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Light scattering by a metallic nanoparticle coated with a nematic liquid crystal

November 25th, 2012 Comments off

V. Yannopapas, N. Fyttas, V. Kyrimi, E. Kallos, A.G. Vanakaras, D.J. Photinos, PSSA, DOI: 10.1002/pssa.201228489.

We study the optical properties of gold nanoparticles (NPs) coated with a nematic liquid crystal (NLC) whose director field is distributed around the NP according to the anchoring conditions at the surface of the NP. The distribution of the NLC is obtained by minimization of the corresponding Frank free-energy functional whilst the optical response is calculated by the discrete-dipole approximation (DDA). We find, in particular, that the anisotropy of the NLC coating does not affect much the (isotropic) optical response of the NP. However, for strong anchoring of the NLC molecules on the surface of NP, the inhomogeneity of the coating which is manifested by a ring-type singularity (disclination or Saturn ring), produces an enhancement of the extinction cross spectrum over the entire visible spectrum.

Categories: 2012, A. G. Vanakaras, D.J. Photinos, Paper, V. Yannopapas Tags:

Layer-multiple-scattering theory for metamaterials made from clusters of nanoparticles

August 26th, 2011 Comments off

V. Yannopapas and A. G. Vanakaras, Phys. Rev. B, 84, 085119 (2011).

We present a layer-multiple-scattering method of electromagnetic waves for the study of periodic metamaterials formed as a lattice of cavities which are filled by clusters of spherical nanoparticles. Our approach is a three-stage process where we take fully into account all the multiple-scattering events involved: (a) among the spheres of the cluster inside the cavity, (b) between the cluster and the cavity, and (c) among the cavities (containing the clusters) within the metamaterial. As an example, we study the transmission, reflectance, and absorbance spectra of light incident on a finite slab of a $SiO_2$-inverted opal whose voids contain clusters of gold nanoparticles. We find, in particular, that finite slabs of this metamaterial act as highly efficient absorbers over a wide frequency range, from 2–4.5 eV. Also, around the local maxima of the absorbance spectrum, the metamaterial exhibits anomalous dispersion, wherein the real part of the group velocity is opposite to (the real part of) the phase velocity. ©2011 American Physical Society

URL:http://link.aps.org/doi/10.1103/PhysRevB.84.085119
DOI: 10.1103/PhysRevB.84.085119
PACS: 42.70.Qs, 42.25.Bs, 42.50.Gy, 78.67.Pt
Categories: 2011, A. G. Vanakaras, Paper, V. Yannopapas Tags:

Dirac point in the photon dispersion relation of a negative/zero/positive-index plasmonic metamaterial

July 21st, 2011 Comments off

V. Yannopapas and A. Vanakaras, Phys. Rev. B., 84, 045128, (2011).

We report on the emergence of a Dirac point in the dispersion relation of a plasmonic metamaterial. It is realized as a three-dimensional crystal (cubic or orthorhombic) whose lattice sites are decorated by aggregates of gold nanoparticles embedded in a high-index dielectric material. The Dirac-type dispersion lines of the photon modes are not a result of diffraction as in photonic crystals but due to subwavelength features and emerge from the gapless transition from a negative to a positive index band. The Dirac point is manifested as a dip in the spectrum of light transmittance through a finite slab of the metamaterial; however, transmittance does not decrease diffusively but exponentially due to the inherent losses of gold in the given spectral regime. ©2011 American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevB.84.045128
DOI: 10.1103/PhysRevB.84.045128
Categories: 2011, A. G. Vanakaras, V. Yannopapas Tags: