  Vanadium dichalcogenides have attracted increasing interests for the charge
density wave phenomena and possible ferromagnetism. Here, we report on the
multiphase behavior and gap opening in monolayer VTe2 grown by molecular beam
epitaxy. Scanning tunneling microscopy and spectroscopy study revealed the
(4*4) metallic and gapped (2root3*2root3)charge-density wave pahses with an
energy gap of ~40 meV. Through the in-plane condensation of vanadium atoms, the
typical star-of-David clusters and truncated triangle-shaped clusters are
formed in (4*4) and (2root3*2root3) phases respectively, resulting in different
surface morphologies and electronic structures as confirmed by density
functional theory calculations with on-site coulomb repulsion. The CDW-driven
reorganization of the atomic structure weakens the ferromagnetic superexchange
coupling and strengthens the antiferromagnetic exchange coupling on the
contrary, suppressing the long-range magnetic order in monolayer VTe2.
