Advances in Atomic Force Microscopy: Imaging of Two- and Three-Dimensional Interfacial Water

Abstract

Interfacial water is closely related to many core scientific and technological issues, covering a broad range of fields, such as material science, geochemistry, electrochemistry and biology. The understanding of the structure and dynamics of interfacial water is the basis of dealing with a series of issues in science and technology. In recent years, atomic force microscopy (AFM) with ultrahigh resolution has become a very powerful option for the understanding of the complex structural and dynamic properties of interfacial water on solid surfaces. In this perspective, we provide an overview of the application of AFM in the study of two dimensional (2D) or three dimensional (3D) interfacial water, and present the prospect and challenges of the AFM-related techniques in experiments and simulations, in order to gain a better understanding of the physicochemical properties of interfacial water.

Keywords: atomic force microscopy; interfacial water; liquid/solid interface; machine learning; structure and dynamics.

FIGURE 1

2D water networks on Ni(111) (A) AFM images of the 2D water networks of the same area on the terraces, the tip height decreases from left to right (B) The proposed structure of the water monolayer based on the AFM images. The gray, cyan, green, yellow and red spheres represent Ni, H, topmost O, middle O and bottommost O atoms, respectively; the unit cell of (√28 × √28) R19 is represented by the gray rhombus; the bottom panels are the side-view of the above structures, without H atoms for clarity (C) The schematic diagram of the tip and step. The gray, cyan, black and red spheres represent Ni, H, C and O atoms, respectively (D) Constant-height AFM images of the water network at the step edge, the tip height decreases from left to right (E) AFM image of the same region in (D), but the tip trajectory is consistent with that of the STM image, as the solid blue line in (C). The red dots in (D–E) represent the O-atom positions (F) The water network structure at the step edge proposed based on the AFM images. Adapted with permission from Shiotari, et al., 2019. Physical Review Materials 3(9): 093,001 (Shiotari et al., 2019).

FIGURE 2

The growth process of zigzag and armchair edges of the 2D bilayer hexagonal ice formed on Au(111) (A–B) Constant-height AFM images and corresponding models of the steady state (1) and metastable states (2–4) of the zigzag (A) and armchair edges (B) (C–D) Time-elapsed snapshots during the growth of zigzag (C) and armchair edges (D) obtained by MD simulation. In (A–B), the proposed growing process (from one to 4) is indicated by blue arrows; the addition of one bilayer water pair is labeled by a red arrow in AFM images; the red balls and sticks in ball-stick models represent the newly added bilayer water pairs, while the blue ones represent the existing structures. In (C–D), the simulation times are shown on bottom right of each snapshot, the bottom- and top-layer water molecules of the preexistent bilayer ice are denoted by the blue and red spheres, respectively; the newly deposited water molecules are denoted by the green spheres. Adapted with permission from Ma, et al. 2020. Nature 577(7788): 60–63 (Ma et al., 2020).