  VS2 is a challenging material to prepare stoichiometrically in the bulk, and
the single layer has not been successfully isolated before now. Here we report
the first realization of single-layer VS2, which we have prepared epitaxially
with high quality on Au(111) in the octahedral (1T) structure. We find that we
can deplete the VS2 lattice of S by annealing in vacuum so as to create an
entirely new two-dimensional compound that has no bulk analogue. The transition
is reversible upon annealing in an H2S gas atmosphere. We report the structural
properties of both the stoichiometric and S-depleted compounds on the basis of
low-energy electron diffraction, X-ray photoelectron spectroscopy and
diffraction, and scanning tunneling microscopy experiments.
