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NEWS

Dr. Silvia Vignolini

Cavendish Laboratory, University of Cambridge

Friday, October 7th, 2011 at 11:00:00 AM

Conference room Querzoli - LENS - via Nello Carrara 1 - Sesto Fiorentino (Florence)

Published on-line at 01:32:16 PM on Thursday, October 6th, 2011

Linear and circular dichroism in a truly three dimensional gold gyroid meta material

Metamaterials aims at achieving a larger optical activity than observed in natural substances: self-assembly methods allows low cost and large-scale production.

A bi-continuous, triply periodic interconnected network of gold has been realized by self assembly method. Spectroscopic characterization revels a large linear and circular dichroism at optical wavelength, directly observed as colour changes dependent on incident polarisation. Both reflection and transmission measurements show strong plasmonic resonances dependent on the optical field orientation.

The design and fabrication of artificial metallic metamaterials aims at achieving a much larger optical activity than observed in natural substances, such as sugar solutions. Different approaches have been proposed for the realization of such kind of structures including electron beam lithography, direct laser writing or atomic layer deposition [J. K. Ganse et al., Science 18, 1513 (2009)]. All these techniques provide design flexibility, but at the same time are greatly limited in the dimensionality, size and cost of samples and in the frequency range in which they are work. Self-assembly methods combine the advantages of low cost fabrication with large-scale production.

Here we demonstrate a novel and unique kind of three-dimensional metatamaterial [S. Vignolini et al., Adv Mat, in press (2011)], based on the gyroid topology. A bi-continuous, triply periodic interconnected network of gold is grown by electrodeposition inside a porous polymer matrix that self-assembles into a complex nanoscale geometry unattainable through any other conceivable fabrication technique. The dimension of the strongly sub-unit cell is 50-100 nm providing a peculiar and polarization-dependent plasmonic response of the structure. Optical characterization of the samples reveal a large and spectrally-dispersive linear and circular dichroism, directly observed as colour changes dependent on incident polarization. Both reflection and transmission shows strong plasmonic resonances dependent on the optical field orientation. The expected difference in transmission is seen for left- and right-handed polarizations as the orientation of the sample is changed with respect to one of its chiral axes.

For further informations, please contact Prof. Massimo Gurioli.