Optical signature of the formation of vertical HfS₂ nanosheets grown on sapphire substrate

Semiconducting hafnium disulfide (HfS₂), a group IVB two-dimensional transition metal dichalcogenide (TMD), has been investigated extensively due to its predicted superior physical properties. Herein, we investigate the formation of vertical HfS₂ nanosheets on a sapphire substrates with diffuse reflectance. The samples were grown using chemical vapor deposition (CVD) by varying HfCl₄ supply to control the evolution of the HfS₂ nanosheets. There is an increase in diffuse reflectance in the range of 400–800 nm, with a peak at 498 nm, once vertical HfS₂ nanosheets are successfully grown with sufficient HfCl₄ supply. Raman scattering spectroscopy, scanning electron microscopy, and 2θ X-ray diffraction measurements confirmed the formation of HfS₂ nanosheets. Our observations can provide guidance on a quantitative and non-destructive route to monitor the evolution and formation of vertical HfS₂ nanosheets.