title: Square ice in graphene nanocapillaries.
abstract: Bulk water exists in many forms, including liquid, vapour and numerous crystalline and amorphous phases of ice, with hexagonal ice being responsible for the fascinating variety of snowflakes. Much less noticeable but equally ubiquitous is water adsorbed at interfaces and confined in microscopic pores. Such low-dimensional water determines aspects of various phenomena in materials science, geology, biology, tribology and nanotechnology. Theory suggests many possible phases for adsorbed and confined water, but it has proved challenging to assess its crystal structure experimentally. Here we report high-resolution electron microscopy imaging of water locked between two graphene sheets, an archetypal example of hydrophobic confinement. The observations show that the nanoconfined water at room temperature forms 'square ice'--a phase having symmetry qualitatively different from the conventional tetrahedral geometry of hydrogen bonding between water molecules. Square ice has a high packing density with a lattice constant of 2.83 Å and can assemble in bilayer and trilayer crystallites. Molecular dynamics simulations indicate that square ice should be present inside hydrophobic nanochannels independently of their exact atomic nature.
authors: Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, University of Ulm, 89081 Ulm, Germany.
authors: G
authors: G
authors: Algara-Siller
authors: Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, University of Ulm, 89081 Ulm, Germany.
authors: O
authors: O
authors: Lehtinen
authors: Chinese Academy of Sciences Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230027, China.
authors: F C
authors: FC
authors: Wang
authors: School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.
authors: R R
authors: RR
authors: Nair
authors: Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, University of Ulm, 89081 Ulm, Germany.
authors: U
authors: U
authors: Kaiser
authors: Chinese Academy of Sciences Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230027, China.
authors: H A
authors: HA
authors: Wu
authors: School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.
authors: A K
authors: AK
authors: Geim
authors: School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.
authors: I V
authors: IV
authors: Grigorieva