Si-based nanoarchitectures are formed with unprecedented precision and reproducibility via templated dewetting of thin SOI.

Optical technologies and devices rely on the controlled manipulation of light propagation through a medium. This is generally governed by the inherent effective refractive index of the material as well as by its structure and dimensionality. Although a precise control over light propagation with sub‐wavelength size objects is a crucial issue for a plethora of applications, the widely used fabrication methods remain cumbersome and expensive. Here, a sol–gel dip‐coating method combined with nanoimprinting lithography on arbitrary glass and silicon substrates is implemented for the fabrication of TiO2‐based dielectric Mie resonators. The technique allows obtaining sub‐micrometric pillars featuring unprecedented vertical aspect ratios (>1) with relatively high fidelity and precision. Spectroscopic characterization at visible and near‐infrared frequencies demonstrate that the resonant properties of these dielectric pillar arrays allow for a drastic reduction of light transmission (cutting more than 50% on glass) and reduced reflection (reflecting less than 3% on glass and 16% on bulk silicon), accounting for an efficient light trapping. These results provide a guideline for the fabrication of Mie resonators using a fast, versatile, low‐cost, low‐temperature technique for efficient light manipulation at the nanoscale.

shaping, [12][13][14] sensing, [15,16] and nonlinear phenomena [17][18][19][20] are few examples demonstrating the strength of this approach for light management with sub-wavelength dielectric structures. However, with a few exceptions based on colloidal assembly, [21][22][23] hydrothermal growth, [20] solid state dewetting, [24][25][26][27][28][29][30] and aerosol spray, [31] most of these achievements were based on complex and expensive fabrication methods involving several steps (such as e-beam lithography and reactive ion etching). Top-down fabrication approaches limit the full exploitation of Mie resonators for unexpensive devices and broad areas production. In particular, given the rapidly rising interest in structural coloring and light filtering with dielectric metasurfaces [32][33][34][35][36][37][38][39][40][41] a versatile and scalable method is highly desirable to overcome the gap separating mere proof of principles and industrial applications. In this framework, a major step forward would be the development of fabrication techniques fully compatible with back-end processing of C-MOS circuitry (e.g., keeping the maximal processing temperature below ≈450 °C) or more generally, on electronic devices such as LEDs and photovoltaic panels.So far, most studies on Mie resonators are based on Si or Ge materials, due to both their very large index of refraction and the possibility to exploit the well-developed nanofabrication approaches of nanoelectronics and nanophotonics. Among other materials, TiO 2 (titania) is recently attracting growing interest [35,[42][43][44][45][46] for its transparency up to near-UV frequencies and its relatively high refractive index. Indeed, TiO 2 -based Mie resonators systems can potentially outperform conventional Si and Ge-based dielectric metasurfaces, which suffer from larger absorption at short wavelength [47,48] (e.g., at 450 nm: n TiO2 = 2.55, k TiO2 = 1.2 × 10 −5 ; n Si = 4.5; k Si = 0.13; n Ge = 4; and k Ge = 2.24). A quite unique peculiarity of titania is the tunable porosity (adjustable by modifying the sol-gel fabrication process) and therefore permeability to liquids and gas. In addition to this, titania is an abundant, cheap, nontoxic, photocatalytic, mechanically strong, and chemically stable material, featuring a relatively low mass density (≈3.8 g cm −3 in the anatase form against ≈5 g cm −3 for MoS 2 ). These features make titania an ideal metamaterial providing several functions (e.g., tunable structural color, sensing small changes in the environment), for a novel photonic platform in view of multifunctional devices. Dielectric Mie resonators are taking momentum in the last years thanks to their peculiar properties in light management at visible and near-infrared frequencies. However, their full exploitation demands for cheap materials and versatile fabrication methods, extendible over large surfaces and potentially C-MOS compatible. Here, a sol-gel deposition and nanoimprint lithography method is used to obtain titania-based Mie resonators over large areas (s...

We review past and recent progress in Nano-Imprint Lithography (NIL) methods to (nano-) structure inorganic materials from sol-gel liquid formulations and colloidal suspensions onto a surface. This technique, first inspired by embossing techniques, was developed for soft polymer processing, as final or intermediate materials, but is today fully adapted to hard inorganic materials with high dielectric constant, such as metal oxides, with countless chemical compositions provided by the sol-gel chemistry. Consequently, NIL has become a versatile, high throughput, and highly precise microfabrication method that is mature for lab developments and scaling up. We first describe the state-of-the-art in nanofabrication methods and the plethora of approaches developed in the last decades to imprint metal oxides from inorganic solutions. These are discussed and compared in terms of performances, issues, and ease of implementation. The final part is devoted to relevant applications in domains of interest. Generalities on Nano fabrication techniques and NILFrom the early ages, technics to cut, sculpt, etch, mold, assemble pieces of matter have been developed and constantly optimized to satisfy the growing demand for functional materials. Since the inception of nanotechnology, these operations have to be mastered at the nanoscale. For these tasks, many top-down and bottom-up methods exist. However, they do not simultaneously fulfill all the necessary criteria of performance such as spatial resolution, pattern complexity, hierarchy, scalability, dimensionality, costeffectiveness, a span of processable materials. Thus, motivations to optimize them and develop new ones persist as a flourishing domain of research and development.Many materials exhibiting various intrinsic properties (mechanical, chemical, electrical, optical, thermal, etc.) are exploited in numberless functions once nanostructured onto a surface. Amongst them, metal oxides are extremely valuable for their extreme chemical, mechanical and thermal stability and range of physicalchemical properties. Thanks to its hardness, chemical inertness, transparency and low background fluorescence, glass is one of the preferred choices for micro-and nano-fluidics device fabrication. In photonics, metasurfaces require optical properties that are found in dielectrics such as SiO2 often combined with high index dielectric TiO2 or (plasmonic) gold 1 . For nano-electronics, silica remains one of the key

Metal oxide (MO) surface nanopatterns can be prepared using Soft-Nano-Imprint-Lithography (soft-NIL) combined with sol-gel deposition processing. Even if sol-gel layers remain gel-like straight after deposition, their accurate replication from a mould remains difficult as a result of the fast evaporation-induced stiffening that prevents efficient mass transfer underneath the soft mould. The present work reports a detailed investigation of the role of the xerogel layer conditioning (temperature and relative humidity) prior to imprinting and its influence on the quality of the replication. This study is performed on four different systems namely titania, alumina, silica and yttria-stabilised zirconia. We demonstrate that the quality of the replica can be considerably improved without the use of sacrificial stabilising organic agents, but by simply applying an optimal aging at controlled temperature and relative humidity specific to each different reported MO. In each case this condition corresponds to swelling the initial xerogels of around 30% by water absorption from humidity. We show that this degree of swelling represents the best compromise for sufficiently increasing the xerogel fluidity while limiting the shrinkage upon final thermal curing.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10. 1002/adfm.201801958. tives to replace complex and bulky optical elements. This unique ability is due to strong modifications of the local density of optical states occurring in sub-micrometric objects made of materials featuring high dielectric constant and sufficiently small absorption losses.Most studies over the last years have mainly addressed silicon- [4][5][6][7][8][9][10] and germanium-based [11][12][13][14] Mie resonators, demonstrating that they could outperform their metallic counterpart supporting localized plasmonic resonances. However, the large absorption of group IV semiconductor compounds at short wavelengths induces strong optical losses, limiting their potential applicability as efficient devices especially at blue and near-UV frequencies [15,16] (e.g. at 450 nm: n Si = 4.5, k Si = 0.13; n Ge = 4.0, k Ge = 2.24). Furthermore, with a few exception based on colloids [4,17,18] and solid state dewetting, [13,[19][20][21][22][23] typical nanofabrication methods of Si(Ge)-based Mie resonators rely on top-down technologies that are not easy to scale-up at affordable prices.TiO 2 -based optical devices are an interesting alternative to Si, since Titania has a relatively high refractive index and is fully transparent up to UV frequencies [24,25] (e.g.: at 450 nm: n TiO2 = 2.55, k TiO2 = 1.2 × 10 −5 ; at 370 nm: n TiO2 = 2.83, k TiO2 = 1 × 10 −3 ) rendering it, for instance, a strategic material to manipulate the light emitted by conventional GaN-based blue LEDs (at about 450 nm). TiO 2 can be prepared by high-throughput chemical processes, which is a prerequisite for applications requiring large surface systems. It also has many other advantages over Si and metals that are its high chemical, mechanical, and thermal stability, nontoxicity, and relative natural abundance.To date, several groups have studied the properties of Titania particles as dielectric resonators prepared using conventional top-down microfabrication technologies [26][27][28][29][30] or soft-nanoimprint lithography. [31,32] They all confirmed that electromagnetic resonances could be generated within these metal oxide objects. However, the limited exploitation of this material is mainly due to the difficulty in applying conventional top-down fabrication methods to TiO 2 . Additionally, such approaches do not allow the preparation of spherical resonators, [33] which may be interesting for many applications with effective metamaterials, such as beam steering and back-scattering-free optics, [11,[34][35][36][37][38][39][40][41][42][43][44][45]

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The amazing properties of 2D materials are envisioned to revolutionize several domains such as flexible electronics, electrocatalysis, or biosensing. Herein we introduce scanning electrochemical microscopy (SECM) as a tool to investigate molybdenum disulfide in a straightforward fashion, providing localized information regarding the electronic transport within chemical vapor deposition (CVD)‐grown crystalline MoS2 single layers having micrometric sizes. Our investigations show that within flakes assemblies some flakes are well electrically interconnected, with no detectable contact resistance, whereas others are not electrically connected at all, independent of the size of the physical contact between them. Overall, the work shows how the complex electronic behavior of MoS2 flake assemblies (semiconducting nature, contact quality between flakes) can be investigated with SECM.