Robustness of Bilayer Hexagonal Ice against Surface Symmetry and Corrugation

Result of the Month

Robustness of Bilayer Hexagonal Ice against Surface Symmetry and Corrugation | © American Physical Society

(a) Close-up STM image (set point: 100 mV, 5 pA) of a monolayer ice island on Au(110)-1 × 2 surface. (b)–(d) Height dependent AFM imaging at tip heights of 100 pm (b), −50 pm (c), −130 pm (d). The isolated H-up water molecule on the topmost gold rows and flat-lying water molecule in the trench is highlighted by yellow circles and red arrow, respectively. The yellow arrow in (b) indicates the jump of the flat-lying water molecule from near-top to near-bridge sites. (e) Top and side views of the atomic model of monolayer ice. Au, H, and O atoms are denoted as yellow, white, and red spheres, while water molecules at the bridge site are highlighted by blue spheres. (f)–(h) Simulated AFM images acquired at tip heights of 11.2 Å (f), 10.1 Å (g), 9.6 Å (h). The dash rectangles indicate the 5 × 2 unit cell. The tip heights of experimental and simulated AFM images are defined in the Materials and Methods.

Author: Pu Yang, Chen Zhang, Wenyu Sun, Jia Dong, Duanyun Cao, Jing Guo, Ying Jiang Institute: ''Beijing Normal University, College of Chemistry, Atomic-scale Surface Chemistry Group'' Physical Review Letters
Date: 2/2023
Instruments: POLAR SPM Lab

Two-dimensional (2D) bilayer hexagonal ice (BHI) is regarded as the first intrinsic 2D ice crystal. However, the robustness of such a structure or its derivatives against surface symmetry and corrugation is still unclear. Here, we report the formation of 2D BHI on gold surfaces with 1D corrugation, using noncontact atomic force microscopy. The hexagonal arrangement of the first wetting layer was visualized on the Au(110)-1 × 2 surface. Upon depositing more water molecules, the first layer would rearrange and shrink, resulting in the formation of buckled BHI. Such a buckled BHI is hydrophobic despite the appearance of dangling OH, due to the strong interlayer bonding. Furthermore, the BHI is also stable on the Au(100)-5 × 28 surface. This work reveals the unexpected generality of the BHI on corrugated surfaces with nonhexagonal symmetry, thus shedding new light on the microscopic understandings of the low dimensional ice formation on solid surfaces or under confinement.

Recently, qPlus-based non-contact atomic force microscopy (NCAFM) enables real-space imaging of interfacial water with superior resolution, such as discerning the O-H directionalities in a nearly noninvasive manner, identifying the atomic H-bonding skeleton, resolving the single ion hydrates and revealing the growth mechanism of a low-dimensional ice by probing the edge structures. In this Letter, using NCAFM in combination with density functional theory (DFT) calculations, we visualized the formation of hydrophobic BHI on both Au(110)-1 × 2 and Au(100)-5 × 28 surfaces, showing periodic 1D reconstruction with the spacing of 8.2 and 14.4 Å, respectively. Our findings indicate the robustness of BHI against the surface morphology and the degree of hydrophobicity.

(a) Overview STM image (set point: 300 mV, 5 pA) of buckled BHI on the Au(110)-1 × 2 surface. The yellow rhombus and rectangle represent the hexagonal and rectangle arrangements of bilayer ice, respectively. (b) Height dependent AFM imaging at tip heights of 320 pm (left), 270 pm (middle), 200 pm (right). (c) Simulated AFM images acquired at tip heights of 14.2 Å (left), 13.6 Å (middle), 13.1 Å (right). (d),(e) Top and side views of the calculated structure of buckled BHI. (f),(g) First layer (f) and second layer (g) structure. The black dash circles in (d),(e),(g) represent the H-up water molecules in the second layer. The yellow and black rectangles in (b)–(g) indicate the 3 × 2 unit cell.

STM and AFM experiments

All the experiments were carried out with an ultra-high vacuum Scienta Omicron POLAR-STM/AFM combined system operated at 4.8 K using a qPlus sensor equipped with a W tip (resonance frequency f0 = 24.7 kHz, spring constant k0 ≈ 1.8 kN m-1 , quality factor Q ≈ 43000).

(a) Schematic model of the reconstructed hexagonal array of the topmost layer (yellow spheres) on the bulk Au(100) surface with square symmetry (green spheres). (b) STM topography of reconstructed Au(100) surface, showing 5 × 28 reconstruction (set point: 100 mV, 50 pA). (c) Overview STM image of 2D ice on reconstructed Au(100) surface (set point: 1 V, 5 pA). (d)–(f) High resolution STM image (set point: 100 mV, 4 pA) (d) and height dependent AFM imaging at tip heights of 320 pm (e) and 290 pm (f). Inset of (e): close-up AFM image of a H-up water in second layer (size: 0.8 nm × 0.8 nm). (g),(h) Top and side views of the flat BHI model with isolated dangling OH (blue spheres).



Pu Yang1†, Chen Zhang1†, Wenyu Sun1, Jia Dong1, Duanyun Cao2,3*, Jing Guo1,5*, Ying Jiang4,5*



1 College of Chemistry, Key Laboratory of Theoretical and Computational Photochemistry, Beijing Normal University, Beijing 100875, China

2 Beijing Key Laboratory of Environmental Science and Engineering, School of Materials Science and Engineering,Beijing Institute of Technology, Beijing 100081, China

3 Beijing Institute of Technology Chongqing Innovation Center, Chongqing 401120, China

4 International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China

5 Interdisciplinary Institute of Light-Element Quantum Materials and Research Center for Light-Element Advanced Materials,Peking University, Beijing 100871, China



Duanyun Cao -

Jing Guo -

Ying Jiang -



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