Jean-François Bardeau

Determination by x-ray reflectivity and small angle x-ray scattering of the porous properties of mesoporous silica thin films

Two-dimensional hexagonal silica thin films templated by a triblock copolymer were investigated by grazing incident small angle x-ray scattering (GISAXS) and x-ray reflectivity (XR) before and after removing the surfactant from the silica matrix. XR curves—analyzed above and below the critical angle of the substrate—are evaluated by the matrix technique to obtain the average electron density of the films, the wall thickness, the electron density of the walls, the radius of the pores, and subsequently the porosity of such mesoporous films. In combination with GISAXS, the surface area of the mesopores is ascertained, thereby providing a complete analysis of the porosity in thin films by x-ray scattering methods.

Synthesis of hollow vaterite CaCO3 microspheres in supercritical carbon dioxide medium

We here describe a rapid method for synthesizing hollow core, porous crystalline calcium carbonate microspheres composed of vaterite using supercritical carbon dioxide in aqueous media, without surfactants. We show that the reaction in alkaline media rapidly conducts to the formation of microspheres with an average diameter of 5 µm. SEM, TEM and AFM observations reveal that the microspheres have a hollow core of around 0.7 µm width and are composed of nanograins with an average diameter of 40 nm. These nanograins are responsible for the high specific surface area of 16 m2 g−1 deduced from nitrogen absorption/desorption isotherms, which moreover confers an important porosity to the microspheres. We believe this work may pave the way for the elaboration of a biomaterial with a large potential for therapeutic as well as diagnostic applications.

Influence of functional organic groups on the structure of CTAB templated organosilica thin films

Highly ordered mesoporous organosilica thin films containing functional organic terminal groups covalently bonded to the silica matrix were synthesized by co-condensation of tetraethylorthosilicate (TEOS) and organotriethoxysilane RSi(OEt)3 (R = Cl(CH2)3, CN(CH2)3) in the presence of cetyltrimethylammonium bromide (CTAB) as structure directing agent under acidic conditions. The influence of the nature and concentration of these organic groups on the structure of the thin films is evidenced by Grazing Incidence Small Angle Scattering (GISAXS) and X-ray reflectivity. We show that the introduction of chloropropyl groups strongly affects the structure of these films while cyanopropyl groups weakly perturb it. In the case of the chloropropyl groups, the presence of trans and gauche conformers in the films is clearly evidenced by using micro-Raman spectrometry. Their effects on the phase behaviour versus the concentration are discussed.

New layered organic-inorganic magnets incorporating azo dyes

New hybrid organic/inorganic magnets have been synthesized by insertion of stilbazolium-carboxylate and/or -sulfonate dyes into cobalt and copper layered hydroxides. Co2(OH)3.57(MR)0.43·1.88 H2O (MR⊂Co (1)) (MRNa: Methyl Red sodium salt: sodium 2-[4-(Dimethylamino)phenylazo]benzoate), Co2(OH)3.27(MO)0.73·2.94 H2O (MO⊂Co (2)) (MONa: Methyl Orange sodium salt: sodium 4-[4-(Dimethylamino)phenylazo]benzenesulfonate), Co2(OH)3.45(OrangeIV)0.55·2.92 H2O (OrangeIV⊂Co (3)) (OrangeIVNa: OrangeIV sodium salt: sodium 4-[4-(Anilino)phenylazo]benzenesulfonate), and Co2(OH)3.46(MY10)0.27·2.34 H2O (MY10⊂Co (4)) (MY10Na2: Mordant Yellow 10 disodium salt: sodium 3-[4-(sodium sulfonate)phenylazo]-6-hydroxybenzoate) have been synthesized by anionic exchange in alkaline media starting from Co2(OH)3(OAc)·H2O. Cu2(OH)3.23(MR)0.77·2.92 H2O (MR⊂Cu (5)), Cu2(OH)3.29(MO)0.71·2.31 H2O (MO⊂Cu (6)), and Cu2(OH)3.39(OrangeIV)0.61·1.80 H2O (OrangeIV⊂Cu (7)) were obtained starting from the pre-intercalated copper hydroxide Cu2(OH)3(DS) (DS−: dodecylsulfate). This is the first time pre-intercalation is used for the insertion of molecules within the interlamellar space of simple layered hydroxides. The hybrid copper layered hydroxides show ferrimagnetic behaviour with ordering at very low temperature (below 1.8 K). The cobalt analogues are ferrimagnets with ordering temperatures ranging from 6.9 K to 18 K.

Vibrational density of states in silicon carbide nanoparticles: experiments and numerical simulations

The vibrational properties of silicon carbide nanoparticles (np-SiC) were investigated as function of the nanocrystal size (5-25 nm) and the features of their outermost surfaces. Raman experiments and numerical methods were conjugated to characterize the signatures from the active SiC normal modes and the vibrational density of states (VDOS). The Raman spectra of the nanopowders were marked by VDOS signals which correlate with the SiC amorphous fractions favoured by the high specific surfaces of the nanoparticles and their surface reconstruction. Quantitative interpretation of the experimental VDOS features, IR absorption and Raman scattering properties in nanosized SiC were carried out by means of numerical methods developed on SiC clusters with suitable structures and sizes.

Characterization and enhanced properties of plasma immersion ion processed diamond-like carbon films

The formation and properties of diamond-like carbon (DLC) films prepared on silicon substrates at room temperature, using C2H2–Ar plasma immersion ion processing, are investigated with respect to film deposition parameters. Decreases in the reactive gas-flow ratios of C2H2 to Ar(FC2H2/FAr) or the gas pressure were found to decrease the hydrogen content, increase the density and hardness, and improve the surface finish of the DLC films, all of which led to enhanced tribological properties. Decreasing the friction coefficient requires increasing the hardness of the film and smoothing its surface, whereas increasing the wear resistance correlates with reducing both the hydrogen content and residual stress in DLC films. High hardness and optimum tribological properties were reached as the growth of DLC films was subjected to low-energy ion impingement, which was induced by a −150 V pulsed bias from the C2H2–Ar plasma produced at low reactive gas pressures with low FC2H2/FAr ratios.

Self-Assembled Monolayers of Bisphosphonates: Influence of Side Chain Steric Hindrance

Bisphosphonates form self-assembled monolayers (SAMs) spontaneously on stainless steel, silicon, and titanium oxidized surfaces. We used contact angle measurements, atomic force microscopy, and X-ray reflectivity analysis to study the formation of SAMs on a model surface of ultraflat titanium (rms = 0.2 nm). The results were extended to standard materials (mechanically polished titanium, stainless steel, and silicon) and showed that water-soluble bisphosphonic perfluoropolyether can easily form SAMs, with 100% surface coverage and a layer thickness of less than 3 nm. Hydrophobic (water contact angle >110 degrees on stainless steel or titanium) and lipophobic (methylene iodide contact angle >105 degrees on titanium) properties are discussed in terms of industrial applications.

Merging models of biomineralisation with concepts of nonclassical crystallisation: is a liquid amorphous precursor involved in the formation of the prismatic layer of the Mediterranean Fan Mussel Pinna nobilis?

The calcitic prisms of Pinna nobilis (Pinnidae, Linnaeus 1758) are shown to be perfect examples of a mesocrystalline material. Based on their ultrastructure and on the occurrence of an amorphous transient precursor during the early stages of prism formation, we provide evidence for the pathway of mesocrystallisation proposed by Seto et al. (2012), which proceeds not by self-organized oriented attachment of crystalline nano-bricks but by aggregation of initially amorphous nanogranules which later transform by epitaxial nucleation to a three-dimensional array of well aligned nanocrystals. We further fathom the role of a liquid amorphous calcium carbonate in biomineralisation processes and provide strong evidence for the occurrence of PILP-like intermediates during prism formation. We develop a new scenario of prism formation based on the presented findings presented findings and discuss the implications of a speculative liquid amorphous calcium carbonate (LACC) intermediate in vivo.

Haslea karadagensis (Bacillariophyta): a second blue diatom, recorded from the Black Sea and producing a novel blue pigment

A new species of raphid pennate diatom producing a blue pigment, Haslea karadagensis Davidovich, Gastineau & Mouget, sp. nov., was recently isolated from the Crimean coast of the Black Sea (Ukraine). This organism is very similar to the well-known Haslea ostrearia, the first described ‘blue’ diatom, which produces marennine, the pigment involved in the greening of oysters. The Ukrainian diatom, H. karadagensis, differs slightly from H. ostrearia in the structure of its frustule, and the two organisms are unable to interbreed. Two molecular markers, rbcL and the ITS1–5.8S–ITS2 sequences, showed 2% and >50% differences, respectively, between the two species. UV-visible spectrophotometry and in vivo confocal micro-Raman spectroscopy were used to compare the pigment of H. karadagensis with marennine. Both pigments showed absorption bands in the UV and red regions, but the positions of the maxima differ between the pigments. Significant differences were observed by micro-Raman spectroscopy in the 1000–1700 cm−1 wavenumber range, revealing that the pigments are different molecules. Haslea karadagensis is the first example of a new ‘blue’ diatom and produces a novel blue pigment.

Cheap and robust ultraflat gold surfaces suitable for high-resolution surface modification.

A simple procedure to elaborate robust ultraflat gold surface without clean room facilities is presented. Self-assembled 3-mercaptopropytriethoxysilane (MPTMS) on silicon was used as a buffer layer on which gold was sputtered using a common sputter-coating apparatus. The optimization of the sample position into the chamber of the sputtering machine yielded the formation of a thin (approximately 8 nm) gold layer. The characterization of the resulting gold surface (i.e., AFM, X-ray reflectivity, and diffraction) has demonstrated its high smoothness (<0.7 nm) over a large scale with a preferred (111) orientation. The robustness of the substrate toward organic solvents and thermal treatment was also tested. The ability of these surfaces to be used as substrates for high-resolution surface modification was confirmed by functionalizing the gold surface using the dip pen nanolithography process.