Checkerboard Nanoplasmonic Gold Structure for Long-Wave Infrared Absorption Enhancement

A localized nanoplasmonic induced absorption enhancement in silicon nitride (Si
₃
N
₄
) dielectric material using a nanoscale novel checkerboard gold (Au) structure is demonstrated. The checkerboard structure is fabricated on a Si
₃
N
₄
layer using electron-beam lithography and sputter deposition techniques. The plasmonic electric field and optical absorption enhancement are measured using scanning near-field optical microscopy. Finite-difference time-domain simulations are utilized to characterize the absorption spectral response enhancement together with its dependence on incidence angle and polarization. The checkerboard shows a broadband average spectral absorption enhancement of 63.2% over the wavelength range 8-12 μm with a maximum enhancement of 107% at 8 μm and a minimum enhancement of 24.8% at 12 μm. The degradation of enhanced absorption with incidence angle variation (00-60ο) is less than 1.6% at 10.6-μm wavelength. The checkerboard device shows polarization-independent absorption enhancement with incidence angles.