Plasmonic Spectral Engineering via Interferometric Illumination of Colloid Sphere Monolayers

A novel method is presented for complex structure fabrication, which is capable of breaking the hexagonal symmetry of the conventional colloid sphere lithography via the interferometric illumination of colloid sphere monolayers (IICSM). It is demonstrated that the perfect lateral synchronization of a linear intensity modulation originating from two-beam interference with respect to a hexagonal colloid sphere monolayer makes it possible to tune four complex structure parameters independently. Based on comparative study of hexagonal and rectangular hole doublet-arrays, which can be generated by linearly polarized light via homogeneous illumination and via IICSM, it is shown that the novel IICSM method enables plasmonic spectral engineering with higher degrees of freedom. The unique spectral properties of the complex patterns attainable via IICSM are more precisely tunable by properly selected azimuthal orientation during illumination and by the surrounding medium. It is shown that coupling phenomena between propagating and localized plasmonic modes on appropriately designed complex structures result in unique charge and near-field distribution accompanied by narrow Fano lines. Optimal configurations of complex plasmonic structures consisting of a rectangular array of hole doublets with different geometrical size parameters are presented, which ensure enhanced sensitivity in bio-detection.