In this study, we extended the plasmon hybridization method from a single nanoparticle to a complex planar nanostructure. This is achieved through a decomposition of the complex nanostructure into nanoparticle building blocks in its most fundamental forms. Using the gammadion planar nanostructure as an example, we validated our theory by comparing the field profile in the gammadion’s arms under the influence of an incident circularly polarized wave. This further allows us to address the origin of the plasmonics modes in the circular dichroism (CD) spectrum of the gammadion nanostructure. The use of this hybridization method provides a simple and intuitive explanation on how conductive and inductive coupling may result from complex planar nanostructures. Understanding these coupling effects open up the path to study the optical properties of a complex nanostructure. With our approach, we will be able to apply such top down hybridization studies to other complex planar structures. With knowledge of the origin of these CD modes, we can gain further insight on the modes of chiral nanostructures, allowing us to further enhance the field for ultrasensitive sensing of chiral micro and macro molecules.
In this paper, the effect of tapered asymmetrical gammadion on the optical rotational properties and sensitivity detection
of biomolecular structures is presented. The asymmetrical structure is made up of gold material on a glass structure and
immersed in water. The chirality of the un-rotated array is first determined by measuring the circular dichroism (CD)
spectrum. Three modes, arising from Bloch periodic theory and surface resonance mode are observed. Then each
asymmetrical gammadion structure is tapered at the arms. Tapering fraction, which define the ratio of tapered end to the untapered end is used for defining the new design. The designs are then fabricated using e-beam lithography and tested using the polarimeter for CD spectra. The spectra show that the three CD modes changes in degree amplitude and wavelength, especially for smaller tapering fractions.
In this paper, we rotate an array of asymmetrical double layer of 4-strips windmill structure to investigate its effect on
the chirality and sensitivity detection of biomolecular structures. The structure is made up of silver material with 300nm
pitch and 10nm separation between layers. The spectrum shows two resonance modes on 600THz and 900THz with
linear polarized light normally incident on the structure. We investigate the CD by rotating one of the layers with respect
to the horizontal axis of the other layer by the angle θ. It is observed that the CD spectra at different angles are different.
The rotation resulted in larger wavelength shift of the CD spectra. In addition, the CD also increases with the rotating
angle given a larger absorption difference between the left and right handed circular polarized light.
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