Papers by Keyword: High Resolution Electron Microscopy (HREM)

Abstract: The aim of the present work is to study the evolution and the annihilation of inversion domain boundaries in 3C-SiC during growth. For this investigation conventional and high resolution transmission electron microscopy were employed. It is shown that the physical mechanism which results in the annihilation of inversion domain boundaries in 3C-SiC starting from the 3C-SiC/Si interface is the change of the crystallographic planes in which inversion domain boundaries propagate into the {111} ones. In all cases modeling and simulation analysis by EMS software [1] are in agreement with the experimental results.

Abstract: Strains around a constricted matrix dislocation in a coherent twin grain boundary in germanium is measured by a combination of high-resolution electron microscopy and geometric phase analysis. Whilst strains in the grains on either side of the twin boundary agree closely with the isolated dislocation case, significant additional strains are localized at the boundary plane. By comparing the stresses and strains across the boundary plane, values for the elastic modulus of the twin boundary are determined. They are found to exhibit a drastic decrease as compared to the bulk and this is interpreted in terms of the non-equilibrium configuration of the boundary.

Abstract: In this paper, we characterized atomic structure of a Σ = 3, [110]/{112} grain boundary in a yttria-stabilized cubic zirconia bicrystal. High-resolution transmission electron microscopy (HRTEM) clearly revealed that the grain boundary migrated to form {111}/{115} periodical facets, although the bicrystal was initially joined so as to have the symmetric straight boundary plane of {112}. Atomic-scale process for the facet growth could be modeled by the continuous flippings of atoms at the boundary core.

Abstract: Crystalline approximants structurally related to decagonal quasicrystal in the as-cast and heat-treated Al75Pd15Fe10 alloys and defect structures in them have been studied by means of high-resolution electron microscopy (HREM). Structural defects of linear and planar types were found to exist extensively in the orthorhombic ε16-phase formed in the as-cast Al75Pd15Fe10 alloy. In contrast with the distribution and configuration of the defects in the as-cast ε16-phase, we found that high-temperature heat treatment promotes the formation of a kind of regular network of structural defects in the ε16-phase. This suggests that rearrangements of atom clusters and as well as defects occurred due to the heat treatment. The relationship between the distribution of atom clusters and the configuration of defects will be discussed.

Abstract: By means of a combination of high-resolution electron microscopy (HREM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) techniques, we have directly revealed that periodic arrangements in different manners for flattened hexagons constructed with atom columnar clusters can form two Al-Ni-Rh crystalline approximant phases. In contrast to periodic arrangements of flattened hexagons, configurations and distributions of various defects in these structurally-complicated alloy phases have been examined and their structural characteristics discussed. HREM observations clearly show that structural defects in Al-Ni-Rh crystalline approximants are of phason type and they are correlated with incorrect arrangements of atom columnar clusters. The distribution of high density planar defects can destroy the long-range periodicity in at least one direction in the pseudo decagonal symmetry plane. By means of the HAADF-STEM imaging technique, the existence of ill-formed atom columnar clusters in the core area of a linear defect, which is usually not visible in HREM observations, has been clearly revealed.

Abstract: Interfacial microstructure of TiN-TiB2 composite, which was synthesized by hot shock compaction combined explosively shock condolidation and self-propagating high-temperature synthesis, was investigated by transmission electron microscopy (TEM). In the TiN-TiB2 composite included 60mol% TiN, an experimentally measured average grain size of the both TiN and TiB2 was approximately 500nm, and it decreased rather than those of the raw powders. By the conventional TEM observations, we clarified that there was a specific orientation relationship between cubic TiN and hexagonal TiB2. The high resolution electron microscopy (HREM) observations revealed that the TiN/TiB2 interphase boudnaries were atomically flat. We also observed grain boundaries of the composite and found that no secondary phases such as amorphous phase and precipitates were observed at the grain boundaries in the composite.

Abstract: By means of high resolution transmission electron microscopy (HREM) and high-angle annular dark-field image technique (HAADF), morphological, structural and compositional characteristics of the precipitates in the Mg-4Y-3Nd alloy aged at 200°C for different periods of time have been studied. On the basis of HREM observations, an atomic structural model for the β’-precipitate with an orthorhombic unit cell has been proposed. The characteristic distribution of the precipitates which are rich in rare-earth elements (Y, Nd) has been clearly revealed by the HAADF imaging technique.

Abstract: A Zr-Ta-Nb alloy made of biocompatible alloy elements only and consisted of single β-phase with bcc structure was prepared by conventional solidification. Electron diffraction, transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM) were used to examine microstructural evolutions of the β-Zr-Ta-Nb alloy subjected to different heat treatments. The results show that the metastable β-phase in the as-solidified Zr-Ta-Nb alloy turned to decompose when annealed at 400°C and this led to the formation of a highly strained structure containing nanosized precipitates and local disordered regions. Striking phase separation including the formation of the equilibrium α-phase was found to occur at 600°C. By means of nanosized electron-probe analysis of energy dispersive X-ray spectroscopy, the compositions for the nanosized phases formed due to different heat treatments were analysis.

Abstract: Ptx-Pd(1-x) nanoparticles supported on amorphous silica (SiO2) were prepared by wetness impregnation techniques with choroplatinic acid (H2PtCl6) and palladium chloride (PdCl4) with different concentrations of Pt and Pd at about 1% in overall metallic weight. The purpose of this study was to evaluate the physical properties as physisorption (BET), X Ray Diffraction XRD, High Resolution Electron Microscopy HREM, Transmission Electron Microscopy TEM couple with XEDS energy dispersive X-ray spectrometry and chemical properties to determine the activity in cyclohexene reaction of these materials supported. Bimetallic nanoparticles are made of a single solid solution of Pt and Pd atoms, and the particles diameter of about 3-5 nm was estimated by HREM and Bright field image, the Pt-Pd nanoparticles were found mainly to have truncated cuboctahedral shape with fcc packing,. by using energy dispersive X-ray spectrometry (XEDS) and their values were found to be close to the stochiometric relative concentrations in weight of the metals in the precursor aqueous solution.