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

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

The origin of the high electrochemical activity of pseudo-amorphous iridium oxides

The origins of the superior catalytic activity of poorly crystallized Ir-based oxide material for the OER in acid is still under debate. Here, authors synthesize porous IrMo oxides to deconvolute the effect of Ir oxidation state from short-range ordering and show the latter to be a key factor

Nanotexturation de couches de métaux nobles par chimie douce

Fabrication of metallic nanostructures in thin films form is a key process to develop new devices in many domains. Soft chemistry approaches are well known to fabricate and structure oxides and hybrids at nanoscale via the “sol-gel” process at low temperature. The main goal of this work is to extend the soft chemistry approaches to the formation of noble metals (including their oxides) at intermediate temperatures. This would allow to develop direct approaches for the structuration of metals, based on self-assembly or on lithographic techniques (nanoimprinting or X-ray lithography). This PhD project will especially present the noble metals’ family (platinum group), including ruthenium, rhodium, iridium and gold. These elements possess interesting properties, such as resistance to corrosion, electric conductivity or chemical and thermal stability, among others. This work includes three parts. The first one will be focused on the state of the art related to metallic texturation and texturation by sol-gel layers. The second one will present the results obtained about metallic texturation by soft chemistry. Finally, the last one will be devoted to the application of noble metals’ oxides for lithography.La fabrication de nanostructures métalliques sous forme de films minces est un processus clé pour le développement de dispositifs dans de nombreux domaines. Les approches "chimie douce" sont déjà bien établies pour fabriquer et structurer des oxydes et des hybrides à l'échelle nanométrique via le procédé "sol-gel" à basse température. L'objectif principal de ce travail est d'étendre les approches de "chimie douce" à la formation de métaux nobles (et aussi de leurs oxydes) à des températures modérées. Cela permettrait le développement d'approches directes de structuration des métaux basées sur l'auto-assemblage ou sur des techniques lithographiques (nano-impression ou lithographie par rayons X). Plus particulièrement, dans cette thèse nous allons nous intéresser à la famille des métaux noble (groupe du platine) à savoir le ruthénium, le rhodium, l’iridium et l'or. Ces éléments présentes des propriétés intéressantes comme la résistance à la corrosion, conductivité électrique, stabilité thermique et chimique, etc. Cette thèse sera divisée en trois parties. La première partie sera axé sur un état de l’art de la texturation métallique et la texturation de couches sol-gel. La seconde partie sera axé sur les résultats sur la texturation métallique par chimie douce que nous avons obtenus au cours de cette thèse. Enfin la dernière partie sera consacrée à l'application des oxydes de métaux nobles pour la lithographie

Nanotexturation of noble metals layers by soft chemistry

La fabrication de nanostructures métalliques sous forme de films minces est un processus clé pour le développement de dispositifs dans de nombreux domaines. Les approches "chimie douce" sont déjà bien établies pour fabriquer et structurer des oxydes et des hybrides à l'échelle nanométrique via le procédé "sol-gel" à basse température. L'objectif principal de ce travail est d'étendre les approches de "chimie douce" à la formation de métaux nobles (et aussi de leurs oxydes) à des températures modérées. Cela permettrait le développement d'approches directes de structuration des métaux basées sur l'auto-assemblage ou sur des techniques lithographiques (nano-impression ou lithographie par rayons X). Plus particulièrement, dans cette thèse nous allons nous intéresser à la famille des métaux noble (groupe du platine) à savoir le ruthénium, le rhodium, l’iridium et l'or. Ces éléments présentes des propriétés intéressantes comme la résistance à la corrosion, conductivité électrique, stabilité thermique et chimique, etc. Cette thèse sera divisée en trois parties. La première partie sera axé sur un état de l’art de la texturation métallique et la texturation de couches sol-gel. La seconde partie sera axé sur les résultats sur la texturation métallique par chimie douce que nous avons obtenus au cours de cette thèse. Enfin la dernière partie sera consacrée à l'application des oxydes de métaux nobles pour la lithographie.Fabrication of metallic nanostructures in thin films form is a key process to develop new devices in many domains. Soft chemistry approaches are well known to fabricate and structure oxides and hybrids at nanoscale via the “sol-gel” process at low temperature. The main goal of this work is to extend the soft chemistry approaches to the formation of noble metals (including their oxides) at intermediate temperatures. This would allow to develop direct approaches for the structuration of metals, based on self-assembly or on lithographic techniques (nanoimprinting or X-ray lithography). This PhD project will especially present the noble metals’ family (platinum group), including ruthenium, rhodium, iridium and gold. These elements possess interesting properties, such as resistance to corrosion, electric conductivity or chemical and thermal stability, among others. This work includes three parts. The first one will be focused on the state of the art related to metallic texturation and texturation by sol-gel layers. The second one will present the results obtained about metallic texturation by soft chemistry. Finally, the last one will be devoted to the application of noble metals’ oxides for lithography

Deep X-ray lithography on "sol-gel" processed noble metal mesoarchitectured films

Noble metal coordination xerogel films (mesostructured with block-copolymers) exhibit solubility switching with increasing X-ray irradiation. Different from other sol-gel systems, these are attributed to film deconstruction under irradiation. These materials can be used as recyclable negative tone resists for deep X-ray lithography that can be further converted into metallic nanoarchitectured films

Increased protein S-nitrosylation in mitochondria: a key mechanism of exercise-induced cardioprotection

International audienceEndothelial nitric oxide synthase (eNOS) activation in the heart plays a key role in exercise-induced cardioprotection during ischemia-reperfusion, but the underlying mechanisms remain unknown. We hypothesized that the cardioprotective effect of exercise training could be explained by the re-localization of eNOS-dependent nitric oxide (NO)/S-nitrosylation signaling to mitochondria. By comparing exercised (5 days/week for 5 weeks) and sedentary Wistar rats, we found that exercise training increased eNOS level and activation by phosphorylation (at serine 1177) in mitochondria, but not in the cytosolic subfraction of cardiomyocytes. Using confocal microscopy, we confirmed that NO production in mitochondria was increased in response to H 2 O 2 exposure in cardiomyocytes from exercised but not sedentary rats. Moreover, by S-nitrosoproteomic analysis, we identified several key S-nitrosylated proteins involved in mitochondrial function and cardioprotection. In agreement, we also observed that the increase in Ca 2+ retention capacity by mitochondria isolated from the heart of exercised rats was abolished by exposure to the NOS inhibitor L-NAME or to the reducing agent ascorbate, known to denitrosylate proteins. Pre-incubation with ascorbate or L-NAME also increased mitochondrial reactive oxygen species production in cardiomyocytes from exercised but not from sedentary animals. We confirmed these results using isolated hearts perfused with L-NAME before ischemia-reperfusion. Altogether, these results strongly support the hypothesis that exercise training increases eNOS/NO/S-nitrosylation signaling in mitochondria, which might represent a key mechanism of exercise-induced cardioprotection