Combining low and high electron energy diffractions as a powerful tool for studying 2D materials

Two-dimensional (2D) materials are among the most studied ones nowadays, because of their unique properties. They are made of single- or few-atom-thick layers whose variation in the stacking sequence may result in a variety of crystallographic structures, whether they are assembled by van der Waals forces or covalently bonded. Although identifying both the number of layers and the stacking sequence is of an utmost importance because of the driving role these parameters have on the properties, there is currently no technique available to do so. We demonstrate here that combining low energy (1–10 keV) electron diffraction with the usual high energy (> 50 keV) electron diffraction on the same 2D object is able to fill the gap. We illustrate this by taking the examples of a variety of 2D materials, built from either a single type of atom with low Z-number such as graphene (C), or two types of atoms with low Z-number such as diamane (C2H), or two types of atoms with high Z-number such as MoS2. Meanwhile, we propose a simplified method for comparing calculated patterns to experimental ones, and discuss the limitation of the technique.