3D electron diffraction of mono- and few-layer MoS2

Evaluation of TEM methods for their signature of the number of layers in mono- and few-layer TMDs as exemplified by MoS2 and MoTe2

“…Therefore, the two strongest peaks of the 10L relrod of a MoS 2 monolayer (at 0.3 Å -1 , see Fig. The symmetry of the MoTe 2 relrods follows the same scheme that was established for MoS 2 crystals (Gorelik et al, 2021b): crystals with odd number of layers show relrods which are symmetric with respect to the base (L = 0), while crystals with even number of layers have asymmetric intensity distributions. An asymmetry in the relrods is clearly seen for bilayers (Fig.…”

“…The main finding of our previous study on 3D ED of 1-4 layered hexagonal MoS 2 (Gorelik et al, 2021b) was that crystals consisting of an odd number of layers have Laue class 6/mmm, while crystals with an even number of layers have Laue class 3m1. The most prominent difference between these two Laue classes is the presence (6/mmm) or absence (3m1) of a mirror plane within the L = 0 plane.…”

“…Optical contrast measurements are routinely used for the determination of the number of layers of 2D materials, provided that the required optical parameters are known (Blake et al, 2007;Benameur et al, 2011;Li et al, 2013). Recently, we already used optical contrast measurements for 1-4-layered MoS 2 (Gorelik et al, 2021b). Here we extend this study to a comprehensive work on optical contrast measurements on 90 nm SiO 2 for 1-7 L MoS 2 and MoTe 2 , combined with contrast calculations and thickness validation by AFM.…”

“…6(a)). In order to evaluate difference in diffraction data, intensities distribution along the selected relrods were calculated (kinematic scattering) for MoS 2 and MoTe 2 for 1-8 layers (simulated data for 1-4 layers of MoS 2 were already presented in (Gorelik et al, 2021b)). The results are summarized in Figs.…”

“…Transmission electron microscopy (TEM) is an indispensable tool for studying the structure of freestanding 2D TMDs and it would be of great advantage, if the number of layers could be directly determined in TEM experiments. Despite the broad spectrum of methods available within TEM, the determination of the number of layers is not a trivial task (Yang and Egerton, 1995;Pozsgai, 1997;Diebold et al, 2003;Heo, 2020;Gorelik et al, 2021b). Here we present a methodological study of the influence of the number of layers on data obtained using high-resolution imaging (HRTEM), electron energy-loss spectroscopy (EELS), and electron diffraction (ED).…”