High-resolution characterization of the diffusion of light chemical elements in metallic components by scanning microwave microscopy.

An original sub-surface, high spatial resolution tomographic technique based on scanning microwave microscopy (SMM) is used to visualize in-depth materials with different chemical compositions. A significant phase difference in SMM between aluminum and chromium buried patterns has been observed. Moreover this technique was used to characterize a solid solution of a light chemical element (oxygen) in a metal lattice (zirconium). The large solubility of the oxygen in zirconium leads to modifications of the properties of the solid solution that can be measured by the phase shift signal in the SMM technique. The signal obtained in cross-section of an oxidized Zr sample shows the excellent agreement between phase shift profiles measured at different depths. Such a profile can reveal the length of diffusion of the oxygen in zirconium under the surface. The comparison with the oxygen concentration measured by nuclear reaction analysis shows excellent agreement in terms of length of diffusion and spatial distribution of the oxygen. A rapid calibration shows a linear dependence between the phase shift and the oxygen concentration. The SMM method opens up new possibilities for indirect measurements of the oxygen concentration dissolved in the metal lattice.

Facile approaches to build ordered amphiphilic tris(phthalocyaninato) europium triple-decker complex thin films and their comparative performances in ozone sensing.

Solution processed thin films of an amphiphilic tris(phthalocyaninato) rare earth triple-decker complex, Eu(2)[Pc(15C5)(4)](2)[Pc(OC(10)H(21))(8)], have been prepared from three different methods: self-assembly (SA) annealed in solvent vapor, quasi-Langmuir-Shäfer (QLS) and drop casting methods. In particular, we successfully developed a simple QLS process for fabricating ordered multilayers with a good thickness control. The films prepared from three different methods were characterized by a wide range of methods including electronic absorption spectra, IR, X-ray diffraction, atomic force microscopy (AFM), and current-voltage (I-V) measurements. J-type aggregates have been formed with the increasing degree of order of molecular stacking Cast < QLS < SA films. Moreover, the gas sensing behavior of the three types of films was investigated towards ozone in the 8-300 ppb range. Unexpectedly good sensitive, stable and reproducible responses to O(3) gas are obtained for these kinds of ultra-thin solution processed films in a fast response/recovery cycle of only 1/4 min. The response of Eu(2)[Pc(15C5)(4)](2)[Pc(OC(10)H(21))(8)] films is linearly correlated to the ozone concentration. The interaction between the Eu(2)[Pc(15C5)(4)](2)[Pc(OC(10)H(21))(8)] films and different ozone concentrations was found to follow first-order kinetics. Strikingly, QLS films showed the most stable response and the largest average sensor response rate constant among the three types of films.

Conformation of adsorbed comb copolymer dispersants.

Comb copolymers with an adsorbing backbone and nonadsorbing side chains can be very effective dispersants, particularly when a high ionic strength strongly penalizes electrostatic stabilization. For this reason, they have become essential components of concrete over the past decade. This article examines the steric hindrance characteristics of such polymers through the use of atomic force microscopy (AFM) on calcium silicate hydrate, the main hydration product of Portland cement. It is found that solution and surface properties (hydrodynamic radius, radius of gyration, surface coverage, steric layer thickness) and force-distance curves obtained during AFM measurements can be well described by a scaling approach derived in this paper. This represents the first real quantitative step in relating these properties directly to the molecular structure of such comb copolymer dispersants.

Nanoscale experimental investigation of particle interactions at the origin of the cohesion of cement.

Atomic force microscopy has been used to investigate the force at the origin of the cohesion of cement. The cohesion of cement grains is caused by surface forces acting between calcium silicate hydrate nanoparticles in interstitial electrolytic solution. Direct measurement of the interaction between two calcium silicate hydrate surfaces is performed in air and different aqueous solutions. In dry air, starting with the van der Waals forces, the interaction area between calcium silicate hydrate nanoparticles can be estimated. In electrolytic solution, the evolution of these forces is extensively dependent on both surface and solution chemistry. The roles of the calcium hydroxide concentration, pH, and ionic strength are investigated. The force measurements allow us to confirm the pre-eminence of ionic correlation forces in the cohesion of cement.

Investigation of the surface structure and elastic properties of calcium silicate hydrates at the nanoscale.

This work is the first step towards the understanding of the structure of calcium silicate hydrate (C-S-H), the main constituent of cement paste, at the nanoscale. The first demonstration of atomic-resolution imaging of the (C-S-H) surface with an atomic force microscope (AFM) was performed. C-S-H nanoparticles (60 x 30 x 5 nm3) were partially recrystallized by Ostwald ripening after long-term equilibrium in saturated calcium hydroxide solution of different concentration, leading to C-S-H of different calcium/silicon ratio (Ca/Si). The results of atomic resolution made possible the investigation of the C-S-H cell surface parameters. The surface layer structure depended on the calcium hydroxide concentration with which it equilibrated. The change in structural properties perpendicular to the C-S-H layer was probed by modifying AFM for nanoindentation hardness measurements with a depth of indentation as low as 1 nm. The change in elastic modulus depending on the calcium/silicon ratio was evaluated and correlated in the change in structural parameters in this direction as estimated by X-ray diffraction.