Influence of 2s Bloch wave state excitations on quantitative HAADF STEM imaging

In this paper the influence of 2s Bloch wave states on high angle annular dark field image contrast is studied quantitatively by Bloch wave and multislice simulations. We show that 2s states are excited beyond a critical Z value and cause a long period oscillation of the electron probe wave function that significantly influences the Z contrast. As a result, we find that the Z contrast for high Z alloys remains thickness dependent up to high sample thicknesses and this effect has to be considered for compositional analysis. In the special case of ordered alloys, the impact of 2s excitations on intensity provides a way to quantify long-range order phenomena in alloys with known composition.