## 4 Results and Discussion
### The Influence of Pressure on MoS2 Growth  
Since pressure can significantly alter the flow field, thereby affecting the concentration of reactants and the reaction rate, we further investigate the influence of pressure. In this section, the growth temperature is fixed at 1053 K, and the impact of different pressures (10 Torr, 40 Torr, 70 Torr, and 100 Torr) on the growth of MoS2 films is explored, with results at 70 Torr presented in the above section. Figures 2b and 6a-c show optical micrographs of samples grown under different pressures. As the pressure increases, the grain size gradually decreases. At 10 Torr, the grain size can reach up to 50, whereas at 100 Torr, it shrinks to approximately 10. Additionally, at both 10 Torr and 100 Torr, some grain centers exhibit distinctly thicker nuclei. Figure 6: Optical microscopic images of the sample grown at a growth temperature of 1053 K under (**a**) 10 Torr, (**b**) 40 Torr, and (**c**) 100 Torr, along with the corresponding (**d**) Raman spectra and (**e**) PL spectra. Figure 6d presents the Raman spectra of MoS\({}_{2}\) films grown under different pressures. For films grown at pressures below 70 Torr, the wavenumber difference between the E\({}_{26}\)1 and A\({}_{16}\) peaks is less than 22 cm\({}^{-1}\), indicating the presence of bilayer MoS\({}_{2}\) films. However, when the pressure increases to 100 Torr, this wavenumber difference rises to 23.5 cm\({}^{-1}\), corresponding to the Raman wavenumber difference of trilayer MoS\({}_{2}\). Figure 6e shows the PL spectra of the samples grown at different pressures. As the film thickness increases, the PL intensity significantly decreases, accompanied by a slight red shift. This is due to the stronger interlayer interactions caused by the increased thickness, which leads to a reduction in the bandgap. Not only does temperature affect the volatility rate of Mo\({}_{3}\)O\({}_{9}\), but pressure also plays a crucial role in influencing its volatility rate. Table 2 shows the volatility rate of Mo\({}_{3}\)O\({}_{9}\) at different pressures when the temperature is 1053 K. As the pressure increases from 10 Torr to 100 Torr, the volatility rate of Mo\({}_{3}\)O\({}_{9}\) rapidly decreases from 9.4 \(\times\) 10\({}^{-4}\) mol min\({}^{-1}\) cm\({}^{-2}\) to 2.4 \(\times\) 10\({}^{-4}\) mol min\({}^{-1}\) cm\({}^{-2}\). In contrast, the pressure has little effect on the volatility rate of S\({}_{2}\), which remains relatively stable at 1.26 \(\times\) 10\({}^{-3}\) mol min\({}^{-1}\) cm\({}^{-2}\). Finite element simulations were then conducted based on these volatility rates. Figure S9 illustrates the temperature distribution in the CVD system at different pressures, along with the cross-sectional temperature distribution at the center of the substrate. The results indicate that pressure has a minimal impact on the temperature. Although additional heat is carried away by the gas flowing through the substrate, varying the pressure does not affect the temperature distribution at the substrate when the gas flow rate remains constant. Figure 7 shows the flow velocity distribution in the CVD system at different pressures, as well as the cross-sectional flow velocity distribution at the center of the substrate. As pressure increases, the gas velocity rises significantly. At 10 Torr, the maximum gas velocities in the IV region and inside the crucible are 0.48 m/s and 0.008 m/s, respectively, while at 100 Torr, these values decrease to 0.05 m/s and 0.0008 m/s. The variation in flow velocity has a significant impact on the convection process of mass transport, leading to a notable increase in the concentration of S\({}_{2}\) within the chamber as pressure rises, as shown in Figure S10. At pressures of 10, 40, 70, and 100 Torr, the S\({}_{2}\) concentrations at the substrate are 0.08, 0.17, 0.40, and 1.40 mol/m\({}^{3}\), respectively.