Optical Characterization of Silver Nanorod Thin Films Grown Using Oblique Angle Deposition

Nanorods are metamaterial structures that have been shown to have wide application, ranging from biomedical uses to photovoltaic materials. These materials have unique optical characteristics. In this paper, two silver (Ag) nanorod thin-film samples are created using Glancing Angle Deposition (GLAD) at both near-room temperature (~300 K) and cryogenic temperature (~100 K). Generalized ellipsometry is used to measure the optical constants of the samples. The strong difference between the optical constants of the constituent materials and those of these thin films shows that the characteristics of the samples are due to how their metamaterial structures are defined. The principle optical axes of the films align well with the morphological characteristics of the nanostructures. The axis with the greatest index of refraction remains aligned to the principle axes but shifts orientation with respect to morphological characteristics between samples. Experimental results show differences in both magnitude and characteristics of the nanorod indexes. Reflectance and transmittance measurements are performed to extract absorptance data. The room temperature deposited sample shows a higher overall absorptance, while the cryogenic sample shows a clear orientation-dependent absorptance. Polarization data is analyzed to show that the 100 K thin film exhibits polarization-dependent absorptance, while the 300 K sample’s absorptance has a strong orientation dependence