Phase-modulated 3D-hierarchical 1T/2H WSe2 nanoscrews by a plasma-assisted selenization process as high performance NO gas sensors with a ppb-level detection limit

Abstract

In this work, we create plasma-engineered-1T/2H 3D-hierarchical WSe₂ nanoscrews derived from WO_x 3D-hierarchical nanoscrews through a low-temperature plasma-assisted selenization process with controlled shapes grown using a glancing angle deposition (GLAD) system. Through a detailed investigation of chemical bonding in WSe₂ by XPS and TEM, it was found that hybrids of 1T and 2H phases can be engineered, depending on substrate temperatures under plasma treatment. The GLAD system was exploited to achieve 1D nanostructures to enhance the surface-area-to-volume ratio compared to that of flat films, thus increasing the capacity for sensing applications. Here, WSe₂ was chosen as the best sensing material for nitric oxide (NO) gas detection because of its p-type semiconducting properties and effective charge transfer with NO molecules. The performance of WSe₂ nanoscrew gas sensors which was closely associated with 1T–2H phases was investigated where the barrier height decreased by the heterojunction of 1T/2H phases in WSe₂ exhibiting the best sensing capability at a ratio of 0.41 between 1T and 2H phases was found. The plasma-engineered-1T/2H WSe₂ 3D-hierarchical nanoscrews exhibited a highly sensitive performance with a response over 40% at 60 ppb at room temperature with a detection limit of approximately ∼15 ppb. Finally, ∼100% response in air using the plasma-engineered-1T/2H WSe₂ 3D-hierarchical nanoscrews was demonstrated, proving their potential for application as next-generation high-performance gas sensors.