Recently, artificially stacked van der Waals materials or sometimes called moiré materials become one of the central topics in condensed matter physics. The emergence of moiré superlattice due to relative rotation or lattice mismatch between constituent materials makes the system as a suitable platform for the research of the correlated electron physics. Superconductivity, correlated insulator, electronic crystals, and many other exotic properties have been reported in this system. However, access to the correlated phenomena in moiré materials is not easy because there are many factors that disturb the formation of ideal moiré superlattice. The poor reproducibility of experiments makes the research of moiré materials challenging. To overcome such problems, a reliable characterization tool for moiré materials is necessary.
Raman spectroscopy is a fundamental optical technique to study the properties of materials. It is known that Raman spectroscopy is especially useful for 2D materials research because it can be used to probe the interlayer interactions which have an important role in determining physical properties of 2D materials. In addition, there are several reports which confirms that the Raman spectrum is affected by moiré superlattice. All of these facts suggest that Raman spectroscopy can be useful for the characterization of moiré materials.
In this thesis, we investigate the vibrational properties of twisted bilayer WS₂ by using Raman spectroscopy. Monolayer WS₂ is synthesized from metal-organic chemical vapor deposition and stacked to construct the twisted bilayer structure. Then, Raman spectroscopy is performed on twisted bilayer WS₂ at various twist angle. By using the identified twist angle-dependent Raman properties, we visualize the angle distribution in twisted bilayer WS₂.
