Extended Data Figure 2: Atomic force microscopy of graphene.

a, Exfoliated, unprocessed monolayer graphene. Step height along the red line shown on the height (z) map is 1.0 ± 0.3 nm. b, c, Representative data from aluminium-free chips that are run in parallel with the devices used in bending stiffness measurements. Step heights are 2.5 ± 0.4 nm and 2.4 ± 0.5 nm. Chips that look clean under the optical microscope typically have 2–4 nm total step heights. We occasionally see higher residue lines at the edges of the graphene, as in c. The PMMA residue is not sufficiently thick to explain the notably increased bending stiffness of the graphene (see Methods). Scale bars are 1 µm.