Nitrogen-Induced Defects in VSe2 Studied by Scanning Tunneling Microscopy

Atomic-scale studies of dopants in transition metal dichalcogenides (TMDs) are important for tailoring their physical and chemical properties and provide a clearer picture of structure–property correlations. Nitrogen atoms as dopants in TMD materials promise tuning of carrier type and enhanced catalytic properties, however, experimental studies have rarely addressed their atomic-scale details. Here, we present a study of nitrogen dopants in nitrogen-plasma-treated 1T-phase VSe₂ bulk crystals by scanning tunneling microscopy (STM) and spectroscopy (STS). Three main N-induced species are classified. One type (type-I) is shown to be substitutional N atoms at the bottom-layer Se sites. Type-II has a not-yet-determined structure. The final type-III N atom is an adsorbed N atom at quasi-bridge sites between Se atoms. This N atom species exhibits distinct tip-induced dynamical motion. Density functional theory (DFT) calculations corroborate experimental STM and STS features, lending support to the proposed models. These results highlight the great variety of even simple atomic dopants in TMD materials and the need to finely control their properties for future applications.