title: An unconventional bilayer ice structure on a NaCl(001) film.
abstract: Water-solid interactions are of broad importance both in nature and technology. The hexagonal bilayer model based on the Bernal-Fowler-Pauling ice rules has been widely adopted to describe water structuring at interfaces. Using a cryogenic scanning tunnelling microscope, here we report a new type of two-dimensional ice-like bilayer structure built from cyclic water tetramers on an insulating NaCl(001) film, which is completely beyond this conventional bilayer picture. A novel bridging mechanism allows the interconnection of water tetramers to form chains, flakes and eventually a two-dimensional extended ice bilayer containing a regular array of Bjerrum D-type defects. Ab initio density functional theory calculations substantiate this bridging growth mode and reveal a striking proton-disordered ice structure. The formation of the periodic Bjerrum defects with unusually high density may have a crucial role as H donor sites in directing multilayer ice growth and in catalysing heterogeneous chemical reactions on water-coated salt surfaces.
authors.affiliation: 1] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China [2].
authors.forename: Ji
authors.initials: J
authors.lastname: Chen
authors.affiliation: 1] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China [2].
authors.forename: Jing
authors.initials: J
authors.lastname: Guo
authors.affiliation: 1] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China [2].
authors.forename: Xiangzhi
authors.initials: X
authors.lastname: Meng
authors.affiliation: International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China.
authors.forename: Jinbo
authors.initials: J
authors.lastname: Peng
authors.affiliation: International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China.
authors.forename: Jiming
authors.initials: J
authors.lastname: Sheng
authors.affiliation: 1] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China [2] Collaborative Innovation Center of Quantum Matter, Beijing 100871, P.R. China.
authors.forename: Limei
authors.initials: L
authors.lastname: Xu
authors.affiliation: 1] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China [2] Collaborative Innovation Center of Quantum Matter, Beijing 100871, P.R. China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: 1] Collaborative Innovation Center of Quantum Matter, Beijing 100871, P.R. China [2] School of Physics, Peking University, Beijing 100871, P.R. China.
authors.forename: Xin-Zheng
authors.initials: XZ
authors.lastname: Li
authors.affiliation: 1] International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P.R. China [2] Collaborative Innovation Center of Quantum Matter, Beijing 100871, P.R. China.
authors.forename: En-Ge
authors.initials: EG
authors.lastname: Wang