  The structural and chemical degradations of phosphorene severely limit its
practical applications despite the enormous promise. In this regard, we
investigate a plethora of microscopic kinetic mechanisms and develop a
degradation phase diagram within the first-principles calculations. At 400 K,
the degradation and the competing self-annealing proceeds through the merger
and annihilation of vacancies, respectively, which are triggered via itinerant
vacancy and adatom. A further increase in temperature beyond 650 K, the
structural degradation results through the emission of the undercoordinated
atoms from the defect and the concurrent pair-wise sublimation. The role of
inter-layer vacancy diffusion is discarded in the context of structural
degradation. The chemical degradation is routed through the dissociation of
oxygen molecule that is either activated at the room-temperature on the
pristine surface or spontaneous at the single-vacancy site. The present results
are in agreement with the few available experimental conjectures and will
motivate further efforts.
