Observation and characterization of grain boundaries in monolayer MoSe₂

Abstract Grain boundaries of MoSe 2 impact their electrical, optoelectronic, and mechanical properties. The simple, efficient and rapid method to visualize the large-area grains and grain boundaries in MoSe 2 is highly demanded but still lacking. Here, we show a simple, efficient, and rapid method for visualization of large-area grain boundaries in continuous CVD monolayer MoSe 2 films that were transferred on a SiO 2 substrate. As the monolayer MoSe 2 was exposed to vapor hydrofluoric acid (VHF), the VHF diffused through grain boundary-based defects in the MoSe 2 films and resulted in differential etching of the SiO 2 at the MoSe 2 grain boundaries and the SiO 2 underneath the MoSe 2 grains. The positions of the grain boundaries were prominent owing to the height difference of SiO 2 and can be observed using optical microscopy, scanning electron microscopy, or Raman spectroscopy. This method would contribute to optimizing the growth process of MoSe 2 and its device application.