The local coordination environment of the silicates and oxides of Hf and Zr have been investigated using both experimental ELNES data and theoretical modelling of the near-edge structures
Summary We review the current state of the art in EELS fingerprinting by computer simulation, focusing on the bandstructure approach to the problem. Currently calculations are made using a one electron theory, but we describe in principle the way to go beyond this to include final state effects. We include these effects within the one electron framework using the Slater transition state formula and assess the errors involved. Two examples are then given which illustrate the use of the one electron approximation within density functional theory. Our approach is to combine predicted atomic structure with predicted electronic structure to assist in fingerprinting of complex crystal structures.
A previous study of chromite and ferrite spinels revealed energy-loss near-edge structure (ELNES) in the oxygen K-edge that could not be reproduced in non-spin polarised calculations. Chromite and ferrite spinels typically undergo transitions to long range ordered magnetic structures at temperatures below ∼15K. A model in which dynamic magnetic short range order (SRO) persists above the Néel temperature until 100K has been proposed using neutron powder diffraction. In the TEM, the interaction time of the fast electron with the specimen is sufficiently short for dynamic magnetic interactions to influence the observed ELNES at 300K. Here we present new spin polarised calculations performed using the commercially available codes FEFF8.2 and Wien97. The calculated oxygen K-edge ELNES show improved agreement with experiment when magnetic interactions are included in the calculation.
In conclusion, this paper reports a number of significant developments in III-V MOSFET devices. Retaining a subthreshold slope of 60-70 mV/decade for gate lengths down to 100 nm with an EOT of 3.4 nm shows for the first time that the flatband mode device architecture is tolerant to short channel effects. In addition, a generic silicon compatible process flow for the realization of fully self-aligned III-V MOSFETs has been demonstrated and shown capable of realizing 100 nm gate length enhancement mode devices.
SUMMARY Modern collimator design for energy‐dispersive X‐ray detectors requires very accurate positioning of the crystal/collimator assembly in order to achieve the maximum solid angle of collection for the irradiated volume on the specimen. Thus it is important to have a method of checking the alignment of the detector when mounted on the microscope and under vacuum. This paper describes a number of techniques, principally X‐ray mapping, for performing such an alignment check. These techniques are applicable to windowless detectors as well as to those with integral windows which will support atmospheric pressure. Methods of obtaining the non‐standard modes of microscope operation suitable for this task are described, and some suggestions are made for ways of moving the crystal/collimator assembly and monitoring this movement while it is in progress.
Abstract The inelastic scattering of fast electrons by the excitation of L-shell electrons at a stacking fault in silicon has been studied with a scanning transmission electron microscope. It was found that the bright-field stacking fault contrast is preserved in the filtered L-shell-loss signal at 100 eV. This result is discussed in terms of the delocalization of the excitation mechanism. It is concluded that localization effects will typically become significant only for energy transfers greater than 1 keV from a fast electron of energy 80 keV.
AbstractA study has been undertaken of four vanadium based steels which have been processed by a simulated direct charging route with processing parameters typical of thin slab casting, where the cast product has a thickness of 50 to 80 mm (in this study 50 mm) and is fed directly to a furnace to equalise the microstructure prior to rolling. In the direct charging process, cooling rates are faster, equalisation times shorter, and the amount of deformation introduced during rolling less than in conventional practice. Samples in this study were quenched after casting, after equalisation, after the fourth rolling pass, and after coiling, to follow the evolution of microstructure. The mechanical and toughness properties and the microstructural features might be expected to differ from equivalent steels which have undergone conventional processing. The four low carbon steels (~0.06 wt-%) which were studied contained 0.1 wt-%V (V – N), 0.1 wt-%V and 0.010 wt-%Ti (V – Ti), 0.1 wt-%V and 0.03 wt-%Nb (V – Nb), and 0.1 wt-%V, 0.03 wt-%Nb and 0.007 wt-%Ti (V – Nb – Ti). steels V – N and V – Ti contained around 0.02 wt-% N, while the other two contained about 0.01 wt-%N. The as cast steels were heated at three equalising temperatures of 1050°C, 1100°C, or 1200°C and held for 30 – 60 min before rolling. Optical microscopy and analytical electron microscopy, including parallel electron energy loss spectroscopy (PEELS), were used to characterise the precipitates. In the as cast condition, dendrites and plates were found. Cuboid particles were seen at this stage in steel V – Ti, but they appeared only in the other steels after equalisation. In addition, in the final product of all the steels, fine particles were seen, but it was only in the two titanium steels that cruciform precipitates were present. PEELS analysis showed that the dendrites, plates, cuboids, cruciforms, and fine precipitates were essentially nitrides. The two Ti steels had better toughness than the other steels but inferior lower yield stress values. This was thought to be, in part, due to the formation of cruciform precipitates in austenite, thereby removing nitrogen and the microalloying elements, which would have been expected to precipitate in ferrite as dispersion hardening particles.Keywords: PARTICLE SIZE DISTRIBUTIONEVOLUTIONTHIN SLAB CASTINGVANADIUM MICROALLOYED STEELSSIMULATION
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