This study presents a method for fabricating binary surface-enhanced Raman scattering substrates using plasmonic Pt@Ag and Pt@Au truncated-octahedral dual-rim nanoframes, which is "nanoalloy." The structural complexity of dual rims on (111) facets, combined with enhanced polarization at the Ag and Au interface, significantly boosts Raman scattering activity, as confirmed by single-particle and bulk measurements and finite element method calculations. Additionally, free-standing superpowders were developed, where the heterogeneous building blocks formed micron-sized supercrystals with adjustable component ratios, demonstrating their potential for practical analyte detection in contaminated areas.

Plasmonic Au nanohexagons are assembled into a planar superlattice with precisely controlled size, shape, and edge gaps, achieving record-high refractive index values in the near-infrared range, surpassing the upper limit of natural materials. The enhanced refractive index results from intensified in-plane surface plasmon coupling, with the edge-gap control enabling systematic tuning of the refractive index as confirmed by numerical analysis using the plasmonic percolation model. Additionally, a one-dimensional photonic crystal composed of alternating layers of Au nanohexagon superlattices and low-index polymers enhances the selectivity of the reflectivity, demonstrating the potential of these superlattices as optical metamaterials for near-infrared applications.

This study introduces an efficient synthetic method for producing free-standing super-powders using various nanoparticle morphologies and compositions, without requiring specific substrates. Au nanorings are used as building blocks, forming densely packed columnar assemblies with exposed gaps aligned perpendicular to the laser beam, enhancing charge separation and creating a highly focused near-field for surface-enhanced Raman spectroscopy analysis. The method is highly versatile, demonstrated by its ability to create super-powders from a wide range of nanoparticle shapes, including rods, hexagons, cubes, and complex frames, making it applicable to diverse applications.