Growth of tungsten disulfide bilayers featuring Moiré superlattices: A surface energy perspective

Abstract

The bilayer (BL) transition metal dichalcogenides (TMDs), with their elevated carrier mobility and narrowed bandgap, are advantageous for future electronic applications in comparison with their monolayer (ML) counterparts. Here, we introduce a facile and efficient approach for the chemical vapor deposition synthesis of BL WS2. The method involves an acetic acid sonication treatment to modify the substrate surface morphology and the surface energy, which regulates the nucleation processes and shapes the growth mode of WS2 crystals. Further modifications to the growth conditions yield high-quality ML and BL WS2 films. A comparative study confirms the superior valley polarization and higher carrier mobility of BL WS2 compared with its ML counterpart. Additionally, a minor twist angle existed between the upper and lower layers, featuring a Moiré superlattice. This work reveals the role of surface morphology and surface energy in the growth of TMDs. Simultaneously, it offers insights into the controlled preparation of vertically stacked homo- and heterojunctions.