Suppression of the Charge Density Wave State in Two‐Dimensional 1<i>T</i>‐TiSe₂ by Atmospheric Oxidation

Abstract Two‐dimensional (2D) metallic transition‐metal dichalcogenides (TMDCs), such as 1 T ‐TiSe 2 , have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1 T ‐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.