Novel 2D transition metal dichalcogenide synthesis methods for electronic and photonic device applications

Abbas, Omar (2020) Novel 2D transition metal dichalcogenide synthesis methods for electronic and photonic device applications. Doctoral Thesis, 218pp.

Record type: Thesis (Doctoral)

Abstract

Soon after the discovery of graphene, two-dimensional transition metal dichalcogenides (2D-TMDC) started to receive global attention. 2D-TMDC are Van der Waals materials like graphene except that they possess excellent semiconducting properties which makes them potential silicon alternatives for next generation electronics and optoelectronics. Nevertheless, finding a technologically applicable production method for these materials is still a key challenge. Despite there is a plethora of precursors that can be used for 2D-TMDC growth, solution-based single source precursors like ammonium tetrathiotungstate (NH₄)₂WS₄ and ammonium tetrathiomolybdate (NH₄)₂MoS₄ are very attractive for industrialization due to their facile processing route to produce scalable TMDC films as well as cost-effectiveness. Hence, this method was studied intensively during the last decade for MoS₂ while for WS₂ there was no such progress due to complications of depositing uniform single source precursor films. Therefore, the main goal of this PhD thesis is to explore novel synthesis methods for 2DWS₂ and 2D-MoS₂ using solution based single source precursors. Additionally, initial validation of these synthesis methods as potential industrial platforms for 2D electronics and photonics was performed by fabricating prototype devices. Leveraging from well-established solution-based synthesis of large area 2D-MoS₂ films, an Indium-2D-MoS₂ metal-semiconductor-metal photodiode was successfully realised using simple metallisation step. Furthermore, for the first time a large area continuous/uniform few-layer WS₂ films via thermolysis of (NH₄)₂WS₄ films was demonstrated which shows a potential application as field effect transistor device.
Finally, using solution-based single source precursors, a revolutionary direct laser synthesis of 2D-WS₂ and 2D-MoS₂ micro-patterns under ambient conditions has been developed.
This method offers versatility, simplicity, patternability and the possibility to create TMDC device arrays, including alloys and heterostructures with minimal lithographic or thermal overheads. The results from this work could be the cornerstone towards laser assisted direct-writing technology of 2D-TMDCs for electronics and photonics devices and circuits fabrication.