Generalized ellipsometry characterization of Ag nanorod arrays prepared by oblique angle deposition

Silver nanorods arrays (AgNRs) prepared by oblique angle deposition were characterized by the generalized ellipsometry method in the spectral range from 370 to 950 nm. Three structure models were used to fit the ellipsometry data, the uniaxial model, the biaxial orthorhombic model, and the biaxial monoclinic model. Unlike the uniaxial model reported in most literature, the biaxial models are found to give better fitting results. The optical properties along the three principle axes are different: along long axis it displays predominantly metallic behavior; along one short axis it approaches to a lossless dielectric while along the other it behaves as an absorbance dielectric. The AgNRs also demonstrate epsilon-near-zero property with the real part of dielectric constant along the rod being very close to zero at wavelength of 416 nm, which is expected to be tuned with changing of the vapor incident angles. (paper)