Pierre Stadelmann

A study of the structure of Lomer and 60° dislocations in aluminium using high-resolution transmission electron microscopy

Abstract The structure of asymmetric [110] tilt boundaries developed during creep of pure aluminium single crystals is studied using high-resolution electron microscopy. The small- and moderate-misorientation boundaries are composed of Lomer and 60° dislocations. Extensive image simulation is used to deduce the detailed core structures of these two dislocations. Comparisons with calculated elastic displacements indicate that the Lomer dislocation is not detectably dissociated in its (001) glide plane, or into the sessile Lomer-Cottrell configuration. The agreement between the observed atomic column positions and continuum elasticity is excellent, except for the innermost positions near the core of the Lomer dislocation. The core structure of these discrete Lomer dislocations also correlates well with previous atomistic calculations for a larger-misorientation Σ = 19 boundary. A similar analysis of the displacements around 60° dislocations using isotropic elasticity indicates a slight dissociation of about...

Dexamethasone-containing biodegradable superparamagnetic microparticles for intra-articular administration: physicochemical and magnetic properties, in vitro and in vivo drug release.

Compared with traditional drug solutions or suspensions, polymeric microparticles represent a valuable means to achieve controlled and prolonged drug delivery into joints, but still suffer from the drawback of limited retention duration in the articular cavity. In this study, our aim was to prepare and characterize magnetic biodegradable microparticles containing dexamethasone acetate (DXM) for intra-articular administration. The superparamagnetic properties, which result from the encapsulation of superparamagnetic iron oxide nanoparticles (SPIONs), allow for microparticle retention with an external magnetic field, thus possibly reducing their clearance from the joint. Two molecular weights of poly(lactic-co-glycolic acid) (PLGA) were used, 12 and 19 kDa. The prepared batches were similar in size (around 10 microm), inner morphology, surface morphology, charge (neutral) and superparamagnetic behaviour. The SPION distribution in the microparticles assessed by TEM indicates a homogeneous distribution and the absence of aggregation, an important factor for preserving superparamagnetic properties. DXM release profiles were shown to be quite similar in vitro (ca. 6 days) and in vivo, using a mouse dorsal air pouch model (ca. 5 days).

Bending of dislocations in GaN during epitaxial lateral overgrowth

Bending of dislocations in GaN during epitaxial lateral overgrowth (ELO) has been experimentally studied using transmission electron microscopy. The orientational dependence of the dislocation energy factor K has been calculated on the basis of anisotropic elasticity theory for different types of perfect dislocation in GaN. Image forces act on dislocations during the growth and dislocations bend to achieve the minimum energy. Bending behavior depends on a dislocation type and we show that the measured bending angles correspond to the calculated energy minima. The results allow us to quantitatively discuss the most advantageous ELO GaN mask direction for the largest dislocation density reduction.

EELS spectroscopy of iron fluorides and FeFx/C nanocomposite electrodes used in Li-ion batteries

A new type of positive electrode for Li-ion batteries has been developed recently based on FeF3/C and FeF2/C nanocomposites. The microstructural and redox evolution during discharge and recharge processes was followed by electron energy loss spectroscopy (EELS) to determine the valence state of Fe by measuring the Fe L3 line energy shift and from Fe L3/L2 line intensity ratios. In addition, transition metal fluorides were found to be electron beam sensitive, and the effect of beam exposure on EELS spectra was also investigated. The EELS results indicate that for both FeF3/C and FeF2/C nanocomposite systems, a complete reduction of iron to FeO is observed upon discharge to 1.5 V with the formation of a finer FeO/LiF subnanocomposite ( approximately 7 nm). Upon complete recharging to 4.5 V, EELS data reveal a reoxidation process to a Fe2+ state with the formation of a carbon metal fluoride nanocomposite related to the FeF2 structure.

Effect of the applied potential of the near surface microstructure of a 316L steel submitted to tribocorrosion in sulfuric acid

The tribocorrosion behaviour of a 316L austenitic stainless steel sliding against alumina was investigated under electrochemical control in sulfuric acid using a tribometer with a ball on flat configuration. Tests were conducted by applying either a passive potential (metal covered by an oxide film) or a cathodic potential (no passive film, negligible corrosion) to the steel. Friction, wear and anodic current were monitored. The near surface microstructure of wear tracks was analysed by transmission electron microscopy (TEM). Significantly higher wear was observed at the passive potential compared with the cathodic potential. Chemical reactions could not account for this difference in deterioration. TEM analysis revealed that the plastic behaviour of the metal, and thus its response to wear, depends on the prevailing electrochemical conditions, the passive potential showing larger deformation than the cathodic. This effect was attributed to the presence of the passive film that induces residual stresses and interferes with dislocation activity.

Core-shell Au@(TiO2, SiO2) nanoparticles with tunable morphology

A novel approach based on the Stöber method allows breaking of the symmetry of core-shell systems based on metallic core and metal oxide shell. By adjusting the proportion of the TiO(2) precursor with regard to the silica precursor, different morphologies of the particles have been obtained displacing the gold particle from center to eccentric positions leading to acorn-like and raspberry-like structure.

Atomic scale study of local TiSi2/Si epitaxies

The TiSi2/Si system is investigated using high‐resolution transmission electron microscopy (HRTEM) and electron diffraction in both cross‐section and flat‐on modes. The results show that the large crystallographic differences between both crystals and the complexity of the reaction path are not obstacles to the formation of flat and well‐defined interfaces. (101) TiSi2 proves to be a preferential plane for epitaxial growth on Si (111). In this case, the terminal TiSi2 plane at the interface is composed of single atomic species. It is proposed that the reasons leading to such an epitaxy are related to the small discrepancy of atomic densities and interplanar spacings characteristic of these planes. Observation of local epitaxial relationships are reported and investigated using a lattice matching model. It turns out that they minimize the two‐dimensional misfit at the interface.

Core-shell gold J-aggregate nanoparticles for highly efficient strong coupling applications

We have developed a straightforward synthetic route to prepare core-shell systems based on gold nanoparticles (NPs) surrounded with J-aggregates molecules. This synthesis allows the direct and efficient coating, at room temperature, of pretreated citrate-stabilized gold NPs with 5, 5′, 6, 6′-tetrachloro-1-1′-diethyl-3, 3′-di (4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), without supplementary adding of salts and bases during the synthesis. As the size of gold particle is tunable, the precise optimization of the strong coupling between the electronic transitions of organic components (TDBC) and the plasmon modes of the gold NPs is achieved corresponding to a Rabi energy of 220 meV, a value not yet obtained in such a system.

Growth and Structural Properties of Epitaxial Pb(ZrxTi1-x)O3 Films and Pb(ZrxTi1-x)O3-Cuprate Heterostructures

We report on the epitaxial growth and structural properties of Pb(ZrxTi1−x)O3 (PZT) thin films and of epitaxial heterostructures containing metallic DyBa2Cu3O7 (DyBCO) and ferroelectric PZT layers grown using an off‐axis rf reactive sputtering technique. On (100) and (110) SrTiO3 substrates, tetragonal (001) and (011) epitaxial Pb(Zr0.52Ti0.48)O3 films have been obtained. Extensive characterization on (001) PZT films using x‐ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy, and atomic force microscopy reveal a very high degree of structural quality, and very smooth surfaces with a root‐mean‐square roughness of 3 A for a 0.5 μm×0.5 μm scan on a 1000 A thick film. TEM studies on DyBCO–PZT structures reveal sharp and clean interfaces without traces of intermixing. Primary dislocations are observed at the DyBCO–PZT interface, which do not propagate through the PZT layer. [101]‐type dislocations are also seen, possibly related to subg...

Evidence for seven-fold cobalt coordination at the CoSi2/Si(111) interface

CoSi2/Si(111) interfaces have been prepared by annealing of a UHV-evaporated, Co layer at 500, 600, and 900 degrees C. Using electron microscopy at atomic-scale resolution, the authors have compared experimental pictures with an extensive set of calculated images. Their observations support Si-Si interfacial bonds consistent with a seven-fold coordination of the first Co layer. This is the first evidence of this interface geometry for CoSi2, other reports being in favour of Co-Si bonds and a five-fold or eight-fold Co coordination.