LAUSR

dD materials, such as graphene, have been hailed as wonder materials due to their enhanced mechanical and electrical properties [1]. These properties change as a function of the sample thickness, specifically with respect to the number of stacked 2D layers. With graphene for example, once a multilayer structure is approximately > 10 layers thick it is no longer referred to as graphene and will exhibit the same properties as bulk graphite [2]. As monolayer graphene has a sample thickness of 0.335 nm and is a repeating lattice of Z=6 carbon atoms, it is challenging to observe and is typically imaged using advanced light microscopy, electron microscopy or AFM. Light microscopy utilises image contrast to calculate the number of 2D layers observed in a sample while AFM can measure the difference in step heights between 2 overlapping layers to determine the number of layers in a stack. Electron microscopy is a powerful tool for imaging 2D materials as it has the ability to resolve 2D materials atomically and gains enhanced contrast from atomic number contrast detectors. Currently the only method to differentiate the number of layers in a transmission electron microscope (TEM) is through the acquisition of selected area electron diffraction (SAED). This does not generate a direct thickness measurement resulting in a calculation of the number of 2D monolayers within an isolated stack. An estimation of the thickness can then be calculated by multiplying the number of monolayers with the reported thickness value of a single layer. This technique can be complicated as it does not directly report any chemical information so the user can not easily differentiate between different 2D materials and contaminants. The ability to chemically characterise 2D materials while imaging them can only be achieved through the combination of electron microscopy and energy dispersive x-ray spectroscopy (EDS).