Phosphorene Degradation: Visualization and Quantification of Nanoscale Phase Evolution by Scanning Transmission X-ray Microscopy

Phosphorene, single- or few-layered black phosphorus, has been rediscovered as a promising two-dimensional material owing to its unique optical, thermal, and electrical properties with potential applications in optoelectronics, nanoelectronics, and energy storage. However, rapid degradation under ambient condition highly limits the practical applications of phosphorene. Solving the degradation problem demands an understanding of the oxidization process. We, for the first time, apply synchrotron-based X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure (XANES), and scanning transmission X-ray microscopy (STXM) for the nanoscale chemical imaging of phosphorene degradation. Through these methods, we have identified chemical details of the morphological effect and clarified thickness and proximity effects, which control the oxidization process. Furthermore, the entire oxidization process of phosphorene has also been studied by in situ XPS and XANES, showing the step-by-step oxidization process under the ambient condition. Theoretical calculations at the density functional theory level support experimental findings. This detailed study provides a better understanding of phosphorene degradation and is valuable for the development of phosphorene-based materials.