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To analyze extended time series of high resolution images, we have employed automated frame-by-frame comparisons that are able to detect dynamic changes in the structure of a grain boundary in Au. Using cumulative averaging of images between events allowed high resolution measurements of the atomic relaxation in the interface with sufficient accuracy for comparison with atomistic models. Cumulative averaging was also used to observe the structural rearrangement of atomic columns at a moving step in the grain boundary. The technique of analyzing changing features in high resolution images by averaging between incidents can be used to deconvolute stochastic events that occur at random intervals and on time scales well beyond that accessible to single-shot imaging. [ABSTRACT FROM AUTHOR]

Green rust (GR) as sodium sulphate form, NaFe(II)6Fe(III)3(OH)18(SO4)2 · 12H2O, is reacted with an aqueous solution of neptunyl ions (NpO2+) and the resulting Np(IV) solid phase is investigated at a nanometer scale by different transmission electron microscopy (TEM) techniques, including high-resolution TEM (HRTEM), high-angle annular dark-field scanning TEM (HAADF-STEM), energy-dispersive X-ray spectroscopy (EDXS), and electron energy-loss spectroscopy (EELS). The aim of the analyses is to achieve insight into the potential immobilization mechanism for Np(V) in the context of safety assessment of a nuclear-waste repository. The neptunium is found to be immobilized at the edge of the green rust platelets, in a rim composed of nanocrystallites about 2-3.5 nm in size. The EELS results and more particularly the HRTEM findings are consistent with NpO2 crystallizing in a fluorite-type structure. Furthermore, the Np-O4,5 edges recorded by EELS at the Np(IV) phase are presented, expanding the EELS-data set currently available in the literature for Np. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) decorated with platinum (Pt) nanoparticles (NPs) have been characterized using a cold field-emission scanning electron microscope (SEM) and a high resolution field-emission transmission electron microscope (TEM). With this particular composite material, the complementary nature of the two instruments was demonstrated. Although the long CNTs were found to be mostly bent and defective in some parts, the nucleation of Pt occurred randomly and uniformly covered the CNTs. The NPs displayed a large variation in size, were sometimes defective with twins and stacking faults, and were found to be faceted with the presence of surface steps. The shape and size of the NPs and the presence of defects may have significant consequences on the activity of the Pt catalyst material. Also, thin layers of platinum oxide were identified on the surface of some NPs. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the formation of super saturated solid solution in the binary Cu–Fe system was investigated. Three powder blends with 30, 50 and 70wt.% of Fe were milled for different times to 96h. The variations of lattice parameter and inter-planar spacing were calculated and analyzed using X-ray diffraction analysis (XDA). The anisotropy of lattice deformation in the FCC phase was studied and the obtained results were compared to milled pure Cu powder. Furthermore, crystallite size was calculated using Scherer formula in comparison with Rietveld full profile refinement method. Considering the previous studies about the formation of non-equilibrium FCC and BCC phases, the phase evolution has been discussed and the proportion of each phase was calculated using Rietveld refinement method. Supplementary studies on the evolution of microstructure and formation of solid solution were carried out using high resolution transmission electron microscopy (HRTEM). Finally, high angle annular dark field (HAADF) imaging was utilized to find out the level of homogeneity in the resulting phases. While true alloying takes place in each phase, the final structure consists of both FCC and BCC nano-crystallites. [Copyright &y& Elsevier]

Abstract: By means of high resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field image technique (HAADF), morphological of plate-shaped σ phase and interfacial characteristics between plate-shaped σ phase and γ phase in Ni-based single crystal superalloys have been studied. On the basis of HRTEM observations, an atomic structural interface between σ phase and γ phase with a step has been proposed. σ Phase has the relationship of [001]γ//[11 ]σ, ( 20)γ//( 10)σ, ( 0)γ//(111)σ; [011]γ//[110]σ, (1 1)γ//(00 )σ with the γ phase. The compositional characteristics of the σ phase which are rich in more heavy elements, such as W, Re, Cr and Ru, has also been clearly revealed by the HAADF imaging technique and Energy Dispersive X-Ray Spectroscopy (EDS) mapping analysis. [Copyright &y& Elsevier]

Abstract: Titania nanotubes synthesized by alkali hydrothermal method were used to support 5–20wt.% of WO x by wet impregnation method. Samples were characterized by in situ thermo-Raman spectroscopy, electronic microscopy and X-ray diffraction. Initially and below 400°C, WO x species have octahedral coordination as isolated species. After annealing at 500°C, the nanotubular support collapsed and transformed into anatase. This event released Na+ ions that reacted with surface WO x species converting into sub-nanometric sodium tungstate (Na2WO4) particles, homogeneously dispersed on the support. At higher temperature, that is at 700°C and 800°C, Na2WO4 nanoparticles were detected on samples with W content ≤10wt.%, whereas a mixture of Na2WO4 and Na2W2 O7 was obtained on samples with W content above 15wt.%. A very thin layer of sodium tungstate covered the titania (anatase or rutile, depending on W loading) support after annealing at 800°C yielding core–shell particles, with titania phase in the core and Na2WO4 and/or Na2W2O7 on the shell. [ABSTRACT FROM AUTHOR]

We review a combination of theoretical and experimental techniques that have been applied to the study of grain boundaries in SrTiO3, with particular attention to Σ3 and ()-oriented grain boundaries. Electron microscopy, which includes high-resolution transmission and high-angle annular dark-field methods, is discussed, with successful applications to mapping atomic columns and testing theoretical models. Then, we compare and contrast different techniques of electron holography that may be used to map electrostatic potentials. Problems with the current methods of interpretation in holography and impedance spectroscopy are highlighted in an attempt to reconcile their respective estimates of electrostatic potentials at grain boundaries. Then, standard theoretical tools for the atomistic simulation of boundary structures are critically reviewed, which include classical potentials and density functional theory. A promising genetic algorithm for discovering low-energy grain boundary structures is described and tested. Finally, the synergy of experiment, theory, and simulation that is required to understand boundaries is demonstrated, and we identify major challenges to understanding multicomponent systems. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure and chemistry of the high-k gate dielectric significantly influences the performance of metal–insulator–metal (MIM) and metal–oxide–semiconductor devices. In particular, the local structure, chemistry, and inter-layer mixing are important phenomena to be understood. In the present study, high resolution and analytical transmission electron microscopy are combined to study the local structure, morphology, and chemistry in MIM capacitors containing a Hf-based high-k dielectric. The gate dielectric, bottom and gate electrodes were deposited on p-type Si(100) wafers by electron beam evaporation. Four chemically distinguishable sub-layers were identified within the dielectric stack. One is an unintentionally formed 4.0nm thick interfacial layer of Ta2O5 at the interface between the Ta electrode and the dielectric. The other three layers are based on HfN x O y and HfTiO y , and intermixing between the nearby sub-layers including deposited SiO2. Hf-rich clusters were found in the HfN x O y layer adjacent to the Ta2O5 layer. [Copyright &y& Elsevier]

Abstract: The objective of this study is to demonstrate the various artificial features introduced into metallic amorphous alloys by improper TEM sample preparation. Such artifacts are often confused with the intrinsic microstructures when examining metallic glasses under TEM. The electropolishing and ion milling procedures are compared in terms of their merits/drawbacks for avoiding/inducing artifacts in metallic glass samples. [Copyright &y& Elsevier]

VDM 780 Premium is a recently developed Ni-based superalloy designed for working at high service temperatures (above 650 °C) while keeping the good workability of alloy 718. VDM 780 Premium is based on the austenitic matrix (γ phase) strengthened by intermetallic Ni 3 Al-like precipitates (γ' phase, fcc L1 2 structure). Other co-precipitates may be formed in function of the applied heat treatment, such as Ni 3 Nb-based (δ phase, orthorhombic DO a structure) or Ni 3 Ti-based (η phase, hexagonal DO 24 structure) precipitates. The amount as well as the size and morphology of the different precipitates depend on the heat treatments performed on the alloy, playing an important role in improving the creep properties or the behavior during forging and recrystallization. This work contains a complex study using various techniques of analytical electron microscopy and synchrotron diffraction intended to clarify the structure of the high-temperature phase formed in the newly developed VDM 780 Premium alloy. The atomic structure of the high-temperature plate-like precipitates formed in VDM 780 Premium after two different thermal treatments has been investigated in relation with the surrounding matrix lattice, proving the stacked δ/η structure of the precipitates. Image 1 • High temperature phase of VDM 780 Premium Ni superalloy shows a layered structure. • Synchrotron and HRTEM show that the layered structure consists on δ and η phases. • The thickness of the plate-like precipitates depends on temperature history. • The η phase is twice as much inside the precipitates with respect to the δ phase. • The chemical composition of the δ and η shows a deficit of Nb or Ti, respectively. [ABSTRACT FROM AUTHOR]