Molecular beam epitaxy growth and scanning tunneling microscopy study of TiSe$_2$ ultrathin films

TL;DR

This study uses molecular beam epitaxy and scanning tunneling microscopy to grow and analyze ultrathin TiSe2 films, revealing defect types and the persistence of charge density waves at atomic scales, with implications for electronic applications.

Contribution

It demonstrates the growth of TiSe2 ultrathin films with layer-by-layer mode and characterizes their defect structures and charge density wave behavior at the single-unit-cell level.

Findings

Charge density waves survive in single-unit-cell TiSe2.

Defect density affects the correlation length of charge density waves.

TiSe2 ultrathin films exhibit specific defect types such as Se vacancies and interstitials.

Abstract

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.