Description: This article discusses hexagonal nickel carbide. Nanocrystals of hexagonal nickel carbide have been synthesized via physical vapor deposition of elemental nickel onto the surface of vertically aligned carbon nanotubes. Combining high-resolution transmission electron microscopy (HRTEM) with three-dimensional atom probe tomography (3DAP) confirmed that these nanocrystals have a hexagonal structure, are enriched in carbon, and have a composition of ~Ni-25 at. % C (Ni3C). This metastable hexagonal nickel carbide phase appears to be stabilized due to the growth of the nanocrystals on the surface of the nanotubes that act as a template and also as a source of carbon. The stability of this nickel carbide phase has also been investigated by density functional theory (DFT) calculations and compared to the experimental results.