Transition metal dichalcogenides have a similar structure to graphene but have a variety of excellent properties that can solve some hindrances of graphene. So it has been studied with a lot of interest from researchers.
Molybdenum disulfide (MoS2), one of the representative 2D transition metal dichalcogenides, has excellent properties such as extremely thin thickness, tunable bandgap, and high mobility. Like other 2D materials, MoS2 has been studied intensively with plenty of attention from researchers.
Molybdenum disulfide (MoS2) consists of one layer of Mo atoms and two layers of S atoms above and below the Mo atom layer with a hexagonal arrangement. These triple planes are stable through their strong covalent bonds between Mo and S, but due to the weak van der Waals forces acting between the layers, the layers are relatively easily separated to form a 2D single-layer sheet.
MoS2 is also known to present differences in its electronic structure depending on the thickness. In particular, 2D MoS2, a single layer, is known to have a direct bandgap of 1.89 eV at the high symmetry point 'K'. In addition, this property and other unique properties such as high light emission efficiency, enable the MoS2 to be widely used in applications, such as optical sensors, field-effect transistors (FETs), solar cells, etc.,
You can directly find out the electronic structure and bandgap by calculating the band structure of MoS2 using Materials Square.
When analyzing the Density of states data, you can add PDOS (Projected density of state) to see which electronic state caused by each atom or orbitals. Likewise, in the band structure, the band contributed by a specific orbital can be indicated. This is called 'Projected band structure', or 'Fatband'.
As mentioned in the previous weekly tip #7, using Quantum Espresso's 'projwfc.x' code, you can obtain the data of the atomic orbitals projected onto the wavefunction. If this is applied to the band structure data, it is possible to plot the band structure that originated from each atomic orbital like PDOS.
In previous weekly tips, we have covered the projected band structure for analysis.
The method of obtaining the projected band structure is almost the same as the method of obtaining the band structure.
In this module tip, you will learn how to obtain the projected band structure with the tutorial video.
2. Structure optimization
3. Band structure & Projection calculation
 Yu, Z., Ong, Z. Y., Li, S., Xu, J. B., Zhang, G., Zhang, Y. W., ... & Wang, X. (2017). Analyzing the Carrier Mobility in Transition‐Metal Dichalcogenide MoS2 Field‐Effect Transistors. Advanced Functional Materials, 27(19), 1604093.
 Mak, K. F., Lee, C., Hone, J., Shan, J., & Heinz, T. F. (2010). Atomically thin MoS 2: a new direct-gap semiconductor. Physical review letters, 105(13), 136805.
 Splendiani, A., Sun, L., Zhang, Y., Li, T., Kim, J., Chim, C. Y., ... & Wang, F. (2010). Emerging photoluminescence in monolayer MoS2. Nano letters, 10(4), 1271-1275.
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