Chemical vapor deposition growth and characterization of drop-like MoS2/MoO2 granular films

Monolayer MoS2 is an emerging two-dimensional semiconductor with wide-ranging potential applications in novel optoelectronic devices and catalysis. Here, we report the growth of drop-like monolayer MoS2/MoO2 granular films on SiO2/Si substrate by chemical vapor deposition method. The as-synthesized films were systematically characterized by various means of optical microscopy, X-ray/ultraviolet photoemission spectroscopy, scanning electron microscopy, atomic/kelvin force microscopy, X-ray diffraction, Raman and photoluminescence techniques. The combined results of atomic force microscopy and scanning electron microscopy clearly present novel drop-like granulars and domain boundaries, ascribed to lower growth temperature. X-ray photoemission spectroscopy results complemented by Raman and X-ray diffraction results confirm the formation of MoS2/MoO2 granular films. The ultraviolet photoemission spectroscopy, along with kelvin force microscopy, reveals a different nature of surface potential of drop-like MoS2 granular films compared with crystalline MoS2, owing to electron transfer from MoS2 to MoO2 and drop-like structure. Our study broadens the scope of two-dimensional transition metal dichalcogenides research and reveals the distinct physical properties of drop-like monolayer MoS2 granular films.