High-yield synthesis and liquid-exfoliation of two-dimensional belt-like hafnium disulphide

Producing environmentally stable monolayers and few-layers of hafnium disulphide (HfS₂) with a high yield to reveal its unlocked electronic and optoelectronic applications is still a challenge. HfS₂ is a layered two-dimensional material of group-IV transition metal dichalcogenides. For the first time, we demonstrate a simple and cost-effective method to grow layered belt-like nanocrystals of HfS₂ with a notably large interlayer spacing followed by their chemical exfoliation. Various microscopic and spectroscopic techniques confirm that these as-grown crystals exfoliate into single or multiple layers in a few minutes using solvent assisted ultrasonification method in N-cyclohexyl-2-pyrrolidone. The exfoliated nanosheets of HfS₂ exhibit an indirect bandgap of 1.3 eV with high stability against surface degradation. Furthermore, we demonstrate that these nanosheets hold potential for electronic applications by fabricating a field-effect transistor based on few-layered HfS₂, exhibiting a field-effect mobility of 0.95 cm²/(V·s) with a high on/off current modulation ratio of 10, 000 in ambient conditions. The method is scalable and has a potential significance for both academic and industrial purposes.