Point defects critically govern the properties of two-dimensional semiconductors, yet their atomic-scale characteristics in the emerging MoSi2N4 family remain unexplored. Here we combine atomic-resolution scanning transmission electron microscopy and first-principles calculations to systematically investigate point defects in monolayer semiconducting WSi2N4 and MoSi2N4. We identify ten distinct defect types, with Si-for-top-N antisites (SiN(t)), double-middle-N divacancies (VN(m)2), and double-top-N divacancies (VN(t)2) being the most abundant. These defects induce mobility modulation and bandgap reduction — in some cases leading to complete band closure and insulator-to-metal transitions — and, in certain configurations, give rise to spin-polarized bands with localized magnetic moments. Additionally, we observe low-dimensional assemblies formed via defect self-organization, including 2D SiN(t) networks and 1D Si2Mo chains. Our findings establish fundamental defect–property relationships and provide insights for defect-driven engineering of electronic and magnetic states in 2D WSi2N4 and MoSi2N4 semiconductors. The MoSi2N4 family is an emerging class of van der Waals materials with interesting properties. Here, the authors report a systematic characterization of point defects in monolayer WSi2N4 and MoSi2N4, showing their influence on the electronic properties of the materials.
Tong et al. (Mon,) studied this question.