The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Yaël Israëli - One of the best experts on this subject based on the ideXlab platform.
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Physico-Chemical Role of CdSe/ZnS quantum dots in the photo-polymerization process of acrylate composite materials.
Physical chemistry chemical physics : PCCP, 2012Co-Authors: Anne Barichard, Tigran Galstian, Yaël IsraëliAbstract:The work presented in this paper is devoted to the physico-Chemical Role of quantum dots (QDs) in the photopolymerization of composite materials. We show first that the photoexcitation of CdSe/ZnS semiconductor quantum dots can initiate the polymerization of an acrylate monomer in association with a tertiary amine and in the absence of a photoinitiator. But by using a holographic technique, among the others, the gratings recorded in such composite materials are not stable and relax once the light interference pattern is switched off. This behaviour is attributed to a very low degree of conversion of monomers, which does not prevent the post-exposure diffusion of monomers and nanoparticles. The comparison with gratings obtained in the presence of a photosensitizer dye (higher hologram quality and stability) highlights the key importance of using such dye in the polymerization process. The gratings recorded in the complete syrup, containing the dye and QDs which differ by their size and UV-visible absorption spectra, exhibit an additional refractive index modulation. The latter results from the spatial distribution of QDs and the change in the kinetics of polymerization. We further focus on understanding the fall of the polymerization rate owing to the presence of QDs. This decrease may result from the trapping of the tertiary amine (co-initiator) at the surface of those QDs, which reduces the rate of decay of the dye and, consequently, the polymerization rate. Under such conditions, the diffusion of QDs and monomers is favoured and their spatial redistribution is enhanced. These features contribute to modify the physical properties of the gratings.
Joseph S. Francisco - One of the best experts on this subject based on the ideXlab platform.
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Red‐Light‐Induced Decomposition of an Organic Peroxy Radical: A New Source of the HO2 Radical
Angewandte Chemie (International ed. in English), 2015Co-Authors: Manoj Kumar, Joseph S. FranciscoAbstract:The gas-phase decomposition of the α-hydroxy methylperoxy radical has been theoretically examined, and the results provide insight into a new source of the hydroperoxy radical (HO2 ) in the troposphere. Bimolecular peroxy decomposition is promoted by the red-light or near-IR radiation excitation. The calculations suggest for the first time, an important Chemical Role for the H2 O⋅HO2 radical complex that exist in significant abundance in the troposphere. In particular, the reaction of organic peroxy radicals with the HO2 radical and the H2 O⋅HO2 radical complex represent an autocatalytic source of atmospheric HO2 . This reaction is a new example of red-light-initiated atmospheric chemistry that may help in understanding the discrepancy between the observed and measured levels of the HOx at sunrise.
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HOCO Radical Chemistry
Accounts of chemical research, 2010Co-Authors: Joseph S. Francisco, James T. MuckermanAbstract:Free radicals are important species in atmospheric chemistry, combustion, plasma environments, interstellar clouds, and biochemistry. Therefore, researchers would like to understand the formation mechanism, structure, stability, reactivity, spectroscopy, and dynamics of these Chemical species. However, due to the presence of one or more unpaired electrons, radicals are often very reactive and have short lifetimes, which makes it difficult to conduct experiments. The HOCO radical appears in the atmosphere as well as in combustion environments and plays an important Role in the conversion of CO to CO2. Through the interplay between theoretical and experimental investigations, researchers have only recently understood the Chemical Role of the HOCO radical. In this Account, we systematically describe the current state of knowledge of the HOCO radical based on recent theoretical and experimental studies. This radical’s two stable conformers, trans- and cis-HOCO, have been identified by high-level ab initio cal...
Anne Barichard - One of the best experts on this subject based on the ideXlab platform.
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Physico-Chemical Role of CdSe/ZnS quantum dots in the photo-polymerization process of acrylate composite materials.
Physical chemistry chemical physics : PCCP, 2012Co-Authors: Anne Barichard, Tigran Galstian, Yaël IsraëliAbstract:The work presented in this paper is devoted to the physico-Chemical Role of quantum dots (QDs) in the photopolymerization of composite materials. We show first that the photoexcitation of CdSe/ZnS semiconductor quantum dots can initiate the polymerization of an acrylate monomer in association with a tertiary amine and in the absence of a photoinitiator. But by using a holographic technique, among the others, the gratings recorded in such composite materials are not stable and relax once the light interference pattern is switched off. This behaviour is attributed to a very low degree of conversion of monomers, which does not prevent the post-exposure diffusion of monomers and nanoparticles. The comparison with gratings obtained in the presence of a photosensitizer dye (higher hologram quality and stability) highlights the key importance of using such dye in the polymerization process. The gratings recorded in the complete syrup, containing the dye and QDs which differ by their size and UV-visible absorption spectra, exhibit an additional refractive index modulation. The latter results from the spatial distribution of QDs and the change in the kinetics of polymerization. We further focus on understanding the fall of the polymerization rate owing to the presence of QDs. This decrease may result from the trapping of the tertiary amine (co-initiator) at the surface of those QDs, which reduces the rate of decay of the dye and, consequently, the polymerization rate. Under such conditions, the diffusion of QDs and monomers is favoured and their spatial redistribution is enhanced. These features contribute to modify the physical properties of the gratings.
Henri Patin - One of the best experts on this subject based on the ideXlab platform.
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Aqueous Rhodium Colloidal Suspension in Reduction of Arene Derivatives in Biphasic System: a Significant Physico-Chemical Role of Surfactant Concentration on Catalytic Activity
Advanced Synthesis & Catalyis, 2002Co-Authors: Jürgen Schulz, Sébastien Levigne, Alain Roucoux, Henri PatinAbstract:The hydrogenation of benzene derivatives represents an important industrial catalytic transformation. An original approach is to use transition metal nanoparticles that are finely dispersed in liquid media. During the last decade, these nanoparticles have been largely characterized by sophisticated techniques. Recently, we have described the hydrogenation of arene derivatives in liquid-liquid systems catalyzed by an aqueous suspension of rhodium nanoparticles stabilized by a cationic surfactant. Here, we demonstrate that the modulation of surfactant concentration fundamentally influences the turnover frequencies (TOF's) in hydrogenation of classical benzene derivatives such as anisole, toluene and p-xylene. A maximum TOF is obtained when the surfactant concentration is about the critical micellar concentration. In this condition, the Rh(0) stabilized nanoparticles are up to 5-fold more active.
Thomas F. Kuech - One of the best experts on this subject based on the ideXlab platform.
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Plasma Induced Chemical Changes at Silica Surfaces During Pre-Bonding Treatments
MRS Online Proceedings Library, 2011Co-Authors: Darren M. Hansen, C. E. Albaugh, P. D. Moran, Thomas F. KuechAbstract:Plasma-treated and DI H_2O rinsed oxide layers are commonly used in wafer bonding applications. Borosilicate glass (BSG) layers deposited by low-pressure Chemical vapor deposition (LPCVD) treated with an O_2 plasma in reactive ion etching (RIE) mode at 0.6 W/cm^2 and rinsed with DI H_2O readily bond to GaAs and Si. The Chemical Role of this pre-bonding treatment was investigated using attenuated total reflection Fourier transform infrared (ATR- FTIR) spectroscopy. The peak intensities for both the Si-O and B-O absorbance bands decreased in intensity as a result the plasma treatment consistent with the uniform sputter etching of BSG. The effect of changing the total plasma treatment time was investigated in terms of the total amount of material removed. Polarization-dependent ATR-FTIR revealed that the H_2O/OH absorbance bands decreased in peak intensity with the OH groups preferentially oriented perpendicular to the sample surface after the plasma treatment. The subsequent DI H_2O rinse restores the water to the surface while changing the surface BSG composition. ATR-FTIR studies suggest that for oxide compositions greater than 10 mole % B_2O_3, the top 4 nm of B_2O_3 was removed or leached from the oxide layer during the DI H_2O rinse.
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Chemical Role of oxygen plasma in wafer bonding using borosilicate glasses
Applied Physics Letters, 2001Co-Authors: Darren Hansen, C. E. Albaugh, P. D. Moran, Thomas F. KuechAbstract:Plasma-treated oxide layers are commonly used in wafer bonding applications. Borosilicate glass (BSG) layers deposited by low-pressure Chemical vapor deposition treated with an O2 plasma in reactive ion etching mode for 5 min at 0.6 W/cm2 and rinsed with DI H2O readily bond to GaAs and Si. The Chemical Role of this prebonding treatment was investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The peak intensities for both the Si–O and B–O absorbance bands decreased in intensity as a result of the plasma treatment is consistent with the uniform sputtering of 9.8 nm±0.8 nm of BSG. Polarization dependent ATR-FTIR revealed that the H2O/OH absorbance bands decreased in peak intensity with the OH groups being preferentially oriented perpendicular to the sample surface after the plasma treatment. The subsequent DI H2O rinse restores the water to the surface while removing B2O3 from the BSG layer. This prebonding treatment, therefore, results in a hydrophilic bond, but...