Finding order in disorder. Electron radial distribution function  and beyond

In case of amorphous phases very little information can be obtained from bulk diffraction techniques based on conventional crystallographic approaches. The Electron Microscopy group is exploring possibilities for studying short- and medium-range order in amorphous and nanocrystaline systems using electron radial distribution functions (eRDFs) and cross-correlation approaches. The eRDF is usually obtained from electron total scattering data, which can be collected on any standard transmission electron microscope within a few seconds making this technique easily accessible to a lot of users. The zero-loss-energy filtering method that we apply allows mainly elastically scattered electrons to contribute to the diffraction signal, improving the signal-to-noise ratio about 5 times and thus allowing to obtain reliable energy-filtered eRDFs even from amorphous materials. Using this technique, we were able to characterize bonding, coordination and the average coherence length, in different materials including carbon-nitrides with different degrees of crystallinity such as polyheptazine imides and amorphous CN (a-CN) covalent networks shown in Figure.

The fact that eRDFs are normally recorded at considerably low electron doses in comparison to TEM imaging techniques makes eRDF analysis ideal for characterizing beam-sensitive and poorly crystalline materials. EF-eRDF in combination with HR-(S)TEM gives a unique set of information at the nanoscale, which is extremely useful to study processes.