Quantitative analysis of EFTEM elemental distribution images

Abstract

Energy-filtering TEM (EFTEM) can be used to record elemental distribution images at nanometer resolution and with short acquisition times. In this paper we show how elemental maps can be converted into concentration maps. In order to demonstrate the application of the quantification procedures, we have chosen a sample consisting of CVD grown titanium carbonitride layers on a hard metal. Two approaches have been tested: Absolute quantification which is successfully applied to biological (amorphous) specimens yields a concentration map in terms of atoms per unit area. However, it turned out that this method is not suitable for crystalline materials due to diffraction and/or thickness variation effects. In the second method, atomic ratio maps are calculated from two elemental maps by ratioing the elemental maps and dividing them by the partial ionization cross-sections (or k-factors). This method yields concentration maps in terms of atomic ratios offering the advantage that diffraction and/or thickness variation effects are eliminated. Therefore, this method is well suited for the quantification of crystalline materials science specimens. In the second part of the paper we describe how related sets of elemental maps can be examined and combined in one chemical phase map. This can be provided by scatter diagram analysis (2-dimensional) and automatic classification procedures (n-dimensional) that show how intensities of corresponding pixels are correlated. These techniques have been applied to a typical material science specimen (Si-nitride ceramics with SiC and carbon inclusions) so that the reader may get a feeling for the advantages and limitations of these techniques in EFTEM-investigations. Finally, it is shown that the scatter diagram technique can be also applied to atomic ratio maps thus providing fully quantitative chemical phase maps.