Quasi-Guided Modes in Titanium Dioxide Arrays Fabricated via Soft Nanoimprint Lithography

Abstract

Reversible quasi-guided modes (QGMs) are observed in titanium dioxide (TiO2) metasurface arrays fabricated via soft nanoimprint lithography. A TiO2 layer between the nanopillar array and the substrate can facilitate the propagation of QGMs. This layer is porous, allowing for the tuning of the layer properties by incorporating another material. The presence of the QGMs is strongly dependent on the refractive index of the TiO2 layer. QGMs are not supported if the refractive index of the porous TiO2 is too low. It is demonstrated that after depositing R6G on the array QGMs can be observed as very strong and narrow reflectance peaks and transmittance dips. Furthermore, as the second material can penetrate through the pores into the layer it can experience the regions of high field enhancement associated with the QGMs. These results are of interest for a wide range of applications including but not limited to sensing, nonlinear optics, and emission control.

Soft Nano‐Imprint Lithography of Rare‐Earth‐Doped Light‐Emitting Photonic Metasurface

“…The simulation of magnetic and electric field distributions in the cross‐cut at 629 nm (Figure 4b) shows that they are both strongly confined in the 2D residual layer underneath the 3D pillars and, from the circulation of the magnetic field intensity H 2 , we conclude that there is an electric guided mode in the layer propagating along the y ‐axis. [ 28 ] Thus, we refer to this mode as E‐QGM1. Following the same argument we can refer to the modes at 575, 468, and 437 nm as M‐QGM1, E‐QGM2, and M‐QGM2, respectively.…”

“…Detailed structural and spectroscopic characterizations account for the high quality of our samples, supported by the comparison with finite‐difference time‐domain (FDTD) simulations: we experimentally observe the formation of sharp resonances typical of a square lattice ascribed to quasi‐guided modes. [ 28 ] The coupling between these resonances and the photoluminescence of Eu 3+ leads to a ≈200 times enhancement of emission with respect to the flat counterpart within a relatively small angle (≈±16° around the vertical direction).…”

“…[25][26][27] However, at visible and near infrared frequency, metals have a relatively large absorption limiting their applicability. Sol-gel chemistry and nano-imprint lithography (soft-NIL) can be combined to obtain, in few simple steps, nano-patterns over large scales [28][29][30][31][32] on arbitrary substrates (e.g., metals, plastic, semiconductors, and glasses). Among the large number of materials that can be molded by soft-NIL, metal oxides are extremely valuable for photonic applications thanks their large refractive index and low absorption coefficient.…”

“…[31,32] It has been recently demonstrated that this residual layer acts as a waveguide. [28] Sharp resonances featuring large-Q factors, in reflection and transmission spring from the coupling of lattice modes of the pillars array and the guided modes in the 2D layer. So far, the integration of light emitters via soft-NIL or similar methods has been limited and the enhancement of light extraction from rare earth emission did not exceed ten times with respect to the flat counterpart.…”

Conductive Materials with Elaborate Micro/Nanostructures for Bioelectronics

“…Nanoimprint lithography (NIL) is another technique to fabricate materials with nanoscale features. [90][91][92] Similarly with the lithography technology mentioned above, pre-prepared masks are fixed on the resist layer to first form patterns, as demonstrated in Figure 3e. [83] Nowadays, NIL has been proven to fabricate nanogaps with parallel grating lines at the scale of around sub-10 nm.…”