Microscopic evidence of strong interactions between chemical vapor deposited 2D MoS2 film and SiO2 growth template

Two-dimensional MoS₂ film can grow on oxide substrates including Al₂O₃ and SiO₂. However, it cannot grow usually on non-oxide substrates such as a bare Si wafer using chemical vapor deposition. To address this issue, we prepared as-synthesized and transferred MoS₂ (AS-MoS₂ and TR-MoS₂) films on SiO₂/Si substrates and studied the effect of the SiO₂ layer on the atomic and electronic structure of the MoS₂ films using spherical aberration-corrected scanning transition electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The interlayer distance between MoS₂ layers film showed a change at the AS-MoS₂/SiO₂ interface, which is attributed to the formation of S-O chemical bonding at the interface, whereas the TR-MoS₂/SiO₂ interface showed only van der Waals interactions. Through STEM and EELS studies, we confirmed that there exists a bonding state in addition to the van der Waals force, which is the dominant interaction between MoS₂ and SiO₂. The formation of S-O bonding at the AS-MoS₂/SiO₂ interface layer suggests that the sulfur atoms at the termination layer in the MoS₂ films are bonded to the oxygen atoms of the SiO₂ layer during chemical vapor deposition. Our results indicate that the S-O bonding feature promotes the growth of MoS₂ thin films on oxide growth templates.