Large-area arrays of three-dimensional plasmonic subwavelength-sized structures from azopolymer surface-relief gratings†
The field of plasmonics allows for confinement and control of light on the nanoscale. Due to potentially strong resonant interactions that light can have with metal nanoscale structures, metals are a good candidate to tailor interactions with light, e.g., periodic arrays of subwavelength metal structures can support extremely narrow resonances and show enhanced transmission. The field of plasmonics has evolved from using simple geometries to the desire to create complex nanostructures for improved control. The availability of fabrication techniques that provide for complex structures, however, is paired with the seemingly inevitable increase in complexity of fabrication techniques themselves. We present a facile and scalable method for the fabrication of periodic arrays of unique three-dimensional subwavelength-sized structures such as tapered holes and pyramidically shaped subwavelength-sized particles. The procedure consists of holographic inscription of a two-dimensional surface-relief grating in an azobenzene-containing polymer film, evaporative gold deposition and broad-beam ion milling of the relief structure. The method allows the fabrication of highly uniform arrays with tunable lattice parameters and dimensions over large sample areas. The optical response of the fabricated structures is determined experimentally and through simulation, which confirm the unique plasmonic response of the structures. While the proposed fabrication method has clear benefits for plasmonics, it could easily be applied also in other fields, for example by using other coating materials.