Probing two-dimensional ices with scanning probe microscopy*

Two-dimensional (2D) water/ices are responsible for a broad spectrum of phenomena in materials science, chemistry, and biology. Particularly, the edges of 2D ice play key roles in the ice growth, melting and catalytic reaction, but atomic-scale structural characterization still remains a big challenge due to the fragileness and high reactivity of the ice edges. Here we report atomic-scale imaging of the edge structures of a 2D bilayer ice grown on Au(111) surface with weakly perturbative non-contact atomic force microscopy (1, 2). We found a new type of edge, aligning along the armchairdirection but reconstructed with 5756-member rings, coexisting with the zigzag edge commonly observed in two-dimensional hexagonal crystals. We were further able to deduce different growth behaviors for the zigzag and armchair edges from the frozen metastable structures at the two edges. In addition, we explore the impact of alkali metal ions on the structure of 2D ice. By changing the concentration of alkali metal ions, various new ice phases can be obtained. Those results reveal new understanding of the stability and growth of 2D ices.