Oxidation of core–shell MoO2–MoS2nanoflakes in different O2ambience

Oxidation of MoO2/MoS2 core–shell nanoflakes (NFs) has been investigated in different oxidation ambients i.e. oxygen (O2) gas and its plasma. Core–shell nanoflakes are oxidized at temperatures varying from 150 °C to 450 °C and the effect of oxidation temperature on the structural and morphological changes of nanoflakes are investigated systematically. High-resolution transmission electron microscopy (TEM) images show that shell of nanoflake is oxidized with varying thicknesses and strongly depending upon the temperature and ambience. X-ray diffraction (XRD) and Raman analysis revealed the formation of MoO3 at low temperature (⩽150 °C) in O2 plasma. Whereas, in O2 gas at a relatively higher temperature (⩾350 °C). Scanning electron microscopy (SEM) results show noticeable changes in the morphology as deformation of nanoflakes after oxidation. X-ray photoelectron spectroscopy (XPS) revealed, oxidizing in O2-plasma led to multiple oxidation states of Mo (4+, 5+, and 6+) and S (2−, 6+). It is evident that the extent of oxidation of MoS2 shell is higher in plasma due to reactive species of oxygen (O+, , O*, etc), as compared to O2 gas.