The CVD of monolayer and few-layer TMDs is a rapidly developing area of materials science. Like graphite, TMD bulk crystals are formed of monolayers bound to each other by van der Waals attraction. These materials in their monolayer or few-layer form offer exciting electrical, optical, thermal and mechanical properties that differ from their bulk form. This makes the fabrication and investigation of TMDs important so that their potential can be understood.

One can separate layers by micromechanical cleavage. Its use in real applications however would be a time consuming and inefficient approach. CVD is a much more attractive option as it can deliver high yields and high-quality material. Furthermore, it is already well established in industry.

The promise of MoSe2

One of the more promising TMD materials for applications is MoSe2. To date, fewer than a handful of research groups been able to demonstrate its synthesis via CVD. Moreover, only oriented few-layer MoSe2 has been made synthetically using CVD. The fabrication of turbostratic or twisted few-layer materials is of interest as the physical properties of twisted-layer TMDs differ from oriented few-layer TMDs. This is because the coupling between layers changes. Thus, the fabrication of twisted few-layer MoSe2 is of fundamental interest.

Twist angles

Here, researchers have achieved this. They synthesize twisted few-layer MoSe2 using CVD. Using both Raman spectroscopy and state-of-the-art aberration corrected transmission electron microscopy the presence of twisted few-layer was confirmed. They also observe the formation of different twist angles, which may provide a way to tune the properties of few-layer MoSe2 and make it even more applicable.

More information about the research can be found in the journal Nanotechnology 25 365603.

Further reading

Manipulating boron-nitride nanotubes unconventionally (Feb 2014)
Tweaking the magnetism of molybdenum sulphide nanoribbons (Mar 2014)
Selective electrochemical biosensing using molybdenum disulphide (July 2014)
Enhancing dielectric growth with two-dimensional materials (Aug 2014)