Pulsed thermal deposition of binary and ternary transition metal dichalcogenide monolayers and heterostructures

The application of transition metal dichalcogenides in optoelectronic, photonic, or valleytronic devices requires the growth of continuous monolayers, heterostructures, and alloys of different materials in a single process. We present a facile pulsed thermal deposition method which provides precise control over the number of layers and the composition of two-dimensional systems. The versatility of the method is demonstrated on ternary monolayers of Mo_1−xW_xS₂ and on heterostructures combining metallic TaS₂ and semiconducting MoS₂ layers. The fabricated ternary monolayers cover the entire composition range of x = 0…1 without phase separation. Bandgap engineering and control over the spin–orbit coupling strength are demonstrated by absorption and photoluminescence spectroscopy. Vertical heterostructures are grown without intermixing. The formation of clean and atomically abrupt interfaces is evidenced by high-resolution transmission electron microscopy. Since both the metal components and the chalcogen are thermally evaporated, complex alloys and heterostructures can thus be prepared.