Self-Limiting Layer-by-Layer Oxidation of Atomically Thin WSe₂

Abstract

Growth of a uniform oxide film with a tunable thickness on two-dimensional transition metal dichalcogenides is of great importance for electronic and optoelectronic applications. Here we demonstrate homogeneous surface oxidation of atomically thin WSe₂ with a self-limiting thickness from single- to trilayers. Exposure to ozone (O₃) below 100 °C leads to the lateral growth of tungsten oxide selectively along selenium zigzag-edge orientations on WSe₂. With further O₃ exposure, the oxide regions coalesce and oxidation terminates leaving a uniform thickness oxide film on top of unoxidized WSe₂. At higher temperatures, oxidation evolves in the layer-by-layer regime up to trilayers. The oxide films formed on WSe₂ are nearly atomically flat. Using photoluminescence and Raman spectroscopy, we find that the underlying single-layer WSe₂ is decoupled from the top oxide but hole-doped. Our findings offer a new strategy for creating atomically thin heterostructures of semiconductors and insulating oxides with potential for applications in electronic devices