M.S. Physics Thesis Talk: Huy Quoc Minh Ho - "The Substrates and Temperature Dependent Behavior of Layered MoS2 from Quantum Mechanical View"

Abstract: 

In this work, we addressed two questions: why the Fano parameter was hard to find experimentally, and how did the reason of that difficulty behave at different temperature (ranging from 1.5 K to 300 K), and on three substrates: hexogonal Boron Nitride, SiO2 and gold. We chose monolayer, bilayer and trilayer MoS2 as our automatically thin 2D semiconductors to conduct our research. The central ideas to answer our questions involved the concept of Raman matrices and the interference of two Raman scattering processes. We extracted the values of Raman matrices and the 

Fano parameter from our experimental data via curved fitting methods based on the Klein’s and Fano’s fitting models. The experimental data confirmed the agreement of two fitting models as well as the substrate and temperature dependent behavior of

Raman matrix, the energy of intermediate state and peak position. We also created the theoretically predicted values of a Raman matrix and energy of virtual states, and observed an agreement with the experimental results. We observed theoretically

and experimentally that the dominance of one Raman scattering process is due to the energy of virtual states are in the vicinity of the incident photon energy. On the other hand, the second Raman process is weak because the Fermi level was higher than valance band maximum, which prohibits transition between the valence bands. Finally, we demonstrate that the temperature-dependent enhancement of the Raman intensity is related to the fluctuations of the susceptibility.