Figure 1. Controlled synthesis of MoS₂ monolayer and bilayer films.

(a) and (b), Optical images of the MoS₂ monolayer and bilayer films grown on sapphire substrates, respectively. The insets are optical images of the MoS₂ monolayer and bilayer films grown on SiO₂/Si substrates. The scale bars in the insets are 80 μm. (c) and (d), AFM height profiles for typical MoS₂ monolayer and bilayer films grown on sapphire, respectively. The insets show the AFM images from which the height profiles are extracted. A larger version of the AFM images is given in Fig.S3 of the Supplementary Information. (e), Raman spectra of the MoS₂ monolayer (1 L) and bilayer (2 L) films grown on sapphire. Also given are the Raman spectra of exfoliated MoS₂ monolayer and bulk MoS₂ dispersed on SiO₂/Si substrates. The two characteristic Raman modes are labeled. The peak at 418 cm⁻¹ is from the sapphire substrate.