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.

 

Lasse Karvonen is currently a post-doctoral researcher in the Department of Micro and Nanosciences at Aalto University in Finland. He is primarily interested in the linear and nonlinear optical properties of atomically thin materials such as graphene, MoS2 and other metal dichalcogenides. He received his PhD degree from Aalto University (2013) with the thesis title of Nanostructures for photonic applications.  After finishing his PhD, he has been working as a project manager in the Finland Distinguished Professor –project, in which he is doing close collaboration with the researchers in College of Optical Sciences in University of Arizona. He is staying in University of Arizona from two to four months every year.