-beam holographic interference lithography technique to fabricate woodpile structures in negative photoresists by using single refracting fused silica prism. Top-cut pyramid prism substitutes complicated optical setups for splitting the laser output into multiple beams, and then superposing them at the exposure area, making it easily accessible experimentally. The fabricated woodpile structures are in good agreement with model simulations, and variable optical reflectance spectra can be obtained by controlling laser exposure intensity and photoacids generator concentration. Furthermore, woodpiles with the diamond-like symmetry are also obtained by exploiting the shrinkage of the photoresists, and photonic bandgaps in the visible range are observed with high reflection intensity. In second part, a method to fabricate micron-scale photonic crystal arrays and freestanding particles with internal woodpile structures is described. Hot-embossing process using elastomeric molds defines a disk-like shape of microarrays and particles, and prism holographic interference lithography induces internal woodpile structures as an information identifier consisting of different reflectance peak position. Freestanding microparticles with internal nanostructures are released from microarrays on a plate by dissolution of a sacrificial layer. Also fluorescence enhancement with fluorescent dye is examined, and immobilization of biomolecules via chemical surface modification of the particles is demonstrated.