Surface Lattice Resonances in Self-Assembled Arrays of Monodisperse Ag Cuboctahedra

Abstract

Plasmonic metal nanoparticles arranged in periodic arrays can generate surface lattice plasmon resonances (SLRs) with high Q-factors. These collective resonances are interesting because the associated electromagnetic field is delocalized throughout the plane of the array, enabling applications such as biosensing and nanolasing. In most cases such periodic nanostructures are created via top-down nanofabrication processes. Here we describe a capillary-force-assisted particle assembly method (CAPA) to assemble monodisperse single-crystal colloidal Ag cuboctahedra into nearly defect-free >1 cm2 hexagonal lattices. These arrays are large enough to be measured with conventional ultraviolet–visible spectroscopy, which revealed an extinction peak with a Q-factor of 30 at orthogonal illumination and up to 80 at oblique illumination angles. We explain how the experimental extinction changes with different light polarizations and angles of incidence, and compare the evolution of the peaks with computational models based on the coupled dipole approximation and the finite element method. These arrays can support high Q-factors even when exposed to air, because of the high aspect ratio of the single-crystal nanoparticles. The observation of SLRs in a self-assembled system demonstrates that a high level of long-range positional control can be achieved at the single-particle level.

Mechanotunable Plasmonic Properties of Colloidal Assemblies

“…The excited electric fields associated with neighboring particles are localized in the surrounding medium and the index mismatch between substrate and the medium is no longer critical. Similar results were provided by Tamulevic ˇius and co‐workers who studied the in‐plane and out‐of‐plane SLRs of hexagonal silver cuboctahedra assemblies …”

“…Such narrow linewidths were shown recently for lattices with gold and silver nanoparticles. In the study of the Tamulevicˇius group, hexagonal lattices with self‐assembled silver cuboctahedra were presented with quality factors (resonance wavelength divided by linewidth) of up to 80, as compared to typical LSPR values of about 10 . The FDTD method is especially useful to calculate the response of plasmonic particles, as there is a wide range of geometries accessible through wet‐chemical synthesis.…”

“…Readily available simulation techniques such as the coupled dipole approximation (CDA) or the finite‐difference time‐domain (FDTD) method can be used to determine the optical parameters and spectroscopic response that lead to the narrow spectral width (down to 1–2 nm) compared to the significantly broader resonances found for single plasmonic particles (>80 nm width) . Such narrow linewidths were shown recently for lattices with gold and silver nanoparticles. In the study of the Tamulevicˇius group, hexagonal lattices with self‐assembled silver cuboctahedra were presented with quality factors (resonance wavelength divided by linewidth) of up to 80, as compared to typical LSPR values of about 10 .…”

Nanocube Imprint Lithography

“…Finally, arrays of isolated nanocubes were printed with good orientational alignment ( Figure 2 m,n), which can be interesting for applications using surface lattice resonances. 59 , 60 …”

Chiral Surface Lattice Resonances

“…[ 14–16 ] Recently, the excitation of SLRs was seen in self‐assembled, large area colloidal systems. [ 17,18 ] Such systems offer the possibility for fast manufacturing and covering large‐areas on different substrate materials. [ 19 ] Colloid‐based materials allow for embedding of nanoparticle arrays into flexible free‐standing polymer films, [ 20 ] enabling the design of mechanically tunable [ 21 ] and stimuli‐responsive hydrogel membranes.…”