On the origin of diffuse intensities in fcc electron diffraction patterns

Interpreting diffuse intensities in electron diffraction patterns can be challenging in samples with high atomic-level complexity, as often is the case with multi-principal element alloys. For example, diffuse intensities in electron diffraction patterns from simple face-centred cubic (fcc) and related alloys have been attributed to short-range order 1 , medium-range order 2 or a variety of different {111} planar defects, including thin twins 3 , thin hexagonal close-packed layers 4 , relrod spiking 5 and incomplete ABC stacking 6 . Here we demonstrate that many of these diffuse intensities, including 1 ⁄ 3 {422} and 1 ⁄ 2 {311} in ⟨111⟩ and ⟨112⟩ selected area diffraction patterns, respectively, are due to reflections from higher-order Laue zones. We show similar features along many different zone axes in a wide range of simple fcc materials, including CdTe, pure Ni and pure Al. Using electron diffraction theory, we explain these intensities and show that our calculated intensities of projected higher-order Laue zone reflections as a function of deviation from their Bragg conditions match well with the observed intensities, proving that these intensities are universal in these fcc materials. Finally, we provide a framework for determining the nature and location of diffuse intensities that could indicate the presence of short-range order or medium-range order. Some of the diffuse intensities observed in electron diffraction patterns of face-centred cubic multi-principal element alloys are due to reflections from higher-order Laue zones.