Atomic Carbon Spraying: Direct Growth of Graphene on Customized 3D Surfaces of Ultrafast Optical Devices

Abstract Despite the long‐standing efforts to develop 3D graphene, which is critical for practical electronic, optoelectronic, and optical devices, the lack of synthetic methods and the use of conventional transfer approaches have limited its realization. Herein, a metal‐free, etching‐free, transfer‐free, direct synthesis of functional graphene is introduced that contours 3D‐structured surfaces of nonlinear optical devices, thereby maximizing the nonlinear interaction of graphene with guided light. Central to this method is the use of γ‐Al₂O₃, a ceramic catalyst, which generates carbon atoms from the precursor molecules and supplies them for the graphene synthesis on the 3D structures located near the catalyst through spatial diffusion, described as atomic carbon spraying (ACS). The optical nonlinearity facilitated by ACS‐processed 3D graphene is experimentally verified by realizing both passively mode‐locked laser with a pulse width of 770 fs and ultrafast optical switching with 67% enhancement in nonlinear effect over 6 mm interaction length.