Phenomenological Interactions during CVT Synthesis of Large Scale MoS2

In the Chemical Vapor Transport (CVT), for deposition of MoS 2 , sulfur and MoO 3 powder is evaporated at 200 0 C and 650 0 C respectively. The Ar flow directs the sulfur atoms to Mo species so as to react chemically as specified in the reactions in Equation-1. During the CVT process there is adsorption of MoS 2 on Si/SiO 2 substrate associated with the exhuast of SO2 as chemical reaction by-product. The MoS 2 is deposited on the substrate by physisorption. Thus, in CVT, the nucleation and growth is a combined effect of chemisorption and physisorption. The three types of nucleation and growth theories for deposition of 2D thin films are presented by a. Volmer–Weber b.Frank–van der Merwe, c. Stranski–Krastanov in Figure 1. Figure 1 [Equation 1] The mechanism for MoS 2 nucleation and growth during CVT involves the evaporation of powdered precursors at a high temperature which leads to decomposition as well, followed by a chemical reaction. Temperature ramping-up rate, positioning of precursors, type and flow rate of carrier gases, Cooling rate, and pressure simultaneously determine the morphology, thickness, and crystallinity of the physisorbed MoS 2 . The highly simplified resolution of forces acting during the nucleation process is represented in Figure 2. The σ F refers to the forces due to surface tension along the droplet, σ S is the force exerted due to the energy associated with the substrate surface, and σ FS is the force due to the interface energy between the droplet and the substrate. A little consideration of the comparison of the magnitude of these three forces leads to the determination of Growth Kinetics. When σ S is smaller than the sum of σ F and σ FS , it favors Weber-Volmer theory; when σ S is greater than the sum of σ F and σ FS , it favors Frank van der Merwe theory, and when the balance of this comparison fluctuates or is equal, it favors the Stranski–Krastanov growth model. In practice, the several parameters other than temperature, pressure, flow rate, and precursor flux that influence the nucleation and growth mechanism involve substrate surface texture, functionalization, availability of active cites, steric hindrance, Columbic interactions etc. Figure 2 Interactions in CVT on the basis of Scientific Theories : Considering that CVT involves the gas phase chemical reaction of precursors and physisorption for the MoS 2 adsorption on the Si/SiO 2 substrate, the modified ideal gas law can be applied more realistically with the introduct