Extended Data Figure 1: 2D water captured between graphene monolayers.

a, Confined water at low magnification. The lateral size of such water pockets was typically ∼100 nm. The chequered pattern reveals a collection of ice crystallites. b, Another example of a high-magnification image of 2D ice. The inset shows selected area electron diffraction from a region approximately 120 nm in diameter. The four diffraction spots connected for clarity by the red lines yield a = 2.83 ± 0.03 Å, the same as the value obtained using the fast Fourier transform in Fig. 1.