a, ToF-SIMS Si+ ion images for a cover glass with graphene-covered fixed A549 cells analyzed with four different ion doses: (left to right) 1.3 × 1013, 1.3 × 1014, 1.3 × 1015, and 1.3 × 1016 ions/cm2. b, HIM images of the bombarded regions of the samples corresponding to ToF-SIMS images in a show no visible large-scale defects in graphene due to ion beam bombardment of at least up to 1.3 × 1014 ions/cm2; however, the ion doses more than 1.3 × 1015 ions/cm2 etch the graphene away. c–d, ToF-SIMS Si+ image counts depending on the ion doses of up to 1.3 × 1015 (c) and 1.3 × 1016 ions/cm2 (d) reveal no ion dose dependence of secondary ion intensity within the ion dose of 1014 ions/cm2, thus indicating that the sputtering through single-layer graphene is not due to the defects generated by the ion beam bombardment. The SIMS images were taken for the ion dose much less than 1014 ions/cm2. The large-scale defects in the HIM images in b are due to the cracks in the graphene layer on the cells. Wet cells under graphene with cracks were generally not used for SIMS imaging. Scale bar, 5 μm (a–b). Results presented are obtained from a single experiment.