Raman investigation of molybdenum disulfide with different polytypes

The Raman spectra of molybdenum disulfide (MoS$_{2})$ with different polytypes are investigated. Although 2H-MoS$_{2}$ is most common in nature, the 3R phase can exist due to a small difference in the formation energy. However, only a few studies are reported for the 3R phase, and most studies have focused on the 2H phase. We found the 2H, 3R and mixed phases of exfoliated few-layer MoS$_{2}$ from natural molybdenite crystals. The crystal structures of 2H- and 3R-MoS$_{2}$ are confirmed by the HR-TEM measurements. By using 3 different excitation energies, we compared the Raman spectra of different polytypes in detail. We show that the Raman spectroscopy can be used to identify not only the number of layers but also the polytypes of MoS$_{2}$.