Phase transition and formation of inorganic fullerene type nanostructure in WS2 nanosheet system under laser excitation

Abstract

Here in, laser power and energy dependant chemical and structural changes in WS2 nanosheets have been reported. The nanosheets were obtained through liquid phase exfoliation in N-methyl pyrrolidone (NMP). Simultaneous laser irradiation and Raman spectral analysis were performed on the nanosheets. It was observed that laser power enhancement leads to further exfoliation and red shift of prominent phonon modes E12g and A1g in the nanosheets. Oxidation of the nanosheets was also witnessed with a minimum 50 mJ of laser irradiation. Raman spectral analysis also reveals the transition of WS2 from 2H (hexagonal symmetry, one layer per repeat, trigonal prismatic coordination to 1T (tetragonal symmetry, one layer per repeat, octahedral coordination) crystallographic arrangements with a minimum 50 mJ of laser energy. Formation of incipient inorganic fullerene type nanostructures was also confirmed in the laser irradiated WS2 nanosheets. It is anticipated that such experimental findings will boost further laser induced treatment of transition metal dichalcogenides for novel applications.