Creating Nanopores in Graphene by Ion Beam Irradiation: Geometry, Quality, and Efficiency.

Ion beam irradiation is a promising approach to fabricate nanoporous graphene for various applications including DNA sequencing, water desalination, and phase separation. Further advancement of this approach and rational design of experiments all require improved mechanistic understanding of the physical "drilling" process. Here, we demonstrate that, by using oblique ion beam irradiation, the nanopore family is significantly expanded to include more types of nanopores of tunable geometries. With the hopping, sweeping, and shoving mechanisms, ions sputter carbon atoms even outside the ion impact zone, leading to extended damage particularly at smaller incident angles. Moreover, with lower energies, ions may be absorbed to form complex ion-carbon structures, making the graphene warped or curly at pore edges. Considering both efficiency and quality, the optimal ion energy is identified to be 1000 eV at an incident angle of 30° with respect to the graphene sheet and 400-500 eV at higher incident angles. All these results suggest the use of oblique ion beam and moderate energy levels to efficiently fabricate high-quality nanopores of tunable geometries in graphene for a wide range of applications.