Aalto University, Department of Micro and Nanosciences, FI-02150 Espoo, Finland
Chemical vapor deposited (CVD) molybdenum disulphide (MoS2) flakes are studied by Raman, photoluminescence and multiphoton microscopies. We use simultaneous second- and third-harmonic generation imaging methods to study the crystal orientations and the grain boundaries of CVD grown MoS2 flakes We show that grain boundaries with large mis-orientations in the crystal structure are clearly observable with Raman, photoluminescence and second-harmonic generation imaging methods. However, these methods have difficulties in distinguishing grain boundaries without mis-orientation or with a small mis-orientation in the crystal structure. In addition to that, we show that third-harmonic generation imaging is very sensitive for the grain boundaries regardless of the crystal mis-orientation. Our multiphoton imaging results demonstrate that third-harmonic generation imaging is a much faster technique than Raman mapping with better sensitivity compared to the photoluminescence mapping and second-harmonic generation imaging methods, and therefore more suitable for high-volume and large-size sample characterization.