A vapor-phase-assisted growth route for large-scale uniform deposition of MoS monolayer films.

In this work a vapor-phase-assisted approach for the synthesis of monolayer MoS is demonstrated, based on the sulfurization of thin MoO precursor films in an HS atmosphere. We discuss the co-existence of various possible growth mechanisms, involving solid-gas and vapor-gas reactions. Different sequences were applied in order to control the growth mechanism and to obtain monolayer films. These variations include the sample temperature and a time delay for the injection of HS into the reaction chamber. The optimized combination allows for tuning the process route towards the potentially more favorable vapor-gas reactions, leading to an improved material distribution on the substrate surface. Raman and photoluminescence (PL) spectroscopy confirm the formation of ultrathin MoS films on SiO/Si substrates with a narrow thickness distribution in the monolayer range on length scales of a few millimeters. Best results are achieved in a temperature range of 950-1000 °C showing improved uniformity in terms of Raman and PL line shapes. The obtained films exhibit a PL yield similar to mechanically exfoliated monolayer flakes, demonstrating the high optical quality of the prepared layers.