Soraya Ababou-Girard

Natural superhydrophilicity and photocatalytic properties of sol–gel derived ZnTiO3-ilmenite/r-TiO2 films

The additive free heteronucleation and nanocrystallization of ternary Zn(x)Ti(y)O(z) sols and coatings is presented. A proper adjustment of the Zn/Ti ratio in the sol allows the formation of elaborate superhydrophilic cubic spinel-like Zn(2)TiO(4), c-ZnTiO(3) or h-ZnTiO(3)-ilmentite/r-TiO(2)-rutile films. Their morphology and natural superhydrophilicity can be fine-tuned by the inclusion of 5% silica. This doping step delivers high dye intake capacities and water contact angle values below 3°. XPS analysis indicates that Zn and Si enrichment enables greater surface hydroxylation and thus improved water wetting behaviour. The transparent h-ZnTiO(3)-ilmenite/r-TiO(2) nanocomposite coatings deposited on glass and Si-wafers show a remarkable activity in the photomineralization of fatty-acids.

Covalent attachment of TEMPO onto a graphite felt electrode and application in electrocatalysis

This work describes a simple method to attach TEMPO by an amide link to a graphite felt electrode. The derivatization of the electrode is highlighted by cyclic voltammetry and XPS analyses. Cyclic voltammetry analyses showed the catalytic activity of the grafted TEMPO in both organic and aqueous media. The electrolyses revealed improved stability of the grafted catalyst in aqueous medium compared to acetonitrile. Furthermore, the catalyst is more stable when it is immobilized onto the electrode than when it is in homogeneous solution. The XPS analyses of the grafted felt after electrocatalysis in aqueous medium shows that the degradation of the modified electrode during the electrolysis is not due to a break of the amide link between the graphite felt and TEMPO.

Covalent immobilization of antibodies on electrochemically functionalized carbon surfaces

A general method is described for the covalent attachment to carbon surfaces of sensitive biomolecules such as antibodies. First, N-hydroxysuccinimide-activated carbon surfaces are prepared by a step by step method involving an electrografting process and a monoprotected homobifunctional linker to ensure a good control of the surface modification. Then, antibodies are introduced, at the last step of the modification procedure, under native conditions at physiological pH, to minimize their denaturation. Comparison with a classical method involving a homobifunctional linker shows a decrease of the degree of coverage of the surface by antibodies, explained by the formation of bridged structures by the linker.

Covalent integration of pyrrolyl units with modified monocrystalline silicon surfaces for macroscale and sub-200 nm-scale localized electropolymerization reactions

Macroscale and localized electrochemical growths of polypyrrole deposits have been performed on monocrystalline Si(111) surfaces modified by pyrrole-terminated organic monolayers. The first approach proposed to induce localized electropolymerization reaction consisted of the high dilution of pyrrole-terminated chains with inert decyl chains in order to have a large separation between the attached monomer units. Unfortunately, this method failed to produce polypyrrole features with precision and control of the structure geometry. More successful results were obtained with the electrochemical dip-pen nanolithography (DPN). A pyrrole-coated conducting AFM tip was brought into contact with a pyrrole-terminated silicon surface and a positive bias of +1.0 V was then applied to the surface for a given period of time. Along this lithographic progress, polypyrrole dots with diameters in the range of 75–200 nm and sub-200 nm-wide lines could be electrogenerated.

Barrier height distribution and dipolar relaxation in metal-insulator-semiconductor junctions with molecular insulator: Ageing effects

Electrical transport through molecular monolayers being very sensitive to disorder effects, admittance and current density characteristics of Hg // C12H25 – n Si junctions incorporating covalently bonded n-alkyl molecular layers, were investigated at low temperature (150-300 K), in the as-grafted state and after ageing at the ambient. This comparison reveals local oxidation effects both at the submicron scale in the effective barrier height distribution and at the molecular scale in the dipolar relaxation. In the bias range dominated by thermionic emission and modified by the tunnel barrier attenuation, , where is the thickness of the molecular tunnel barrier and is the inverse attenuation length at zero applied bias, some excess current is attributed to a distribution of low barrier height patches. Complementary methods are used to analyze the current density J(V, T) characteristics of Metal-Insulator-Semiconductor tunnel diodes. Assuming a Gaussian distribution of barrier heights centered at provides an analytical expression of the effective barrier height, ; this allows fitting of the distribution standard deviation and tunnel parameter over a wide temperature range. In a more realistic modeling including the voltage dependence of barrier height and circular patch area, the so-called “pinch-off” effect is described by a distribution of parameter which combines interface potential modulation and patch area variations. An arbitrary distribution of  values, fitted to low-temperature J(V) data, is equally well described by Gaussian or exponential functions. Ageing in air also increases the interface oxidation of Si substrate and affects the density of localized states near mid gap, which typically rises to the high 1011 eV-1.cm-2 range, as compared with < 1011 eV-1.cm-2 in the as-grafted state. The bias-independent relaxation observed near 1 kHz at low temperature may be attributed either to dipoles in the alkyl chain induced by the strong permanent dipoles of interface silicon oxide or to a local relaxation of water molecules trapped at the OML / silicon interface. The respective roles of SiO2 formation and water physisorption on the decrease of patch barrier height are also discussed.

Tunnel barrier parameters derivation from normalized differential conductance in Hg/organic monomolecular layer-Si junctions

The shape of tunnel barrier junctions is derived from experimental current density versus bias, J(V), using the normalized differential conductance, NDC=d log J/d log V, to discriminate barrier height, ΦT, and barrier width, dT, effects. Parameterization of the Simmons model for a rectangular tunnel barrier, with NDC≈dTV/(ΦT-qV)1/2, provides physical (dT,ΦT) values for Hg∥monomolecular layer—n Si(111) junctions incorporating functionalized n-alkyl layers covalently bonded to silicon.

Localization and Quantitative Analysis of Antigen−Antibody Binding on 2D Substrate Using Imaging NanoSIMS

Iron containing-antigen bound specifically to antibody immobilized on a surface is analyzed by nanoscale secondary ion mass spectrometry (NanoSIMS). This technique is well adapted compared with X-ray photoelectron spectroscopy and energy dispersive spectroscopy, which do not allow the detection of iron. The obtained Fe(+) map gives a good representation of the antigen repartition on the surface. NanoSIMS analysis of competition experiments performed with albumin and iron-free antigen are in good accordance with results obtained by a classical fluorescence microscopy approach. These results underline the interest of imaging NanoSIMS as a label-free method, allowing the localization and quantitative analysis of antigen-antibody binding with better spatial resolution than imaging ellipsometry and SPR.

Spatially resolved band alignments at Au-hexadecanethiol monolayer-GaAs(001) interfaces by ballistic electron emission microscopy

We study structural and electronic inhomogeneities in Metal—Organic Molecular monoLayer (OML)—semiconductor interfaces at the sub-nanometer scale by means of in situ Ballistic Electron Emission Microscopy (BEEM). BEEM imaging of Au/1-hexadecanethiols/GaAs(001) heterostructures reveals the evolution of pinholes density as a function of the thickness of the metallic top-contact. Using BEEM in spectroscopic mode in non-short-circuited areas, local electronic fingerprints (barrier height values and corresponding spectral weights) reveal a low-energy tunneling regime through the insulating organic monolayer. At higher energies, BEEM evidences new conduction channels, associated with hot-electron injection in the empty molecular orbitals of the OML. Corresponding band diagrams at buried interfaces can be thus locally described. The energy position of GaAs conduction band minimum in the heterostructure is observed to evolve as a function of the thickness of the deposited metal, and coherently with size-dependent electrostatic effects under the molecular patches. Such BEEM analysis provides a quantitative diagnosis on metallic top-contact formation on organic molecular monolayer and appears as a relevant characterization for its optimization.

Oxidation mechanism of thin Cu films: A gateway towards the formation of single oxide phase

Controlled thermal oxidations of thin copper films at relatively lower temperatures (up to 500°C) leading towards the formation of a single phase of copper oxide are investigated where the oxidation temperature, duration, oxygen partial pressure, film thickness and the crystallographic orientations play very crucial roles to significantly control the final phase of the copper oxide. Thin Cu films of thicknesses 100-1000 nm were deposited on glass and silicon substrates using the vacuum assisted thermal evaporation technique. Oxidations of those Cu films were performed at different temperatures for variable durations in air ambient as well as oxygen ambient conditions. Four probe resistivity measurement, x-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM) and x-ray photoemission spectroscopy (XPS) techniques have been used to characterize the oxide films. At a thermodynamic equilibrium, it has been observed that the oxide phase is solel...