Straightening of the 2D black phosphorus using electron beam irradiation

Large area 2D nanomaterials are susceptible to formation of surface corrugations during synthesis, transfer and handling of samples and their physicochemical properties are extraordinarily affected by the formation of surface corrugations. Even though several strategies have been devised by researchers for smoothing the 2D flakes, the issue is far from resolved. Here, we report the straightening of Black Phosphorus (BP) flakes using electron beam irradiation that enables the removal of ripples, disclination and line defects from lattice. The crystallinity and buckling of flake is controlled by varying the electron fluence rate and irradiation time in a high resolution transmission electron microscopy set-up. Experimental results show that the optimal electron beam exposure (20 to 30 minutes of exposure at fluence rate = 1.02 ×10²⁹ m^-2 s^-1) de-stresses/ relaxes the lattice and the maximum ordering of lattice planes is achieved; beyond which, the stress in lattice rises again and lattice planes start buckling. Thus, straightening of the 2D flakes using electron beam ensures removal of surface corrugations with nanoscale precision and allows for real-time monitoring of the process.