2.3.2 Synthesis of 2D TMDs
In general, there are two major classifications for making 2D materials which includes top-down exfoliation from bulk materials and bottom-up synthesis. Both methods would be reviewed for making 2D TMDs in this paper.
Top-down methods fabrications
Thin flakes of TMDs can be peeled off from bulk materials using adhesive tape, applied to the substrates and then identified by light interference using similar techniques used to develop graphene. Fig 6c shows a thin monolayer flake peeled off from the bulk material (Fig 6a) mechanically with the tape. Oxide nanosheets as well as other materials can be obtained using this method. Using the mechanical method of exfoliation helps to produce flakes of high purity that…show more content…
Chemical vapor deposition(CVD) on metal substrates enables large scale development of TMDs for device fabrication. Reported CVD methods for growing thin film MoS2 involves heating to high temperature Sulphur powder and MoS2 powder onto the substrate. In these reported methods, the thickness of the MoS2 layer is dependent on the concentration of the MoS2 layer. Some other reported methods for making TMDs include using molybdic acid or tungstic acid with thiourea or selenourea, reasonably quality TMD is obtained with this method with thickness of a few hundred nanometers. Figure 7. (a-c) Different shapes of MoS2 grown by CVD methods based on MoO3 precursors and Sulphur 
2.3.2 Applications of 2D TMDs
The major advantage of TMDs over graphene for electronic applications is the presence of a bandgap which is needed for a high in/off ratio as well as absence of dangling bonds, flexibility and high carrier mobility. The earliest application of TMDs for FETs dates back to 2004 and this showed mobility comparable to conventional silicon based FETs (500cm2v-1s-1 at room temperature). A while after, FETs based on MoS2 were fabricated and they had similar mobility values and excellent on/off