Energy-filtering transmission electron microscopy in materials science

Abstract

Energy-filtered transmission electron microscopy (EFTEM) can be used to acquire elemental distribution images at high lateral resolution within short acquisition times. In this article, we present an overview of typical problems from materials science which can be preferentially solved by means of EFTEM. In the first example, we show how secondary phases in a steel specimen can be easily detected by recording jump ratio images of the matrix element under rocking beam illumination. Secondly, we describe how elemental maps can be converted into concentration maps. A Ba-Nd-titanate ceramics serves as a typical materials science example exhibiting three different compounds with varying composition. In order to reduce diffraction and/or thickness variation effects which may be a problem for quantification of crystalline specimens, we calculated atomic ratio maps by dividing two elemental maps and subsequent normalizing by the partial ionization cross-sections (or k-factors). Additionally, the atomic ratio maps are correlated using the scatter diagram technique thus leading to quantitative chemical phase maps. Finally, we show how the near-edge structures (electron energy-loss near edge fine structures, or ELNES) can be used for mapping chemical bonding states thus differentiating between various modifications of an element. In order to distinguish between diamond and non-diamond carbon in diamond coated materials, we have investigated a diamond layer on a substrate with the help of ELNES mapping utilizing the π*-peak of the C-K ionization edge.