Marie-José Casanove

Synthesis and characterization of monodisperse zinc and zinc oxide nanoparticles from the organometallic precursor [Zn(C6H11)2]

Abstract Decomposition of the organometallic precursor [Zn(C6H11)2] in wet anisole leads to the formation of monodisperse spherical Zn particles of 6 nm mean diameter. High resolution electron microscopy (HRTEM) indicates the crystalline nature of these particles and photoelectron studies (XPS) are consistent with the presence of both zinc and zinc oxide. In the presence of polyvinylpyrolidone (PVP), the decomposition leads to well dispersed nanoparticles for which HRTEM studies evidenced the presence of hexagonal zinc (0) surrounded by a thin layer of hexagonal zinc oxide of wurtzite type. The thermal oxidation of these zinc nanoparticles yields well-crystallized nanoparticles of ZnO without coalescence or size change. An X-ray diffraction pattern shows that the powder consists of pure hexagonal wurtzite-type phase.

Novel, Spongelike Ruthenium Particles of Controllable Size Stabilized Only by Organic Solvents

Soluble ruthenium nanoparticles of uniform size (see picture) with a porous spongelike structure were obtained by the reaction of [Ru(C(8)H(10))(C(8)H(12))] with H(2) in methanol or THF/methanol. The particle size can be controlled in the range 15-100 nm by varying the MeOH/THF ratio. The particles catalyze benzene hydrogenation without modification of their size or structure. Their formation is proposed to occur in the droplets of a nanosized emulsion, which act as nanoreactors.

Synthesis and Self-Assembly of Monodisperse Indium Nanoparticles Prepared from the Organometallic Precursor [In(η5-C5H5)]

Spontaneous decomposition of [In(η5 -C5 H5 )] in the presence of poly(vinyl pyrrolidone) or trioctylphosphane oxide (TOPO) as a stabilizer gave monodisperse indium nanoparticles with a mean diameter of about 5-6 nm. In the case of TOPO, self-organization of the nanoparticles in two- and three-dimensional superlattices is observed.

Quantitative analysis of strain field in thin films from HRTEM micrographs

Abstract A method for measuring and mapping displacement fields and strain fields has been developed. It is based on the Fourier analysis of a HRTEM lattice image selecting a strong Bragg reflection and performing an inverse Fourier transform. The phase component of the resulting complex image gives information on local displacements of atomic planes. The two-dimensional (2D) displacement field can then be derived by applying the method to two non-collinear Fourier components. Local strain tensor components e xx ( r → ), e yy ( r → ), e xy ( r → ) and e yx ( r → ) can be obtained by analysing the derivative of the displacement field. Applied to HRTEM images of thin films, this technique gives quantitative information on the variations of the strain relaxations in the different layers. The method is illustrated studying a fully relaxed GaSb/GaAs interface.

Investigation of the evolution of hardening precipitates during thermal exposure or creep of a 2650 aluminium alloy

Abstract In a 2650-T8 aluminium, the initial bi-modal homogeneous precipitation (GPB fine needles and S ′ precipitates) evolves during a thermal exposure at 150 °C: the GPB fine needles disappear. This dissolution is accelerated by creep and leads to a loss of mechanical resistance.

Magnetic nanoparticles through organometallic synthesis: evolution of the magnetic properties from isolated nanoparticles to organised nanostructures.

Co and NiFe nanoparticles (2.7 to 3.3 nm mean diameter) of narrow size distribution have been obtained through the decomposition of organometallic precursors in organic solutions of long alkyl chain ligands, namely oleic acid and hexadecylamine. Materials of various volume fractions were produced. The particles have been structurally characterised by WAXS. Both adopt the bulk structure: HCP in the case of cobalt; a mixture of FCC and BCC for NiFe. Their aptitude to self-assemble either on flat supports or in bulk solid state has been investigated by means of TEM and SAXS. This study suggests the crystallisation of the nanoparticles upon solvent evaporation, especially a local FCC arrangement was observed for the NiFe material. Magnetic measurements (SQUID) confirm this tendency. The blocking temperature depends on the metal volume fraction, i.e. on the anisotropy generated by the dipolar couplings (Ki). We show that, for dense samples, the particles of high intrinsic anisotropy, Ku, (Co) still display an individual behaviour while the soft ones (NiFe) display a collective behaviour.

High-resolution transmission electron microscopy and tomographic atom probe studies of the hardening precipitation in an Al–Cu–Mg alloy

The hardening precipitation of an Al–Cu–Mg aluminium alloy designed for aeronautics was investigated using high-resolution transmission electron microscopy (HREM) and tomographic atom probe techniques. The observed precipitates clearly belong either to the Guinier–Preston–Bagaryatskii (GPB) zones type or to the so-called S-Al2CuMg precipitation. We analysed a large number of precipitates in order to obtain statistical information on the precipitation. We focused on the structural and/or chemical composition of the different precipitates. It was found, in particular, that the very numerous GPB zones do not present a single chemical composition. Evidence is also given for the presence of two different kinds of S-precipitate/matrix orientation relationships, strongly linked to the morphology of the precipitate. The structure of the S precipitates was confirmed by direct comparison with simulated HREM images. Particular attention was paid to the nature of the S-precipitate/matrix interfaces.

Determination of precipitate strength in aluminium alloy 6056-T6 from transmission electron microscopy in situ straining data

Abstract The transmission electron microscopy in-situ straining technique is employed to measure the breaking angles of strengthening precipitates in aluminium alloy 6056-T6 as they are sheared by dislocations. The experimental determination of the character of bowed dislocation segments when dislocations are pinned on precipitates allows us to calculate the corresponding line tensions. From this, the maximum forces F m that precipitates can sustain before being sheared by dislocations are deduced. It is suggested that F m may be regarded as a quantitative parameter which includes the effects of the various strengthening mechanisms operative in precipitation-hardened alloys. An attempt is made to relate the maximum force calculated from in-situ straining data to the macroscopic yield strength of the material.

Straining mechanisms in aluminium alloy 6056. In-situ investigation by transmission electron microscopy

TEM in-situ straining tests, performed in precipitation hardened aluminium alloy 6056-T6, show that precipitates are sheared or by-passed by dislocations. By-passing, assisted by dislocation cross-slip, results in the formation and stress-induced spreading of non-planar loops. The relationship between those elementary mechanisms and the mechanical properties of the alloy is discussed.

Misfit relaxation of La0.7Sr0.3MnO3 thin films by a nanodot segregation mechanism

Partially segregated La0.7Sr0.3MnO3 (LSMO) nanocomposite films are shown to exhibit a thickness dependent self-assembled structure. The morphological evolution of the nanocomposite and the misfit strain of the LSMO phase are linked through the topological distribution of La–Sr oxide nanodots within the film. Misfit relaxation occurs above a critical thickness, hc, coinciding with the nucleation of La–Sr oxide nanodots at the film-substrate interface. Below hc, the same dots outcrop the film surface, forming islands. As a consequence of this misfit relaxation mechanism, an enhancement in the magnetoresistance with increasing thickness is measured.