Extended Data Fig. 1: Experimental evidence for the bilayer nature of 2D ice.
From: Atomic imaging of the edge structure and growth of a two-dimensional hexagonal ice
a, d, STM images of a bilayer ice island (a) and cluster (b). Set point, 100 mV and 10 pA. b, e, AFM images of the same ice island (b) and cluster (e). b was acquired at the constant-current mode with set point 100 mV and 50 pA. e was recorded at a constant height of 280 pm, referenced to the set point of 100 mV and 50 pA on the Au(111) substrate. c, Height-distribution diagram within the red dashed rectangular area in a. The red arrow denotes the bottom layer of the bilayer ice, proving the bilayer nature of the 2D ice. f, Height profile across the red line shown in d, giving two different steps with heights of about 150 pm and about 250 pm, consistent with the results of the 2D ice island. g, False-colour STM image of a 2D ice island grown on a Au(111) surface, where the honeycomb structure of the 2D ice and the herringbone reconstruction of the Au(111) surface are distinguishable. The atomically resolved STM images of the Au(111) lattice are superimposed within the face-centred cubic (fcc) and hexagonal close-packed (hcp) regions, showing good registry between the 2D ice and the Au substrate. The set points are 100 mV and 10 pA and 5 mV and 6 nA for the ice island and the Au(111) lattice, respectively. The white dashed grids correspond to the 1 × 1 lattice of Au(111) within the fcc and hcp regions. The inset at the upper-right corner is a composite 2D-FFT image of the Au(111) and 2D-ice lattice, and shows the corresponding 1 × 1 and \(\sqrt{3}\times \sqrt{3}\) periodicities.
