Photonic metamaterials by direct laser writing and silver chemical vapour deposition

Abstract

Metamaterials are artificial materials that-unlike natural substances-enable magnetism to be achieved at optical frequencies 1-3 . The vast majority of photonic metamaterials 4,5 has been fabricated by electron-beam lithography and evaporation of metal films, both of which are well-established twodimensional (2D) technologies. Although stacking of three 6 or four 7 functional layers made using these methods has been reported, a truly 3D fabrication approach would be preferable for 3D photonic metamaterials. Here, we report first steps in this direction by using a combination of direct laser writing 8,9 and silver chemical vapour deposition 10,11 -the 3D analogues of electron-beam lithography and evaporation, respectively. The optical characterization of a planar test structure composed of elongated split-ring resonators is in good agreement with theory. Retrieval of the effective optical parameters reveals the importance of bi-anisotropy. Once suitable theoretical blueprints are available, our fabrication approach will enable rapid prototyping of truly 3D photonic metamaterials.The emerging field of photonic metamaterials is driven by the fascinating visions of perfect lenses 12 , optical cloaking 13,14 or quantum levitation 15 . Realizing these visions clearly ultimately requires large-scale three-dimensional (3D) metamaterials operating at optical frequencies. One of the major challenges concerns the (realistic) design and the nanofabrication of such structures. The latter is related to the fabrication of 3D (dielectric) photonic crystals, for which extensive literature is available (see, for example, the references in a recent review 16 ). It has become clear that polymeric templates made using holography and/or direct laser writing (DLW) can subsequently be converted into, for example, silicon structures using chemical vapour deposition (CVD) and/or atomic-layer deposition (ALD). In the context of metamaterials, however, metals are crucial; silver leads to the lowest losses at optical frequencies 17 . Yet, it has been unclear whether structures made using DLW and silver CVD would ever have sufficient quality and whether achievable feature sizes would result in metamaterials operating at optical frequencies. Fortunately, we report here that the answer is positive in both regards. Combined with suitable theoretical blueprints, which still need to be developed, this result means that one of the major hurdles in the field of photonic metamaterials is starting to disappear.Lithography of 3D polymeric templates by DLW with lateral feature sizes in the 100 nm range has become routine 8,9,18 and is even available commercially 19 . Our vision is to take such a template and coat it with a silver film of a few tens of nanometres in thickness, for example leading to the 3D arrangement of magnetic split-ring resonators (SRR) shown in Fig. 1a. Several questions arise immediately. (1) Silver films made using these methods are obviously always inherently connected-in sharp contrast to those made by electron-beam lithography...

Directly patterned substrate-free plasmonic “nanograter” structures with unusual Fano resonances

“…Many micro/nano fabrication techniques featuring 3D structures that could be applied to photonic and MMs have been developed in recent years. These techniques include layer-by-layer stacking 3,14,15 , structural rolling 16,17 , shadow evaporation 18 , multilayer electroplating 19 , membrane projection lithography 20,21 , stress-driven assembly 22 , direct laser writing 8,[23][24][25][26][27][28] , and ion-beam irradiation [29][30][31] . However, effective fabrication of nanoscale 3D plasmonic structures that can be spatially oriented with a hierarchical geometry remains challenging.…”

3D microfabrication of single-wall carbon nanotube/polymer composites by two-photon polymerization lithography

“…A near-infrared (NIR) pulsed laser beam tightly focused onto a photo-polymerizable monomer solidifies a nanometric volume of the monomer in the focus spot through TPP, and thus, arbitrary 3D micro/nano-sized polymer structures can be fabricated with a sub-diffraction-limit spatial resolution by scanning the focus spot three-dimensionally. Applications of the TPP lithography are extended to various research fields, such as photonic crystals [20,21], photonic quasicrystals [22], metamaterials [23,24], novel mechanical micro/nanostructures [25], microfluidics [26], functional micro/nano mechanical devices [27], cell culturing 3D scaffolds for tissue engineering [28], and novel platforms of optical data storage [29]. TPP lithography is also an ideal tool for developing nanomaterials/polymer composite based micro/nano-structures.…”

Metamaterial-based wireless strain sensors

“…To date, metamaterials have been widely investigated 4-7 and exploited for numerous functions, e.g., to obtain negative refraction, [8][9][10] cloaking, 11 superlenses, 12 antennas, 13 plasmons with nanowires, 14 laser output facets, 15 and focused light. 16 However, metamaterial architectures have not been studied for sensing till date.…”