Event date:
Jan 14 2022 4:00 pm

Photoluminescence and Raman of MoS2 under Biaxial Strain

Dr. Ata UlHaq
Fatima Rehman
SBASSE Building, 3rd Floor, Room No. 10-304
MS Synopsis defense


Two-dimensional (2D) materials have attracted intense research interest over the past decades after the discovery of graphene. Transition metal dichalcogenides (TMDC) are an especially important class of 2D materials as they possess bandgap and behave as semiconductor unlike graphene. Importantly, the bandgap depends on the number of layers. Molybdenum disulphide (MoS2) is an important member of the TMDC family. Monolayer MoS2 behaves as a direct bandgap material and is therefore important for photonic devices. Strain is an important engineering parameter to control the band structure of these TMDC materials. However, most of the studies on TMDC have employed uniaxial strain. There are very few reports on the Physics of few layers TMDCs under biaxial strain. In this thesis, we plan to investigate excitons and phonon physics in TMDC under biaxial strain.

We used mechanical exfoliation to transfer flakes of 2D layers MoS2 from bulk crystal onto a stretchable substrate. Microscopy of the exfoliated flakes is performed to find the number of molecular layers in exfoliated flakes. This is then confirmed using Raman spectroscopy. We perform photoluminescence (PL) and Raman on these flakes. The PL spectrum provide information about the excitons within the flakes. Biaxial strain is applied using a machined stages where is a movable pillar is used to exert determinist magnitude of biaxial strain into the flakes. PL and Raman spectroscopy of the strained flakes are performed and the results will be discussed in my presentation. We will report flakes of monolayer and bilayers of MoS2