Biologically Enabled Syntheses of Freestanding Metallic Structures Possessing Subwavelength Pore Arrays for Extraordinary (Surface Plasmon‐Mediated) Infrared Transmission

Abstract

AbstractA scalable wet chemical process has been used to convert the intricate silica microshells (frustules) of diatoms into gold structures that retained the three‐dimensional (3‐D) frustule shapes and fine patterned features. Combined use of an amine‐enriching surface functionalization protocol and electroless deposition yielded thin (<100 nm) conformal nanocrystalline gold coatings that, upon selective silica dissolution, were converted into freestanding gold structures with frustule‐derived 3‐D morphologies. By selecting a diatom frustule template with a quasi‐regular hexagonal pore pattern (Coscinodiscus asteromphalus, CA), gold replica structures possessing such pore patterns were produced that exhibited infrared transmission maxima/reflection minima that were not observed for the starting silica diatom frustules or for flat nonporous gold films; that is, such extraordinary optical transmission (EOT) resulted from the combined effects of the quasi‐periodic hexagonal hole structure (inherited from the CA diatom frustules) and the gold chemistry. Calculated and measured IR transmission spectra obtained from planar gold films with quasi‐periodic hexagonal CA‐derived hole patterns, or with short‐range periodic hexagonal hole patterns, indicated that the enhanced IR transmission exhibited by the gold CA frustule replicas was enabled by the generation and transmission of surface plasmons. This scalable bio‐enabled process provides a new and attractive capability for fabricating self‐supporting, responsive, 3‐D metallic structures for use as dispersible/harvestable microparticles tailored for EOT‐based applications.