Control of composition and atomic distribution in ternary molybdenum tungsten disulfide monolayers by sub-atomic layer deposition

Both homogeneous and inhomogeneous alloying significantly extend the spectrum of available materials and properties. In this study, (Mo,W)S 2 monolayer alloys in the full composition range were grown by a modified atomic layer deposition process. The mixture of Mo and W in the crystal lattice can be controlled by the pulsed precursor schema and either a homogeneous distribution or nanostructures such as line structures and elongated islands were realized. The distribution of metal atoms is visualized by transmission electron microscopy. Raman spectroscopy is used to determine the composition x in Mo x W 1− x S 2 by the shift of the A₁^ A 1 ′ mode. The optical properties are analyzed by photoluminescence spectroscopy, resulting in the determination of bowing parameters for the A and B excitonic emission. Deviations from the expected bowing are explained by a change of the energy landscape due to the presence of nanostructures. Besides the composition control, this sub-atomic layer deposition approach could pave the way to the intended formation of quantum dot and wire structures in 2D transition metal dichalcogenide heterostructures.