Quantitative analysis of an Yb³⁺-doped YAG optical ceramic at the atomic level by STEM-HAADF

EMC2012: The 15th European Microscopy Congress, 16th - 21st September 2012, Manchester Central, United Kingdo

Multi-L1₀ domain CoPt and FePt nanoparticles revealed by electron microscopy

The atomic structure of CoPt and FePt nanoparticles (with a diameter between 2 and 5 nm) has been studied by transmission electron microscopy. The particles have been produced by a laser vaporization cluster source and annealed under vacuum in order to promote chemical ordering. For both alloys, we observe a coexistence of crystalline and multiply twinned particles with decahedral or icosahedral shapes. In addition to particles corresponding to a single L1₀ ordered domain, we put into evidence that even small particles can display several L1₀ domains. In particular, the chemical order can be preserved across twin boundaries which can give rise to spectacular chemically ordered decahedral particles made of five L1₀ domains. The stability of such structures, which had been recently predicted from theoretical simulations, is thus unambiguously experimentally confirmed. © 2013 American Physical Society.F. Tournus, K. Sato, T. Epicier, T. J. Konno, and V. Dupuis, Phys. Rev. Lett. 110, 055501, 2013

Effects of heat treatments on the microstructure and mechanical properties of a 6061 aluminium alloy

International audienceThis paper describes the mechanical behavior of the 6061-T6 aluminium alloy at room temperature for various previous thermal histories representative of an electron beam welding. A fast-heating device has been designed to control and apply thermal loadings on tensile specimens. Tensile tests show that the yield stress at ambient temperature decreases if the maximum temperature reached increases or if the heating rate decreases. This variation of the mechanical properties is the result of microstructural changes which have been observed by Transmission Electron Microscopy

Multi-L1₀ domain CoPt and FePt nanoparticles revealed by electron microscopy

EMC2012: The 15th European Microscopy Congress, 16th - 21st September 2012, Manchester Central, United Kingdo

Low temperature precipitation kinetics of niobium nitride platelets in Fe

International audienceSingle plane platelets of niobium nitride have been observed to form in a Fe-Nb-N alloy during ageing at 600 degrees C, using High Resolution Electron Microscopy, Field Ion Microscopy and Atom Probe Tomography. Small-angle neutron scattering has been used to investigate the kinetics of formation of these platelets. They are shown to nucleate in less than 5 min at this ageing temperature, and subsequently to grow in-plane to a size of about 10 nm without experiencing any change in thickness

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 Dichro\"{i}sm (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

Dynamic study of carbon nanotube growth and catalyst morphology evolution during acetylene decomposition on Co/SBA-15 in an environmental TEM

International @ SURFACES+FCA:MAO:ATUInternational audienceNon

CARACTERISATION FINE DE CARBURES REFRACTAIRES PAR MICROSCOPIE ELECTRONIQUE EN TRANSMISSION

l'intérêt de la Microscopie Electronique en Transmission, et en particulier des techniques de haute résolution (champ sombre en faisceau faible et obtention de franges de réseaux cristallins), pour la caractérisation fine des dislocations et des microstructures ordonnées dans les carbures métalliques est illustré par quelques exemples, VC~0.83, Nb6C5, Mo2C et W2C.the interest of the weak beam dark field and lattice imaging techniques in Transmission Electron Microscopy applied to the fine characterisation of dislocations and ordered microstructures in metallic carbides is shown through various examples, VC~0.83, Nb6C5, Mo2C and W2C