Tunable Optical and Electronic Properties of Two-Dimensional Transition Metal Dichalcogenide Alloys

Two-dimensional transition metal dichalcogenide (TMD) alloys, comprising atomically thin layers of MX₂ (where M is Mo, W, Ni or other transition metals and X is S, Se or Te), exhibit highly tunable optical and electronic characteristics through precise control of composition, structure and dimensionality. By alloying at the metal or chalcogen sites, the direct band gap of monolayer TMDs can be continuously varied across the visible and near-infrared spectrum, enabling tailored absorption and emission wavelengths. Concurrently, spin–orbit coupling and valley-dependent phenomena can be engineered via the choice and ratio of heavy atoms, yielding adjustable spin splitting in conduction and valence bands and modulated exciton dynamics. Synthetic techniques such as chemical vapour deposition, atomic layer deposition and post-growth chalcogen exchange enable homogeneous mixing or gradient compositions within single crystals, facilitating studies of strain, defect density and interlayer interactions. The interplay of composition and heterostructure design has led to enhanced photoluminescence quantum yields, controllable dark and bright exciton populations, and efficient separation of photoexcited carriers. These advances underpin applications in flexible electronics, photodetectors, light-emitting diodes, spin- and valleytronic devices, and quantum light sources, and point to the global potential of TMD alloys for next-generation optoelectronic and information-processing platforms.

Research from Nature Portfolio

Recent studies have demonstrated spin-orbit engineering in Mo₁₋ₓWₓSe₂ monolayers, revealing that incremental tungsten incorporation modulates conduction-band spin splitting and alters the balance of bright versus dark exciton states. By tuning the W fraction to around 40 %, striking enhancements in valley polarisation and temperature-dependent photoluminescence were achieved, highlighting the potential of compositional control for spin- and valley-selective optoelectronics. In parallel, vertically composition-controlled Mo₁₋ₓWₓS₂ multilayers have been synthesised via sequential atomic layer deposition and sulphurisation, yielding abrupt and graded interfaces within a single crystal. Spectroscopic measurements confirmed a systematic shift in band gap across the layers, while photodetector devices based on these vertically structured alloys exhibited three- to four-fold increases in photocurrent relative to binary MoS₂ and WS₂, underscoring the power of multilayer compositional architecture for broadband light harvesting and photoconductive gain.

Tunable Optical and Electronic Properties of Two-Dimensional Transition Metal Dichalcogenide Alloys publication trend

The graph below shows the total number of articles in tunable optical and electronic properties of two-dimensional transition metal dichalcogenide alloys across all publications each year (not limited to Nature Index journals).

Technical terms

Transition Metal Dichalcogenide (TMD): A layered material with formula MX₂, where M is a transition metal and X is a chalcogen, exhibiting strong in-plane covalent bonding and weak interlayer van der Waals interactions.

Band gap engineering: The deliberate modification of the energy difference between valence and conduction bands through composition, strain or external fields to tune optical absorption and emission.

Spin–orbit coupling: An interaction between an electron’s spin and its orbital motion around the nucleus, leading to energy band splitting, especially prominent in heavy-atom TMDs.

Exciton: A bound state of an electron and a hole attracted by Coulomb interaction, central to light-matter interactions in semiconductors.

Valley polarisation: The preferential occupation of energy extrema (valleys) in momentum space, enabling information encoding in valley degrees of freedom.

Chemical vapour deposition (CVD): A synthesis technique in which gaseous precursors react or decompose on a substrate to form thin films or monolayers with controlled composition.

References

1. Spin-orbit engineering in transition metal dichalcogenide alloy monolayers. Nature Communications (2015).
2. Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer. Nature Communications (2015).
3. Atomically Substitutional Engineering of Transition Metal Dichalcogenide Layers for Enhancing Tailored Properties and Superior Applications. Nano-Micro Letters (2024).
4. Machine-learned interatomic potentials for transition metal dichalcogenide Mo1−xWxS2−2ySe2y alloys. npj Computational Materials (2024).