The Post Annealing to Control the Number of Layers of 2D MoS2 and SnS2

Abstract

We have demonstrated that post annealing could control the layer thickness of 2D MoS2 and SnS2 films transferred on a SiO2/Si substrate by varying the annealing temperature and time. Atomic force microscopy and Raman spectroscopy characterizations revealed that higher annealing temperature and longer treatment time led to thinner films, lower residues and fewer impurities on the surface of 2D materials. In addition, a higher possibility to attain few-layers on both 2D films was achieved using post annealing. The multiple layers of pristine films having the thickness over 15 nm were reduced down to bi-layers after annealing. We observed that the moderate annealing temperature of 450 degrees C on led to effective layer-thinning compared to the films annealed at 340 degrees C. The post annealing at 450 degrees C produced very smooth few-layers (<= 4 nm thickness, >1 mu m size) of 2D MoS2 and SnS2. However, the 2D films decomposed or disappeared at temperature greater than 650 degrees C. In addition, process time also affected the number of layers and the sweet spot turned out to be 2 to 3 hours in our experiment.