B.J. Kooi

Electron diffraction and high-resolution transmission electron microscopy of the high temperature crystal structures of GexSb2Te3+x (x=1,2,3) phase change material

The crystal structures of GeSb2Te4, Ge2Sb2Te5, and Ge3Sb2Te6 were determined using electron diffraction and high-resolution transmission electron microscopy. The structure determined for the former two crystals deviates from the ones proposed in the literature. These crystal structures were developed jointly upon cooling of liquid Ge2Sb2Te5. A stacking disorder parallel to the basal plane was observed that increases with increasing cooling rates. For the GexSb2Te3+x (x=1,2,3) crystals it is shown that an a,b,c stacking holds with an alternating stacking of x GeTe double layers identically present in binary GeTe and one Te–Sb–Te–Te–Sb– repeat unit also present in binary Sb2Te3. A stacking disorder is a logical consequence of building crystals with these two principal units. On the other hand, it is likely that all stable crystals of the Ge–Sb–Te systems are an ordered sequence of these two units. Some of the implications of these findings of the stable and metastable crystal structures that develop from am...

In situ transmission electron microscopy study of the crystallization of Ge2Sb2Te5

Crystallization of amorphous Ge2Sb2Te5 films (10, 40, and 70 nm thick) was studied by in situ heating in a transmission electron microscope (TEM). Electron irradiation-induced crystallization is possible at room temperature using a 400 kV electron beam where the reciprocal of the incubation time for crystallization scales linearly with the current density during electron irradiation. Without electron-beam exposure, crystallization starts at 130 °C. Using a 200 kV beam, crystallization also occurred in the temperature interval between 70 and 130 °C. In principle, electron irradiation always affects the crystallization kinetics, strongly promoting nucleation and probably not hampering growth. At 130 °C without electron-beam exposure, 400 nm diameter colonies of 10–20 nm grains develop in the 40 and 70 nm thick films showing clear symmetric bending contour contrast. These spherulites prefer to have in their center the 〈111〉 zone axis of the Fm3m structure perpendicular to the surface of the film and show a ...

The evolution of microstructure in a laser clad TiB-Ti composite coating

Abstract The microstructure of a TiB/Ti composite coating, obtained by laser cladding a Ti–6Al–4V substrate with a Ti/TiB2 powder mixture, was scrutinized using transmission electron microscopy. TiB showed three different morphologies: fine needles (200 nm diameter, 15 μm length); plates (thickness 1 μm, short length 3 μm and long length 15 μm); and coarse needles (diameter 3 μm and length of 50 μm). All TiB is composed of both the stable B27 and the metastable Bf crystal structures. Intimate mixing of B27 and Bf is possible because B27(200) planes fit excellently on Bf(110) or ( 1 1 0 ) planes (with B27[010]//Bf[001]) that easily leads to stacking disorder. Aspects of disorder are quantitatively analyzed using high-resolution transmission electron microscopy (HRTEM). Throughout the fine needles, extensive stacking disorder occurs. In the plates a core of B27 (with relatively low stacking-fault (SF) density) is present, with faulted Bf on the outer surfaces that has a rough but fully faceted interface with the Ti matrix. The coarse needles consist predominantly of nearly defect-free B27. It is noteworthy about the coarse needles that they have a large core composed of Ti. On a much finer scale Ti is also dispersed in the plates and fine needles. It will be shown that the differences in microstructure among the three types of TiB morphologies provide important clues about the evolution of the TiB under the conditions of rapid growth.

Electron microscopy of reaction layers between SiC and Ti-6Al- 4V after laser embedding

Abstract A detailed electron microscopic examination of the interface between Ti and SiC is concentrated on. The metal–matrix-composites (MMCs) are produced by the laser particle injection processing route. SiC particles are entrapped during solidification of liquid Ti. Since the injected particles partially dissolve, depending on the process conditions, new phases are formed in the matrix. The degree of dissolution will significantly influence the mechanical performance of the MMC. In particular, the interfacial region with the various phases between Ti and SiC particles is closely investigated with (high resolution) transmission electron microscopy. Furthermore, hardness indents are performed to examine the crack initiation and the crack propagation behaviour at the interface.

On the crystallization of thin films composed of Sb3.6Te with Ge for rewritable data storage

This article addresses the crystallization of amorphous Sb3.6Te films (40 nm thick) and 5 at. % Ge containing Sb3.6Te films (10, 20, and 40 nm thick) as studied with transmission electron microcopy using in situ annealing. These materials exhibit growth-dominated crystallization, in contrast to the usual Ge2Sb2Te5 that shows nucleation-dominated crystallization. Particularly the crystal-growth velocity in these systems has been measured as a function of temperature from which the activation energy for growth can be derived. The strong effect of the 5 at. % Ge addition on the total crystallization behavior is revealed by the following four phenomena: Ge increases the crystallization temperature (from 95 to 150 °C), increases the activation energy for growth (from 1.58 to 2.37 eV), increases the nucleation rate and decreases the growth anisotropy. The crystallites have a special transrotational structure and a mechanism responsible for the development of this special structure is delineated.

On the Oxidation of α-Fe and ε-Fe2N1-z: I. Oxidation Kinetics and Microstructural Evolution of the Oxide and Nitride Layers

The oxidation of α-Fe and ɛ-Fe2N1−z at 573 K and 673 K in O2 at 1 atm was investigated by thermogravimetrical analysis, X-ray diffraction, light-optical microscopy, scanning electron microscopy and electron probe X-ray microanalysis. Upon oxidation at 573 K and 673 K, on α-Fe initially α-Fe2O3 develops, whereas on ɛ-Fe2N1−z initially Fe3O4 develops. In an early stage of oxidation the oxidation rate of ɛ-Fe2N1−z appears to be much larger than of α-Fe. This can be attributed largely to an effective surface area available for oxygen uptake, which is much larger for ɛ-Fe2N1−z than for α-Fe due to the porous structure of ɛ-Fe2N1−z as prepared by gaseous nitriding of iron. The development of a magnetite layer in-between the hematite layer and the α-Fe substrate, at a later stage of oxidation, enhances layer-growth kinetics. After 100 min oxidation at 673 K the (parabolic) oxidation rates for α-Fe and ɛ-Fe2N1−z become about equal, indicating that on both substrates the oxide growth is controlled by the same rate limiting step which is attributed to short-circuit diffusion of iron cations. Oxidizing ɛ-Fe2N1−z increases the nitrogen concentration in the remaining ɛ-iron nitride, because the outward flux of iron cations, necessary for oxide growth, leads to an accumulation of nitrogen atoms left behind.

Hybrid Polyamide/Silica Nanocomposites : Synthesis and Mechanical Testing

A hybrid inorganic-polymer composite was formed through nanosize silica filler particles ( 0.5.

Gas-phase synthesis of magnesium nanoparticles: A high-resolution transmission electron microscopy study

Magnesium nanoparticles with size above 10nm, prepared by gas-phase syntheses, were investigated by high-resolution transmission electron microscopy. The dominant particle shape is a hexagonal prism terminated by Mg(0002) and Mg{101¯0} facets. Oxidation of Mg yields a MgO shell (∼3nm thick), which has an orientation relation with the Mg. Inhomogeneous facet oxidation influences their growth kinetics resulting in a relatively broad size and shape distribution. Faceted voids between Mg and MgO shells indicate a fast outward diffusion of Mg and vacancy rearrangement into voids. The faceting of polar {220} planes is assisted by electron irradiation.

An Evaluation of the Fe-N Phase Diagram Considering Long-Range Order of N Atoms in γ'-Fe4N1-x and ε-Fe2N1-z

The chemical potential of nitrogen was described as a function of nitrogen content for the Fe-N phases α-Fe[N], γ′-Fe4N1-x, and ε-Fe2N1-z. For α-Fe[N], an ideal, random distribution of the nitrogen atoms over the octahedral interstices of the bcc iron lattice was assumed; for γ′-Fe4N1-x. and ε-Fe2N1-z, the occurrence of a long-range ordered distribution of the nitrogen atoms over the octahedral interstices of the close packed iron sublattices (fcc and hcp, respectively) was taken into account. The theoretical expressions were fitted to nitrogen-absorption isotherm data for the three Fe-N phases. The α/α+ γ′, α +γ′/γ′, γ′/γ′ + ε, andγ′ + ε/ε phase boundaries in the Fe-N phase diagram were calculated from combining the quantitative descriptions for the absorption isotherms with the known composition of NH3/H2 gas mixtures in equilibrium with coexisting α andγ′ phases and in equilibrium with coexistingγ′ and ε phases. Comparison of the present phase boundaries with experimental data and previously calculated phase boundaries showed a major improvement as compared to the previously calculated Fe-N phase diagrams, where long-range order for the nitrogen atoms in theγ′ and ε phases was not accounted for.

Mega-electron-volt ion beam induced anisotropic plasmon resonance of silver nanocrystals in glass

30 MeV Si ion beam irradiation of silica glass containing Ag nanocrystals causes alignment of Ag nanocrystals in arrays along the ion tracks. Optical transmission measurements show a large splitting of the surface plasmon resonance bands for polarizations longitudinal and transversal to the arrays. The splitting is in qualitative agreement with a model for near-field electromagnetic plasmon coupling within the arrays. Resonance shifts as large as 1.5 eV are observed, well into the near-infrared.