Electrodeposited Negative Index Metamaterials with Visible and Near Infrared Response

Abstract

by the geometry rather than the constituent materials, which led to the field of metamaterials. Over the last decades, metamaterials research has grown exponentially due to the exceptional possibilities that they offer to manipulate light. Examples of extraordinary properties include artificial chirality, [1] super absorption, [2] extraordinary optical transmission, [3] optical magnetism, [4] or negative refraction. [5] From the several reported structures for achieving negative index metamaterials (NIMs) at optical frequencies, the multilayer fishnet design stands out as the most promising architecture in terms of tunability, figure of merit (FOM), and strong negative values. [6] Its design lies on metal-insulator-metal (MIM) stacks drilled with a 2D periodic array of holes. When the metallic layers are close enough, the propagating surface plasmon polaritons (SPPs) at the internal interfaces overlap, leading to the excitation of so-called gap surface plasmons (GSPs). [7] In this situation, out-of-phase currents are generated in the metallic strips, inducing a magnetic dipole in the insulator layer. This artificial magnetism along with the electric response arising from the metallic layers are the source of the negative refractive index (RI). [8] In the recent years, there has been an increasing interest in the commercial applications of metamaterials. However, the implementation of these architectures in an actual device is not an easy task. Recent advances in nanofabrication have enabled the high-throughput and up scalable production of NIMs using patterning methods such as self-assembly [9-11] or nanoimprint lithography (NIL), [12,13] where the proper arrangement gave rise to negative index at optical frequencies. In particular, the inspiring works by Gao et al. [13] demonstrated large area metamaterials operating at visible and telecommunication frequencies using a subtractive lift-off process combined with metal evaporation and reactive ion etching. Despite the scalability of the patterning techniques used in these works, most of them involve several steps, make use of top-down expensive methods such as electron beam evaporation or implies transferring steps that can damage the structures. In terms of the absolute values achieved, there is still room for improvement for large area NIMs. A record value of −0.73 at 710 nm being the lowest negative refractive index achieved in the visible range with an scalable technique so far. [13] It is also worth noting that obtaining NIMs with a negligible angular Negative index metamaterials have revolutionized the field of photonics because of their unconventional electromagnetic properties absent in naturally occurring materials. It remains a challenge however, to achieve strong negative refractive index at optical frequencies over large areas in a device compatible fashion. In this work, a scalable method for the straightforward production of fishnet-like negative index metamaterials combining soft nanoimprinting and electrodeposition is reported. In four simple steps...

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“…However, while the position of the minimum remains the same for various values of d 1 (Figures 2 and 7a), its size and line width change significantly, which affects performance estimates, such as the Q factor and figure of merit. These parameters, presented in Figure 8, are similar to the results presented in [21].…”

“…The change of the oxide layer thickness d 2 resulted in a considerable shift of the minimum but had only a minimal influence on how the system responded to the changes of n 4 . The rate of change of the wavelength of the reflectance dip λ d in response to the changes of n 4 was the sensitivity S = ∂λ d /∂n [21]. To accurately resolve the location of the dip, the full-width half-maximum (FWHM) of the minimum should be small.…”

“…In particular, one can obtain either a comparable sensitivity S ∼ 200, the figure of merit F ∼ 9, and factor Q ∼ 9 as in [21], or superior sensitivity S ∼ 480 at the expense of the F and Q factor. These values can be further fine-tuned by changing d 2 and the angle of incidence.…”

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“…Metamaterials are three-dimensional artificial composite nanostructures that can manipulate electromagnetic waves and have versatile functionalities [ 3 , 4 , 5 , 6 ]. Metasurface, characterized by reducing the dimension of metamaterials, has attracted much attention due to integrating other optical components beyond the planar interfaces [ 7 , 8 , 9 ].…”

Ultralow loss topological metamaterial in the visible spectrum

“…As a result, mainstream fabrication methods for optical metamaterials nowadays employ various etching techniques to forms meta-atoms 12 , such as the double-fishnet structure 16,14 and the 3D wedge-shaped fishnet structure 13,17 . Much progress has been made in recent years with respect to developing bottom-up preparation approaches for metamaterials [18][19][20][21] . However, metamaterials based on the concept of noble metallic meta-atoms structure suffer from many inherent performance limitations including considerable ohmic loss, optical anisotropy, and difficulty in tuning 9,11 .…”