Atomic-Scale Mechanisms of MoS₂ Oxidation for Kinetic Control of MoS₂/MoO₃ Interfaces

Oxidation of transition metal dichalcogenides(TMDs) occurs readilyunder a variety of conditions. Therefore, understanding the oxidationprocesses is necessary for successful TMD handling and device fabrication.Here, we investigate atomic-scale oxidation mechanisms of the mostwidely studied TMD, MoS2. We find that thermal oxidationresults in & alpha;-phase crystalline MoO3 with sharp interfaces,voids, and crystallographic alignment with the underlying MoS2. Experiments with remote substrates prove that thermal oxidationproceeds via vapor-phase mass transport and redeposition, a challengeto forming thin, conformal films. Oxygen plasma accelerates the kineticsof oxidation relative to the kinetics of mass transport, forming smoothand conformal oxides. The resulting amorphous MoO3 canbe grown with subnanometer to several-nanometer thickness, and wecalibrate the oxidation rate for different instruments and processparameters. Our results provide quantitative guidance for managingboth the atomic scale structure and thin-film morphology of oxidesin the design and processing of TMD devices.