## 4 Results and Discussion
### The Influence of Temperature on MoS\({}_{2}\) Growth
This is mainly due to the fact that with the further increase in temperature, the reverse reaction rates of the intermediate products Mo\({}_{2}\)O\({}_{6}\)S\({}_{4}\) and MoO\({}_{3}\)S\({}_{2}\) are accelerated, which limits the progression of the reaction, preventing the complete reaction of Mo\({}_{3}\)O\({}_{9}\) and S\({}_{2}\) and causing an increase in their concentrations at the substrate position. After the reaction of Mo\({}_{3}\)O\({}_{9}\) with S\({}_{2}\), intermediate products are rapidly formed. Figure 4 shows the concentration distribution of Mo\({}_{3}\)O\({}_{9}\)S\({}_{4}\) under different growth temperatures at a pressure of 70 Torr. As the set temperature increases from 1033 K to 1073 K, the concentration of Mo\({}_{3}\)O\({}_{9}\)S\({}_{4}\) at the substrate position increases significantly from 0.006 mol/m\({}^{3}\) to 0.24 mol/m\({}^{3}\). This can be attributed to both the increased evaporation rate of Mo\({}_{3}\)O\({}_{9}\) and the accelerated reverse reaction rates of Mo\({}_{2}\)O\({}_{6}\)S\({}_{4}\) and MoO\({}_{3}\)S\({}_{2}\). The concentration distributions of other intermediate products at a pressure of 70 Torr and a temperature of 1053 K  
Figure 3: Radial cross-section of Mo\({}_{3}\)O\({}_{9}\) concentration distribution at the center of the substrate when the pressure is 70 Torr and the temperature in growth region is set to (**a**,**b**) 1033 K, (**c**,**d**) 1053 K, and (**e**,**f**) 1073 K.  
are shown in Figure S7. The concentrations of all intermediate products are concentrated above the precursor inside the crucible, and the concentrations at the substrate position are significantly lower, indicating that the reaction proceeds rapidly. The concentration of Mo\({}_{3}\)O\({}_{9}\)S\({}_{4}\) is approximately 0.09 mol/m\({}^{3}\), much higher than that of other intermediate products (e.g., the concentration of MoO\({}_{3}\)S\({}_{2}\) is 1 \(\times\) 10\({}^{-4}\) mol/m\({}^{3}\)). This suggests that the reaction involving Mo\({}_{3}\)O\({}_{9}\)S\({}_{4}\) is the rate-limiting step for the entire reaction. Figure 5 shows the concentration distribution of MoS\({}_{6}\) products at different growth temperatures. At 1033 K, 1053 K, and 1073 K, the concentration of MoS\({}_{6}\) at the substrate position is 0.19 mol/m\({}^{3}\), 0.31 mol/m\({}^{3}\), and 0.24 mol/m\({}^{3}\), respectively. As the temperature increases, the evaporation rate of Mo\({}_{3}\)O\({}_{9}\) rises, while the reverse reaction rates of Mo\({}_{2}\)O\({}_{6}\)S\({}_{4}\) and MoO\({}_{3}\)S\({}_{2}\) accelerate, resulting in a non-monotonic change in the concentration of MoS\({}_{6}\). Figure 5c,f,i shows a symmetric distribution of MoS\({}_{6}\) concentration along the center of the substrate inside the crucible, indicating that the diffusion of reactants is the dominant factor in the mass transfer process within the crucible. This is mainly due to the relatively low gas flow rate inside the crucible. Figure 4: Radial cross-section of the concentration distribution of Mo\({}_{3}\)O\({}_{9}\)S\({}_{4}\) at the center of the substrate when the temperature in growth region is set to (**a**) 1033 K, (**b**) 1053 K, and (**c**) 1073 K at a pressure of 70 Torr. Figure 5: Concentration distribution of MoS\({}_{6}\) when the temperature in growth region is set to (**a**–**c**) 1033 K, (**d**–**f**) 1053 K, and (**g**–**i**) 1073 K at a pressure of 70 Torr, where (**b**,**e**,**h**) are the radial cross-sectional views at the center of the substrate and (**c**,**f**,**i**) are the axial cross-sectional views at the center of the substrate. Based on the above observations, the state of the substrate can be summarized as follows: During the early stages of growth, the substrate surface is characterized by the coexistence of both MoS6 and Mo3O9S4. MoS6, as the final reactant before MoS2 film growth, directly contributes to the formation of the MoS2 film after diffusing to the edges of the MoS2 grains.