Defect engineering on MoS2 surface with argon ion bombardments and thermal annealing

Various approaches have been developed to produce MoS2 monolayers and multilayers. Using plasma and thermal thinning, layer-by-layer thinning processes were developed to produce MoS2 monolayer and multilayers. However, an atomic-level understanding of the thinning mechanism and defects created in these processes is not clear. In this paper, we studied the impact on surface structures of bulk MoS2 by argon ion (Art(+)) bombardments and thermal annealing using an ultra-high vacuum (UHV) scanning tunneling microscope (STM). The STM images obtained before and after Ar+ bombardments show that low-energy (50 eV) Ar+ ions can remove single atoms from the surface and fragment the top sulfur layer resulting in single sulfur vacancy point defects and atomic pits on the MoS2 surface. Higher energy (100 eV) Ar+ ions can penetrate deeper and remove the topmost MoS2 trilayer. After bombardment with an Ar+ beam of 500 eV, the MoS2 surface appeared as granulated nanostructures consisting of 1-3 nm nanoparticles. Upon thermal annealing, topmost sulfur atoms were removed through sublimation after heating at 650 degrees C for 5 min and deeper atom sublimation was observed with longer annealing time, resulting in granulated nanostructures on the MoS2 surface.