Anisotropic Diffraction from Inclined Silver Nanorod Arrays on Grating Templates

Abstract

Inclined silver nanorods (AgNRs) are highly anisotropic, with various applications in energy conversion, plasmonic and photonic devices, and sensing. So far, related studies have focused on the reflection or transmission, whereas studies on the diffraction and scattering from anisotropic AgNRs are still lacking. We investigate the anisotropic radiative properties of novel micro/nanoscale hybrid structures of inclined AgNRs deposited on compact disk (CD) gratings, which were fabricated with an oblique angle deposition technique. The reflectance of each diffraction peak and directional–hemispherical reflectance are characterized with a laser scatterometer and an integrating sphere, respectively, for both polarizations at a wavelength of 635 nm. The ordinary and extraordinary optical constants predicted from the effective medium theory (EMT) are incorporated into a rigorous coupled-wave analysis (RCWA) algorithm to estimate the diffraction efficiencies. The effect of scattering (mainly due to surface roughness) is also examined. The result shows that the orientation of the tilted nanorods with respect to the direction of grooves has a significant effect on both the energy distribution of the diffraction rays and the angular distribution of the scattered light for different polarizations. Such a hybrid structure may offer an alternative solution to engineering the radiative properties of a surface.

Keywords:

• diffraction
• effective medium theory
• light scattering
• micro/nanostructure
• optical anisotropy

Acknowledgments

The work at Georgia Tech was supported by the Department of Energy (DE-FG02-06ER46343). The work at the University of Georgia was supported by the National Science Foundation (ECCS-1029609) (YPZ) and USDA CSREES Grant No. 2009-35603-05001 (JLA). Liping Wang of Georgia Tech is acknowledged for help with the RCWA modeling.