Synthesis and optical properties of silver nanowire arrays embedded in anodic alumina membrane

Transparent Ag nanowire arrays embedded in anodic alumina membranes were prepared by a template-based approach combined with ac electrodeposition and subsequent etching of substrate. The optical response of the structure could be attributed to surface plasmon resonance (SPR) of Ag nanowires. When the incident light was perpendicular to the surface of the composite film, only the transverse resonant mode was excited, and a dual peak line shape appeared at about 400 nm in the optical absorption spectrum. The longitudinal resonance mode appeared at a longer wavelength when polarized light illuminated the film with an angle of incidence of about 70degrees, where the angle was defined with respect to the surface normal. The resonant positions and relative intensities of the two resonant modes were affected by the diameter and aspect ratio of nanowires as well as the polarization direction of incident light. In contrast to the prediction of quasistatic theory, the longitudinal resonance peak did not red shift any more while the aspect ratio was large enough.