Fabrication of three-dimensional photonic crystals via direct laser writing in an all-inorganic photoresist

A novel procedure to fabricate three-dimensional photonic crystal in an all-inorganic photoresist via a two-step method of direct laser writing and chemical wet etching is reported. Arsenic trisulfide is thermally evaporated to generate a thin film of As4S4 molecules. The As 4S4 is then photo-polymerized back into arsenic trisulfide using a sub-bandgap laser light source. This light source enables the photoresist to be directly patterned in three-dimensions thus allowing direct writing of 3-D structures. The patterned photoresist is then placed in an organic solution that selectively etchs away only the monomer and leaves a material that has an index of refraction 2.45, which enables the final structure to possess a full three-dimensional photonic bandgap in the infrared frequencies.; The structure of the three-dimensional photonic crystals was examined using scanning electron microscopy and the analysis of the optical properties of these structures was done through the comparison of collect spectral data with calculated band-structures. The chemistry of the polymerization and the etching process are discussed, and directions and outlooks towards future research into this system are provided.