Paper EM-ThP7
The Effect of Processing Conditions on the Growth of Transition Metal Dichalcogenides by Molecular Beam Epitaxy

Thursday, October 24, 2019, 6:30 pm, Room Union Station B

The synthesis of high-quality transition metal dichalcogenides films is of significant interest for potential applications in nanoelectronic and thermoelectric devices. Molecular beam epitaxy is a promising route towards this aim, providing fine control over growth conditions. To further the present understanding of growth conditions on the quality of transition metal dichalcogenide thin films, we study the effect of growth temperature, chalcogen to metal flux ratio, and the use of a ripening step on the stoichiometry and surface morphology of grown WSe₂ thin films. In-situ X-ray photoelectron spectroscopy is performed to analyze the intrinsic chemical composition of the grown material prior to atmospheric exposure, and ex-situ atomic force microscopy is employed to study the surface morphology of grown, sub-monolayer films. We find that both low and high growth temperature ranges can be detrimental to the chemical makeup of the grown material and that these results are echoed in the resulting grain morphology. An intermediate growth temperature produced chemically superior films over a wide range of chalcogen to metal flux ratios. The chalcogen to metal flux ratio was seen to provide some control of the film morphology, with high fluxes producing films with cleaner grain boundaries. Lastly, we show that the use of a ripening step in the early stages of growth results in a chemically superior material. This ripening step has the added benefit of producing films which are chemically more consistent than those grown in the absence of this step. There is also evidence to suggest that utilizing a ripening step may expand the processing window for film growth, allowing the use of higher processing temperatures and consequently better control over film quality.