  Realizing van der Waals (vdW) epitaxy in the 80s represents a breakthrough
that circumvents the stringent lattice matching and processing compatibility
requirements in conventional covalent heteroepitaxy. However, due to the weak
vdW interactions, there is little control over film qualities by the substrate.
Typically, discrete domains with a spread of misorientation angles are formed,
limiting the applicability of vdW epitaxy. Here we report the epitaxial growth
of monocrystalline, covalent Cr5Te8 2D crystals on monolayer vdW WSe2 by
chemical vapor deposition, driven by interfacial dative bond formation. The
lattice of Cr5Te8, with a lateral dimension of a few ten microns, is fully
commensurate with that of WSe2 via 3 x 3 (Cr5Te8)-7 x 7 (WSe2) supercell
matching, forming a single crystalline moire superlattice. Our work has
established a conceptually distinct paradigm of thin film epitaxy termed dative
epitaxy, which takes full advantage of covalent epitaxy with chemical bonding
for fixing the atomic registry and crystal orientation, while circumventing its
stringent lattice matching and processing compatibility requirements;
conversely, it ensures the full flexibility of vdW epitaxy, while avoiding its
poor orientation control. Cr5Te8 2D crystals grown by dative epitaxy exhibit
square magnetic hysteresis, suggesting minimized interfacial defects that can
serve as pinning sites.
