Probing Subnanometric-Scale Hotspots in Metallic Interfaces

Abstract

Metallic gap-nanoantennas with separation distances (d) in the nanometer and/or even subnanometer scale are known to produce nanoscale localization and enhancement of optical field in the gap region, making them interesting for various optical applications. Here, using the time-dependent density functional theory calculations, we present a comprehensive study of the evolution of the absorption spectra, the response charge densities, and the electric field enhancements in a thin Na nanoplatelet dimer as a function of d in the range of 1.5 to 10 A. Three interaction regimes have been identified. At large widths of the gap between nanoplatelets (8 < d< 10 A), the main features of the absorption spectra remain unchanged, response charge densities exhibit plasmon resonances, and electric field enhancement confined to the individual nanoplatelets itself. For d in the range of 4 to 7 A, electron tunneling between the nanoplatelets produce significant response modulations. For 3 < d< 1.5 A, chemical bonding between the nanoplatelets produce noticeable modulations in both the response charge density and the electric field enhancement. The findings in this work may have an impact in the design of novel quantum nano-optic devices.