Shaping light spectra and field profiles in metal-coated monolayers of etched microspheres

International audienceHybrid colloidal plasmonic-photonic crystals (HPPCs) are known for their interesting optical properties, which are relevant both fundamentally and for their applicative potential. The optical response of HPPCs is easily tunable from the visible to the infraredspectral range, while their fabrication, based on colloidal self-assembly, keeps production costs rather low. Both arguments make HPPCs a class of attractive functional materials. Here, we explore the optical properties of HPPCs obtained by gradual etching of a hexagonal closepacked monolayer of polystyrene microspheres, subsequently covered by a thin metal layer. We analyze the optical transmission characteristics of these etched colloidal crystals and HPPCs as a function of the etching degree. Finite-difference time-domain simulations allowed us to explain the correlations between the observed optical response and morphology. The transmission gap in bare colloidal crystals can be blue-shifted up to at least 50 nm, and its depth increased by more than 20%. In HPPCs on the other hand, it is possible to tune not only the wavelength of the enhanced plasmonic fields, but also their locations within the nanostructure. Thus, both spectra and near-field profiles can be fine-tuned in a controlledmanner by plasma etching in these hybrid plasmonic-photonic structures, expanding the current understanding of the physical working principles of HPPCs and their applications