Synthesis Of Vertical Moo2/Mos2 Core-Shell Structures On An Amorphous Substrate Via Chemical Vapor Deposition

Vertical MoO2/MoS2 core-shell structures were synthesized on an amorphous surface (SiO2) by chemical vapor deposition at a high heating rate using a configuration in which the vapor phase was confined. The confined reaction configuration was achieved by partially covering the MoO3-containing boat with a substrate, which allowed rapid buildup of the partially reduced MoO3-x crystals in an early stage (below 680 degrees C). Rapid temperature ramping to 780 degrees C enabled spontaneous transition of the reaction environment from sulfur-poor to sulfur-rich, which induced a sequential phase transition from MoO3-x to intermediate MoO2 and finally to MoO2/MoS2 core-shell structures. The orthorhombic crystal structure of MoO3-x contributed to the formation of vertical crystals on the amorphous substrate, whereas the nonvolatility of the subsequently formed MoO2 enabled layer-by-layer sulfurization to form MoS2 on the oxide surface with minimal resublimation loss of MoO2. By adjustment of the sulfurization temperature and time, excellent control over the thickness of the MoS2 shell was achieved through the proposed synthesis method.