Suppression of the Charge Density Wave State in Two-Dimensional $\mathrm{1T-TiSe_{2}}$ by Atmospheric Oxidation

Two‐dimensional (2D) metallic transition‐metal dichalcogenides (TMDCs), such as 1T‐TiSe$_2$, have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1T‐TiSe$_2$ undergoes rapid oxidation under ambient conditions, significantly affecting its CDW phase‐transition behavior. We comprehensively investigate the oxidation process of 2D TiSe$_2$ by tracking the evolution of the chemical composition and atomic structure with various microscopic and spectroscopic techniques and reveal its unique selenium‐assisting oxidation mechanism. Our findings facilitate a better understanding of the chemistry of ultrathin TMDCs crystals, introduce an effective method to passivate their surfaces with capping layers, and thus open a way to further explore the functionality of these materials toward devices