Suppression of the Charge Density Wave State in Two-Dimensional 1T-TiSe₂ by Atmospheric Oxidation

Two-dimensional (2D) metallic transition-metal dichalcogenides (TMDCs), such as 1T-TiSe₂ , have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1T-TiSe₂ undergoes rapid oxidation under ambient conditions, significantly affecting its CDW phase-transition behavior. We comprehensively investigate the oxidation process of 2D TiSe₂ 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.