In Situ Closing the van der Waals Gap of Two-Dimensional Materials

Self-intercalation in two-dimensional (2D) materials, converting 2D materials into ultrathin covalently bonded materials, presents great possibilities for studying a new family of quantum-confined materials with the potential to realize multifunctional behavior. However, understanding the mechanisms and associated in situ kinetics of synthesizing self-intercalated 2D (ic-2D) materials, particularly at the atomic scale, remains elusive, greatly hindering the practical applications of ic-2D crystals. Here, we successfully in situ synthesized ic-2D thin films via thermal annealing of their parental TMDCs inside an electron microscope. We atomically visualized the evolution from TaS