Growth of Wafer-Scale ReS₂ with "Tunable" Geometry toward Electron Field-Emission Application

Despite high potential, the promise of 2D materials has not been realized practically because of limits of tiny grown size and difficult manipulation of the active spot. The utilization of 2D layers is the ultimate approach, which should be supported by large-scale production. In this very first report, we demonstrate the wafer-scale production of ReS₂ using the conventional sputtering method. The controllability of ReS₂ geometry has been investigated to form typical thin films or vertically aligned layers that are further applied for field emission. The vertically aligned ReS₂ layers exhibit ultralow turn-on electric field (0.6 V μm^-1) with the current density (0.6 mA cm^-2) and significantly low threshold electric field (0.8 V μm^-1), respectively, along with outstanding emission stability. The results are attributed to weakly coupled ReS₂ layers and the high geometrical field enhancement factor (∼1.08 × 10⁵). Further, Kelvin probe force microscopy measurements confirm that lowering the work function is not solely responsible to achieve the ultralow operative field. Moreover, finite element simulation suggests that not only the length, width, and separation of the nanostructures but also the local slope plays an important role in suppressing screening effects.