Optical characterization of silver nano-wire metamaterials
Silver nanowires with diameters of a few tens of nanometers have gained a lot interest recently. An array of such nanowires within a dielectric host matrix are considered as an indefinite anisotropic metamaterial. These metamaterials exhibit negative refraction due to hyperbolic dispersion character...
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Queen's University Belfast
2012
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| Online Access: | http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557635 |
| Summary: | Silver nanowires with diameters of a few tens of nanometers have gained a lot interest recently. An array of such nanowires within a dielectric host matrix are considered as an indefinite anisotropic metamaterial. These metamaterials exhibit negative refraction due to hyperbolic dispersion characteristics for extraordinary waves. The overall purpose of this research is to study the optical characteristics of such an indefinite system. First, an analytical formula was developed which describes the image formation due to a plane parallel slab of such a metamaterial for light emanating from a point source. The results of this analytic flat lens equation were compared with two- dimensional (2D) full wave simulations. One of the objectives of this work was to fabricate such delicate nanostructures. This was achieved by nano-porous alumina templates obtained following the novel two step anodization procedure. Afterwards an electrochemical plating technique was applied to deposit silver into the nano-channels forming a silver nanowire array. The inter-wire distance was only 60 nm so the metamaterial is considered as an effective medium for visible and infrared (IR) light. The optical characteristics of such a system were studied using angular resolved transmission measurements. In particular, a thorough analysis of the transmitted light was applied to determine the principal effective dielectric constants in the visible and IR range. In addition the equifrequency surfaces of the ordinary and extraordinary waves were mapped experimentally in a wave vector diagram for the first time. A comparison of the experimental results with Maxwell-Garnett effective medium theory showed a very good agreement and confirmed the original prediction that the silver nanowire arrays can be described as uniaxial indefinite metamaterials within visible and IR region. |
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