Abstract
We report findings on the structural stability of exfoliated monolayer MnO2 sheets. Our study reveals that monolayer MnO2 sheets display two specific kinds of structural modification under electron irradiation. An atomic reconstruction (2 x 1) and a phase of MnO, induced by ordered oxygen vacancies, were identified by transmission electron microscopy techniques and further characterized by comparison with density-functional theory calculations. These findings are expected to significantly broaden current knowledge of the structural stability of ultrathin layered sheets.