Tuning the Refractive Index in Gyroid Photonic Crystals via Lead‐Chalcogenide Nanocrystal Coating

Abstract

wileyonlinelibrary.com COMMUNICATIONamplitude of the PBG. Compared with the other approaches used to tune the dielectric contrast of 3D structures, [14][15][16][17][18][19][20][21] our AC-LBL method offers signifi cant advantages because the use of charged compounds ensures that the coating penetrates deep and uniformly inside 3D complex structures. Moreover, this low cost, fast and room-temperature method can be applied to different coating materials, such as quantum dots and other nanocrystals. [22][23][24] It is also possible to functionalize the particles used to coat the PhCs in order to add new functionalities to the structures.The 3D PhCs considered in this work are 1-srs networks, intricate structures inspired by the gyroid minimal surface discovered by Schoen in 1970, [ 25 ] and observed in butterfl y wing scales ( Figure 2 a). [ 26,27 ] The space group of the 1-srs network is I 4 1 32 and it can be infl ated with constant pressure according to the Young-Laplace equation to form the single gyroid structure of constant mean curvature. [ 28,29 ] Due to their unique geometrical properties, gyroids host a rich variety of optical phenomena, from linear and circular dichroism, [ 29 ] to optical activity, [ 30 ] and the recent demonstration of Weyl points. [ 8 ] PhCs with gyroid symmetry have placed the most signifi cant demands on high refractive index. [ 8 ] On the polymer templates, we deposited high refractive-index PbS thin fi lms with thickness controllable at a nanometre-scale, in order to increase the effective refractive index of the structure. The protocol is optimized for the controlled deposition of PbS nanocubes over the entire surface of a 3D PhC fabricated with a zirconium-based organic-inorganic photosensitive material. [ 31 ] Combining simulation and experimental study, we confi rm that the effective refractive index of the PhCs is increased by ≈40% after only six deposition cycles. This leads to an increase in the width and the strength of the PBG by more than 90% and 40%, respectively.The AC-LBL method consists of the alternating deposition of two oppositely charged species: the negatively charged PbS nanocubes and a positively charged polymer. This approach has the advantage of creating a tunable and homogenous coating on the entire surface of the 3D PhC, overcoming the issue related to directional coating techniques, such as thermal evaporation or chemical vapour deposition. To create the micron-scale corecladding structure illustrated in Figure 1 , we fi rst fabricated a polymer template (Figure 2 b,c) using a galvo-dithered DLW method, [ 6 ] which can create 3D PhCs with cubic symmetry, good mechanical strength, and high resolution ( Figure S1, Supporting Information).To boost the effective refractive index of the polymeric 1-srs PhCs, we adopt PbS nanocubes (Figure 2 e,f) for the coating because this material can be rapidly synthesised with high yield, high refractive index, and good transparency in the visible and near-infrared (NIR) wavelength region. [ 32,33 ] The PbS

Perspective on photonic memristive neuromorphic computing

“…Antimony telluride (Sb 2 Te 3 ) and other lead-based phase OPCMs are extensively applied in optical data storage [105,106], photo-lithography [107,108], holography [109], and topological photonics [110]. All these applications depend on the response of the material to the applied electromagnetic field, the temperature or the interaction between material and laser pulses [111].…”

“…Alternatively, techniques such as laser nano-lithography [110,140] and SPIN [135][136][137] provide an accessible and controllable approach for the realisation of intricate systems, but due to limited availability of high refractive index photoresists, achieving nonlinearity in systems realised with these methods can be done using inversion techniques [141], and coating methods [107,108].…”

Gyroid “srs” Networks: Photonic Materials Beyond Nature

“…Materials are playing a central role in the evolution of photonic and optical technologies, since they can alter how light interacts with the photonic structures, can add functionality, or enhance optical properties (Table 2). [81][82][83][84][85][86][87][88][89][90][91] Gyroids are predicted to possess among the widest complete 3D PBGs and also exhibit frequency isolated WPs. [22] However, in order to achieve complete 3D control of photon propagation and exhibit topological complexity, a highrefractive index contrast is required as well as a high precision in the geometry of the structures over a large area.…”

Impact of Cubic Symmetry on Optical Activity of Dielectric 8-srs Networks

“…Experimentally, many micro-and nano-fabrication methods can be used for accurate formation of PhCs and metamaterials from single and double srs-networks [23][24][25][26][27]. For more complex composite networks such as 8-srs and for a high degree of design flexibility, the direct laser writing (DLW) technique has proven to be particularly valuable [20,[28][29][30][31][32][33][34] for PhC formation. However, the DLW method suffers from an elongated cross-section of the writing focal spot, i.e., unequal sizes in lateral and vertical axes of the voxel.…”

“…Various methods have been developed to correct for asymmetry due to elongation of the focal spot, including apodization [35] and multi-line writing techniques [36,37]. Whilst these methods can significantly reduce elongation, to remove asymmetry completely the most effective method is galvo-dithered direct laser writing (GD-DLW) [29][30][31]33]. This fabrication method uses a galvo-mirror system to trace the focal spot in a circular motion within the focal plane.…”