Local crystal textures: experimental techniques and future trends

Abstract

Transmission electron microscopy enables crystal textures to be determined in small specimen areas by measuring SAD or RHEED pole figures. SAD (transmission) pole figures are acquired either by deflecting the diffraction patterns or the primary beam along a cone of 2 · Θ semi-apex angle, or by grabbing the whole diffraction patterns with a CCD camera. RHEED pole figures are obtained from the bulk surface by rotating, at grazing beam incidence, the specimen about its surface normal and grabbing a sequence of RHEED patterns. Since the specimen has to be tilted through large angles, spatial resolution is limited to 1.5 μm in SAD and to 0.1 mm in RHEED pole figure measurement. The major benefits over x-ray diffraction are a high speed and sensitivity. Spatial resolution of individual grain orientation measurement is in the range of 0.1 μm in the SEM with backscatter Kikuchi patterns (BKP) from the bulk, respectively 10 nm in the TEM with transmission Kikuchi patterns (TKP). Using a computer controlled SEM and digital beam scan, more than 10,000 grain orientations per hour are acquired unattendedly. Crystal orientation maps (COM) are constructed by a pseudo-color representation of the individual orientations in the area under study. An x-ray scanning apparatus with energy dispersive spectrometer enables the acquisition of texture as well as element distribution (X-ray microfluorescence analysis) maps at a spatial resolution of some 10 μm.