Improved imaging of secondary phases in solids by energy-filtering TEM

Energy-filtering transmission electron microscopy (EFTEM) has been used for imaging of secondary phases in materials, e.g. precipitates and grain boundary phases. The investigations have been performed with a Philips CM20 equipped with a Gatan imaging filter at 200 kV acceleration voltage. In order to visualize the secondary phases in a steel sample we have recorded jump ratio images using the ionization edge of the matrix element (Fe M23-edge, division of post-edge image by pre-edge image). This method reduces unwanted diffraction contrast in crystalline specimens considerably when compared with the elemental maps which have been recorded with the three window method. In this work we show that an essential improvement of the jump ratio method is still possible by recording the jump ratio images under rocking beam illumination, because residual diffraction contrasts are completely eliminated in these images. This new method allows the rapid and unequivocal visualization of all chemical heterogeneities in crystalline solids (and also amorphous materials) at a nanometer scale.