Near-field optical resonance and enhancement of a plasmonic nanocrescent cylinder tuned by a proximal plasmonic nanostructure

摘要

Sharp geometrical features in crescent-shaped plasmonic nanostructures facilitate electromagnetic hot spots that can be harnessed for sensitive detection of molecules and nanomaterials. For a given geometry of nanocrescent cylinder, the near-field optical resonance and enhancement are constants. It is desirable to tune this resonance and enhancement without altering the geometry of the nanocrescent cylinder. Herein, we numerically show how the near-field resonance and enhancement at the tip of a nanocrescent cylinder can be proximally tuned by incorporating a plasmonic nanostrip in the vicinity. Geometrical parameters, such as the nanocrescent cylinder-nanostrip distance (g) and length (l) of the nanostrip, were varied to tune the near-field optical properties. Our analysis revealed (i) an increment in near-field enhancement at the tip of the nanocrescent cylinder in the presence of a plasmonic nanostrip; (ii) a redshift in the dipolar plasmon mode accompanied by an increase in the nearfield enhancement by decreasing g and increasing l, independently; and (iii) variation in the near-field enhancement of plasmonic modes as a function of the excitation angle. Such tunable plasmonic configurations offer capabilities to design wavelength-tuned optical devices without altering the base geometry.