Provided is a method of forming a transition metal chalcogenide thin-film and the method includes preparing a first substrate having formed thereon a transition metal-containing precursor thin-film; displacing a second substrate separately with a constant distance from the first substrate by using a bridge unit while the second substrate is facing the first substrate, thereby securing a gas flowing path between the first substrate and the second substrate; heating the first and second substrates to a reaction temperature; and introducing a chalcogen-containing gas from an end of a reactor, such that the chalcogen-containing gas flows via the path.

A method for forming a transition metal dichalcogenide monolayer, which includes depositing a transition metal, a transition metal oxide, or a mixture thereof, on a substrate, introducing a chalcogen precursor to the transition metal, the transition metal oxide, or the mixture thereof, in the presence of an etching gas and a carrier gas at a first temperature, to form a transition metal dichalcogenide on the substrate from the transition metal, the transition metal oxide, or the mixture thereof, and subliming the transition metal dichalcogenide on the substrate in the presence of a pulsating supply of a vapor of the chalcogen precursor to form the transition metal dichalcogenide monolayer at a second temperature, wherein the vapor of the chalcogen precursor comprises a chalcogen vapor.