Tunable Photonic Nanostructures 2: Semi-Transparent Metallic Opal Replicas and Nanocomposites.

摘要

The same free electron plasma that causes usual metals to be conducting also causes them to be non-transmissive to electromagnetic waves. As well known at frequency (omega) below the plasma frequency (omega)p, the dielectric permittivity (Epsilon = 1 - (omega p/omega)squared) becomes negative and the refractive index (n(omega) = (epsilon mu))(exp 1/2) where mu is the magnetic permeability becomes imaginary. Therefore, electromagnetic waves can not effectively propagate inside metals, but are instead reflected for good metals and both reflected and absorbed for less conductive metals. This point emphasizes that high transparency (T) and high electrical conductivity (sigma) are contradictory properties, and that the product T x sigma can not be maximized in the usual bulk materials found in nature. The motivation of the present work was to create photonic crystals (PC), not of conventional dielectric type 1- 2, but of metallic periodic nanostructures or metallo- dielectric nanocomposite PC in which T x sigma can be maximized. Moreover optical and electronic properties can be made tunable because of the utilization of geometry and topology of interpenetrating components separated by a large interfacial area A(sub upsilon) in a photonic crystal structure.