Highly Ordered Arrays of Particle-in-Bowl Plasmonic Nanostructures for Surface-Enhanced Raman Scattering

A highly ordered particle‐in‐bowl (PIB) nanostructure array is designed and fabricated to achieve large field enhancement for the surface‐enhanced Raman scattering (SERS) application. This new type of PIB structure is composed of an Ag particle located at the bottom of an Au bowl, and the two are separated by a precisely controlled nanoscale dielectric layer. The fabrication of the PIB structure is based on the self‐assembly of polystyrene spheres and atomic layer deposition (ALD), which allows good control of the metal particle size and gap distance, as well as large‐scale ordering. Numerical simulation reveals a high enhancement of the local field at the nanogaps. The SERS performance of the PIB arrays, and the effects of the Ag particle size and the ALD dielectric layer thickness are characterized, results of which are in reasonable agreement with simulation. With Rhodmaine 6G as the probe molecule, the spatially averaged SERS enhancement factor is on the order of 3.8 × 107 and the local field enhancement from simulation can be up to 108. A new plasmonic particle‐in‐bowl array is fabricated based on nanosphere self‐assembly (NSL) and atomic layer deposition (ALD). The strong electric field at the ALD Al2O3 gap separating the Ag particle from the Au bowl is revealed by numerical simulation and demonstrated by surface‐enhanced Raman scattering (SERS) measurements; both show that the field enhancement is strongly dependent on the Ag particle size and gap distance.