Severe carbon accumulation on black phosphorous flakes induced by synchrotron x-ray radiation

Two-dimensional (2D) materials, such as black phosphorus (BP) and transition metal dichalcogenide, recently gained much interest due to their unique electronic, photonic, and mechanical properties. Synchrotron-based scanning photoelectron microscopy (s-SPEM) with a spatial resolution (down to 70 nm) has actively applied for exploring the relationship between chemical information and electronic structure of 2D materials on concerned local surface area. Here, we compare carbon accumulation on the surface of BP and MoS2 during synchrotron beam irradiation. During the BP characterization, carbon was rapidly accumulated on BP surface as irradiation progress, while MoS2 demonstrated better resistance to carbon accumulation in comparison to BP. Our work suggests that the higher surface reactivity of BP results in the formation of even BP-carbide structure upon the irradiation, while MoS2 with relatively low reactivity is rather stable against carbon accumulation. This photon-induced carbon accumulation causes the misleading result of surface chemical information and electronic structure in highly reactive 2D materials or nanostructures.