Magnetic-field enhancement in gold nanosandwiches

Abstract

Using dispersive finite-difference time-domain (D-FDTD) simulations, we show that a pair of gold nanodisks stacked in a 'sandwich'-like (end-fire) configuration produces a large enhancement of the magnetic field when irradiated with a plane optical wave, if the distance between the nanodisks is optically small. The effect, which can be rationalized in terms of a magnetic dipole resonance, is due the excitation of a hybridized asymmetric plasmon mode, in which the induced electrical dipoles in the two disks oscillate out-of-phase. The strong magnetic response, together with the simple morphology, suggests that Au nanosandwiches are suitable elementary building blocks for optical metamaterials that exhibit negative refraction.

Optical response of supported gold nanodisks

“…One of the Au nanodisks was capped with a SiO 2 layer in order to investigate the effect of partial embedding on the optical properties of metallic nanoparticles. Also, this structure is part of composite structures like Au-SiO 2 -Au nanosandwiches which have shown very interesting optical properties [9][10][11]. Details of thickness and diameter control during fabrication of Au nanodisks can be found elsewhere [7,10,11,14].…”

“…Therefore, the inhomogeneous incident field at larger angles of incidence and the sharp edges of the nanodisks real shape contribute to the quadrupolar feature. Finally, the results of this work will be valuable for a better understanding of the optical response of more complex nanostructures where nanodisks are the building blocks, for example as in nanosandwiches [9][10][11]44]. …”

“…Of special interest are nanostructured arrays supported on a substrate as those fabricated by hole-mask colloidal lithography [8]. This technique allows control of shapes and sizes in the fabrication of an ample variety of nanostructures including disks, ellipses, cones, binary nanoparticles [8] as well composite nanostructures like metal-dielectric-metal structures [9][10][11]. Besides the LSPR observed in metallic nanostructures, the scientific literature reports on other interesting phenomena like optical magnetism in nanosandwiches [9][10][11], intrinsic Fano interference of localized plasmons in Pd nanoparticles [12], and plasmon induced magneto-optical activity [13].…”

Magnetic metamaterials in the blue range using aluminum nanostructures

“…In particular, metal/dielectric/metal multilayers, such as cutwire nanopairs, fishnet nanostructures, and nanoparticle pairs, have enabled metamaterials operating at optical frequencies. These structures exhibit strong antisymmetric eigenmodes providing magnetic resonances and negative permeability, which is the prerequisite of negative refractive index metamaterials [3,4,5,6,7]. With such designs magnetic metamaterials at about 1.2 µm have been realized using interference lithography [8] In these aforementioned and many other works demonstrating metamaterials with negative refractive index or negative permeability mostly Au and Ag were used, which are, in fact, the conventional choice in plasmonics.…”

Giant Magnetic Field Enhancement in Hybridized MIM Structures

“…As a result, the magnetic plasmon resonance appears in the optical-NIR range of the spectrum [2,3]. Several structures have been proposed in the literature to demonstrate magnetic hot spots including nanorings [4], MIM nanosandwiches [5][6][7] and nanoparticle clusters [8,9]. The MIM structure (nanosandwich) consists of two metallic strips separated by a dielectric layer.…”