Figure 3. Atomic force microscopy characterization of blister formation at different assembly temperatures.

(a) Optical image of graphene/hBN stack on PPC (after step iv in Fig. 1f), picked up from pristine SiO₂ at 40 °C. (b) AFM topography image of region indicated in (a) – blisters are visible across the stacked region in AFM with heights of ≈50 nm. (c) The marked region in b with periodic colourscale to emphasize height variations across blisters. (d) Optical image of G/hBN stack dropped down onto a second hBN flake after approaching at 40 °C on SiO₂ (step vii in Fig. 1f). Many hemispherical blisters are visible over the stack surface. (e) AFM topography image. Encapsulated graphene flake is visible, indicated by dotted line. (f) topography line profile of blister from indicated region in d. Panel g as a, but with pick-up performed at 110 °C. (h) AFM image shows smaller overall height variation and large blister-free regions. (i) The marked region in h have two orders of magnitude less height variation compared with the region c of same size. Panel j as d, but with drop-down performed at 110 °C. No trapped blisters are visible optically or (k) in the AFM scanned region. Encapsulated few-layer graphene regions are indicated. (l) AFM line profile from i showing uniform height across the stack.