Structural changes in HfSe₂ and ZrSe₂ thin films with various oxidation methods

HfSe₂ and ZrSe₂ transition metal dichalcogenide (TMD) films are of interest for their potential applications in field-effect transistors. To implement the use of these materials in devices, the formation of an oxide/TMD interface with well-defined dielectric/semiconductor properties is essential. The method by which the oxide is created, as well as any structural changes in the TMD under the conditions used for oxide formation, will affect the performance of both the dielectric and the semiconductor. In this work, we describe the structure of the oxide and the morphological changes occurring in HfSe₂ and ZrSe₂ under several oxidation conditions. Using in situ transmission electron microscopy, we show that room temperature oxidation in air causes segregation of Se and uneven surface oxidation. Exposure to O₂ at high temperatures readily forms a crystalline oxide layer, although defects and cavities are also detectable. Finally, plasma oxidation forms a smoother and more uniform oxide layer than that formed by thermal oxidation.