Christian Tessarek, Tim Grieb, Florian F Krause, Christian Petersen, Alexander Karg, Alexander Hinz, Niels Osterloh, Christian Habben, Stephan Figge, Jon-Olaf Krisponeit, Thomas Schmidt, Jens Falta, Andreas Rosenauer, Martin Eickhoff
2D Materials 11(2) (2024): 025031
MoS2 and WS2 mono- and multilayers were grown on SiO2/Si substrates. Growth by atomic layer deposition (ALD) at fast growth rates is compared to sub-ALD, which is a slow growth rate process with only partial precursor surface coverage per cycle. A Raman spectroscopic analysis of the intensity and frequency difference of the modes reveals different stages of growth from partial to full surface layer coverage followed by layer-by-layer formation. The initial layer thickness and structural quality strongly depend on the growth rate and monolayers only form using sub-ALD. Optical activity is demonstrated by photoluminescence (PL) characterization which shows typical excitonic emission from MoS2 and WS2 monolayers. A chemical analysis confirming the stoichiometry of MoS2 is performed by x-ray photoelectron spectroscopy. The surface morphology of layers grown with different growth rates is studied by atomic force microscopy. Plan-view transmission electron microscopy analysis of MoS2 directly grown on freestanding graphene reveals the local crystalline quality of the layers, in agreement with Raman and PL results.
