Replacing Metals with Oxides in Metal-Assisted Chemical Etching Enables Direct Fabrication of Silicon Nanowires by Solution Processing

Metal-assisted chemical etching (MACE) has emerged as an effective method to fabricate high aspect ratio nanostructures. This method requires a catalytic mask that is generally composed of a metal. Here, we challenge the general view that the catalyst needs to be a metal by introducing oxide-assisted chemical etching (OACE). We perform etching with metal oxides such as RuO2 and IrO2 by transposing materials used in electrocatalysis to nanofabrication. These oxides can be solution-processed as polymers exhibiting similar capabilities of metals for MACE. Nanopatterned oxides can be obtained by direct nanoimprint lithography or block-copolymer lithography from chemical solution on a large scale. High aspect ratio silicon nanostructures were obtained at the sub-20 nm scale exclusively by cost-effective solution processing by halving the number of fabrication steps compared to MACE. In general, OACE is expected to stimulate new fundamental research on chemical etching assisted by other materials, providing new possibilities for device fabrication

Bimodal mesoporous titanium dioxide anatase films templated by a block polymer and an ionic liquid: influence of the porosity on the permeability

In the present paper, we report the synthesis of bimodal mesoporous anatase TiO2 films by the EISA (Evaporation-Induced Self-Assembly) method using sol-gel chemistry combining two porogen agents, a low molecular weight ionic template and a neutral block copolymer. The surfactant template (C(16)mimCl) generates non-oriented worm-like pores (8 to 10 nm) which connect the regularly packed ellipsoidal mesopores (15 to 20 nm diameter) formed by an amphiphilic block copolymer of the type poly(isobutylene)-b-poly(ethylene oxide) (PIB-PEO). The surfactant template can also significantly influence the size and packing of the ellipsoidal mesopores. The mesostructural organization and mesoporosity of the films are studied by Environmental Ellipsometry-Porosimetry (EEP), Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) and electron microscopy techniques. Electrochemical characterization is performed to study the permeability of the films to liquid solutions, using two types of probe moieties (K3FeIII(CN)(6) and Ru(bpy)(3)(2+)) by the wall-jet technique. An optimum ratio of C(16)mimCl/PIB-PEO provides anatase films with a continuous bimodal mesopore structure, possessing a permeability up to two times higher than that of the mesoporous films templated by PIB-PEO only (with partially isolated mesopores). When C(16)mimCl is used in large quantities, up to 20% weight vs. PIB-PEO, large overall porous volume and surface area are obtained, but the mesostructure is increasingly disrupted, leading to a severe loss of permeability of the bimodal films. A dye-sensitized solar cell set-up is used with anatase films as the photoelectrode. The photosensitizer loading and the total energy conversion efficiency of the solar cells using the mesoporous films templated by an optimal ratio of the two porogen agents C(16)mimCl and PIB-PEO can be substantially increased in comparison with the solar cells using mesoporous films templated by PIB-PEO only.DFG/SM 199/6-1DFG/OE 420/5-1BMBF/SOHyb/03X3525

Block-Copolymers Enable Direct Reduction and Structuration of Noble Metal-Based Films

Noble metal nanostructured films are of great interest for various applications including electronics, photonics, catalysis, and photocatalysis. Yet, structuring and patterning noble metals, especially those of the platinum group, is challenging by conventional nanofabrication. Herein, an approach based on solution processing to obtain metal-based films (rhodium, ruthenium (Ru) or iridium in the presence of residual organic species) with nanostructuration at the 20 nm-scale is introduced. Compared to existing approaches, the dual functionality of block-copolymers acting both as structuring and as reducing agent under inert atmosphere is exploited. A set of in situ techniques has allowed for the capturing of the carbothermal reduction mechanism occurring at the hybrid organic/inorganic interface. Differently from previous literature, a two-step reduction mechanism is unveiled with the formation of a carbonyl intermediate. From a technological point of view, the materials can be solution-processed on a large scale by dip-coating as polymers and simultaneously structured and reduced into metals without requiring expensive equipment or treatments in reducing atmosphere. Importantly, the metal-based films can be patterned directly by block-copolymer lithography or by soft-nanoimprint lithography on various substrates. As proof-of-concept of application, the authors demonstrate that nanostructured Ru films can be used as efficient catalysts for H-2 generation into microfluidic reactors

Les femmes de l’Égée vues par les voyageurs britanniques aux xviiie et xixe siècles

Lord Byron, par son importance littéraire, forgea en grande partie l’image que les Britanniques se faisaient de la Grèce au début du xixe siècle, grâce à des œuvres telles que Childe Harold’s Pilgrimage ou Don Juan. Dans le Chant II de ce poème, il décrit la beauté d’Haidée : La plus riche héritière des Îles du Levant ;Si belle était-elleQue sa dot n’était rien comparée à son sourire. Sa servante Zoé était elle aussi très belle, et cette beauté des Grecques fut une image récurrente de la litt..

Thin Film Deposition Techniques

International audienceThis chapter focuses on chemical liquid deposition methods that involve controlled covering of surfaces with a chemical liquid solution, the sol-gel solution, of known composition. The techniques include dip coating, spin coating, roll-to-roll coating, droplet-assisted deposition and electro-assisted deposition. The chapter presents briefly the different steps involved in the process of thin film formation that are common to all techniques. To have a better understanding, all available liquid deposition techniques are usually described with an identical sequence of successive steps: initial chemical solution formulation, solution spreading on the surface of the substrate, evaporation of the liquid solution layer, layer post-processing, and final treatment of the layer for stabilization. These steps can be addressed individually because they are separated in time. Important progress made in the past few decades highlights the importance of the evaporation conditions in controlling the structure of the coating, which is better achieved in dip coating

Ultrasonic characterization of mesoporous thin films

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A pure aqueous route to mesoporous silica thin films via dip-coating of prefabricated hybrid micelles

International audienceMesoporous thin films were prepared by dipcoating with a purely aqueous method, as a substitute for the alcohol-based evaporation-induced self-assembly route. Unlike other aqueous routes that require a very slow pulling rate possible only using high performance dip-coaters, as a result of the high surface tension of water, this new process works with standard dip-coaters and at similar pulling rates as are used for the evaporation-induced self-assembly route. This unique asset is the result of the synthesis of prefabricated self-assembled silicate/organic hybrid micelles. These building blocks are concentrated before use, which provides a gelling edge after moderate evaporation. As a result, defect-free continuous mesoporous films with wellorganized hexagonally packed pores were prepared after optimization of both the evaporation rate of the solution of hybrid micelles and the dip-coater pulling rate