The controlled synthesis of Janus WSeS monolayers

Although Janus transition metal dichalcogenides (TMDCs) have emerged as promising two-dimensional (2D) materials due to their broken out-of-plane mirror symmetry and the resulting intrinsic dipole moment, achieving the controlled synthesis of high-quality Janus structures remains a significant challenge. In this study, we report a precise and controllable approach for the synthesis of monolayer Janus WSeS structures through the combined use of hydrogen inductively coupled plasma (H2-ICP) treatment and thermal sulfurization. Initially, high-quality monolayer WSe2 was successfully synthesized via the CVD method. Subsequently, controlled Se vacancy defects were introduced into the upper chalcogen layer of WSe2 by adjusting the H2-ICP exposure duration. According to the structural and morphological characterization results, the upper Se layer of monolayer WSe2 was completely removed after 12 min of H2-ICP treatment, resulting in a WSe structure suitable for Janus conversion. In the second stage, time-dependent thermal sulfurization was applied to the obtained WSe monolayer, leading to the successful formation of Janus WSeS structures, with the optimum sulfurization duration determined to be 30 min. The formation and quality of the Janus WSeS layers were systematically confirmed by Raman spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL), and optical microscopy analyses. The obtained results demonstrate that precise control of both H2-ICP treatment and sulfurization duration is critical for achieving stable and high-quality Janus WSeS monolayers. We believe that the proposed synthesis strategy and the findings presented in this work will provide valuable insights for the development of next-generation Janus-based electronic and optoelectronic devices.