In everyday life we are familiar with ice as a transparent, regularly packed three-dimensional crystal. But when water molecules are confined to an extremely thin layer, their crystallization behavior is completely different. Now, a joint team led by Prof. XU Limei, Prof. JIANG Ying, Dr. TIAN Ye of the International Center for Quantum Materials (ICQM), School of Physics, Peking University, and CAS Member Wang Enge has unveiled, atom by atom, how two-dimensional (2-D) ice laces itself into order through a unique “web-weaving” pathway. The work appears in Nature Communications.
Using an atomically flat graphite surface as their laboratory bench, the researchers deposited water molecules at cryogenic temperatures to create a disordered bilayer of 2-D ice. Slow, step-wise annealing then allowed the film to crystallize. Images recorded with a home-built, high-resolution scanning-probe microscope—recently commercialized from the group’s own design—show the first atomic-scale movie of ice evolving from slender, branched fronds into wider ribbons that eventually zip together into patch-like islands.
Figure 1. Atomic-scale view of a nucleus-free 2-D ice crystallization. Yellow dots highlight hexagonal rings that evolve from branched to island morphology as the annealing temperature rises. (a–c) AFM images; (d–f) molecular-dynamics snapshots.
Strikingly, the transformation never follows the classical script of “critical-nucleus” growth. Instead, adsorbed water molecules hovering above the surface tow the entire hydrogen-bond network into a cooperative dance, much like a spider spinning its web strand by strand. The finding shows that 2-D ice ordering is not a simple in-plane reshuffle but a three-dimensional team effort, driven by ad-molecules that shuttle between the bilayer and the vacuum interface.
To dissect the mechanism, the team forged an “experiment–simulation–computation–AI” pipeline: molecular-dynamics reproduced the observed morphing; first-principles calculations quantified the energetics of each molecular handshake; and machine-learning algorithms reconstructed three-dimensional molecular coordinates from AFM images. This tool-chain delivered the first fully atom-resolved “spider-web” Crystallization map for 2-D ice, rewriting the textbook picture of low-dimensional ordering and offering a theoretical platform for the controllable growth, atomic-scale design and fictionalization of low-dimensional materials.
Figure 2. Surface-ad-molecule-induced 2-D crystallization. (a) AFM image and (b) 3-D configuration of adsorbed molecules (green circles) at the advancing edge of 2-D ice. (c) Cartoon of the 3-D-assisted 2-D web-spinning process (web spider courtesy of the internet).
The study was jointly conducted by the International Center for Quantum Materials (ICQM), School of Physics, Peking University and the Interdisciplinary Institute of Light-Elements Quantum Materials (LEQM) at the Beijing Huairou National Comprehensive Science Center. Co-first authors are YUAN Zifeng (molecular dynamics), TIAN Ye (SPM experiments), TANG Binze (machine-learning 3-D analysis) and LIANG Tiancheng (first-principles calculations); XU Limei, JIANG Ying, TIAN Ye and WANG Enge are co-corresponding authors. Funding was provided by the National Natural Science Foundation of China, the Ministry of Science and Technology, and the New Cornerstone Science Foundation.