Photochemically Patterning Graphene in a Highly Efficient, Anisotropic, and Clean Way

Photochemical oxidation is usually used for mild surface treatment rather than graphene patterning and is acknowledged to be far inferior to the traditional reactive ion etching. Some strategies have even been taken gradually to widen its applications, but the low efficiency makes it a big challenge. In this study, we report a way to pattern graphene in a highly efficient, anisotropic, and clean way by the H2O-based photochemical oxidation under irradiation of the xenon excimer lamp (lambda = 172 nm). In a gradient magnetic field, the photodissociated paramagnetic OH(X-2 Pi) and H(1(2)S) radicals drift directionally toward graphene at a speed of wind. The anisotropic photochemical etching is tunable and has an etching rate exceeding 21 nm/min, applicable to making higher quality graphene micro/nanostructures under shadow masks. When combined with the traditional e-beam lithography, the photoinduced cross-linking of poly(methyl methacrylate) 495 resist leads to fabricating clean graphene patterns by peeling off the mask, even removing the initial organic residues. The surface chemical analyses and first-principles calculation reveal that the directional OH(X-2 Pi) radical plays a vital role in etching graphene. This study opens up an avenue of photochemical oxidation for material functionalization, etching, and clean patterning.