Development of a new analytical electron microscopy technique to quantify the chemistry of planar defects and to measure accurately solute segregation to grain boundaries.
A new technique of analytical transmission electron microscopy called ConceptEM has been developed for determining highly accurately small amounts of solute or dopant atoms incorporated into well-defined planar defects such as stacking faults, grain boundaries or interfaces. The method is based on recording series of analytical spectra taken with different electron beam diameters on the same position centred above a defect that is orientated either edge-on or slightly inclined with respect to the electron beam. It can be applied to energy-dispersive X-ray spectroscopy or electron energy-loss spectroscopy and necessitates only a nano-probe modus but no scanning unit. Reliability and accuracy have been tested numerically under various conditions using simulations for a specific geometry, as a function of specimen thickness, material, acceleration voltage, collection angle, random beam displacements and solid solubility. The accuracy has been found to be substantially better (by factors of 5-10) than that of any other current standard technique based on single measurements. Our calculations suggest an accuracy in the determination of the Gibbsian solute excess at a special grain boundary down to +/- 1% of a monolayer, i.e. around +/- 0.1 atoms nm(-2) under typical experimental conditions, with a maximum error about twice as large. The parameter limiting a straightforward analysis is found to be the solid solubility, which itself, however, can be measured accurately by the technique so that it can be taken into account quantitatively and the above-stated precision is retained.
Institut für Anorganische Chemie, Universität Bonn, Römerstr. 164, 53117 Bonn, Germany. walther@sg4.elmi.uni-bonn.de
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