Molecular beam epitaxy growth and scanning tunneling microscopy study of TiSe2 ultrathin films

Molecular beam epitaxy is used to grow TiSe2 ultrathin films on a graphitized SiC(0001) substrate. TiSe2 films 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 a 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 waves in TiSe2, and also pave a material foundation for potential applications based on the collective electronic states.