Optical properties of silver nanorod arrays prepared by oblique angle deposition

摘要

In this work, we use oblique incident deposition technique to fabricate silver nanorod arrays (NRA). It is found that the orientation of nanorod growth does not obey the traditional tangent rule (empirical relation between the deposition angle and column growth angle). The maximum Ag nanorods tilt angle with respect to the substrate normal can reach to 76 deg. The Ag nanorods almost lie on the substrate and the array behaves as a polarizer. The transmittance versus the polarization direction of normal incident ray is presented in this paper. For a Ag nanorod array with thickness 220 nm and nanorod tilt angle 76 deg, the extinction ratio at wavelength 632.8 nm becomes 0.12 that is better than previous work. The extinction ratio of the polarizer would be further reduced to be less than 0.05 by arranging an isotropic Ag film between the Ag nanorod array and the substrate. On the other hand, it is interesting to show that Ag nanorod array is isotropic for normal incident ray with any polarization direction at a certain critical wavelength λ_c. In the wavelengthrange λ>λ_c, the maximum absorption occurs when the polarization is TM mode (electric field direction parallel to thedeposition plane). In the wavelength rangeλ<λ_c, the maximum absorption occurs when the polarization is TE mode(electric field direction perpendicular to the deposition plane). The critical wavelengths for Ag nanorod arrays fabricated by different deposition angles are measured and analyzed in this paper.