Particle interactions, from pronounced dipolar plasmon coupling to noncoupling in colloidal monolayers with interparticle distances of hundreds of nanometers, are demonstrated. Macroscopically sized, hexagonal monolayers with exceptionally high degrees of order are fabricated in one step. Time controls the interparticle spacing and no further processing is required.

Periodic arrays of plasmonic nanostructures can support surface lattice resonances emerging from coupling between localized and diffractive modes. This allows the confinement of light at the nanometer scale with significantly increased resonance lifetimes as compared to those of purely localized modes. Here, we demonstrate that self‐assembly of plasmonic hybrid nanoparticles allows the simple and fast fabrication of periodic plasmonic monolayers featuring macroscopic dimensions and easily controllable lattice spacings. Electromagnetic coupling between diffractive and localized modes is significantly enhanced when the arrays are embedded in a homogeneous refractive index environment. This is realized through spin‐coating of a polymer film on top of the colloidal monolayer. Narrow surface lattice resonances are detected by far‐field extinction spectroscopy while optical microscopy reveals a homogeneous coupling strength on cm‐sized substrates. The surface lattice resonance position is changed by manipulation of the refractive index of the polymer film through the immersion into different organic solvents. Capitalizing on the thermoresponsive behavior of the polymer film we modulate the surface lattice resonance by temperature in a fully reversible, dynamic manner. The findings demonstrate the potential of colloidal self‐assembly as a bottom‐up approach for the fabrication of future nanophotonic devices.

Homogeneous, cm-scale, plasmonic monolayers with defined plasmon resonance positions and intensities are fabricated by interface assembly of core–shell colloids.

We report the observation of optical near fields in a photonic waveguide of conductive indium tin oxide (ITO) using multiphoton photoemission electron microscopy (PEEM). Nonlinear two-photon photoelectron emission is enhanced at field maxima created by interference between incident 410-nm and coherently excited guided photonic waves, providing strong phase contrast. Guided modes are observed under both transverse magnetic field (TM) and transverse electric field (TE) polarized illuminations and are consistent with classical electromagnetic theory. Implications on the role of multiphoton PEEM in optical near-field imaging are discussed.