Not yet reviewed by Pith; the record is open.

Although two-dimensional (2D) oxide semiconductors exhibit remarkable oxidation resistance compared to conventional 2D materials, the microscopic physical processes that govern this behavior at the atomic scale remains elusive. Using first-principles calculations, we investigated the defect formation and oxidation dynamics of the GeO${_2}$ monolayer (ML). The investigations reveal that the intrinsic GeO${_2}$ ML is resistant to oxidation due to strong electrostatic repulsion between surface oxygen ions and approaching O$_2$ molecules, effectively suppressing chemisorption. In contrast, defective GeO$_2$ ML with surface O vacancies shows vulnerability to oxidation with the O$_2$ molecule occupying the vacancy through a low-energy activation energy ($E_a$) of 0.375 eV. Remarkably, the subsequent O$_2$ dissociation into atomic species faces a higher activation barrier ($E_a$ = 1.604 eV), suggesting self-limiting oxidation behavior. Electronic structure analysis demonstrates that oxidation primarily modifies the valence bands of defective GeO${_2}$ MLs through oxygen incorporation, while the conduction bands and electron effective mass recover to pristine-like characteristics. We further proved that the high O$_2$ pressure hinders the formation of the O vacancy, while high temperature increases the oxidation rate in GeO$_2$ ML. These atomic-level insights not only advance our understanding of oxidation resistance in 2D oxides but also provide guidelines for developing stable GeO${_2}$-based nanoelectronic devices.