F. Ozanam - Academia.edu (original) (raw)

Papers by F. Ozanam

Research paper thumbnail of Mechanisms of Thermal Decomposition of Organic Monolayers Grafted on (111) Silicon

Langmuir, 2007

The thermal stability of different organic layers on silicon has been investigated by in situ inf... more The thermal stability of different organic layers on silicon has been investigated by in situ infrared spectroscopy, using a specially designed variable-temperature cell. The monolayers were covalently grafted onto atomically flat (111) hydrogenated silicon surfaces through the (photochemical or catalytic) hydrosilylation of 1-decene, heptadecafluoro-1-decene or undecylenic acid. In contrast to alkyl monolayers, which desorb as alkene chains around 300 degrees C by the breaking of the Si-C bond through a beta-hydride elimination mechanism, the alkyl layers functionalized with a carboxylic acid terminal group undergo successive chemical transformations. At 200-250 degrees C, the carboxyl end groups couple forming anhydrides, which subsequently decompose at 250-300 degrees C by loss of the functional group. In the case of fluorinated alkyl chains, the C-C bond located between CH2 and CF2 units is first broken at 250-300 degrees C. In either case, the remaining alkyl layer is stable up...

Research paper thumbnail of Grafting and Polymer Formation on Silicon from Unsaturated Grignards:  II. Aliphatic Precursors

The Journal of Physical Chemistry B, 2007

Anodic decomposition of a phenylmagnesium halide at a surface-hydrogenated silicon electrode lead... more Anodic decomposition of a phenylmagnesium halide at a surface-hydrogenated silicon electrode leads to formation of polymeric layers covalently anchored to the silicon surface. These layers have been characterized using spectroellipsometry, photoluminescence, infrared, and X-ray photoelectron spectroscopies. The phenyl ring appears preserved in the process, and the polymer formed is a polyphenylene. Contamination by aliphatic groups from the solvent may be minimized by using a solvent resistant to hydrogen abstraction by the phenyl radicals. Regioselectivity of the branching may be oriented to the para form by using 4-chlorophenylmagnesium bromide as the precursor.

Research paper thumbnail of The Role of Atomic Ensembles in the Reactivity of Bimetallic Electrocatalysts

Science, 2001

Bimetallic electrodes are used in a number of electrochemical processes, but the role of particul... more Bimetallic electrodes are used in a number of electrochemical processes, but the role of particular arrangements of surface metal atoms (ensembles) has not been studied directly. We have evaluated the electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111). These properties are derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces for which the concentration and distribution of the respective metal atoms are determined in situ by atomic resolution scanning tunneling microscopy with chemical contrast. Palladium monomers are identified as the smallest ensemble ("critical ensemble") for carbon monoxide adsorption and oxidation, whereas hydrogen adsorption requires at least palladium dimers.

Research paper thumbnail of Electrochemical formation of porous silica: toward an understanding of the mechanisms

physica status solidi (a), 2007

Research paper thumbnail of Semiquantitative Study of the EDC/NHS Activation of Acid Terminal Groups at Modified Porous Silicon Surfaces

Langmuir, 2010

Infrared spectroscopy is used to investigate the transformation of carboxyl-terminated alkyl chai... more Infrared spectroscopy is used to investigate the transformation of carboxyl-terminated alkyl chains immobilized on a surface into succinimidyl ester-terminated chains by reaction with an aqueous solution of N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The acid chains are covalently grafted at the surface of hydrogenated porous silicon whose large specific surface area allows for assessing the activation yield in a semiquantitative way by infrared (IR) spectroscopy and detecting trace amounts of surface products and/or reaction products of small IR cross section. In this way, we rationalize the different reaction paths and optimize the reaction conditions to obtain as pure as possible succinimidyl ester-terminated surfaces. A diagram mapping the surface composition after activation was constructed by systematically varying the solution composition. Results are accounted for by NHS surface adsorption and a kinetic competition between the various EDC-induced surface reactions.

Research paper thumbnail of Quantitative Analysis of the Morphology of Macropores on Low-Doped p-Si

Journal of The Electrochemical Society, 2002

The formation of macropores by anodization of low-doped p-Si in HF electrolyte has been investiga... more The formation of macropores by anodization of low-doped p-Si in HF electrolyte has been investigated quantitatively. As anodization proceeds, structures of increasing characteristic size are formed, then a steady state is reached, where macropores grow parallel. The intermediate regime is well understood on the basis of a linear stability approach, incorporating the known physics and chemistry of the Si/electrolyte interface: semiconductor space charge and interface reaction velocity. The characteristic size of the macropores and their dependence on Si doping and electrolyte resistivity and composition are quantitatively accounted for after realizing that parallel growth is strongly favored by the channeling of the current in the macropores. Below a critical resistivity, no macropores are observed. It is shown, through a numerical simulation, that this change of behavior results from a loss of the insulating character of the walls, due to effects of disorder in a depletion layer when doping increases.

Research paper thumbnail of Chemical limitations to the anodic dissolution of p-Si in fluoride media in the presence of alkali metal cations

Journal of Electroanalytical Chemistry, 1995

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Research paper thumbnail of Microscopic, self-oscillating domains at the silicon surface during its anodic dissolution in a fluoride electrolyte

Electrochimica Acta, 1993

Altatract-During the anodic dissolution of silicon in fluoride electrolytes, for a given potentia... more Altatract-During the anodic dissolution of silicon in fluoride electrolytes, for a given potential E 3 3v,,, any variation of the electrode potential (even very small) makes the current undergo damped oscillations. Correspondingly, the admittance of the interface exhibits resonances at the same frequency and at its overtones. This resonant behavior is well understood in the framework of a macroscopic model, based upon the picture of a heterogeneous surface, partitioned into small, independent, self-oscillating domains. Noise measurements, which give access to the typical size of these domains, have been performed and give a typical dimension for the domains of the order of 1000 A.

Research paper thumbnail of In situ infrared monitoring of electrochemical adsorption/desorption of hydrogen on germanium

Chemical Physics Letters, 1998

Research paper thumbnail of In Situ Spectroelectrochemical Study of the Anodic Dissolution of Silicon by Potential-Difference and Electromodulated FT-IR Spectroscopy

Applied Spectroscopy, 1997

ABSTRACT The anodic dissolution of p -Si has been investigated by in situ infrared spectroscopy. ... more ABSTRACT The anodic dissolution of p -Si has been investigated by in situ infrared spectroscopy. The combination of potential-difference and electromodulated spectroscopies allows for the acquisition of a rather complete picture of the various regimes of the dissolution. After a review of general principles for studying electrochemical interfaces, a study of the interfacial oxide layer formed in the electropolishing regime is presented. Quantitative analysis shows that the thickness and quality of the oxide (density and defect content) depend upon electrode potential. Free-carrier absorption detected in electromodulated spectra shows that the blocking character of the oxide is correlated with the buildup of a stoichiometric oxide of low defectivity at sufficiently positive potentials. Furthermore, the dynamic response to the modulation reveals that oxides formed at weak positive potentials interact with electrolyte species through electro-induced adsorptions/desorptions on charged SiOH sites. At more positive potentials, charge is transported across the oxide by charged defects which could be associated with tricoordinated, positively charged SiO species. Finally, results obtained during porous silicon formation at weak positive potentials are presented. Potential-difference spectroscopy indicates that the electrode exhibits a very large specific surface area, and that the surface is covered by SiH bonds. Electromodulated infrared spectroscopy reveals that the SiH species are generated upon anodic current flowing and that the breaking of these bonds is the rate-limiting step of the anodic reaction. These unexpected results have given rise to the elaboration of new microscopic models for the direct anodic dissolution of silicon in fluoride electrolytes.

Research paper thumbnail of Interphase chemistry of Si electrodes used as anodes in Li-ion batteries

Applied Surface Science, 2013

The effect of the Si electrode morphology (amorphous hydrogenated silicon thin films -a-Si:H as a... more The effect of the Si electrode morphology (amorphous hydrogenated silicon thin films -a-Si:H as a model electrode and Si nanowires -SiNWs electrode) on the interphase chemistry was thoroughly investigated by the surface science techniques: X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS analysis shows a strong attenuation and positive shift of the Si 2p peaks after a complete charge/discharge performed in PC-and EC:DMC-based electrolytes for both electrodes (a-Si:H and SiNW), confirming a formation of a passive film (called solid electrolyte interphase -SEI layer). As evidenced from the XPS analysis performed on the model electrode, the thicker SEI layer was formed after cycling in PC-based electrolyte as compared to EC:DMC electrolyte. XPS and ToF-SIMS investigations reveal the presence of organic carbonate species on the outer surface and inorganic salt decomposition species in the inner part of the SEI layer. Significant modification of the surface morphology for the both electrodes and a full surface coverage by the SEI layer was confirmed by the scanning electron microscopy (SEM) analysis.

Research paper thumbnail of Mechanisms of Thermal Decomposition of Organic Monolayers Grafted on (111) Silicon

Langmuir, 2007

The thermal stability of different organic layers on silicon has been investigated by in situ inf... more The thermal stability of different organic layers on silicon has been investigated by in situ infrared spectroscopy, using a specially designed variable-temperature cell. The monolayers were covalently grafted onto atomically flat (111) hydrogenated silicon surfaces through the (photochemical or catalytic) hydrosilylation of 1-decene, heptadecafluoro-1-decene or undecylenic acid. In contrast to alkyl monolayers, which desorb as alkene chains around 300 degrees C by the breaking of the Si-C bond through a beta-hydride elimination mechanism, the alkyl layers functionalized with a carboxylic acid terminal group undergo successive chemical transformations. At 200-250 degrees C, the carboxyl end groups couple forming anhydrides, which subsequently decompose at 250-300 degrees C by loss of the functional group. In the case of fluorinated alkyl chains, the C-C bond located between CH2 and CF2 units is first broken at 250-300 degrees C. In either case, the remaining alkyl layer is stable up...

Research paper thumbnail of Grafting and Polymer Formation on Silicon from Unsaturated Grignards:  II. Aliphatic Precursors

The Journal of Physical Chemistry B, 2007

Anodic decomposition of a phenylmagnesium halide at a surface-hydrogenated silicon electrode lead... more Anodic decomposition of a phenylmagnesium halide at a surface-hydrogenated silicon electrode leads to formation of polymeric layers covalently anchored to the silicon surface. These layers have been characterized using spectroellipsometry, photoluminescence, infrared, and X-ray photoelectron spectroscopies. The phenyl ring appears preserved in the process, and the polymer formed is a polyphenylene. Contamination by aliphatic groups from the solvent may be minimized by using a solvent resistant to hydrogen abstraction by the phenyl radicals. Regioselectivity of the branching may be oriented to the para form by using 4-chlorophenylmagnesium bromide as the precursor.

Research paper thumbnail of The Role of Atomic Ensembles in the Reactivity of Bimetallic Electrocatalysts

Science, 2001

Bimetallic electrodes are used in a number of electrochemical processes, but the role of particul... more Bimetallic electrodes are used in a number of electrochemical processes, but the role of particular arrangements of surface metal atoms (ensembles) has not been studied directly. We have evaluated the electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111). These properties are derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces for which the concentration and distribution of the respective metal atoms are determined in situ by atomic resolution scanning tunneling microscopy with chemical contrast. Palladium monomers are identified as the smallest ensemble ("critical ensemble") for carbon monoxide adsorption and oxidation, whereas hydrogen adsorption requires at least palladium dimers.

Research paper thumbnail of Electrochemical formation of porous silica: toward an understanding of the mechanisms

physica status solidi (a), 2007

Research paper thumbnail of Semiquantitative Study of the EDC/NHS Activation of Acid Terminal Groups at Modified Porous Silicon Surfaces

Langmuir, 2010

Infrared spectroscopy is used to investigate the transformation of carboxyl-terminated alkyl chai... more Infrared spectroscopy is used to investigate the transformation of carboxyl-terminated alkyl chains immobilized on a surface into succinimidyl ester-terminated chains by reaction with an aqueous solution of N-ethyl-N'-(3-(dimethylamino)propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The acid chains are covalently grafted at the surface of hydrogenated porous silicon whose large specific surface area allows for assessing the activation yield in a semiquantitative way by infrared (IR) spectroscopy and detecting trace amounts of surface products and/or reaction products of small IR cross section. In this way, we rationalize the different reaction paths and optimize the reaction conditions to obtain as pure as possible succinimidyl ester-terminated surfaces. A diagram mapping the surface composition after activation was constructed by systematically varying the solution composition. Results are accounted for by NHS surface adsorption and a kinetic competition between the various EDC-induced surface reactions.

Research paper thumbnail of Quantitative Analysis of the Morphology of Macropores on Low-Doped p-Si

Journal of The Electrochemical Society, 2002

The formation of macropores by anodization of low-doped p-Si in HF electrolyte has been investiga... more The formation of macropores by anodization of low-doped p-Si in HF electrolyte has been investigated quantitatively. As anodization proceeds, structures of increasing characteristic size are formed, then a steady state is reached, where macropores grow parallel. The intermediate regime is well understood on the basis of a linear stability approach, incorporating the known physics and chemistry of the Si/electrolyte interface: semiconductor space charge and interface reaction velocity. The characteristic size of the macropores and their dependence on Si doping and electrolyte resistivity and composition are quantitatively accounted for after realizing that parallel growth is strongly favored by the channeling of the current in the macropores. Below a critical resistivity, no macropores are observed. It is shown, through a numerical simulation, that this change of behavior results from a loss of the insulating character of the walls, due to effects of disorder in a depletion layer when doping increases.

Research paper thumbnail of Chemical limitations to the anodic dissolution of p-Si in fluoride media in the presence of alkali metal cations

Journal of Electroanalytical Chemistry, 1995

RefDoc Bienvenue - Welcome. Refdoc est un service / is powered by. ...

Research paper thumbnail of Microscopic, self-oscillating domains at the silicon surface during its anodic dissolution in a fluoride electrolyte

Electrochimica Acta, 1993

Altatract-During the anodic dissolution of silicon in fluoride electrolytes, for a given potentia... more Altatract-During the anodic dissolution of silicon in fluoride electrolytes, for a given potential E 3 3v,,, any variation of the electrode potential (even very small) makes the current undergo damped oscillations. Correspondingly, the admittance of the interface exhibits resonances at the same frequency and at its overtones. This resonant behavior is well understood in the framework of a macroscopic model, based upon the picture of a heterogeneous surface, partitioned into small, independent, self-oscillating domains. Noise measurements, which give access to the typical size of these domains, have been performed and give a typical dimension for the domains of the order of 1000 A.

Research paper thumbnail of In situ infrared monitoring of electrochemical adsorption/desorption of hydrogen on germanium

Chemical Physics Letters, 1998

Research paper thumbnail of In Situ Spectroelectrochemical Study of the Anodic Dissolution of Silicon by Potential-Difference and Electromodulated FT-IR Spectroscopy

Applied Spectroscopy, 1997

ABSTRACT The anodic dissolution of p -Si has been investigated by in situ infrared spectroscopy. ... more ABSTRACT The anodic dissolution of p -Si has been investigated by in situ infrared spectroscopy. The combination of potential-difference and electromodulated spectroscopies allows for the acquisition of a rather complete picture of the various regimes of the dissolution. After a review of general principles for studying electrochemical interfaces, a study of the interfacial oxide layer formed in the electropolishing regime is presented. Quantitative analysis shows that the thickness and quality of the oxide (density and defect content) depend upon electrode potential. Free-carrier absorption detected in electromodulated spectra shows that the blocking character of the oxide is correlated with the buildup of a stoichiometric oxide of low defectivity at sufficiently positive potentials. Furthermore, the dynamic response to the modulation reveals that oxides formed at weak positive potentials interact with electrolyte species through electro-induced adsorptions/desorptions on charged SiOH sites. At more positive potentials, charge is transported across the oxide by charged defects which could be associated with tricoordinated, positively charged SiO species. Finally, results obtained during porous silicon formation at weak positive potentials are presented. Potential-difference spectroscopy indicates that the electrode exhibits a very large specific surface area, and that the surface is covered by SiH bonds. Electromodulated infrared spectroscopy reveals that the SiH species are generated upon anodic current flowing and that the breaking of these bonds is the rate-limiting step of the anodic reaction. These unexpected results have given rise to the elaboration of new microscopic models for the direct anodic dissolution of silicon in fluoride electrolytes.

Research paper thumbnail of Interphase chemistry of Si electrodes used as anodes in Li-ion batteries

Applied Surface Science, 2013

The effect of the Si electrode morphology (amorphous hydrogenated silicon thin films -a-Si:H as a... more The effect of the Si electrode morphology (amorphous hydrogenated silicon thin films -a-Si:H as a model electrode and Si nanowires -SiNWs electrode) on the interphase chemistry was thoroughly investigated by the surface science techniques: X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). XPS analysis shows a strong attenuation and positive shift of the Si 2p peaks after a complete charge/discharge performed in PC-and EC:DMC-based electrolytes for both electrodes (a-Si:H and SiNW), confirming a formation of a passive film (called solid electrolyte interphase -SEI layer). As evidenced from the XPS analysis performed on the model electrode, the thicker SEI layer was formed after cycling in PC-based electrolyte as compared to EC:DMC electrolyte. XPS and ToF-SIMS investigations reveal the presence of organic carbonate species on the outer surface and inorganic salt decomposition species in the inner part of the SEI layer. Significant modification of the surface morphology for the both electrodes and a full surface coverage by the SEI layer was confirmed by the scanning electron microscopy (SEM) analysis.