Fig. 5

a Raman spectra of the WSe₂ after annealing in ambient at 200 °C for 60 min (black line), at 350 °C for 60 min (red line), and at 500 °C for 5 min (blue line). Inset images correspond to the optical images before and after annealing in 500 °C, respectively. Scale bar = 15 μm. b Raman mapping images after annealing at 500 °C integrating with bands at 712 cm⁻¹ and 806 cm⁻¹, respectively. Scale bar = 10 μm. c Optical bandgap of the WSe₂ before, after annealing in ambient at 250 °C for 30 min, and for 60 min. An inset image is the optical image of a monolayer WSe₂ flake (labeled as sample 1) with scale bar = 10 μm. d Maximum PL intensity and corresponding PL mapping images with a scale bar of 10 μm