Thierry Epicier

Toward an image-guided microbeam radiation therapy using gadolinium-based nanoparticles.

Ultrasmall gadolinium-based nanoparticles (GBNs) induce both a positive contrast for magnetic resonance imaging and a radiosentizing effect. The exploitation of these characteristics leads to a greater increase in lifespan of rats bearing brain tumors since the radiosensitizing effect of GBNs can be activated by X-ray microbeams when the gadolinium content is, at the same time, sufficiently high in the tumor and low in the surrounding healthy tissue. GBNs exhibit therefore an interesting potential for image-guided radiotherapy.

Neutron powder diffraction studies of transition metal hemicarbides M2C1−x—II. In situ high temperature study on W2C1−x and Mo2C1−x

Abstract In the first part of this paper [Acta metall.36, 1891 (1988)], we have presented the experimental background for a high temperature neutron powder diffraction study of transition metal hemicarbides M2C1−x having various compositions. In this second part, we report the results: in Mo2C1−x, a first order transformation between an orthorhombic ζ-Fe2N-type superstructure and a hexagonal ϵ-Fe2N-type one has been identified in a middle temperature range (1100–1400°C); in the case of W2C1−x, the same ϵ-Fe2N-type phase appears to be the major constituent in our powders. In both carbides, the disordering of this ϵ-phase occurs through a second order transition at elevated temperatures. The ζ-Fe2N-type phase is also observed as a minor constituent of a W2C0.91 powder; a consistent discussion of these results points out a general scheme for the structural evolution of these M2C1−x compounds as a function of the temperature; this conclusion is also correlated to the refinement of the ζ and ϵ-type structures which has been performed at room temperature.

Microstructural study of silica-doped zirconia ceramics

Abstract The aim of this study was to show the effects of small silica additions on the microstructures and mechanical properties of 3 mol% yttria-stabilised zirconia (3Y-TZP) ceramics. Experiments were conducted on different batches of 3Y-TZP (pure to 2.5 wt% silica-doped). Microstructures were characterised mainly by transmission electron microscopy (TEM), but also by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Silica was found at triple junctions, but neither at grain boundaries nor in the lattice. Undoped zirconia ceramics exhibited faceted grains and significant internal stresses, while doped zirconias showed a much more rounded microstructure and a lower level of internal stresses. Low-temperature degradation (LTD) and slow crack growth (SCG) measurements were conducted on the different batches. The addition of silica strongly increases LTD resistance without affecting the SCG behaviour. The microstructural origins of the different behaviours are discussed.

Neutron powder diffraction studies of transition metal hemicarbides M2C1−x—I. Motivation for a study on W2C and Mo2C and experimental background for an in situ investigation at elevated temperature

Abstract The crystallography of hexagonal hemicarbides of the sixth group transition metals (Mo2C, W2C) has been investigated by many workers, and an up to date review is presented herein (Section I); it appears that controversies concerning the various ordered structures (i.e. C6, ϵ-Fe2N and ζ-Fe2-N-type phases) exist in the case of W2C, while the crystallography of Mo2C seems to be more consistently established, although one can be surprised that it is significantly different from that of the similar W2C carbide (the ϵ-Fe2N-type phase was not observed in the system MoC). These remarks show that a high temperature (up to 2200°C) in situ powder neutron diffraction study on these compounds is needed in order to confirm their high temperature forms. In view of the peculiarities of such an experiment, we have concentrated our attention to detail in this first part the different aspects of our experimental approach (Section 2). The results will appear as part 2 of the present article.

Structural and magnetic properties of CoPt mixed clusters

In this present work, we report a structural and magnetic study of mixed Co58Pt42 clusters. MgO, Nb and Si matrix can be used to embed clusters, avoiding any magnetic interactions between particles. Transmission Electron Microscopy (TEM) observations show that Co58Pt42 supported isolated clusters are about 2nm in diameter and crystallized in the A1 fcc chemically disordered phase. Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence Wide Angle X-ray Scattering (GIWAXS) reveal that buried clusters conserve these properties, interaction with matrix atoms being limited to their first atomic layers. Considering that 60% of particle atoms are located at surface, this interactions leads to a drastic change in magnetic properties which were investigated with conventional magnetometry and X-Ray Magnetic Circular Dichroism (XMCD). Magnetization and blocking temperature are weaker for clusters embedded in Nb than in MgO, and totally vanish in silicon as silicides are formed. Magnetic volume of clusters embedded in MgO is close to the crystallized volume determined by GIWAXS experiments. Cluster can be seen as a pure ferromagnetic CoPt crystallized core surrounded by a cluster-matrix mixed shell. The outer shell plays a predominant role in magnetic properties, especially for clusters embedded in niobium which have a blocking temperature 3 times smaller than clusters embedded in MgO.

Chemical 3D tomography of 28nm high K metal gate transistor: STEM XEDS experimental method and results.

A new STEM XEDS tomography technique is proposed thanks to the implementation of multi EDX SDD detectors in analytical TEMs. The technique flow is presented and the first results obtained on a 28nm FDSOI transistor are detailed. The latter are compared with 2D XEDS analysis to demonstrate the interest of the slice extraction in all directions from a large analyzed volume without any 3D overlap effect issues.

Direct synthesis of amorphous silicon dioxide nanowires and helical self-assembled nanostructures derived therefrom

Bulk quantities of amorphous silica nanowires and novel braided helical silica nanostructures have been synthesized by a simple and cheap route. Actually, direct thermal treatment of a commercial silicon powder in the presence of graphite yields pure amorphous silica nanowires with lengths up to 500 µm for diameters in the range 10–300 nm. Electron Energy-Loss Spectroscopy (EELS) analysis indicates that the nanowires consist of Si and O elements in atomic ratio 1 ∶ 2, corresponding to SiO2. The formation of silicon dioxide nanowires can be related to the in-situ formation and subsequent decomposition of silicon oxide SiO (g). The nanowires are gathered to form bundles and braid-like nanostructures have been observed in some cases. The formation of these helical nanoobjects results from the self-assemblage of silica nanowires, may be due to the gas flowing during the process.

Direct synthesis of β-SiC and h-BN coated β-SiC nanowires

Abstract β-Silicon carbide (β-SiC) nanowires (NWs) have been grown by thermal treatment of commercial silicon particles disposed in a graphite crucible under nitrogen atmosphere. By the same way, treatment under argon of a mixture of a boron nitride (BN) based powder and silicon particles led to h-BN coated β-SiC nanowires. The structures of both nanoobjects have been investigated by HRTEM, EDX and EELS.

Evidence of the Inhomogeneous Ce3+ Distribution across Grain Boundaries in Transparent Polycrystalline Ce3+-Doped (Gd,Y)3Al5O12 Garnet Optical Ceramics

This paper characterizes the inhomogeneous rare earth activator distribution across grain boundaries in transparent rare earth doped optical ceramics. Ce3+ has been selected due to its high intensity fluorescence in visible range under blue or UV excitations, especially in (Gd,Y)3Al5O12 disordered garnet ceramic for scintillator application. Optical spectroscopy and visualization of grains and grain boundaries based on spatially resolved techniques as imaging confocal microscopy (ICM) and transmission electronic microscopy (TEM) have been used for 0.5% Ce3+-doped (Gd,Y)3Al5O12 ceramic. A strong Ce3+ segregation and spatial distribution between grains and grain boundaries were observed.

Correlation between the microstructural evolution of a 6061 aluminium alloy and the evolution of its thermoelectric power

Abstract The thermoelectric power (TEP) of a 6061 Al alloy was measured during isothermal ageing performed between 200 and 500°C. A correlation between the change in TEP and the precipitation kinetics of various metastable phases was established using TEM and HRTEM observations and resistivity measurements. It was demonstrated that the TEP kinetics allow an assessment of the residual concentration of solute in the final equilibrium state. Furthermore, it was shown that the non-monotonous TEP changes reflect the microstructural transformations occurring in the alloy. In particular, the transition between two phases can be detected, owing to the change of the intrinsic effect or of the chemical composition of the precipitates.