HfO ₂ on UV–O ₃ exposed transition metal dichalcogenides: interfacial reactions study

The surface chemistry of MoS2, WSe2 and MoSe2 upon ultraviolet (UV)–O3 exposure was studied in situ by x-ray photoelectron spectroscopy (XPS). Differences in reactivity of these transition metal dichalcogenides (TMDs) towards oxidation during UV–O3 were observed and correlated with density functional theory calculations. Also, sequential HfO2 depositions were performed by atomic layer deposition (ALD) while the interfacial reactions were monitored by XPS. It is found that the surface oxides generated on MoSe2 and WSe2 during UV–O3 exposure were reduced by the ALD process ('self-cleaning effect'). The effectiveness of the oxide reduction on these TMDs is discussed and correlated with the HfO2 film uniformity.