Reversible self-intercalation in trilayer 1T-NiTe₂

Self-intercalation in layered transition metal dichalcogenides provides a promising route for modulating lattice structures and electronic properties without introducing extrinsic species. As an emerging type-II Dirac semimetal, 1T-NiTe_2 has attracted considerable interest in the two-dimensional limit. However, reversible self-intercalation in atomically thin NiTe_2 has not been reported. Here, we report a reversible self-intercalation process in trilayer 1T-NiTe_2 synthesized on a graphene substrate via van der Waals epitaxy. Upon post-annealing, Te desorption drives the spontaneous incorporation of Ni atoms into the van der Waals gaps, forming an ordered \surd 3\times \surd 3 superstructure, which can be fully reversed under Te-rich conditions. Scanning tunneling microscopy reveals the formation of this superstructure, accompanied by a modulation of the electronic states near the Fermi level. Furthermore, field emission resonance measurements demonstrate a clear modulation of the local work function induced by self-intercalation, indicative of an intercalation-driven redistribution of electronic density. Our work establishes reversible self-intercalation as an effective route for engineering superlattice potentials and tuning surface electronic properties in two-dimensional materials.