Thin metallic films deposited from a suspension of nanoparticles in ionic liquids

Les nanoparticules (NPs) métalliques présentent un grand intérêt dans de nombreuses applications, pour lesquelles un contrôle précis de la taille, de la composition et de la morphologie est requis. Cependant, ce contrôle demeure un défi. Les liquides ioniques (LIs) sont des sels fondus liquides à température ambiante. Ils possèdent des propriétés uniques, à michemin entre le liquide (ce sont des solvants, de bons électrolytes,…) et du solide (ils ne s’évaporent pas). Les LIs sont connus pour être des solvants intelligents, qui permettent, par décomposition de précurseur organométallique, de former des NPs de taille calibrée et contrôlée. Ceci en absence de ligands organiques contrairement aux solvants conventionnels. Cependant, le mécanisme de leur formation reste mal connu. Dans cette thèse, nous identifions les facteurs clés influant sur la taille finale des NPs. Cela permettra de développer des voies de synthèse de NPs de tailles prédéterminées. Par ailleurs, le silicium poreux (PSi) est un matériau prometteur qui peut trouver de multiples utilisations dans les systèmes intégrés ou dans les secteurs photovoltaïque et biomédical. Ses propriétés peuvent être ajustées par l'introduction de métaux dans ses pores. Dans ce cas également, les LIs peuvent être avantageusement utilisés. Dans ce travail, la métallisation de PSi par Cu est réalisée par imprégnation du PSi puis décomposition d’une solution de CuMes dans le LI. En fait, il est observé que c’est le PSi qui décompose le précurseur. Pour cette raison, l’utilisation d’analogues solubles du PSi est étudiée pour remplacer H2 dans la synthèse des NPs. Cela pourrait permettre d’améliorer encore le contrôle de ce procédéAmong nano-objects, metallic nanoparticles (NPs) certainly have a prominent position. This is because they offer a variety of compositions, sizes, shapes and structures that make them suitable for a variety of applications. In the same time, the accurate control of their size, shape and structure is still a challenge, mainly because NPs do not correspond to the thermodynamic stable state of metals. Recently, ionic liquids (ILs) have been shown to stabilize metallic NPs without the need of ligands required in conventional solvents. ILs are liquid molten salt at room temperature. These compounds uniquely combine properties of the liquid (they are good solvents, electrolytes…) and of the solid (they do not evaporate). In the process of decomposing organometallic precursors into metallic NPs, ILs play a central role in controlling the size and ensuring narrow size distribution. However, the corresponding mechanism remains unclear. This PhD work aims at identifying key factors influencing the final size (average and distribution) of metallic NPs chemically formed in ILs. Among nanoporous materials, porous silicon (PSi) is popular due to its exceptional characteristics for microelectronics, integrated optoelectronics, microelectromechanical systems (MEMS), layer transfer technology, solar and fuel cells, biomedicine, etc. Its properties are modified by introducing different materials into its pores. Unique properties of ILs may also be advantageous. In this work, the process used to synthesize metallic NPs is adapted into an easy, efficient, versatile, and safe process to metallise PSi. The metallisation of PSi by Cu is tentatively conducted by impregnation with a solution of CuMes in IL followed by the decomposition of the precursor. In fact, CuMes is shown to be readily decomposed by PSi. Finally, this knowledge is transposed back to the synthesis of metallic NPs, replacing H2 by chemical analogues of PSi as alternative reducing agents. This approach is believed to bring even more control in this proces

An Efficient, Versatile, and Safe Access to Supported Metallic Nanoparticles on Porous Silicon with Ionic Liquids

The metallization of porous silicon (PSi) is generally realized through physical vapor deposition (PVD) or electrochemical processes using aqueous solutions. The former uses a strong vacuum and does not allow for a conformal deposition into the pores. In the latter, the water used as solvent causes oxidation of the silicon during the reduction of the salt precursors. Moreover, as PSi is hydrophobic, the metal penetration into the pores is restricted to the near-surface region. Using a solution of organometallic (OM) precursors in ionic liquid (IL), we have developed an easy and efficient way to fully metallize the pores throughout the several-µm-thick porous Si. This process affords supported metallic nanoparticles characterized by a narrow size distribution. This process is demonstrated for different metals (Pt, Pd, Cu, and Ru) and can probably be extended to other metals. Moreover, as no reducing agent is necessary (the decomposition in an argon atmosphere at 50 °C is fostered by surface silicon hydride groups borne by PSi), the safety and the cost of the process are improved

Imidazolium-based ionic liquids with cyano groups for the selective absorption of ethane and ethylene

International audienceThe density, viscosity and absorption of ethane and ethylene were determined experimentally, as a function of temperature and at atmospheric pressure, in different imidazolium-based ionic liquids: 1-methyl-3-octylimidazolium bis(trifluoromethanesulfonyl)imide, [C1C8Im][NTf2], 1-methyl-3-(propyn-3-yl)imidazolium bis(trifluoromethanesulfonyl)imide [C1(C2H2CH)Im][NTf2], 1-(3-cyanopropyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C1C3CNIm][NTf2], 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide [C1C3CNIm][DCA], 1-butyl-3-methylimidazolium dicyanamide, [C1C4Im][DCA] and 1-butyl-3-methylimidazolium methylphosphite [C1C4Im][C1HPO3]. The densities and viscosities of the ionic liquids studied are strongly dependent on the anion and, at 313 K, follow the order: [C1(C2H2CH)Im][NTf2] > [C1C3CNIm][NTf2] > [C1C3CNIm][DCA] > [C1C4Im][C1HO3] > [C1C4Im][DCA] and [C1C3CNIm][NTf2] > [C1C3CNIm][DCA] > [C1C4Im][C1HPO3] > [C1(C2H2CH)Im][NTf2] > [C1C4Im][DCA], respectively. The differences in the molecular structures of the ionic liquids allowed the identification of the influence of increasing the alkyl side chain of the cation, of the presence of unsaturated Ctriple bond; length of mdashC and Ctriple bond; length of mdashN bonds on the alkyl side chain of the cation and finally of a phosphite based anion on the selective absorption of ethane and ethylene. The solubility of ethylene is higher than that of ethane in the ionic liquids studied and varies from 18.41 × 10−3 in [C1C8Im][NTf2] at 303.17 K to 1.603 × 10−3 in [C1C4Im][DCA] at 343.61 K. The introduction of the different functional groups leads to a decrease on the gas absorption compared with that of [C1C8Im][NTf2] but to an increase of the ideal separation selectivity of ethane and ethylene

Impact of Surface Chemistry on Copper Deposition in Mesoporous Silicon

CAPLUS AN 2016:1100917(Journal; Online Computer File)An easy, efficient, and safe process is developed to metalize mesoporous Si (PSi) with Cu from the decompn. of a soln. of mesitylcopper (CuMes) in an imidazolium-based ionic liq. (IL), [C1C4Im][NTf2]. The impregnation of a soln. of CuMes in IL affords the deposition of metallic islands not only on the surface but also deep within the pores of a mesoporous Si layer with small pores <10 nm. Therefore, this process is well suited to efficiently and completely metalize PSi layers. An in-depth mechanistic study shows that metal deposition is due to the redn. of CuMes by surface silane groups rather than by Si oxidn. as obsd. in aq. or H2O-contg. media. This could open a new route to the chem. metalization of PSi by less-noble metals difficult to attain by a conventional displacement reaction. [on SciFinder(R)