  Molecular beam epitaxy is used to grow TiSe2 ultrathin films on graphitized
SiC(0001) substrate. TiSe2films proceed via a nearly layer-by-layer growth mode
and exhibit two dominant types of defects, identified as Se vacancy and
interstitial, respectively. By means of scanning tunneling microscopy, we
demonstrate that the well-established charge density waves can survive in
single unit-cell (one triple layer) regime, and find a gradual reduction in
their correlation length as the density of surface defects in TiSe2 ultrathin
films increases. Our findings offer important insights into the nature of
charge density wave in TiSe2, and also pave a material foundation for potential
applications based on the collective electronic states.
