蓝宝石和二氧化硅上单层MoS2的晶片级MOCVD生长

The typical growth of MoS₂ involves carrier gases of 350 sccm Ar, 10 sccm of H₂ and 8 sccm of diethyl sulphide at the growth temperature of 850◦ C for  ~20 min. The hydrogen flow plays double roles during the synthesis process: Vaporization of precursors and desulfurization of MoS₂ flakes,  which lead to growing and etching of MoS₂ flakes, individually.1,2 Thus, it is important to apply the appropriate amount of H₂ during the  synthesis of the MoS₂. To optimize the H2 flow, different flows of H₂ were applied during the growth procedures. Figure S₁ shows the effect  of various H₂ flow rates on the quality of the MoS₂ film on SiO₂ at the sodium molybdate (Na₂MoO₄) concentration of 0.006 M. Clearly, the  nucleation density of MoS₂ can be substantially decreased at the optimal H₂ flow rate of 10 sccm.

The fingerprint Raman peaks of MoS₂ at 384 cm⁻¹  and 403 cm⁻¹  correspond to the in- plane vibrational mode E’_2g and out-of-plane mode A_1g respectively for as-grown MoS₂ on sapphire. The relative distance of the two peaks is strongly refected by the thickness of MoS₂ film.3  Figure S₃  shows the widths for monolayer, bilayer, and multilayer (at the nucleation sites) of MoS₂ are 19 cm⁻¹ , 21.3 cm⁻¹ and 25.7 cm⁻¹ , individually.

To check the atomic structure of grown MoS₂, as-grown MoS₂ films need to be transferred onto transmission electron microscopy (TEM) grids.  Figure S5 shows a representative trans- ferred MoS₂ film on a SiN TEM grid with multi-magnification of optical images.

After transferring as-grown MoS₂ onto SiO₂ or TEM grids, the remained sapphire substrates were cleaned in an ultrasonic bath with acetone,  isopropanol and deionized (DI) water. Subsequently, the cleaned sapphire substrates were annealed in the quartz tube in air at 1100◦ C for 1 h.

Afterward, these sapphire substrates were treated with KOH, spin-coated with sodium molybdate, and then placed in the quartz tube for the  second time of growth. After finishing growth, the MoS₂ film was transferred, and the sapphire substrate is again used for the third time of  growth after the cleaning cycle. The repeated growth samples were checked with an optical microscope, as displayed in the Figure S6.

Fig s4

The XPS survey spectra of as-grown monolayer MoS₂ on sapphire, on SiO₂, and after transfer onto SiO₂ and SiN substrates in Figure 3 of the main  text were measured before and after the wet-transfer, as displayed in Figure S4.